Metal Thermal Interface Material for the Next Generation FCBGA

Thermal interface materials (TIMs) have been widely adopted for improved thermal dissipation in flip chip ball grid array (FCBGA), flip chip lidded ball grid array (FCLGA) and flip chip pin grid array (FCPGA) packaging. As the next generation devices' requirements for power get even higher, enhanced thermal performance at the package level is increasingly important. A typical TIM applies a polymer type, but the current polymer TIM products are insufficient to meet the advanced product roadmap requirements due to lack of thermal conductivity, TIM delamination on large size die, unstable process workability and other reasons. Even potential candidates for a high thermal conductivity TIMs, such as silver (Ag)-Sintered TIM and graphite sheet have difficulties covering all the development goals of a large body package due to high thermal resistance, poor TIM coverage or too thick bond line thickness (BLT). To meet the high-end central processing unit (CPU) market's needs, an indium (In) TIM has been selected for FCLGA or FCPGA products. A pure indium TIM has a low liquidus point and provides a good way to reduce stress during In TIM soldering. However, this characterization of Indium TIM could be a weak point for FCBGAs which need an additional reflow process after TIM and lid attachment. TIM re-melting could occur during the reflow process and affect TIM coverage, cause delamination and create a component shortage issue. This is one of the main reasons that a pure indium TIM is hard to apply on FCBGA devices. In this paper, a metal TIM (In and tin (Sn) alloy) will be discussed as a solution for next generation FCBGAs that have a large body size and require high thermal conductivity. These new alloy TIMs are expected to provide better thermal dissipation performance due to both a “high liquid phase point” and a “low solid phase point.”.