Three zone-reactive wetting ring structure at interface between lead-free Sn-Ag-Cu solder and Ni pad

The wetting behavior of Sn-Ag-Cu solder ball on nickel pad has been studied. SEM and EDX were employed to analyze the solder joint interfacial microstructure. Three zone-reactive wetting ring structure was found at the interface. To further study this kind of structures, solder ball attachment (SBA) and surface mount technology (SMT) were performed to prepare more samples. Experimental results show that the reactive wetting ring is a characteristic of wetting behavior of Sn-Ag-Cu solder ball on Ni or Cu pad. It forms in ball attach reflow and sometimes can remain after SMT. A model was proposed to illustrate the three zone structure. Effects of the reactive wetting ring on the joint adhesion quality are discussed in this paper.