Process for assembling and resin-encapsulating a semiconductor power device mounted on a heat sink

Claim 1

A process for assembling and encapsulating in resin a die of a semiconductor wafer having metallized pads for wiring connections, which comprises fastening together a patterned metal frame and a flat metallic heat sink baseplate, disposed in respectively parallel planes, by wedging fastening tabs of said metal frame into indentations formed on opposite sides of said heat sink, and successively cementing said die on said heat sink, connecting said pads to the ends of coplanar fingers of said patterned frame by means of metal wires welded thereto, placing the mounted assembly in a mold capable of defining a cavity for containing said metal heat sink, said die, said connecting wires and an inner portion of said coplanar fingers, which extend beyond the perimeter of said cavity by passing between perimetral mating surfaces of said mold and of a counter-mold, and injecting resin into said cavity for encapsulating the assembly while leaving exposed a surface of said heat sink baseplate and ensuring the electric isolation of each of said coplanar fingers from said metallic heat sink, characterized by comprising the following steps fastening said metal frame to said heat sink while maintaining said coplanar fingers of the metal frame resting on the surface of the heat sink; welding said metal wires on the ends of said coplanar fingers resting on the surface of the heat sink; placing the mounted assembly on a substantially flat mold provided with raised portions for supporting the heat sink by said surface thereof, the supports being arranged along the sides of the perimeter of the heat sink on which said tabs of the metal frame are anchored thereto; closing the mold by means of a counter-mold having a substantially flat mating surface provided with a cavity capable of completely containing said heat sink, said-counter mold pushing said fingers while bending said fastening tabs against the surface of said flat mold thus spacing said coplanar fingers from the surface of the heat sink; injecting an encapsulation resin in the cavity defined between the surface of said mold and the opposed surface of the heat sink and laterally by said counter-mold and, partially, by the inner face of said raised supports of the mold; and solidifying the injected resin within the space comprised between said surface of the heat sink and said fingers of the metal frame before opening the mold and recovering the encapsulated device.