JPS6281047A - Semiconductor device - Google Patents

Abstract

PURPOSE:To miniaturize a semiconductor device restricting thermal stress on a semiconductor chip to minimum by a method wherein the semiconductor chip is fixed to a thermal stress cushioning member made of molybdenum sheet through the intermediary of a silicon base insulating sheet. CONSTITUTION:Molybdenum sheet 2 is fixed by silver brazing process 3 on the surface of heat sink 1 made of metallic base such as copper etc. and then a silicon base insulating sheet (silicon carbide) 5 both sides of which are preliminarily plated with nickel 4 is welded into the surface of molybdenum sheet 2 by high temperature soldering process. Besides, a semiconductor ship 7 is likewise welding into said insulating sheet 5 by high temperature soldering process 8. In such a constitution, the molybdenum sheet 2 is firmly fixed to the metallic base (copper) 1 having a large thermal expansion coefficient difference by silver brazing process to be formed into a structure that can withstands thermal stress.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor device, and particularly to a heat dissipation structure for a high power semiconductor with excellent heat conduction.

[Background of the invention]

Conventionally, relays have been frequently used as high-current switching means used in automotive electrical components.
There are problems with switching speed and durability, so there is a tendency to gradually replace them with semiconductor types (transistors). However, the collector loss of a switching transistor is as large as 50 to 100 (W) depending on the application, and a heat sink with a considerably large heat dissipation structure and an insulating plate with high thermal conductivity are required.

A semiconductor device with this type of countermeasure was published in Japanese Patent Application Laid-Open No. 55-1186.
It is known from Publication No. 41. That is, based on the publication (1
0), an insulating board for semiconductor devices (3), and a molybdenum sheet (
31), a technique is disclosed in which transistor chips (32) are stacked and each is bonded using solder. However, since alumina, which has a low thermal conductivity, is used as the insulating plate, the thermal conductivity of that part is extremely poor at 29 (W/m-K). If the heat loss of the semiconductor chip is not small (approximately 10 W or less), it will not be practical, and the device will inevitably become larger. Also, thermal stress will easily be applied to the semiconductor chip, reducing its durability and reliability. There was a problem with sexuality.

[Purpose of the invention]

An object of the present invention is to provide a small and highly reliable semiconductor device.

[Summary of the invention]

The present invention includes a semiconductor chip that is fixed on a metal base constituting a heat sink via an insulating plate, and a semiconductor chip that is fixed between the insulating plate and the metal base to absorb thermal stress caused by the difference in coefficient of thermal expansion between the two members. In the semiconductor device, the semiconductor chip is fixed to a thermal stress buffering member made of molybdenum via a silicon-based insulating plate.

As a result, thermal stress applied to the semiconductor chip can be suppressed, and a small and highly reliable semiconductor device can be obtained.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, a molybdenum sheet 2 is arranged and fixed by silver soldering 3 on the upper surface of a heat sink 1 made of a metal base such as steel, and the upper surface is pre-plated with nickel on both sides as shown in FIG. ) 4 is welded and fixed via high temperature solder 6 to a silicon-based insulating plate (silicon carbide) 5 . On the other hand, the semiconductor chip 7 is welded and fixed to the insulating plate 5 via high temperature solder 8 as described above.

In the semiconductor device constructed in this manner, the molybdenum plate 2, the insulating plate 5, and the semiconductor chip 7 are soldered at high temperature using a heating furnace or the like, and then silver soldered to the metal base 1 at a temperature lower than the heating temperature. is preferable for work.

As shown in the attached table, the silicon carbide insulating plate 5 has a thermal conductivity of 267 (W/m-K), which is about 10 times that of alumina, and has a thermal conductivity comparable to that of metals. The surface of this insulating plate is plated with nickel 4 so that it can be soldered to the molybdenum sheet 2 and semiconductor chip 7, which are other components. The molybdenum sheet 2 is firmly fixed to a metal base (copper) 1 having a large difference in coefficient of thermal expansion by silver brazing, and has a structure that is durable against thermal stress.

