Interfacial reactions between CuxNiy alloy underbump metallurgy and Sn-Ag-zCu solders

Abstract

A reaction study of CuxNiy alloy (x = 0.2-0.95) under bump metallization (UBM) with Sn-Ag-zCu solder (z = 0-0.7) was conducted. Formation and separation of intermetallic compounds (IMCs), effect of Cu addition to the CuxNiy, alloy and the solders, and compatibility of reaction products with currently available phase diagrams are extensively investigated. The increase of Cu content both in the CuxNiy alloy and in the solder promoted IMC growth and CuxNiy consumption; though, with regard to solder composition, the reverse trend was true of the solder reactions in the literature. The liquid + Cu6Sn5 area in the Sn-rich corner needs to be larger compared to the currently available Cu-Ni-Sn ternary phase diagram, and the maximum simultaneous soluble point of Ni and Cu in Sn needs also to be moved to the Ni-Sn side (e.g., Sn-0.6Cu-03Ni).