Microstructure and Solderability of Zn-6Al-xSn Solders

Abstract

The eutectic point of Zn-6Al alloy is 381°C, and the peritectic reaction of Zn-Al-Sn alloy occurs at 280°C. In order to find an alloy with an appropriate melting point between 280°C and 340°C, Zn-6Al-5Sn, Zn-6Al-10Sn, Zn-6Al-15Sn, and Zn-6Al-20Sn alloys were prepared. The microstructure, melting behavior, and wettability of the Zn-6Al-xSn solder alloys were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and the sessile drop method. The results show that the alloys were composed of Zn-rich phase, Zn-Al structure, Sn-Zn-Al peritectic structure, and Sn-Zn eutectic structure. The progressive decrease of the liquidus temperature of the Zn-6Al-xSn solders was confirmed by the DSC results in the order: Zn-6Al-5Sn, Zn-6Al-10Sn, Zn-6Al-15Sn, Zn-6Al-20Sn. A decrease of the wetting angle, selected for evaluation of the solderability of the Zn-6Al-xSn solders, was observed in the same order. The cross-section of a solder joint on a Cu substrate was examined by SEM coupled with energy-dispersive x-ray (EDS) analysis.