Conductor joining structure

Abstract

To solve the problem that it is difficult to obtain a stable bonding state when performing ultrasonic bonding in a conventional conductor bonding structure.SOLUTION: In a conductor-joining structure in which a bonding wire (2) made of a rectangular wire is ultrasonically joined to a conductive body (1), the bonding wire (2) has a plurality of recessed tool marks (S) in a joining region with the conductive body (1), and a depth of a tool mark S1 at a center of the joining region among the plurality of tool marks (S) is maximum.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a conductor joining structure used to connect a bonding wire to a conductor such as a substrate. [Background technology]

[0002] An example of a conventional conductor joining structure is described in Patent Document 1. Patent Document 1 describes an ultrasonic joining device that ultrasonically joins a conductor and a strip-shaped metal plate having a bent neck portion, in which a pressing section that presses a flat portion of the metal plate is provided with first protrusions that bite into the metal plate and second protrusions that are taller than the first protrusions, and the first protrusions and second protrusions are arranged in multiple rows, with the first protrusions arranged in at least the first row of the multiple rows so as to bite into the neck portion side of the metal plate.

[0003] When the ultrasonic bonding device described above is used to bond a metal plate to a conductor such as a circuit pattern in a case-type semiconductor device, the depth of the indentation formed by the first protrusion is shallow, thereby suppressing a decrease in the rigidity of the metal plate at the end of the bonding surface on the neck side, and as a result, suppressing cracks that start from the end of the bonding surface on the neck side and preventing peeling of the metal plate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5884752 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned conductor bonding structure, a band-shaped metal plate, i.e., a ribbon wire having a flat wire shape to allow a large current to flow, is used as the bonding wire, which results in a larger bonding area with the conductor and a larger load during ultrasonic bonding compared to a wire with a circular cross section. However, with the conventional conductor bonding structure, during ultrasonic bonding, bonding begins at any position on the contact surface between the conductor and the bonding wire, and the bonding start position is indefinite, making it difficult to obtain a stable bonded state.

[0006] The present invention has been made in consideration of the above-mentioned conventional situation, and aims to provide a conductor joining structure in which a bonding wire made of a flat wire is ultrasonically joined to a conductor, which can obtain a stable joining state with a constant joining start position and can realize improved joining quality. [Means for solving the problem]

[0007] The conductor bonding structure according to the present invention is a conductor bonding structure in which a bonding wire made of a rectangular wire is ultrasonically bonded to a conductor. The conductor bonding structure is characterized in that the bonding wire has a plurality of concave tool marks in the bonding area with the conductor, and the depth of the tool marks at the center of the bonding area is greatest among the plurality of tool marks. [Effects of the Invention]

[0008] Since the conductor bonding structure of the present invention adopts the above-mentioned configuration, the starting position of bonding between the conductor and the bonding wire is fixed to the center of the bonding area, thereby achieving a stable bonding state and improving bonding quality. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are explanatory views showing a first embodiment of a conductor joint structure. [Figure 2] FIG. 2 is a plan view showing a main part of the conductor joint structure. [Figure 3]FIG. 3 is a cross-sectional view taken along line BB in FIG. 2. [Figure 4] 4 is a cross-sectional view illustrating a state during ultrasonic bonding of the conductor bonding structure shown in FIG. 3. FIG. [Figure 5] 5 is a cross-sectional view showing the ultrasonic bonding process following FIG. 4. [Figure 6] FIG. 10 is a plan view of a main part showing a second embodiment of a conductor joint structure. [Figure 7] FIG. 7 is a cross-sectional view taken along line CC in FIG. [Figure 8] 8 is a cross-sectional view illustrating the state of the conductor joining structure shown in FIG. 7 during ultrasonic joining. [Figure 9] FIG. 10 is a plan view showing a third embodiment of a conductor joint structure. [Figure 10] FIG. 10 is a cross-sectional view showing a fourth embodiment of a conductor joint structure. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment The conductor joining structure shown in Figure 1 is formed by ultrasonically joining a conductor 1 and a bonding wire 2 made of a rectangular wire. The conductor 1 is not particularly limited, but is typically a printed circuit board. As shown on the left side of Figure 1, the bonding wire 2 is formed in a bridge shape overall, with joining pieces 2A and 2B at both end leg portions that come into surface contact with the conductor 1. As shown on the right side of Figure 1 (as viewed from the arrow AA on the left side), this bonding wire 2 is a ribbon wire with a flat rectangular cross section.

