Copper wire bonding connection device
The use of copper bond wires with flattened ends addresses the robustness and stress issues in copper bonding for power semiconductors, enabling thinner electrical contact layers and reducing process loads, thus enhancing the semiconductor's structural integrity and production efficiency.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2025-11-05
- Publication Date
- 2026-05-15
AI Technical Summary
Existing copper wire bonding techniques for power semiconductors, such as those made of silicon, silicon carbide, or gallium nitride, face challenges in increasing robustness and process loads due to the shift from aluminum to copper, which exacerbates stress concentrations and limits the thickness of electrical contact layers.
A connection device using copper or copper alloy bond wires with flattened sections at the ends, allowing for secure attachment to thin metal layers, particularly those less than 30 μm thick, through a process that includes pre-deforming the wire ends to create a larger contact area and reducing stress concentrations using ultrasonic bonding.
This approach enhances the robustness and cycleability of power semiconductors by enabling thinner electrical contact layers, reducing stress concentrations, and protecting the semiconductor's layer structure during bonding, facilitating production of thinner wafers.
Smart Images
Figure EP2025082028_15052026_PF_FP_ABST
Abstract
Description
[0001] R.414053
[0002] - 1 -
[0003] Description
[0004] title
[0005] Connection device for copper wire bonding
[0006] State of the art
[0007] The present invention relates to a connection device for stress reduction in copper wire bonding, a power semiconductor and a method for producing an electrically conductive connection.
[0008] For power semiconductors made of materials such as silicon, silicon carbide, or gallium nitride, it is common practice to implement a chip-top interconnection technique using wire bonding based on an aluminum alloy. This involves metallizing the semiconductor with an aluminum-containing metal, for example, an aluminum-copper alloy or an aluminum-silicon-copper alloy. While this interconnection technique has proven effective, increasing electrical power necessitates increased robustness of the connections. Therefore, a shift from the standard aluminum technology to copper is being pursued for chip-top interconnection. However, copper bonding increases the process loads across the entire layer structure of the power semiconductor.
[0009] Disclosure of the invention
[0010] The connection device according to the invention, with the features of claim 1, enables the use of bond wires made of copper or a copper alloy for the bonding process, thus enabling a significant increase in the robustness of a power semiconductor. In particular, its cycleability is also improved. The connection device according to the invention therefore enables an electrical connection using copper bond wires and, in particular, R.414053.
[0011] - 2 - also thinner electrical contact layers on a power semiconductor. In particular, the invention enables electrical contact layers on the power semiconductor of less than 30 pm. This is achieved according to the invention by the fact that the connection device is configured for the electrical connection of a first electrical or electronic component with a second electrical or electronic component (hereinafter referred to simply as electronic component). The connection device comprises a bond wire made of copper or a copper alloy for the electrical connection of the two components, wherein the copper bond wire has a flattened section at at least one wire end. The flattened section is configured to be placed on an electrical contact point of one of the electronic components and to perform an electrical contact in a bonding step.Thus, the bond wire has a cross-section at one wire end which consists of the flattened section and a remaining, in particular arc-shaped, circumferential area of the wire.
[0012] The flattened section at the end of the bond wire comprises a flattened circumferential region of the wire, resulting in a change in cross-section at the wire end that deviates from a circular shape. The remaining circumferential region at the wire end is preferably arc-shaped, particularly as a semicircle, and geometrically unchanged. The flattened circumferential region is thus a portion of the wire's circumference at the wire end.
[0013] The dependent claims describe preferred embodiments of the invention.
[0014] Preferably, the flattened section at the wire end lies in a plane E. This plane preferably does not pass through the center point of a cross-section of the wire. The flattened section is therefore itself a flat surface.
[0015] Alternatively, preferably, the flattening comprises an arc-shaped circumferential region, wherein the arc-shaped circumferential region has a larger radius than the radius of the remaining circumferential region of the wire.
[0016] Preferably, the flattening at the wire end is designed such that a maximum distance of a point on the flattening to a point of the unformed circumferential area of the bond wire is less than 90%, in particular R.414053
[0017] - 3 -
[0018] 80%, and in particular 70%, of the diameter of the unformed bond wire.
[0019] Preferably, the flattened circumferential area is a first circular segment and the remaining circumferential area of the wire is a second circular segment with a different radius to the first circular segment.
[0020] Preferably, the bond wire has a first flattened section at a first wire end and a second flattened section at a second wire end. This allows both wire ends of the bond wire, which are designed for electrical contact, to be securely attached to thin metal layers, particularly copper layers or copper-containing layers with a thickness of less than or equal to 30 pm, by means of a bonding process.
[0021] The invention further relates to a power semiconductor comprising a first and a second electronic component and a connection device according to the invention, which connects the first to the second electronic component.
