WO1999049325A1

WO1999049325A1 - Automatic fixture building for electrical testing

Info

Publication number: WO1999049325A1
Application number: PCT/IL1998/000133
Authority: WO
Inventors: Zvi Netter
Original assignee: Nit Systems Ltd.
Priority date: 1998-03-24
Filing date: 1998-03-24
Publication date: 1999-09-30
Also published as: AU6417898A; IL125749A0

Abstract

A method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles, and encapsulating the thus positioned pins in a substantially rigid, preferably, non-conducting stabilizing medium such that the pins are held laterally to their axes.

Description

AUTOMATIC FIXTURE BUILDING FOR ELECTRICAL TESTING FIELD OF THE INVENTION

The present invention relates generally to automatic testing of printed circuit boards and the like, and specifically to fixtures for "Bed of Nails" testing and methods and apparatus for producing such fixtures.

BACKGROUND OF THE INVENTION Testing of Printed Circuit Boards (hereinafter PCB), during various stages of production and final testing, generally includes electrical testing to verify the continuity and impedance of the conductors and to ensure that there are no open or short circuits or points of inadequate insulation on the boards. Various methods of PCB testing are known in the art, as described, for example, in Chapter 26 of the Printed Circuits Handbook, Clyde F. Coombs, Jr., ed. (Fourth Edition, McGraw Hill, 1996), which is incorporated herein by reference. The most common of such methods is the well-known Bed of Nails method.

Fig. 1 is a schematic illustration showing a portion of a so-called Universal Electrical Tester 20, including a test fixture 22, as is known in the art, for use in Bed of Nails testing of a printed circuit board (PCB) 24. Fixture 22 includes a plurality of pins 26, which are typically made of stiff wire and may have heads 27 at ends thereof. Pins 26 are held in place by a top plate 28, adjacent to PCB 24, and a bottom plate 30, adjacent to a test head 32 of tester 20. Top plate 28 and bottom plate 30 of fixture 22 are made of insulating material and are held at a desired spacing by spacers 34. Top plate 28 includes a plurality of holes 36, which are placed so that pins 26 protruding through the holes will contact conductors 37 of PCB 24 at desired test points thereon. Bottom plate 30 similarly includes holes 38, mutually spaced in accordance with a standard grid, typically having hole-to-hole spacing of 0.1, 0.07, or 0.05 inches. Holes 36 in top plate 28 are generally spaced differently, and in many cases more closely, than holes 38 in the bottom plate.

To test PCB 24, a mechanical press in tester 20 (not shown in the figures) applies pressure to fixture 20, between test head 32 and PCB 24. Test head 32 includes a plurality of probes 40, spaced according to the same standard grid as holes 38. Probes 40 are spring- mounted, as shown in the figure, so that when board 24, fixture 22 and head 32 are pressed together, probes 40 may move axially and compensate for various mechanical irregularities.

This axial motion thus assures electrical contact to corresponding pins 26 and will simultaneously force the pins upward to make electrical contact with corresponding conductors 37. Fixture 22 thus enables tester 20, whose test head 32 has its probes spaced on a standard grid, to make contact with and electrically test conductors 37 at the test points thereon, which may be relatively arbitrarily spaced.

Retention of pins 26 within holes 36 and 38 is frequently problematic. The holes must be large enough to enable the pins to be inserted at different angles, as shown in Fig. 1. Therefore, the pins cannot be held too firmly in the holes. Lateral movement of the pins within the holes, however, can cause them to miss their appropriate contacts with conductors 37, resulting in erroneous fault readings, or the pins may score and create defects in the conductors that they do contact. Furthermore, for testing double-sided PCBs, a second fixture 22 (similar to the other one but with layout of pins adjusted to the layout of the other side of the PCB) and test head 32 are typically pressed down on the board from above. In this case, with fixture 22 upside down, pin heads 27 will not be effective in holding the pins in place, as they are in the configuration shown in Fig. 1, and additional measures must be taken to ensure that the pins do not fall out of their holes in the fixture. U.S. patent 5,493,230, which is incoφorated herein by reference, provides a solution to this problem, but at the expense of additional complexity and cost.

Fig. 2 schematically illustrates a partial solution, known in the art, to the problem of fixing pins 26 in fixture 22. Intermediate plates 41 are added between top plate 28 and bottom plate 30. Each of the intermediate plates includes holes 42 through which the pins are inserted. Each plate 41 must be individually drilled, since a pin 26 that passes through fixture 22 at an angle will require a different hole location in each plate. Even though plates 28, 30 and 41 are generally produced automatically, using CAD/CAM methods and equipment, producing all the plates is time-consuming and costly, and still does not entirely solve the problems of pin retention and movement described above.

Once plates 28, 30 and, optionally, 41 have been drilled, they are assembled into a "sandwich," as shown in Fig. 2, and pins 26 are inserted through the appropriate holes 36, 38 and 42. A typical fixture 22 may include thousands of pins, so that manual insertion is extremely time-consuming and painstaking work. Automated systems known in the art, such as a "shaker" or pin-feeding machine, may be used to assist in loading the pins. An exemplary automated pin-feeding system is described in U.S. patent 5,307,560, which is incorporated herein by reference. Even with automated assistance, however, the assembly of fixtures 22 is slow, costly and prone to faults in the placement and retention of pins 26.

US Patent 5,493,230 describes a number of systems retaining test pins in a fixture. In particular, this patent shows (as prior art) multi-plate fixtures in which the region between two of the plates is filed with a sponge material which is pierced by and holds the pins when they are inserted. It also shows a multi-plate system in which the pins are retained by bulges on the pins which do not fit through holes in intermediate and/or external plates. It also a methods of retaining pins using an elastic sheets formed with an undersized hole. Alternatively, the pin diameter is reduced where it is positioned at the hole such that an elastic sheet captures the pin. SUMMARY OF THE INVENTION

It is an object of the present invention to provide improved test fixtures for use in electrical testing.

In one aspect of the present invention, the test fixtures are used in Bed of Nails testing of printed circuit boards with so called Universal Electrical Testers. In other aspects of the present invention, the test fixtures are used in electrical testing of other printed or other flat wiring assemblies, such as hybrid circuits on ceramic substrates.

It is another object of the present invention to provide methods and systems for producing such improved test fixtures.

In preferred embodiments of the present invention, a test fixture comprises a plurality of grid pins and a stabilizing, insulating medium, which holds the pins substantially laterally rigidly therein. The fixture is preferably of a size and shape suitable for use in so called Universal Electrical Testers or in other electrical testers, as is known in the art. The pins are positioned in the fixture so as to pass through the fixture from a first side to a second, opposite side thereof. Each pin is placed in a respective, predetermined position and angular inclination within the medium, such that on the first side of the fixture, the positions of the pins correspond to a standard grid, so that the pins will engage grid probes on a test head of the tester. On the second side of the fixture, the positions of the pins correspond to and engage respective, predetermined test points on a PCB to be tested by the tester.

In the description that follows, the first side of the fixture, communicating with the Electrical Tester, will be referred to as the "ET side," and the second side as the "PCB side."

