WO1997006917A2 - Wire clamp - Google Patents

Abstract

A wire clamp has two jaws that can be moved with respect to each other by a drive. The jaws are provided with surfaces for clamping and moving or holding bond wires of various diameters for ultrasonic wire bonding devices in which the wire clamp is arranged directly behind a bonding tool (wedge). One of the jaws (2) of the wire clamp (1) is joined to the bonding device in an adjustable manner in relation to the bonding wire (12) and the second movable jaw (3) is joined by a parallel guide to the first jaw (2) in such a way that the jaws (2, 3) may be moved away from each other and closed transversely to the longitudinal direction of the bonding wire (12). The invention also relates to such a wire clamp joined by a parallel guide to the bonding device or head.

Description

 Fadenklamπier

The invention relates to a thread clamp with two jaws that can be moved relative to one another by a drive and provided with jaw surfaces for clamping and moving or holding bonding wires of different diameters, for ultrasonic wire bonding devices, the thread clamp being directly behind a bonding tool (wedge). is arranged.

In the production of semiconductor components, it is necessary to establish electrical connections between the semiconductor chips and interconnects on carrier elements. The carrier elements can then be used in printed circuit boards or the like. In many semiconductor components, this electrical connection is established by making wire bridges between the bond pads or bond pads and contact areas on the carrier element on the carrier element. The contact is made by welding with the aid of ultrasonic vibrations, which are transmitted to an bonding tool by an ultrasonic oscillator via a transducer or ultrasound transducer. In this case, aluminum or copper wire is used as the bonding wire. If gold wire is to be used, thermal connection methods can also be used. The electrical connection between the two contact surfaces themselves is established by pulling a wire bridge from the first contact to the second contact. When pulling this wire bridge, the geometric conditions of the semiconductor component to be produced must be taken into account, so that in particular a certain wire arch height must be maintained in order to avoid particularly short circuits to adjacent bond pads or structural elements of the semiconductor component.

During this process, the bonding wire must on the one hand use the bonding tool that is used for ultrasonic wire bonding is designed as a bond wedge or wedge, is fed and, on the other hand, is held in place during the bonding itself and, if necessary, is subsequently pushed in when the wire bridge is pulled. In the first bonding process in each case, it is also necessary that the bonding wire is pushed forward under the bonding tool. Wire or thread clips are usually used for this process, which are arranged in the immediate vicinity of the bonding tool or immediately behind the bonding tool and hold or release the bonding wire depending on the current method step, or after the second bonding process by clamping the edge wire and then pulling it back from the second bond point.

The feeding of the bonding wire from a supply spool via guide elements to the guide bore generally takes place with a thread clip, the bonding wire being aligned axially to the guide bore. In DE 43 26 478 AI, in order to avoid any wire abrasion, it is important that the thread clip used to move the bonding wire is moved exactly parallel to the course of the bonding wire. Before the first bonding process of a wire bridge, the bonding wire is first pushed with the thread clip through the guide hole under the working surface of the bonding tool.

As a result of the feed movement aligned with the guide bore, the free end of the bonding wire extends straight from the guide bore, with edge contact with the working surface of the bonding tool occurring at best. This feed movement is achieved by a more or less rectilinear feed movement of the thread clamp and the bonding wire held in it.

However, the result of this feed movement shows a serious disadvantage, which can be seen in the fact that the free wire end only has an edge contact with the working surface of the bonding tool. When executing the first bond of a wire bridge, ie while contacting the Contact point, the free end of the bonding wire is bent upwards in the direction of the working surface of the bonding tool until the bonding wire lies parallel below the working surface. Only then can the bonding process be started

In this process, a force component acts on the bond wire in its longitudinal direction, causing it to be pushed back. This force component depends on the angle of attack of the guide bore with respect to the horizontal, which is usually 45 ° or 60 °.

The result of this push back is a non-constant waist length that can lead to bond errors. If the bond wire were held with the help of the thread clamp, a largely constant waist length would be achieved, but at the same time a kink would occur in the bond wire.

The specification of a larger waist length to compensate for the push-back movement is likewise not expedient, since then there is a risk of a short circuit to neighboring bond islands.

Another disadvantage, which is particularly evident in the case of particularly small bond pads, is the risk that the bond wire will move out of its central position under the work surface during the bending process, so that the bond pad is no longer hit optimally. Such a bonding error can only be determined after the bonding tool has been lifted off the bonding pad.

