JP7316958B2 - Bonding tool and method for manufacturing power semiconductor device - Google Patents

Description

The present disclosure relates to a bonding tool for ultrasonic bonding and a method of manufacturing a power semiconductor device.

Conventional bonding tools have a step at the tip of the bonding tool to suppress slippage between the bonding tool and the wire, efficiently transmit ultrasonic energy, and achieve defect-free bonding in a short time. Is going. (For example, see Patent Document 1)

JP-A-7-263478 (paragraphs 0016-0017, FIGS. 1-2)

However, metal chips may be generated in the process of ultrasonic bonding, and the metal chips may short-circuit adjacent electrodes, resulting in problems. Therefore, a process for removing metal scraps had to be provided after the completion of ultrasonic bonding. Metal scraps cannot be completely removed only by air blowing, and it is necessary to manually remove metal scraps individually, which causes problems such as a decrease in productivity and an increase in manufacturing costs.

The present disclosure has been made to solve the above-described problems, and aims to provide a bonding tool capable of improving productivity and reducing manufacturing costs by abolishing the manual work of individually removing metal scraps. and

Another object of the present invention is to provide a method of manufacturing a power semiconductor device that eliminates manual work for individually removing metal scraps in ultrasonic bonding using a bonding tool, thereby improving productivity and reducing manufacturing costs.

Another object of the present invention is to provide a power semiconductor device with improved productivity and reduced manufacturing cost.

A bonding tool according to the present disclosure includes a plurality of convex portions having a first flat portion at the tip parallel to the joint surface of the joint, and a second flat portion provided between the adjacent convex portions and parallel to the joint surface. The width of the first flat portion is larger than the width of the second flat portion, and a pair of grooves are provided on both ends of the tip portion with a plurality of protrusions interposed therebetween, and the outer side of the pair of grooves in a cross-sectional view. is provided with a protrusion that is lower than the second flat portion with respect to the first flat portion .

In the method for manufacturing a power semiconductor device according to the present disclosure, a plurality of convex portions having first flat portions parallel to the joint surface of the joint at the tip end portion and between the convex portions adjacent to each other are provided in the ultrasonic bonding apparatus. a bonding tool having a second flat portion parallel to the bonding surface, wherein the width of the first flat portion is larger than the width of the second flat portion; an insulating substrate on which a semiconductor element is mounted; and a metal pattern on the insulating substrate. A bonding tool and a semi-finished product preparation step in which the electrode terminal held so as to be in contact with is placed in the ultrasonic bonding device, and the tip of the bonding tool moves to the bonding location, applies a load and pushes it in while ultrasonic vibration Then, an ultrasonic bonding process for bonding the electrode terminal and the metal pattern, an air blowing process for removing metal scraps generated in the ultrasonic bonding process, and an appearance inspection process for inspecting the appearance of the joint and its surroundings. A pair of grooves are provided on both ends of the tip portion with a plurality of protrusions interposed therebetween, and a protrusion lower than the second flat portion with respect to the first flat portion is provided outside the pair of grooves in a cross-sectional view. It is

According to the bonding tool according to the present disclosure, metal scraps generated during ultrasonic bonding are cut and separated from the electrode terminals, so that metal scraps can be easily removed thereafter, improving productivity and reducing manufacturing costs. can be done.

In addition, according to the method of manufacturing a power semiconductor device according to the present disclosure, there is no need for manual work to individually remove metal scraps generated during ultrasonic bonding, and metal scraps can be easily removed only by an air blow process. , productivity improvement and manufacturing cost reduction can be achieved.

3 is a cross-sectional view showing a configuration for ultrasonic bonding with the bonding tool according to the first embodiment; FIG. 4 is a cross-sectional view showing a joint ultrasonically joined by the bonding tool according to the first embodiment; FIG. 4 is a top view showing a joint portion ultrasonically joined by the bonding tool according to the first embodiment; FIG. 4 is a flow chart showing a method for manufacturing a power semiconductor device ultrasonically bonded by the bonding tool according to the first embodiment; FIG. 10 is a cross-sectional view showing a configuration for ultrasonic bonding with a bonding tool according to a second embodiment;

Embodiment 1.
Embodiment 1 will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration for ultrasonic bonding using a bonding tool. FIG. 2 is a cross-sectional view showing a joint ultrasonically bonded by a bonding tool. FIG. 3 is a top view showing a joint ultrasonically bonded by a bonding tool.

