Sn-Ag-Cu Soldering Reliability Influenced by Process Atmosphere

To develop an optimal soldering process of Sn-Ag-Cu soldered joints, the influences of atmosphere and cooling speed during reflow treatment on soldering reliability have been examined through the use of Sn plated chip components and of Pd plated small outline packages (SOPs) on a printed circuit board (PCB) soldered with Sn-3wt.%Ag-0.5wt.%Cu, Sn-3.8wt.%Ag-0.75wt.%Cu and Sn-4wt.%Ag-0.9wt.%Cu solder pastes under air or N₂ atmospheres. In the case of chip component joints, the solder compositions, cooling speed and atmospheres during reflow treatment slightly affect the dendritic microstructure. Those parameters rarely affect the wetting behavior and mechanical properties. In the case of SOP joints, however, the atmospheres during reflow treatment and fluxes strongly affect the appearances of fillet surfaces structure. Despite the types of solder fluxes, N₂ process atmosphere obviously improved wettability of solder on lead-frame of the SOP.