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Owing to the toxicity of lead, much effort has been put in studies on lead-free solders after environmental legislations prohibited the use of lead in these parts worldwide. Here, Bi-Ag and Bi-Sb alternative solder alloys containing 1•5-5 wt-% Ag and Sb were investigated. The effect of the reflow number and weight percentage of Ag and Sb on the surface properties of solders and interfacial reactions between the solder bulk and the Cu substrate were analysed by optical microscopy and scanning electron microscopy-energy dispersive X-ray. The results show that by increasing the reflow number and wt-% of Ag and Sb in the solder bulk, the thickness of the mechanical grain boundary grooving is increased. However, the thickness of the Cu3Sb intermetallic compound layer at the interface of Bi-5Sb decreased by increasing the reflow number. Moreover, our findings show that the amount of Ag and Sb in solder alloys and the reflow number have different behaviours on the wettability properties. By increasing the reflow number, the wetting angle decreased in Bi-Ag solder alloys, whereas it increased in Bi-Sb solder alloys.

An impetus has been provided towards the development of lead-free solders by worldwide environmental legislation that banned the use of lead in solders due to the lead toxicity.This study focus on Bi-Ag and Bi-Sb solder alloys, in compositions from 1.5 to 5 wt % Ag and Sb. The effects of Ag and Sb amount, and reflow number on the microstructure and morphology of solder bulk were analysed by optical microscope and scanning electron microscope-energy dispersive X-ray. Based on the results, the grain boundary grooving was observed in all samples except Bi-5Sb in all three reflows. Metallurgical and chemical reaction between interface and solders were found in Bi-5Sb solder alloys in different reflow numbers which lead to appearance of Cu3Sb intermetallic compound layer at the interface. Reflow numbers had a significant effect on the size of Cu-rich phase. Also it was observed that, with increasing reflow number Bi-Cu phase found in Bi-2.5Sb solder dissolves into the solder bulk.

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