[0011] In the above-described conductor joining structure, after setting the bonding wire 2 on the conductor 1, a tool T is pressed against the joining pieces 2A and 2B of the bonding wire 2 and ultrasonic vibration is applied, thereby forming joints 3, 3 between the conductor 1 and the bonding wire 2. The joining area, which is the area of ​​the joint 3, corresponds to the area of ​​the contact surface of the tool T. The method for joining the conductor 1 and the bonding wire 2 will be described later.

[0012] 2, the conductor bonding structure has a bonding wire 2 with multiple recessed tool marks S in the bonding area with the conductor 1. In this embodiment, in the bonding piece 2A of the bonding wire 2, seven tool marks S are arranged in the longitudinal direction, which is the left-right direction in FIG. 2, and three tool marks S are arranged in the width direction, which is the up-down direction in FIG. 2, for a total of 21 tool marks S.

[0013] 3, the tool marks S are deepest at the center of the bonding area, and in the illustrated example, the depths of the three tool marks S1 at the center in the longitudinal direction are greatest. Note that while FIG. 2 shows one bonding piece 2A of the bonding wire 2, the same is true for the other bonding piece 2B, not shown.

[0014] The tool marks S in this embodiment are square in shape in the plan view shown in Fig. 2, have the same bonding area, and are arranged at equal intervals in the vertical and horizontal directions, i.e., the width direction (vertical direction) and the longitudinal direction (horizontal direction) of the bonding piece 2A. The bonding area of ​​the tool marks S is the area of ​​the range bonded with the formation of the tool marks S during ultrasonic bonding of the conductor 1 and the bonding wire 2. In addition, in the embodiment shown in Fig. 3, the depth of the three tool marks S1 arranged in the width direction is greatest at the center in the longitudinal direction, and the depth of each mark gradually decreases from the center of the bonding area to the outside.

[0015] In the illustrated example, the three tool marks S arranged in the width direction all have the same depth, while the seven arranged in the length direction have the greatest depth of the central tool mark S1, with the depth gradually decreasing on both sides of the center.

[0016] The tool marks S are not limited to a square shape, but may be other polygonal or circular shapes, and marks of different shapes may be arranged. Furthermore, in the case of the configuration shown in FIG. 2, the depth of only one tool mark S1 at the center of the vertical and horizontal arrangement may be maximum, and the depth of each may gradually decrease in the direction from the center to the outside. Furthermore, the multiple tool marks S may have different bonding areas and different spacings between adjacent marks, as will be described in other embodiments below.

[0017] The conductor joining structure having the above configuration can be obtained by the following joining method when ultrasonically joining the conductor 1 and the bonding wire 2, using a tool T having multiple protrusions on the contact surface with the bonding wire 2.

[0018] That is, in the method for joining a bonding wire 2 and a conductor 1, when joining a bonding wire 2 made of a rectangular wire to a conductor 1, a tool T having a plurality of protrusions P on the contact surface facing the joining piece 2A of the bonding wire 2 is used, as shown in Fig. 4. The shape, height (protrusion dimension) and arrangement of the protrusions P of the tool T correspond to the tool marks S shown in Figs. 2 and 3, with the height of the protrusion P1 at the center being the greatest and the height gradually decreasing toward the outside.

[0019] In the bonding method, after setting the bonding wire 2 on the conductor 1 in an ultrasonic bonding device (not shown), a tool T is pressed against the bonding piece 2A of the bonding wire 2 and ultrasonic vibration is applied, thereby ultrasonically bonding the bonding wire 2 to the conductor 1. At this time, in the bonding method, the central protrusion P1 among the multiple protrusions P of the tool T has the greatest height, and the height gradually decreases in a direction from the center to the outside. Therefore, as shown in the upper part of Fig. 5, the central protrusion P1 abuts against the bonding wire 2, and an initial bond 3 between the conductor 1 and the bonding wire 2 is formed below it.

