Effect of supersaturation of Cu on reaction and intermetallic compound formation between Sn–Cu solder and thin film metallization

Interfacial reactions and intermetallic compound formation of the eutectic Sn–0.7Cu and hypereutectic Sn–3Cu on thin film metallization of Al/Ni/Cu, Al/Cu, and Al/Ni were investigated. While the Ni layer of Al/Ni/Cu was almost consumed by Sn–0.7Cu after one reflow at 240 °C, most of it was preserved with Sn–3Cu even after ten reflows. Since the Cu content in Sn–0.7Cu is below the solubility limit of Cu in Sn at 240 °C, the Cu layer of Al/Ni/Cu was dissolved completely into Sn–0.7Cu, and the Ni was exposed to the molten solder to form intermetallics. As Cu content in Sn–3Cu is more than the solubility limit, intermetallics formed between the solder and the Cu layer, but not the Ni layer, of Al/Ni/Cu. The supersaturation of Cu in Sn–3Cu was found to be beneficial in reducing the interfacial intermetallic compound formation and in improving the interfacial stability.