Wire Bonding Structure

Abstract

The electronic component 3 has an upper surface electrode 3b made of a first metal. The composite metal film 6 has a first metal portion 6a and a second metal portion 6b formed side by side on the upper surface electrode 3b. The wire 7 is made of a second metal different from the first metal, and one end is bonded to the composite metal film 6. The first metal portion 6a is made of the first metal. The second metal portion 6b is made of the second metal.

Description

Technical Field

[0001] The present disclosure relates to a wire bonding structure.

Background Art

[0002] When bonding a wire to an electrode, the same material as that of the electrode is used as the material of the wire (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The materials of the electrodes of two electronic components connected by wire may be different from each other. 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.

Means for Solving the Problems

[0006] The wire bonding structure according to the present disclosure includes an electronic component having an upper surface 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 surface 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. and the lower surface of the upper electrode is flat It is characterized by: [Effects of the Invention]

[0007] In this 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 formed by the top electrode and the first metal portion and the second metal mass formed by the second metal portion and the wire is uneven. Therefore, the area of the bonding interface between the first metal and the second metal is large, so the bonding strength of the wire can be ensured even if the wire and the top electrode are made of different materials. [Brief description of the drawings]

[0008]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0009] The wire bonding structure according to the embodiment will be described with reference to the drawings. The same or corresponding components may be denoted by the same reference numerals, and repeated description may be omitted.

[0010] Embodiment 1 FIG. 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 peripheral portion 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 has a substrate 2a made of a compound semiconductor, an electrode 2b formed on the upper surface of the substrate 2a, and a lower surface electrode 2c formed on the lower surface of the substrate 2a. The electrode 2b and the lower surface electrode 2c are made of gold.

[0012] The electronic component 3 is a capacitor having a dielectric film 3a, an upper surface electrode 3b formed on the upper surface of the dielectric film 3a, and a lower surface electrode 3c formed on the lower surface of the dielectric film 3a. The upper surface electrode 3b and the lower surface electrode 3c are made of aluminum. Note that the electronic component 3 is not limited to a capacitor and may be a resistor or the like.

[0013] The lower surface electrode 2c of the compound semiconductor chip 2 and the lower surface 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 surface electrode 3b. One end of a wire 7 made of gold 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. Thereby, the compound semiconductor chip 2 and the electronic component 3 are electrically connected by the wire 7.

[0014] FIG. 2 is a top view showing the electronic component according to Embodiment 1. FIG. 3 is a top view showing a state where wire bonding is performed on the electronic component of FIG. 2. FIG. 4 is a cross-sectional view taken along line I-II of FIG. 3. The composite metal film 6 has a first metal portion 6a and a second metal portion 6b formed side by side on the upper surface electrode 3b. The first metal portion 6a and the second metal portion 6b are alternately arranged in a strip shape. The upper surface electrode 3b and the first metal portion 6a are directly joined to form a mass of aluminum. The second metal portion 6b and the wire 7 are directly joined to form a mass of gold. The joining interface between these masses of aluminum and gold is uneven in a cross-sectional view.

[0015] 5-9 are cross-sectional views showing the steps of forming a composite metal film according to the first embodiment. First, an electronic component 3 shown in FIG. 5 is prepared. Next, as shown in FIG. 6, a striped resist 8 is formed on the upper electrode 3b of the electronic component 3 by photolithography or the like. Next, as shown in FIG. 7, a first metal portion 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 striped resist 9 is formed on the first metal portion 6a by photolithography or the like as shown in FIG. 8. Next, as shown in FIG. 9, a second metal portion 6b is formed on the upper electrode 3b by plating or vapor deposition using the resist 9 as a mask. Thereafter, 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 a comparative example. Fig. 10 is a top view showing a state in which wire bonding is performed on an electronic component according to the comparative example. The comparative example does not have a composite metal film 6, and a gold wire 7 is directly bonded to the aluminum upper surface electrode 3b. Since aluminum and gold interdiffuse at the joint to form an alloy 10, the bonding strength of the wire 7 is reduced.