[0020] Then, in the bonding method, as the ultrasonic bonding progresses, the protrusions P of the tool T bite into the bonding wire 2, as shown in the lower part of Fig. 5, and the bonded portion 3 between the bonding wire 2 and the conductor 1 expands outward from the center, and finally, as shown in Fig. 3, the bonded portion 3 is formed over the entire bonding area between the conductor 1 and the bonding piece 2A of the bonding wire 2. In this way, concave tool marks S, which are the inverted shapes of the multiple protrusions P, are formed on the bonding piece 2A of the bonding wire 2, and a conductor bonding structure is obtained in which the depth of the tool mark S1 at the center of the bonding portion (bonding area) 3 among the multiple tool marks S is greatest.

[0021] In the above-described conductor joining structure, in which bonding wire 2 made of a rectangular wire is ultrasonically joined to conductor 1, the joining start position between conductor 1 and bonding wire 2 is determined at the center of the joining area, and joint 3 is formed expanding over the entire joining area, thereby achieving a stable joining state and improving joining quality. Because the above-described conductor joining structure is intended for bonding wire 2 made of a rectangular wire, it is suitable for joining wires for large currents in inverters that drive motors.

[0022] Furthermore, in the above-described joining method, when ultrasonically joining the conductor 1 and the bonding wire 2, the joining start position is determined at the center of the joining area, and the joining portion 3 is formed throughout the entire joining area by spreading outward from the center, so that a stable joining state between the conductor 1 and the bonding wire 2 can be obtained, and a conductor joining structure with excellent joining quality can be obtained.

[0023] Furthermore, the above-mentioned conductor joining structure gradually (stepwise) reduces the depth of the tool mark S from the center to the outside of the joining area between the conductor 1 and the bonding wire 2, so that during ultrasonic joining, the amount of pressure applied at the center is greatest, and the joining piece 2A of the bonding wire 2 gradually expands and collapses from the center, finally forming the joining portion 3, thereby stabilizing the joining quality.

[0024] Furthermore, in the above-described conductor bonding structure, the depth of the tool marks S varies from the center to the outside in the bonding area (area of ​​the bonding portion 3) of the bonding wire 2, which enables highly accurate automatic visual inspection of the bonding portion 3. Contact or non-contact sensors can be used for this inspection.

[0025] 6 to 10 are diagrams illustrating second to fourth embodiments of the conductor connection structure according to the present invention. In the following embodiments, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0026] Second Embodiment 6 and 7, a plurality of tool marks S caused during ultrasonic bonding are formed on a bonding piece 2A of a bonding wire 2 bonded to a conductor 1. The depth of each tool mark S in the conductor bonding structure is greatest at the tool mark S1 in the center of the bonding area, and the depth of each tool mark S gradually decreases in the direction from the center to the outside, and further, the bonding area of ​​each tool mark S gradually increases in the direction from the center to the outside of the bonding area.

[0027] More specifically, in the conductor joining structure of this embodiment, each tool mark S is square in shape, the depth of the tool mark S1 at the center of the joining area (joint 3) is the greatest, and the joining area of ​​the central tool mark S1 is the smallest.

[0028] In the above-mentioned conductor joining structure, eight intermediate tool marks S2 are formed so as to surround the central tool mark S1 on all four sides. These intermediate tool marks S2 have a depth smaller than that of the central tool mark S1 and a joining area larger than that of the central tool mark S1.

[0029] 6, two outer tool marks S3 are arranged on each side of the intermediate tool mark S2 (four in total). These outer tool marks S3 have a depth smaller than that of the intermediate tool mark S2 and a bonding area larger than that of the intermediate tool mark S2.

[0030] In the above-described conductor bonding structure, a tool T shown in Fig. 8 is used to ultrasonically bond the conductor and the bonding wire 2. This tool T has a central protrusion P1, an intermediate protrusion P2, and an outer protrusion P3 in the same arrangement on the surface that contacts the bonding wire 2, which correspond to the central, intermediate, and outer tool marks S1, S2, and S3, respectively.

[0031] Then, after the bonding wire 2 is set on the conductor 1, the tool T is pressed against the bonding piece 2A of the bonding wire 2 and ultrasonic vibration is applied, thereby ultrasonically bonding the bonding wire 2 to the conductor 1.

[0032] At this time, in the bonding method, as in the first embodiment (see FIG. 5), the central protrusion P1 abuts against the bonding wire 2, forming an initial bond 3 between the conductor 1 and the bonding wire 2, and as the ultrasonic bonding progresses, the bond 3 between the bonding wire 2 and the conductor 1 expands outward from the center. Finally, as shown in FIG. 7, the bond 3 is formed over the entire bonding area between the conductor 1 and the bonding piece 2A of the bonding wire 2. As a result, concave tool marks S1 to S3, which are the inverted shapes of the multiple protrusions P1 to P3, are formed on the bonding piece 2A of the bonding wire 2.

