Effects of nano-structured reinforcements on the recrystallizationand damage mode of of Sn-3.0Ag-0.5Cu solder joints

Abstract

The research on lead-free solders has become the focus in electronic industry, conventional lead-free solder technology may not meet the increasingly severe service environment, so an attractive and potentially method to enhance the performance of a lead-free solder is to introduce reinforcements into a conventional alloy. This study employed polyhedral oligomeric silsesquioxanes (POSS) nano-particles as reinforcements for Sn3.5Ag0.5Cu (SAC) solder matrix. It was aimed at investigating the effect of POSS on the microstructure evolution and recrystallization behavior of ball grid array (BGA) solder joints under thermal fatigue. 3wt% POSS were incorporated into Sn3.5Ag0.5Cu (SAC) solder matrix by mechanical ball milling followed by reflow process, and found to be homogeneously dispersed into the solder matrix by EDX analysis. Then, two kinds of different components BGA assemblies were subjected to thermal cycling, and the surface morphology change and orientation evolution of solder joints before and after the thermal shock was respectively characterized by using SEM and EBSD. Experimental results revealed that the microstructure of solder matrix could be markedly refined with the addition of POSS, because of the reinforcements retarded the element diffusion and intermetallic compound aggregation. Vickers hardness has obviously improved, composite solder joint shows a better mechanical properties. After the thermal fatigue test of 928 cycles, at the interfaces extrusion deformation produced, the recrystallization accompanied with initiation and propagation of cracks in the BGA of SAC305 solder joint. But after the addition of nanoparticles, composite solder resulted in less grain boundaries in the same time, and it can prevent the appearance of recrystallization in solder.