[0017] In contrast, in the present embodiment, a composite metal film 6 in which a first metal portion 6a and a second metal portion 6b are formed side by side is formed on the top electrode 3b of the electronic component 3, and a wire 7 is bonded to the composite metal film 6. The bonding interface between the aluminum block formed by the top electrode 3b and the first metal portion 6a and the gold block formed by the second metal portion 6b and the wire 7 is uneven. Therefore, the area of the bonding interface between aluminum and gold is large, and the bonding strength of the wire 7 can be ensured even if the wire 7 and the top electrode 3b are made of different materials.

[0018] For example, when a compound semiconductor chip 2 manufactured in-house is wire-connected to an electronic component 3 purchased from another company, the bonding strength of the wire 7 can be ensured regardless of the electrode material of the other company's electronic component 3.

[0019] In addition, since the first metal portion 6a and the second metal portion 6b are arranged alternately with each other in a strip shape, the bonding strength of the wire 7 can be ensured particularly in the direction in which the first metal portion 6a and the second metal portion 6b are alternately arranged.

[0020] Interdiffusion also occurs between the first metal portion 6a and the second metal portion 6b, but the alloying is about several microns. Therefore, the lateral width of each strip of the first metal portion 6a and the second metal portion 6b is set to 10 μm or more. Thereby, it is possible to prevent the first metal portion 6a and the second metal portion 6b from being completely alloyed, and it is possible to maintain the unevenness of the interface and ensure the bonding strength. In addition, in order to ensure the bonding strength of the wire 7, it is preferable that there are a plurality of unevennesses formed by the first metal portion 6a and the second metal portion 6b at the bonding portion between the wire 7 and the composite metal film 6. The bonding portion of the wire 7 bonded to the composite metal film 6 spreads, and the diameter of the bonding portion of the wire 7 is 60 to 75 μm. Therefore, the lateral width of each strip of the first metal portion 6a and the second metal portion 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 problem.

[0022] There is also a problem of deterioration of the bonding strength due to alloying of gold and iron in addition to the deterioration of the bonding strength due to alloying of gold and aluminum. For this reason, when the electrode 2b of the compound semiconductor chip 2 and the wire 7 are made of gold and the upper surface electrode 3b of the electronic component 3 is made of iron, the first metal portion 6a of the composite metal film 6 is made of iron and the second metal portion 6b is made of gold. The same effect can be obtained in this case.

[0023] FIG. 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 portion 6a and the second metal portion 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 FIG. 12 is a top view of an electronic component according to a second embodiment. FIG. 13 is a top view of the electronic component according to the second embodiment after wire bonding. The first metal portions 6a and the second metal portions 6b are arranged in a lattice pattern. Even in this case, the area of the bonding interface between aluminum and gold is large, thereby ensuring bonding strength. Furthermore, since the first metal portions 6a and the second metal portions 6b are alternately arranged in two horizontal directions, the bonding strength of the wire 7 can be ensured in both horizontal directions. The width of each lattice of the first metal portions 6a and the second metal portions 6b is 10 μm or more and 30 μm or less. Furthermore, a metal film 11 made of gold may be formed on the first metal portions 6a and the second metal portions 6b, as in FIG. 11.

[0025] Embodiment 3 Fig. 14 is a top view showing an electronic component according to embodiment 3. Fig. 15 is a top view showing the electronic component of Fig. 14 in a wire-bonded state. Fig. 16 is a cross-sectional view taken along line I-II in Fig. 15. The first metal portion 6a and the second metal portion 6b are concentrically arranged. Even in this case, the area of the bonding interface between aluminum and gold is large, ensuring the bonding strength of the wire 7.

[0026] FIG. 17 is a top view showing a modified example of the electronic component according to the third embodiment. FIG. 18 is a top view showing the electronic component of FIG. 17 after wire bonding. FIG. 19 is a cross-sectional view taken along line I-II of FIG. 18. The first metal portion 6a and the second metal portion 6b are arranged in multiple concentric circles. This increases the area of the aluminum-gold bonding interface compared to the structures of FIGS. 14-16, further increasing the bonding strength of the wire 7. Furthermore, since the first metal portion 6a and the second metal portion 6b are alternately arranged 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 portion 6a and the second metal portion 6b is 10 μm or more and 30 μm or less. Furthermore, a metal film 11 made of gold may be formed on the first metal portion 6a and the second metal portion 6b, as in FIG. 11.

