WO2015024597A1 - Method for wire bonding and device produced thereby - Google Patents

Method for wire bonding and device produced thereby Download PDF

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Publication number
WO2015024597A1
WO2015024597A1 PCT/EP2013/067400 EP2013067400W WO2015024597A1 WO 2015024597 A1 WO2015024597 A1 WO 2015024597A1 EP 2013067400 W EP2013067400 W EP 2013067400W WO 2015024597 A1 WO2015024597 A1 WO 2015024597A1
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WO
WIPO (PCT)
Prior art keywords
bond
wire bond
wire
capillary
substrate
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Application number
PCT/EP2013/067400
Other languages
French (fr)
Inventor
Wei Chin KHAW
Original Assignee
Osram Opto Semiconductors Gmbh
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Publication date
Application filed by Osram Opto Semiconductors Gmbh filed Critical Osram Opto Semiconductors Gmbh
Priority to PCT/EP2013/067400 priority Critical patent/WO2015024597A1/en
Publication of WO2015024597A1 publication Critical patent/WO2015024597A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L24/85—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a wire connector
    • H—ELECTRICITY
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    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/42—Wire connectors; Manufacturing methods related thereto
    • H01L24/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L24/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
    • H01L2224/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
    • H01L2224/45001—Core members of the connector
    • H01L2224/4501—Shape
    • H01L2224/45012—Cross-sectional shape
    • H01L2224/45015—Cross-sectional shape being circular
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    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
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    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
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    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
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    • H01L2224/484—Connecting portions
    • H01L2224/4846—Connecting portions with multiple bonds on the same bonding area
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    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
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    • H01L2224/484—Connecting portions
    • H01L2224/48463—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond
    • H01L2224/48465—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond the other connecting portion not on the bonding area being a wedge bond, i.e. ball-to-wedge, regular stitch
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    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
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    • H01L2224/484—Connecting portions
    • H01L2224/4847—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a wedge bond
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    • H01L2224/78—Apparatus for connecting with wire connectors
    • H01L2224/7825—Means for applying energy, e.g. heating means
    • H01L2224/783—Means for applying energy, e.g. heating means by means of pressure
    • H01L2224/78301—Capillary
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    • H01L2224/8518—Translational movements
    • H01L2224/85181—Translational movements connecting first on the semiconductor or solid-state body, i.e. on-chip, regular stitch
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    • H01L2224/8512—Aligning
    • H01L2224/85148—Aligning involving movement of a part of the bonding apparatus
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    • H01L2224/8518—Translational movements
    • H01L2224/85186—Translational movements connecting first outside the semiconductor or solid-state body, i.e. off-chip, reverse stitch
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    • H01L2224/85—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a wire connector
    • H01L2224/8512—Aligning
    • H01L2224/85148—Aligning involving movement of a part of the bonding apparatus
    • H01L2224/85169—Aligning involving movement of a part of the bonding apparatus being the upper part of the bonding apparatus, i.e. bonding head, e.g. capillary or wedge
    • H01L2224/8518—Translational movements
    • H01L2224/85191—Translational movements connecting first both on and outside the semiconductor or solid-state body, i.e. regular and reverse stitches
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    • H01L2224/85—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a wire connector
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    • H01L2224/85148—Aligning involving movement of a part of the bonding apparatus
    • H01L2224/85169—Aligning involving movement of a part of the bonding apparatus being the upper part of the bonding apparatus, i.e. bonding head, e.g. capillary or wedge
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    • H01L2224/85196—Translational movements involving intermediate connecting steps before cutting the wire connector
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    • H01L2224/852—Applying energy for connecting
    • H01L2224/85201—Compression bonding
    • H01L2224/85205—Ultrasonic bonding
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    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/42—Wire connectors; Manufacturing methods related thereto
    • H01L24/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
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    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/00014—Technical content checked by a classifier the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details

Definitions

  • Various embodiments relate generally to a method for wire bonding and to an arrangement.
  • Fig. 1 shows the situation after a conventional forward bonding process, wherein a bond pad 12 on a die 10 is electrically coupled to an electric contact area 16 on a substrate 14 via a wire bond 20.
  • a first bond ball 22 is formed on the bond pad 12 on the die 10 and afterwards the wire bond 20 is lead towards the substrate 14 and a bond stitch 26 is formed on the electric contact area 16 of the substrate 14.
  • the wire bond 20 comprises a neck 24 which extends nearly rectangular, for example perpendicular, to the surface of the bond pad 12 away from the die 10.
  • a first height HI of a loop of the bonded wire bond 20 consists of a second height H2 of the bond ball 22 and the height of the neck 24.
  • a lower loop height than that of the first height HI is not possible with conventional forward bonding.
  • a grain size of the wire bond 20 is changed by the high temperature and the neck 24 normally appears to comprise a weak point to break in reliability stress tests.
  • FIG. 2 shows the situation after a conventional reverse bonding process, wherein a second bond ball 28 is formed on the electric contact area 16 on the substrate 14.
  • a second bond ball 28 is formed on the electric contact area 16 on the substrate 14.
  • the first bond ball 22 is formed on the bond pad 12.
  • the wire bond 20 is broken off and the second bond ball 28 is formed on the electric contact area 16.
  • the wire bond 20 being connected with the second bond ball 28 is lead to the first bond ball 22 and is coupled to the first bond ball 22.
