Evaluation of DIG (direct immersion gold) as a new surface finishes for mobile applications

DIG (direct immersion gold) is evaluated as an alternative surface finish solution to Ni/Au system for mobile electronics. Three key points are studied in this paper. First, Au capping layer optimization was studied. At least 0.14mum Au thickness is needed to prevent Cu out-diffusion and achieve reasonable assembly process window. Second, compared interfacial microstructures and morphologies of IMCs formed on DIG and Ni/Au surface finishes. DIG provide uniform IMC layer with no void, defect and Au-Sn intermetallic compounds (IMC). Finally, reliability and fracture modes were studied. SAC 405 performs better than eutectic Pb-Sn for the temperature cycling test. Crack in Pb-Sn + DIG system is initiated from interface of Cu₆Sn₅ and bulk solder and propagated to bulk solder while crack path of Pb-Sn + Electrolytic Ni/Au is interface of Au-Sn IMC and bulk solder. For drop test, SAC405 + DIG system has mix fracture modes of bulk and IMC brittle fracture while SAC405 + electrolytic Ni/Au has shows complete IMC fracture mode