HK1171264B - Electrically conductive kelvin contacts for microcircuit tester - Google Patents

Description

Conductive Kelvin contact for microcircuit tester

Inventor(s):

JoelN.erdman, U.S. citizen, Waconia, MinnesotaJeffreyC.Sherry, U.S. citizen, Savage, MinnesotagaryW.Michalco, U.S. citizen, HamLake, Minnesota

Statement regarding federally sponsored research or development

Not applicable to

Background

Technical Field

The present invention is directed to an apparatus for testing microcircuits.

Background

As microcircuits continue to evolve smaller and more complex, test equipment for testing microcircuits is also evolving. Efforts are now being made to improve microcircuit test equipment, which results in increased reliability, increased throughput, and/or reduced overhead.

The cost of placing defective microcircuits on a circuit board is relatively high. Mounting typically involves soldering the microcircuit to the circuit board. Once placed on the circuit board, removal of the microcircuit becomes problematic because the act of melting the solder a second time destroys the circuit board. Thus, if the microcircuit is defective, the board itself may also be damaged, which means that all the value added to the board is lost at this time. For all these reasons, microcircuits are often tested prior to mounting on a circuit board.

Each microcircuit must be tested to identify all defective devices, but good devices cannot be falsely identified as defective. Any error, if it occurs frequently, can add significantly to the overall cost of the circuit board manufacturing process and can increase the cost of retesting devices that are erroneously identified as defective.

Microcircuit test equipment is itself very complex. First, the test equipment must make precise and low resistance, non-destructive, temporary electrical contact with each of the closely spaced microcircuit contacts. Even small errors in making contact will result in incorrect connections due to the small size of the microcircuit contacts and the spaces between them. A microcircuit that is misaligned or otherwise incorrect will cause the test equipment to identify the Device Under Test (DUT) as defective, although the cause of this error is a defective electrical connection between the test equipment and the DUT, rather than a defect in the DUT itself.

Another problem in microcircuit test equipment occurs in automated testing. The test rig may test 100 devices per minute or even more. The large number of tests results in wear on the tester contacts making electrical connections with the microcircuit terminals during testing. Such wear can result in conductive debris being dislodged from the tester contacts and DUT terminals, which can contaminate the test equipment as well as the DUT itself.

The debris can eventually lead to poor electrical connections during testing and to false indications that the DUT is defective. Unless the debris is removed from the microcircuit, debris that adheres to the microcircuit may cause the package to malfunction. Removing the debris again adds cost and introduces another source of defects in the microcircuit itself.

Other considerations also exist. A well-performing and inexpensive tester contact is advantageous. It is also desirable to minimize the time required to replace the tester contacts, since test equipment is expensive. The cost of testing an individual microcircuit can increase if the test equipment is taken off-line for extended periods of normal maintenance.

Currently used test equipment has an array of tester contacts that simulate the pattern of the microcircuit terminal array. The array of tester contacts is supported in a structure that accurately maintains the alignment of the contacts with respect to each other. The microcircuit itself is aligned with the test contacts by an alignment plate or pad. Many times, the alignment plate is separate from the housing that encases the contacts because the alignment plate is prone to wear and requires frequent replacement. The test housing and the alignment plate are mounted on a load board having conductive pads electrically connected to the test contacts. The load board pads are connected to circuit paths that carry signals and power between the test equipment electronics and the test contacts.

For electrical testing, it is desirable to make temporary electrical connections between each terminal on the device under test and a corresponding electrical pad on the load board. Generally speaking, it is impractical to solder and remove each electrical terminal on the microcircuit that is contacted by a corresponding electrical probe on the test stand. Instead of soldering and removing each terminal, the tester may employ a series of conductive contacts arranged in a pattern corresponding to terminals on the device under test and electrical pads on the load board. When a force is applied to bring the device under test into contact with the tester, the contacts complete the circuit between each device under test contact and the corresponding load board pad. After testing, when the device under test is released, the terminals are separated from the contacts and the circuit is opened.

The present application is directed to improvements in such contacts.

There is a type of test known as the "Kelvin" test, which measures the resistance between two terminals on a device under test. Basically, the kelvin test involves forcing a current to flow between two terminals, measuring the voltage difference between the two terminals, and deriving the resistance between the terminals using ohm's law, i.e. given by the voltage divided by the current. Each terminal on the device under test is electrically connected to two contacts on the load board and their associated pads. One of the two pads provides a known amount of current. The other pad (referred to as the "sense" connection) is a high impedance connection that acts as a voltmeter, drawing only a small amount of current. In other words, each terminal on the device under test undergoing kelvin testing is electrically connected to two pads on the load board at the same time, one pad providing a known amount of current and the other pad measuring the voltage and drawing only a small amount of current at the same time. Kelvin testing is performed on two terminals at a time, so that a single resistance measurement uses two terminals and four contact pads on the load board.

In the present application, the contacts that form the temporary electrical connection between the device under test and the load board may be used in several ways. In "standard" testing, each contact connects a particular terminal on the device under test to a particular pad on the load board, where the terminal is in a one-to-one relationship with the pad. For these standard tests, each terminal corresponds to exactly one pad, and each pad corresponds to exactly one terminal. In the "kelvin" test, there are two contacts that contact each terminal on the device under test, as described above. For these kelvin tests, each terminal on the device under test corresponds to two pads on the load board, and each pad on the load board corresponds to exactly one terminal on the device under test. Although the test protocol may be different, the mechanical structure and use of the contacts is essentially the same regardless of the test protocol.

Many aspects of the test station may be incorporated from legacy or existing test stations. For example, many mechanical infrastructures and circuits from existing test systems may be used that are compatible with the conductive pins disclosed herein. Such prior systems are listed and summarized below.

An exemplary microcircuit tester is disclosed in U.S. patent application publication No. US2007/0202714A1 entitled "test contact System for testing Integrated circuits having arrays of Signal and Power contacts," published at 30.8.2007, which is incorporated herein by reference in its entirety.

For the' 714 tester, a series of microcircuits are tested sequentially, with each microcircuit (or "device under test") being attached to a test station, electrically tested and then removed from the test station. The mechanical and electrical aspects of such test stations are typically automated so that the throughput of the test station can be kept as high as possible.

In' 714, a test contact element for making temporary electrical contact with a microcircuit terminal includes at least one malleable finger protruding from an insulating contact membrane to act as a cantilever beam. The fingers have conductive contact pads on their contact sides for contacting the microcircuit terminals. The test contact element preferably has a plurality of fingers, which may advantageously have a pie-shaped arrangement. In such an arrangement, each finger is at least partially defined by two radially-directed grooves in the membrane that mechanically separate each finger from each other finger of the plurality of fingers forming the test contact element.

In' 714, the plurality of test contact elements may form an array of test contact elements comprising test contact elements arranged in a predetermined pattern. A plurality of connection vias are arranged substantially according to a predetermined pattern of test contact elements, each of said connection vias being aligned with one of the test contact elements. Preferably, the plurality of connecting passages are supported by the interface membrane in a predetermined pattern. Many vias may be embedded in the pie piece away from the device contact area to extend the useful life. The grooves separating the fingers may be plated to produce I-beams, thereby preventing finger deformation and also extending the useful life.

The connection via of' 714 may be cup-shaped with an open end, wherein the open end of the cup-shaped via contacts the aligned test contact element. Debris resulting from loading and unloading DUTs from the test rig can fall through the test contact elements, with the cup-shaped passages receiving the debris.

The contact and interface membranes of' 714 may be used as part of a test vessel that includes a load plate. The load board has a plurality of connection pads substantially in accordance with a predetermined pattern of test contact elements. The load board supports the interface membrane with each of the connection pads on the load board substantially aligned with and in electrical contact with one of the connection vias.

In' 714, the device uses a very thin conductive plating with retention properties that adheres to a very thin non-conductive insulator. The metal portion of the device provides multiple contact points or paths between the contact I/O and the load board. This can be achieved with a plated through hole housing or with a plated through hole via or with a raised surface (possibly in combination with a spring) having a first surface in contact with a second surface (i.e., device I/O). The device I/O may be physically close to the load board, improving electrical performance.

One particular type of microcircuit that is often tested prior to installation has a package or housing that is commonly referred to as a Ball Grid Array (BGA) terminal arrangement. A typical BGA package may have the form of a flat rectangular block with typical dimensions in the range of 5mm to 40mm on one side and 1mm thick.

A typical microcircuit has an enclosure that encloses the actual circuit. Signal and power (S & P) terminals are on one of the two larger flat surfaces of the housing. In general, the terminals occupy a majority of the area between the surface edge and any one or more of the spacers. It should be noted that in some cases, the spacers may be encapsulated chips or ground pads.

Each terminal may include a small, approximately spherical solder ball that adheres securely to leads penetrating the surface from the internal circuitry, hence the name "ball grid array". Each terminal and spacer protrudes a small distance from the surface, wherein the terminals protrude a longer distance from the surface than the spacers. During assembly, all terminals are simultaneously melted and adhered to the properly positioned wires previously formed on the circuit board.

The terminals themselves may be in relatively close proximity to each other. The centerlines of some terminals may be spaced as little as 0.25mm and even relatively widely spaced terminals may still be spaced apart by about 1.5 mm. The spacing between adjacent terminals is often referred to as the "pitch".

