A study of Ag micro-particle reinforced Sn-Zn matrix composite solder

In this work, Ag micro-particles content in the range between 0-4.0 wt.% with Sn-Zn eutectic system, were examined in order to understand the effect of Ag addition on the microstructural and mechanical properties as well as the thermal behavior of the composite solders. The shear strengths and the interfacial reactions of Sn-Zn micro-composite eutectic solders with Au/Ni/Cu ball grid array (BGA) pad metallization were systematically investigated. The three distinct intermetallic compound (IMC) layers were formed at the solder interface of the Au/electrolytic Ni/Cu bond pad with Sn-Zn composite alloys. The more Ag particles added to the Sn-Zn solder, the more Ag-Zn compound formed to thicken the uppermost IMC layer. The dissoluted Ag-Zn IMCs formed in the bulk solder redeposited over the initially formed interfacial Au-Zn IMC layer, prevented the whole IMC layer lift-off from the pad surface. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces.