JPS61177762A - Semiconductor device - Google Patents

Abstract

PURPOSE:To contrive to improve the product yield by eliminating the generation of cracks in the insulation plate even when the insulation plate is thinned or pads and adhesion copper plates are thickened in order to improve thermal conduction to a heat dissipating plate, by method wherein the corners of pads and the like directly joined to an insulation plate are rounded. CONSTITUTION:Wire bonding pads 23 and chip mounting pads 24 are joined to the top of an insulation plate (DBC substrate) 33 by direct junction, the corners of which pads are rounded at R=1.0mm. This rounding can be easily carried out by etching or press punching. The value of R can be selected suitably without restriction to 1mm. Otherwise, only the corners of each chip constituting squares of a pad group including the wire bonding apds 23 and the chip mounting pads 24 can be rounded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a semiconductor device comprising a power semiconductor device block, and more specifically, a power semiconductor device block having a structure called an insulating plate unit structure and suitable for modularization. used for.

[Technical background of the invention]

When manufacturing power transistors and power transistor modules in which power transistors are connected in series or parallel, it is convenient to configure them with highly commonly compatible power transistor blocks. A block serving as a unit of such a module needs to have a small number of parts and a simple assembly process, and also need to be easy to connect terminals for modularization.

The present inventor previously filed a patent application (Japanese Unexamined Patent Application Publication No. 57-1999) regarding a semiconductor device consisting of a power transistor block as described above.
No. 11054, Japanese Unexamined Patent Publication No. 57-166037, etc.).
This will be explained with reference to the figures. In addition, in the description of the drawings, the same elements are indicated by the same reference numerals.

FIG. 8 is a sectional view of a main part when a power transistor block having an insulating plate unit structure is assembled into a molded module. That is, the power transistor block 20 includes an insulating plate 33, wire bonding pads 22 and 23 and chip mounting pads 24 provided on the surface of the insulating plate 33.
have.

Then, the semiconductor chip 5 is mounted on the mounting pad 24 and wire-bonded to the pads 22 and 23. Then prepare two of these blocks 20.20',
It is made into a module by adhering it onto the heat sink 7 via an adhesive copper plate 25 or the like, connecting external terminals, and sealing it with resin.

This type of device has only five parts in total: the insulating plate 33, the wire bonding pads 22, 23, the chip mounting pads 24, and the bonded copper plate 25.

Furthermore, when the wire bonding pads 22, 23 and the chip mounting pads 24 are made of copper plates similar to the adhesive copper plate 25, and they are directly bonded onto the ceramic insulating plate 33, a particularly large process is required. The number can be reduced.

The method of directly bonding a copper plate to a ceramic plate as described above is to hold a copper plate with an oxidized surface on top of a ceramic plate at a substantial temperature of 1065°C or more and 1085°C or less, and then bond the Cu20-Cu eutectic melt bonding surface. This refers to a method developed by General Electric Company in the United States, in which the materials are wetted, cooled, and directly bonded. Copper plates particularly suitable for this direct bonding method include tough pitch steel, 0FHC copper, silver copper, and the like, and ceramic plates particularly suitable include alumina and the like. FIG. 9 is a perspective view of a block formed by the direct bonding method. In the same figure, the insulating plate 33 has a thickness of 0.635
An AS+ 96% alumina plate was used, and the wire bonding pads 22 and 23, the chip mounting pad 24, and the adhesive copper plate 25 were tough pitch copper plates with a thickness of 0.3 am, and were passed through a nitrogen atmosphere at 1063°C in one step. Make them stick firmly.

Next, attach the terminal to the terminal area around the block 4.41°42
The chip 5 is mounted on the chip mounting pad 24, and if necessary, the diode 51, etc. are mounted on the chip mounting pad 24, and connected with the bonding wire 6 to form the power transistor block 2.
Get 0.

