WO2009076048A1

WO2009076048A1 - Method of forming a wire loop including a bend

Info

Publication number: WO2009076048A1
Application number: PCT/US2008/084503
Authority: WO
Inventors: Ivy Wei Qin; Romeo Olida
Original assignee: Kulicke And Soffa Industries, Inc.
Priority date: 2007-12-05
Filing date: 2008-11-24
Publication date: 2009-06-18

Abstract

A method of forming a wire loop on a workpiece using a wire bonding machine is provided. The method includes the steps of: (1) forming a first bond of a wire loop at a first bonding location of the workpiece using a bonding tool of the wire bonding machine; (2) extending a length of wire from the first bond of the wire loop using the bonding tool; (3) forming a bend in the length of wire by shaping the wire against a structure using the wire bonding tool; and (4) forming a second bond at a second bonding location of the workpiece.

Description

METHOD OF FORMING A WIRE LOOP INCLUDING A BEND

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No.

60/992,341, filed December 5, 2007, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to the formation of wire loops using a wire bonding machine, and more particularly, to improved methods of forming wire loops.

BACKGROUND OF THE INVENTION

[0003] In the processing and packaging of semiconductor devices, wire bonding continues to be the primary method of providing electrical interconnection between two locations within a package (e.g., between a die pad of a semiconductor die and a lead of a leadframe). More specifically, using a wire bonder (also known as a wire bonding machine) wire loops are formed between respective locations to be electrically interconnected. Wire loops are typically formed using ball bonding or wedge bonding.

[0004] An exemplary conventional ball bonding, wire bonding sequence includes: (1) forming a free air ball on an end of a wire extending from a bonding tool; (2) forming a first bond on a die pad of a semiconductor die using the free air ball; (3) extending a length of wire in a desired shape between the die pad and a lead of a leadframe; (4) stitch bonding the wire to the lead of the leadframe; and (5) severing the wire. In forming the bonds between (a) the ends of the wire loop and (b) the bond site (e.g., a die pad, a lead, etc.) varying types of bonding energy may be used including, for example, ultrasonic energy, thermosonic energy, thermocompressive energy, amongst others.

[0005] In certain applications sharp bends are to be formed in wire loops.

Consider, for example, the application where a first bond is on a semiconductor d ie, and a second bond is to be formed on a substrate (e.g., a leadframe) supporting the semiconductor die. If the second bond site (e.g., a lead of the leadframe) is very close to the edge of the semiconductor die it may be difficult to bend the wire towa rd the second bond site. More specifically, the angle of the desired bend may be too difficult to achieve using conventional shaping techniques (e.g., shaping the wire using the capillary bonding tool alone). In such a situation, wire bonding may be impractical, or if the wire bonding is performed, looping problems (e.g., contact between the loop and the die, wire sag, etc.) may reduce the yield of the wire bonding operation.

[0006] Accordingly, it would be desirable to provide improved methods of shaping wire loops with sharp bends.

SUMMARY OF THE INVENTION

[0007] According to an exemplary embodiment of the present invention, a method of forming a wire loop on a workpiece using a wire bonding machine is provided. The method includes the steps of: (1) forming a first bond of a wire loop at a first bonding location of the workpiece using a bonding tool of the wire bonding machine; (2) extending a length of wire from the first bond of the wire loop using the bonding tool; (3) forming a bend in the length of wire by shaping the wire against a structure using the wire bonding tool; and (4) forming a second bond at a second bonding location of the workpiece.

[0008] The structure may be, for example, a portion of the workpiece such as a portion of a semiconductor die, a portion of a substrate, or another component (e.g., an active component, a passive component) of the workpiece. In another example, the structure may be a portion of the wire bonding machine such as a portion of the clamp insert of the wire bonding machine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:

FIGS. 1A-1C are block diagram side views illustrating a process of forming a wire loop in accordance with an exemplary embodiment of the present invention;

FIGS. 2A-2B are block diagram side views illustrating certain benefits of the present invention; FIG. 3A is a block diagram top view of a clamp insert used to secure a workpiece in accordance with an exemplary embodiment of the present invention;

FIG. 3B is a block diagram side view of a portion of the workpiece of FIG. 3A;

FIG. 4A is a diagram of a conventional wire looping trajectory;

FIG. 4B is a detailed view of a portion of the FIG. 4A;

FIG. 5A is a diagram of a wire looping trajectory in accordance with an exemplary embodiment of the present invention;

