Thermal Reliability and Electrical Properties of Integrated Copper Inverse Opal Structures

Templating with self-assembled colloidal crystals has enabled fabrication of porous materials with potential for sensing, heat transfer, and energy storage applications. Herein, electrical, thermal, and mechanical properties of templated electroplated metallic copper inverse opals (CIO) containing close-packed 500 nm pores are evaluated via a four-point probe, eddy current, lap shear measurements, thermal cycling, and finite-element analysis (FEA). CIOs are found to have an electrical conductivity of ≈4 × 10⁶ S m⁻¹, about 15% of pure copper, about the expected value based on the measured electroplated copper conductivity and the CIO pore structure. The good electrical and thermal properties of this structure, coupled with its connected porosity, make it attractive for two-phase cooling applications. However, the thermal reliability of this structure raises questions about its integrity. It is found that this structure fails around 150 cycles when cycled between −40 and 200 °C at 10 °C min⁻¹. Scanning electron micrograph (SEM) images of failed samples show that the failure plane lies within the CIO and generally at the thinnest interconnects in the structure, which agrees with FEA of the CIO structure, which shows stress concentrations at thin regions of the interconnects in the structure.