Contribution of Ni microalloying to Cu dissolution in In–35Sn/Cu solder joints after multiple reflows

Abstract

Multiple reflow processes are utilized in complex electronic devices with multi-layered PCBs, stacked components, or 3D configurations to ensure reliable connections and minimize defects. A systematic analysis was performed to examine the influence of multiple reflow cycles on the microstructure and interfacial reaction of In–35Sn microalloyed with 0.05 wt% Ni on a Cu substrate. The size of the primary IMC particles in the In–35Sn solder was observed during multiple reflow process on Cu using in-situ real-time synchrotron radiography imaging. Multiple reflow soldering caused the primary Cu(In,Sn)2 and interfacial Cu3(Sn,In) layer to coarsen. The Ni was present in the primary (Cu,Ni)1(In,Sn)2 particles and interfacial (Cu,Ni)3(Sn,In) layer and caused grain size refinement of the IMCs after multiple reflow soldering. The shear test showed that there was a minor increase in shear force after multiple reflows. However, the shear energy decreased, indicating a more notable decrease in displacement to fracture rather than shear force which suggests a higher tendency towards ductile fracture.