Microstructure of interface between Sn-Cu solder with Ni and Cu plate

The interfacial reaction between Sn-0.7 mass% Cu solder with Ni and a Cu substrate was investigated to reveal the effect of the addition of Ni to Sn-Cu solder on the microstructure of the interface. Sn-0.7Cu-xNi solders (x=0, 0.05, 0.1, 0.2 mass%) were used in this study. The results showed that, just after the reflow process at 523 K, the morphology of the intermetallic compound (IMC) formed between ternary Sn-0.7Cu-Ni solder and the Cu substrate is quite different from the intermetallic compound formed between binary Sn-0.7Cu solder and the Cu substrate. The added Ni converts the feature of IMC from a scallop morphology to a flat morphology. The Ni added to solder is contained in the IMC layer and the intermetallic phase between Sn-0.7Cu-Ni solder and Cu substrate can be expressed as (Cu1-yNiy)(6)Sn-5. On the other hand, the IMC thickness for Sn-0.7Cu-0.05Ni solder is the minimum in all solders regardless of aging time. Therefore it is found that the addition of 0.05%Ni to Sn-0.7Cu solder is certainly effective for reducing the formation of IMC layer at the interface during reflow process and for inhibiting the growth of IMC during the aging process.