Diffusion reaction-induced microstructure and strength evolution of Cu joints bonded with Sn-based solder containing Ni-foam

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Sn based composite solder, reinforced with low porosity Ni-foam, was used to fabricate high melting point Cu interconnects by soldering at 260 °C. The effects of soldering time on the microstructure and mechanical properties of the joints were investigated. The Sn matrix was rapidly consumed by the formation of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 phases in under 10 min. With increasing soldering time, the (Cu,Ni)6Sn5 phase was largely transformed into the (Ni,Cu)3Sn4 phase, accompanied by the refinement in the size of the phases. The average shear strength of the joint soldered for 60 min was up to 76.9 MPa, which is significantly stronger than commonly reported for Cu joints soldered with Sn based alloys.