Fig. 10 is a plan view of parallel and series connected molded power transistor modules, Fig. 11 (a) is an external terminal arrangement diagram used in the parallel connection module, Fig. 11 (b) is an equivalent circuit diagram, and Fig. 12 ( a) A diagram showing the arrangement of external terminals used in the series-connected module, and (b) the equivalent circuit diagram. 10 to 12, 7 is a heat sink, 8 is an external terminal, 91 is a case, TR1 and TR2 are transistor elements, and DI and D2 are diode elements.

[Problems with background technology]

In the conventional device as described above, each pad that is directly bonded to the insulating plate has a sharp corner. 13th
The figure is a plan view of an insulating plate to which pads are bonded, and FIG. 14 is a partially enlarged view thereof. As shown in the figure, the corners of the wire bonding pad 23, the chip mounting pad 24, etc. are sharp, and therefore stress tends to concentrate on the corners.

By the way, in order to improve heat conduction to the heat sink, it is desirable that the thickness of the insulating plate be small and the thickness of the pad and bonded copper plate be relatively large. For example, in the conventional example shown in FIG. Pads 22 to 24 and bonded copper plate 25 have a thickness of 0.3 am to plate 33 of 0.635 ag+. In recent years, this trend has progressed further due to higher integration and larger capacity of circuits, and insulating plates with a thickness of 0.4 m or less and pads and bonded copper plates with a thickness of 0.4 m or more are now required. However, if this is achieved with the conventional type, the concentration of stress at the corners of the pad will increase, and on the other hand, the strength of the edge plate will decrease.
Therefore, "cracks" are likely to occur at the corners. This insulation board 3
The cracks No. 3 appear as indicated by the reference numeral 101 in FIGS.

[Object of the Invention] The present invention has been made to overcome the drawbacks of the prior art as described above. Another object of the present invention is to provide a semiconductor device in which "cracking" does not occur in an insulating plate.

[Summary of the invention]

In order to achieve the above object, the present invention provides rounded corners of wire bonding pads, chip mounting pads, etc. that are bonded by direct bonding to an insulating plate of a semiconductor device having an insulating plate unit structure. The present invention provides a semiconductor device. Furthermore, the present invention provides an insulating plate and an adhesive metal (
For example, the present invention provides a semiconductor device with rounded corners for a copper plate as well.

[Embodiments of the invention]

Hereinafter, some embodiments of the present invention will be described with reference to FIGS. 1 to 7 of the accompanying drawings.

FIG. 1 is a perspective view of the main parts of the same embodiment. Insulating board (DB
G board) 33 has a wire bonding pad 2 on the top surface.
3 and a chip mounting pad 24 are joined by a direct joining method, and their corners are rounded to R-1,0. This roundness can be easily imparted by etching, press punching, or the like. Also, the value of R is 1
It can be selected as appropriate without being limited to jIII.

FIG. 2 is a plan view of a main part of a modification of the embodiment shown in FIG. 1. Figure 2(a) shows the wire bonding pad 23.
and 4 of the pad group including the chip mounting pad 24.
Only the corners of each chip that make up the corners are rounded. The concentration of stress is particularly significant at the four corners of the pad group, and therefore "cracks" are likely to occur in the insulating plate 33 in these parts, so by rounding only these parts, the yield of the product can be considerably improved.

In FIG. 2(b), only the corners of each chip on the four sides of the pad group are rounded. Next to the corner portions of each pad at the four corners of the pad group, stress is most concentrated at the corner portions of each pad at the four sides of the pad group. Therefore, by rounding these parts, the yield of the product can be greatly improved.

In FIG. 2(C), the corners of each pad other than the obtuse angle portions are rounded. Next to the corners of each pad on the four sides of the pad group, stress is likely to be concentrated at the inner corners other than the obtuse angle portions. Therefore, by rounding these parts, most of the "cracks" in the insulation board can be eliminated.

FIG. 2(d) is equivalent to that in FIG. 1, and the maximum effect can be obtained by doing so. In addition, the above figure 2 (
In the modified examples b) to (d), it is more effective to change the value of R depending on the magnitude of stress concentration.