As shown in FIG. 1, an electrode terminal 1 is provided on a metal pattern 2 a of an insulating substrate 2 , and the electrode terminal 1 is pressed toward the insulating substrate 2 by a bonding tool 3 . As shown in FIG. 1, the direction from the tip of the electrode terminal 1 to the L-shaped bent portion is defined as the X-axis, and the direction from the metal pattern 2a of the insulating substrate 2 to the electrode terminal 1 is defined as the Z-axis.

A load of several tens to several hundred N is applied from the bonding tool 3 , and the electrode terminal 1 is pushed toward the metal pattern 2 a of the insulating substrate 2 . While applying the above load, the bonding tool 3 is ultrasonically vibrated at several tens of kHz in the horizontal direction (X-axis direction in FIG. 1) to bond the interface between the electrode terminal 1 and the metal pattern 2a. As shown in FIG. 3, the overall size of the joint 4 is, for example, 5 mm×5 mm. The direction of ultrasonic vibration is not limited to one direction, and may be two directions.

Moreover, the above load is a value that takes into account the structure of the joint 4 . That is, in addition to the thickness and material of the electrode terminal 1, the thickness and material of the metal pattern 2a, the insulating plate 2b, and the metal pattern 2c determine the load. In particular, since it is necessary to ensure insulation, it is necessary to set the load so as not to crack the insulating plate 2b.

The electrode terminal 1 has a flat shape on one tip side, and the bonding tool 3 vibrates ultrasonically while applying a load to the flat shape of the electrode terminal 1, so that the electrode terminal 1 and the metal pattern 2a are bonded. be done. The electrode terminal 1 is bent, and the other end of the electrode terminal 1 is electrically connected to the outside (not shown). The thickness of the electrode terminal 1 is 0.4 to 1.2 mm, and the material of the electrode terminal 1 is a conductive metal material containing Cu as a main component. For example, a composite material such as Al, Cu/Invar/Cu may be used, or an alloy such as CuMo may be used.

The insulating substrate 2 has an insulating plate 2b sandwiched between metal patterns 2a and 2c. The insulating plate 2b has a thickness of 0.2 to 1 mm and is made of insulating ceramic. The ceramic is either _{Si3N4 , Al2O3} , or _AlN . The material of the metal pattern 2a and the metal pattern 2c is a conductive metal material containing Cu as a main component. The thickness of metal pattern 2a is preferably greater than the thickness of metal pattern 2c. For example, the thickness of the metal pattern 2a is 0.8 mm, and the thickness of the metal pattern 2c is 0.7 mm.

The bonding tool 3 is made of cemented carbide, for example. The bonding tool 3 has a bar shape as a whole and has a tip at one end. In addition to the shape, size and thickness of the electrode terminal 1, Yes. The bonding tool 3 is mounted in an ultrasonic bonding device (not shown) and ultrasonically vibrated. Also, the bonding tool 3 can be replaced at any time according to the required bonding area.

As shown in FIG. 1, the tip of the bonding tool 3 that is pushed into contact with the joint of the electrode terminal 1 has a shape with a plurality of protrusions 3a having a first flat portion 3b parallel to the joint surface of the joint. It has become. Further, a second flat portion is formed between the convex portions 3a adjacent to each other and parallel to the joint surface of the joint. The width of the first flat portion 3b of the convex portion 3a in the X-axis and Y-axis directions is greater than the width of the second flat portion 3c. For example, the width of the first flat portion 3b of the convex portion 3a is 0.15 mm, and the width of the second flat portion 3c is 0.1 mm.

Further, the convex portion 3a of the bonding tool 3 is tapered toward the first flat portion 3b of the convex portion 3a. The bonding tool 3 applies a large load to the electrode terminal 1 in the direction of the metal pattern 2a and pushes the electrode terminal 1 in the direction of the metal pattern 2a. The convex portion 3a rises (in the Z-axis direction) from the joint portion 4 to facilitate separation.

