Creep is the deformation of a work piece exposed to comparatively low voltage for a longer period of time. As the figure shows, creep may be of three sorts.
1: deformation within a short time;
2: deformation occurring in a relatively slow pace ;
3: sudden deformation leading to fracture of the work piece.
Since recrystallization is low in Sn-Pb solder alloys, creep deformation happens at room temperatures as well . At elevated temperatures, this phenomenon is even more pronounced . Adding small amounts of Cu and Sb makes this alloy less susceptible to creep. The pressure on the creep curve which leads to the rupture of the work piece is referred to as creep strength.