The thread clamp generally consists of two jaws which can be pivoted relative to one another, each with a jaw surface, between which the bonding wire can be clamped. The bond wire is clamped here by swiveling the jaws together under the action of an adjustable spring force until their jaw surfaces bear against the bond wire with a predetermined force. Since the thread clip is generally arranged vertically, in order to ensure good accessibility and visibility of the To achieve the bond wedge, there is an angular offset between the axis of rotation of the thread clamp and the course of the bond wire, which is to be fed to the bond tool at an angle, which, depending on the application, can be between 30 ° and 60 °. Because of this and because of the relatively large distance between the axis of rotation of the thread clamp and the position of the bonding wire, the problem arises that the bonding wire is only partially clamped and consequently undergoes a cross-sectional change which can later lead to wire breakage.

For this reason, extremely high demands are placed on the manufacturing accuracy of the thread clamp. Since the pliers gap must correspond to the bond wire diameter to avoid a change in cross-section or a weakening of the material, the jaws must be exactly parallel to each other. Even the smallest dimensional deviations in the micrometer range have the effect that the bonding wire is only partially clamped and thus a cross-sectional change is the result, which can lead to wire breakage even during the bonding process. Even the smallest dimensional deviations of the bond wire used lead to the same negative result. With these thread clips, only the processing of bond wire with an identical diameter is possible, or defective bonds must be expected. From this follows the need for a special thread clip to be made and kept ready for each common wire diameter.

If the bonder is to be converted to other wire diameters, the thread clamp must also be replaced in addition to the bond wedge, among other things.

Since the new thread clamp has to be readjusted after its assembly, the entire changeover process is extremely time-consuming.

Although thread clips of this type only have to make small travel ranges in the range of 50 micrometers or less, they are nevertheless subject to considerable wear due to the large number of clamping processes, which also results in inaccurate wear. the clamping process. In addition, wear of the jaw surfaces must be expected, which leads to the jaw surfaces becoming uneven, so that a higher load or crushing of the bonding wire is also the result.

In such a case, it is only possible to replace the thread clamp, since regrinding of the jaw surfaces would be conceivable, but there is hardly any possibility of carrying out the grinding process in such a way that the jaw surfaces are again exactly parallel to one another when they are pressed against the bonding wire become.

These problems can only be reduced if care is taken to ensure that the axis of rotation of the thread clip runs parallel to the bonding wire, which is, however, practically not possible.

Another disadvantage of the known thread clips results from the fact that as a drive for the relative movement of the jaws against one another, i.e. for the opening process against a spring force, a lifting magnet is usually used, which is firmly connected to one of the jaws. The plunger of the solenoid actuates the opposite jaw. The mass of the thread clamp is significantly increased by the magnet, which is a disadvantage particularly in the case of the rapid feed movement of the thread clamp.

The invention is therefore based on the object of providing a thread clip which can be produced simply and inexpensively and in which the disadvantages described at the outset do not occur and with which bond wires of different diameters can be processed without restrictions.

The problem underlying the invention is solved in a thread clip of the type mentioned in that one of the jaws of the thread clip is adjustably connected to the bonding device with respect to the bonding wire and that the second jaw is connected to the first jaw via a parallel guide in such a way that the jaws can be raised and closed transversely to the longitudinal extension of the bonding wire.

With this surprisingly easy-to-implement solution, all problems that would otherwise result from an unwanted crushing of the wire are avoided. It does not matter at what angle the wire is guided between the jaw surfaces to the bonding tool or at what angle the thread clip is attached to the bonding head. In particular, the use of bonding wire with different diameters or with diameter tolerances does not lead to the problems described above. Since the jaw surfaces are moved parallel to each other, there is the possibility of regrinding them in the event of wear and the clamp can thus be used again. This results in considerable cost advantages in the assembly of semiconductor components.

In a first embodiment of the invention, the parallel guide is designed as a linear guide with a ball or slide bearing in the foot part of the first jaw, the foot part of the second jaw being coupled to the linear guide. A parallel movement of the jaw surfaces to one another during the opening and closing process is thus easily achieved. At the same time, the dimensions of the thread clip can be kept as small as possible. Due to the small dimensions of the thread clip, it is possible in principle to replace it with the thread clip previously used.

So that the bond wire can be clamped with a defined closing force of the thread clamp, the jaws are pressed together by an adjustable spring force. The jaws are opened by the drive against the spring force.

In a further embodiment of the invention, one of the jaws is arranged in a stationary manner and the other jaw is coupled to a linear drive. In a special embodiment of the invention, the jaws of the thread clamp are connected to one another via a parallel guide with solid-state joints which consist of two flat bending beams which are spaced parallel to one another. In this way, a thread clamp is realized which can be produced inexpensively and which has a long service life, in particular with a particularly low mass, since the pliers jaws are movably connected to one another without slide or ball bearings.

