Solder bars, solder wires and solder paste are various forms of filler metal used for joining two or more metal objects together. Solder is heated to melt and flow over the metals to be joined and requires a lower melting point. Traditional, lead-based solders are made of alloys of tin and lead of varying percentages. Silver may be added for higher melting points. Solders for aluminum are made of alloys of zinc, aluminum and tin. Lead-free alloys have become necessary to meet environmental demands and are composed of various combinations of materials including tin, copper, silver, bismuth, indium, zinc and antimony.