Reliability Risk Assessment of Server CPU Package in Single Phase Hydrocarbon-Based Immersion Fluid

This paper presents a detailed methodology to determine the thermo-chemical and thermo-mechanical reliability risks of high-performance lidded server CPU package in a single-phase immersion cooling fluid, such as Poly-alpha Olefin 6 cSt (PAO 6). Coupon-level testing on immersion sensitive package materials, including sealant, encapsulant and underfill, was performed to evaluate material interactions with the immersion fluid. Reliability of the package assembly was assessed by stressing the Thermal Test Vehicles (TTVs) of Intel XeonTM CPU in an isothermal bath of PAO6 fluid at an elevated temperature for 2,500 hours. Post-stress measurements on the TTVs showed no significant impact to solder TIM1 integrity, sealant strength and junction to case thermal resistance (Rjc) performance. These results provide a reference dataset of a first-ever immersion reliability assessment on a server CPU package with solder TIM1 under accelerated stress conditions.