Patent Application
20250096195
Semiconductor devices are typically provided within a package that houses and protects the dies and associated electrical connections from the exterior environment. A discrete package may include one or more semiconductor dies mounted on a metal lead frame. A power module may include several dies mounted on a power electronics carrier, e.g., DBC (direct bonded copper) substrate, IMS (insulated metal substrate) or AMB (active metal brazed) substrate, and an enclosure over the power electronics carrier. In either type of package, electrical interconnections must be made between the various components, e.g., die to lead connections, die to die connections, bond pad to bond pad connections, etc. There are various ways to form these electrical interconnections. One such way is a wire bonding technique. It would be desirable to improve the quality, performance, and cost of wire bonding.
A method of forming a bond wire connection is disclosed. According to an embodiment, the method comprises providing a wire bonder comprising a bond wedge with a wire guide, and forming a wire bond loop by initially bonding a bond wire to a first bonding surface using the bond wedge, then moving the bond wedge in a loop pattern whereby the bond wire passes through the wire guide, and then bonding the bond wire to a second bonding surface using the bond wedge, wherein moving the bond wedge in the loop pattern comprises a retrograde movement whereby the bond wedge moves away from the second bonding surface after bonding the first bond, and wherein the wire guide is formed from a material with a higher material hardness than the bond wire.
A semiconductor device is disclosed. According to an embodiment, the semiconductor device comprises a bond wire connection that forms an electrical connection of a semiconductor device, wherein the bond wire connection comprises a wire bond loop between a first bonding surface and a second bonding surface, wherein the wire bond loop is formed from a bond wire comprising copper with a diameter of between 400 μm and 500 μm, wherein a bond loop length of the wire bond loop is ≤5,500 μm, and wherein a bond loop height of the wire bond loop is ≤2,5000 μm.
The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. The features of the various illustrated embodiments can be combined unless they exclude each other. Embodiments are depicted in the drawings and are detailed in the description which follows.
Embodiments of a method of forming a bond wire connection and corresponding bond wire connection are disclosed herein. The bond wire connection comprises a wire bond loop between a first bonding surface and a second bonding surface. The physical attributes of the wire bond loop, specifically the relation between the bond loop height and the bond loop length, are advantageous. Conventionally when forming wire bond loops, there is a tradeoff between the minimum attainable bond loop height relative bond loop length. As the bond loop length decreases, the bond loop height must be increased to reliably effectuate the bond wire connection. The methods disclosed herein facilitate the formation of otherwise unattainably low bond loop height values relative to bond loop length. In particular, the methods comprise using a bond wedge with a wire guide that is harder than the bond wire form the wire bond loop. In addition, the methods comprise using a retrograde movement into the loop pattern wherein the bond wedge moves backwards and away from the intended subsequent bonding point. The combination of the stiffer wire guide bond wedge and retrograde movement cause a shaping of the bond wire during the loop formation that reliably creates low-profile wire bond loops.
Referring to
The wire bond loop 102 is formed by a bond wire 108. The bond wire 108 comprises a low electrical resistance metal that is suitable for semiconductor device interconnection. For example, the metal bond wire 108 may comprise copper, aluminum, silver, and alloys thereof. According to an embodiment, the metal bond wire 108 is a copper bond wire 108, i.e., a bond wire 108 formed of substantially pure copper, e.g., 95% pure or 99% pure copper. A diameter of the bond wire 108 may be in the range of 25 μm and 750 μm, for example. According to an embodiment, the diameter of the bond wire 108 is in the range of 300 μm and 500 μm. In a more particular embodiment, the bond wire 108 is a copper bond wire 108 with a diameter of 400 μm, meaning that the nominal diameter value of the wire is 400 μm. The bond wire 108 may have a rounded cross-section. Other cross-sectional geometries such as rectangular geometries are possible as well.
