Study of microstructure and shear strength of Cu/AuSn20/Ni joints

The Cu/AuSn20/Ni(mass percent) joint was prepared by the reflow bonding process,and the microstructure and shear strength of the Cu/AuSn20/Ni joint were investigated.The results showed that,the solder formed a(Au5Sn+AuSn) eutectic microstructure after reflow at 300℃ for a short time,and the cellular-like(Au,Cu)5Sn intermetallic compound(IMC) was formed at the upper Cu/AuSn20 interface,while the flake-like(Ni,Au)3Sn2 IMC was formed at the lower AuSn20/Ni interface.Upon increasing the reflow time,more and more Cu(Ni) atoms from the subtrates diffused into the solder,resulting the shift of chemical composition of the solder.So that the(Au,Cu)5Sn phase at the upper Cu/AuSn20 interface transformed into the ζ(Cu) solid solution.The(Ni,Au)3Sn2 phase at the lower AuSn20/Ni interface grew gradually to form a continuous IMC layer.The eutectic microstructure in the solder vanished and the final microstructure of Cu/AuSn20/Ni joint was composed of the ζ(Cu) solid solution and(Ni,Au)3Sn2 IMC layer.The shear strength of the Cu/AuSn20/Ni joint increased slightly with the increasing of the reflow time.