Formation of bonded wire vertical interconnects

Abstract

A wire bonding method comprising the steps of extending a bonding wire from a capillary bonding tip to form a wire tail, deforming a point on the wire tail to form a weakened portion between the wire tail and a remaining portion of the bonding wire that remains within the capillary bonding tip, and retracting at least a portion of the wire tail, including the weakened portion, into the capillary bonding tip prior to bonding the wire tail to at least one of a bond pad and a substrate.

Description

Technical Field

[0001] This invention relates to techniques for forming lead interconnect structures for semiconductor packaging, and more particularly to the formation of lead interconnect structures with vertical orientation. Background Technology

[0002] Wire bonding machines can be used to form bond via array (BVA) wire interconnects at different locations on a substrate. Typically, the bonding wires are transported via a capillary bonding head. The free end of the bonding wire is bonded to a bonding pad at a first location on the substrate using the capillary bonding head. The capillary bonding head then moves from this location, allowing more bonding wire to be transported through it. The capillary bonding head then reaches a second location on the substrate, arching the wire from the first location and pressing it against the second location to weaken the bond. After the capillary bonding head returns to a position above the bonding pad, the wire is clamped and pulled out, leaving a wire interconnect bonded to the bonding pad at one end and extending perpendicularly from the pad, terminating at the free end. This process is repeated at other locations to form the desired wire interconnects. This method is described in more detail in U.S. Patent 9,502,371 (B2), entitled “Method for Forming a Lead Interconnect Structure”.

[0003] While the above method can be used to provide vertical lead interconnects, it has undesirable consequences. In particular, the device formats for which bonding operations can be performed using this method may be limited. Therefore, an improved method for forming vertical lead interconnect structures is desired. Summary of the Invention

[0004] Therefore, the object of the present invention is to provide a method that overcomes at least some of the aforementioned problems in the prior art.

[0005] According to a first aspect of the present invention, a wire bonding method is provided, comprising the following steps: Extend a bonding wire from the capillary bonding head to form a lead tail; Deformation, causing the point on the lead tail to deform to form a weakened portion between the lead tail and the remaining portion of the bonding lead retained within the capillary bonding head; and Retraction: Before bonding the lead tail to at least one of the bonding pad and the substrate, at least a portion of the lead tail, including the weakened portion, is retracted into the capillary bonding head.

[0006] The first aspect recognizes that the problem with existing methods is that the lead tail is first fixed to the bonding pad or substrate at its free end, and a weakened portion is created by translating the capillary bonding head to a new position and pressing the tip of the capillary bonding head against the substrate at that new position. This results in an arching of the bonded lead between the two positions, thereby introducing a bend in the bonded lead along its longitudinal length. Moreover, this requires sufficient space on the substrate between the two positions to extend the lead tail to the desired length, and requires translation of the capillary bonding head between the different positions on the substrate. Furthermore, the first bonding neck may be damaged during various bending movements, the bending of the lead tail makes it difficult to maintain a straight vertical orientation, resulting in false marks at the new position when the capillary bonding head is pressed, and the need for two positions imposes a practical limitation on the height of the lead tail.

[0007] Therefore, a method is provided that can be used for wire bonding. The method may include extending or providing a section of bonding wire from a capillary bonding head to form or provide an unbonded lead tail. The method may include deforming a point, location, or portion on the lead tail to form a weakened portion between the lead tail and the remaining portion of the bonding wire passing through the capillary bonding head. The method may include retracting or withdrawing at least that portion of the lead tail, including the weakened portion, into the capillary bonding head. This allows selection of the lead tail length without translating the capillary bonding head between different locations. Similarly, a weakened portion can be formed between the lead tail and the remaining portion of the bonding wire without contacting the capillary bonding head with surfaces at two different locations, and without forming an arched lead between these two locations or introducing bends in the bonding wire along its longitudinal length. Furthermore, any bends in the bonding wire formed during the formation of the weakened portion can be straightened before bonding the lead tail to the bonding pad and / or substrate.

[0008] In one embodiment, the lead tail has a free end away from the capillary bonding head, and a weakened portion close to the capillary bonding head. Thus, the lead tail can have a free end and a weakened portion. The weakened portion can be positioned towards the capillary bonding head, while the free end can be positioned away from the capillary bonding head.

[0009] In one embodiment, the modified step described above includes pressing the lead tail against at least one of the substrate and bonding pad using a capillary bonding head. Thus, the weakened portion can be formed by pressing or pushing the point on the lead tail against the substrate and / or bonding pad using a capillary bonding head.

[0010] In one embodiment, the modified step described above includes pressing a point on the lead tail against at least one of the substrate and the bonding pad.

