Wire bonding structure
A composite metal film with alternating metal portions on the electrode addresses the issue of reduced bonding strength in wires connecting components with different materials by increasing the interface area and preventing complete alloying, ensuring robust joint strength.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2024-11-06
- Publication Date
- 2026-05-15
AI Technical Summary
The bonding strength of wires is compromised when connecting electronic components with different electrode materials, such as gold and aluminum, due to alloy formation at the joint.
A composite metal film is formed on the electrode with alternating first and second metal portions, allowing the wire to bond to this film, increasing the bonding interface area and preventing complete alloying.
Ensures strong bonding by maintaining an uneven bonding interface, even when materials differ, thereby enhancing the joint strength and preventing complete alloying.
Smart Images
Figure JP2024039444_15052026_PF_FP_ABST
Abstract
Description
Wire Bonding Structure
[0001] The present disclosure relates to a wire bonding structure.
[0002] When bonding a wire to an electrode, the same material as the electrode is used as the material of the wire (see, for example, Patent Document 1).
[0003] Japanese Patent Application Laid-Open No. 2011-142265
[0004] There are cases where the materials of the electrodes of two electronic components connected by wire are different. In such a case, the material of the wire is selected according to the material of one of the electrodes. For example, when the electrode of a compound semiconductor chip is made of gold and the electrode of a capacitor is made of aluminum, a gold wire is used. However, when bonding a gold wire to an aluminum electrode, there is a problem that aluminum and gold diffuse into each other at the joint to form an alloy, resulting in a decrease in the bonding strength of the wire.
[0005] The present disclosure has been made to solve the above-described problems, and an object thereof is to obtain a wire bonding structure capable of ensuring the bonding strength of a wire.
[0006] The wire bonding structure according to the present disclosure includes an electronic component having a top electrode made of a first metal, a composite metal film having a first metal portion and a second metal portion formed side by side on the top electrode, and a wire made of a second metal different from the first metal and having one end bonded to the composite metal film, wherein the first metal portion is made of the first metal and the second metal portion is made of the second metal.
[0007] In the present disclosure, a composite metal film in which a first metal portion and a second metal portion are formed side by side is formed on the top electrode of an electronic component, and a wire is bonded to the composite metal film. The bonding interface between the first metal mass composed of the top electrode and the first metal portion and the second metal mass composed of the second metal portion and the wire becomes uneven. Therefore, since the area of the bonding interface between the first metal and the second metal increases, the bonding strength of the wire can be ensured even when the materials of the wire and the top electrode are different.
[0008] This is a cross-sectional view showing a semiconductor device according to Embodiment 1. This is a top view showing an electronic component according to Embodiment 1. This is a top view showing the electronic component of Figure 2 wire-bonded. This is a cross-sectional view along line I-II in Figure 3. This is a cross-sectional view showing the composite metal film formation process according to Embodiment 1. This is a cross-sectional view showing the composite metal film formation process according to Embodiment 1. This is a cross-sectional view showing the composite metal film formation process according to Embodiment 1. This is a cross-sectional view showing the composite metal film formation process according to Embodiment 1. This is a top view showing the electronic component according to a comparative example wire-bonded. This is a cross-sectional view showing a modified version of the electronic component according to Embodiment 1. This is a top view showing an electronic component according to Embodiment 2. This is a top view showing the electronic component according to Embodiment 2 wire-bonded. This is a top view showing an electronic component according to Embodiment 3. This is a top view showing the electronic component of Figure 14 wire-bonded. This is a cross-sectional view along line I-II in Figure 15. This is a top view showing a modified version of the electronic component according to Embodiment 3. This is a top view showing the electronic component of Figure 17 wire-bonded. This is a cross-sectional view along line I-II in Figure 18. This is a top view showing an electronic component according to Embodiment 4. This is a cross-sectional view showing the electronic component according to Embodiment 4 with wire bonding. This is a cross-sectional view showing a modified example of the electronic component according to Embodiment 4. This is a cross-sectional view showing the electronic component of Figure 22 with wire bonding.
[0009] A wire bonding structure according to an embodiment will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repetition of the description may be omitted.