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According to an embodiment, the wire guide 204 is formed from a material with a higher material hardness than the bond wire 108. Material hardness refers to the degree to which the material irreversibly deforms in response to an applied force, i.e., the plasticity of the material. Material hardness may be measured according to the measured according to the Rockwell, Vickers, Shore, or Brinell scale. Thus, in the case that the bond wire 108 comprises, copper, aluminum, or alloys thereof, the wire guide 204 may be formed from a metal with a higher material hardness than metal which forms the bond wire 108. According to an embodiment, the wire guide 204 comprises any one or more of: Cu, Ni, Ti, Zn, Fe, and alloys thereof, wherein these metals or alloys are selected harder than the bond wire 108. In one particular example, the wire guide comprises K88 copper, which is a metal alloy of copper that is harder than typical copper used in for bond wires. The wire guide 204 may alternatively be formed of or comprise other materials with a higher material hardness than the bond wire 108, e.g., diamond, sapphire, etc. Additionally, the wire guide 204 is formed with a high stiffness. Stiffness refers to the propensity of the wire guide 204 to return to its original position after being subjected to a high force. In this case, the wire guide 204 may have a sufficiently high stiffness to perform the wire bonding process disclosed herein with a bond wire 108, e.g., a copper bond wire at least 500 μm in diameter, and return to its original position with negligible bending or warpage. This high stiffness is obtained through a combination of using high material harness materials as disclosed above and through appropriate dimensioning and configuration of the bond wedge 202.
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The ratio between the height H1 of the wire bond loop 102 and the length L1 of the wire bond loop 102 is an important parameter that impacts cost and performance of the bond wire connection 100. By reducing the height H1 of the wire bond loop 102 at a given length L1, the electrical resistance of the connection may be reduced and the material costs for forming the bond wire connection 100 may be reduced. When compounded across a device with tens, hundreds or even thousands of these wire bond loops 102, the benefits of such a height reduction may be significant. Current wire bonding technologies are limited in their ability to lower the height H1 of a wire bond loop 102. Moreover, there is an inverse relationship between the length L1 of the wire bond loop 102 and the lowest achievable height H1 of the wire bond loop 102. That is, shorter wire bond loops 102 may require a higher wire bond loop 102 height H1 in order to ensure that the bond wire 108 deviates from the bonding plane and does not cause an electrical short. Using a copper bond wire 108 with a diameter of 400 μm as an example, the minimum achievable height H1 of the wire bond which enables a stable loop shaping by a conventional wire bonding technique is 2000 μm for a wire bond length L1 of 5,500 μm, is 2,200 μm for a wire bond length L1 of 5,000 μm, is 2,400 μm for a wire bond length L1 of 4,500 μm, is 2,800 μm for a wire bond length L1 of 4,000 μm, is 3,000 μm for a wire bond length L1 of 3,500 μm, and is 3,500 μm for a wire bond length L1 of 3,000 μm. In this context, a conventional wire bonding technique refers to a technique wherein the bond wedge 202 does not move in a retrograde movement and/or does not use a wire guide 204 with a high stiffness that is formed from a material with a higher material hardness than the bond wire.
The combination of moving the bond wedge 202 in a loop pattern that comprises a retrograde movement and using a wire guide with a high stiffness that is formed from a material with a higher material hardness than the bond wire 108 allows for the formation of wire bond loops 102 with a significantly lower ratio between the height H1 of the wire bond loop 102 and the length L1 of the wire bond loop 102 than the conventional wire bonding technique. Table 1 below provides exemplary values for the height H1 of the wire bond loop 102 and the length L1 of the wire bond loop 102 that may be obtained in a copper bond wire 108 with a diameter of 400 μm according to the presently disclosed techniques.
The above provided values are illustrative of a beneficial ratio between the height H1 of the wire bond loop 102 and the length L1 of the wire bond loop 102 that may be obtained by the presently disclosed technique. An equivalent beneficial improvement to the ratio may be obtained with different types of bond wires 108, e.g., bond wires 108 having different thickness, hardness, material composition, etc., while not necessarily having the same absolute values as provided above.
