A semiconductor device having both high strength and high thermal
radiation that is capable of being applied to mounting on automobiles
experiencing many thermal cycles, and a manufacturing method thereof are
provided. A circuit board 1a for a resin encapsulated semiconductor
module device has a configuration where a silicon nitride plate 2 with a
thickness of 0.635 mm has copper plates of 1.0 mm and 0.8 mm bonded to
both sides thereof via active metal. A copper plate 3a is bonded to the
surface side of the silicon nitride plate 2, and a prescribed circuit
pattern is formed on the copper plate 3a. Tin-silver-copper cream solder
layers 4a and 4b with a thickness of 200 .mu.m are formed at a prescribed
location on the circuit pattern 3a on which a semiconductor element 6 is
mounted and at a prescribed location of a base plate 1 on which the
circuit board 1a is disposed. Nickel particles 5 having a maximum
particle size of 100 .mu.m and an average particle size of 70 .mu.m are
dispersed in the solder 4a on the base plate 1 of good thermal
conductivity. A semiconductor element (chip) 6, the circuit board 1a, and
the base plate 1 are disposed on predetermined locations. Thereafter,
they are set in a reflow oven (not shown in the drawings) for reflow
soldering. After the inside of the reflow oven is replaced by a nitrogen
atmosphere, the reflow oven is heated to 280.degree. C. At the time when
solder is melted, the inside of the oven is decompressed to 1 Pa,
nitrogen is introduced, and the reflow oven is cooled to about room
temperature, thereby completing the solder bonding step. After flux is
washed, an outer case 7 with an insert-molded outlet terminal 8 is
adhered to the base plate 1 and a predetermined connection is conducted
via an aluminum bonding wire 9. Then, silicone gel 10 is injected into a
package delimited via the base plate 1 and the outer case 7, and the
silicone gel 10 is heat-hardened, thereby completing a resin encapsulated
semiconductor device A.