TIM Selection Methodology for High Power Flip Chip Packages

Flip-chip packages are currently used for various applications such as desktop computers, servers, gaming, telecommunications, etc. Due to tremendous demand of die functionality, the power levels and more importantly the die heat-flux densities are drastically increasing, thus customers are constantly pushing packaging industries to lower thermal impedance of TIM for very high power flip chip packages. To achieve the target, TIM formulation focuses on filler type, size, loading, etc. Typically low modulus gel and grease type TIM are filled with Al2O3, Ag, Ga, Al, etc filler. Fillers are designed for high-performance, and high power application. The cross-linking properties of gel or grease type TIM should have enough strength so it can comfortably overcome squeeze or pump-out issue during highly accelerated package reliability tests. Package designers typically focus more on the thermal issues for TIM performance evaluation, characterization, and formulation, but there is not much study available [2-9] on TIM degradation in the packages and its actual thermal performance. Costly gel, grease, or solder polymer type materials have very good thermal properties, but during actual package reliability test sometimes they perform poorly due to excessive voids, pump-out, interface delamination, and other degradation issues [1]. This study started to meet more demanding thermal solutions by maintaining comprehensive TIM selection methodology with standard testing processes and materials to quantify future thermal load. While thermal performance is the primary target, mechanical vs thermal performance tradeoffs are investigated through extensive package reliability analysis for high power flip chip packages.