Green Tape via design-FEM and proposed design philosophy

A design method of thermal paths in Green Tape ceramics for chip cooling is described. Data from experimental substrates are examined both by thermal resistance measurements and finite element modeling to extract the major thermal characteristics of the Green Tape and the via materials. Curves are generated showing variation of the thermal impedance of the composite material as a function of via density and via fill material. A design example is given which shows how this method can be used to equalize junction temperatures in chips with different power densities. This design would be useful in bipolar circuits due to the clock skew induced by different V/sub be/ and switching thresholds when junction temperatures differ from one chip to the next.<>