Microstructural changes of lead-free solder joints during long-term ageing, thermal cycling and vibration fatigue

Purpose - The purpose of this paper is to investigate the microstructural development of SnAgCu solder joints under different loading conditions (isothermal storage, thermal cycling and vibration).Design methodology approach - The observed microstructural changes have been studied with respect to grain growth and grain refinement, crack formation and crack growth. The growth kinetics of the intermetallic phases encountered as particles in the bulk as well as a reaction layer on the copper pad, were studied in the temperature range of 125-175°C.Findings - Dynamic recrystallisation of the tin matrix leads to a change in the diffusion controlled growth mechanism, which causes an increase of the particle growth rate compared to isothermal storage. Thus, these grain boundaries are separated forcibly by crack growth during thermal cycling. This stress causes intergranular cracks while vibration stress induces transgranular cracks.Originality value - The paper adds insight into microstructural changes of lead-free solder joints during long-term ageing, thermal cycling and vibration fatigue.