In this way, as shown in FIG. 1, the bonding tool 3 having the convex portion 3a having the first flat portion 3b at the tip applies a large load to the electrode terminal 1 in the direction of the metal pattern 2a and pushes it. However, by entering the electrode terminal 1 without any gap, the energy of the ultrasonic vibration can be efficiently transmitted to the joint portion 4 without waste. As a result, as shown in FIGS. 2 and 3, a sufficient bonding area can be secured, so that a highly reliable bonding portion 4 having sufficient bonding strength can be obtained. FIG. 3 is a top view of the joint 4 viewed from the Z-axis direction in FIG. 2, and the X-axis and Y-axis are in the plane direction parallel to the joint surface of the joint.

Even if metal chips are generated on the electrode terminal 1 during ultrasonic bonding, the tip of the bonding tool 3 having a convex portion 3a at the tip thereof is pressed into the electrode terminal 1 without any gap while applying a load. Therefore, the tip of the bonding tool 3 vibrating ultrasonically and having the projection 3 a cuts the metal scraps and separates them from the electrode terminal 1 . As a result, the cut metal scraps are easily removed by air blowing in the next step, so that the metal scraps are connected to the electrode terminals 1 and short-circuiting with the adjacent electrode terminals 1 does not occur. .

In addition, since there is no need for manual work to individually remove metal scraps after ultrasonic bonding is completed, productivity can be greatly improved and manufacturing costs can be reduced.

Next, a method for manufacturing a power semiconductor device will be described.

FIG. 4 shows a flowchart relating to the method of manufacturing a power semiconductor device.

First, a plurality of convex portions 3a having a first flat portion 3b parallel to the joint surface of the joint at the tip portion, and a second flat portion provided between the adjacent convex portions 3a and parallel to the joint surface. 3c, the width of the first flat portion 3b is larger than the width of the second flat portion 3c, prepare a bonding tool 3, attach it to a predetermined position in an ultrasonic bonding apparatus (not shown), and mount a semiconductor element. A semi-finished product having the insulating substrate 2 and the electrode terminals 1 held so as to be in contact with the metal pattern 2a of the insulating substrate 2 by a jig or the like (not shown) is placed in an ultrasonic bonding apparatus (not shown). (S101).
A bonding tool 3 suitable for the model of the power semiconductor device is selected from among various bonding tools 3 having different tip areas in contact with the bonding portion of the electrode terminal 1 . If the tip of the bonding tool 3 is dirty, clean it or replace it. Also, if the bonding tool 3 is deformed, replace it.

As shown in FIG. 1, an electrode terminal 1 fixed and held by a jig (not shown) to a metal pattern 2a of an insulating substrate 2 is moved onto a stage (not shown) in an ultrasonic bonding apparatus. Then, the bonding tool 3 descends toward the electrode terminal 1 (in the Z-axis direction), applies a load to the electrode terminal 1 in the direction of the metal pattern 2a, and pushes the electrode terminal 1 in while ultrasonically vibrating in the horizontal direction (X-direction). , joining is performed (S102).

Scattered metal chips generated during ultrasonic bonding are removed by air blow (S103). The air blower may be installed inside the ultrasonic bonding device (not shown). A dust collector may be used instead of the air blow, but it is preferable to suck the metal chips with the dust collector while blowing the air. Metal chips generated on the electrode terminal 1 are pushed into the electrode terminal 1 without gaps and cut by the bonding tool 3 which is ultrasonically vibrated, so the metal chips can be easily removed.

As shown in FIGS. 2 and 3, it is confirmed by visual inspection that the electrode terminal 1 is bonded to the metal pattern 2a of the insulating substrate 2 (S104), and the ultrasonic bonding process is completed. Note that the joint portion 4 may be provided at a plurality of locations with respect to the electrode terminal 1, and the joint strength and current-carrying area can be ensured.

