Comparative Study on the Effect of Surface Finish on Mechanical Properties of Solder Joints

We present the results of an experimental study comparing the effect of PCB surface finishes on the mechanical properties of soldered joints: maximum strength, strain hardening area, necking area (tendency to brittle failure), and energy consumed to break the joint. For the study, 4 types of standard PCB surface finishes were used, which we compare with various non-standard SnAg-based surface finishes. The measurements were carried out through shear tests. Failure mode, strength and fracture energy data, and analysis of the strain hardening area of brittle failure or necking were supplemented by microscopic SEM analyses of surfaces after failure. Our results show the influence of the surface finish type on the joints’ quality and reliability when applying SAC 305 solder after one and 5 reflows. Our previous analyzes showed that the SnAg5 surface finish had demonstrably better wettability. Still, a comparative study of the surface finish’s effect on the joints’ mechanical properties showed that the SnAg7 surface finish shows better properties even after repeated reflow processes. In both cases, the SnAg surface finish group has comparable properties to the ENIG finish.