[0010] Embodiment 1 Figure 1 is a cross-sectional view showing a semiconductor device according to Embodiment 1. A compound semiconductor chip 2 and an electronic component 3 are mounted on a metal base plate 1. A case side wall 4 is joined to the outer periphery of the upper surface of the base plate 1 so as to surround the compound semiconductor chip 2 and the electronic component 3.
[0011] The compound semiconductor chip 2 comprises a substrate 2a made of a compound semiconductor, an electrode 2b formed on the upper surface of the substrate 2a, and a lower electrode 2c formed on the lower surface of the substrate 2a. The electrode 2b and the lower electrode 2c are made of gold.
[0012] Electronic component 3 is a capacitor having a dielectric film 3a, an upper electrode 3b formed on the upper surface of the dielectric film 3a, and a lower electrode 3c formed on the lower surface of the dielectric film 3a. The upper electrode 3b and the lower electrode 3c are made of aluminum. Note that electronic component 3 is not limited to a capacitor; it may also be a resistor or other component.
[0013] The lower electrode 2c of the compound semiconductor chip 2 and the lower electrode 3c of the electronic component 3 are each joined to the base plate 1 by solder 5. A composite metal film 6 is formed on the upper electrode 3b. One end of a gold wire 7 is ball-bonded to the composite metal film 6 of the electronic component 3, and the other end of the wire 7 is stitch-bonded to the electrode 2b of the compound semiconductor chip 2. As a result, the compound semiconductor chip 2 and the electronic component 3 are electrically connected by the wire 7.
[0014] Figure 2 is a top view showing an electronic component according to Embodiment 1. Figure 3 is a top view showing the electronic component of Figure 2 with wire bonding. Figure 4 is a cross-sectional view along line I-II in Figure 3. The composite metal film 6 has a first metal portion 6a and a second metal portion 6b formed side by side on the top electrode 3b. The first metal portion 6a and the second metal portion 6b are arranged alternately in a strip-like shape. The top electrode 3b and the first metal portion 6a are directly joined to form an aluminum block. The second metal portion 6b and the wire 7 are directly joined to form a gold block. The bonding interface between these aluminum blocks and gold blocks is uneven in cross-sectional view.
[0015] Figure 5-9 is a cross-sectional view showing the process of forming a composite metal film according to Embodiment 1. First, an electronic component 3 is prepared as shown in Figure 5. Next, as shown in Figure 6, a stripe-shaped resist 8 is formed on the upper electrode 3b of the electronic component 3 by photolithography or the like. Next, as shown in Figure 7, the first metal part 6a is formed on the upper electrode 3b by plating or vapor deposition using the resist 8 as a mask. After removing the resist 8, a stripe-shaped resist 9 is formed on the first metal part 6a by photolithography or the like, as shown in Figure 8. Next, as shown in Figure 9, the second metal part 6b is formed on the upper electrode 3b by plating or vapor deposition using the resist 9 as a mask. After that, the composite metal film 6 is formed by removing the resist 9.
[0016] Next, the effects of this embodiment will be explained in comparison with the comparative example. Figure 10 is a top view showing the wire bonded state of an electronic component according to the comparative example. In the comparative example, there is no composite metal film 6, and the gold wire 7 is directly bonded to the aluminum top electrode 3b. Because the aluminum and gold mutually diffuse at the joint to form an alloy 10, the bonding strength of the wire 7 decreases.
[0017] In contrast, in this embodiment, a composite metal film 6 is formed on the upper electrode 3b of the electronic component 3, in which a first metal part 6a and a second metal part 6b are formed side by side, and the wire 7 is bonded to the composite metal film 6. The bonding interface between the aluminum mass formed by the upper electrode 3b and the first metal part 6a and the gold mass formed by the second metal part 6b and the wire 7 becomes uneven. Therefore, the area of the bonding interface between aluminum and gold is increased, so the bonding strength of the wire 7 can be ensured even if the materials of the wire 7 and the upper electrode 3b are different.
[0018] For example, when connecting a compound semiconductor chip 2 manufactured in-house with an electronic component 3 purchased from another company using wires, the bonding strength of the wire 7 can be ensured regardless of the electrode material of the electronic component 3 from the other company.
[0019] Furthermore, since the first metal part 6a and the second metal part 6b are arranged alternately in a strip-like shape, the joint strength of the wire 7 can be ensured especially in the direction in which the first metal part 6a and the second metal part 6b are arranged alternately.