[0033] As in the first embodiment, the above-mentioned conductor joining structure has the joining start position between the conductor 1 and the bonding wire 2 determined in the center of the joining area, and the joining portion 3 is formed over the entire joining area, thereby achieving a stable joining state and improving joining quality.

[0034] Furthermore, in the above-described conductor bonding structure, if the surfaces of the conductor 1 or bonding wire 2 are difficult to bond due to an oxide film, the oxide film can be removed by applying a large vibration energy at the beginning of ultrasonic bonding. By minimizing the area of ​​the tip surface of the central protrusion P1, which has the greatest protrusion (height) among the multiple protrusions P1 to P3 of the tool T, the load and vibration energy per unit area are increased, resulting in a reliable bond 3 in the center at the beginning of bonding. As the ultrasonic bonding progresses, the bonding piece 2A of the bonding wire 2 is gradually crushed, and finally, a conductor bonding structure having a stable bond 3 between the conductor 1 and the bonding wire 2 is obtained.

[0035] Third Embodiment The conductor joining structure shown in Figure 9 has a basic configuration equivalent to that of the first embodiment, and in the joining area between the conductor 1 and the bonding wire 2, five tool marks S are arranged in the longitudinal direction, which is the left-right direction in Figure 9, and three tool marks S are arranged in the width direction, which is the up-down direction in Figure 9, for a total of 15 tool marks S.

[0036] Although the tool marks S in the illustrated example are all square, it goes without saying that the shape and number are not limited. Furthermore, the depth of the tool marks S can be the same as in the first embodiment.

[0037] In the above-mentioned conductor joining structure, each tool mark S is arranged at equal intervals in the vertical and horizontal directions in the joining area, i.e., the width direction (vertical direction) and the longitudinal direction (horizontal direction) of the joining piece 2A, and in a more preferred embodiment, in the width direction of the bonding wire 2 (up and down direction in the figure), the total length bn of the tool marks S can be made more than half (a / 2≦bn) of the width dimension a of the bonding wire 2.

[0038] In the illustrated example, three tool marks S are arranged in the width direction of the bonding wire 2, so the relationship between the width dimension a of the bonding wire 2 and the total number bn of tool marks S is a / 2≦b×3.

[0039] The conductor joining structure having the above configuration can obtain the same effects as the first embodiment, and by arranging the tool marks S vertically and horizontally, a well-balanced joining state can be obtained without bias from the center to the end of the joining portion 3 between the conductor 1 and the bonding wire 2.

[0040] Furthermore, in the above-mentioned conductor joining structure, the walls (protrusion portions) between adjacent tool marks 2, 2 in both the vertical and horizontal directions are connected, which increases rigidity and reduces stress applied to the joint 3. Furthermore, by adding a confirmation item in the automatic visual inspection process that "a symmetrical grid shape has been formed left and right and front and back," it is possible to confirm that more uniform bonding has been achieved and perform high-precision inspection.

[0041] Furthermore, in the above-mentioned conductor bonding structure, by setting the relationship between the width dimension a of the bonding wire 2 and the total length b of the tool marks S, bn, to A / 2≦b×n in the width direction, it is possible to ensure a wide bonding area in the width direction, thereby ensuring a sufficient current-carrying area and also ensuring bonding strength.

[0042] <Fourth embodiment> The conductor bonding structure shown in Figure 10 is a structure in which the conductor 1 includes a homogeneous conductor 1A, which is the same metal as the bonding wire 2, and a dissimilar conductor 1B, which is a dissimilar metal to the bonding wire 2. One joining piece 2A of the bonding wire 2 (on the right in the figure) is connected to the homogeneous conductor 1A, and the other joining piece 2A (on the left in the figure) is connected to the dissimilar conductor 1B. As an example, the bonding wire 2 is made of aluminum (including alloys), the homogeneous conductor 1A is made of aluminum (including alloys), and the dissimilar conductor 1B is made of copper (including alloys). Symbol G in Figure 10 is a guide that holds the bonding wire 2.