In this manner, in an ultrasonic bonding apparatus (not shown), a plurality of protrusions 3a having a first flat portion parallel to the joint surface of the joint and adjacent protrusions 3a are provided at the distal ends of the protrusions 3a. , a bonding tool 3 having a second flat portion parallel to the bonding surface, the width of the first flat portion being larger than the width of the second flat portion, is mounted in an ultrasonic bonding apparatus (not shown), and a semiconductor element is mounted. A bonding tool and a semi-finished product for placing the electrode terminal 1 held so as to contact the metal pattern 2a of the insulating substrate 2 by the insulating substrate 2 and a jig (not shown), etc., in an ultrasonic bonding apparatus (not shown). , an ultrasonic bonding step in which the tip of the bonding tool 3 applies a load to the bonding portion of the electrode terminal 1 and pushes it in while ultrasonically bonding, and an air blowing step in which metal scraps generated in the ultrasonic bonding process are removed. and an appearance inspection step of inspecting the appearance of the joint and its surroundings.

A plurality of convex portions 3a having a first flat portion parallel to the joint surface of the joint at the tip portion, and a second flat portion provided between the mutually adjacent convex portions 3a and parallel to the joint surface. The width of the first flat portion is such that the bonding tool 3 having the convex portion 3a larger than the width of the second flat portion applies a load to the electrode terminal 1 in the direction of the metal pattern 2a and pushes the electrode terminal 1 in the direction of the metal pattern 2a. Thus, the metal pattern 2a of the insulating substrate 2 and the electrode terminal 1 are joined. Even if metal chips are generated in the electrode terminal 1 during ultrasonic bonding, the tip of the bonding tool 3 enters the electrode terminal 1 without any gap, so the tip of the bonding tool 3 is ultrasonically vibrated. It is cut and separated from the electrode terminal 1 by the convex portion 3a provided on the portion. Therefore, metal scraps can be easily removed by air blow.

After the ultrasonic bonding is completed, a part of the electrode terminal 1 and the insulating substrate 2 are surrounded by a case (not shown) and sealed with silicone gel (not shown) or epoxy resin (not shown) to form a power semiconductor. It is packaged as a device (not shown).

Next, the power semiconductor device will be explained.

Although not shown, at least one semiconductor element (not shown) is mounted on the metal pattern 2a of the insulating substrate 2, and a circuit is formed by the electrode terminals 1 and metal wires (not shown). . The semiconductor element is a so-called power semiconductor element that is made of Si and controls power. Examples include IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), and FWDs (Free Wheeling Diodes). One side of the semiconductor element is 3 mm to 13 mm. It should be noted that the element is not limited to Si, and may be a wide bandgap semiconductor element such as SiC or GaN.

A plurality of convex portions 3a having a first flat portion parallel to the joint surface of the joint at the tip portion, and a second flat portion provided between the mutually adjacent convex portions 3a and parallel to the joint surface. The width of the first flat portion is larger than the width of the second flat portion. Since the bonding tool 3 presses the electrode terminal 1 in the direction of the metal pattern 2a by applying a load, the joint portion 4 of the electrode terminal 1 is The shape of the projection 3a at the tip of 3 is reflected. That is, as shown in FIGS. 2 and 3, the surface of the joint portion 4 of the electrode terminal 1 has a shape having a concave portion 4a. It has a plurality of recesses 4a having a third flat portion 4b at the bottom that is parallel to the joint surface of the joint, and a fourth flat portion 4c having a smaller width than the third flat portion 4b between the adjacent recesses 4a. there is The bonding area of one recess 4a is, for example, 0.5 mm×0.5 mm. Further, the maximum height (in the Z-axis direction) of the fourth flat portion 4c in the bonding portion 4 is about 3/4 of the thickness of the electrode terminal 1 before bonding because the tip of the bonding tool 3 pushes the fourth flat portion 4c.

In this way, a plurality of concave portions 4a having third flat portions 4b are formed, and a sufficient bonding area can be secured, so that sufficient bonding strength can be obtained. Therefore, it is possible to obtain a power semiconductor device having a highly reliable joint portion 4 .