[0022] The power semiconductor preferably has a surface layer on the first component with a metallization thickness of less than or equal to 30 pm on a component surface of the first component. The metallization thickness is further preferably less than or equal to 20 pm, particularly less than or equal to 15 pm, and more particularly less than or equal to 10 pm.
[0023] The metallic surface layer of the power semiconductor is preferably designed as a semiconductor pad. The semiconductor pad is preferably a copper semiconductor pad or a semiconductor pad made of a copper alloy.
[0024] Preferably, the flattening at the wire end extends in the wire direction over a length corresponding to the length of the electrical connection between the bond wire and the first component.
[0025] Thus, bonding of the wires can be achieved by selectively pre-deforming the wire end to create a larger contact area on the semiconductor pad. The actual bonding of the wire to the electronic component is preferably carried out using ultrasonic wire bonding R.414053.
[0026] - 4 - executed. Thus, the ultrasound can act on the semiconductor surface over a larger area.
[0027] Furthermore, the present invention relates to a method for producing an electrical connection between a first and a second electronic component. The method comprises the following steps: providing a copper bonding wire, providing a flattened circumferential region at one end of the copper bonding wire, arranging the flattened circumferential region on a surface of the first component, and connecting, in particular bonding, and more specifically ultrasonically bonding, the wire end with the flattened circumferential region to the surface of the first component. Particularly when using an ultrasonic wire bonding contact, local stress concentrations during the production of the electrical connection can thus be reduced.The flattened circumferential area, produced in particular by means of an embossing process, is preferably produced during the manufacture of the copper bonding wire during a cutting process or alternatively achieved by higher application forces during the application process of the bond connection.
[0028] The flattened circumferential area is particularly preferred when produced at both the first and second ends of the copper bonding wire.
[0029] Drawings
[0030] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawings. The drawing shows:
[0031] Figure 1 shows a schematic representation of a power semiconductor with a connection device according to a first preferred embodiment of the invention.
[0032] Figure 2 is a schematic end-face view of a wire end.
[0033] Connecting device of Figure 1, and
[0034] Figure 3 shows a schematic, end-face view of a connection device of a power semiconductor according to a second embodiment of the invention. R.414053
[0035] - 5 -
[0036] Preferred embodiments of the invention
[0037] With reference to Figures 1 and 2, a power semiconductor 1 with a connecting device 2 and a method according to the invention for producing an electrical connection are described in detail below.
[0038] As can be seen from Figure 1, a power semiconductor 1 comprises a first electronic component 11 and a second electronic component 12, which must be electrically connected to each other by means of bond wires 20.
[0039] The first electronic component 11 has a metal pad 3 made of copper or a copper alloy. The metal pad 3 has a contact surface on which a copper bonding wire 20 is attached.
[0040] The copper bond wire 20 has a first wire end 20a with a first flattening 21 and a second wire end 20b with a second flattening 22 (see Figure 1).
[0041] The first flattening 21 is formed at the electrical contacting of the metal pad 3 and the second flattening 22 is arranged at the electrical contacting to the second component 12.
[0042] Figure 1 schematically shows two bond connections 4, one to the first component 11 and one to the second component 12, with corresponding flattened sections. The other bond connections visible in Figure 1 are provided in the same way, each with flattened sections at both wire ends, and are not labeled with reference numerals for clarity.
[0043] Figure 2 shows a detailed end-face view of one end of the copper bond wire 20. As can be seen in Figure 2, the flattened section has a flattened circumferential region 23 and an arc-shaped remaining circumferential region 24. The remaining circumferential region 24 is preferably unformed. The electrical contact side is located on the flattened circumferential region 23. R.414053
[0044] - 6 -
[0045] Figure 2 shows, in dashed lines, the view of the copper bonding wire 20 without flattening, i.e., in its original state. The copper bonding wire 20 preferably has a circular cross-section. However, the cross-section can also deviate slightly from a circular shape.
[0046] Thus, the flattened circumferential area 23 is designed to be placed on an electrical contact point of the first and second electronic components 11, 12 and to be fixed by means of a bond connection. The bond connection is preferably produced by means of ultrasound.
[0047] As shown in Figure 2, the maximum distance between a point on the flattened circumferential region 23 and a point on the remaining circumferential region 24 of the wire is less than 90% of the wire's diameter D. This demonstrates that the invention can be advantageously implemented even with relatively small forming processes. The flattened circumferential region 23 is formed such that it constitutes a first circular segment. The remaining circumferential region 24 of the wire is preferably a second circular segment with a smaller radius than the radius of the first circular segment. M denotes a center point of the original bond wire before forming.
[0048] The two wire ends 20a, 20b are preferably formed with the same flattening.
