Low thermal resistance, low stress semiconductor package

A semiconductor device having low thermal impedance and low electrical resistance comprising:

• a base member adapted to be mounted to an external heatsink in low thermal impedance connection therewith;
• an insulating member disposed on said base member and bonded thereto with a low thermal impedance bonding layer;
• a thin highly annealed current spreading layer disposed on said insulating layer in low thermal impedance relation therewith, said current spreading layer characterized by low electrical resistance;
• an electrically and thermally conductive stress relief means on said current spreading layer for matching the thermal coefficient of expansion of said semiconductor element and said current spreading layer;
• a semiconductor element on said stress relief means in low stress bonding relationship therewith for minimizing the stress on said semiconductor element due to the difference in coefficient of thermal expansion between said current spreading layer and said semiconductor element;
• and
• an electrode on said current-spreading layer surrounding said stress relief means but laterally spaced apart therefrom to form a capillary chamber between the sidewalls of said stress relief means and the inside wall of said electrode, a solder layer in said capillary chamber thermally and electrically connecting said electrode to said stress relief member for providing electrical connection between said semiconductor element and said electrode without contributing to the thermal impedance between said semiconductor element and said base member.