Growth kinetics of Ni3Sn4 and Ni3P layer between Sn-3.5Ag solder and electroless Ni-P substrate

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 degreesC for up to 60 days. The IMC formed at the interface was mainly Ni3Sn4. Also, a P-rich Ni (Ni3P) layer was observed as a by-product of the Ni-Sn reaction. The Ni3P layer was between the Ni3Sn4 IMC and the electroless Ni-P deposit layer. The thickness results fitted a power-law relationship with exponent of 0.4 for the Ni3Sn4 layer. The interface between electroless Ni-P and Ni3P was planar and the thickness of the Ni3P layer also was found to increase linearly with the square root of aging time. The thickness of the Ni3Sn4 and Ni3P layer reached about 3 and 2 mum after 60 days of aging at 170 degreesC, respectively. The activation energy for the growth of the Ni3Sn4 IMC equals 49 kJ/mol. (C) 2004 Published by Elsevier B.V.