In Embodiment 1, the tip of the bonding tool 3 has a plurality of projections 3a. The projections 3a have a first flat portion 3b at the tip parallel to the joint surface of the joint, and a second flat portion 3c provided between adjacent projections 3a parallel to the joint surface. , the width of the first flat portion 3b in the X-axis and Y-axis directions is greater than the width of the second flat portion 3c. The electrode terminal 1 and the metal pattern 2a of the insulating substrate 2 are bonded by ultrasonically vibrating while the tip of the bonding tool 3 applies a load to the electrode terminal 1 and presses the electrode terminal 1 in the direction of the metal pattern 2a. With the configuration as described above, even if metal chips are generated during ultrasonic bonding, the tip of the bonding tool 3 is pushed into the electrode terminal 1 without a gap, so that ultrasonic vibration is generated. At the tip of the bonding tool 3 located there, the metal scrap is cut and separated from the electrode terminal 1 . As a result, it is possible to eliminate the need for manual work for individually removing the metal scraps, and the metal scraps can be easily removed by an air blow, thereby achieving the effects of improving productivity and reducing manufacturing costs.

Moreover, since a plurality of convex portions 3a having the first flat portions 3b are formed at the tip portion of the bonding tool 3, a sufficient bonding area can be secured at the bonding portion 4. FIG. Therefore, it is possible to obtain a power semiconductor device having a highly reliable joint portion 4 with sufficient joint strength.

Note that the insulating substrate 2 is not limited to a substrate using ceramic, and may be, for example, a substrate insulated with resin. A Cu plate may also be used.

Moreover, since the electrode terminal 1 is directly bonded to the metal pattern 2a without using a bonding material such as solder, a highly reliable and long-lasting bonded portion 4 that can withstand high temperatures can be obtained. Therefore, when a wide bandgap semiconductor element such as SiC or GaN capable of coping with high temperature is mounted as a semiconductor element, the effect becomes remarkable.

Although not shown, a cooler may be attached to the metal pattern 2c of the insulating substrate 2. FIG. The cooler is, for example, a metal plate, a metal plate with fins or a water cooler. As a result, the heat generated by the semiconductor element (not shown) can be efficiently dissipated, so that the semiconductor element (not shown) can operate as desired.

Embodiment 2.
FIG. 5 is a cross-sectional view showing a configuration for ultrasonic bonding using the bonding tool 3 according to the second embodiment. The bonding tool, the method for manufacturing a power semiconductor device, and the power semiconductor device according to the present embodiment have many configurations in common with those of the first embodiment. Therefore, the points different from the first embodiment will be described, and the same or corresponding configurations will be denoted by the same reference numerals, and the description thereof will be omitted. As shown in FIG. 5, the configuration of the bonding tool 3 differs from the first embodiment in that a pair of grooves 5 are provided at both ends of the tip portion.

FIG. 5 is a diagram seen from the X-axis direction of FIG. As shown in FIG. 5, at the tip of the bonding tool 3, a plurality of protrusions 3a having at their tips first flat portions 3b parallel to the bonding surface of the bonding portion and adjacent protrusions 3a are provided. A second flat portion 3c is formed parallel to the bonding surface, and a second flat portion 3c is formed in the Z-axis direction at both ends of the tip so as to easily catch metal chips generated during ultrasonic bonding. A pair of grooves 5 having a depth (in the Z-axis direction) of about several millimeters from the portion 3c is provided. As a result, since the tip of the bonding tool 3 is pushed into the electrode terminal 1 without any gap, metal chips generated during ultrasonic bonding are cut by the tip of the bonding tool 3 and separated from the electrode terminal 1. A pair of grooves 5 provided at both ends of the tip portion of the bonding tool 3 collect metal chips and hold the metal chips without scattering around.

In this way, it is possible to suppress scattering of metal scraps generated during ultrasonic bonding and cut by the tip of the bonding tool 3 and separated from the electrode terminal 1 into the power semiconductor device. This effect is remarkable for power semiconductor devices with a large package size, such as those for electric railways, industry, and automobiles.

