Ultrasonic-assisted rapid fabrication of Cu foam/Cu-Sn IMC composite interlayers for high-temperature die-attach applications

The development of full intermetallic compound (IMC) joints with high melting temperatures is critical for advanced die-attach in third-generation semiconductor power devices. This study demonstrates an innovative ultrasonic-assisted manufacturing strategy to fabricate high-performance Cu foam/Cu-Sn IMC composite interlayers, consisting of three-dimensional continuous Cu foam skeletons, Cu₆Sn₅ and Cu₃Sn IMCs, by low-power ultrasonic-assisted immersion soldering (260 °C, 180 s). The rapid fabrication of composite interlayer was attributed to that the cavitation erosion effect promoted the wettability of the molten Sn on Cu surface, and the acoustic cavitation and streaming effects simultaneously enhanced both the dissolution rate and the diffusivity of substantial Cu atoms from high specific surface area Cu foam into the molten Sn. The composite joints prepared by diffusion bonding of two Cu substrates with the composite interlayers achieved the metallurgical bonding through the formation of thin interfacial Cu₃Sn IMCs. The optimized composite joint demonstrated exceptional mechanical performance with a shear strength of 65.3 MPa and fracture elongation of 33.1 %, owing to the combined effects of the fine grain strengthening of Cu-Sn IMCs induced by the ultrasonic vibration and the ductile three-dimensional continuous Cu foam skeletons.