FIG. 5B is a detailed view of a portion of the FIG. 5A;

FIG. 6A is a diagram of a wire looping trajectory in accordance with another exemplary embodiment of the present invention;

FIG. 6B is a detailed view of a portion of the FIG. 6A;

FIG. 7A is a diagram of a wire looping trajectory in accordance with yet another exemplary embodiment of the present invention;

FIG. 7B is a detailed view of a portion of the FIG. 7A;

FIG. 8A is a diagram of a wire looping trajectory in accordance with yet another exemplary embodiment of the present invention; and

FIG. 8B is a detailed view of a portion of the FIG. 8A.

DETAILED DESCRIPTION OF THE INVENTION

[0010] In accordance with various exemplary embodiments of the present invention, improved methods of creating a sharp bend in a wire loop are provided. More specifically, sharp bends may be formed by using coordinated XYZ motions to bend/shape a portion of the wire loop around a surface of a structure such as the edge of a semiconductor die. By forming bends according to the present invention, the desired shape of the wire loop may be achieved, including desired clearances and the like. As used herein, the term "bend" is intended to broadly refer to any type of bending, shaping, kinking of the wire around the structure. [0011] According to certain exemplary embodiments of the present invention, a structure adjacent the bond site area (e.g., the edge of a semiconductor die) is used to bend/shape the wire. This is in direct contrast to conventional shaping methods which form the wire loop by capillary shaping only. According to exemplary embodiments of the present invention where the edge of a semiconductor is used to bend/shape the wire loop (e.g., as in FIGS. 1A-1C described below), it may be desirable to know the precise location of the die edge. Often, this information is not known during conventional wire bonding processes. Thus, in certain exemplary embodiments of the present invention, an additional step may be used to teach the location of the die edge, for example, relative to an eye point (e.g., an eyepoint of the semiconductor die). As is known to those skilled in the art, teaching operations are typically performed using an optics assembly of the wire bonding machine. In connection with present invention, during run time of the wire bonding machine, the die edge may be found using (1) the eyepoint found location which provides a relative location of the die edge, or (2) using the machine vision system to locate the actual die edge. Further, a series of XYZ motions may be added to a conventional looping motion to perform the shaping motion around the die edge.

[0012] Referring now to FIG. IA, semiconductor die 102 is supported by substrate 100 (e.g., a leadframe 100). Of course, only a portion of these elements are shown in FIG. IA for simplicity. It is desired to extend wire loop 104 between die pad 102a of semiconductor die 102 and conductive region 100a of substrate 100 (e.g., lead 100a of leadframe 100). First bond 104a of wire loop 104 (in the illustrated example, first bond 104a is a ball bond) has been bonded to die pad 102a of semiconductor die 102, and a length of wire included in wire loop 104 has been extended from first bond 104a toward second bond location 100a on substrate 100 using bonding tool 106. As is shown in FIG. IA, second bond location 100a is close to edge 102b of semiconductor die 102. Therefore, in order to form a desirable wire loop shape at edge 102b of semiconductor die 102, a sharp bend in the wire is desirably formed.

[0013] In order to form the sharp bend, at FIG. IB, bonding tool 106 is moved downward and inward toward edge 102b of semiconductor die 102 such that the wire contacts edge 104b. The actual motion of bonding tool 106 toward edge 102b of semiconductor die 102 (and the associated XYZ parameters used in connection with the motion of bonding tool 106) will vary, for example, depending upon the desired bend shape. In some applications the motion may be a pure z (i.e., vertical) motion of bonding tool 106 which causes the wire to be bent around edge 102b of semiconductor die 102. In other applications the motion may be a pure sideways (inward) motion of bonding tool 106 toward semiconductor die 102, which causes the wire to be bent around edge 102b of semiconductor die 102. In other applications the motion may be a combination of downward z motion and inward sideways motion of bonding tool 106 which causes the wire to be bent around edge 102b of semiconductor die 102 (of course, such a combination may be discrete downward and sideways motions, or may be a diagonal motion). These bonding tool motions are exemplary in nature, as it is clear that a plurality of motions may be made in order to bend the wire as desired around edge 102b of semiconductor die 102. Further, the motions will likely vary from one wire loop location to another in certain applications. For example, in a device which includes wire loops to be formed around an entire periphery of a semiconductor die, the motion of the tool may change as desired given the wire loop to be formed.