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Although the present disclosure is not so limited, the following numbered examples demonstrate one or more aspects of the disclosure.
Example 1. A method of forming a bond wire connection, the method comprising: providing a wire bonder comprising a bond wedge with a wire guide; and forming a wire bond loop by initially bonding a bond wire to a first bonding surface using the bond wedge, then moving the wire bonder in a loop pattern whereby the bond wire passes through the wire guide, and then bonding the bond wire to a second bonding surface using the bond wedge, wherein moving the wire bonder in the loop pattern comprises a retrograde movement whereby the wire bonder moves away from the second bonding surface, and wherein the wire guide is formed from a material with a higher material hardness than the bond wire.
Example 2. The method of example 1, wherein the loop pattern comprises a first movement immediately after bonding the bond wire to the first bonding surface and a second movement immediately after the first movement, wherein the first movement moves the bond wedge vertically away from the first bonding surface, and wherein the second movement is the retrograde movement.
Example 3. The method of example 2, wherein the retrograde movement moves the wire bonder in a lateral direction that is substantially parallel to the first bonding surface.
Example 4. The method of example 2, wherein the loop pattern comprises a third movement immediately after the second movement, and wherein the third movement moves the wire bonder vertically away from the first bonding surface.
Example 5. The method of example 4, wherein the loop pattern moves the wire bonder laterally towards the second bonding surface immediately after the third movement.
Example 6. The method of example 5, wherein the loop pattern comprises a fourth movement immediately after the third movement and a fifth movement immediately after the fourth movement, wherein the fourth movement moves the wire bonder in a tilted direction that moves vertically away from the first bonding surface and laterally towards the second bonding surface, and wherein the fifth movement moves the wire bonder in a tilted direction that moves vertically towards from the first bonding surface and laterally towards the second bonding surface.
Example 7. The method of example 1, wherein the bond wire is a copper or copper alloy wire, and wherein the wire guide is formed from a metal with a higher material hardness than the copper or copper alloy wire.
Example 8. The method of example 7, wherein the wire guide comprises any one or more of: Cu, Ni, TI, Zn, Fe, and alloys thereof.
Example 9. The method of example 1, wherein the bond wire is a copper or copper alloy wire with a diameter of between 300 μm and 500 μm.
Example 10. The method of example 9, wherein the diameter of the bond wire is 400 μm.
Example 11. The method of example 10, wherein a bond loop length of the wire bond loop is ≤5,500 μm, and wherein a bond loop height of the wire bond loop is ≤1,800 μm.
Example 12. The method of example 11, wherein the bond loop length of the wire bond loop is ≤4,000 μm.
Example 13. The method of example 11, wherein the bond loop height of the wire bond loop is ≤1,400 μm.
Example 14. A semiconductor device, comprising: a bond wire connection that forms an electrical connection of a semiconductor device, wherein the bond wire connection comprises a wire bond loop between a first bonding surface and a second bonding surface, wherein the bond wire is a copper or copper alloy wire with a diameter of between 300 μm and 500 μm, wherein a bond loop height of the wire bond loop is between 1,200 μm and 2,200.
Example 15. The semiconductor device of claim 14, wherein the bond loop height is less than or equal to 2,000 μm.
Example 16. The semiconductor device of example 15, wherein the bond loop height is less than or equal to 1,400 μm.
Example 17. The semiconductor device of example 14, wherein a bond loop length of the wire bond loop is between 3,500 μm and 6,000 μm.
Example 18. The semiconductor device of example 17, wherein the bond loop length is less than 5,000 μm.
Example 19. The semiconductor device of example 18, wherein the bond loop length is less than 4,000 μm.
Example 20. The semiconductor device of example 14, wherein the bond wire is a copper wire, and wherein the diameter is 400 μm.
Spatially relative terms such as “under,” “below,” “lower,” “over,” “upper,” “main”, “rear”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first,” “second,” and the like, are also used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description.
As used herein, the terms “having,” “containing,” “including,” “comprising” and the like are open-ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a,” “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