FIG. 3 is a plan view of essential parts of another embodiment of the present invention. This differs from the one shown in FIG. 2(a) in that not only the corners of the pad group but also the corners of the insulating plate are rounded. In this way, it is possible to sufficiently cope with stress from below the insulating plate 32.

FIG. 4 is a sectional view of a semiconductor device for explaining this situation. An epoxy resin cover 26 is fixed to the heat sink 7 with an adhesive 27 so as to surround the semiconductor module, and the chip 5 is covered with a rubber-like chip cap 28. The inside of the cover 26 is filled with a gel-like encapsulant 29.

In such a semiconductor device, the adhesive 27 is attached to the insulating plate 3.
3 and the heat dissipating plate 7, and stress tends to concentrate on the corners of the insulating plate 33 due to these factors. Therefore, if the corners of the insulating plate are rounded as shown in Figure 3, the pad 2
Not only stress concentration due to 3.24 etc. but also stress concentration from below due to adhesive 27 etc. can be alleviated. In addition, the third
In the figure, only the corners of each pad constituting the four corners of the pad group are rounded, but other corners of each pad may also be rounded as shown in Figure 2 (b) to (d). Needless to say.

FIG. 5 is a bottom view of the main parts of still another embodiment of the present invention. In this embodiment, the four corners of the bonded copper plate 25 bonded to the bottom surface of the insulating plate 33 by a direct bonding method are rounded. If this method and the above method are used together, even greater effects can be achieved.

Note that in the embodiments shown in FIGS. 1 to 5 above,
Although the thickness of the insulating plate, pad, and bonded copper plate is not particularly limited, it is particularly effective when the thickness of the insulating plate is about 0.4 aa+.

Next, the effects of the above embodiment will be explained with reference to FIGS. 6 and 7.

FIG. 6 is a characteristic diagram showing the relationship between the presence or absence of roundness at the corners of the pad and the occurrence rate of "cracking". As is clear from the figure, when the thickness of the insulating plate (A1203) is t-0,635am+, if the corners of the pad are not rounded, the thickness of the pad must be 0.4 or less. When the corners of the pad are rounded, the thickness of the pad can be 0.6 m or more. In addition, when the thickness of the insulating plate is t = 0.4 am, if the corners of the pad are not rounded, the thickness of the pad must be 0.15 am or less, which makes it difficult to put it into practical use. By rounding the corners of the pad, the thickness of the pad can be made 0.4 am or more, and a large heat dissipation effect can be achieved.

Rounding the corners of the pad is also effective in reducing stress concentration due to soldering of external terminals. FIG. 7 is for explaining the situation; FIG. 7(a) is a perspective view, and FIG. 7(b) is an A-All sectional view thereof. In FIG. 7, the thickness tl of the external terminal 8 is approximately 0.7 to 0.8 mm.
The thickness t2 of the solder 43 also reaches about 0.5 seconds. Therefore, stress concentration is particularly significant at the corners of the wire bonding pads 23 near the external terminals, and "cracking" is likely to occur. However, if the corners are rounded as in the present invention, stress concentration can be reduced and the yield of products can be improved.

Further, according to the present invention, there is a special effect that the thickness of the insulating plate or pad or the heat dissipation effect can be displayed depending on the presence or absence of roundness of the corners. In other words, as mentioned above, there is a phase relationship between the thickness of insulating plates, pads, etc. and the heat dissipation effect, and the thinner the insulating plate is, the more likely it is that cracks will occur; Therefore, in order to maximize the heat dissipation effect, the material that is most likely to "break" is configured as shown in Figure 2 (d), and then the material that is most likely to "break" is The configuration is as shown in FIG. 2(C), and the heat dissipation effect is increased, that is, the one that is more likely to break, as shown in FIG. 2(b).

The configuration is as shown in (a). In this way, it is possible to determine the magnitude of the heat dissipation effect, the magnitude of the allowable calorific value, etc.