[0027] Embodiment 4 FIG. 20 is a top view of an electronic component according to a fourth embodiment. FIG. 21 is a cross-sectional view showing a state in which the electronic component according to the fourth embodiment is wire-bonded. As in the first embodiment, the first metal portions 6a and the second metal portions 6b are alternately arranged in strips. In this embodiment, a barrier metal 12 is inserted between the first metal portions 6a and the second metal portions 6b. The barrier metal 12 is formed by plating or vapor deposition, similar to the first metal portions 6a and the second metal portions 6b. The order in which the first metal portions 6a, the second metal portions 6b, and the barrier metal 12 are formed is not limited. The barrier metal 12 may be inserted between the first metal portion 6a and the second metal portion 6b in the second or third embodiment.

[0028] The barrier metal 12 is made of titanium or tungsten. Titanium and tungsten are less likely to interdiffuse with aluminum and gold. Therefore, the barrier metal 12 prevents interdiffusion between aluminum and gold. This ensures a stronger bond than in the first embodiment.

[0029] FIG. 22 is a cross-sectional view showing a modified example of the electronic component according to the fourth embodiment. FIG. 23 is a cross-sectional view showing the electronic component of FIG. 22 after wire bonding. The barrier metal 12 is thicker than the first metal portion 6a and the second metal portion 6b, and protrudes from the upper surfaces of the first metal portion 6a and the second metal portion 6b. Titanium and tungsten of the barrier metal 12 are harder than aluminum and gold. Therefore, the protruding barrier metal 12 penetrates the bonding portion of the wire 7, further improving the bonding strength of the wire 7. [Explanation of symbols]

[0030] 2 compound semiconductor chip, 2b electrode, 3 electronic component, 3a dielectric film, 3b upper electrode, 3c lower electrode, 6 composite metal film, 6a first metal portion, 6b second metal portion, 7 wire, 11 metal film, 12 barrier metal

Claims

1. An electronic component having a top electrode made of a first metal, A composite metal film having a first metal part and a second metal part formed side by side on the top electrode, A wire made of a second metal different from the first metal, with one end bonded to the composite metal film, The first metal part is made of the first metal, The second metal part is made of the second metal, A wire bonding structure characterized in that the lower surface of the top electrode is flat.

2. An electronic component having a top electrode made of a first metal, A composite metal film having a first metal part and a second metal part formed side by side on the top electrode, A wire made of a second metal different from the first metal, with one end bonded to the composite metal film, and A semiconductor device having an electrode made of the second metal, The first metal part is made of the first metal, The second metal part is made of the second metal, A wire bonding structure characterized in that the other end of the wire is bonded to the electrode.

3. The top electrode and the first metal part constitute a mass of the first metal, The second metal part and the wire constitute a mass of the second metal, The wire bonding structure according to claim 1 or 2, characterized in that the bonding interface between the mass of the first metal and the mass of the second metal is uneven in cross-section.

4. The electronic component is a capacitor having a dielectric film, the top electrode formed on the upper surface of the dielectric film, and a bottom electrode made of the first metal formed on the lower surface of the dielectric film. The wire bonding structure according to claim 1 or 2.

5. The first metal is aluminum or iron, and the second metal is gold. The wire bonding structure according to claim 1 or 2.

6. The wire bonding structure according to claim 1 or 2, characterized in that the first metal part and the second metal part are arranged alternately in strip 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 claim 1 or 2, 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 claim 1 or 2, wherein the first metal part and the second metal part are arranged concentrically.

10. The wire bonding structure according to claim 1 or 2, wherein the first metal part and the second metal part are arranged in multiple concentric circles.

11. The composite metal film is formed on the first metal part and the second metal part, and further has a metal film made of the second metal. The wire bonding structure according to claim 1 or 2, wherein one end of the wire is bonded to the metal film.

12. The wire bonding structure according to claim 1 or 2, wherein the composite metal film is inserted between the first metal part and the second metal part, and further has a barrier metal for preventing mutual diffusion of the first metal and the second metal.

13. The wire bonding structure according to claim 12, wherein the barrier metal has a higher hardness than the first metal and the second metal, a greater thickness than the first metal part and the second metal part, and protrudes from the upper surfaces of the first metal part and the second metal part.

14. The wire bonding structure according to claim 12, wherein the barrier metal is titanium or tungsten.

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