[0049] Ultrasound is preferably used to create the bond. The targeted pre-deformation of the copper bonding wire to create the flattened circumferential area 23 results in a larger contact area on the semiconductor pad 3 at the beginning of the ultrasonic process.
[0050] This allows the ultrasound to act on the semiconductor surface over a larger area. This results in a significant reduction in the stress on the electrical contact point at metal pad 3.
[0051] The pre-deformation of the wire end of the flattened circumferential region 23 is preferably achieved during a cutting operation of the bond wire 20 or by higher application forces during the application of the wire or a preceding bond connection. R.414053
[0052] - 7 -
[0053] Thus, the metal pad 3 can have a significantly reduced thickness of less than or equal to 30 pm. This ensures sufficient protection of active structures on the internal semiconductor architecture of the power semiconductor during the bonding process. Therefore, the method according to the invention enables gentle bonding of copper bonding wires 20 to significantly reduced thicknesses (<30 pm) of metal pads 3 or the like.
[0054] In particular, semiconductor pad metallization in copper can be implemented in series production during wafer manufacturing. This allows for a significant reduction in future wafer thicknesses compared to the current approximately 180 pm thick wafers, especially to around 40 pm for GaN wafers.
[0055] Thus, a semiconductor-top bonding technique, particularly for power semiconductors, can be implemented using copper wire bonding. This reduces process loads during the process and, in particular, protects the layer structure of a power semiconductor during the bonding process, especially ultrasonic bonding.
[0056] Figure 3 schematically shows an end view of a copper bonding wire according to a second embodiment. In the second embodiment, the flattened circumferential region 23 is flattened such that it lies in a plane E. The plane E lies outside a center point M of the copper bonding wire 20. This allows, in particular, a flat contact surface to be achieved on metal pads 3.
Claims
R.414053 - 8 - Claims 1. Connection device, designed for electrical connection of a first electronic component (11) to a second electronic component (12) comprising: a copper bonding wire (20) for electrically connecting the first electronic component (11) to the second electronic component (12), wherein the copper bonding wire (20) has at least one wire end a flattening with a flattened circumferential region (23) and a remaining, in particular unformed, circumferential region (24), wherein the flattened circumferential region is configured to be placed on an electrical contact point of the first electronic component in order to realize the electrical connection.
2. Connecting device according to claim 1, wherein the flattened circumferential region (23) lies in a plane E 3. Connecting device according to claim 1, wherein the remaining circumferential region (24) is an arc-shaped circumferential region with a first radius and the flattened circumferential region is an arc-shaped circumferential region with a second radius, wherein the first radius is smaller than the second radius.
4. Connecting device according to one of the preceding claims, wherein a maximum distance of a point of the flattened circumferential region (23) to a point on the remaining circumferential region (24) of the copper bond wire (20) is less than 90% of a diameter of the bond wire.
5. Connecting device according to one of claims 3 or 4, wherein the flattened circumferential region (23) is a first circular segment and the remaining circumferential region of the wire at the wire end is a second circular segment with a smaller radius than the first circular segment. R.414053 - 9 - 6. Connecting device according to one of the preceding claims, wherein the copper bonding wire (20) has a first flattening (21) at a first wire end and a second flattening (22) at a second wire end.
7. Connection device according to one of the preceding claims, wherein the flattening extends in the wire direction over a length corresponding to the length of the electrical connection between the copper bond wire (20) and the first component (11).
8. Power semiconductor comprising a first electronic component (11) and a second electronic component (12) and a connecting device (2) according to any of the preceding claims, which connects the first to the second electronic component.
9. Power semiconductor according to claim 8, wherein the first electronic component (11) has a surface layer of copper or a copper alloy with a thickness of less than or equal to 30 pm, in particular less than or equal to 20 pm, and further in particular less than or equal to 10 pm, on the component surface.
10. Power semiconductor according to claim 9, wherein the surface layer is designed as a semiconductor pad.
11. Power semiconductor according to one of claims 8 to 10, wherein a plurality of connecting devices are formed between the first and the second component (11, 12).
12. Method for establishing an electrical connection between a first electronic component (11) and a second electronic component (12) encompassing the steps: Providing a copper bonding wire (20), Providing a flattening (21) with a flattened circumferential area (23) at one wire end of the copper bonding wire (20), Arranging the flattened circumferential region (23) on a copper-containing surface layer of the first electronic component (11), and R.414053 - 10 - Connecting, in particular bonding, in particular ultrasonic bonding, the wire end to the flattened portion (21) on the copper surface layer of the first component (11).
13. Method according to claim 12, wherein a first flattened portion (21) is formed at a first wire end and a second flattened portion (22) is formed at a second wire end.
14. Method according to one of claims 12 or 13, wherein the copper-containing surface layer of the first component (11) has a thickness of less than or equal to 30 pm.