Refers to solders based on tin (Sn), silver (Ag) and copper (Cu). The common abbreviation “SAC” stands for the initial letters of the chemical elements. The ratio is given as the following combination of numbers. SAC305 means 3% silver and 0.5% copper. The large remainder consists of tin. Other combinations are for example SAC405 or SAC+X. The letter X is used for other additions such as bismuth (Bi) or indium (In).