Low Cycle Fatigue of Sn96 Solder With Reference to Eutectic Solder and a High Pb Solder

Abstract

This paper describes the 35°C and 150°C low cycle fatigue behavior of Sn96 solder (96.5 Sn/3.5 AG), the tin silver eutectic. There is a considerable amount of anecdotal information which says that this solder is superior to eutectic solder in its fatigue resistance. This study generally supports this assertion, but not for all plastic strain ranges. This solder has an excellent balance of strength, ductility and fatigue life under strain cycling. Furthermore, it is also shown that this solder is superior to a high Pb solder (92.5 Pb/2.5 Ag/5.0 Sn). The only drawback of the tin silver eutectic is that it has a higher melting point than the melting point for the Sn/Pb eutectic (221°C versus 183°C), and this requires a higher soldering temperature. This higher temperature necessitates some process alterations in order to use this solder.