The thread clamp can be produced particularly inexpensively if it is made in one piece, including the bending beams connecting the jaws to one another.

In a variant, the parallel guide with solid-state joints consists of two supports arranged parallel to one another, which are connected to one another via bending beams, the jaws of the thread clamp being screwed to the supports in such a way that the supports are located between extensions of the jaws. This variant has the particular advantage that the thread clamp can be dismantled for the purpose of regrinding the pliers jaws. This variant therefore has similar advantages to the version with a parallel guide with ball or slide bearing.

If the beams are screwed to the jaws under pre-tensioning of the bending beams, there is no need for an additional compression spring to compress the jaws of the pliers.

In a further embodiment of the invention, an electromagnetic drive for opening the jaws actuates the non-stationary jaw against a stop. This prevents an unnecessarily wide opening movement of the jaws.

In a variant of the invention, the jaws are driven with a piezo bimorph, which enables particularly rapid and effective actuation of the thread clamp. Another special variant of the invention is characterized in that the thread clamp is connected to the bonding device or the bonding head via a parallel guide with solid-state joints, consisting of two bending beams arranged parallel to one another. This enables a wear-free translation movement of the thread clamp to advance the bonding wire.

The bending beams of the parallel guide are preferably located between rigid beams which are arranged parallel to one another, the bending beams and the beams being cut in one piece from a blank.

For easy replacement of the thread clamp, the bending beams are detachably connected to the supports both with the thread clamp and with the bonding device.

Another variant of the invention is characterized by a combination of the features of independent claims 5 and 11. In this way, a wear-free thread clamp and a wear-free parallel guide for the thread clamp can be realized with the same means and inexpensively.

The invention will be explained in more detail below using exemplary embodiments. In the accompanying drawing:

Fig. 1 is a front view of the thread clip;

FIG. 2 shows the side view of the thread clip according to FIG. 1;

Fig. 3 is a side view, partly in section, taken along the line I-I in Fig. 1;

4 shows a schematic illustration of a thread clip formed in one piece with a parallel guide made of bending beams; 5 shows the thread clip partially shown in section with a drive for actuating the jaws;

6 shows a multi-part variant of the thread clip according to FIG. 1;

7 shows a thread clip with a drive for the movable part of the thread clip; and

Fig. 8 shows a variant of the drive for the thread clip.

As can be seen from FIGS. 1-3, the thread clamp 1 consists of a first jaw 2 and a second jaw 3 arranged opposite the first jaw 2. Both jaws 2, 3 are at one end each with a jaw surface 4, 5 see ver, which are directed towards each other.

Furthermore, the jaws 2, 3 are each provided with a foot part 6, 7, the foot part 6 of the first jaw 2 being provided with a linear guide 8 to which the foot part 7 of the second jaw 3 is coupled. As can be seen from FIGS. 2 and 3, the linear guide has two rows of balls 9 which run in grooves 10.

Through this ball-bearing linear guide, a slight and extremely precise parallel movement of the jaws 2, 3 or the jaw surfaces 4, 5 with respect to one another is achieved. When assembling the thread clamp 1, it is only necessary to ensure that the jaw surfaces 4, 5 are aligned exactly parallel to one another.

A lifting magnet can advantageously be used as the drive 11 for the thread clamp 1, which magnet is fastened to the first jaw 2 and acts directly on the second jaw 3, as can be seen from FIG. 1. However, it is also possible to arrange the drive 11 at a different location, for example in front of the foot parts 6, 7. In order to be able to clamp the bonding wire 12 between the jaw surfaces 4, 5 with a defined force, the jaw 3 is pressed onto the first jaw 2 in a spring-loaded manner. A spring 13 assigned to the jaws 4, 5 can serve this purpose. According to FIG. 1, the spring 13 is designed as a compression spring, and a tension spring can also be arranged in a corresponding manner in an analog arrangement. The jaws 4, 5 are opened to release the bonding wire with the aid of the drive 11 against the spring force.

In order to be able to attach the thread clip 1 in a favorable manner to a bondhead (not shown), there is a space 14 between the jaws through which an ultrasound transmitter with an associated bond wedge can be passed.

Due to the exact parallel movement of the jaw surfaces 4, 5 to one another, a large-area clamping of the bonding wire is achieved in the closed state of the thread clamp, the cross-section of which is not reduced at any point in this way. In addition, it is completely irrelevant at what angle the bond wire runs between the jaw surfaces 4, 5. The thread clip 1 can thus be attached to the bonding head in the most favorable position in each case.