  • the first height HI of the loop of the wire bond 20 is again given by the second height H2 of the first bond ball 22 and the height of the neck 24, because in general the upper surface of the die 10 has a positive distance to the upper surface of the substrate 14, wherein the distance normally is larger than the height of the second bond ball 28. Therefore the minimum height of the wire bond 20 in the reverse bonding process is constrained amongst others by the second height H2 of the first bond ball 22. Further, the stitch formation for breaking off the wire bond 20 creates a thin heel. The thin heel normally may easily broken at a reliability stress test.
  • a method for wire bonding which enables less deformation of a bond stitch and therefore lesser risk of a broken stitch at a reliability stress test and/or an enhancement of wire strength and/or a lower height of a loop of the wire bond and/or to use a wire bond having a small wire diameter while maintaining a given current conductivity.
  • an arrangement which comprises a bond connection between a bond pad of a die and an electrical contact area on a substrate and which comprises a relatively less deformated bond stitch having a lesser risk of a broken stitch at a reliability stress test and/or which has an enhanced total wire strength and/or a lower height of a loop of the wire bond and/or which comprises a wire bond having a small wire diameter while maintaining a given current conductivity.
  • Ultrasonic energy is applied on the wire bond on the bond pad in order to fix the wire bond to the bond pad.
  • a first portion of the wire bond extends from the bond ball on the substrate to the bond pad on the die. The clearance between the bond pad and the capillary tip is increased. The wire bond is lead back to the substrate. The wire bond is fixed to the substrate.
  • a second portion of the wire bond extends from the bond pad on the die to the bond ball on the substrate.
  • the clearance between the bond pad and the capillary leads to a relative small deformation of the bond stitch at the bond pad. Therefore, there is a small risk of a broken stitch at a reliability stress test. Further, the total wire strength may be enhanced due to the first and the second portion of the wire bond. Further, a lower loop height is possible as there is no bond ball on the bond pad. For example, when using a wire bond having a diameter of about 40 ⁇ , the bond ball normally would have a height of 30 ⁇ which may be saved with not forming the bond ball on the bond pad.
  • a wire bond having a smaller diameter may be used to further reduce the loop height without losing the current conductivity, because a wire bond having a diameter of about 40 ⁇ in a conventional bonding process may be replaced by a wire bond having a diameter of 20 ⁇ wherein the first and the second bond portion are formed.
  • the capillary is lead towards the bond pad such that the clearance between the tip of the capillary and the bond pad is not smaller than approximately the thickness of the wire bond. This contributes to less or not weakening the wire bond.
  • the capillary after increasing the clearance between the bond pad and the capillary tip, the capillary is moved and, after moving, lead towards the bond pad again such that the tip of the capillary presses the second portion of the wire bond against the first portion of the wire bond and that there is a clearance between the tip of the capillary and the first portion of the wire bond. This contributes to improve the connection of the wire bond to the bond pad.
  • the capillary after increasing the clearance between the bond pad and the capillary tip, the capillary is moved and, after moving, lead towards the bond pad again such that the tip of the capillary presses the second portion of the wire bond against the bond pad and that there is a clearance between the tip of the capillary and the bond pad. This contributes to improve the connection of the wire bond to the bond pad.
  • the wire bond after leading back the wire bond to the substrate, the wire bond is fixed to the substrate by leading the tip of the capillary towards the substrate such that the wire bond is pressed against the substrate and by applying ultrasonic power to the wire bond on the substrate. This contributes to improve the connection of the wire bond to the bond pad.
  • the wire bond is broken off after fixing the second end of the wire bond to the substrate.
  • the second end of the wire bond is fixed to the electric contact area of the substrate by applying ultrasonic energy to the second end of the wire bond.
  • the amount of ultrasonic energy for fixing the wire bond to the bond pad is for example 20% to 60%, for example 30% to 50% of the amount of ultrasonic energy for fixing the second end of the wire bond to the electric contact area of the substrate. This contributes to less or not weakening the wire bond and to save energy.
  • the second end of the wire bond is fixed to the electric contact area of the substrate by applying mechanical pressure to the second end of the wire bond towards the substrate.
  • the amount of mechanical pressure for fixing the wire bond to the bond pad is for example 20% to 60%, for example 30% to 50% of the amount of mechanical pressure for fixing the second end of the wire bond to the electric contact area of the substrate. This contributes to less or not weakening the wire bond and to save energy.
  • the substrate having the electric contact area and the die having the bond pad are provided.
  • the wire bond electrically couples the bond pad on the die with the electric contact area on the substrate.
  • the bond ball is formed on the electric contact area by a first end of the wire bond.
  • a first portion of the wire bond extends from the bond ball to the bond pad with the wire bond being fixed to the bond pad.
  • a second portion of the wire bond extends from the bond pad on the die back to the electric contact area of the substrate with the wire bond being fixed to electric contact area of the substrate at a second end of the wire bond.
  • the wire bond is fixed to the bond pad twice. This contributes to improve the connection of the wire bond to the bond pad.
  • the bond pad is free from any bond ball of the wire bond. This contributes to a small height of the loop of the wire bond.
  • the thickness of the wire bond is in a range of 10 ⁇ to 20 ⁇ . This contributes to a small height of the loop of the wire bond.