[0043] In this case, for example, a tool Ta (see tool T in Figure 8) having protrusions P1 to P3 described in the second embodiment can be used to ultrasonically bond one joining piece 2A of the bonding wire 2 to the homogeneous conductor 1A, and for example, a tool Tb (see tool T in Figure 4) having protrusion P described in the first embodiment can be used to ultrasonically bond the other joining piece 2B of the bonding wire 2 to the heterogeneous conductor 1B.

[0044] As a result, the conductor joining structure is such that the joining area of ​​the tool mark S formed by joining one joining piece 2A of the bonding wire 2 with the same type of conductor 1A is larger than the joining area of ​​the tool mark S formed by joining the other joining piece 2B of the bonding wire 2 with the different type of conductor 1B, as shown in the plan view of both joining pieces 2A and 2B in Figure 10.

[0045] The conductor joining structure having the above configuration is effective when joining the bonding wire 2 to a bus bar or semiconductor on the conductor 1 side.

[0046] That is, when bonding a bonding wire 2 and a bus bar (dissimilar conductor 1B), for example, dissimilar metals such as Al-Cu are bonded together, which raises the risk of oxidation. Therefore, by using a tool Tb with a protrusion P having a small tip surface area in ultrasonic bonding, a state close to point contact is achieved, increasing the energy density and improving bonding reliability. As a result, a tool mark S with a small bonding area is formed on the bonding piece 2A of the bonding wire 2 bonded to the bus bar (dissimilar conductor 1B).

[0047] In contrast, when bonding a bonding wire 2 to a semiconductor (homogeneous conductor 1A), the bonding is between similar metals, such as Al-Al, and there is little concern about oxidation. Therefore, in ultrasonic bonding, a tool Ta having protrusions P1 to P3 with large tip surface areas is used to achieve a state close to surface contact and reduce energy density. At this time, it is possible to avoid applying high heat to the semiconductor (homogeneous conductor 1A). As a result, tool marks S1 to S3 with large bonding areas are formed on the bonding piece 2A of the bonding wire 2 bonded to the semiconductor (homogeneous conductor 1A).

[0048] The details of the configuration of the conductor joining structure according to the present invention are not limited to the above-described embodiments, and can be modified as appropriate within the scope of the present invention, and the configurations of the above-described embodiments can also be combined. [Explanation of symbols]

[0049] 1 conductor 1A homogeneous conductor 1B Heterogeneous conductors 2 Bonding Wire 3 Joint (joint area) P1~P3 protrusion S, S1 to S3 Tool marks T, Ta, Tb Tools

Claims

1. A conductor bonding structure in which a bonding wire made of a flat wire is ultrasonically bonded to a conductor, the bonding wire has a plurality of concave tool marks in a bonding area with the conductor, A conductor joining structure, characterized in that the depth of the tool marks at the center of the joining region among the plurality of tool marks is greatest.

2. 2. The conductor joint structure according to claim 1, wherein the depth of each of the tool marks gradually decreases in a direction from the center of the joint area to the outside.

3. 3. The conductor joint structure according to claim 2, wherein the plurality of tool marks have a joint area that gradually increases in a direction from the center of the joint area to the outside.

4. the conductors include a homogeneous conductor that is the same metal as the bonding wire and a heterogeneous conductor that is a different metal from the bonding wire, The conductor joining structure according to claim 2, characterized in that the joining area of ​​the tool mark in the joining region between the bonding wire and the same type of conductor is larger than the joining area of ​​the tool mark in the joining region between the bonding wire and the different type of conductor.

5. 3. The conductor joint structure according to claim 2, wherein a plurality of the tool marks are arranged vertically and horizontally at predetermined intervals in the joint region.

6. In the width direction of the bonding wire, 6. The conductor joint structure according to claim 5, wherein the total length bn of the tool marks is equal to or greater than half the width a of the bonding wire (a / 2≦bn).

7. When joining a bonding wire made of a flat wire to a conductor, a tool having a plurality of protrusions on a contact surface facing the bonding wire; The tool has a plurality of protrusions, the height of which is greatest at a center of the protrusions, After the bonding wire is set on the conductor, A method for joining a bonding wire and a conductor, characterized in that the tool is pressed against the bonding wire and ultrasonic vibration is applied, thereby ultrasonically joining the bonding wire to the conductor and forming concave tool marks on the bonding wire that are the inverse shape of multiple protrusions.

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