Effect of temperature on microstructural changes of the Sn–9 wt.% Zn lead-free solder stripe under current stressing

Microstructural changes of the Sn–9 wt.% Zn solder stripe under current stressing with a density of 105 A cm−2 at 80–140 °C for 240 h were investigated. Two different cooling conditions, furnace and fan cooling, were used in the reflow of the solder. Sn hillocks/whiskers were formed across the furnace-cooled solder stripe, mainly in front of the coarse Zn-rich precipitates and the anode-side Cu electrode, at all temperatures. In the fan-cooled solder stripe, the microstructure was almost unchanged at 80 and 100 °C, but changes significantly at 140 °C where large quantities of solder were depleted but accumulated at the cathode and anode sides, respectively. Temperature was found to be an important factor that affected the electromigration behavior of the Sn–Zn solder and its influence was more significant in the fan-cooled solder.