[0020] Mutual diffusion occurs between the first metal part 6a and the second metal part 6b, but alloying is limited to a few microns. Therefore, the width of each strip of the first metal part 6a and the second metal part 6b is set to 10 μm or more. This prevents complete alloying of the first metal part 6a and the second metal part 6b, maintaining the unevenness of the interface and ensuring bonding strength. Furthermore, to ensure the bonding strength of the wire 7, it is preferable that there are multiple irregularities caused by the first metal part 6a and the second metal part 6b at the joint between the wire 7 and the composite metal film 6. The joint of the wire 7 bonded to the composite metal film 6 expands, and the diameter of the joint of the wire 7 is 60 to 75 μm. Therefore, the width of each strip of the first metal part 6a and the second metal part 6b is set to 30 μm or less, preferably 20 μm or less.
[0021] One end of the wire 7 may be bonded to the electronic component 3, and the other end of the wire 7 may be bonded to a lead frame or the like instead of the compound semiconductor chip 2. The bonding strength between the copper of the lead frame and the gold of the wire 7 is not a concern.
[0022] In addition to the deterioration of bonding strength due to the alloying of gold and aluminum, there is also the problem of deterioration of bonding strength due to the alloying of gold and iron. For this reason, when the electrodes 2b and wire 7 of the compound semiconductor chip 2 are made of gold, and the upper electrode 3b of the electronic component 3 is made of iron, the first metal part 6a of the composite metal film 6 is made of iron, and the second metal part 6b is made of gold. The same effect can be obtained in this case as well.
[0023] Figure 11 is a cross-sectional view showing a modified example of the electronic component according to Embodiment 1. The composite metal film 6 is formed on the first metal part 6a and the second metal part 6b and further has a metal film 11 made of gold. One end of the wire 7 is bonded to this metal film 11. Since the metal film 11 and the wire 7 are made of the same metal, the bonding strength of the wire 7 can be ensured.
[0024] Embodiment 2 Figure 12 is a top view showing an electronic component according to Embodiment 2. Figure 13 is a top view showing the electronic component according to Embodiment 2 with wire bonding. The first metal part 6a and the second metal part 6b are arranged in a grid pattern. Even in this case, the area of the bonding interface between aluminum and gold is large, so bonding strength can be ensured. Also, since the first metal part 6a and the second metal part 6b are arranged alternately in two lateral directions, bonding strength of the wire 7 can be ensured in two lateral directions. The width of each grid of the first metal part 6a and the second metal part 6b is 10 μm or more and 30 μm or less. Alternatively, a metal film 11 made of gold may be formed on the first metal part 6a and the second metal part 6b, similar to Figure 11.
[0025] Embodiment 3 Figure 14 is a top view showing an electronic component according to Embodiment 3. Figure 15 is a top view showing the electronic component of Figure 14 with wire bonding. Figure 16 is a cross-sectional view along line I-II in Figure 15. The first metal part 6a and the second metal part 6b are arranged concentrically. Even in this case, the area of the bonding interface between aluminum and gold is large, so the bonding strength of the wire 7 can be ensured.
[0026] Figure 17 is a top view showing a modified example of the electronic component according to Embodiment 3. Figure 18 is a top view showing the electronic component of Figure 17 with wire bonding. Figure 19 is a cross-sectional view along line I-II in Figure 18. The first metal part 6a and the second metal part 6b are arranged in a multi-concentric pattern. As a result, the area of the bonding interface between aluminum and gold is larger than that of the structure in Figures 14-16, and the bonding strength of the wire 7 is further increased. In addition, since the first metal part 6a and the second metal part 6b are arranged alternately in all lateral directions, the bonding strength of the wire 7 can be ensured in all lateral directions. The width of each concentric circle of the first metal part 6a and the second metal part 6b is 10 μm or more and 30 μm or less. Alternatively, a metal film 11 made of gold may be formed on the first metal part 6a and the second metal part 6b, similar to Figure 11.
