Optimization of Direct Bonding Process for Lotus-Type Porous Copper to Alumina Substrates

The effects of processing conditions and holding time on the direct bonding (DBC) of lotus-type porous copper to alumina substrates were systematically investigated. The evolution of copper morphology and the resulting shear strength were evaluated under varying pressures (0.3–0.6 Torr) and bonding durations (5–160 min) at a fixed bonding temperature. It was found that pressure within the tested range exerted a negligible influence on joint quality, as direct bonding occurred consistently. In contrast, holding time was found to be a critical factor: a duration of 10 min yielded optimal bonding with high shear strength while preserving the porous structure, whereas shorter times led to incomplete bonding, and longer times caused structural collapse due to liquid-phase flow. The oxidation behavior, governed by parabolic growth kinetics, was identified as the primary mechanism controlling morphological evolution. These findings provide practical guidance for optimizing DBC bonding of porous copper in power semiconductor applications, balancing joint strength and structural integrity.