Thermal resistance (Rth) enhancement by optimizing TO package thermal contact

The trend for package size shrinkage has created challenges to thermal performance while improving the cost performance. When TO package size shrink by minimizing the leadframe copper usage, challenges in package warpage and thermal contact become great. TO High Creepage (a shrink version of new generation TO247) introduced difference copper thicknesses at die pad and heatsink for better material cost has created difference warpage profile which resulted loosing of the thermal contact area. The optimization of mold compound CTE for minimizing the mismatch with copper leadframe did not demonstrate positively on warpage reduction. The loss of thermal contact area and increase of thermal resistance due to warpage were characterized to determine the most effective approach to enlarge the thermal contact area. The new approach is to design-in an appropriate feature on the package to optimize the thermal contact area. The pre-shaping of package mold body as a design-in feature for compensating the loss of thermal contact area has been introduced. By this design-in feature, the package thermal contact area has been optimized and therefore the thermal performance is enhanced to the acceptable level.