[0014] After the wire is bent around edge 102b of semiconductor die 102 to have the desired bend shape, bonding tool 106 is moved to form second bond 104c as shown in FIG. 1C. As is clear from FIG. 1C, because of the bending of the wire around edge 102b of semiconductor die 102 in FIG. IB, there is adequate clearance provided between edge 102b of semiconductor die 102 and bent portion 104b of wire loop 104.

[0015] FIG. 2A illustrates wire loop 204 extended between die pad 202a of semiconductor die 202 and second bond location 200a of substrate 200 (e.g., lead 200a of leadframe 200, where semiconductor die 202 is supported by leadframe 202). Second bond location 200a is close to edge 202b of semiconductor die 202. Wire loop 204 has been shaped using conventional techniques. There are numerous problems with wire loop 204 shown in FIG. 2A including, for example; a large radius around second bond; inadequate clearance between edge 202b and wire loop 204 (e.g., at bent portion 204b of wire loop 204 which is in contact with edge 202b); and poor wire straightness due to wire whipping on the surface of semiconductor die 202.

[0016] FIG. 2B illustrates wire loop 104 formed in accordance with an exemplary embodiment of the present invention, where the wire loop has been shaped/bent around edge 102b of semiconductor die 102 prior to formation of second bond 104c (using a method such as that shown in FIGS. 1A-1C). As is evident, there are numerous improvements in FIG. 2B when compared to the wire loop in FIG. 2A including, for example: a small radius around second bond; adequate clearance 108 between edge 102b and wire loop 104 (e.g., at bent portion 104b of wire loop 104 there is adequate clearance from die edge 102b); and improved wire straightness. [0017] Although the present invention is illustrated and described in FIGS. IA-

IC with respect to bending/shaping the wire against an edge of a semiconductor die, it is not limited thereto. Any of a number of structures may be used (in conjunction with the motion of the bonding tool) for the bending operation. For example, any part of the workpiece being wirebonded (e.g., a part of a semiconductor die, a part of a substrate such as a lead of a leadframe, an active component of the workpiece, a passive component of the workpiece) may be used. Further, other structures may be used such as a portion of a wire bonding machine adjacent the wire bonding area such as a part of a clamp insert (also known as a window clamp or a device clamp) used to secure the workpiece. FIG. 3A illustrates such an example.

[0018] More specifically, FIG. 3A is a top view of clamp insert 310 of a wire bonding machine, clamp insert 310 being used to secure a workpiece to be wirebonded (e.g., clamp insert 310 secures the workpiece to a bonding surface such as a heat block of the wire bonding machine, where the bonding surface is not shown). Clamp insert 310 defines window aperture 310c, whereby access to the workpiece is provided for the wire bonding operation through window aperture 310c. In this example, the workpiece includes semiconductor die 302 mounted to substrate 300. Semiconductor die 302 includes a first row of first bonding locations (e.g., die pads 302a, 302b through 302n), and a second row of first bonding locations (e.g., die pads 303a, 303b through 303n). Likewise, substrate 300 includes a first row of second bonding locations 300a, 300b through 30On, and a second row of second bonding locations 301a, 301b through 301n. As is known to those skilled in the art, a workpiece having two rows of die pads and two rows of second bonding locations as shown in FIG. 3A may be a memory device. Clamp insert 310 includes shaping elements 310a and 310b which extend from a top surface of clamp insert 310 across and/or above at least a portion of aperture 310c by length

[0019] It is desired to form wire loops between (1) corresponding ones of die pads 302a, 302b through 302n, 303a, and 303b through 303n, and (2) corresponding ones of second bonding locations 300a, 300b through 30On, 301a, 301b through 301n. FIG. 3B shows exemplary wire loop 304a providing electrical interconnection between die pad 302a and second bonding location 300a. Likewise, wire loop 304b provides electrical interconnection between die pad 303a and second bonding location 301a. Wire loop 304a has been formed by: (1) forming a first bond on die pad 302a, (2) extending a length of wire from the first bond and toward second bonding location 300a, (3) bending the length of wire by shaping the wire against shaping element 310a, and (4) forming a second bond on second bonding location 300a. Likewise, wire loop 304b has been formed by: (1) forming a first bond on die pad 303a, (2) extending a length of wire from the first bond and toward second bonding location 301a, (3) bending the length of wire by shaping the wire against shaping element 310b, and (4) forming a second bond on second bonding location 301a. Because each of wire loops 304a and 304b has been bent through contact with a respective one of bending structures 310a and 310b, desirable bends "B" shown in FIG. 3B may be formed.

