Low mechanical stress, high electrical and thermal conductance

Abstract

This invention includes semiconductor devices including the heat sink with a slitted metal strip, such as copper, which is coiled or folded to produce an array of flexible flat fingers for mechanical, thermal and electrical contact with the silicon die, such as a power transistor. The use of a slitted metal strip instead of a bundle of wires makes fabrication of the flexible mount simpler and more economical. The flexible flat fingers are able to accommodate hot spots on the semiconductor device and change in thermal gradients as the device is operated. The slitted metal strip reduces mechanical stress on the die and the die attach solder to avoid solder fatigue which is a wear-out,mechanism that can cause failure of the semiconductor device; keep the magnitude of mechanical stresses from becoming large enough to fracture the silicon die; permit the use of higher melting temperature hard solders which are more resistant to solder fatigue; and permit peak operating temperatures of the semiconductor device to be higher than possible with devices that are mounted with soft die attach solder.