[0011] In one embodiment, the deformation step includes translating the lead tail toward at least one of the substrate and the bonding pad, such that the free end contacts at least one of the substrate and the bonding pad, the continuous translation of the lead tail causing the free end to move above the surface of at least one of the substrate and the bonding pad with axial misalignment from the remaining portion of the bonding lead retained within the capillary bonding head. Thus, the lead tail can move toward the substrate and / or the bonding pad. This results in the free end contacting the substrate and / or the bonding pad. As the lead tail moves continuously, the free end moves past the surface of the substrate and / or the bonding pad. This results in axial misalignment between the lead tail and the remaining portion of the bonding lead within the capillary bonding head.

[0012] In one embodiment, the deformation step includes simultaneously displacing the capillary bonding head in a displacement direction toward at least one of the substrate and bonding pad, and translating the capillary bonding head in a direction transverse to the displacement direction. By moving the capillary bonding head in the displacement direction while simultaneously translating it in one direction, it helps to move the lead tail to be axially misaligned with the capillary bonding head.

[0013] In one embodiment, the deformation step includes compressing the cross-section of the lead tail to form a weakened portion. Therefore, a weakened portion can be formed by compressing or squeezing the lead tail.

[0014] In one embodiment, the deformation step further includes forming a lead tail around the tip of the capillary bonding head. Thus, the tip of the capillary bonding head can be shaped to facilitate the movement of the lead tail away from axial alignment and to facilitate the formation of a weakened portion.

[0015] In one embodiment, the retraction step further includes aligning the lead tail with the remaining portion of the bonding lead retained within the capillary bonding head before bonding. Thus, retracting the lead tail into the capillary bonding head helps restore the axial alignment of the lead tail with the remaining portion of the bonding lead and the capillary bonding head.

[0016] In one embodiment, the retraction includes retracting the weakened portion back into the capillary bonding head.

[0017] In one embodiment, the method includes forming a bonding ball on the free end of the lead tail prior to bonding.

[0018] In one embodiment, the method includes moving a bonding ball to bond with a bonding pad, thereby forming a spherical wire bond.

[0019] In one embodiment, the method includes repeatedly translating a capillary bonding head in a direction transverse to the displacement direction to weaken the weakened portion. Translation of the capillary bonding head facilitates further weakening of the weakened portion.

[0020] In one embodiment, the method includes repeatedly translating the capillary bonding head in a direction transverse to the displacement direction to weaken the weakened portion, while aligning the opening of the capillary bonding head through which the bonding wire extends to approach the weakened portion. Positioning the weakened portion near the outside of the opening of the capillary bonding head helps to maximize the weakening of the weakened portion.

[0021] In one embodiment, the method includes moving the remaining portion of the bonding wire and clamping the remaining portion of the bonding wire to separate it from the ball wire bonding portion at the weakened portion (point).

[0022] According to the second aspect, an apparatus and embodiments thereof are provided that are configured to perform the method of the first aspect.

[0023] These and other features, aspects and advantages will be better understood based on the specification, the appended claims and the drawings. Attached Figure Description

[0024] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which...

[0025] Figure 1 The main components of a wire bonding apparatus for forming wire interconnects according to one embodiment are shown.

[0026] Figures 2 to 9 The operation of the wire bonding apparatus when fabricating wire bonding interconnects according to a preferred embodiment of the present invention is illustrated.

[0027] In the accompanying drawings, the same parts are indicated by the same reference numerals. Detailed Implementation

[0028] Before discussing embodiments of the invention in more detail, an overview will first be provided. In one embodiment, a lead is released from a capillary bonding head, and the unbonded lead is pre-cut (deformed, typically by compression to form a wedge) at the first bonding location. The lead is then retracted, leaving a lead tail, and an air-free ball is formed at the lead tail for the first bonding. After the first bonding, the capillary bonding head is lifted and the lead is disconnected.

[0029] Figure 1The main components of a wire bonding apparatus 100 for forming a wire interconnect according to one embodiment are shown. For clarity, other components of the wire bonding apparatus 100 have been omitted. A capillary bonding head 103 is configured to be axially aligned with a lead holding mechanism such as a proximal lead clamp 102 and a distal lead clamp 101. A continuous length of bonding lead 105, provided by a bonding lead reel (not shown), passes through the lead clamps 101, 102 and through the capillary bonding head 103. The bonding lead 105 can pass freely through the capillary bonding head 103, but the lead clamps 101, 102 are operable to independently clamp or release the bonding lead 105. The distal lead clamp 101 has a substantially fixed height, while the proximal lead clamp 102 can move independently along the axial direction of the bonding lead 105, as will be described in more detail below.