  • FIG. 1 shows an example of a bonding connection of the related art
  • FIG. 2 shows an example of a bonding connection of the related art
  • FIG. 3 shows a detailed sectional view of a capillary
  • FIG. 4 a first step of an exemplary embodiment of a bonding process
  • FIG. 6 a third step of an exemplary embodiment of a bonding process
  • FIG. 7 a fourth step of an exemplary embodiment of a bonding process
  • FIG. 8 a fifth step of an exemplary embodiment of a bonding process
  • FIG. 9 a sixth step of an exemplary embodiment of a bonding process
  • FIG. 10 a seventh step of an exemplary embodiment of a bonding process
  • FIG. 11 an optional step of an exemplary embodiment of a bonding process
  • the word “over” used with regards to a deposited material formed “over” a side or surface may be used herein to mean that the deposited material may be formed “directly on”, e.g. in direct contact with, the implied side or surface.
  • the word “over” used with regards to a deposited material formed “over” a side or surface may be used herein to mean that the deposited material may be formed "indirectly on” the implied side or surface with one or more additional layers being arranged between the implied side or surface and the deposited material.
  • Fig. 1 shows an arrangement comprising a first conventional bonding connection, in particular a forward bonding connection.
  • the arrangement comprises a die 10 having a bond pad 12 on a top of the die 10.
  • the arrangement further comprises a substrate 14 having an electric contact area 16 on top of the substrate 14.
  • the bond pad 12 of the die 10 is electrically connected with the electric contact area 16 of the substrate 14 by a wire bond 20.
  • the wire bond 20 comprises a first bond ball 22 at one end of the wire bond 20 which is fixed to the bond pad 12.
  • the first bond ball 22 mechanically and electrically connects the rest of the wire bond 20 with the bond pad 12.
  • At an end of the wire bond 20 facing away from the first bond ball 22 the wire bond 20 is electrically coupled to the electric contact area 16 by a stitch bond 26.
  • the wire bond 20 forms a loop and has a neck 24.
  • the loop of the wire bond 20 has a first height HI.
  • the first height HI consists of a second height H2 of the bond ball 22 and a
  • a ball (not shown in figure 1) is formed at one end of the wire bond 20 by an electrode firing and the wire bond 20 with the ball is mechanically pressed down to the bond pad 12. Additionally to the mechanical pressure ultrasonic energy is applied to the ball and in result the ball forms the bond ball 22. Afterwards the wire bond 20 is led away from the bond pad 12 in such a way that the neck 24 is formed and then the wire bond 20 is led to the electric contact area 16 of the substrate. The wire bond 20 is pressed down on the electric contact area 16 in such a way that the wire bond 20 is strongly deformed and that the stitch 26 is formed. Afterwards, the wire bond 20 is lifted up and lead away from the electric contact area 16 in such a way that the wire bond 20 breaks off at the stitch 26.
  • Fig. 2 shows a second conventional bonding connection, in particular a reverse bonding connection.
  • the reverse bonding connection additionally comprises a second bond ball 28 which is formed on the electric contact area 16 of the substrate 14 and the neck 24 is formed over the second bond ball 28.
  • the stitch 26 is formed on the bond ball 22 on the bond pad 12.
  • the ball is formed on the wire bond 20 and then the ball is pressed down towards the bond pad 12 in such a way that the first bond ball 22 on the bond pad 12 is formed. Then the wire bond 20 is led away from the bond pad 12 in such a way that the wire bond 20 is cut off, wherein the first bond ball 22 stays on the bond pad 12. Then another ball is formed on the wire bond 20 and the ball is pressed down on the electric contact area 16 of the substrate 14 in such a way that the second bond ball 28 is formed on the electric contact area 16. Afterwards the wire bond 20 is lifted up in such a way that the neck 24 is formed and then the wire bond 20 is led to the first bond ball 22.
  • the wire bond 20 is connected to the first bond ball 22 via the stitch 26, wherein again the wire bond 20 is pressed down towards the first bond ball 22 and the bond pad 12 such that the wire bond 20 is strongly deformed, in particular in such a way, that it may be easily broken off when leading away the wire bond 20 from the first bond ball 22.
  • the loop of the wire bond 20 has the first height HI and the first neck 24.
  • the first height HI of the loop of the wire bond 20 consists of the second height H2 of the first bond ball 22 and the height of the neck 24.

Abstract

In various embodiments a method is provided, comprising the steps of: Arranging a wire bond (20) in a capillary (50) for wire-bonding such that a first end of the wire bond (20) extends from a tip of the capillary (50); forming a ball (27) out of the first end of the wire bond (20); leading the wire bond (20) with the ball (27) towards a substrate (14) such that a bond ball (28) is formed on an electric contact area (16) of the substrate (14) by the ball (27); leading the capillary (50) with the wire bond (20) away from the bond ball (28) towards a bond pad (12) on a die (10); leading the capillary (50) towards the bond pad (12) such that the tip of the capillary (50) presses the wire bond (20) against the bond pad (12) and that there is a clearance between the tip of the capillary (50) and the bond pad (12); applying ultrasonic energy on the wire bond (20) on the bond pad (12) in order to fix the wire bond (20) to the bond pad (12), wherein a first portion (54) of the wire bond (20) extends from the bond ball (28) on the substrate (14) to the bond pad (12) on the die (10); increasing the clearance between the bond pad (12) and the capillary (50) tip; leading the wire bond (20) back to the substrate (14); fixing the wire bond (20) to the substrate (14), wherein a second portion (56) of the wire bond (20) extends from the bond pad (12) on the die (10) to the bond ball (28) on the substrate (14).

Description

METHOD FOR WIRE BONDING AND DEVICE PRODUCED THEREBY
Technical Field
[0001] Various embodiments relate generally to a method for wire bonding and to an arrangement.