In addition to the aforementioned factors, BGA microcircuit testing involves additional factors.

First, the tester should not damage the S & P terminal surface in contact with the circuit board when making temporary contact with the ball terminal, since such damage may affect the reliability of the solder joint corresponding to the terminal.

Secondly, the test process is more accurate if the wires carrying the signals are kept short. An ideal test contact arrangement has a short signal path.

Third, the solder typically used today for device terminals is primarily tin for environmental reasons. Tin-based solder alloys may produce poorly conductive oxide films on the outer surface. Early solder alloys included large amounts of lead, which did not form oxide films. The test contacts must be able to penetrate the oxide film present.

BGA test contacts currently known and used in the art employ spring contacts made of multiple parts that include a spring, a body, and top and bottom plungers.

U.S. patent application publication No. US2003/0192181a1 entitled "method for making electronic contact", published on 16/10/2003, shows a device equipped with non-planar microelectronic contacts, such as flexible sheet-like cantilever contacts, arranged in a regular pattern. Each unevenness has a sharp feature at its tip remote from the contact surface. As the mating microelectronic element engages the contact, a wiping action (wipingaction) causes the non-planar sharp features to scrape against the mating element, thereby providing an effective electrical interconnection and, optionally, an effective metallurgical bond between the contact and the mating element upon activation of the bonding material.

According to U.S. patent application publication No. US2004/0201390a1 entitled test interconnect and manufacturing method for bumped semiconductor components, which is published 10, 14, 2004, the interconnect for testing the semiconductor components includes a substrate and contacts on the substrate for temporary electrical connection with the bumped contacts on the component. Each contact includes a recess and a pattern of leads suspended over the recess configured to electrically engage a bump contact. The leads are adapted to move in the z-direction within the recess to accommodate variations in the height and planarity of the bumped contacts. Further, the lead may include a protrusion for penetrating the bump contact, a non-adhesive outer layer for preventing adhesion to the bump contact, and a curved shape matching a topology of the bump contact. The leads may be formed by forming a layer of mold metal on a substrate, by attaching a polymer substrate having leads thereon to the substrate, or by etching the substrate to form conductive beams.

A semiconductor inspection apparatus performs a test on a device under inspection having ball-shaped connection terminals according to U.S. patent application No. US6,246,249B1 entitled "semiconductor inspection apparatus and inspection method using the apparatus", issued on 12.6.2001 to Fukasawa et al. The device includes a conductor layer formed on a support film. The conductor layer has a connection portion. The ball-shaped connection terminal is connected to the connection portion. At least the shape of the connecting portion is changeable. The apparatus further comprises a shock-absorbing member made of an elastically deformable insulating material so as to support at least the connection portion. The inventive test contact element for making temporary electrical contact with a microcircuit terminal comprises at least one malleable finger projecting from an insulating contact membrane to act as a cantilever beam. The fingers have conductive contact pads on their contact sides for contacting the microcircuit terminals.

In U.S. patent No. 5,812,378 entitled "microelectronic connectors for engaging bump leads," issued on 22/9/1998 to Fjelstad et al, the connector for a microelectronic device includes a laminar body having a plurality of holes desirably arranged in a regular grid pattern. Each hole is provided with a flexible laminar contact, such as a thin sheet metal ring, having a plurality of protrusions extending inwardly over the holes of the first major surface of the body. The terminals on the second surface of the connector body are electrically connected to the contacts. The connector may be attached to a substrate, such as a multilayer circuit board, such that the terminals of the connector are electrically connected to leads within the substrate. A microelectronic element having raised leads thereon can be bonded to the connector and thus to the substrate by advancing the raised leads into the holes of the connector to bond the raised leads to the contacts. The kit may be tested and, if found acceptable, the projecting leads may be permanently bonded to the contacts.

According to U.S. patent application publication No. US2001/0011907a1 entitled "test interconnect for bumped semiconductor components and method of manufacturing" which is published on 8, 9, 2001, an interconnect for testing a semiconductor component includes a substrate and contacts on the substrate for making temporary electrical contact with the bumped contacts on the component. Each contact includes a recess and a support member suspended over the recess and configured to electrically engage a bump contact. The support member is suspended over the recess on a spiral lead formed on a surface of a substrate. The spiral leads allow the support member to move in the z-direction within the recess to accommodate variations in the height and planarity of the bumped contacts. In addition, the spiral lead twists the support member relative to the bump contact so as to penetrate an oxide layer thereon. The spiral leads may be formed by attaching a polymer substrate having leads thereon to the substrate or by forming a mold metal layer on the substrate. In an alternative embodiment of the contact, the support member is suspended above the substrate surface on the raised spring segment leads.

Consider an electronic chip that is manufactured for incorporation into a larger system. In use, the chip electrically connects the device to a larger system through a series of contacts or terminals. For example, contacts on an electronic chip may be inserted into corresponding sockets on a computer so that computer circuitry may be electrically connected to chip circuitry in a predetermined manner. An example of such a chip may be a memory or processor for a computer, each of which may be plugged into a specific slot or socket in which one or more electrical connections are made to the chip.

It is highly desirable to test these chips before shipping or before installing them into other systems. Such component level testing can help diagnose problems in the manufacturing process and can help improve system level yield for systems incorporating the chip. Therefore, complex test systems have also been developed to ensure that the circuits in the chip perform as designed. The chip is attached to a tester for testing as a "device under test" and then removed from the tester. In general, it is desirable to install, test, and remove as quickly as possible so that the throughput of the tester is as high as possible.

The test system accesses the chip circuitry through the same contacts or terminals that will be used to connect the chip in its final application. As a result, there may be some general requirements for a test system to perform the test. Generally, the tester should establish electrical contact with the various contacts or terminals so that the contacts are not damaged and so that a reliable electrical connection is made with each contact.

Most testers of this type use mechanical contact between the chip I/O contacts and the tester contacts, rather than soldering and de-soldering or some other method of attachment. When the chip is attached to the tester, each contact on the chip will be brought into mechanical and electrical contact with a corresponding pad on the tester. After testing, the chip is removed from the tester and the mechanical and electrical contacts are broken.

In general, it is highly desirable that both the chip and the tester experience as little damage as possible during the attachment, testing, and removal processes. The pad layout on the tester may be designed to reduce or minimize wear or damage to the chip contacts. For example, it may be undesirable to scrape device I/O (leads, contacts, pads, or solder balls), bend or deflect the I/O, or perform any operation that may permanently alter or damage the I/O in any way. Typically, the tester is designed to bring the chip to a final state that is as similar as possible to the initial state. In addition, it is desirable to avoid or reduce any permanent damage to the tester or tester pads so that the tester components can last longer before replacement.

Tester manufacturers currently expend a great deal of effort on pad placement. For example, the pads may include a spring-loaded mechanism that receives the chip contacts with a specified resistance. In some applications, the pad may have an optional hard stop at the extreme end of the spring-loaded force stroke range. The goal of the pad layout is to establish reliable electrical connections with the corresponding chip contacts that can be as close as possible to a "closed" circuit when the chip is attached, and as close as possible to an "open" circuit when the chip is removed.

Because it is desirable to test these chips as quickly as possible, or to simulate their practical application in larger systems, it may be desirable to drive and/or receive electrical signals from the contacts at very high frequencies. The test frequency of current testers can reach 40GHz or higher, and the test frequency is likely to increase with the advent of future generations of testers.

For low frequency tests, such as tests performed close to DC (0Hz), the electrical performance can be moved quite simply: an infinitely high resistance would be desirable when the chip is removed and an infinitely low resistance would be desirable when the chip is attached.

At higher frequencies, other electrical properties come into play, not just resistance. Impedance (or, in essence, resistance as a function of frequency) becomes a more appropriate measure of electrical performance at these higher frequencies. Impedance may include phase effects as well as amplitude effects, and may also contain and mathematically describe the effects of resistance, capacitance, and inductance on the electrical path. In general, it is desirable that the contact resistance on the electrical path formed between the chip I/O and the corresponding pad on the load card be low enough to maintain a target impedance of 50 ohms so that the tester itself does not significantly alter the electrical performance of the chip under test. Note that most test equipment is designed to have 50 ohm input and output impedances.

For contemporary chips with many very closely spaced I/Os, it becomes helpful to simulate the electrical and mechanical performance at the device I/O interface. Two-dimensional or three-dimensional finite element modeling has become the tool of choice for many designers. In some applications, once a basic geometric pattern is selected for a tester pad configuration, the electrical performance of the pad configuration is simulated, and then specific dimensions and shapes are iteratively adjusted until the desired electrical performance is achieved. For these applications, once the simulated electrical performance reaches a certain threshold, the mechanical performance is determined almost in a remedial manner afterwards.

