Effect of interfacial reaction layer on the brittle fracture of the SAC305 solder joint on ENIG and ENEPIG surface finish

Brittle fracture generally occurred when a high level of strain and strain rate is applied. Since the brittle fracture takes place in the layer of intermetallic compound(IMC), the controlling of the IMC layer is important to lower the occurrence of the brittle fracture. In this study, the IMC structure of the solder joints on electroless nickel immersion gold (ENIG) and electroless nickel electroless palladium immersion gold (ENEPIG) surface finish was observed and the brittle fracture behaviors of solder joints were analyzed with a high speed shear (HSS) test. The HSS test was carried out at various speeds of 100-2000mm/s and fracture surface was observed to understand the failure modes. The brittle fracture increased with increasing shear speed. In case of the ENIG sample, the IMC thickness and the percentage of brittle fracture increased as the increase of the metal turnover(MTO) increased. On the other hand, the ENEPIG sample did not show a significant increase of IMC thickness or the percentage of brittle fracture as the MTO increased. From TEM observation, nano-sized voids were formed in the NiSnP layers. As the MTO of the electroless Ni plating solution increased, the amount of the nano-sized voids increased.