Boiling-induced thermal degradation of copper inverse opals and its mitigation

Abstract

Thermal management in power electronics relies on active and passive cooling devices that use porous copper structures. However, these critical components, such as sintered copper and copper inverse opals (CuIOs), degrade rapidly when exposed to working fluids like water and oxygen. This study investigates the thermal reliability of CuIO structures subjected to harsh boiling environments using pool-boiling tests. 10–30 μm-thick porous CuIO structures with a constant 5 μm pore diameter and neck openings of 0.6–1.4 μm are fabricated using electrodeposition on silicon through a polystyrene-sintered template. Pool-boiling heat transfer is mainly performed under a constant heat flux of ∼115 W cm−2 at a saturation temperature of 100 °C. As a result, severe degradation of CuIO structures occurs over 72 h. Therefore, A 50 nm-thick direct gold immersion coating is considered as a mitigation strategy. The gold-coated CuIO surface exhibits structural stability, maintaining a stable temperature and heat transfer coefficient compared to pristine CuIOs. Moreover, a reliability test in HFE-7100 is also conducted for applications with lower heat flux and operating temperature requirements. Extensive reliability tests on CuIOs with and without an Au protective coating reveal no noticeable degradation over 11 days at 50% and 67% of critical heat flux. This study provides essential reliability data for failure modeling and offers valuable insights into mitigation strategies and predictive tools for improving the reliability and life expectancy of CuIOs.