Disclosure of Invention

One embodiment is an apparatus for forming a plurality of temporary mechanical and electrical connections between a device under test having a plurality of terminals and a load board having a plurality of contact pads, each contact pad being laterally arranged to correspond to exactly one terminal, the apparatus comprising: a laterally directed electrically insulative housing longitudinally adjacent to the contact pads on the load board; a plurality of electrically conductive force contacts extending through the longitudinal aperture in the housing toward the device under test and being depressible/deflectable through the aperture in the housing, each of the plurality of force contacts being transversely aligned to correspond to exactly one of the terminals; and a plurality of electrically conductive sense contacts, each of the plurality of sense contacts being laterally aligned to correspond to exactly one force contact and exactly one terminal, each of the plurality of sense contacts extending toward the device under test proximate the respective force contact. Each of the plurality of sense contacts includes a fixed portion, a free portion extending in an articulated manner away from the housing, and an articulated portion connecting the fixed portion and the free portion. The hinge portions are laterally separated from the respective force contact members. The free portion includes a forked portion at its distal end that extends on opposite sides of the distal end of the corresponding force contact. The fixed portion is meant to mean that it is the point along the contact at which the bending of the contact is limited so as to be prevented. The position of the fixation section or point relative to the tip determines the degree of curvature, all else being equal.

An additional embodiment is an apparatus for forming a plurality of temporary mechanical and electrical connections between a device under test having a plurality of terminals and a load board having a plurality of contact pads, each contact pad being laterally arranged to correspond to exactly one terminal, the apparatus comprising: a laterally directed electrically insulative housing longitudinally adjacent to the contact pads on the load board; a plurality of electrically conductive force contacts extending through the longitudinal aperture in the housing toward the device under test and being depressible/deflectable through the aperture in the housing, the depression including a transverse translation of a cross-section of each of the force contacts, each of the plurality of force contacts being transversely aligned to correspond to exactly one of the terminals; and a plurality of electrically conductive sense contacts, each of the plurality of sense contacts being laterally aligned to correspond to exactly one force contact and exactly one terminal, each of the plurality of sense contacts laterally surrounding a respective force contact and being horizontally/laterally slidable along the housing corresponding to a horizontal lateral translation of a horizontal/lateral cross-section of the respective force contact such as shown in fig. 8.

Yet another embodiment is an apparatus for forming a plurality of temporary mechanical and electrical connections between a device under test having a plurality of terminals and a load board having a plurality of contact pads, each contact pad being laterally aligned to correspond to exactly one terminal, the apparatus comprising: a laterally directed electrically insulative housing longitudinally adjacent to the contact pads on the load board; a plurality of electrically conductive force contacts extending through the longitudinal aperture in the housing toward the device under test and being depressible/deflectable through the aperture in the housing, each of the plurality of force contacts being transversely aligned to correspond to exactly one of the terminals; and a plurality of electrically conductive sense contacts, each of the plurality of sense contacts being laterally aligned to correspond to exactly one force contact and exactly one terminal. Each of the plurality of sense contacts includes a pair of conductive posts extending generally transversely along the housing. The pair of conductive rods fit into corresponding grooves on the electrically insulating housing. Each of the pair of conductive bars has an end bent out of the plane of the housing toward the device under test to hit an exposed I/O pad under the device under test. The two ends of each pair of sense bars are directly adjacent to and on opposite sides of the respective force contact.

Drawings

FIG. 1 is a side view of a portion of test equipment for receiving a Device Under Test (DUT) for standard electrical testing.

FIG. 2 is a side view of the test rig of FIG. 1 electrically engaged with a DUT.

FIG. 3 is a side view of a portion of test equipment for receiving a Device Under Test (DUT) for Kelvin testing.

FIG. 4 is a side view of the test setup of FIG. 3 electrically engaged with a DUT.

FIG. 5 is a plan view of a first design of force and sense contacts on a test rig.

FIG. 6 is a plan view of a second design of force and sense contacts on a test rig.

FIG. 7 is a plan view of a third design of force and sense contacts on a test rig.

FIG. 8 is a plan view of a fourth design of force and sense contacts on a test rig.

FIG. 9 is a plan view of a fifth design of force and sense contacts on a test rig.

FIG. 10 is a plan view of a sixth design of force and sense contacts on a test rig.

FIG. 11 is a plan view of a seventh design of force and sense contacts on a test rig.

Fig. 12 is a side view of two sets of terminals/contacts for the test setup of fig. 3 and 4 electrically engaged with a DUT.

Fig. 13 is a side cross-sectional view of a sample geometry of a sense (voltage) contact on its path from a terminal on a device under test to a contact pad on a load board.

Fig. 14 is a side cross-sectional view of another sample geometry of a sense (voltage) contact on its path from a terminal on a device under test to a contact pad on a load board.

FIG. 15 is a side schematic view of a pair of sense contacts with tips that are angled outward from a central force (current) contact.

FIG. 16 is a schematic top view of a pair of sense contacts that include laterally extending portions at their ends that extend toward each other.

FIG. 17 is a schematic top view of a pair of sense contacts including laterally extending portions extending toward each other at their ends.

FIG. 18 is a schematic top view of a single sense contact that includes a laterally extending portion at its distal end that extends partway around the force contact.

FIG. 19 is a schematic top view of a single sense contact that includes a laterally extending portion at its distal end that does not extend partway around the force contact.

FIG. 20 is a side schematic view of a pair of sense contacts having tips that are angled toward each other and cross each other over or beside a center force contact.

FIG. 21 is a schematic top view of a pair of sense contacts that include laterally extending portions at their ends that extend upward out of the page.

Fig. 22 is a perspective schematic view of a leaded integrated circuit package and its kelvin contact system.

FIG. 23 is a compact perspective view of the system of FIG. 22 with a portion removed for clarity.

Fig. 24 is a view similar to fig. 23, but from the other side.

Fig. 25 is a side view schematic of a system applied to a leaded device under compression.

Fig. 26 is a view similar to fig. 25, except with the resilient portion removed.

FIG. 27 is a view similar to FIG. 25 except that the pinch condition and sense contacts are designed to impinge only on the front of the leads protruding from the device.

Fig. 28 is a view similar to fig. 27, but from the other side, and this scheme has tines bent upward (interdigitated) to more quickly initiate contact with the device, providing greater compliance.

Fig. 29 is a schematic diagram showing both an uncompressed state and a compressed state of the concept of connecting only the front portions of the device leads.

FIG. 30 is a schematic view similar to FIG. 29, showing both the uncompressed and compressed states of the double-pronged concept of the sense tines spanning the force contact.

FIG. 31 is a perspective view showing a forked sense lead spanning a force contact with reduced tip thickness.

FIG. 32 is a perspective view similar to FIG. 31 showing a single side sense lead and a force contact with an offset.

Fig. 33 is a perspective view similar to fig. 29.

Detailed Description

The following is a general summary of the disclosure.

The terminals of the device under test are temporarily electrically connected to corresponding contact pads on the load board by a series of conductive contacts. These terminals may be pads, solder balls, wires (leads) or other contact points. Each terminal to be kelvin tested is connected to both a "force" contact and a "sense" contact, each of which is electrically connected to a respective single one of the contact pads on the load board. The force contact delivers a known amount of current to or from the terminal, the sense contact measures the voltage at the terminal and draws a negligible amount of current to or from the terminal. The sense contact partially or completely laterally surrounds the force contact so that it does not have to be elastic itself, but it can also be elastic in its own right. This helps to ensure alignment of the force contact by preventing lateral rocking. In the first case, the sense contact has a forked end with prongs that extend to opposite sides of the force contact. In the second case, the sense contact completely laterally surrounds the force contact and slides horizontally/laterally during vertical compression of the force contact to match the horizontal translation component of the horizontal cross section of the force contact. In a third case, the sense contact includes two rods with ends located on opposite sides of the force contact and the two rods are parallel and extend laterally away from the force contact. In these cases, the sense contact extends in a horizontal direction along the diaphragm or housing that supports the force contact. The rods may be seated in corresponding grooves along the partition or on the housing.

The preceding is merely a summary of the invention and should not be considered limiting in any way. The test device will be described in more detail below.

Fig. 1 and 2 show a tester performing conventional electrical testing, where there is a one-to-one correspondence between terminals on the device under test and contact pads on the load board. In contrast, fig. 3 and 4 show a tester performing kelvin testing, where there are two contact pads on the load board that are connected to each terminal on the device under test. Despite the differences between conventional testing and kelvin testing, tester components have many in common. Thus, it is first described with respect to fig. 1 and 2. After the conventional test is described, the components used in the kelvin test are then described, as shown in fig. 3 and 4. The difference between the two cases is highlighted in the description at this time.

FIG. 1 is a side view of a portion of test equipment for receiving a Device Under Test (DUT) for conventional electrical testing. DUT1 is placed onto tester 5, electrical tests are performed, and DUT1 is then removed from tester 5. Any electrical connection is made by pressing the assembly into electrical contact with the other components; in the testing of DUT1, there was no soldering or no soldering at any point.

The entire electrical test process may only last for a moment of time, so that rapid, precise placement of the device under test 1 becomes very important to ensure efficient use of the test equipment. High throughput of the tester 5 typically requires the use of a robot to grip the device under test 1. In most cases, the robotic system places DUT1 on tester 5 prior to testing and removes DUT1 once testing is complete. The grip and place mechanism may use mechanical and optical sensors to monitor the position of DUT1, and a combination of translational and rotational actuators to align and place DUT1 on the test stand. Such robotic systems are well established and have been used in many known electrical testers; these known robotic systems may also be used with any or all of the tester elements disclosed herein. Alternatively, the DUT1 may be placed by hand, or by a combination of hand and automated equipment.

