Abstract
The interface structure between Sn–3Ag solder and electroless plated Ni film and the structure near that interface were examined. Plated electroless Ni films contained 3.7 mass% phosphorus or 8.5 mass% phosphorus. A P-enriched layer is formed at the joining interface between plated electroless Ni film and Sn–3Ag solder, in each sample with 3.7 mass%P and 8.5 mass%P. P-enriched layers of both P concentration samples contained double the P concentration than the original plated Ni films. Also, the P-enriched layer of the Ni–8.5 mass%P sample was much thicker than that of the Ni–3.7 mass%P sample. Both P-enriched layers have been composed of Ni–Sn–P layer and P enriched Ni–P layer. Kirkendall voids were formed between the 1st Ni–Sn–P layer and 2nd Ni–P layer. The number of voids observed in Ni–8.5 mass%P sample was much greater than those in the Ni–3.7 mass%P sample. Intermetallic compounds, mixtures of Ni3Sn2 and Ni3Sn4, were formed by the interfacial reaction. In the case of the Ni–3.7 mass%P sample, Ni–Sn intermetallic compounds continuously crystallized on the P-enriched layer, while in the case of the Ni–8.5 mass%P sample, Ni–Sn intermetallic compound crystallized dispersively in the solder.
