Solder is used to make a permanent solder connection between two wires or a wire and a trace or pad. For this purpose, the solder is heated above the melting point with a soldering iron or soldering gun and liquefied. A flux, which may be inside the solder, is used to achieve good wetting of the contact points. As the solder cools, it solidifies so that the two wires are firmly bonded together.
The melting point of solder depends on the percentages of tin and lead and other elements. In the case of solder, the designation indicates the percentage ratios of the individual elements. For example, the classic solder Sn60Pb40, which was used for decades, consisted of 60% tin and 40% lead. This solder had its melting point at a temperature of 183 °C and liquefied at 191 °C. Since leaded solder may no longer be used in industrial electronics since 2006, lead-free solder has been used since then. This solder consists of over 90% tin and a few percent silver. The melting point is about 217 °C.
Solder is supplied as approx. 1 mm thin thread wound on a roll.