Metalworking oxidation is one of the main reasons that gold is found in nuggets. These nuggets are relatively pure gold and are workable as they are found. Copper ore, being relatively abundant, and tin ore became the next important players in the story of metalworking. Using heat to smelt copper from ore, a great deal of copper was produced. It was used for both jewelry and simple tools. However, copper by itself was too soft for tools requiring edges and stiffness. At some point tin was added into the molten copper and bronze was born. Bronze is an alloy of copper
Tin-silver-copper (95%+) tin. For example, the common "SAC305" solder is 3.0% silver and 0.5% copper. Cheaper alternatives with less silver are used in some applications, such as SAC105 and SAC0307 (0.3% silver, 0.7% copper), at the expense of a somewhat higher melting point. SAC alloys are the main choice for lead-free surface-mount technology (SMT) assembly in the electronics industry. SMT is a process where components of circuit assemblies are mounted directly onto the surface of a printed circuit board and soldered in place. SMT has largely replaced “through-hole technology” where components are fitted with wire leads into holes in the circuit