[0020] FIG. 3A also illustrates alternative shaping elements 311a and 311b shown in dashed lines. In contrast to shaping elements 310a and 310b which are provided horizontally beyond the second bond locations, shaping elements 311a and 311b are provided between the first bond locations (e.g., die pads 302a, 302b, etc.) and the second bond locations (e.g., second bond location 300a, 300b, etc.). Using such shaping elements in this position, after the wire loops are formed the shaping elements are desirably moved out of the way prior to indexing of the device after wirebonding. Thus, shaping elements 311a and 311b are shown as retractable elements in FIG. 3A (as indicated by the double arrows at the upper part of each of the elements in FIG. 3A). For example, the shaping elements may be retractable with respect to a part of clamp insert 310 (e.g., with respect to the top surface of clamp insert 310). By retracting shaping elements 311a, 311b away from the bond site area, clamp insert 310 may then be raised to allow for indexing of the device without damaging the wire loops formed on the device (e.g., the wire loops formed between die pad 302a and second bond location 300a, etc.).

[0021] Of course, any of a number of variations of these examples may be utilized in connection with the present invention. For example, different structures (which may or may not be part of the workpiece or the clamp insert) may be utilized. Further, various types of workpieces may be wirebonded using the inventive techniques including die to die bonding, stacked die bonding, reverse bonding, stand-off stitch (SSB) bonding, etc., and as such, one portion of a workpiece (one semiconductor die in a multi-die workpiece) may be used to bend the wire for bonding to another portion of the workpiece (another semiconductor die in a multi-die workpiece).

[0022] As described above, the actual motion of the bonding tool (i.e., the XYZ trajectory of the bonding tool) used when bending the wire around the structure (e.g., the edge of the semiconductor die) may vary depending upon the desired loop shape and other factors. FIGS. 4A-4B illustrate an example of a looping trajectory used to form a conventional wire loop. FIGS. 5A-5B, 6A-6B, 7A-7B, and 8A-8B are looping trajectories used in various exemplary embodiments of the present invention. Of course, countless other trajectories may be used to bend the wire within the scope of the present invention. Thus, it is clear that FIGS. 5A-5B, 6A-6B, 7A-7B, and 8A-8B are exemplary in nature.

[0023] Referring now to FIG. 4A, a conventional wire looping trajectory is provided. The vertical axis represents the motion along the z-axis, while the horizontal axis represents motion along the x-axis and/or the y-axis, which may be in the same direction as the die pad and the second bond location. These vertical and horizontal axis representations are the same for each of FIGS. 5A-5B, 6A-6B, 7A-7B, and 8A-8B. As is understood by those skilled in the art, the horizontal motion (i.e., the motion along the x-axis and/or the y-axis) may be different from one wire to another because some wire loops may be formed at the 12 o'clock position, while others may be formed at the 3 o'clock position, and so on, while still others may be formed along a diagonal horizontal path (with both x and y components), etc. FIG. 4B shows a conventional approach to second bond which is a substantially straight motion (with a slight arc).

[0024] FIG. 5A is an exemplary trajectory for a wire loop in accordance with the present invention. Most of the trajectory shown in FIG. 5A is a basic looping trajectory (similar to that shown in FIG. 4A) which is not relevant to the present invention, whi le FIG. 5B shows the most relevant portion of the trajectory. As can be seen from FIG. 5B, at about 8 mils above second bond the trajectory shifts to a downward (and outward, that is, away from the die edge) trajectory. Then, at about 5 mils above second bond, the trajectory shifts to a substantially straight and direct motion to second bond.

[0025] FIG. 6A (with the detail provided in Fig. 6B), FIG. 7A (with the detail provided in FIG. 7B), and FIG. 8A (with the detail provided in FIG. 8B) are alternative exemplary trajectories used in connection with bending the wire against an edge of a semiconductor die or some other structure.

[0026] Although the looping trajectories shown in FIGS. 5A-5B, 6A-6B, 7A-7B, and 8A-8B relate to basic looping trajectories (except for the inventive portions shown in the details views approaching second bond), the present invention may apply to any of a number of different and more complex loops. The critical point of the present invention is that at some point in the trajectory, the wire loop is bent using a structure (e.g., the die corner/edge) other than capillary bonding tool shaping.

