Thermal analysis of plastic QFP with high thermal dissipation

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Abstract
Thermal analysis was performed on various recently proposed LSI packages by the finite element method. Initially, to confirm the effectiveness of modeling, calculated results were compared with measured thermal resistances of some kinds of packages, and they showed good agreement. The influence of a difference in materials or dimensions of a lead frame with a heat spreader on the thermal resistance was then analyzed. The results showed that a heat spreader attached on a lead frame had an excellent effect on the thermal resistance, approximately a 10 degrees C/W or larger reduction. But it depends on an internal design or other specifications of the heat spreader. The thermal performance of various other QFP (quad flat pack) type packages was also analyzed. Among those packages, a structure which was assumed to have a lead frame put between a metal base and cap had the lowest thermal resistance, approximately 20 degrees C/W, with natural convection. Furthermore, it was possible to reduce the thermal resistance of molded packages below 25 degrees C/W, in the case of a two-layer lead frame, by using an additional heat spreader on the package surface.

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