In test fixtures in accordance with preferred embodiments of the present invention, the stabilizing medium - while allowing some small axial movement with respect to the pin - holds the pins firmly, laterally in place, thus alleviating the problems of pin retention and movement described above with respect to fixtures known in the art. Furthermore, test fixtures in accordance with many of the preferred embodiments of the present invention, require no custom-drilled plates. As will be described below, the fixtures may be assembled automatically from standard components, which may be prepared at low cost in large quantities. In some preferred embodiments of the invention, a single custom drilled plate is utilized. In some preferred embodiments of the present invention, the fixture includes a generally rigid grid plate on the ET side thereof. The grid plate has a plurality of holes, preferably arranged on a standard grid of 0.1, 0.07 or 0.05 inches, corresponding to the spacing of the grid probes on the grid head of the tester with which the fixture is to be used. In many preferred embodiments of the invention, the stabilizing medium is added after the pins are placed in their correct position and orientation. In these embodiments, the pins are preferably held in this position by one or more of the following methods.

In one preferred embodiment of the invention, the grid plate comprises substantially rigid, insulating material, and the holes are filled completely or partly with soft filler material, for example rubber or other soft plastic material. Each pin is inserted through a respective hole at its predetermined angular inclination and is held in that position and orientation by the filler material. In one preferred variant of this embodiment, the material in the holes is hardened after insertion of the pins by a chemical reaction which is initiated by heat or more preferably, by radiation, such as ultraviolet radiation. Alternatively, the grid plate may comprise alternating layers of rigid and relatively soft insulating materials, such as Plexiglas, latex rubber or polyurethane. The holes in the grid plate are formed in the rigid layer or layers, whereas there are initially no corresponding holes in the soft layer or layers. When the pin is inserted through one of the holes, it penetrates the soft layer or layers, which then hold the pin at its predetermined angular inclination. In one preferred variant of this embodiment, the material in the holes is hardened after insertion of the pins by a chemical reaction which is initiated by heat or more preferably, by radiation, such as ultraviolet radiation.

Further alternatively, the grid plate may comprise a sheet of firm, sponge-like or mesh material, for example a polyurethane sponge, and the pin itself forms a hole in the plate as it is inserted therethrough. Preferably, the sponge-like or mesh material is attached to a rigid, apertured, plate

When all the pins have been inserted through the generally rigid grid plate, the stabilizing medium, for example, a solidifying gel such as polyurethane, in substantially pourable form (or in a thicker form which can be introduced after the pins are in place), is introduced into the space occupied by the pins. A form surrounding the pins, one side of which may be the grid plate, holds the liquid medium in place. When the medium hardens, it holds the pins substantially rigidly in their predetermined positions and orientations, and the fixture is ready for use. The sides of the form may be removed or left in place. Alternatively, the form is designed for the specific electrical tester and may include provisions for positioning and holding the fixture in place during testing.

In a preferred embodiment of the invention, two layers of stabilizing material are used. In particular, a first rigid layer of material, such as high density polyurethane, fills a first portion of the volume containing the pins, preferably forming a layer adjacent to the grid plate. A second softer layer, for example, low density polyurethane, fills nearly all of the rest of the volume. In a preferred embodiment of the invention the hardened softer layer is covered with a protective layer, such as a layer of hard polyurethane in order to protect the soft layer from damage. The use of the first and second layers provides for a number of advantages. First, the structure is much lighter than when a rigid material is used to fill the entire volume. Second, recovery of the pins is simplified. Third, the pins may be formed with thicker or thinner portions, preferably situated within the softer material, such that the pins are relatively free to move axially, but do not fall out of the structure. Fourth, the use of a soft layer makes the recovery of pins simpler, since the soft layer may be relatively easily removed and the pins recovered. Such a disassembled fixture may be reused if it is suitable for other testing tasks.

In some preferred embodiments of the present invention, a retaining plate is placed at the PCB-side of the fixture during insertion of the pins, preferably with the grid plate on the opposite, ET-side. The retaining plate is preferably made of a soft material, such as cardboard. As each of the pins is inserted through the grid plate, the end of the pin penetrates the retaining plate, which then holds the pin at its proper inclination, preferably in cooperation with the soft material in the grid plate. After all the pins have been inserted, the stabilizing medium is introduced into the space between the grid plate and the retaining plate. After the stabilizing medium hardens, the retaining plate is preferably removed and discarded.

Alternatively, the retaining plate may be used as described above on either the PCB- or the ET-side of the fixture, but without the use of a grid plate.

Alternatively, a custom PC side plate may be provided to hold the pins. However, this requires that a special plate be designed and manufactured for each PCB to be tested.

Alternatively, a sheet of puncturable material may be provided between the grid plate and the PCB side of the fixture, preferably closer to the PCB side of the fixture. This sheet may be a thin sheet of plastic which may be punctured by a laser or a water jet in conjunction with or just prior to placement of the individual pins. Alternatively, it may be a sheet of silk or other closely woven material through which the pin is inserted. In either case, the pin need only be supported by the material until the stabilizing material is inserted and hardens. In some preferred embodiments of the invention, the sheet is very near the PCB side of the finished fixture. In other preferred embodiments of the invention, the sheet is placed nearer the middle of the fixture in order to reduce the density of holes in the sheet.

In a further preferred embodiment of the invention, the pins are individually glued into place as they are inserted, by providing glue at the grid plate. Preferably, the glue sets, at least partially, before the pin is released from the placement mechanism. Alternatively, the glue material is present in the holes during insertion of the pins and is hardened after insertion of the pins by a chemical reaction which is initiated by heat or more preferably, by radiation, such as ultraviolet radiation. Alternatively or additionally, the pins may be coated with a catalyst or accelerator to initiate or speed the hardening process. A further alternative method of holding the pins until the stabilizing medium is in place is to provide a second standard grid plate between the normal grid plate and the PCB side of the fixture. The holes in the second grid plate are preferably oversized such that pins may be inserted in the normal grid plate at an angle and still pass through the holes in the second grid plate. Each pin is provided with a "sticker" which has a larger diameter than the holes in the second grid plate, such that the pins are held in place until the stabilizing material fills the fixture. In a preferred embodiment of the invention, the region between the first and second grid plates is filed with high density material and the region between the second grid plate and the PCB side of the fixture is filled with low density material.

Alternately or additionally, the pin may be held temporarily in position by a mechanism utilizing a thick grid plate. In this embodiment of the invention, conical holes are produced in the grid plate, such that the cone angle is sufficient to accommodate the full range of pin angles. As each pin is placed in the conical hole, glue is added to fill the hole to hold the pin in place, until the stabilizing medium is added. Alternatively, the glue is in place prior to the insertion of the pins and the glue is hardened after insertion of the pins by a chemical reaction which is initiated by heat or more preferably, by radiation, such as ultraviolet radiation. Alternatively or additionally, the pins may be coated with a catalyst or accelerator to initiate or speed the hardening process.

In other preferred embodiments of the present invention, the stabilizing medium comprises a substantially solid substance. For example, the medium may comprise macromer, which is soft enough to receive the pins and hold them at their appropriate inclinations during insertion, and then hardens after all the pins have been inserted, for example by application of heat or other means known in the art. Preferably, some other means as described above, is used to hold the pins during the solidification of the stabilizing medium. Alternatively, in some embodiments of the invention, the medium may comprise rigid material, such as polyurethane, into which holes are drilled, for example, by a laser, in order to receive the pins at their appropriate inclinations. In these preferred embodiments, a grid plate is not required.

In some preferred embodiments of the present invention, the fixture is assembled using pins of different lengths, wherein the length of each pin is preferably automatically chosen based on its inclination angle. Generally, the greater the inclination angle of a pin, the greater the length that is chosen. By appropriate choice of pin lengths, the fixture is made so that all the pins protrude from the PCB side of the finished fixture, as well as from the ET side, by substantially equal amounts. In test fixtures known in the art, in which all the pins are of substantially equal length, damage to the PC board sometimes results at points at which pins of small inclination angle (i.e., nearly vertical orientation) protrude excessively, while there may be poor contact with the PC board at points at which pins of large inclination angle do not protrude sufficiently. These problems are preferably alleviated by the use of pins of different lengths.

