JP4462250B2 - Ceramic circuit board and semiconductor device using the same - Google Patents

Description

  The present invention relates to a ceramic circuit board and a power semiconductor module for electric power using the same.

As the ceramic circuit board for the power semiconductor module mentioned above, a copper circuit board, which is a conductor pattern, is joined to the surface of a ceramic substrate made of alumina or aluminum nitride with excellent heat dissipation, electrical insulation, and high frequency characteristics. Ceramic circuit boards obtained by bonding a copper plate to the back surface are widely used.
This ceramic circuit board is mounted on a copper base plate (heat sink plate) and soldered, and a plurality of power semiconductor elements are mounted on the copper circuit board of the ceramic circuit board, and then the surrounding resin case and external lead-out terminal A power semiconductor module product is configured by combining the above.
JP 9-312357 Japanese Patent Laid-Open No. 10-4156 Japanese Unexamined Patent Publication No. 9-275165

  By the way, although ceramic circuit boards have excellent characteristics in terms of heat dissipation, electrical insulation, etc., ceramic boards themselves are brittle and have low bending strength. Due to the recent thinning of ceramic boards, they have become practical as power semiconductor module products. If a thermal or mechanical stress is applied in connection with the heat cycle associated with energization control in the state of use or the screw fastening when attaching to the radiating fin, cracks and cracks are likely to occur in the ceramic substrate where the stress is concentrated.

In addition, when cracks or cracks occur in the ceramic substrate, the portion may be poorly insulated and may develop damage such as a ground fault, resulting in reduced product reliability.
Therefore, if the ceramic substrate is cracked or cracked during actual use as a power semiconductor module, as a measure to prevent it from developing into damage due to defective insulation, the copper circuit board (conductor pattern) on the ceramic substrate is removed. A snap line is formed in advance on the substrate surface along the part where the thermal and mechanical stress applied during actual use of the product is intentionally concentrated on this snap line, and even if a crack occurs in this part, the power semiconductor As a module, a structure in which the module does not progress to damage due to insulation failure has been proposed (see JP-A-9-31357: Patent Document 1).

However, the above proposal does not always give the expected results from the results of many product tests conducted thereafter. In particular, the copper base (ground potential) and the copper circuit board (charged part) are connected to each other through the crack occurrence point of the ceramic substrate. It was found that the creepage insulation strength was determined during this period, causing problems such as failure to improve withstand voltage.
In addition, for copper-clad ceramic circuit boards, there are known measures to prevent cracks and cracks by devising the pattern shape of the copper circuit board. However, this method limits the circuit pattern and circuit design. , Cost problems remain.

  The present invention has been considered in view of the above points. The object of the present invention is to solve the above-mentioned problems, and for a power semiconductor module with higher reliability against cracks and cracks without requiring a design change on the circuit surface. The object is to provide a ceramic circuit board.

In order to achieve the above object, according to the present invention, in a ceramic circuit board for a power semiconductor module in which a copper circuit board is bonded to a ceramic board, thermal and mechanical stress is applied in an actual use state as a power semiconductor module. An insulator reinforcement material is bonded to the surface of the ceramic substrate where the stress concentration is predicted and the edge of the copper circuit board facing the portion where the stress concentration is predicted with an adhesive. It shall join (Claims 1 and 2).

  The concentration of thermal and mechanical stress applied to the ceramic substrate in actual use as a power semiconductor module can be predicted by knowledge obtained from the results of many product tests, computer simulation methods, and the like. Therefore, the ceramic substrate is bonded to the surface of the ceramic substrate where the stress concentration is predicted and the edge of the copper circuit board facing the portion where the stress concentration is predicted. As a result, the bending strength of the ceramic substrate can be increased, and the occurrence of cracks and cracks in the ceramic substrate due to the thermal and mechanical stress applied in the actual use state of the power semiconductor module product can be prevented.

For reference, a ceramic substrate to which thermal and mechanical stress is applied in the actual use state as a power semiconductor module has high adhesion and high elongation on the surface of the ceramic substrate along the location where the stress concentration is predicted. There is a configuration in which a silicone resin having a coating is applied and cured.
As a result, even if a ceramic substrate is cracked or cracked due to thermal or mechanical stress applied during actual use of a power semiconductor module product, a silicone resin with excellent electrical insulation is preliminarily applied to this part. Since it is installed, it does not cause insulation failure (deterioration of creeping insulation strength) to the circuit (charged part) and can effectively prevent a reduction in withstand voltage as a product.

