Temperature dependence on ripening and spalling of interfacial (Cu,Ni)6Sn5 compound at SnAgCu(Ni)/Ni(P) interface

In this work, the in situ Cu and Ni contents in the molten SnCuAg(Ni) solder reflowed on Ni(P) were calculated against the reflowing time at 250 °C, 265 °C, and 280 °C. The phases and morphology of the interfacial compound forming at the SnAgCu(Ni)/Ni(P) reaction interface were also determined with time and temperature. The phases corresponding to the present determined Cu, Ni, and Sn composition in the reported Cu–Sn–Ni ternary phase diagram at 250 °C did not match the interfacial (Cu,Ni)₆Sn₅ compound formed in the 250 °C case. Thus, the reported Cu–Sn–Ni ternary phase diagram at 250 °C was modified to fit the present experimental results. At 250 °C, ripening occurred on the interfacial (Cu,Ni)₆Sn₅ compound grains and eventually caused them to spall from the interface. For the 265 °C case, the faster ripening caused the earlier formation of valleys and small spacing between the (Cu,Ni)₆Sn₅ compound grains after a 10-s reflowing. After a 20-s reflowing, the needle-shaped (Ni,Cu)₃Sn₄ compound phase began to form at the valley sites of the interfacial (Cu,Ni)₆Sn₅ compound layer, which hindered the spalling of the (Cu,Ni)₆Sn₅ compound grains. After a 40-s reflowing, (Cu,Ni)₆Sn₅ compound grains remained attached and mixed with the (Ni, Cu)₃Sn₄ compound. For the 280 °C case, we believe that the ripening of the (Cu,Ni)₆Sn₅ compound grains quickly occurred (within seconds). Hence, the needle-shaped (Ni,Cu)₃Sn₄ compound largely formed between (Cu,Ni)₆Sn₅ compound grains in the 10-s reflowing. After a prolonged 40-s reflowing, the (Cu,Ni)₆Sn₅ compound grains completely spalled off from the interface and the needle-shaped (Ni,Cu)₃Sn₄ compound covered and dominated the entire reaction interface.