Similarly, the electrical algorithms for testing each of the terminals on DUT1 are well established and have been applied to many known electronic testers. These known electrical algorithms may also be used with any or all of the tester elements disclosed herein.

The device under test 1 typically includes one or more devices and includes signal and power supply terminals connected to the devices. The device and terminals may be located on one side of the device under test 1 or may be located on both sides of the device under test 1. For use in tester 5, all terminals 2 should be accessible from one side of device under test 1, although it should be understood that there may be one or more elements on the other side of device under test 1, or there may be other elements and/or terminals on the other side that may not be tested by accessing terminals 2.

Each terminal 2 is formed as a small pad on the bottom side of the device or may be a lead protruding from the body of the device. Prior to testing, the pads or leads 2 are attached to electronic leads that are internally connected to other leads, to other electronic components, and/or to one or more chips in the device under test 1. The volume and size of the pads or leads can be controlled with considerable precision and pad-to-pad or lead-to-lead variations or position variations do not generally pose great difficulties. During testing, the terminals 2 remain in a solid state without melting or reflowing any of the solder 2.

The terminals 2 may be arranged in any suitable pattern on the surface of the device under test 1. In some cases, the terminals 2 may have the form of a generally square grid, which is the starting point of a representation describing the device under test 1, QFN, DFN, MLF or QFP for the lead portions. Forms other than rectangular meshes may also exist, including irregular spacing and geometric shapes. It will be appreciated that the specific location of the terminals may be varied as desired and the corresponding locations of the pads on the load board and the contacts on the spacer or housing may be selected to match the location of the terminals 2 of the device under test. Generally, the pitch between adjacent terminals 2 is in the range of 0.25mm to 1.5mm, and this pitch is generally referred to as "pitch".

When viewed from the side, as shown in fig. 1, the device under test 1 appears as a row of terminals 2, the row of terminals 2 optionally including gaps and irregular spacing. These terminals 2 are made generally planar, or as planar as possible, according to typical manufacturing processes. In many cases, if there is a chip or other component on the device under test 1, the protrusion height of the chip will typically be less than the protrusion height of the terminals 2 from the device under test 1.

The tester 5 of fig. 1 includes a load board 3.

The load board 3 includes a load board substrate 6 and circuitry for electronically testing the device under test 1. Such circuitry may include drive electronics capable of generating one or more AC voltages having one or more particular frequencies and detection electronics capable of sensing the response of the device under test 1 to these drive voltages. Sensing may include detection of current and/or voltage at one or more frequencies. These drive and sense electronics are known in the industry, and any suitable electronics from known testers may be used with the tester elements disclosed herein.

In general, it is highly desirable that the features on the load board 3 be aligned with corresponding features on the device under test 1 when mounted. Typically, the device under test 1 and load board 3 are mechanically aligned with one or more positioning elements on the tester 5. The load board 3 may include one or more mechanical positioning elements, such as datum or precisely located holes and/or edges that ensure that the load board 3 can be accurately placed on the tester 5. These locating features typically ensure lateral (x, y) and/or longitudinal (z) alignment of the load board. These mechanical positioning elements are known in the industry and any suitable electronics from known testers may be used with the tester elements disclosed herein. The mechanical locating elements are not shown in fig. 1.

In general, the load board 3 may be a relatively complex and expensive component. In many cases, it is advantageous to incorporate additional, relatively inexpensive elements in tester 5 that protect contact pads 4 of load board 3 from wear and damage. This further element may be an inserter spacer 10. Interposer spacer 10 is also mechanically aligned with tester 3 using appropriate positioning elements (not shown) and resides within tester 5 above load board 3, facing device under test 1.

The interposer spacer 10 includes a series of conductive contacts 20 that extend longitudinally outward on both sides of the spacer 10. Each contact 20 may comprise a resilient element, such as a spring or an elastomeric material, and is capable of conducting current from/to the device under test to/from the load board with a sufficiently low resistance or impedance. Each contact may be a separate conductive element or alternatively may be formed as a combination of conductive elements.

Generally, each contact 20 connects one contact pad 4 on the load board 3 to one terminal 2 on the device under test 1, although such a test scheme is also possible: a plurality of contact pads 4 is connected to a single terminal 2 or a plurality of terminals 2 is connected to a single contact pad 4. For simplicity, it is assumed herein and in the drawings that a single contact 20 connects a single pad to a single terminal, although it should be understood that any of the tester elements disclosed herein may be used to connect multiple contact pads to a single terminal, or multiple terminals to a single contact pad. Typically, interposer spacer 10 electrically connects the load board contacts and the bottom contact surfaces of the test contacts. Alternatively, it can be used to convert an existing load board pad configuration to a medium that is a test socket for connecting and testing a device under test.

Interposer spacer 10 is considered part of tester 5 for purposes of this document, although interposer spacer 10 may be removed and replaced relatively easily as compared to removal and replacement of load board 3. During operation, tester 5 includes load board 3, interposer spacer 10, and mechanical structures (not shown) that mount and hold them in place. Each device under test 1 is placed against tester 5, electrically tested, and removed from tester 5.

A single interposer web 10 can test many devices under test 1 before it wears out, and typically can continue for thousands of tests or more before replacement is needed. In general, it is desirable that replacement of the inserter septum 10 be relatively quick and simple so that only a small amount of downtime needs to be experienced in order to replace the septum tester 5. In some cases, the speed of replacing the interposer web 10 may be even more important than the actual cost of each web 10, since during operation, the increase in tester run time results in a reasonable cost savings.

Fig. 1 shows the relationship between a tester 5 and a device under test 1. When each device 1 is tested, it is placed into a suitable robotic manipulator with sufficiently precise placement properties so that a particular terminal 2 on device 1 can be precisely and reliably placed (in the x, y and z directions) with respect to a corresponding contact 20 on interposer spacer 10 and a corresponding contact pad 4 on load plate 3.

A robotic manipulator (not shown) forces each device under test 1 into contact with the tester 5. The magnitude of the force depends on the exact configuration of the test, which includes the number of terminals 2 to be tested, the force for each terminal, typical manufacturing and alignment tolerances, etc. Typically, the force is applied by a manipulator (not shown) of the tester, acting on the device under test 1. Generally, the force is generally longitudinal and generally parallel to the surface normal of the load plate 3.

Fig. 2 shows the tester and device under test 1 in contact, with sufficient force applied to the device under test 1 to engage the contacts 20 and form electrical connections 9 between each terminal 2 and its corresponding contact pad 4 on the load board 3. As mentioned above, there may alternatively be a test scheme: a plurality of terminals 2 are connected to a single contact pad 4 or a plurality of contact pads 4 are connected to a single terminal 2, but for the sake of simplicity it is assumed in the figures that a single terminal 2 is uniquely connected to a single contact pad 4.

The above-mentioned figures 1 and 2 show a conventional electrical test, which essentially answers such a question: "is terminal a completely electrically connected to terminal B? "Current is driven from the load board to a particular terminal on the device under test, flows inside the device under test to another terminal, and then returns to the load board.

Unlike traditional electrical testing, kelvin testing essentially answers such a question: "what is the resistance between terminals a and B? "as with conventional testing, current is driven from the load board to a terminal, flows internally to another terminal, and then returns to the load board. However, in the kelvin test, each terminal electrically contacts two contacts at the same time. One of the pair of contacts supplies a known amount of current (I), as is done in conventional tests, while the other of the pair of contacts measures the voltage (V) without drawing a significant amount of current. From a known amount of current (I) and voltage (V), ohm's law (V ═ IR) can be used to determine the resistance R (═ V/I) between two specific terminals on the load board.

The force or "current" contacts may be considered low resistance or low impedance contacts, while the sense or "voltage" contacts may be considered high resistance or high impedance contacts. Note that typical voltmeters operate in a manner similar to high resistance sensing or "voltage" contacts.

Fig. 3 and 4 show a tester performing kelvin testing. Many of the elements are similar to those of the conventional tester shown in fig. 1 and 2 and are numbered accordingly.

Note that for each terminal 2 there is a pair of contact pads 4, one of the pair for current and the other for voltage. For each terminal 2 and each pair of contact pads 4, there is also a pair of contacts 20, each of which electrically connects a contact pad 4 with a respective terminal 2. Note that the two contacts in each pair are typically electrically isolated from each other and form an electrical connection 9 between the terminal 2 and the contact pad 4. Fig. 12 shows a close-up view of two pairs of terminals/contacts for the test rig of fig. 3 and 4.

In the schematic views of fig. 3 and 4, the contacts 20 are all similarly shaped and sized and positioned adjacent to each other so that the terminals make contact with both contacts simultaneously. Although this is sufficient from an electronic point of view, it has many mechanical disadvantages. For example, the terminals may be laterally misaligned with respect to the contacts such that the terminals only contact one contact and not the other. Furthermore, a spacer with such a kelvin test scheme may be mechanically more complex than a comparable conventional test method because the number of contacts is effectively doubled, while the side area available for the contacts remains unchanged. In general, placing so many contacts in such a small area is mechanically challenging due to the small size of the components and the need for springs, elastomers, or some other mechanical resistance-generating device to generate z-axis compliance for each contact. As a result, there is a need for an improved mechanical arrangement of the electrical scheme shown in fig. 3 and 4. The remainder of this document addresses this need and presents a variety of different mechanical layouts that are superior to the side-by-side design of fig. 3 and 4.