Also, the metal chips held in the pair of grooves 5 provided at both ends of the tip of the bonding tool 3 can be easily removed by air blowing after the completion of ultrasonic bonding. Alternatively, the bonding tool 3 may be moved to a standby position away from the bonding portion 4 and removed by an air blow while the bonding tool 3 is ultrasonically vibrated. By doing so, metal scraps can be removed more easily.

Also in the second embodiment, the tip of the bonding tool 3 is provided between a plurality of convex portions 3a having a first flat portion 3b parallel to the joint surface of the joint and adjacent convex portions 3a, It has a second flat portion 3c parallel to the joint surface, and the width of the first flat portion 3b in the X-axis and Y-axis directions is greater than the width of the second flat portion 3c. Further, a pair of grooves 5 deeper than the second flat portion 3c are provided at both ends of the tip portion of the bonding tool 3. As shown in FIG. The bonding tool 3 applies a load to the electrode terminal 1 in the direction of the metal pattern 2a and pushes the electrode terminal 1 in the direction of the metal pattern 2a. With the configuration as described above, even if metal chips are generated during ultrasonic bonding, the tip of the bonding tool 3 is pushed into the electrode terminal 1 without any gap, so bonding is performed with ultrasonic vibration. At the tip of the tool 3 , the metal scrap is cut and separated from the electrode terminal 1 . The cut metal scraps are collected and held in a pair of grooves 5 provided at both ends of the tip of the bonding tool 3 . As a result, as in Embodiment 1, manual work for individually removing metal scraps is not required, and metal scraps can be easily removed by air blowing, resulting in the effects of improving productivity and reducing manufacturing costs. can.

In addition, a pair of grooves 5 provided at both ends of the tip portion of the bonding tool 3 catch metal scraps cut by the bonding tool 3 during ultrasonic bonding, suppressing scattering to the surroundings. be able to.

Moreover, since a plurality of convex portions 3a having the first flat portions 3b are formed at the tip portion of the bonding tool 3, a sufficient bonding area can be secured at the bonding portion 4. FIG. Therefore, a highly reliable joint 4 having sufficient joint strength can be obtained.

In addition, it is possible to freely combine each embodiment, and to modify or omit each embodiment as appropriate.

Reference Signs List 1 electrode terminal 2 insulating substrate 2a metal pattern 3 bonding tool 3a convex portion 3b first flat portion 3c second flat portion 4a concave portion 4b third flat portion 4c fourth flat portion 5 groove

Claims (3)

a plurality of protrusions provided at the tip portion in contact with the joint and having at the tip a first flat portion parallel to the joint surface of the joint;
a second flat portion provided between the convex portions adjacent to each other and parallel to the joint surface;
with
The width of the first flat portion is larger than the width of the second flat portion,
A pair of grooves are provided on both ends of the tip portion with the plurality of protrusions sandwiched therebetween,
A bonding tool , wherein a protrusion lower than the second flat portion with respect to the first flat portion is provided outside the pair of grooves in a cross-sectional view. 2. The bonding tool according to claim 1, wherein said convex portion tapers toward said first flat portion. A step of preparing a bonding tool and a semi-finished product in which a bonding tool is installed in an ultrasonic bonding apparatus, and an insulating substrate on which a semiconductor element is mounted and electrode terminals held so as to be in contact with the metal pattern of the insulating substrate are placed;
an ultrasonic bonding step in which the tip of the bonding tool moves to a bonding location, applies a load to the bonding location and pushes it in, and ultrasonically vibrates to bond the electrode terminal and the metal pattern;
An air blowing step for removing metal scraps generated in the ultrasonic bonding step;
an appearance inspection step of inspecting the appearance of the joint and its surroundings;
with
The bonding tool includes a plurality of convex portions having a first flat portion parallel to the bonding surface of the bonding portion at the tip portion, and a second flat portion provided between the adjacent convex portions and parallel to the bonding surface. a portion, wherein the width of the first flat portion is greater than the width of the second flat portion;
A pair of grooves are provided on both ends of the tip portion with the plurality of protrusions sandwiched therebetween,
A method of manufacturing a power semiconductor device, wherein a protruding portion lower than the second flat portion with respect to the first flat portion is provided outside the pair of grooves in a cross-sectional view.

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