Investigation of FeCoNiCu properties: thermal stability, corrosion behavior, wettability with Sn-3.0Ag-0.5Cu and interlayer formation of multi-element intermetallic compound

Abstract High-entropy alloy (HEA) FeCoNiCu (FCNC) can be potentially employed in electronic packaging because it contains commonly used substrate metals. However, its microstructure, thermal stability, corrosion behavior, and wettability toward Sn-3.0Ag-0.5Cu (SAC305, wt.%) solder have never been examined in detail, especially in terms of the microstructure and reactivity of the SAC305/FCNC interface. In this study, FCNC consisted of a dominant phase and a Cu-rich phase characterized by excellent thermal stability during thermal aging at 150-450 °C for 150 h and high corrosion resistance against 3.5% NaCl solution. Additionally, its good wettability toward SAC305 solder corresponding to a contact angle of 20.1° after reflow at 250°C. Furthermore, a multi-element intermetallic compound layer composed of 17.73% Fe, 11.68% Co, 6.54% Ni, 3.81% Cu, and 60.23% Sn (at.%) with a thickness of 0.68 μm was formed at the SAC305/FCNC interface. Finally, (Cu-rich, Fe, Co, Ni)6Sn5 IMC was formed from the Cu atoms sourced by the solder on the (Fe, Co, Ni, Cu)Sn2 IMC layer during thermal aging at 150 °C for 150 h, while the growth of the latter compound was limited. The findings of this work suggest possible applications of FCNC in HEA-related fields and electronic packaging.