In addition, diameter tolerances of the bond wires or the use of bond wires of different diameters have no disadvantageous consequences, so that the assembly process as a whole can be made more cost-effective. This also results from the fact that the jaw surfaces 4, 5 can be reground at any time without this having any influence on the bond wire 13 to be clamped.

In addition, such a thread clip 1 allows the production with larger manufacturing tolerances, so that the overall manufacturing costs are reduced. The jaws 2, 3 and the associated jaw surfaces 4, 5 are preferably formed in one piece. In principle, it is also possible to manufacture the jaws 2, 3 from a light metal and to glue the jaw surfaces 4, 5, for example made of stainless steel, and the jaw surfaces 4, 5 to the jaws 2, 3. Such a thread clip 1 has a particularly low weight.

A special variant of the invention can be seen in FIGS. 4-8, the same advantages being achieved in principle as in the case of the thread clamp with parallel guidance by means of ball or slide bearings. The thread clip 1 is only drawn in a schematic diagram here. 4 shows a schematic representation of a one-piece thread clamp 1 with a parallel guide made of bending beams 15, 16 for the jaws 2, 3. The pretensioning of the jaws 2, 3 is generated here by an additional spring 22 .

The jaws 2, 3 are arranged on a further parallel guide, consisting of the bending beams 18, 19 between supports 20, 21, for executing a translational movement of the thread clamp 1, the parallel guide being oriented such that the translation movement of the thread clamp 1 is approximately in Axial direction of the bond wire 12 takes place. The bending beams 18, 19 preferably consist of spring steel and are fastened to the supports 20, 21 as separate components. The bending beams 18, 19 between the beams 20, 21 are mounted without pretension.

The one-piece design of the thread clamp 1 is inexpensive to produce, but has the disadvantage that no pre-tension can be generated by the bending beams 15, 16 and that the regrinding of the jaw surfaces is only possible to a limited extent.

5 shows a thread clip 1, shown partly in section, with a drive 17 for actuating the jaws 2, 3.

For the thread clamp 1 with parallel bending beams 15, 16 (Fig. 4 - 6) the moving mass is less, whereby different wire thicknesses can be processed with the same thread clip 1.

Fig. 6 shows a multi-part variant of the thread clip 1 according to Fig. 4, in which the bending beams 15, 16 are arranged as a separate assembly between the carriers 20, 21, which in turn are screwed to the jaws 2, 3 of the thread clip 1. The attachment of the carrier 20, 21 was carried out here so that the bending beams are under tension and the jaws 2, 3 press against each other with a defined closing force. This eliminates the need for an additional spring. This variant has a number of advantages. On the one hand, the parallel movement of the pliers jaws is guaranteed, and on the other hand, this variant is suitable for clamping different wire thicknesses. A particular advantage of this variant can also be seen in the fact that the jaws 2, 3 can be reworked.

7 also shows a thread clip 1 with a drive 17 for the movable part of the thread clip 1 (jaw 3). The drive consisting of a magnet is no longer mechanically connected to the thread clamp 1, so that the magnet is relatively fixed during the feed movement. The drive 17, consisting of an armature 24 with an associated coil 25, is arranged here between the bending beams. The yoke 26 is located here on the movable jaw 3.

Another variant of the drive 6 for the thread clamp 1 can be seen in FIG. 8, in which the maximum opening movement of the jaws 2, 3 is limited by an adjustable stop 27, thereby preventing overloading of the bending beams during the opening process of the jaws.

In the thread clips shown in FIGS. 7 and 8, the pretension required to generate the necessary pretension can be achieved by an additional spring 10 analogous to FIGS. 4 and 5 or by a separate assembly with bending beams 7, 8 are generated analogously to FIG. 6.

A gentle wire feed can be achieved with the wire pliers described above, the bond wire 12 not necessarily being fed exactly axially to the guide bore in the bond tool. For example, the bonding wire can be fed in such a way that it is fed to the guide bore in the bonding tool with an angular deviation α relative to the opening angle β of the guide bore. As a result, a pre-deformation of the same is achieved during the advance of the bonding wire 12. This pre-deformation causes the bonding wire to largely contact the work surface 4 of the bonding tool from below, so that the disadvantages of the prior art described at the outset can be avoided. In practice, this can be achieved simply by setting the parallel guide for the thread clamp 1, consisting of the bending beams 18, 19 (FIG. 4), at the desired angle relative to the axial extension of the bonding wire 12.

In particular, the invention prevents the bond wire 12 from being pushed back onto the bond pad during the placement movement.

