Reliability Improvement Mechanisms of Lotus-Type Porous Copper-Based Joining Technologies for Power Semiconductor Packaging

Lotus-type porous Cu combines the high thermal conductivity of copper with a low transverse elastic modulus and anisotropic deformation, making it attractive as a functional interlayer for power-semiconductor packaging. This review synthesizes four recent studies in which lotus-type porous Cu was applied to active-metal-brazed (AMB) Al2O3 substrates, SAC305-soldered lotus-type porous Cu/Al joints, Ag-sintered Si/Cu joints, and Cu-Sn transient-liquid-phase (TLP) joints. Across these systems the porous structure consistently lowers the initial joint strength relative to bulk Cu, yet markedly improves displacement tolerance and thermal-cycling reliability. In AMB joints, capillary infiltration of the active filler enlarges the reaction area while the low modulus reduces ceramic residual stress, cutting the post-thermal-shock strength loss from 64.5% to about 12%. In soldered joints, residual solder retained in the pores converts brittle intermetallic fracture into ductile fracture, limiting strength degradation to 7-8% versus 39.8% for bulk Cu. In Ag-sintered and TLP joints, the pores redistribute thermo-mechanical stress, deflect crack paths, and relocate damage to less critical interfaces. Design parameters governing this behavior, namely porosity, pore filling ratio, intermetallic growth, and bonding pressure, are discussed, and directions for reliable high-temperature integration are proposed.