Integrated Package-to-System Thermal Solution Evolution for High-Performance 2.5D CoWoS-R Advanced Packaging Technology Development

2.5D/3D stacked heterogeneous integration packages, like CoWoS (Chip on Wafer on Substrate) technology, are increasingly adopted in high-performance computing (HPC) for data centers and AI systems for the integration of large interposers with SoC chips and HBM cubes. CoWoS-R, a variant with a flexible RDL interposer, enhances integration and scalability. It provides low RC interconnect with good signal integrity, design scalability, and structural reliability. However, the high-performance capabilities of the CoWoS-R package also introduce significant thermal management challenges, which necessitates advanced thermal and cooling solutions. This study involved assembling a 2.5D CoWoS-R thermal test vehicle package (3.3x interposer) with advanced thermal interface materials (TIM) for high-power HPC systems. Three TIM materials-graphite film, liquid metal, and indium metal-were tested for thermal performance evaluation. A computational thermal model was built and calibrated to study the package thermal performance with a liquid cooling system. Experiments showed that indium metal TIM, with high thermal conductivity, effectively managed power inputs over 1200W while maintaining junction temperature at 105°C. Bond line thickness and contact resistance of the TIM were studied. With the optimization of system cooling solution, it is shown that we can achieve 2000W power dissipation. A micropillar thermal solution enabling direct liquid contact with silicon is studied to enhance cooling by eliminating thermal interface material and resistance. Integrating this with CoWoS-R packaging shows potential to exceed 2000W cooling power, benefiting device and package design.