Abstract
We examined the interfacial reactions between Sn–3.0Ag–0.5Cu (SAC305)/FeCoNiCu (FCNC), SAC305/Cu-rich FCNC, and Sn3.5Ag (SA3.5)/FCNC alloys. FCNC and Cu-rich FCNC showed various face-centered cubic structures, and SAC305/Cu-rich FCNC showed slightly better contact angles than SAC305/FCNC. However, the former had an interfacial layer of (Fe, Co, Ni, Cu)Sn2 thicker than that of the latter. SAC305/FCNC and SA3.5/FCNC exhibited good thermal stability in liquid-state reactions because the difference in the thickness of their intermetallic compound (IMC) after the second reflow was small. Conversely, the growth of the interfacial IMC in SAC305/FCNC was more rapid than that in SA3.5/FCNC during solid-state aging at 150 °C due to the presence of Cu in SAC305. Furthermore, the Cu/SA3.5/FCNC sandwich structure showed a 582% difference in the IMC thickness at the Cu and FCNC sites. These findings indicate that Cu addition has a significant effect on the interfacial reactions between Sn-based solders and FCNC alloys. SA3.5/FCNC with good liquid- and solid-state thermal stability is promising as a diffusion barrier in solder microbumps with small solder volumes.
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