[0027] Embodiment 4 Figure 20 is a top view showing an electronic component according to Embodiment 4. Figure 21 is a cross-sectional view showing the electronic component according to Embodiment 4 in a wire-bonded state. Similar to Embodiment 1, the first metal part 6a and the second metal part 6b are arranged alternately in a strip-like shape. In this embodiment, a barrier metal 12 is inserted between the first metal part 6a and the second metal part 6b. The barrier metal 12 is formed by plating or vapor deposition, similar to the first metal part 6a and the second metal part 6b. Note that the formation order of the first metal part 6a, the second metal part 6b and the barrier metal 12 is not limited. The barrier metal 12 may also be inserted between the first metal part 6a and the second metal part 6b in Embodiment 2 or 3.
[0028] The barrier metal 12 is made of titanium or tungsten. Titanium and tungsten are less prone to interdiffusion with aluminum and gold. Therefore, the barrier metal 12 prevents interdiffusion between aluminum and gold. This allows for greater bonding strength than in Embodiment 1.
[0029] Figure 22 is a cross-sectional view showing a modified example of the electronic component according to Embodiment 4. Figure 23 is a cross-sectional view showing the electronic component of Figure 22 wire-bonded. The barrier metal 12 is thicker than the first metal part 6a and the second metal part 6b and protrudes from the upper surfaces of the first metal part 6a and the second metal part 6b. The titanium and tungsten of the barrier metal 12 have higher hardness than aluminum and gold. Therefore, the protruding barrier metal 12 pierces the bonding portion of the wire 7, further improving the bonding strength of the wire 7.
[0030] 2 Compound semiconductor chip, 2b Electrode, 3 Electronic component, 3a Dielectric film, 3b Top electrode, 3c Bottom electrode, 6 Composite metal film, 6a First metal part, 6b Second metal part, 7 Wire, 11 Metal film, 12 Barrier metal
Claims
1. A wire bonding structure comprising: an electronic component having an upper electrode made of a first metal; a composite metal film having a first metal portion and a second metal portion formed side by side on the upper electrode; and a wire made of a second metal different from the first metal, with one end bonded to the composite metal film, wherein the first metal portion is made of the first metal, and the second metal portion is made of the second metal.
2. The wire bonding structure according to claim 1, characterized in that the upper electrode and the first metal part constitute the first metal mass, the second metal part and the wire constitute the second metal mass, and the bonding interface between the first metal mass and the second metal mass is uneven in cross-sectional view.
3. The wire bonding structure according to claim 1 or 2, further comprising a semiconductor device having an electrode made of the second metal, wherein the other end of the wire is bonded to the electrode.
4. The wire bonding structure according to any one of claims 1 to 3, characterized in that the electronic component is a capacitor having a dielectric film, an upper electrode formed on the upper surface of the dielectric film, and a lower electrode formed on the lower surface of the dielectric film and made of the first metal.
5. The wire bonding structure according to any one of claims 1 to 4, characterized in that the first metal is aluminum or iron, and the second metal is gold.
6. The wire bonding structure according to any one of claims 1 to 5, characterized in that the first metal part and the second metal part are arranged alternately with respect to each other in a strip-like shape.
7. The wire bonding structure according to claim 6, characterized in that the width of each strip of the first metal part and the second metal part is 10 μm or more and 30 μm or less.
8. The wire bonding structure according to any one of claims 1 to 5, characterized in that the first metal part and the second metal part are arranged in a grid pattern.
9. The wire bonding structure according to any one of claims 1 to 5, characterized in that the first metal part and the second metal part are arranged concentrically.
10. The wire bonding structure according to any one of claims 1 to 5, characterized in that the first metal part and the second metal part are arranged in a multi-concentric manner.
11. The wire bonding structure according to any one of claims 1 to 10, characterized in that the composite metal film is formed on the first metal portion and the second metal portion, and further comprises a metal film made of the second metal, and one end of the wire is bonded to the metal film.
12. The wire bonding structure according to any one of claims 1 to 10, characterized in that the composite metal film further comprises a barrier metal inserted between the first metal portion and the second metal portion to prevent mutual diffusion between the first metal and the second metal.
13. The wire bonding structure according to claim 12, characterized in that the barrier metal has a higher hardness than the first metal and the second metal, is thicker than the first metal portion and the second metal portion, and protrudes from the upper surfaces of the first metal portion and the second metal portion.
14. The wire bonding structure according to claim 12 or 13, characterized in that the barrier metal is titanium or tungsten.