Corrosion of Sn-3.0Ag-0.5Cu thin films on Cu substrates in alkaline solution

Purpose– The purpose of this paper is to examine the corrosion behaviors of SAC305 thin film solder alloy in 6 M KOH solution.Design/methodology/approach– The corrosion behavior of bare Cu, as-deposited SAC305/Cu and as-reflowed SAC305/Cu thin films at varying temperatures, was investigated by means of potentiodynamic polarization in a 6 M KOH solution. The microstructure, phase and thickness of the intermetallic compounds formed were determined before and after polarization.Findings– Bare Cu was found to possess the best corrosion resistance, whereas the as-deposited SAC305/Cu had the lowest corrosion resistance. As-reflowed SAC305/Cu with an exposed Cu3Sn layer exhibited better corrosion resistance than did Cu6Sn5. The Ag3Sn phase has the noblest characteristic because it was retained and did not dissolve in the KOH solution. All of the samples contained the corrosion products of oxide. Bare Cu obeys the well-known duplex structure of a Cu2O/CuO, Cu(OH)2layer. For as-reflowed SAC305/Cu, the corroded surface was also mainly composed of SnO and SnO2.Originality/value– New analysis on the polarization of thin film characteristics of SAC305 lead-free solder in alkaline solution.