Additionally or alternatively, in some preferred embodiments of the present invention, bent pins are used in the fixture, so that the ends of the pins protruding at the PC side of the fixture contact the PC board substantially perpendicularly, thus providing a more positive electrical contact between the tester and the board. Preferably, the bent pins are of different lengths and have different bend angles, dependent on the respective inclination angles of the pins. In preferred embodiments of the invention, the pins are coated with a coating to which the stabilizing material does not bond. In this way, while the pins are held transversely while they are free to move axially. In order to prevent too much axial movement (and the pins falling out of the fixture), the pins are formed with bulges, preferably in the portion of the stabilizing material which is of low density. Thus, movement of the pins axially may also be resiliently opposed by the stabilizing material which is somewhat compressed by the bulges when the pins move axially. Alternatively, depressions may be formed in the pins. The depressions have a similar function to that of the bulges.

In some embodiments of the present invention, for testing PC boards having large through-holes, as are known in the art, pins having large-diameter heads are used in the fixture to contact these large through-holes. Since the large-headed pins cannot normally be inserted through the holes in a grid plate at the ET-side of the fixture, these pins may preferably inserted, either automatically or manually, from the PCB-side of the fixture, even when the other pins are inserted from the ET side. More preferably, as described below, all of the pins are inserted automatically from the PCB side of the fixture. In preferred embodiments of the present invention, the fixture is produced using an automatic fixture assembly system. Preferably, the system receives CAD data regarding a PCB for which a test fixture is to be prepared, and accordingly determines the positions and inclination angles of the pins to be inserted. The system comprises at least one pin feeder, which selects the pins from a pin storage unit and inserts them at the positions and angles that have been determined. Preferably, the system includes an automated verification and control mechanism, such as machine vision and/or electrical contact testing apparatus, as are known in the art, for ascertaining that the pins have been inserted correctly and/or for controlling the pin feeder to remove or adjust incorrectly-inserted pins. The pins may also be color coded to aid the vision system in determining if the correct pin has been gripped.

In preferred embodiments of the invention, the pins are inspected prior to, during and/or after insertion. If faulty pin insertion is detected it can be automatically corrected.

In one preferred embodiment of the invention, each pin is passed before a video camera as it is removed from storage by the gripper. A frame grabber acquires an image and in case of a fault in the way the pin is held or a damaged pin is detected, the insertion of the pin is aborted and another pin is used. Alternatively, the video camera may be mounted on an arm holding the gripper.

During insertion, in a preferred embodiment of the invention, at least one camera views the pin and the gripper to determine if the pin is being inserted in the proper direction and that no other pins are in the path of the pin or arm to interfere with the insertion. The camera or cameras may be mounted on the gripper arm or a separate arm or on the edge of the fixture or in any other position from which the relevant object may be seen.

After insertion the pins are preferably further visually inspected using at least one camera, a frame grabber or frame grabbers and associated software, to determine if they are properly placed, prior to the addition of the stabilizing medium.

Although preferred embodiments are described herein with reference to certain types of test pins, grid plates and stabilizing media, it will be understood that the principles of the present invention may be applied to produce test fixtures using any suitable types of pins and media and any suitable grid plate, or no grid plate. Furthermore, although the preferred embodiments described herein make reference to testing of PC boards in Universal Electrical Testers, fixtures in accordance with the present invention may be produced and used in electrical testing of substantially any type of printed wiring-based device or any other, substantially, planar device were electrical conductance and isolation have to be tested, including, for example, internal layers of PC boards, multi-wire boards, hybrid ceramic circuits, and the like, LCD panels, suspended particle displays, etc.

There is thus provided, in accordance with a preferred embodiment of the invention, a method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles; and encapsulating the thus positioned pins in a substantially rigid, preferably nonconducting, stabilizing medium such that the pins are held laterally to their axes. Preferably, the method comprises determining the positions and inclination angles according to the positions of test points on an electrical circuit to be tested. Preferably, determining the positions and inclination angles comprises calculating parallax corrections for use in positioning the pins.

In a preferred embodiment of the invention, positioning the plurality of pins at predetermined positions comprises positioning the pins so that one of the ends of each of the pins is positioned at a point on a grid at a first side of the fixture.

Preferably, positioning the pins so that one of the ends of each of the pins is positioned at a point substantially on a grid comprises passing the pins through respective holes in a plate situated at the first side of the fixture. Preferably, positioning comprises introducing the pins into the fixture from a second side opposite the first side thereof. Preferably, positioning comprises holding the pins at their respective positions and inclination angles, prior to encapsulation. Preferably, positioning the pins comprises providing an orifice into which the pin is passed and holding the pin at the orifice. Preferably, the orifice is at least partly filled with a permeable material which holds the pin.

In a preferred embodiment of the invention, positioning the pins comprises providing a pierceable material, piercing the material with the pins, and holding the pins in the pierceable material.

Preferably, the method includes hardening the material after positioning the pin therein. In a preferred embodiment of the invention, the method comprises providing pins of differing lengths, wherein positioning the pins at predetermined positions and inclination angles comprises selecting a relatively longer pin for each of the positions for which the pins have relatively greater inclination angles. In a preferred embodiment of the invention, the method comprises providing pins that are bent in differing bend configurations, wherein positioning the pins at predetermined positions and inclination angles comprises selecting a pin for each of the positions having a bend configuration corresponding to a respective inclination angle. Preferably, encapsulating the pins in the medium comprises introducing the medium in a hardenable form into a space containing the pins.

In a preferred embodiment of the invention, the method comprises providing a solid, permeable medium, wherein positioning the pins comprises advancing the pins through the medium, and wherein encapsulating the pins comprises hardening the medium. In a preferred embodiment of the invention, positioning the pins comprises advancing the pins so that the ends thereof engage a test plate. Preferably, advancing the pins so that the ends thereof engage the test plate comprises bringing the pins into contact with a conductive layer of the plate, and comprising receiving electrical signals from the layer to verify the contact of the pins therewith. Preferably, receiving electrical signals to verify the contact of the pins comprises analyzing the signals to determine the respective positions at which the pins contact the layer.

In a preferred embodiment of the invention, encapsulating comprises encapsulating the pin over a substantially continuous portion of its length in a first, relatively rigid material, and encapsulating the pin over a substantially continuous portion of its length in a second relatively soft material.

Preferably, the method comprises providing at least some of the pins with bulges or depressions along a portion of a length thereof and positioning the pins such that the bulges or depressions are within the relatively soft material.

In a preferred embodiment of the invention, the method comprises providing a guide plate having holes therein which aid in the positioning of the pins, wherein the holes are drilled on a standard grid, independent of the spacing of the specified locations.

In a preferred embodiment of the invention positioning does not utilize any guide plates having holes drilled on other than a standard grid, independent of the spacing of the specified locations. There is further provided, in accordance with a preferred embodiment of the invention a method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising:

10 positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles utilizing guide plates having holes therein at positions unrelated to the locations; and holding the pins at their respective positions and angles. Preferably the method utilizes a plurality of guide plates having holes therein at positions unrelated to the locations.

There is further provided in accordance with a preferred embodiment of the invention, a method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles utilizing a plurality of plates having holes therein at positions unrelated to the locations, for guidance of the pins; and holding the pins at their respective positions and angles.

