Drawbacks of the nanoparticle reinforced lead-free BGA solder joints

In this study, 0.5 wt.% CNTs-doped solder paste, that prepared by mechanical stirring, was used to detect the redistribution phenomenon of nanoparticles in the solder ball. Some of nanoparticles seriously separated out with the outward flow of solder flux, making related quantitative experiments loss their accuracy. Some of nanoparticles seriously gathered in the solder ball, having negative effects on the solder joint and making the phenomenon of degradation of reinforcement become serious. To study the degradation phenomenon of nanoparticle reinforced solder joint, mechanical properties of Sn58Bi, Sn57.6Bi0.4Ag and doped Sn58Bi+0.4Ag were compared during aging. According to the result of ball shear test, the degradation of reinforcement was seriously happened in the doped Sn58Bi+0.4Ag solder joints. Caused by the gathered Ag₃Sn IMCs, the doped Sn58Bi+0.4Ag solder joints lost its mechanical advantages after 100h aging, comparing with Sn58Bi and Sn57.6Bi0.4Ag solder joints.