A preform is a piece of solder in a wide variety of shapes. Often, the preforms are coated with solder flux or have flux in the center of the metal. Preforms formed with a flux in the center like this are typically called flux-cored. However, preforms come in six solder families: gallium, bismuth, indium, tin, lead and gold-based. There are more than 200 different alloys that can be formed into preforms.