The effects explained above are not limited to the case where Al2O3 ceramic is used as the insulating plate, but can also be achieved when using AIN, etc., and when a metal plate other than a copper plate is used as the pad etc. It can also be played.

〔Effect of the invention〕

As described above, in the present invention, the corners of the pads, etc. directly bonded to the insulating plate of a semiconductor device having an insulating plate unit structure are rounded, so that the insulating plate is insulated to improve heat conduction to the heat dissipation plate. Even when the plate is made thinner or the pads and bonded copper plate are made thicker, the insulating plate does not "crack" and therefore a semiconductor device can be obtained which can significantly improve the product yield. Further, since rounding of the corners can be easily achieved, the manufacturing cost does not particularly increase.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the main part of an embodiment of the present invention, FIG. 2 is a plan view of the main part of a modification of the same embodiment, and FIG. 3 is a plan view of the main part of another embodiment of the invention. FIG. 4 is a sectional view for explaining effects specific to the same embodiment, FIG. 5 is a bottom view of a main part of still another embodiment of the present invention, and FIG. 6 is a detailed explanation of the present invention. 7 is a perspective view and a sectional view for explaining the special effects of the present invention, FIG. 8 is a sectional view of the main part of a conventional module using an insulating substrate, and FIG. 9 is a characteristic diagram of this insulating substrate. FIG. 10 is a plan view of this module before completion; FIG. 11 is a plan view and an equivalent circuit diagram of this module; FIG. 12 is a plan view and an equivalent circuit diagram of another example of this module. An equivalent circuit diagram, FIG. 13 is a plan view of the main part of the conventional device, and FIG. 14 is a partially enlarged view. 5... Chip, 7... Heat sink, 8... External terminal,
23... Pad for wire bonding, 24... Pad for chip mounting, 25... Adhesive copper plate, 26...
- Cover, 27... Adhesive, 28... Chip encap, 33... Insulating plate. Applicant's agent Inomata Affair Figure 1j Figure 2 (a) Figure 2 (c) LI Figure 2 (d) J Figure 3 Figure 4 Figure 5 Figure 7 (a) ''l Figure 7 (b) Figure 8 Figure 9 Figure 10 Figure 1U'/lLJ'dlFigure 11 (a) (b) Figure 12

Claims (1)

[Claims] 1. A pad group including at least a wire bonding pad and a chip mounting pad is bonded to the upper surface of a substantially rectangular insulating plate by a direct bonding method, and a pad group including at least a wire bonding pad and a chip mounting pad is bonded to the lower surface of this insulating plate via an adhesive metal plate. What is claimed is: 1. A semiconductor device in which a heat sink is bonded by a direct bonding method, characterized in that corners of each pad constituting the pad group are rounded. 2. The semiconductor device according to claim 1, wherein the corners of each of the pads constituting the four corners of the pad group are rounded. 3. The semiconductor device according to claim 1, wherein corners of each of the pads within four sides of the pad group are rounded. 4. The semiconductor device according to claim 1, wherein the corners of each pad other than the obtuse angle portions are rounded. 5. A group of pads including at least wire bonding pads and chip mounting pads are bonded to the top surface of a substantially rectangular insulating plate by a direct bonding method, and a heat sink is bonded to the bottom surface of this insulating plate by a direct bonding method via an adhesive metal plate. A semiconductor device in which the corners of each pad constituting the pad group are rounded, and the four corners of the insulating plate are rounded. 6. The semiconductor device according to claim 5, wherein corners of each of the pads constituting the four corners of the pad group are rounded. 7. A group of pads, including at least wire bonding pads and chip mounting pads, is bonded to the upper surface of a substantially rectangular insulating plate by a direct bonding method, and a heat sink is bonded to the bottom surface of this insulating plate by a direct bonding method via an adhesive metal plate. A semiconductor device in which the corners of each pad constituting the pad group are rounded, and the four corners of the insulating plate and the adhesive metal plate are rounded. 8. The semiconductor device according to claim 7, wherein corners of each of the pads constituting four corners of the pad group are rounded.