Foam Ni-cu enhancement of ultrasound-assisted cu/Sn58Bi/cu joint properties

Foam Cu-Ni possesses a three-dimensional continuous structure, making it a practical reinforcing phase to enhanced joint strength. This study employed ultrasound-assisted soldering to strengthen the bonding between foam Cu-Ni, Sn58Bi solder, and Cu substrates. The microstructure of the composite joints, the growth behavior of interfacial intermetallic compounds (IMCs), and the shear strength were systematically investigated. The study results demonstrated that ultrasonication enhanced the metallurgical reaction between Cu/Sn58Bi-foam Cu-Ni/Cu, achieving excellent metallurgical bonding and accelerated the shaping of interfacial (Cu, Ni)₆Sn₅ IMC and altered the composition of the IMC layer. The average thickness of the IMC layer increased with prolonged ultrasonic time. The thickness of IMC was 2.04 μm when no ultrasound was applied and increased to 2.79 μm when ultrasound time reached 30s. When the ultrasonic time was lengthened, (Cu, Ni)₆Sn₅ grew within the matrix, establishing structural continuity with the foam Cu-Ni, significantly improved joint strength. The joint strength reached 62.47 MPa, 17.71 MPa higher strength than joints without ultrasonic treatment while the fracture characteristics showed a mixed fracture mode.