High-power-used thermal gel degradation Evaluation on board-level HFCBGA subjected to reliability tests

HFCBGA is a thermally enhanced FCBGA with its heat spreader extending heat conduction area by connecting itself to the rear side of the silicon die. A thermal interface material plays an important role as a heat conduction path. The thermal performance should be checked not only at time zero, several types of reliability tests have to be examined to cover the field condition faced by end user. Temperature cycling test, highly-accelerated temperature and humidity stress test and multiple reflows are chosen for investigating thermal resistance of junction to case of a selected thermal gel.

INTRODUCTION

Thermal interface materials (TIMs) are an important component in the thermal management solutions by providing a path of low thermal resistance between the heat generating devices and the heat spreader/sink Due to poor thermal conductor as air behaves, rough interfacial surfaces are needed to be sandwiched the TIMs between either heat generating die and heat spreaders or heat spreaders and heat sinks to maintain heat conducting paths [1]. These materials consist of two or three key components: a polymeric binder, an inorganic filler, and sometimes a reinforcement layer. The filler promote the bulk thermal conductivity of the TIM while the binder provides the matrix for the material and is critical for surface wetting. A reinforcement layer can be incorporated to provide mechanical integrity, or to improve electrical isolation.