**2. Composition**

To improve Sn‐based solders for specific applications, various alloying elements have been studied, e.g., Ag, Bi, Al, Cu, In, Sb, Zn and so on. The selection of alloying elements is generally

used to tackle problems regarding to pure Sn, to control the formation of intermetallic com‐ pounds (IMC), to keep the melting point at eutectic or near eutectic, to improve corrosion resistance and improve mechanical properties and so on [1, 2].

Several publications have already reported on these elements used to form various alloy compositions. Examples of basic compositions are Au‐Sn, Bi‐Sn, Sn‐Ag, Sn‐Cu, Sn‐In and Sn‐Zn. However, the properties of these binary alloy systems are far away from any applica‐ tions [3]. In the next development, ternary solders are proposed, such as Sn‐Ag‐Cu, Sn‐Ag‐ Bi and Sn‐Zn‐Bi solders. However, the formation of brittle failure behavior of IMC during soldering of both phases remains a problem. Now, trending in solder research is composite solders.
