Interfacial Microstructure and Mechanical Reliability of Sn-58Bi/ENEPIG Solder Joints

The 42 wt.% Sn-58 wt.% Bi (Sn-58Bi) Ball Grid Array (BGA) solder balls were mounted to electroless nickel-electroless palladium-immersion gold (ENEPIG) pads by employing the reflow process profile. The effects of reflow cycles and aging time on the interfacial microstructure and growth behavior of intermetallic compounds, as well as the mechanical properties, were investigated. Pd-Au-Sn intermetallic compound (IMC) was formed at the Sn-58Bi/ENEPIG interface. With the increase in reflow cycles and aging time, the IMC grew gradually. After five reflow cycles, the shear strength of the Sn-58Bi/ENEPIG solder joints first decreased and then increased. After 500 h of aging duration under -40 degrees C, the shear strength of the Sn-58Bi/ENEPIG solder joints decreased by about 12.3%. The fracture mode transferred from ductile fracture to ductile and brittle mixed fracture owing to the fact that the fracture location transferred from the solder matrix to the IMC interface with the increase in reflow cycles and aging time.

Automated summary

The effects of reflow cycles and aging time on the microstructure, growth behavior of intermetallic compounds, and mechanical properties of Sn-58Bi/ENEPIG solder joints were investigated. Pd-Au-Sn intermetallic compound was formed at the interface and grew gradually with increasing reflow cycles and aging time. The shear strength initially decreased and then increased after five reflow cycles. After 500 hours of aging at -40 degrees C, the shear strength decreased by approximately 12.3%. The fracture mode changed from ductile fracture to a mixed fracture with the increase in reflow cycles and aging time, due to the shift in fracture location from the solder matrix to the intermetallic compound interface.