Study on the growth kinetics of Ag3Sn alloy layer and fatigue lifetime prediction of PV interconnection

Abstract

The electrical conductivity and reliability performances of modules remains a challenge for extending the life-cycling in the widely practical crystalline silicon photovoltaic. Photovoltaic module reliability is severely destroyed by the stress accumulation resulted from the non-stop growth of Ag₃Sn intermetallic compounds at the solder joint. The growth behavior and microstructural evolution of Ag₃Sn intermetallic compounds during continuous aging was thoroughly investigated, which provided a method for predicting the fatigue life of solder joints. The results indicated that the Ag₃Sn intermetallic compounds at the solder joint were formed by continuous diffusion between the brazing material and the Ag electrode in a porous silver electrode, which was significantly affected by temperature and time. When the stress of Ag₃Sn intermetallic compounds was less than 26.7 MPa, the equivalent Ag₃Sn thickness was greater than 1.67 μm. During the soldering process, a reasonable soldering force of 1.44 N was required, corresponding to an initial Ag₃Sn thickness of 1.67–3.02 μm. Moreover, the growth of the intermetallic compounds layer was found to be logarithmic with respect to time and exponential with temperature. Based on the dynamic model of Ag₃Sn and outdoor temperature data of typical cities in Munich, Taizhou, and Sydney with variable latitudes, the fatigue life of solder joints was accurately predicted through finite element analysis. The work provides a theoretical foundation for the precise categorization of photovoltaic modules in diverse applications.