Background
[0002] Conventional wire bonding, for example forward bonding and reverse bonding, needs to form a ball at the wire bond and a bond ball on the bond pad on the die. The methodology of forming the bond ball on the bond pad on the die restricts a low loop height of the bonded wire bond and exposes weaker wire bond strength in a reliability stress test. Reverse bonding exposes a thin stitch heel on the bond ball resulting in a broken stitch after being stressed. Similarly, with forward bonding it is also possible that a broken neck may occur.
[0003] Fig. 1 shows the situation after a conventional forward bonding process, wherein a bond pad 12 on a die 10 is electrically coupled to an electric contact area 16 on a substrate 14 via a wire bond 20. At first, a first bond ball 22 is formed on the bond pad 12 on the die 10 and afterwards the wire bond 20 is lead towards the substrate 14 and a bond stitch 26 is formed on the electric contact area 16 of the substrate 14. Starting from the first bond ball 22 on the bond pad 12 the wire bond 20 comprises a neck 24 which extends nearly rectangular, for example perpendicular, to the surface of the bond pad 12 away from the die 10. [0004] With this forward bonding connection it is necessary to form the bond ball 22 on the bond pad 12, wherein a first height HI of a loop of the bonded wire bond 20 consists of a second height H2 of the bond ball 22 and the height of the neck 24. A lower loop height than that of the first height HI is not possible with conventional forward bonding. Further, due to an electrode firing when forming the ball (not shown in figure 1) for the bond ball 22, a grain size of the wire bond 20 is changed by the high temperature and the neck 24 normally appears to comprise a weak point to break in reliability stress tests.
[0005] Fig. 2 shows the situation after a conventional reverse bonding process, wherein a second bond ball 28 is formed on the electric contact area 16 on the substrate 14. In particular, at first, the first bond ball 22 is formed on the bond pad 12. Then, the wire bond 20 is broken off and the second bond ball 28 is formed on the electric contact area 16. Afterwards the wire bond 20 being connected with the second bond ball 28 is lead to the first bond ball 22 and is coupled to the first bond ball 22.
[0006] As shown in fig. 3, for the bonding of the wire bond 20 to the bond pad 12 on the die 10 a direct contact of the tip of the capillary 50 onto the bond pad 12 is necessary. However, the direct contact may result in a crack 42 in a passivation layer 18 on the bond pad area surruounding the bond bad 12. The crack 42 then may cause current to leake to the inner layers of the chip. Within the conventional bond formation it is not possible to cut the wire bond 20 without a direct contact of the capillary 50 to the surface of the bond pad 12. In particular, the wire bond 20 has to be pre-deformed by the tip of the capillary 50 on the flat surface of the bond pad 12 prior to the breaking off of the wire bond 20 by a wire clamp (not shown in fig. 3). [0007] In this reverse bonding process the first height HI of the loop of the wire bond 20 is again given by the second height H2 of the first bond ball 22 and the height of the neck 24, because in general the upper surface of the die 10 has a positive distance to the upper surface of the substrate 14, wherein the distance normally is larger than the height of the second bond ball 28. Therefore the minimum height of the wire bond 20 in the reverse bonding process is constrained amongst others by the second height H2 of the first bond ball 22. Further, the stitch formation for breaking off the wire bond 20 creates a thin heel. The thin heel normally may easily broken at a reliability stress test.
Summary
[0008] In various embodiments, a method for wire bonding is provided which enables less deformation of a bond stitch and therefore lesser risk of a broken stitch at a reliability stress test and/or an enhancement of wire strength and/or a lower height of a loop of the wire bond and/or to use a wire bond having a small wire diameter while maintaining a given current conductivity.
[0009] In various embodiments, an arrangement is provided which comprises a bond connection between a bond pad of a die and an electrical contact area on a substrate and which comprises a relatively less deformated bond stitch having a lesser risk of a broken stitch at a reliability stress test and/or which has an enhanced total wire strength and/or a lower height of a loop of the wire bond and/or which comprises a wire bond having a small wire diameter while maintaining a given current conductivity.
[0010] In various embodiments a method for wire bonding is provided, wherein a wire bond is arranged in a capillary for wire-bonding such that a first end of the wire bond extends from a tip of the capillary. A ball is formed out of the first end of the wire bond. The wire bond with the ball is lead towards a substrate such that a bond ball is formed by the ball on an electric contact area of the substrate. The capillary with the wire bond is lead from the bond ball on the substrate towards a bond pad on a die. The capillary is lead to the bond pad such that the tip of the capillary presses the wire bond against the bond pad and that there is a clearance between the tip of the capillary and the bond pad. Ultrasonic energy is applied on the wire bond on the bond pad in order to fix the wire bond to the bond pad. A first portion of the wire bond extends from the bond ball on the substrate to the bond pad on the die. The clearance between the bond pad and the capillary tip is increased. The wire bond is lead back to the substrate. The wire bond is fixed to the substrate. A second portion of the wire bond extends from the bond pad on the die to the bond ball on the substrate.
[0011] The clearance between the bond pad and the capillary leads to a relative small deformation of the bond stitch at the bond pad. Therefore, there is a small risk of a broken stitch at a reliability stress test. Further, the total wire strength may be enhanced due to the first and the second portion of the wire bond. Further, a lower loop height is possible as there is no bond ball on the bond pad. For example, when using a wire bond having a diameter of about 40 μπι, the bond ball normally would have a height of 30 μπι which may be saved with not forming the bond ball on the bond pad. Alternatively or additionally, a wire bond having a smaller diameter may be used to further reduce the loop height without losing the current conductivity, because a wire bond having a diameter of about 40 μπι in a conventional bonding process may be replaced by a wire bond having a diameter of 20 μπι wherein the first and the second bond portion are formed. [0012] According to various embodiments the capillary is lead towards the bond pad such that the clearance between the tip of the capillary and the bond pad is not smaller than approximately the thickness of the wire bond. This contributes to less or not weakening the wire bond.
