Direct-to-Silicon Liquid Cooling Integrated on Cowos® Platform

Direct-to-silicon liquid cooling has shown promise in managing high power and high power densities driven by 2.5D/3D advanced packaging for HPC/AI applications. In this work, a silicon-based liquid cooling solution, Si-integrated micro cooler (IMC-Si), was demonstrated on a 3.3X-reticle CoWoS^®-R package. The integration required minimal modifications to the existing CoWoS^® process flow. A warpage-tolerant sealant was dispensed between the silicon logic dies and the liquid manifold lid to form leak-proof plenums for direct liquid cooling. The integrated system can dissipate uniform power up to 3.4 kW(2.5 W/mm² on 1.6X-reticle SoCs) at a flow rate of 10 LPM using 40 °C water as coolant. A critical water leak rate of 115 cc/year (4.4 x 10⁻⁶ Pa·m³/s in helium leak rate), derived from a typical data center environment, was employed to assess the sealant's robustness and reliability. Experimental results showed that the integrated system passed stressing tests, including multiple reflows (3 cycles), TCG (2000 cycles) and HTS (150 °C for 1000 hours), with helium leak rates at least an order of magnitude below the critical leak rate. Additionally, an accelerated liquid immersion test (150 °C and 4.8 bar pressure) was conducted to evaluate the sealant's resilience to liquid leakage. CoWoS^® integrated with IMC-Si has been successfully demonstrated for the first time as a viable solution to meeting thermal, in addition to electrical, performance requirements for increasingly demanding HPC/AI applications.