Growth kinetics of Ni 3Sn 4 and Ni 3P layer between Sn–3.5Ag solder and electroless Ni–P substrate

Abstract

Interfacial reactions and growth kinetics of intermetallic compound (IMC) layers formed between Sn–3.5Ag solder and electroless Ni–P substrate were investigated at temperature between 100 and 170 °C for up to 60 days. The IMC formed at the interface was mainly Ni 3Sn 4. Also, a P-rich Ni (Ni 3P) layer was observed as a by-product of the Ni–Sn reaction. The Ni 3P layer was between the Ni 3Sn 4 IMC and the electroless Ni–P deposit layer. The thickness results fitted a power-law relationship with exponent of 0.4 for the Ni 3Sn 4 layer. The interface between electroless Ni–P and Ni 3P was planar and the thickness of the Ni 3P layer also was found to increase linearly with the square root of aging time. The thickness of the Ni 3Sn 4 and Ni 3P layer reached about 3 and 2 μm after 60 days of aging at 170 °C, respectively. The activation energy for the growth of the Ni 3Sn 4 IMC equals 49 kJ/mol.