[0013] According to various embodiments, after increasing the clearance between the bond pad and the capillary tip, the capillary is moved and, after moving, lead towards the bond pad again such that the tip of the capillary presses the second portion of the wire bond against the first portion of the wire bond and that there is a clearance between the tip of the capillary and the first portion of the wire bond. This contributes to improve the connection of the wire bond to the bond pad.
[0014] According to various embodiments, after increasing the clearance between the bond pad and the capillary tip, the capillary is moved and, after moving, lead towards the bond pad again such that the tip of the capillary presses the second portion of the wire bond against the bond pad and that there is a clearance between the tip of the capillary and the bond pad. This contributes to improve the connection of the wire bond to the bond pad.
[0015] According to various embodiments, after leading back the wire bond to the substrate, the wire bond is fixed to the substrate by leading the tip of the capillary towards the substrate such that the wire bond is pressed against the substrate and by applying ultrasonic power to the wire bond on the substrate. This contributes to improve the connection of the wire bond to the bond pad.
[0016] According to various embodiments, the wire bond is broken off after fixing the second end of the wire bond to the substrate. [0017] According to various embodiments, the second end of the wire bond is fixed to the electric contact area of the substrate by applying ultrasonic energy to the second end of the wire bond. The amount of ultrasonic energy for fixing the wire bond to the bond pad is for example 20% to 60%, for example 30% to 50% of the amount of ultrasonic energy for fixing the second end of the wire bond to the electric contact area of the substrate. This contributes to less or not weakening the wire bond and to save energy.
[0018] According to various embodiments, the second end of the wire bond is fixed to the electric contact area of the substrate by applying mechanical pressure to the second end of the wire bond towards the substrate. The amount of mechanical pressure for fixing the wire bond to the bond pad is for example 20% to 60%, for example 30% to 50% of the amount of mechanical pressure for fixing the second end of the wire bond to the electric contact area of the substrate. This contributes to less or not weakening the wire bond and to save energy.
[0019] In various embodiments the substrate having the electric contact area and the die having the bond pad are provided. The wire bond electrically couples the bond pad on the die with the electric contact area on the substrate. The bond ball is formed on the electric contact area by a first end of the wire bond. A first portion of the wire bond extends from the bond ball to the bond pad with the wire bond being fixed to the bond pad. A second portion of the wire bond extends from the bond pad on the die back to the electric contact area of the substrate with the wire bond being fixed to electric contact area of the substrate at a second end of the wire bond.
[0020] According to various embodiments the wire bond is fixed to the bond pad twice. This contributes to improve the connection of the wire bond to the bond pad. [0021] According to various embodiments the bond pad is free from any bond ball of the wire bond. This contributes to a small height of the loop of the wire bond.
[0022] According to various embodiments the thickness of the wire bond is in a range of 10 μπι to 20 μπι. This contributes to a small height of the loop of the wire bond.
Brief Description of the Drawings
[0023] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:
FIG. 1 shows an example of a bonding connection of the related art;
FIG. 2 shows an example of a bonding connection of the related art ;
FIG. 3 shows a detailed sectional view of a capillary;
FIG. 4 a first step of an exemplary embodiment of a bonding process;
FIG. 5 a second step of an exemplary embodiment of a bonding process;
FIG. 6 a third step of an exemplary embodiment of a bonding process;
FIG. 7 a fourth step of an exemplary embodiment of a bonding process;
FIG. 8 a fifth step of an exemplary embodiment of a bonding process;
FIG. 9 a sixth step of an exemplary embodiment of a bonding process;
FIG. 10 a seventh step of an exemplary embodiment of a bonding process;
FIG. 11 an optional step of an exemplary embodiment of a bonding process; Description
[0024] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced.
[0025] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
[0026] The word "over" used with regards to a deposited material formed "over" a side or surface, may be used herein to mean that the deposited material may be formed "directly on", e.g. in direct contact with, the implied side or surface. The word "over" used with regards to a deposited material formed "over" a side or surface, may be used herein to mean that the deposited material may be formed "indirectly on" the implied side or surface with one or more additional layers being arranged between the implied side or surface and the deposited material.
[0027] Fig. 1 shows an arrangement comprising a first conventional bonding connection, in particular a forward bonding connection. The arrangement comprises a die 10 having a bond pad 12 on a top of the die 10. The arrangement further comprises a substrate 14 having an electric contact area 16 on top of the substrate 14. The bond pad 12 of the die 10 is electrically connected with the electric contact area 16 of the substrate 14 by a wire bond 20. The wire bond 20 comprises a first bond ball 22 at one end of the wire bond 20 which is fixed to the bond pad 12. The first bond ball 22 mechanically and electrically connects the rest of the wire bond 20 with the bond pad 12. At an end of the wire bond 20 facing away from the first bond ball 22 the wire bond 20 is electrically coupled to the electric contact area 16 by a stitch bond 26. The wire bond 20 forms a loop and has a neck 24. The loop of the wire bond 20 has a first height HI. The first height HI consists of a second height H2 of the bond ball 22 and a height of the neck 24 of the wire bond 20.