One simple feature is that the force (current) contact, which is relied primarily or solely on, is resilient, i.e., an elastic or resistive force that pushes back on the terminal when the device under test is forced into contact with the tester. This reduces the mechanical complexity required for sensing (voltage) contacts.

Furthermore, in some cases, the sense contact may have less stringent electrical requirements than the force contact because the purpose of the sense contact is to measure voltage without drawing a large amount of current. Such a low current flow may allow the sense contact to be thinner than the force contact, and may allow the sense contact to bend into a wide variety of shapes and orientations. Some of these shapes are acceptable for sense contacts, but may exhibit unacceptably high frequency performance if they are used for force contacts that are more electrically demanding.

Removing the spring back force from the sense contact and relaxing the criteria for electrical performance may allow the sense contact to have a wide variety of orientations and shapes.

For example, one end of the sense contact can be located adjacent to the tip of the force contact. The sense contacts may then extend generally laterally along the top surface of the interposer or housing (also sometimes referred to as a bulkhead), may bend downward through holes in the housing, and may contact corresponding contact pads on the load board after passing through the housing.

Design 50 of fig. 5 shows a portion of an exemplary housing 51, an array of holes 53 through the housing 51 arranged laterally to correspond to terminals 2 on the device under test 1, two exemplary force (current) contacts projecting up (toward the device under test 1) through the holes 53, two exemplary sense (voltage) contacts 54 extending laterally away from the top of the force contact 52, and two exemplary terminals 2 on the device under test 1 contacting both the force contact 52 and the sense contact 54, respectively. The leftmost exemplary terminal 2 corresponds to a state when the device under test 1 just contacts the tester 5, and the rightmost exemplary terminal 2 corresponds to a state when the device under test 1 is forced into contact with the tester 5.

On each force contact 52, there is a notch removed from the top that receives a portion of the distal end of the sense contact 54. When the device under test 1 is forced into contact with the tester 5, each terminal 2 is in mechanical and electrical contact with both the respective force contact 52 and the respective sense contact 54. The contact 54 has a planar arm 54a, a projection 54b, the projection 54b preferably rising from the housing surface along a line to a contact point 54 c. The projection 54b may also be arcuate, concave or convex. The contact point 54c preferably has an acute angle intersection at its distal end. The sharp angle helps remove oxide on the terminal 2 during insertion.

For the case where little or no contact force is applied (the leftmost terminal 2 shown in fig. 5), the force contact 52 projects upward under its own resilient force. A portion of the distal end of the sense contact 54 is also bent upward so that its tines 54a (in fig. 6) are at an angle of 20 to 30 degrees (i.e., 20 degrees or 21,.., 30 degrees) to the plane of the portion 64. Tines 54a are also tapered inwardly toward force contact 62, preferably forming a triangular tip (fig. 6) or rectangle (fig. 5) along a straight line, but may also follow an arcuate line to the tip. The sense contact 54 may have a fixed portion attached to the housing 51 or integrally formed with the housing 51, a hinged portion laterally separated from the force contact 52, and a free portion extending beyond the hinged portion toward the tip of the force contact 52.

The sense contact 54 may be formed in multiple layers and may be mounted to the top surface of the housing 51 or to a spacer that rests on the housing 51. For example, the layer closest to the housing 51 may be a semi-rigid film layer that is not electrically conductive. This layer may be made of polyimide, kapton, PEEK or any other suitable material. A conductive layer may be deposited on top of the film-like insulator and may be deposited in non-intersecting strips, wherein each strip corresponds to a particular terminal 2.

Such a layered structure of the sense contacts 54 may be used with any suitable configuration of the force contacts 52, as no elements are added directly inside the housing between any of the force contacts 52. An example force contact 52 that may be used is disclosed in U.S. patent No. 5,749,738 entitled "electrical interconnecting contact system" to Johnson et al at 12.5.1998. Other suitable force contacts 52 may also be used.

Note that scraping of the terminal 2 from the sense contact 54 is beneficial for reducing contact resistance due to oxide layer build-up. Since the hinge portion is relatively close to the current contact piece, the free portion is relatively short compared to the vertical deflection range of the current contact piece. As a result, there is a significant lateral component to the vertical compression of the sense contact 54. In practice, this means that when a terminal 2 on the device under test 1 first contacts the sense contact 54, it makes contact at a specific location on the terminal 2. As the terminal 2 deflects/presses the sense contact 54 further, the sense contact 54 slides in a horizontal direction, but does not slide sideways over the terminal 2 toward the force contact. This sliding is generally considered to be beneficial because it can penetrate any oxide layer that has built up on the terminal 2.

The specific geometry of the contact determines the precise amount of sliding. For a rigid free section of length L starting its stroke extending upwards at an angle a and ending its stroke flush with the casing (angle 0), the horizontal range of the scraping stroke is L (1-cosA). Note that the vertical extent of this stroke is l (sina). In fact, if the free portion is too long, there will not be enough lateral travel to cause significant scratching. Similarly, if the free portion is too short, there is a risk of damaging the free portion by bending or breaking the extended portion of the contact during use.

Fig. 6 shows another mechanical design 60 of the sense (voltage) contact 64. Here, each sense contact 64 forms a fork shape having prongs that extend to opposite sides of the corresponding force contact 62. The prongs of the sense contact 64 help to maintain the force contact 62 in lateral alignment during use by preventing or reducing lateral wobble. Any misalignment of the device will result in contact with at least one side of the fork due to possible connections on both sides of the force contact 62.

In this case, off the fork shape, the sense contact 64 is a solid conductive member that sits on top of the test contactor housing 61. The sense contact 64 extends horizontally away from the force contact 62, bends downward through an aperture in the housing 61, emerges from the housing 61 and contacts a corresponding contact pad 4 on the load board 3, as shown in fig. 13 and 14.

Each prong on the fork comprises an upwardly bent tip which is inclined partially or completely towards the device under test 1. When the device under test 1 is forced into contact with the tester 5, the terminals 2 contact the tips of the force contacts 62 and the upwardly bent tips of the prongs of the sense contacts 64. The upwardly bent tip may be rigid (with a well-defined angle that does not change significantly during use) or may be spring flexible. The upwardly bent tip also enables the sense contact to avoid any protruding burrs on the device itself.

In the case of a rigid (unbent) tip, some oxide may be scraped off the terminal. The sharp point of the tip penetrates the oxide on the terminal. In the case of a flexible tip, there will be significant scratching in the manner previously described with reference to fig. 5. As the terminal 2 contacts the sense contact tip, the sense contact deflects vertically so that the horizontal portion of the sense contact telescopes along the surface of the housing. This provides a contact force between the sense contact and the terminal 2.

In the design 60 of FIG. 6, the housing 61 may include a groove in the area around or near the force contact 62 so that the sense contact 64 may be slightly recessed into the housing. Contact 64 may include a planar portion 64a, a raised portion 64b, and a pair of tines 64 c. Tines 64c may have a sharp or pointed contact engagement surface that will remove oxide from terminal 2. The rising portion 64b may be linear (straight) or follow a curved path to the tip 64 c. Tines 64c may have triangular teeth as shown or other tapered or non-tapered configurations. Preferably, tines 64b surround side 2, side 3, or side 4 of contact 62 to help guide alignment thereof.

FIG. 11 shows a design 110 in which the sense contact 114 may have an additional spring-back force provided by an elastomeric material "pad" 119 (or column 519 in FIG. 22) disposed between the prongs of the sense contact 114 and the housing 111. This "pad" 119 can provide additional resiliency to the contact in addition to any existing resiliency from the force contact 112.

FIG. 7 shows another fork design in which the sense contacts are formed in multiple layers, as previously done in accordance with FIG. 5.

For the design 70 of FIG. 7, each sense (voltage) contact 74 has a portion 75 along the diaphragm or housing 71 that may or may not be fixed and a free portion 76 that hingedly extends away from the housing 71. There is a hinge portion 77 connecting the fixed portion 75 with the free portion 76, the hinge portion 77 being laterally spaced from the respective force (current) application contact 72. The free portion 76 has a forked portion 78 at its distal end, the forked portion 78 extending on opposite sides of the distal end of the corresponding force contact 72. Note that in fig. 6, the free portion of contact 64 is longer than in fig. 7, allowing for greater flexing and deflection. In other words, by moving the fixed point farther from the tip, the degree of stretch is increased, all else being equal.

When the device under test 1 is forced towards the tester 5, the respective terminals 2 on the device under test 1 simultaneously press the force contacts 72 through the respective holes 73 on the housing 71 and press the free portions 76 of the sense contacts 74 towards the housing 71.

As with the other designs shown herein, each terminal 2 on the device under test 1 makes direct electrical and mechanical contact with the top end of a corresponding force contact 72. The terminals 2 on the device under test 1 are also in direct electrical and mechanical contact with the fork portions 78 of the corresponding sense contacts 74. The force contact 72 does not make electrical contact with the sense contact 74, although both of them will mechanically and electrically contact the terminal 2 on the device under test 1.

