Characterizations of Metal-based Thermal Interface Materials (TIM) in a Singulated Flip Chip Ball Grid Array Package

With the fast growth in semiconductor industry, packaging solutions of processor units and application specific integrated circuit (ASIC) devices to meet the needs of advanced Silicon (Si) nodes, thermal efficiency enhancement, and multi-functional integration become more challenging than ever before. Especially when the high performance computing (HPC) and artificial intelligence (AI) functionality adds in the integrated circuit (IC) design, it always causes much larger power and the resulted heat generation must to be dissipated effectively. The flip chip ball grid array (fcBGA) package with extremely efficient thermal dissipation manners has been viewed as an attractive solution when larger power and heat generation is designed. Although the adder of heat spreader has been proven to assist the heat dissipation in effect, it is highly rely on the adoption of thermal interface material (TIM) to transfer the heat from silicon die, through the heat spreader to the ambient air effectively. For the purpose of studying flipchip package assembly process characterizations in a 23×23mm fcBGA package with a metal-based TIM, the composition of 90% indium and 10% silver (In10Ag) TIM with thermal conductive coefficient of ∼67W/mK is evaluated. The implement of gold material for the backside metallization on die surface and the surface finish of heat spreader is performed. The evaluations with and without the assist of sprayed flux on In10Ag TIM surface and different reflow profiles in heat spreader attach (SDA) reflow process are assessed. In order to prove the reliable quality and assembly yield of the evaluated TIM in the fcBGA package, long-term package-level reliability tests are implemented for TIM coverage ratio assessment. The satisfactory result of TIM thickness without any delamination or crack between heat spreader and backside metallization of die surface are observed through X-ray and scanning acoustic tomography (SAT) with transmitted signal (T-Scan) inspections. The proper TIM coverage ratio after reliability tests is also illustrated. Bases on the examined characterization result, it shows the good assembly yield achievement and the direction to improve metal-based TIM coverage ratio in a fcBGA package for thermal dissipation performance enhancement.