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In the big data era, Si chips are integrated more and more to satisfy the fast growing demand from customers. In addition, in the post-COVID-19 virus era, the trend of distance teaching and home office has increased greatly the need of advanced consumer electronic products. To provide more processing tolerance and to build a wider temperature window in manufacturing, it becomes necessary to develop low melting temperature solders because a hierarchy of solders is needed in the packaging technology. Much research has been on Pb-free and Sn-based solders with a melting point from 180 to 230 °C. In this review, we will concentrate on low melting point solder alloys with a melting point lower than 180 °C and even below 100 °C. We review eutectic SnBi, eutectic SnIn, and the alloys with trace addition of a third element to them. Eutectic Sn-Bi solder is too brittle, and Sn-In solder is too soft. However, third element addition can only improve the solder properties partially; thus, we will further review the properties of Sn-Bi-In ternary alloys and the effect on the addition of a fourth element to them. This approach, when we include the Cu substrate, becomes a 5-element system, which leads us to consider high entropy alloys for soldering. With these Sn-, Bi-, and In-based alloys, we hope to develop new ways to design industrial applicable low melting point solders.
Liu et al. (Fri,) studied this question.