As with the design shown in fig. 5, the fixed portion 75 may be plated onto the housing 71, or the fixed portion 75 may be free-floating and facing the device under test 1. When the sense contacts 74 are formed by such plating, each sense contact 74 is generally planar, including a conductive layer 79A facing the device under test 1, and including an electrically insulating layer 79B facing away from the device under test 1.

For the fork design of FIG. 7, each sense contact 74 is generally planar, each fork portion 78 includes two parallel prongs, and each prong includes a raised edge that extends out of the plane of the sense contact 74 directly adjacent to the corresponding force contact 72. The raised or upwardly bent edge (in the case of the leaded configuration below, the downward bend) may be formed by bending a rectangular portion of the prong towards the device under test 1 out of its plane, which may be defined by an adjacent portion (typically planar) of the sense contact.

For the exemplary design 70 of fig. 7, the respective terminals 2 on the device under test 1 are larger than the respective force contacts 72 along a dimension perpendicular to the fork 78 and parallel to the housing 71. This helps to ensure that the device I/O or terminal 2 is in direct contact with both the force contact 72 and the sense contact 74, because even if there is misalignment between the terminal 2 and the contact along the aforementioned dimension, the terminal 2 will directly contact at least one prong of the forked portion 78 of the sense contact 74 in addition to directly contacting the force contact 72.

The design of fig. 7 may allow for advantageous scraping of oxide from the terminals, as previously described with reference to fig. 5.

In fig. 8, as the force (current) contact 82 is squeezed throughout its squeezing range, the sense (voltage) contact 84 remains generally parallel to the housing 81 and can slide or translate laterally along the housing 81. In this design, the sense contact 84 completely laterally surrounds the force contact 82, so that if the force contact 82 translates laterally, the sense contact 84 can follow.

More specifically, the sense contact 84 can translate along a transverse cross-section of the force contact 82. There are some clarifying examples. If the force contact 82 is entirely cylindrical (i.e., the cross-section in each transverse plane is the same, wherein each cross-section need not be circular or oval), is entirely longitudinally directed, and is entirely longitudinally compressed, then the force contact 82 does not translate laterally at all, and the sense contact 84 does not move. If the force contact 82 is cylindrical in shape, but is tilted with respect to the longitudinal direction, and is pressed purely in the longitudinal direction, then the cross section of the force contact 82 will translate, and the sense contact 84 will follow this translation and will also translate in the lateral direction. If the force contact 82 is cylindrical in shape and has a rotational component as it is squeezed, as if it had an off-axis pivot point for its squeezing, then its squeezing would have a lateral component, the extent of which is determined by the pivot point location. If the force contact 82 is not truly cylindrical in shape, the sense contact 84 can move along its cross-section through changes in shape, size, and/or orientation. For example, the force contact 82 may have a particular edge that rises or falls laterally within a longitudinal squeezed range, and the sense contact 84 may move with that particular edge for all or a portion of the squeezed range.

This lateral translation of the sense contact 84 may enable advantageous scraping of oxides off the terminal 2, as previously described. For example, the sense contact 84 may include a particular element, such as a prong, bracket, flange, or arm, that extends out of the plane of the sense contact 84. This extension element 85 can act like a knife edge on the terminal 2 and can help scrape off any oxide layer that is present. It also acts as a guide to help maintain the alignment of the contact 82. In the exemplary design 80 of FIG. 8, the sense contact 84 includes an arm that is bent upward toward the device under test 1 and is generally parallel to the adjacent face of the force contact 82. Other suitable orientations are possible.

In most cases, the force contact cross-section is translated laterally less than the size of the terminals 2 on the device under test 1 in the longitudinally compressed range so that the force contact 82 does not "walk off" the device I/O or terminals 2 during use.

In the exemplary design 80 of FIG. 8, the sense contact 84 extends completely laterally around the force contact 82. Alternatively, there may be one or more gaps in the sense contact 84 such that it extends only partially around the force contact 82. For example, there may be a gap along one or more sides so that the sense contact 84 can still "grab" the force contact 82 for lateral translation. In some cases, the sense contact 84 includes a partial or complete fork structure surrounding the force contact 82 and a partial or complete portion perpendicular to the prongs capable of engaging one or both of the opposing sides of the force contact 82 within its compressed range.

FIG. 9 shows a contact design 90 similar to FIG. 5, but using a relatively rigid rod 95 as the sense (voltage) contact 94. The force (current) contact 92 has a notch that receives the end of the sense contact bar 95 so that the terminal 2 on the device under test 1 can independently directly contact both the force contact 92 and the sense contact 94. An optional electrically insulating coating on the sense contact 94 and/or the force contact 92 can help prevent shorting of the two contacts.

The rods 95 extend laterally away from the force contact 92 along the side of the housing 91 facing the device under test 1, then pass through holes in the housing 91, out of the housing 91 and contact corresponding contact pads 4 on the load board 3. Note that any or all of the segments of the shaft 95 may be straight, may have a periodic or irregular curvature, and/or may be convoluted.

For the exemplary bar 95 shown in fig. 9, the bar 95 does not significantly scrape any oxide layer on the terminals.

The single bar variation of fig. 9 is a double bar, as shown in fig. 10.

In the design 100 of fig. 10, the sense (voltage) contact 104 includes two rods 105, one on each side of the force (current) contact 102, that extend laterally away from the force contact 102 along the top side of the housing 101. The rods 105 may be joined together at a point to form a fork-shaped portion, similar to the fork-shaped structure shown previously. Alternatively, the rods 105 may remain separated as they extend across the housing 101. The rods 105 may be brought together through a single aperture in the housing 101 or passed separately through the housing 101 through respective apertures in the housing 101. Similar to many of the designs shown previously, having two sense contacts 104 on each side of the force contact 102 increases redundancy in misalignment and also acts as a self-aligning tool to center the force contact 102 on the device I/O or terminal 2. The bar 105 preferably has a straight (straight) portion, and then a curved or inclined portion extending generally perpendicular to the straight portion.

In some cases, the rod or rods 105 may be lowered into a corresponding groove or grooves on the housing 101. Such a groove may protect the rod 105 from damage. In addition, these grooves can help attach the lever 105 to the housing 101 or help position the lever in close proximity to the force contact 102. Furthermore, because rods 105 may be electrically conductive, housing 101 may be made of an electrical insulator and may help to electrically insulate each rod 105 from other rods 105 and from other elements proximate to rods 105. Also, the rods 105 may be coated with an electrically insulating material to prevent shorting with their respective force contacts 102. A wide variety of materials can be used, including parylene, Teflon、Peek、KaptonAnd so on.

In some cases, each bar 105 has an end bent out of the plane of the housing 101 towards the device under test 1. Such bent ends may improve the electrical contact with the terminals 2 on the device 1 to be tested. Such a bent end may also position electrical contacts on the region proximate the bend so that, away from the bend, each rod 105 is electrically insulated by the surrounding channel in which it is located.

In some cases, there is a pair of rods 105 associated with each force contact 102, the pair of rods 105 being positioned on opposite sides of the force contact 102. The rods 105 have ends that are bent out of the plane of the housing 101 towards the device under test 1 as the case may be, these ends spanning the force contacts 102. The rod 105 then extends in the same direction along the housing 101 away from the force contact 102, optionally in parallel grooves on the housing 101. These parallel grooves may alternatively be formed on separate alignment plates mounted to the housing 101. The ends may also point to a point of convergence.

Along the dimension perpendicular to the bar 105 and parallel to the housing 101, the respective terminal 2 on the device under test 1 is larger than the respective force contact 102. In general, when a device under test 1 is forced toward the housing 101, the respective terminals 2 on the device under test 1 simultaneously press the force contacts 102 through the respective holes 103 on the housing 101 and contact the ends of the at least one conductive rod 105 of the respective sense contacts 104.

In some cases, the stem 105 is directly adjacent to the force contact 102. These levers may help to hold the force contact 102 in place during use and may help to prevent rocking, which is advantageous.

In some cases, each rod 105 is an elongated column, optionally having a circular cross-section. In other cases, each bar 105 may have a rectangular or square cross-section. In some cases, each post 105 may be formed separately from the housing 101 and then attached to the housing 101 or held in place by an alignment plate that may be mounted to the housing. In other cases, each bar 105 may be integrally formed with the housing 101, such as by plating onto a surface of the housing 101 or plating into a groove on the housing 101.

Fig. 13 is a side cross-sectional view of design 130 showing a sample geometry of sense (voltage) contacts 134 on their way from terminals 2 on the device under test to contact pads 4 on a load board 3, the load board 3 having a plurality of apertures 142 with predetermined gaps.

The contact 134 extends laterally away from the terminal 2 along the surface of the housing 131, bends approximately 90 degrees (perpendicular) extending through the hole (portion 134b) in the housing 131, and bends (portion 134c) are generally equal to or preferably slightly less than 90 degrees to be generally parallel to the opposite face of the housing 131 after passing through the aperture 142. This bend, generally equal to or preferably less than 90 degrees, provides a certain biasing force for the load board pad 4, thereby ensuring a tight connection. When contacting the electrical contact pads 4 on the load board 3, a portion of the contact 134 is disposed longitudinally between the contact pads 4 and the housing 131. The aperture 142 is sized to be larger than the thickness of the contact portion therethrough. In a preferred embodiment, the aperture is rectangular or the same shape as the contact passing through it, and the gap created between the contact portion 134b and the aperture wall should be large enough that rotational forces (leverage) can be transmitted from the force applied to the contact 134c/d by pad 4 (or 2) to the contact 134 on pad 2 (or 4). In this way, the gap is wide enough to control the position of the contact through the aperture, but still be able to transmit such forces. Typically, an aperture having a width two or three times the thickness of the contact may suffice.