[0030] like Figure 1 As shown, the bonding apparatus 100 is positioned above the bonding location where wire interconnection will be performed, for example, above the bonding pad 202 on the substrate 201. The distal lead clamp 101 does not clamp the bonding lead 105, but the proximal lead clamp 102 clamps the bonding lead 105. A portion of the bonding lead 105 has passed through the capillary bonding head 103 (at reset height), such that the bonding lead 105 extends from the tip 106 of the capillary bonding head 103 to form a lead tail 104. For example, this lead tail 104 can be obtained by performing a previous wire bonding operation. Therefore, the lead tail 104 is positioned above the bonding pad 202, ready to be transported toward the bonding pad 202 in direction A.

[0031] Now go to Figure 2 The proximal lead clamp 102 and the capillary bonding head 103 typically move together toward the substrate 201 in direction A. The distal lead clamp 101 remains loose to allow lead movement. Figure 2 As shown, by translating the capillary bonding head 103 in a direction transverse to direction A during the movement of the capillary bonding head 103, the proximal lead clip 102 and the capillary bonding head 103 are moved toward the bonding pad 202 along a curved trajectory, so as to cause the lead tail 104 to bend when it contacts the substrate 201.

[0032] Therefore, when the free end 107 of the lead tail 104 extending from the tip 106 contacts the substrate 201, this contact causes the lead tail 104 to bend and lay generally along the surface of the substrate 201. The mechanical properties of the bonding lead 105 cause it to generally tend to bend sharply around the tip 106, while the tail 104 generally remains straight. Thus, a tight elbow 110 is formed between the lead tail 104 and the remainder of the bonding lead 105 within the capillary bonding head 103. This results in a generally right-angled bend near the tip 106, the elbow 110 being formed to surround and follow the shape of the tip 106. The tip 106 is chamfered to define annular protrusions 108 that facilitate the formation of the bend.

[0033] Alternatively, the orientation of the capillary bonding head 103 can be changed to be off-axis to help the lead tail 104 contact the substrate 201 at a greater tilt angle, thereby facilitating bending.

[0034] Continuous movement of the capillary bonding head 103 in direction A causes the annular protrusion 108 to deform the bonding lead 105 by creating indentations, compressions, depressions, or wedges in its vicinity, thereby providing a weakened portion or weakened point between the lead tail 104 and the remainder of the bonding lead 105 within the capillary bonding head 103. In other words, the capillary bonding head 103 moves downward to bend and deform the lead tail using a cherry-pit bonding method. Alternatively, in addition to using the annular protrusion 108 of the capillary bonding head 103, the deformation of the bonding lead 105 can also be achieved by introducing an external tool (not shown).

[0035] Therefore, as in Figure 2 As can be seen, the lead tail 104 has been bent into a state of misalignment with the remaining portion of the bonding lead 105 within the capillary bonding head 103. Moreover, a weakened portion has formed between the two.

[0036] from Figure 3 As can be seen, the distal lead clamp 101 remains loose, and the capillary bonding head 103 and the proximal lead clamp 102 move together in direction B away from the substrate 201. This causes the lead tail 104 to lift off the substrate 201, and the capillary bonding head returns to the reset height.

[0037] from Figure 4As can be seen, the distal lead clamp 101 now clamps the bonding lead 105, while the proximal lead clamp 102 releases the bonding lead 105. When the proximal lead clamp 102 and the capillary bonding head 103 are lowered in direction A and away from the distal lead clamp 101, the distal lead clamp 101 is operable to hold the bonding lead. This causes the lead tail 104 to be at least partially retracted into or pulled back into the capillary bonding head 103. Specifically, the weakened portion on the elbow 110 is retracted into the capillary bonding head 103, thereby straightening the lead tail 104 again to align with the remaining portion of the bonding lead 105. Thus, the bonding lead is restored to its original position. Figure 1 The structure shown is now modified, except that the bonding wire now has a lead tail 104, which is formed to the desired length and has a weakened portion located within the capillary bonding head 103.

[0038] Now go to Figure 5 The distal portion of the lead tail 104, protruding from the tip 106, has a bonding ball 501 formed using conventional techniques. The distal lead clamp 101 is released, and the proximal lead clamp 102 clamps the bonding lead 105. The proximal lead clamp 102, together with the capillary bonding head 103, moves in direction A toward the bonding pad 202 on the substrate 201.

[0039] from Figure 6 As can be seen, the bonding ball 501 contacts the bonding pad 202 to form a wire bonding portion. Then, the proximal lead clip 102 releases the bonding lead 105.

[0040] from Figure 7 As can be seen, the distal lead clamp 101 clamps the bonding lead 105 to prevent its movement, while the proximal lead clamp 102, together with the capillary bonding head 103, moves upward along the bonding lead in direction B. Therefore, the capillary bonding head 103 retracts along the bonding lead 105, leaving a lead tail 104 bonded to the bonding pad 202, with a weakened portion 120 located between the lead tail 104 and the remaining portion of the bonding lead 105. When the capillary bonding head 103 is in the position of the weakened portion 120, the capillary bonding head 103 can further translate repeatedly in a direction transverse to direction B to further weaken the weakened portion 120. Thereafter, the proximal lead clamp 102, together with the capillary bonding head 103, moves further upward to form a lead tail 104 of the desired length for subsequent wire bonding operations.