Therefore, since the metal base 1 and the molybdenum sheet 2 are silver-brazed and the molybdenum sheet with a small expansion coefficient is firmly fixed, there is a difference in the thermal expansion coefficient between other materials, that is, between the molybdenum sheet and the silicon insulating plate. becomes small, resulting in a configuration in which thermal stress is less likely to occur. This allows other parts to be bonded together using normal high-temperature soldering (button: tin: silver = 95:3.
5:1.5) peeling due to thermal stress even when soldering
! It is less susceptible to phenomena and can increase durability.

The thermal resistance in the case of 25 mm'' is as follows.

0.86 0.2 Q, l116 0.6 0.86 0.4 0.86 1.6 0.86 0.6 From the above, the total thermal resistance θ7. when using alumina as the insulating plate. c11=0.3. +〇No+θ7kRf+θcu
= 1, 28 (deg/W) SIC, θJ*Cu” θ7s1+θsrc+θMO+ Ocu
= 0, 54 [dag/Wl, and a heat dissipation structure with approximately three times better heat conduction than normal alumina can be realized.

Specifically, when the loss of the semiconductor chip is 50W, the temperature T1 of the chip with respect to the copper base is (Tcu: temperature of the bottom surface of the copper base) In the case of alumina, TJ = 1,28 x 50 + TCLl = 64 + Tc
u (degrees) For silicon carbide Ta = 0.54 x 50 +Tcu = 27 +Tc
It becomes u (degrees).

Therefore, with alumina and silicon carbide, the semiconductor junction temperature can be lowered by about 37 degrees. Conversely, silicon carbide has the advantage that it can be used in locations where the ambient temperature is 37 degrees higher than that of copper bases.

〔Effect of the invention〕

According to the following embodiments of the present invention: 1) By using a highly thermally conductive insulating plate, the structure of the heat sink (surface area of the heat sink) can be made smaller, resulting in a resource-saving structure.

2) Since both the semiconductor chip and the insulating plate are made of silicon, thermal stress is less likely to be applied to the semiconductor chip, resulting in a durable and highly reliable product.

3) Since the insulating plate is soldered directly below the semiconductor, the high potential part is limited to the top of the semiconductor chip, and the area below the insulating plate can be grounded, resulting in an easy structure for casing.

4) The coefficient of thermal expansion of a copper heat sink and a semiconductor chip is about 10 times different, but this difference in coefficient of thermal expansion can be resolved by silver brazing between metals with high tensile strength (molybdenum and copper). It is possible to create a structure in which thermal stress is less likely to occur between other materials (semiconductor chips, insulating plates, molybdenum). This has the effect of increasing the reliability of the joint (solder).

〔Effect of the invention〕

As described above, according to the present invention, a small and highly reliable semiconductor device can be obtained.

[Brief explanation of drawings]

The drawings show one embodiment of the semiconductor device of the present invention.
The figure is a partially sectional side view, and FIG. 2 is an enlarged view of the main part of FIG. 1. 1... Heat sink, 2... Molybdenum sheet, 3
... Gold solder, 4... Plating layer, 5... Silicon-based insulating plate, 6... High-temperature solder, 7... Semiconductor chip.

Claims (1)

[Scope of Claims] 1. A semiconductor chip is fixed on a metal base constituting a heat sink via an insulating plate, and a semiconductor chip is fixed between the insulating plate and the metal base, and is generated due to the difference in coefficient of thermal expansion between the two members. 1. A semiconductor device comprising a thermal stress buffering member made of molybdenum, wherein the semiconductor chip is fixed to the thermal stress buffering member made of molybdenum via a silicon-based insulating plate. 2. A semiconductor device according to claim 1, wherein the insulating plate is made of silicon carbide. 3. A semiconductor device according to claim 1, wherein the heat sink is made of a copper base and is fixed to molybdenum constituting the thermal stress buffering member by silver brazing.