Thermal study for flip chip on FR-4 boards

Thermal characteristics of flip chip on FR4 boards are presented. The thermal resistances are determined for different die and board constructions, underfill material, and heat sink applications. Thermal paths are analyzed to understand the flip chip heat dissipation mechanism. It is realized that the junction to ambient thermal resistance is dominated by the system environment. The package resistance is only a trivial portion of the total resistance. Improvement of thermal performance should be concentrated on the system level. Thermal performance of flip chip is compared to that of PQFP and PBGA. Recommendations in flip chip thermal management are given at the end. This work is based on both experimental and numerical studies.