Cu interconnects soldered with a novel Sn-based composite solder reinforced by Ni-Cu alloy foam

A Ni-Cu alloy foam strengthening Sn-based composite solder foil was utilized to fabricate Cu alloy interconnects by soldering at 260 °C in a vacuum furnace. The effects of bonding times on the microstructures and shear strength of Cu joints were investigated in this study. Results showed that the Ni-Cu alloy foam strengthening Sn-based composite solder could accelerate the reaction rate with Sn and refine the (Cu,Ni)6Sn5 grains. The extensive spalling phenomenon was mainly driven by the fast reaction rate of Ni-Cu alloy skeleton with Sn matrix. Massive dissolution of the Ni-Cu alloy foam increased the Ni content and refined the grain size of (Cu,Ni)6Sn5 phase in the soldering seam. The Ni-Cu alloy skeletons strengthening and (Cu,Ni)6Sn5 grain refinement enhanced the shear strength of Cu interconnects. The Cu/Ni-Cu-Sn/Cu joint bonding for 60 min had the highest shear strength of 62.7 MPa, and the cracks chiefly expanded along the internal Ni-Cu alloy skeletons and failed in the (Cu,Ni)6Sn5 layer.