Fluxless Bonding of Ni-P/Cu Plated Al Alloy and Cu Alloy with Lead-Free Sn-Cu Foil

Abstract

To improve the joint strength of the joint of the Ni-P/Cu plated Al alloy and the Cu alloy for a water cooling system, fluxless bonding was conducted with Sn-Cu solder foil in a vacuum. In the joint bonded at 250°C, fracture easily occurs at the joint interface due to insufficient interfacial reaction and shear strength is relatively low. In the joint bonded at 350°C, the excess growth of the Cu₃Sn layer in the Cu₆Sn₅/Cu interface and the large void formation in the joint degrade shear strength. On the contrary, in the joint bonded at 300°C, both the excess growth of the Cu₃Sn layer and the large void formation are prevented, and thus shear strength becomes relatively high. When bonding was conducted under the optimum conditions, which are bonding temperature of 300°C, bonding time of 20 min and applied stress of 0.2 MPa, shear strength became 33.4 MPa. This value is approximately four times that of the joint bonded with flux.