Note that this cross-sectional view may be suitable for any of the designs shown previously in which the sense contacts are generally planar (fig. 5-8 and 11) or generally rod-shaped (fig. 9-10). In those cases where the sense contacts are self-supporting conductive substrates (such as wires or metal plates), the substrate may be bent according to the geometry of FIG. 13. In those cases where the sense contacts are coated or plated onto an electrically insulating substrate, the insulating substrate can be bent according to the geometry of FIG. 13.

In the specific design 130 of fig. 13, both ends of the contact 134 are bent toward the terminal 2 on the device under test. There are numerous other alternatives to this geometry.

For example, fig. 14 shows a design 140 similar to design 130, in which contacts 144 extend laterally away from terminal 2 along the surface of housing 141, are bent 90 degrees (portion 134b) through holes 142 in housing 141, and are bent (portion 134d) approximately equal to or preferably slightly less than 90 degrees to be approximately parallel to the opposite face of housing 141. This bend, generally equal to or preferably less than 90 degrees, provides a certain biasing force for the load board pad 4, thereby ensuring a tight connection. Unlike the design 130 of fig. 13, the design 140 of fig. 14 has opposite ends of the contact 144 extending in opposite directions, rather than both ends extending toward the terminal 2.

Design 140 of fig. 14 may have advantages over design 130 of fig. 13. For example, the contacts 144 themselves may be easier to manufacture and assemble. In some cases, such contacts 144 may be more easily bent than the corresponding contacts 134. In some cases, the geometry of FIG. 14 may force the push pin into position (see the pivoting force above) to ensure the securement of the assembled parts. In some cases, it may be desirable for the torque generated by terminals 2 or 4 to force the ends of contacts 144 into contact with contact pads 4 or 2 on load board 3, as per the geometry of fig. 14, with respect to the holes in housing 141. This provides a bias that pushes the sense contact towards the device under test and makes it easier to align the terminal 2 with the sense contact 141.

The term "substantially parallel," as used previously, means that the 90 degree bend in the contacts 134 and 144 immediately adjacent to the contact pad 4 may actually be less than 90 degrees. For example, the bend may be in the following range: 70-90 degrees, 75-90 degrees, 80-90 degrees, 85-90 degrees, 70-85 degrees, 75-90 degrees, 70-80 degrees, 75-85 degrees, 80-90 degrees, 70-75 degrees, 75-80 degrees, 80-85 degrees, and/or 85-90 degrees. In some cases, the bend angle may be 80 degrees.

Note that any or all of the bends on contacts 134 and 144 may alternatively be radiused, rather than being acute as depicted in fig. 13 and 14. These arcs may simplify the manufacturing process of contacts 134 and 144.

To this end, the sense (voltage) contacts have been generally shown as a bar or set of prongs that extend upward toward the terminals 2 on the device under test 1. The ends of the sense contacts optionally have a structure that may in some cases help to achieve the scraping function described above. Some examples are shown in fig. 15-20.

FIG. 15 is a side view of a pair of straddle sense contacts 154 with tips 155 angled outward from a central force (current) contact 152. The tilt may be limited to the plane of the paper or may alternatively extend out of or into the plane of the paper.

FIG. 16 is a schematic top view of a pair of sense contacts 164, at their ends, the pair of sense contacts 164 including laterally extending portions 166 that extend toward each other to meet at a distal point. The sense contacts 164, including their laterally extending portions 166, surround the central force contact 162.

Further, the laterally extending portion 166 projects out of the paper toward the terminal 2 (not shown) on the device under test 1. In the diagram of fig. 16, the terminal 2 would be between the page and the viewer. The tip 167 of the laterally extending portion 166 will be closer to the viewer than the remainder of the contact 164. Note that the contacts 166, 167 extend generally perpendicularly away from the arm 165 so that they are parallel to each other and intersect a longitudinal axis 169 drawn through the contact 162.

FIG. 17 is a schematic top view of a pair of sense contacts 174. at their ends 175, the pair of sense contacts 174 include laterally extending portions 176 that extend toward each other and generally orthogonal to their arms 174. The sense contacts 174, including their laterally extending portions 176, do not surround the central force contact 172, but intersect the longitudinal axis 169 passing through 172. The center force contact 172 can be thought of as being "outside" the polygon formed by the pair of sense contacts 174 and their laterally extending portions 176.

As in fig. 16, the laterally extending portion 176 extends out of the page, the terminal will be between the page and the viewer, and the tip 177 of the laterally extending portion 176 will be closer to the viewer than the remainder of the contact 174.

FIG. 21 is a schematic top view of a pair of sense contacts 214, at their ends 215, the pair of sense contacts 214 including laterally extending portions 216 that extend toward each other. The sense contacts 214, including their generally orthogonal lateral extensions 216, surround the center force contact 212, with the center force contact 212 passing through the gap between the contacts 214 and 215. The tip 217 of the laterally extending portion 216 will be closer to the viewer than the rest of the contact 214. Here, the laterally extending portions 216 are on opposite sides of the force contact 212.

FIG. 18 is a schematic top view of a single sense contact 184, at its tip 185, this sense contact 184 including a laterally extending portion 186 that extends partway around the force contact 182. As with fig. 16 and 17, the laterally extending portion 186 extends out of the page, the terminal will be between the page and the viewer, and the tip 187 of the laterally extending portion 186 will be closer to the viewer than the remainder of the contact 184.

FIG. 19 is a schematic top view of a single sense contact 194, at its end 195, the sense contact 194 including a laterally extending portion 196 that does not extend partway around the force contact 192. The laterally extending portion 196 is on the opposite side of the force contact 192 as the laterally extending portion 186 shown in FIG. 18. As with fig. 16-18, the laterally extending portion 196 extends out of the page, the terminal would be between the page and the viewer, and the tip 197 of the laterally extending portion 196 would be closer to the viewer than the rest of the contact 194.

FIG. 20 is a side view schematic of a pair of sense contacts 204 having tips 206 that are angled toward each other and cross each other over or beside a center force contact 202. The tongue or tip 206 may span the force contact 202 after or before the force contact 202. During contact with terminal 2 on the device under test, the terminal pushes down on tips 206, forcing them away from each other, causing a scrubbing action to penetrate the oxide layer on terminal 2. Oxide removal is an important outcome in this embodiment. The tilt may be limited to the plane of the paper or may alternatively extend out of or into the plane of the paper. The crossing arms can have a non-conductive coating on at least their back side to prevent shorting to the contacts 202, or the contacts 202 can just be formed so that they cannot contact the tips 206.

In general, the sense contacts may have tips or tabs that may extend out of the plane of the spacer toward terminals on the device under test. The tongue may flex or flex when contacting the terminal independent of the movement or orientation of the rest of the sense contact. This movement may be a bending movement, such as with a generally elastic material, and optionally includes a hinge structure at the proximal end of the tab connecting it with the rest of the sense contact. The tab optionally extends laterally toward, across, or around the force contact. In some cases, there is a single sense contact that has a tip that extends laterally past the force contact so that the force contact is partially "within" or partially "outside" the confines of the sense contact. In other cases, there are two sense contacts that are generally parallel to each other, with tips that extend toward each other, such that the force contact is partially "in" or partially "out" of the range of the two sense contacts. Alternatively, the tips may extend laterally away from each other, or may extend in any generally lateral direction, except out of plane toward terminals on the device under test.

Although the force (current) contact is typically thicker than the sense (voltage) contact, and this is assumed in the foregoing description, it should be noted that the function of the two contacts can be switched so that the thinner contact carries current and the thicker contact measures voltage. A preferred application for this would be to make the contacts in the housing slots thinner and the contacts above the housing thicker to handle more current.

In addition to Ball Grid Arrays (BGAs) and other leadless packages with pads on the bottom side of the device, the structures of the present invention may also be applied to components in certain specific integrated circuits with leads or wires, referred to as lead contact packages.

Fig. 22-32 illustrate kelvin contacts for a leaded package. To the extent that components for BGA packages or packages with pads on the bottom layer of the device are similar, they will have the same part number increased by 500. Thus, the contacts 2 in a BGA are in the form of contacts 502 in a leaded package, and so on.

Fig. 22, 23 and 24 show a lead Device (DUT)501 with a plurality of leads 502a, each lead 502a having a contact 502. As in the pad package, the force contact 552 makes contact with the lead 502, typically at its central portion. Contact 552 is biased upwardly by member 519, which is similar to pad 119 (fig. 11), but is preferably cylindrical. (note that a cylindrical profile may also be used in a pad or BGA configuration.) a second biasing block 519a is used to apply a downward force to the rocker pin 600. The swing pin 600 is similar to the type shown in U.S. patents 5069629 and 7445465, and is incorporated herein by reference.

