Ultrasound-assisted brazing of large area Cu/Al dissimilar metals used for package heat dissipation substrate

Cu/Al joints with large faying surface and high bonding ratio were fabricated with an ultrasound-assisted fluxless brazing method using a Zn-3Al near eutectic filler metal. The microstructure, tensile strength, and corrosion resistance of the joints were investigated in terms of brazing temperature. Results showed that, in the joint brazed at 440 °C, the filler metal layer showed a refined and dispersed microstructure, and a serrate Al4.2Cu3. ₂Zn₀.7 IMC layer with a thickness of approximately 1.9 μm was found on the Cu interface. Decreasing the brazing temperature to 400 °C or increasing the brazing temperature to 480 °C both resulted in a coarsening of the filler metal layers, and a significant growth of the Cu interfacial layers. Tensile tests showed that all the Cu/Al joints were failed in the Cu interfacial regions, among which the joint brazed at 440 °C had the highest tensile strength of 78.93 MPa. Corrosion resistance tests showed that the joint brazed at 440 °C exhibited the smallest corrosion depth after immersing in a 3.5% NaCl aqueous solution for 40 days.