Preferably, positioning includes providing a single plate having holes therein drilled at positions that are dependent on the specified locations wherein the holes are at positions different from said locations.

There is further provided, in accordance with a preferred embodiment of the invention, a method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: providing a single plate having holes therein drilled at positions that are dependent on the specified locations, wherein the holes are at positions different from said locations; positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles, such that said pins pass through said holes locations, wherein one end of the pins is situated at said locations; and holding the pins in the fixture, in said positions.

Preferably, positioning comprises providing a guide structure having holes drilled therein, said holes being drilled at an angle to the thickness of the fixture. In a preferred embodiment of the invention positioning comprises: providing a store of pins of at least two sizes; providing a controller having stored therein a plurality of pairs of positions and inclinations, together with a pin size associated with each said pair; providing a gripper which grips a pin of a size specified by said controller for a position and inclination; and

11 positioning the pin by the gripper in the fixture, responsive to the position and inclination.

There is further provided, in accordance with a preferred embodiment of the invention, a method for producing an electrical test fixture for testing a printed circuit board at specified locations, comprising: providing a store of pins of at least two sizes; providing a controller having stored therein a plurality of pairs of predetermined positions and inclinations, together with a pin size associated with each said pair; providing a gripper which grips a pin of a size specified by said controller for a position and inclination; and positioning the pin by the gripper in the fixture, responsive to the position and inclination.

In a preferred embodiment of the invention, the method comprises providing a solid medium and drilling holes in the medium at the predetermined positions and inclinations. There is further provided, in accordance with a preferred embodiment of the invention, a method for producing an electrical fixture for testing a printed circuit utilizing pins positioned at specified locations and inclinations, comprising: providing a solid, medium having holes formed at the predetermined positions and inclinations; and inserting the pins in the holes.

Preferably, the pins are held over substantially their entire length except at end portions of the pins.

There is also provided, in accordance with a preferred embodiment of the invention, an electrical test fixture produced according to the method of the invention. there is further provided, in accordance with a preferred embodiment of the invention, a fixture for electrical testing, said fixture having first and second sides, and comprising: a substantially rigid, non-conducting stabilizing medium; and a plurality of electrically conductive pins penetrating through the medium, which holds the pins firmly, over a substantially continuous portion of their length, at predetermined positions and angles of inclination therein, whereby the pins establish a plurality of conducting paths from the first side to the second side of the fixture.

Preferably, the pins protrude from the first side so as to engage test probes and from the second side so as to engage test points on a circuit.

12 In some preferred embodiments of the invention, at least some of the pins are bent so as to engage the test points substantially perpendicularly.

Preferably, the pins protrude from the first and second sides of the fixture by generally equal distances. Preferably, at the first side of the fixture, the pins are mutually spaced so as to generally describe points on a grid.

Preferably the fixture comprises a grid plate at the first side of the fixture, the grid plate having a plurality of holes spaced according to the grid, through which holes the pins pass.

Preferably, the grid plate comprises substantially rigid, non-conducting material. Preferably, the fixture comprises a second plate having holes therein and spaced from the grid plate.

Preferably, the holes in the second plate are drilled according to said grid.

In a preferred embodiment of the invention, the stabilizing medium comprises a solidified liquid or gel.

In a preferred embodiment of the invention, the stabilizing medium comprises a first relatively rigid layer which holds the pins over a substantially continuous portion of their length and a second softer layer which holds the pins over a second substantially continuous portion of their length. Preferably, the fixture further comprises a third relatively harder protective layer overlying and external to the second layer.

In a preferred embodiment of the invention, the pins are formed with bulges or depressions and wherein the bulges or depressions are situated in the second layer.

There is further provided, in accordance with a preferred embodiment of the invention, a fixture according to the invention for use in Bed of Nails testing of printed wiring boards. There is further provided, in accordance with a preferred embodiment of the invention, a fixture according to the invention for use in a Universal Electrical Tester. There is further provided, in accordance with a preferred embodiment of the invention, a method for electrical testing of an electrical circuit layout, comprising providing a test fixture according to the invention, bringing the circuit layout into contact with the fixture and measuring electrical characteristics of the circuit layout using the fixture.

There is further provided, in accordance with a preferred embodiment of the invention, a system for producing an electrical test fixture, comprising: at least one pin feeder, which positions grid pins in the fixture at predetermined positions and inclination angles; and a controller, which receives data regarding an electrical layout to be tested and controls the at least one pin feeder to position and angle the pins responsive to the data.

13 Preferably, the system comprises a translation table, on which the pin feeder is mounted for lateral motion relative to the fixture.

Preferably, the at least one pin feeder comprises at least one pin gripper, which holds the pins at an angle relative to the fixture, wherein the angle is varied responsive to the inclination angles of the pins.

Preferably, the system comprises a pin store, which contains pins of differing lengths. Preferably the at least one gripper chooses pins from the pin store by length according to the position and angle of the pin in the fixture.

Preferably, the system comprises a retaining plate, into which the pin feeder inserts the pins and which holds the pins in position during production of the fixture. Preferably, the retaining plate comprises a soft, non-conducting material. Preferably the soft, non-conducting material comprises a carton or cardboard material.

In a preferred embodiment of the invention, the retaining plate comprises a layer of conductive material, and wherein the pin feeder is coupled to a voltage source so that when a pin held by the pin feeder contacts the conductive layer, an electrical current flows between the pin feeder and the layer. Preferably, the layer of conductive material comprises a grid of conductors. Preferably, the controller senses the electrical current so as to verify that the pin has been properly positioned.

In a preferred embodiment of the invention the system includes at least one camera which verifies the position and inclination of the pin.

There is further provided, in accordance with a preferred embodiment of the invention, a method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles, said pins having a bulge or depression along a portion of their length; and encapsulating at least a portion of the pins in a relatively soft stabilizing medium such that the bulges or depressions are situated within the relatively soft material the soft material allowing for some axial movement of the pins, but resisting removal of the pins from the fixture. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which:

Fig. 1 is a schematic, sectional illustration showing elements of a Universal Electrical Tester for testing printed circuit boards, as is known in the art;

14 Fig. 2 is a schematic, sectional illustration showing details of a test fixture, known in the art, for use in the Universal Electrical Tester of Fig. 1;

Fig. 3 A is a schematic, sectional, partial illustration of a test fixture, in accordance with a preferred embodiment of the present invention; Fig. 3B is a schematic, sectional, partial illustration of a pin being held in a test fixture according to a preferred embodiment of the invention;

Fig. 3C is a schematic, sectional, partial illustration of a pin placement method utilizing a second grid plate, in accordance with a preferred embodiment of the invention;

Fig. 3D is a schematic, sectional, partial illustration of the use of a thick grid plate, in accordance with a preferred embodiment of the invention.