[0028] When forming the forward bonding connection according to figure 1 , at first, a ball (not shown in figure 1) is formed at one end of the wire bond 20 by an electrode firing and the wire bond 20 with the ball is mechanically pressed down to the bond pad 12. Additionally to the mechanical pressure ultrasonic energy is applied to the ball and in result the ball forms the bond ball 22. Afterwards the wire bond 20 is led away from the bond pad 12 in such a way that the neck 24 is formed and then the wire bond 20 is led to the electric contact area 16 of the substrate. The wire bond 20 is pressed down on the electric contact area 16 in such a way that the wire bond 20 is strongly deformed and that the stitch 26 is formed. Afterwards, the wire bond 20 is lifted up and lead away from the electric contact area 16 in such a way that the wire bond 20 breaks off at the stitch 26.
[0029] With the forward bonding connection it is necessary to form the first bond ball 22 on the bond pad 12. A lower total height HI is not a possible because of the first bond ball 22 and the neck 24. Further, due to the electrode firing to form the ball 27 on the wire bond 20 a wire grain size changes by the high temperature and the wire neck 24 normally forms a weak point of the forward bond connection when being stressed.
[0030] Fig. 2 shows a second conventional bonding connection, in particular a reverse bonding connection. In contrast to the forward bonding connection the reverse bonding connection additionally comprises a second bond ball 28 which is formed on the electric contact area 16 of the substrate 14 and the neck 24 is formed over the second bond ball 28. Further, in contrast to the forward bonding connection, the stitch 26 is formed on the bond ball 22 on the bond pad 12.
[0031] When forming the reverse bonding connection, at first, the ball is formed on the wire bond 20 and then the ball is pressed down towards the bond pad 12 in such a way that the first bond ball 22 on the bond pad 12 is formed. Then the wire bond 20 is led away from the bond pad 12 in such a way that the wire bond 20 is cut off, wherein the first bond ball 22 stays on the bond pad 12. Then another ball is formed on the wire bond 20 and the ball is pressed down on the electric contact area 16 of the substrate 14 in such a way that the second bond ball 28 is formed on the electric contact area 16. Afterwards the wire bond 20 is lifted up in such a way that the neck 24 is formed and then the wire bond 20 is led to the first bond ball 22. Then, the wire bond 20 is connected to the first bond ball 22 via the stitch 26, wherein again the wire bond 20 is pressed down towards the first bond ball 22 and the bond pad 12 such that the wire bond 20 is strongly deformed, in particular in such a way, that it may be easily broken off when leading away the wire bond 20 from the first bond ball 22. The loop of the wire bond 20 has the first height HI and the first neck 24. The first height HI of the loop of the wire bond 20 consists of the second height H2 of the first bond ball 22 and the height of the neck 24.
[0032] With the reverse bonding connection again the loop height HI may not be lowered because of the height of the first bond ball 22 and the neck 24. In both cases, the forward and the reverse bonding connection, the formation of the stitch 26 may lead to weaken the wire bond 20 and the wire bond connection because of the strong deformation of the wire bond 20. Another problem when forming the stitch 26 is explained in the following with the reference to figure 3.
[0033] Fig. 3 shows a detailed view of a tool for wire bonding and the bond pad 12 on the die. The tool comprises a capillary 50 for leading the wire bond 20 to the bond pad 12 and the electric contact area 16, and for holding and deforming the wire bond 20. The tool further comprises a clamp 52 for fixing the wire bond 20 in a fixed position relative to the capillary 50. If the clamp 52 is open, the wire bond 20 may be moved relative to the capillary 50. For example, the wire bond 20 may be pulled out of the capillary 50. If the clamp 52 is closed, the wire bond 20 is fixed relative to the capillary 50 and the wire bond 20 may be broken off with the help of the tool by lifting the capillary 50. The capillary 50 has a recess 32 through which the wire bond is led. The wire bond 20 extends from the tip of the capillary 50. At least a part of the extending part of the wire bond 20 is deformed by the tip of the capillary 50 in a deformation area 40 in which the tip of the capillary 50 presses the wire bond 20 deeply down against the bond pad 12. In particular, the wire bond 20 is pressed towards the die 10 in such a way that the tip of the capillary 50 touches the bond pad 12.
[0034] The bond pad 12 is at least in part surrounded by a passivation layer 18 which electrically isolates the surface of the die 10. However, when pressing down the wire bond 20 against the bond pad 12 and when strongly deforming the wire bond 20 in the deformation area 40 the passivation layer 18 may be damaged. For example, a crack 42 may be formed in the passivation layer 18. The crack 42 enables a current flow through the passivation layer 18 which may render the die 10 malfunctioning. [0035] Fig. 4 shows a first step of an exemplary embodiment of a method for wire bonding. In the first step the capillary 50 is led over the electric contact area 16 and a ball 27 is formed at a first end of the wire bond 20 which extends from the tip of the capillary 50. The clamp 52 of the capillary 50 is opened so that the wire bond 20 may be pulled out of the capillary 50.
[0036] Fig. 5 shows a second step of the method for wire bonding in which the capillary 50 presses down the ball 27 on the contact area 16 and ultrasonic energy is applied to the ball 27 in such a way that the second bond ball 28 is formed on the electric contact area 16.
[0037] Fig. 6 shows a third step of the method for wire bonding in which the capillary 50 is led away from the electric contact area 16 in such a way that, at first, the neck 24 is formed and that the wire bond 20 is then led over the bond pad 12 of the die 10. During this movement the clamp 52 is opened such that the wire bond 20 may be pulled out of the capillary 50.
