tin pest. Should be avoided on zinc, cadmium, or galvanized metals as the resulting joint is brittle. Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder. Such joints are also prone to cracking. Alloys with more than 47% Bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses. Retards growth of tin whiskers. Relatively expensive, limited availability. Copper improves resistance to thermal cycle fatigue, and improves wetting properties of the molten solder. It also slows down the rate of dissolution of copper from the board and part leads in the liquid solder. Copper in solders forms intermetallic compounds. Supersaturated (by about 1%) solution of copper in tin may be employed to inhibit dissolution of thin-film under-bump metallization of BGA chips, e.g. as . Nickel can be added to the solder alloy to form a supersaturated solution to inhibit dissolution of thin-film under-bump metallization. In tin-copper alloys, small addition of Ni (<0.5 wt%) inhibits the formation of voids and interdiffusion of Cu and Sn elements. Inhibits copper dissolution, even more in synergy with bismuth. Nickel presence stabilizes the copper-tin intermetallics, inhibits growth of pro-eutectic β-tin dendrites (and therefore increases fluidity near the melting point of copper-tin eutectic), promotes shiny bright surface after solidification, inhibits surface cracking at cooling; such alloys are called "nickel-modified" or "nickel-stabilized". Small amounts increase melt fluidity, most at 0.06%. Suboptimal amounts may be used to avoid patent issues. Fluidity reduction increase hole filling and mitigates bridging and icicles. Cobalt is used instead of nickel to avoid patent issues in improving fluidity. Does not stabilize intermetallic growths in solid alloy. Indium lowers the melting point and improves ductility. In presence of lead it forms a ternary compound that undergoes phase change at 114 °C. Very high cost (several times of silver), low availability. Easily oxidizes, which causes problems for repairs and reworks, especially when oxide-removing flux cannot be used, e.g. during GaAs die attachment. Indium alloys are used for cryogenic applications, and for soldering gold as gold dissolves in indium much less than in tin. Indium can also solder many