Fig. 4 is a schematic illustration of a pin, for use in the test fixture of Fig. 3A, in accordance with a preferred embodiment of the present invention;

Figs. 5A, 5B and 5C are schematic, sectional, partial illustrations of grid plates, for incorporation in the test fixture of Fig. 3, in accordance with preferred embodiments of the present invention;

Fig. 6 is a schematic, sectional, partial illustration of a pin inserted in a test fixture, for testing oversize through-hole contacts on a printed circuit board, in accordance with a preferred embodiment of the present invention;

Fig. 7 is a schematic illustration of a system for producing test fixtures, such as the fixture shown in Fig. 3, in accordance with a preferred embodiment of the present invention;

Fig. 8 is a schematic, partly sectional illustration showing a detail of the system of Fig. 6, wherein a pin is inserted through a grid plate in the course of producing a test fixture, in accordance with a preferred embodiment of the present invention;

Fig. 9 is a schematic, partly sectional illustration showing insertion of pins from the PCB side of the fixture, in accordance with a preferred embodiment of the invention; and

Fig. 10 is an isometric view of a fixture form, useful in preferred embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 3A, which is a schematic, sectional, partial illustration of a test fixture 46, for use in Bed of Nails testing in an electrical tester, in accordance with a preferred embodiment of the present invention. Fixture 46 comprises a plurality of pins 48, held substantially laterally rigidly within a stabilizing medium 54. One preferred stabilizing material is polyurethane. Pins 48 are preferably comprised of stiff wire made of steel, beryllium/copper plated with silver or gold, as is known in the art. Pins 48 may be of any

15 diameter known in the art. However, the present invention is believed to allow for the use of pins which are thinner than the present commonly used minimum of about .017". In particular, pins having a diameter of 0.10" or less may be used. In some embodiments of the invention, the pins may be coated with a non-conducting coating, in which case the stabilizing medium may be conducting.

The external dimensions of fixture 46 are preferably substantially the same as those of test fixtures known in the art, such as fixture 22 (as shown in Figs. 1 and 2). Generally, such fixtures have a thickness of between 1.5" and 3.75". Preferably, fixture 46 may thus be directly substituted for fixture 22 in testers such as tester 20, shown in Fig. 1. In the description that follows, it will be assumed, where appropriate, that fixture 46 is installed in tester 20. Reference will be made to elements of the tester and of PC board 24 being tested thereby, as shown in Fig. 1, in order to explain aspects of the present invention.

As shown in Figs. 3A-3D, pins 48 (or 148, 248), are positioned in fixture 46 so that at the upper, PCB-side 49 of the fixture, the pins protrude and can make electrical contact with respective, selected test points on conductors 37 of board 24. At the lower, ET-side 51 of fixture 46, each of pins 48 protrudes through a respective hole 50 (or 150)in a grid plate 52. Preferably, grid plate 52 includes indentations 56 (of which only one is shown in Fig. 3), for establishing a strong, permanent mechanical bond between the grid plate and stabilizing medium 54. Alternatively or additionally, the surface of the plate may be roughened and/or coated with an adhesive substance. As shown in Figs 3B and 3C, two or more layers of stabilizing material may be used.

In these preferred embodiments of the present invention, fixture 46 is assembled, preferably utilizing the methods described herein, by inserting pins 48 through holes 50 and holding the pins in their respective, predetermined positions and angular orientations, as shown schematically in Figs. 3A-3D. Stabilizing medium 54 is then added in a substantially gel or liquid form. When medium 54 hardens, it holds pins 48 with very little or no freedom of motion laterally but with some flexibility for axial motion of the pin. It also holds the pin permanently in place.

Fig. 3A shows a very simplified embodiment of a fixture, in accordance with a preferred embodiment of the invention. In this embodiment of the invention, a single layer of stabilizing material 54 holds a plurality of straight pins 48. It should be understood that in this preferred embodiment of the invention, the pins may be inserted from either the ET or PCB side of the fixture. Preferably, the pins have different lengths, dependent on their angle.

16 Fig. 3B shows a single pin held in a fixture according to a preferred embodiment of the invention which differs from the preferred embodiment of Fig. 3 A in four important ways.

First, the stabilizing material is formed of two layers a first, relatively harder, layer 154', preferably of high density polyurethane (as for example type Z.131, manufactured by Polyurethane, Ltd., Haifa, Israel). This layer is preferably situated adjacent to a grid plate 152. A second, relatively softer, layer 154", preferably of lower density (and lower weight) polyurethane such as, for example, polyurethane foam designated as series "IN2529F" by Polyurethane, Ltd. of Haifa, Israel. These material solidify in a time scale of a few minutes. The use of a low density material for part of the thickness allows for a lighter fixture (a major consideration for large fixtures) and for easier recovery of pins when the fixture is no longer needed.

Second the softer layer is overlaid by a thin hard layer 153, for example also of relatively hard polyurethane. This layer protects the softer layer from damage during use and avoids cantilever forces on the pins. Third, grid plate 152 is formed with conical holes 150 such that the pins can be held at a lower cylindrical portion 155 and yet be free to be inserted at an angle as shown in Fig. 3B. As described below, during fabrication of the fixture and prior to the addition of the stabilizing medium, the pins may be held in position using fast drying glue placed in the conical section of hole 150. One such material, which may be pre-placed in the holes prior to insertion of the pins is 99% Cray Valley SR 454 with 1% added photo-initiator such as Darocure 1173 (Ciba- Geigy). This glue, when so mixed comprises an ethoxylated Tri-methylol propan-triacrylate (86%), 1-6 hexandiol diacrylate (10%), benzophenol (3%) and photo-initiator (1%). However, it should be understood that many other mixtures of materials are well known to have the properties required, namely requisite rheology prior to cure and very fast UV curing. As in this and other cases where a glue or other material is used to hold the pins temporarily, the pins may be coated with a catalyst or accelerator to initiate or speed the hardening process.

Fourth, pins 148 are formed with a bulge 157. As shown, this bulge is preferably situated in layer 154". Furthermore, the pins are preferably coated with a release agent such as release agent 439 (Polyurethane Ltd. of Haifa Israel) to which the polyurethane does not stick. This allows for the polyurethane to hold the pins relatively rigidly transversely to their axis while allowing for some axial freedom of motion of the pins. Furthermore, the bulge performs two functions. One of these is to keep the pins from falling or being easily removed from the fixture. Second, it provides a resilient force opposing the axial motion of the pins. Alternatively, the pins may be formed with a slight taper. Alternatively, the pins may be

17 formed with depressions that are filled with the polyurethane. These depressions provide the same function as the bulges. The choice of using bulges or depressions, depends to some extent on the diameter of the pins, with bulges being more suitable for thin pins and depressions for thick pins. Fig. 3C shows a single pin held in a fixture having a second grid plate 252. Grid plate

252 differs from grid plate 152 in that it is preferably thinner and, more importantly, that it is formed with holes 250 which are much larger than the holes in grid plate 150. This increase in diameter of the holes allows for pins 248 to be placed at angles as required. Pins 248 have attached stickers 253 which stick to grid plate 252 and hold pins 252 in place until the stabilizing material is inserted.

Fig. 3D shows yet another method of holding the pins in place until the stabilizing material is added. In Fig. 3D, glue 160 is inserted into the holes while the pin is held in place (or is already in place when the pins are inserted). Once the glue sets, the pin is held in place. Preferably a very fast hardening glue as described above is used. Fig. 4 schematically illustrates a bent pin 48 for use in fixture 46, in accordance with a preferred embodiment of the present invention. Pin 48 contacts grid probe 40 of test head 32 (Fig. 1) at a lower end 57 of the pin, and contacts a test point on conductor 37 of PCB 24 at the opposite, upper end 58 thereof. Each probe 40 defines a respective vertical axis 60, which axes are uniformly spaced on a standard grid, as described above. Generally, however, the upper end 58 of the probe is displaced from axis 60 by a displacement D, due to the different, typically non-uniform spacing of the test points on conductors 37, and probe 48 is oriented at an inclination angle dictated by this distance.