[0038] Fig. 7 shows a fourth step of the method for wire bonding in which the tip of the capillary 50 presses down the wire bond 20 towards the bond pad 12 in such a way that there is a minimum clearance between the tip of the capillary 50 and the bond pad 12. In particular, the tip of the capillary 50 is not pressed in such a way towards the bond pad 12 that there is a direct contact between the tip of the capillary 50 and the surface of the bond pad 12. For example, the clearance corresponds to approximately a diameter of the wire bond 20. For example, if the wire bond diameter is 40 μπι, the clearance is approximately 40 μπι. Alternatively, if the diameter of the wire bond 20 is about 20 μπι the clearance may also has about 20 μπι. So the wire bond 20 is slightly pressed against the bond pad 12 by mechanical energy, wherein the amount of this mechanical energy may be in a range of for example 20% to 60%, for example 30% to 50% of the amount of mechanical energy which is used for forming the stitch 26 in the conventional forward or reverse bonding connection.
[0039] While pressing down slightly the wire bond 20 towards the bond pad 12, ultrasonic energy is applied to the wire bond 20 on the bond pad 12. The ultrasonic energy may be for example in a range between 20% to 60%, for example 30% to 50% of the ultrasonic energy which is applied to the wire bond 20 during the conventional forward or reverse bonding process. With this slight mechanical pressure and low ultrasonic energy the wire bond 20 is fixed to the bond pad 12.
[0040] Fig. 8 shows a fifth step of the method for wire bonding in which the wire bond 20 is led away from the bond pad 12 in such a way that another neck of the wire bond 20 is formed over the bond pad 12 and that the wire bond 20 is led back over the electric contact area 16.
[0041] Fig. 9 shows a sixth step of the method for wire bonding in which the wire bond 20 is again led down towards the electric contact area 16 and the wire bond 20 is connected to the electric contact area 16 by mechanical pressure and/or ultrasonic energy. The wire bond 20 may be fixed to the electric contact area 16 in accordance with a conventional stitch forming process or the wire bond 20 is fixed to the electric contact area 16 like it is connected to the bond pad 12 in the fourth step of the method, shown in figure 7. [0042] Fig. 10 shows an seventh step of the method for wire bonding in which the clamp 52 is closed and a capillary 50 is lifted up such that the wire bond 20 is broken off. So, the wire bond connection is finished.
[0043] Because the bond connection consists of a wire bond 20 having a first portion 45 extending from the electric contact area 16 to the bond pad 12 and a second portion 56 extending from the bond pad 12 back to the electric contact area 16 the wire bond 20 may be half in diameter than a conventional wire bond in a conventional wire bonding connection, while having the same electric conductivity and/or electric resistance.
However, when using the wire bond 20 having half of the size of the conventional diameter of the wire bond the second bond ball 28 may also have only the half of the height of the conventional second bond ball 28 and therefore, the total height of the loops of the wire bond 20 may be lowered compared to the conventional loops of the conventional forward and/or reverse bonding connection. Further, because only a slight pressure is applied on the wire bond 20 and the bond pad 12 damaging of the passivation layer 18, in particular the formation of cracks 42, is avoided.
[0044] Fig. 11 shows an optional step of the method for wire bonding which may be carried out between the fourth step shown in figure 7 and the fifth step shown in figure 8. In this optional step, after the connection of the wire bond 20 with the bond pad 12, the capillary 50 again presses down the wire bond 20 towards the bond pad 12. Again the wire bond 20 is slightly pressed down to the bond pad 12, wherein there is again the minimum clearance between the tip of the capillary 50 and the bond pad 12. The clearance may be similar to or the same as the clearance of fourth step shown in figure 7. Alternatively, the wire bond 20 may be pressed down to the first portion 54 of the wire bond 20 and the clearance may be between the tip of the capillary 50 and the bond pad 12 or between the tip of the capillary 50 and the first portion 54 of the wire bond 20. This leads to a second connection of the wire bond 20 to the bond pad 12 which strengthens the bonding force between the wire bond 20 and the bond pad 12. Again, because only a slight mechanical pressure and low ultrasonic energy are applied on the wire bond 20, the wire bond 20 is not weakened by this second connection to the bond pad 12.
[0045] The invention is not restricted on the explained embodiment . For example further portions of the wire bond 20 may be formed between the electric contact area 16 and the bond pad 12. Further, alternative diameters of the wire bond 20 may be used. Further, the die 10 may be arranged on the substrate 14 next to the electric contact area 16.
[0046] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

Claims claimed is:
A method for wire bonding, comprising the steps of:
- arranging a wire bond (20) in a capillary (50) for wire-bonding such that a first end of the wire bond (20) extends from a tip of the capillary (50),
- forming a ball (27) out of the first end of the wire bond (20),
- leading the wire bond (20) with the ball (27) towards a substrate (14) such that a bond ball (28) is formed by the ball (27) on an electric contact area (16) of the substrate (14),
- leading the capillary (50) with the wire bond (20) away from the bond ball (28) towards a bond pad (12) on a die (10),
- leading the capillary (50) towards the bond pad (12) such that the tip of the capillary (50) presses the wire bond (20) against the bond pad (12) and that there is a clearance between the tip of the capillary (50) and the bond pad (12),
- applying ultrasonic energy on the wire bond (20) on the bond pad (12) in order to fix the wire bond (20) to the bond pad (12), wherein a first portion (54) of the wire bond (20) extends from the bond ball (28) on the substrate (14) to the bond pad (12) on the die (10),
- increasing the clearance between the bond pad (12) and the capillary (50) tip,
- leading the wire bond (20) back to the substrate (14),
- fixing a second end of the wire bond (20) to the substrate (14), wherein a second portion (56) of the wire bond (20) extends from the bond pad (12) on the die (10) to the bond ball (28) on the substrate (14).
