Interfacial embrittlement by bismuth segregation in copper/tin-bismuth Pb-free solder interconnect

Microchemistry and mechanical properties of a copper/tin-bismuth Pb-free so lder interconnect were examined in the as-reflowed and aged conditions by i n situ Auger fracture and interface fracture mechanics techniques. In the a s-reflowed condition, the solder-copper interface was highly resistant to f racture, and the fracture mechanism was ductile with the crack path followi ng the interface between the solder alloy and the copper-tin intermetallic phase. Upon thermal aging, bismuth segregation was found to occur on the co pper-intermetallic interface. Auger depth profiling indicated that the segr egation was confined to about one monolayer from the interface. The segrega tion was shown to embrittle the interface, resulting in an approximately 5- fold decrease in the interfacial fracture resistance.