The contact extensions 544 are formed as shown in figure 22 so that they extend along a path to the load board 503 where they make electrical contact. The extensions provide for easier loadboard layout and facilitate easier trace routing on the loadboard. The sensing contact tip in fig. 22 has a bifilar fork design. In this case, the tip of the fork is flat in the horizontal direction, without being bent upward as in fig. 6. This enables the terminal lead edges of the device under test to scrape along the top surface of the fork and remove oxide.

FIGS. 25, 26, 27, 28, 29, 30, 31, and 32 provide more detail on how the force contact 552 and sense contact 554 function with three different concepts. The force contact in fig. 27, 28 and 29 has a full width force contact 600. The force contact in FIGS. 25, 26, 30, 31 and 32 has a tip 552 of reduced thickness to prevent shorting to the sense contact 554 and to provide a more knife-edged edge (i.e., the tip is narrower than the substrate) to penetrate the oxide layer on the leads of the device under test. In fig. 31, a flange 620 is shown, the flange 620 being a portion where the tip 552 narrows. Fig. 27 shows an alternative to fig. 26, in which the end of sense contact 554 is lifted out of the paper plane, similar to the concept shown in fig. 20 and 21. First, the force contact tip 552 preferably has a "tooth-like crown" with a ramp or depression 552 a. Sense contact 554 in FIGS. 25, 26, 30 and 31 has a fork-shaped end terminating in two tines 554a and 554b, with the tines at their distal ends angled downward (opposite the pad packaging tines 554 a) at an angle of 20-30 degrees (i.e., 20, 21,. or 30 degrees) from the plane of contact 554. FIG. 32 shows an alternative to the dual-prong approach, where the force contact tip 552 is offset to one side and the sense contact 554 has only one prong. The gap between the force contact tip and the sensing tines is centered on the device lead centerline to ensure adequate contact. The end of contact 554 may be chamfered or rounded on its lower surface to provide a suitable clearance. The inner perimeter 602 of the force contact 600 is cut away (i.e., reduced in front-to-back thickness) to ensure clearance from the sense contact 554 as it moves.

In operation, the contact 600 "swings" from the two positions shown in fig. 29 in response to contact with the lead contact 502. Similarly, sense contact 554 moves between the two positions shown. The movement of the various components of FIG. 30 is the same as FIG. 29, except that FIG. 30 shows a sense contact with downwardly angled tines and a contact 600 with a reduced tip width. Note that the tines need not be angled downward to function.

Fig. 32 shows a variation of the double tine configuration of fig. 31. In this case, sense contact 554 has only a single prong 554a, which prong 554a may or may not have a portion that is sloped downward (such as shown in FIG. 31). This allows the force contact to have a larger contact surface area if desired. In this design, the force contact tips are offset and not centered on the width of the contact 600.

Figure 33 provides clarification in the following manner. In this embodiment, sense contact 554 is not forked. Further, the sense and force contacts are preferably collinear, but preferably never contact each other. For these two contacts, they may be in brief contact with each other upon insertion, and if so configured, fig. 33 shows the lead contact 502 in two positions. The last issue is where the first contact is made. The sense contact 554 first hits the lead 502 and as 554 is stressed by its own resilience or alternatively against the resilient element 519a, there will be a scraping action between the two contacts. As shown in the previous contact, the sense contact 554 is pressed downward until it is behind and adjacent to the swinging force contact 552. It is clear that they are always aligned collinearly. There may also be a scraping action between contacts 502 and 552 as contacts 552 rock in response to elastomer 519.

The present disclosure also inherently includes methods of constructing devices in accordance with the present invention. In addition, there is a method of minimizing contact resistance when making temporary contact between a device under test and a test fixture having test contacts. Minimizing the resistance is the goal of the scraping action described previously. The test fixture has force and sense fixture contacts for receiving the test contacts and includes at least some or all of the following steps:

a. collinearly aligning sense and force contacts

b. The sense contact is resiliently positioned in a plane above the force contact, but laterally of the force contact,

c. bringing the test contact into physical contact with the sense contact

d. Deflecting the sense contact by the test contact, causing the sense contact to scrape against the test contact during deflection

Furthermore, the method may further comprise the following steps or components thereof: by configuring the force contact to have a swing in response to an impact, the force contact can be deflected when it impacts the test contact.

The description of the invention and its applications as set forth herein are illustrative and are not intended to limit the scope of the invention. Variations or modifications of the embodiments disclosed herein are possible, and practical alternatives to and equivalents of the various elements of the embodiments will be understood by those of ordinary skill in the art after studying this patent document. These and other modifications and variations to the embodiments disclosed herein may be made without departing from the scope and spirit of the present invention.

Claims (17)

1. An apparatus for forming a plurality of temporary mechanical and electrical connections between a device under test having a plurality of terminals, comprising:

a plurality of conductive force contact pieces extending toward the device under test and being deflectable, each of the plurality of force contact pieces being arranged laterally to correspond to one of the terminals; and

a plurality of electrically conductive sense contacts, each of the plurality of sense contacts being laterally aligned to correspond to one force contact and one terminal, each of the plurality of sense contacts extending toward a device under test proximate a respective force contact;

wherein each of the plurality of sense contacts comprises a freely movable portion that elastically extends towards the device under test;

wherein the sense contacts are laterally separated from the respective force contacts; and is

Wherein said freely movable portion includes a forked portion at an end thereof extending on opposite sides of the end of the respective force contact;

the device is characterized wherein the force contact and the sense contact are independently suspended apart from each other by connection to a load board such that the sense contact forms a cantilever separate from the force contact.

2. The apparatus of claim 1, wherein the forked portion includes a gap between the separated portions of the sense contact, and wherein the force contact extends through the gap.

3. The device of claim 1 wherein said freely movable portion is planar and extends distally from said fork portion past said force contact to form an elongated cantilevered beam.

4. The apparatus of claim 1 wherein when a force is applied downwardly to the device under test, the corresponding terminal on the device under test applies a force to both the force contact and the free portion of the sense contact.

5. The device as set forth in claim 1, wherein,

wherein each of the plurality of sense contacts is generally planar, an

Wherein each fork portion comprises two parallel tines; and is

Wherein each tine includes a lip extending out of the plane of the sense contact directly adjacent the respective force contact.

6. The apparatus of claim 5, wherein the lip is formed by bending the rectangular portion of the tine out of its plane toward the device under test.

7. The apparatus of claim 1, wherein the fork portions include tips at ends thereof that extend transversely toward each other at least partially converging.

8. The device of claim 1, wherein the sense contact comprises a distal fork end comprising a pair of tines.

9. The device of claim 8, wherein the tines are downwardly inclined.

10. The device of claim 1, wherein the force contact comprises a tip,

and wherein the tip includes a recess therein.

11. The device of claim 1, wherein the force contact is aligned co-linearly with the sense contact, and wherein the force contact is formed such that: when the terminal deflects the sense contact downward, no impact is placed on the sense contact.

12. The device of claim 8 wherein the force contact has a tip that is thinner than its base, and wherein the tip passes through a pair of tines that surround the tip on at least two sides.

13. A method of minimizing contact resistance when using the apparatus of claim 1 for temporary contact between a device under test and a test fixture having test contacts, the test fixture having test contacts including force contacts and sense contacts and for receiving the device under test, the method comprising:

a. the sense and force contacts are aligned co-linearly,

b. the sense contact is resiliently positioned in a plane above the force contact, but laterally of the force contact,

c. so that the device under test makes physical contact with the sense contacts,

d. the sense contact is deflected by the device under test causing the sense contact to scrape against the device under test during deflection.

14. The method of claim 13, further comprising the step of: by configuring the force contact to have a swing in response to an impact, the force contact can be deflected when it impacts the test contact.

15. An apparatus for forming a plurality of temporary mechanical and electrical connections between a device under test having a plurality of terminals and a load board having a plurality of contact pads, each contact pad being laterally arranged to correspond to exactly one terminal, the apparatus comprising:

a laterally directed electrically insulative housing longitudinally adjacent to the contact pads on the load board;

a plurality of electrically conductive force contacts extending through the longitudinal aperture in the housing toward the device under test and deflectable through the aperture in the housing, each of the plurality of force contacts being transversely aligned to correspond to exactly one of the terminals; and

a plurality of electrically conductive sense contacts, each of the plurality of sense contacts being laterally aligned to correspond to exactly one force contact and exactly one terminal;

wherein each of the plurality of sense contacts comprises a pair of conductive rods extending generally transversely along the housing;

wherein the pair of conductive rods fit within corresponding grooves on the electrically insulating housing;

wherein each conductive rod of the pair of conductive rods has a terminal end bent out of the plane of the housing toward the device under test; and is

Wherein the two ends of each pair of levers are directly adjacent to and on opposite sides of the respective force contact.

16. The apparatus of claim 15, wherein:

when a force is applied to the device under test toward the housing, each of the plurality of terminals simultaneously presses a respective force contact such that the force contact passes through a respective hole in the housing, and the each terminal slides a respective sense contact laterally along the housing.

17. The apparatus of claim 15, wherein when a force is applied to the device under test toward the housing, a respective terminal on the device under test simultaneously presses the force contact such that the force contact passes through a respective hole on the housing and the terminal contacts an end of at least one conductive rod of a respective sense contact.