Comparison of Ag Wire and Cu Wire in Memory Package

Abstract

Recently, there is growing interest in other bonding wire material alternative to Au, because the cost of Au has dramatically increased. In these studies, Cu wire is the most popular candidate due to its cost savings, better electrical and mechanical properties. But the high hardness of Copper is the ineluctable and fatal problem in it, which will limit the ball bonding process and the applications of Cu wire. Therefore, as another alternative choice to Au wire, Ag wire is investigated.Ag wire and Cu wire were evaluated on the Aluminum pad of memory device. The interface was characterized and the bondability was compared. Pad crack has been observed in Cu wire, which induced leakage fail in electrical test. Contrastively, in case of Ag wire, good interface and bondablity could be got. Reliability behaviors were also examined, especially uHAST (85%RH, 130’C) and HTS (150’C) test. After reliability test, the interfaces were characterized by FIB, TEM and EDS. The characterization of IMC was verified. The founds show that degradation of reliability is caused by IMC corrosion and the corrosion can be suppressed significantly by increased Pd content .The improved Ag wire can pass uHAST 480h and HTS 1000h. From this study, Ag bonding wire, as the low cost wire, is proposed as an alternative to Cu wire on fragile Aluminum pad in memory device.