  By assembling a power semiconductor module product using the ceramic circuit board according to the present invention, the bending strength of the ceramic substrate is enhanced by joining the reinforcing material, and thermal and mechanical stress is applied to the ceramic substrate in the actual use state of the product. However, cracks and cracks can be effectively prevented from occurring in the ceramic substrate, and the reliability of the product can be improved.

  Hereinafter, an embodiment of the present invention will be described based on the embodiment shown in FIG.

  FIG. 1 shows an embodiment corresponding to claim 1 of the present invention. In the figure, 1 is a ceramic circuit board in which a copper circuit board 1b for forming a conductor pattern is bonded to the main surface of a ceramic substrate 1a, and a copper board 1c is bonded to the back surface, 2 is a power semiconductor element mounted on the copper circuit board 1a, Reference numeral 3 denotes a copper base plate (heat sink) on which the ceramic circuit board 1 is mounted. A copper plate 1 c of the ceramic circuit board 1 is joined to the copper base plate 3 with solder 4.

Here, for the ceramic substrate 1a, the surface of the ceramic substrate is reinforced with an insulator along the portion P where the concentration of thermal and mechanical stress is predicted in the actual use state as a power semiconductor module product. The material 5 is joined by an adhesive 6. In addition, joining of the reinforcing material 5 shall be performed in the middle of the assembly process of a power semiconductor module.
It should be noted that the point P where stress concentration is predicted is determined by the copper circuit board along the gap between the copper circuit boards 1b bonded on the ceramic substrate 1a based on knowledge obtained from many product test results, computer simulation, and the like. It has been found that a large number of uncovered portions occur, and based on the verification result, an insulating reinforcing material 5 is laid along the edges between the copper circuit boards 1b as shown in FIG. 6 is bonded to the surface of the ceramic substrate 1a.

According to such a configuration, by joining the reinforcing material 5, the bending strength of the ceramic substrate 1a at that portion is enhanced, and cracks and cracks are generated due to thermal and mechanical stress applied during actual use as a power semiconductor module. No strength can be ensured.
[Reference example]

  FIG. 2 shows this reference example. In this embodiment, a copper circuit is formed on the surface of the ceramic substrate 1a along a location P (the same location as in FIG. 1) where thermal and mechanical stress concentration is predicted in the actual use state as a power semiconductor module. A silicone resin (compound) 7 having high adhesion and high elongation (rubber property) is applied and cured so as to fill the gap between the plates 1b.

  As a result, even if cracks or cracks 8 occur in the portion P due to thermal and mechanical stress concentration applied to the ceramic substrate 1a in the actual use state as a power semiconductor module product, the peripheral area is made of the silicone resin 7. Since it is covered, it is possible to prevent a decrease in creeping insulation strength and withstand voltage between the copper base plate (earth potential) 3 and the copper circuit plate (charging part) 1b, and maintain high reliability of the product.

Power semiconductor module structure diagram corresponding to an embodiment of the present invention Power semiconductor module structure diagram corresponding to a reference example of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ceramic circuit board 1a Ceramic board 1b Copper circuit board 1c Copper board 2 Power semiconductor element 3 Copper base board 5 Reinforcement material 6 Adhesive 7 Silicone resin 8 Crack, crack P Predicted part of stress concentration

Claims (2)

In a ceramic circuit board for a power semiconductor module in which a copper circuit board is bonded to a ceramic board, the stress concentration of the ceramic board is predicted against a ceramic board to which thermal and mechanical stress is applied in actual use as a power semiconductor module. A ceramic circuit for a power semiconductor module, wherein a reinforcing material of an insulator is bonded with an adhesive to a surface of a portion to be applied and an edge of a copper circuit board facing the portion where the stress concentration is predicted substrate. In a semiconductor device in which a power semiconductor is mounted on a ceramic circuit board in which a copper circuit board is bonded to a ceramic board, the surface of the ceramic board where the concentration of thermal and mechanical stress is predicted in the actual use state of the power semiconductor A semiconductor device characterized in that an insulating reinforcing material is joined to an edge of a copper circuit board facing each other across a portion where the stress concentration is predicted with an adhesive .

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