Preferably, when straight pins are used (and optionally when bent pins are used) the length of pin 48 is chosen so that for all the pins in fixture 46, a distance h defined by the geometrical projection of the length of the pin along axis 60, from probe 40 to board 24, is substantially the same. Further preferably, as shown in Fig. 4, when pin 48 is bent at an appropriate angle so that its upper end 58 contacts conductor 37 in a generally perpendicular direction. In this way a more positive electrical contact is established between the pin and the conductor. Fig. 5A is a schematic, sectional, detail illustration of grid plate 52 shown in Fig. 3A, in accordance with a preferred embodiment of the present invention. Grid plate 52 preferably comprises rigid, non-conducting material, such as glass-epoxy board, as is known in the art. Plate 52 includes holes 50a, 50b, 50c, etc., drilled preferably on a standard grid of 0.1, 0.07 or 0.05 inch (depending on the type of universal electrical test machine and type of PCB to be

18 tested), or alternatively with any other desired hole spacing according to the electrical test machine grid spacing. The holes are large enough so that pins 48 may be inserted therethrough at any angle up to a typical maximum inclination angle of about 10°, so that the pins can be held firmly in the holes during assembly, as will be described below. Preferably, holes 50a, 50b, 50c, etc., are filled entirely or partially with a soft material for retaining pins 48 therein at their predetermined inclination angles, until medium 54 is introduced and hardens in place. For example, hole 50a is partly filled with sponge rubber or polyurethane foam 62, or the like, leaving a central channel through the hole that is generally of smaller diameter than the pin 48 to be inserted therethrough. Alternatively, hole 50b is entirely filled with a soft material 64, which is penetrated by pin 48 during insertion. Hole 50c, which is initially partly filled with soft material 62, has a pin 48 inserted, at an angle, therein. Pin 48 displaces the material as it is inserted in hole 50c. The remaining material in the hole forms a seal around the pin, so that when stabilizing medium 54 is introduced above plate 52, in generally liquid form, as described above, the medium is prevented from leaking through holes 50. In one preferred variant of this embodiment, the material in the holes is hardened after insertion of the pins by a chemical reaction which is initiated by heat or more preferably, by radiation, such as ultraviolet radiation.

Fig. 5B is a schematic, sectional, detail illustration of grid plate 52 in accordance with an alternative preferred embodiment of the present invention. In this case, grid plate 52 comprises two layers 68 of substantially rigid material, such as fiberglass-epoxy board, as described above, with a generally softer, easily permeable layer 66 of latex rubber for example, sandwiched between them. Holes 50 are drilled only through rigid layers 68. When pin 48 is inserted through one of holes 50, it penetrates soft layer 66, which then holds the pin at its predetermined inclination angle until medium 54 hardens and prevents leakage of the liquid medium, as described above. In one preferred variant of this embodiment, the material in the holes is hardened after insertion of the pins by a chemical reaction which is initiated by heat or more preferably, by radiation, such as ultraviolet radiation.

Fig. 5C is a schematic, sectional, detail illustration showing still another, alternative preferred embodiment of the present invention, in which grid plate 52 comprises a substantially rigid layer 70, pre-drilled with holes 50, sandwiched between easily permeable layers 72. Layers 72 hold pins 48 in place more stabley than in the preceding preferred embodiments, since each pin is held at two points, at the upper and lower surfaces of grid plate 52.

19 Although Figs. 5A-5C illustrate certain types of prefabricated grid plates 52 with circular holes, any other suitable type of grid plate may similarly be used. For example, although in Figs. 5B and 5C, grid plate 52 comprises three layers, "sandwiches" having a larger number of alternating rigid and soft layers may equally be used for this purpose. Alternatively, grid plate 52 may comprise a mesh or foam-type material, (for example, a macromer may be used for this purpose) into which holes 50 are not pre-drilled, but are rather made by pins 48 themselves as they are inserted through the material. In any case, grid plate 52 is a standard part, which may be prepared in advance in large quantities and at low cost, unlike plates 28, 30 and 41, shown in Fig. 2, as are known in the art, which must be custom- drilled for each PC board to be tested.

Furthermore, although in some of the preferred embodiments described herein, pins 48 are generally inserted from below (in the view of Fig. 3 A), through the lower, ET-side 51 of grid plate 52, in other preferred embodiments of the present invention, some or all of the pins are inserted from PCB-side 49 of fixture 46. Specifically, certain PC boards include oversize, plated through-holes, as are known in the art, which are generally tested using grid pins having correspondingly oversize heads. Fixture 46 preferably includes pins of this type as required, which pins are preferably inserted into fixture 46 from PCB-side 49.

It should be noted that for the embodiments shown in Figs. 3B, 3C and 3D, all of the pins are preferably inserted from the PCB side. Fig. 6, illustrates a grid pin 74 having an oversize head 76, inserted into fixture 46 from

PC side 49 of medium 54, as described above. When fixture 46 is brought into contact with PC board 24, as shown in Fig. 6, head 76 engages an oversize, plated through-hole 78 in the board.

Fig. 7 is a schematic illustration of a system 80 for automated assembly of fixtures 46, in accordance with a preferred embodiment of the present invention. System 80 comprises a stable frame 82, onto which grid plate 52 is mounted prior to insertion of pins 48. Preferably, the position of grid plate 52 is adjusted and aligned with system 80 using registration pins 86 or other means known in the art. In some embodiments of the invention, especially for high density precision alignment, the position of the pins is further verified and coordinates fine tuned using camera 99. Further preferably, a retaining plate 84 is mounted to frame 82 above grid plate 52, leaving a space 100 between plates 50 and 84. Plate 84, which will be described further below with reference to Fig. 8, generally defines the upper, PCB-side 49 of fixture 46 to be assembled.

20 System 80 further comprises a pin store 88 and a pin feeder 90, which is mounted for X-Y lateral translation on a translation stage 94, and is controlled by a system controller 98. Pin store 88 is loaded with pins 48, preferably including a variety of pins of different lengths and/or bend angles, as described above, suitably stored in separate bins. Under the instructions of controller 98, pin feeder 90 selects and removes pins 48 from pin store 88, and then feeds the pins into a gripper 92, which inserts them through grid plate 52 in their predetermined positions and inclinations, as described above.

Controller 98 preferably receives CAD data regarding the PC board 24 for which fixture 46 is to be prepared, and uses the data to calculate the positions and inclination angles of pins 48. Preferably, controller 98 also calculates a "parallax correction" for each pin 48, i.e., a translational offset of gripper 92 relative to the pin's respective hole 50, as a function of the pin's inclination and/or bend angle. After all the required pins 48 have been inserted through grid plate 52, stabilizing medium 54 is introduced, in a hardenable viscous liquid or gel form, into space 100. When the medium has hardened, fixture 46 is removed from system 80 and is substantially ready for use. Alternatively, two layers of stabilizing material, as described above, may be used.