[0027] Although the present invention is illustrated and described primarily with respect to forming the bend (using a structure other than conventional capillary bonding tool shaping) just prior to second bond in a wire loop where the second bond site is close to the die edge, it is not limited thereto. For example, it may be desired to shape a wire loop at any portion of the length of the wire loop based on the desired shape. Thus, the present invention relates to shaping/bending any portion of a wire loop using any structure other than conventional capillary bonding tool shaping techniques.

[0028] Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope of the invention.

Claims

What is Claimed:

1. A method of forming a wire loop on a workpiece using a wire bonding machine, the method comprising the steps of:

(1) forming a first bond of a wire loop at a first bonding location of the workpiece using a bonding tool of the wire bonding machine;

(2) extending a length of wire from the first bond of the wire loop using the bonding tool;

(3) forming a bend in the length of wire by shaping the wire against a structure using the wire bonding tool; and

(4) forming a second bond at a second bonding location of the workpiece.

2. The method of claim 1 wherein step (1) includes forming the first bond on a semiconductor die of the workpiece.

3. The method of claim 1 wherein step (1) includes forming the first bond on a substrate of the workpiece.

4. The method of claim 1 wherein step (1) includes forming the first bond on a semiconductor die of the workpiece, and step (4) includes forming the second bond on a substrate of the workpiece.

5. The method of claim 1 wherein step (1) includes forming the first bond on a semiconductor die of the workpiece, and step (4) includes forming the second bond on another semiconductor die of the workpiece, such that the wire loop provides electrical interconnection between the semiconductor die and the another semiconductor die.

6. The method of claim 1 wherein step (2) includes extending the length of wire from the first bond such that the length of wire and the first bond are continuous with one another.

7. The method of claim 1 wherein the structure is a portion of the workpiece such that step (3) includes forming the bend by shaping the length of wire against a portion of the workpiece using the bonding tool.

8. The method of claim 7 wherein step (3) includes forming the bend by shaping the wire against a portion of a semiconductor die of the workpiece using the wire bonding tool.

9. The method of claim 8 wherein step (3) includes forming the bend by shaping the wire against an edge portion of the semiconductor die of the workpiece using the wire bonding tool.

10. The method of claim 7 wherein step (1) includes forming the first bond on a semiconductor die of the workpiece, and step (3) includes forming the bend by shaping the wire against a portion of the semiconductor die of the workpiece using the wire bonding tool.

11. The method of claim 10 wherein step (3) includes forming the bend by shaping the wire against an edge portion of the semiconductor die of the workpiece using the wire bonding tool.

12. The method of claim 7 wherein step (3) includes forming the bend by shaping the wire against a substrate of the workpiece.

13. The method of claim 7 wherein step (3) includes forming the bend by shaping the wire against an active component of the workpiece.

14. The method of claim 7 wherein step (3) includes forming the bend by shaping the wire against a passive component of the workpiece.

15. The method of claim 1 wherein the structure is a portion of the wire bonding machine such that step (3) includes forming the bend by shaping the length of wire against the portion of the wire bonding machine using the bonding tool.

16. The method of claim 15 wherein step (3) includes forming the bend by shaping the length of wire against a portion of a clamp insert of the wire bonding machine using the bonding tool.

17. The method of claim 16 wherein step (3) includes forming the bend by shaping the length of wire against a shaping element of the clamp insert using the bonding tool, the shaping element extending above at least a portion of the window aperture of the clamp insert.

18. The method of claim 16 wherein step (3) includes forming the bend by shaping the length of wire against a shaping element of the clamp insert using the bonding tool, the shaping element extending across at least a portion of the window aperture of the clamp insert.

19. The method of claim 1 wherein the shaping of step (3) includes moving the bonding tool in a vertical direction such that the wire is shaped against the structure.

20. The method of claim 1 wherein the shaping of step (3) includes moving the bonding tool in a horizontal direction such that the wire is shaped against the structure.

21. The method of claim 1 wherein the shaping of step (3) includes moving the bonding tool in each of a vertical direction and a horizontal direction such that the wire is shaped against the structure.

22. The method of claim 1 wherein the shaping of step (3) includes moving the bonding tool in a downward diagonal direction such that the wire is shaped against the structure.

23. The method of claim 1 further comprising the step of performing a teaching operation of at least a portion of the structure using a vision system of the wire bonding machine.