[0041] from Figure 8As can be seen, the proximal lead clamp 102 then clamps the bonding lead 105, while the proximal lead clamp 102, together with the capillary bonding head 103, moves further in direction B. This movement causes the remaining portion of the bonding lead 105 to move, while the lead tail 104 is retained on the bonding pad 202 through the ball-shaped lead bonding portion. This causes the lead to break at the weakened portion 120, thereby leaving the lead tail 104 in place in the vertical direction.

[0042] from Figure 9 As can be seen, this process is repeated to bond adjacent lead tails 104 to different positions on the substrate 201.

[0043] Understandably, unlike existing methods, lead tail 104 does not bend along its length because lead tail 104 never bends into an arched lead between two points on substrate 201. Moreover, it is formed as... Figure 2 The sharp elbow 110 shown is as follows before bonding: Figure 4 The wire is further straightened. Furthermore, since the lead tail 104 can be formed and bent at any single location, rather than having to form an arched lead between two locations, the limitations inherent in bonding on the substrate (obstacles on the substrate around the bonding point that restrict deformation at a second point around that bonding point) are avoided. Additionally, the accuracy of vertical interconnect orientation is improved due to the need for less translational movement. Neck stress on the wire bond is avoided because bending at the neck of the wire bond portion to form a weakening portion 120 after wire bonding is not necessary.

[0044] The embodiment avoids neck damage to the lead tail, unlike what is observed in conventional methods. The straightness of the lead tail is also improved compared to conventional methods. The accuracy of lead tail placement (particularly the X & Y offset in the orthogonal directions to the displacement directions A / B) can be improved by approximately 50% compared to conventional methods. The lead cutting position and the first bonding position can be the same, eliminating the need for additional space to cut / deform the lead. Therefore, a wider range of different lead tail heights can be achieved compared to conventional methods.

[0045] Although the invention has been described in considerable detail with reference to certain embodiments, other embodiments are also possible.

[0046] Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.

Claims

1. A wire bonding method for forming vertical lead interconnects on a substrate or bonding pad, comprising the following steps: Extend a bonding wire from the capillary bonding head to form a lead tail; Deformation, using the capillary bonding head to press the lead tail against the substrate or the bonding pad to deform the point on the lead tail to form a weakened portion between the lead tail and the remaining portion of the bonding lead retained in the capillary bonding head. as well as The capillary bonding head is lifted from the substrate and retracted. Before bonding the lead tail to the substrate or bonding pad, at least a portion of the lead tail, including the weakened portion, is retracted into the capillary bonding head, and a bonding ball is formed on the lead tail.

2. The method according to claim 1, wherein, The lead tail has a free end away from the capillary bonding head, and the weakened portion is close to the capillary bonding head.

3. The method according to claim 1, wherein, The deformation step includes pressing the point on the lead tail against at least one of the substrate and the bonding pad.

4. The method according to claim 2, wherein, The deformation step includes: translating the lead tail toward at least one of the substrate and the bonding pad, such that the free end contacts at least one of the substrate and the bonding pad, the continuous translation of the lead tail causing the free end to move above the surface of at least one of the substrate and the bonding pad in an axially misaligned manner with the remaining portion of the bonding lead retained within the capillary bonding head.

5. The method according to claim 1, wherein, The deformation step includes displacing the capillary bonding head in a displacement direction toward at least one of the substrate and the bonding pad, while simultaneously translating the capillary bonding head in a direction transverse to the displacement direction.

6. The method according to claim 1, wherein, The deformation step includes compressing the cross-section of the lead tail to form the weakened portion.

7. The method according to claim 1, wherein, The deformation step further includes forming the lead tail around the tip of the capillary bonding head.

8. The method according to claim 1, wherein, The retraction step further includes aligning the lead tail with the remaining portion of the bonding lead retained within the capillary bonding head before bonding.

9. The method according to claim 2, comprising: Before bonding, the bonding ball is formed on the free end of the lead tail.

10. The method of claim 9, comprising: The bonding ball is moved to bond with the bonding pad to form a spherical wire bond.

11. The method of claim 5, comprising: The capillary bonding head is repeatedly translated in a direction transverse to the displacement direction to weaken the weakened portion.

12. The method of claim 11, comprising: While repeatedly translating the capillary bonding head in a direction transverse to the displacement direction to weaken the weakened portion, the opening of the capillary bonding head through which the bonding lead extends is aligned to approach the weakened portion.

13. The method of claim 10, comprising: Move and clamp the remaining portion of the bonding wire so that the remaining portion separates from the ball wire bonding portion at the weakened portion.

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