Thread clip

Reference list

1 thread clip

2 first jaw

3 second jaw

4 jaw surface

5 jaw surface

6 foot section

7 foot section

8 linear guide

9 bullet

10 groove

11 drive

12 bond wire

13 spring

14 free space

15 bending beams

16 bending beams

17 drive

18 bending beams

19 bending beams

20 carriers

21 carriers

22 spring

23 tie rod

24 anchors

25 coil 26 yoke

27 stop

Claims

Thread clip patent claims 1. Thread clamp (1) with two jaws (2, 3) which can be moved relative to one another by a drive (11; 17) and are provided with jaw surfaces for clamping and moving or holding bonding wires (12) of different diameters, for ultrasonic wire bonding devices, wherein the thread clip (1) is arranged directly behind a bonding tool (wedge), characterized in that one of the jaws (2) of the thread clip (1) is adjustably connected to the bonding device relative to the bonding wire (12) and that the second movable jaw (3) is connected to the first jaw (2) via a parallel guide in such a way that the jaws (2, 3) can be lifted and closed transversely to the longitudinal extension of the bonding wire (12). 2. Thread clamp according to claim 1, dadurchge ¬ indicates that the parallel guide is designed as a linear guide (8) with a ball or slide bearing in the foot part (6) of the first jaw (2) and that the foot part (7) of the second jaw (3) is coupled to the linear guide (8). 3. Thread clamp according to claim 1, so that the jaws (2, 3) can be lifted off from one another by an adjustable spring force and by the drive (11, 17). 4. Thread clamp according to claims 1 to 3, characterized in that one of the jaws (2; 3) is arranged in a stationary manner and that the other jaw (3) is coupled to a linear drive. 5. thread clamp (1) with two jaws (2, 3) which can be moved relative to one another by a drive (11; 17) and are provided with jaw surfaces for clamping and moving or holding bonding wires (12) of different diameters, for ultrasonic wire bonding devices, wherein the thread clamp (1) is arranged directly behind a bonding tool (wedge), characterized in that the jaws 2, 3) of the thread clamp (1) are connected to one another via a parallel guide with solid-state joints which are spaced apart from one another in parallel ¬ th flat bending beam (15, 16) exist. 6. Thread clamp according to claim 5, so that the thread clamp (1), including the bending beams (15, 16) connecting the jaws (2, 3), is made in one piece. 7. Thread clip according to claim 5 and 6, dadurchge ¬ indicates that the parallel guide with solid joints consists of two parallel supports (20, 21) which are connected to each other via bending beams (15, 16) and that the jaws (2nd , 3) the thread clamp (1) is screwed to the carriers (20, 21) in such a way that the carriers (20, 21) are located between extensions of the jaws (2, 3). 8. Thread clip according to claim 7, d a d u r c h g e ¬ k e n n z e i c h n e t that the carrier (20, 21) under tension of the bending beam (18, 19) with the jaws (2, 3) are screwed. 9. Thread clamp according to one of claims 1 to 8, d a ¬ d u r c h g e k e n n z e i c h n e t that the drive (17) electromagnetically actuates the non-stationary jaw (3) against a stop (27). 10. Thread clamp according to claim 9, dadurchge ¬ indicates that the drive of the jaws (2, 3) done with a piezo bimorph. 11. Thread clamp (1) with two jaws (2, 3) which can be moved relative to one another by a drive (11; 17) and are provided with jaw surfaces for clamping and moving or holding bonding wires (12) of different diameters, for ultrasonic wire bonding devices, wherein the thread clamp (1) is arranged directly behind a bonding tool (wedge), characterized in that the thread clamp (1) is connected to the bond device via a parallel guide with solid body joints, consisting of two bending beams (18, 19) arranged parallel to one another ¬ device, or the bond head is connected. 12. Thread clamp according to claim 11, dadurchge ¬ indicates that the bending beams (15, 16; 18, 19) are located between mutually parallel rigid beams (20, 21), the bending beams (15, 16; 18, 19th ) and the carriers (20, 21) are cut in one piece from a blank. 13. Thread clip according to claims 11, d a d u r c h g e ¬ k e n n z e i c h n e t that the bending beams (18, 19) with the carriers (20, 21) are releasably connected both to the thread clip (19, and with the bonding device. 14. Thread clamp (1) with two jaws (2, 3) movable relative to one another by a drive (11; 17) and provided with jaw surfaces for clamping and moving or holding bonding wires (12) of different diameters, for ultrasonic wire bonding devices, wherein the thread clamp (1) is arranged directly behind a bonding tool (wedge), characterized by the features of claims 5 and 11.