Preferably, system 80 also includes assembly testing and verification apparatus, such as machine vision camera 99 or other such apparatus known in the art. Camera 99 preferably captures images of gripper 92, pin 48 and grid plate 52, and conveys these images to controller 98. The images are processed to verify that each pin 48 is properly gripped, is not damaged, is being inserted in its appropriate hole 50 at the predetermined angle. Camera 99 may further be used to provide real-time feedback to controller 98, enabling the controller to adjust and correct the operation of feeder 90 and gripper 92. In some preferred embodiments of the invention, more than one camera may be used. The testing and verification apparatus of system 80 preferably further includes means

(not shown in Fig. 7) for verifying that upper ends 58 of pins 48 are properly positioned before medium 54 is introduced. For example, an additional camera for this purpose may preferably be positioned above system 80. Alternatively, an electrical conductivity tester may be combined with retaining plate 84, as will be described below with reference to Fig. 8. Although in system 80 as shown in Fig. 7, pins 48 are inserted through grid plate 52 from ET-side 51, in other preferred embodiments of the present invention, the pins may be inserted from PCB-side 49 of the fixture under assembly. Such PCB-side insertion is useful, for example, for inserting pins having oversize heads, as described above. Alternatively, when a relatively small number of such oversize-headed pins are needed, feeder 90 in system 80 can

21 insert special pins of normal diameter, for example, color-coded pins, through grid plate 52 at the locations requiring the oversize-headed pins. Pins having oversize heads are then substituted by hand for these special pins, working from PCB-side 49 of fixture 46. In other preferred embodiments of the invention, as described below, insertion of ordinary pins is also from the PCB side.

Furthermore, while system 80 is shown with a single gripper system for inserting pins, in preferred embodiments of the invention, system 89 may have a plurality of grippers for increased throughput.

Fig. 8 is a schematic, sectional, detail illustration of system 80, showing aspects of the insertion of pin 48 by gripper 92, in accordance with a preferred embodiment of the present invention. Pin 48 is advanced by gripper 92 through hole 50, at the predetermined inclination angle, preferably until the pin engages retaining plate 84. The retaining plate preferably comprises at least one layer of permeable material 102, such as modeling cardboard or multiply carton material, which is soft enough for pins 48 to penetrate easily, but firm enough to hold the pins in place until stabilizing medium 54 has been introduced and hardened. After medium 54 has hardened, retaining plate 84 is preferably removed from fixture 46 and discarded.

As shown in Fig. 8, gripper 92 advances pin 48 until it has penetrated a predetermined distance through layer 102, preferably until upper end 58 of the pin reaches a second, harder layer 104 above permeable material 102. Preferably, layer 104 comprises conductive material, such as a metal foil or sheet. A low voltage is applied between gripper 92 and layer 104, such that when pin 48 contacts layer 104, an electrical current flows through the pin. This current is sensed and provides an input to controller 98 to verify that the pin has been inserted to a proper depth. Additionally, layer 104 may comprise a grid of electrically conducting strips or rectangular pads, connected to a suitable switching network, as is known in the art. Thus, when pin 48 contacts layer 104, the location of the contact can be ascertained and input to controller 98. In this way, plate 84 enables verification not only that the pin has been inserted to the proper depth, but also that it is at the correct position and angular inclination. As indicated above, pins may be inserted from the PCB side as illustrated in Fig. 9.

Insertion from the PCB side is especially desirable when the embodiments of Figs. 3B, 3C or 3D are used. It should be noted that, especially for insertion from the PCB side, not only must the position and angle of the insertion be very precise, but the gripper tips must be formed so that they can insert pins in close proximity to other pins which are already in place. The

22 gripper should also make a good electrical connection to the pin (when the positioning of the pin is to be tested electrically during insertion). These problems may be at least partially overcome by suitable planning of the pin insertion sequence.

While pin insertion devices in accordance with the invention are described for use with fixtures according to the invention, it should be understood that such pin insertion devices can also be used for insertion of pins in convention fixtures or other fixtures which are not produced in accordance with the invention.

For insertion from the PCB side, the pins a preferably inserted from above and a prefabricated fixture form is utilized. Such a fixture is shown in Fig. 10. Although preferred embodiments have been described herein with reference to certain types of grid plates 52 and stabilizing medium 54, it will be appreciated that the principles of the present invention may be applied to produce test fixture using any of a wide variety of suitable stabilizing media known in the art, as well as using different types of grid plates, or no grid plate at all. Specifically, medium 54 may comprise a macromer or other suitable non- conducting material, which is initially firm and solid, but still soft and permeable enough for pins 48 to be inserted therethrough. After all the pins have been inserted, the medium is processed, for example by heating, to fix the pins permanently in place. Preferably, additional methods of holding the pin in place are used to assure that the pins do not move during hardening of the macromer. Alternatively, medium 54 may comprise a block of hard, solid, non-conducting material, such as, for example, acrylic, Plexiglas or other plastic. The medium is drilled, for example, using a laser, to create channels in predetermined positions and inclination angles, each such channel sized to receive snugly a corresponding pin 48. After all the channels have been drilled, pins 48 are inserted. Furthermore, it is not essential that medium 54 fill substantially the entire volume of fixture 46, as shown in the figures. Rather, the medium need fill only a sufficient portion of the volume to hold pins 48 firmly in place. Preferably, the pin is held over a substantial portion of its length, such as over more than 25% of its length, but more preferably, over more than 35%. It may be useful to hold the pins over more than half their length or over as much as 80% or 90% of their length.

It will be appreciated that the preferred embodiments described above are cited by way of example, and the full scope of the invention is limited only by the claims.

23

Claims

1. A method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles; and encapsulating the thus positioned pins in a substantially rigid, stabilizing medium such that the pins are held laterally to their axes.

2. A method according to claim 1, and comprising determining the positions and inclination angles according to the positions of test points on an electrical circuit layout to be tested.

3. A method according to claim 2, wherein determining the positions and inclination angles comprises calculating parallax corrections for use in positioning the pins.

4. A method according to any of the preceding claims, wherein positioning the plurality of pins at predetermined positions comprises positioning the pins so that one of the ends of each of the pins is positioned at a point on a grid at a first side of the fixture.

5. A method according to claim 4, wherein positioning the pins so that one of the ends of each of the pins is positioned at a point substantially on a grid comprises passing the pins through respective holes in a plate situated at the first side of the fixture.

6. A method according to claim 4 or claim 5 wherein positioning comprises introducing the pins into the fixture from a second side opposite the first side thereof.

7. A method according to any of the preceding claims wherein positioning comprises holding the pins at their respective positions and inclination angles, prior to encapsulation.

8. A method according to any of the preceding claims wherein positioning the pins comprises providing an orifice into which the pin is passed and holding the pin at the orifice.

24

9. A method according to claim 8 wherein the orifice is at least partly filled with a permeable material which holds the pin.

10. A method according to any of the preceding claims wherein positioning the pins comprises: providing a pierceable material; piercing the material with the pins; and holding the pins in the pierceable material.

11. A method according to claim 9 or claim 10 and including hardening the material after positioning the pin therein.

12. A method according to any of the preceding claims, and comprising providing pins of differing lengths, wherein positioning the pins at predetermined positions and inclination angles comprises selecting a relatively longer pin for each of the positions for which the pins have relatively greater inclination angles.

13. A method according to any of the preceding claims, and comprising providing pins that are bent in differing bend configurations, wherein positioning the pins at predetermined positions and inclination angles comprises selecting a pin for each of the positions having a bend configuration corresponding to a respective inclination angle.

14. A method according to any of the preceding claims, wherein encapsulating the pins in the medium comprises introducing the medium in a hardenable form into a space containing the pins.

15. A method according to any of claims 1-14, and comprising providing a solid, permeable medium, wherein positioning the pins comprises advancing the pins through the medium, and wherein encapsulating the pins comprises hardening the medium.

16. A method according to any of the preceding claims, wherein positioning the pins comprises advancing the pins so that the ends thereof engage a test plate.

25

17. A method according to claim 16, wherein advancing the pins so that the ends thereof engage the test plate comprises bringing the pins into contact with a conductive layer of the plate, and comprising receiving electrical signals from the layer to verify the contact of the pins therewith.

