Formation of intermetallic compounds in the Ni bearing lead free composite solders

Quaternary Sn-Ag Cu-Ni composite solders were made with several different ratios of Cu/Ni to study the effect of Cu/Ni on the type of intermetallic compound phase at the joint interface. The eutectic solders of Sn-3.5Ag and Sn-3.5Ag-0.7C (numbers are all in mass% unless specified otherwise) were used as references together with the ternary composite solder of Sn-3.0Ag-7.0Cu tested previously. When the ratio of excess Cu/Ni alloyed in the original composite solder was 7 : 3, 6 : 4 and 5 : 5. the reinforcing intermetallic compound (IMC) was (Cu,Ni)(6)Sn-5. When the ratio was Cu : Ni = 3 : 7, both phases of (Cu,Ni)(6)Sn-5 and (Ni,Cu)(3)Sn-14 showed up while only the (Ni.Cu)(3)Sn-4 phase was observed in the solder with a Cu : Ni ratio of 1 : 9. For the interfacial reaction of the eutectic Sn-3.5Ag-0.7Cu with the rolled Ni substrate, the thick (Cu,Ni)(6)Sn-5 layer was formed on the thin (Ni.Cu)(3)Sn-4 layer. The addition of Ni was effective to suppress the formation of the thick (Cu.Ni)(6)Sn-5 IMC. When the (CuxNi1-x)(6)Sn-5 IMC layer was formed, the value of x was lager than 0.6 while for the case of (NyCu1-y)(3)Sn-4 the value of y was larger than 0.8. The addition of Ni enhanced the bonding properties and retarded the growth of IMC. In the Ni bearing composite solder, there was no significant sedimentation of reinforcing particles during reflow, which took place commonly in the other composite solders. Wettability and mechanical properties of the Ni bearing solders were also compared.