2. Method in accordance with claim 1, wherein the capillary (50) is lead towards the bond pad (12) such that the clearance between the tip of the capillary (50) and the bond pad (12) is not smaller than approximately the thickness of the wire bond (20).
3. Method in accordance with one of the preceding claims, wherein, after increasing the clearance between the bond pad (12) and the tip of the capillary (50), the capillary (50) is moved and, after moving, lead towards the bond pad (12) again such that the tip of the capillary (50) presses the second portion (56) of the wire bond (20) against the first portion (54) of the wire bond (20) and that there is a clearance between the tip of the capillary (50) and the first portion (54) of the wire bond (20).
4. Method in accordance with one of claims 1 or 2, wherein, after increasing the clearance between the bond pad (12) and the tip of the capillary (50), the capillary (50) is moved and, after moving, lead towards the bond pad (12) again such that the tip of the capillary (50) presses the second portion (56) of the wire bond (20) against the bond pad (12) and that there is a clearance between the tip of the capillary (50) and the bond pad (12).
5. Method in accordance with one of the preceding claims, wherein, after leading back the wire bond (20) to the substrate (14), the wire bond (20) is fixed to the substrate (14) by leading the tip of the capillary (50) towards the substrate (14) such that the wire bond (20) is pressed against the substrate (14) and by applying ultrasonic power on the wire bond (20) on the substrate (14).
6. Method in accordance with one of the preceding claims, wherein the wire bond (20) is cut off after fixing the second end of the wire bond (20) to the substrate (14).
7. Method in accordance with one of the preceding claims, wherein the second end of the wire bond (20) is fixed to the electric contact area (16) of the substrate (14) by applying ultrasonic energy to the second end of the wire bond (20), wherein the amount of ultrasonic energy for fixing the wire bond (20) to the bond pad (12) is 20% to 60% or 30% to 50% of the amount of ultrasonic energy for fixing the second end of the wire bond (20) to the electric contact area (16) of the substrate (14).
8. Method in accordance with one of the preceding claims, wherein the second end of the wire bond (20) is fixed to the electric contact area (16) of the substrate (14) by applying mechanical pressure to the second end of the wire bond (20) towards the substrate (14), wherein the amount of mechanical pressure for fixing the wire bond (20) to the bond pad (12) is 20% to 60% or 30% to 50% of the amount of mechanical pressure for fixing the second end of the wire bond (20) to the electric contact area (16) of the substrate (14).
9. Arrangement, comprising:
- a substrate (14) having an electric contact area (16),
- a die (10) having a bond pad (12),
- a wire bond (20) electrically connecting the bond pad (12) on the die (10) with the electric contact area (16) on the substrate (14),
- a bond ball (28) formed on the electric contact area (16) by a first end of the wire bond (20), wherein a first portion (54) of the wire bond (20) extends from the bond ball (28) to the bond pad (12) with the wire bond (20) being fixed to the bond pad (12) and wherein a second portion (56) of the wire bond (20) extends from the bond pad (12) on the die (10) back to the electric contact area (16) of the substrate (14) with the wire bond (20) being fixed to the electric contact area (16) of the substrate (14) at a second end of the wire bond (20).
10. Arrangement in accordance with claim 9, wherein the wire bond (20) is fixed to the bond pad (12) twice.
11. Arrangement in accordance with one of claims 9 or 10, wherein the bond pad (12) is free of any bond ball (28) of the wire bond (20).
12. Arrangement in accordance with one of claims 9 to 11, wherein the thickness of the wire bond (20) is in a range of 10 μπι to 20 μπι.
PCT/EP2013/067400 2013-08-21 2013-08-21 Method for wire bonding and device produced thereby WO2015024597A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2604433A (en) * 2020-12-23 2022-09-07 Skyworks Solutions Inc Apparatus and methods for tool mark free stitch bonding

Citations (3)

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Publication number Priority date Publication date Assignee Title
JPS6464229A (en) * 1987-09-03 1989-03-10 Nec Corp Diode
JPH02215137A (en) * 1989-02-16 1990-08-28 Sanyo Electric Co Ltd High-frequency semiconductor device
JP2005123388A (en) * 2003-10-16 2005-05-12 Sony Corp Bonding structure, bonding method, semiconductor device and its manufacturing method

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6464229A (en) * 1987-09-03 1989-03-10 Nec Corp Diode
JPH02215137A (en) * 1989-02-16 1990-08-28 Sanyo Electric Co Ltd High-frequency semiconductor device
JP2005123388A (en) * 2003-10-16 2005-05-12 Sony Corp Bonding structure, bonding method, semiconductor device and its manufacturing method

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2604433A (en) * 2020-12-23 2022-09-07 Skyworks Solutions Inc Apparatus and methods for tool mark free stitch bonding
GB2604433B (en) * 2020-12-23 2023-05-03 Skyworks Solutions Inc Apparatus and methods for tool mark free stitch bonding
GB2615441A (en) * 2020-12-23 2023-08-09 Skyworks Solutions Inc Apparatus and methods for tool mark free stitch bonding

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