18. A method according to claim 17, wherein receiving electrical signals to verify the contact of the pins comprises analyzing the signals to determine the respective positions at which the pins contact the layer.

19. A method according to any of the preceding claims wherein encapsulating comprises: encapsulating the pin over a substantially continuous portion of its length in a first, relatively rigid material; and encapsulating the pin over a substantially continuous portion of its length in a second relatively soft material.

20. A method according to claim 19 and comprising: providing at least some of the pins with bulges or depressions along a portion of a length thereof; and positioning the pins such that the bulges or depressions are within the relatively soft material.

21. A method according to any of the preceding claims and comprising providing a guide plate having holes therein which aid in the positioning of the pins, wherein the holes are drilled on a standard grid, independent of the spacing of the specified locations.

22. A method according to any of the preceding claims wherein positioning does not utilize any guide plates having holes drilled on other than a standard grid, independent of the spacing of the specified locations.

23. A method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles utilizing guide plates having holes therein at positions unrelated to the locations; and

26 holding the pins at their respective positions and angles.

24. A method according to claim 23 utilizing a plurality of guide plates having holes therein at positions unrelated to the locations.

25. A method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles utilizing a plurality of plates having holes therein at positions unrelated to the locations, for guidance of the pins; and holding the pins at their respective positions and angles.

26. A method according to any of the claims 1-21 wherein positioning includes: providing a single plate having holes therein drilled at positions that are dependent on the specified locations wherein the holes are at positions different from said locations.

27. A method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising: providing a single plate having holes therein drilled at positions that are dependent on the specified locations, wherein the holes are at positions different from said locations; positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles, such that said pins pass through said holes locations, wherein one end of the pins is situated at said locations; and holding the pins in the fixture, in said positions.

28. A method according to any of claims 1-21 wherein positioning comprises: providing a guide structure having holes drilled therein, said holes being drilled at an angle to the thickness of the fixture.

29. A method according to any of the preceding claims wherein positioning comprises: providing a store of pins of at least two sizes; providing a controller having stored therein a plurality of pairs of positions and inclinations, together with a pin size associated with each said pair;

27 providing a gripper which grips a pin of a size specified by said controller for a position and inclination; and positioning the pin by the gripper in the fixture, responsive to the position and inclination.

30. A method for producing an electrical test fixture for testing a printed circuit board at specified locations, comprising: providing a store of pins of at least two sizes; providing a controller having stored therein a plurality of pairs of predetermined positions and inclinations, together with a pin size associated with each said pair; providing a gripper which grips a pin of a size specified by said controller for a position and inclination; and positioning the pin by the gripper in the fixture, responsive to the position and inclination.

31. A method according to claim 30 and including: providing a solid medium; and drilling holes in the medium at the predetermined positions and inclinations.

32. A method for producing an electrical fixture for testing a printed circuit utilizing pins positioned at specified locations and inclinations, comprising: providing a solid medium having holes formed at the predetermined positions and inclinations; and inserting the pins in the holes.

33. A method according to any of the preceding claims wherein the pins are held over substantially their entire length except at end portions of the pins.

34. An electrical test fixture produced according to the method of any of claims 1-33.

35. A fixture for electrical testing, said fixture having first and second sides, and comprising: a substantially rigid, non-conducting stabilizing medium; and

28 a plurality of electrically conductive pins penetrating through the medium, which holds the pins firmly, over a substantially continuous portion of their length, at predetermined positions and angles of inclination therein, whereby the pins establish a plurality of conducting paths from the first side to the second side of the fixture.

36. A fixture according to claim 35, wherein the pins protrude from the first side so as to engage test probes and from the second side so as to engage test points on a circuit layout.

37. A fixture according to claim 35 or claim 36, wherein at least some of the pins are bent so as to engage the test points substantially perpendicularly.

38. A fixture according to any of claims 35-37, wherein the pins protrude from the first and second sides of the fixture by generally equal distances.

39. A fixture according to any of claims 35-38, wherein at the first side of the fixture, the pins are mutually spaced so as to generally describe points on a grid.

40. A fixture according to claim 39, and comprising a grid plate at the first side of the fixture, the grid plate having a plurality of holes spaced according to the grid, through which holes the pins pass.

41. A fixture according to claim 40, wherein the grid plate comprises substantially rigid, non-conducting material.

42. A fixture according to claim 40 or claim 41 and including a second plate having holes therein and spaced from the grid plate.

43. A fixture according to claim 42 wherein said holes in said second plate are drilled according to said grid.

44. A fixture according any of claims 35-43, wherein the stabilizing medium comprises a solidified liquid or gel.

29

45. A fixture according to any of claims 35-44 wherein the stabilizing medium comprises a first relatively rigid layer which holds the pins over a substantially continuous portion of their length and a second softer layer which holds the pins over a second substantially continuous portion of their length.

46. A fixture according to claim 45 and further comprising a third relatively harder protective layer overlying and external to the second layer.

47. A fixture according to claim 45 or claim 46 wherein the pins are formed with bulges or depressions and wherein the bulges or depressions are situated in the second layer.

48. A fixture according to any of claims 34-47, for use in Bed of Nails testing of printed wiring boards.

49. A fixture according to any of claims 34-47, for use in testing of printed wiring boards in a Universal Electrical Tester.

50. A method for electrical testing of an electrical circuit layout, comprising: providing a test fixture according to any of claims 35-49; bringing the circuit layout into contact with the fixture; and measuring electrical characteristics of the circuit layout using the fixture.

51. A system for producing an electrical test fixture, comprising: at least one pin feeder, which positions grid pins in the fixture at predetermined positions and inclination angles; and a controller, which receives data regarding an electrical circuit layout to be tested and controls the at least one pin feeder to position and angle the pins responsive to the data.

52. A system according to claim 51, and comprising a translation table, on which the pin feeder is mounted for lateral motion relative to the fixture.

53. A system according to claim 51 or claim 52, wherein the at least one pin feeder comprises at least one pin gripper, which holds the pins at an angle relative to the fixture, wherein the angle is varied responsive to the inclination angles of the pins.

30

54. A system according to any of claims 51-53, and comprising a pin store, which contains pins of differing lengths.

55. A system according to claim 54 wherein the at least one gripper chooses pins from the pin store by length according to the position and angle of the pin in the fixture.

56. A system according to any of claims 51-55, and comprising a retaining plate, into which the pin feeder inserts the pins and which holds the pins in position during production of the fixture.

57. A system according to claim 56, wherein the retaining plate comprises a soft, nonconducting material.

58. A system according to claim 57, wherein the soft, non-conducting material comprises a carton or cardboard material.

59. A system according to any of claims 56-58, wherein the retaining plate comprises a layer of conductive material, and wherein the pin feeder is coupled to a voltage source so that when a pin held by the pin feeder contacts the conductive layer, an electrical current flows between the pin feeder and the layer.

60. A system according to claim 59, wherein the layer of conductive material comprises a grid of conductors.

61. A system according to claim 59 or claim 60, wherein the controller senses the electrical current so as to verify that the pin has been properly positioned

62. A system according to any of claims 51-61 and including at least one camera which verifies the position and inclination of the pin.

63. A method for producing electrical test fixtures for testing printed circuit boards at specified locations, comprising:

31 positioning a plurality of electrically-conductive pins at predetermined positions and inclination angles, said pins having a bulge or depression along a portion of their length; and encapsulating at least a portion of the pins in a relatively soft stabilizing medium such that the bulges or depressions are situated within the relatively soft material the soft material allowing for some axial movement of the pins, but resisting removal of the pins from the fixture.

32