Microstructure Evolution of Solder Joints with Different Pb Contents at Ultra-low Temperature [超低温下不同Pb含量焊点组织演变规律]

作者：Wu M.; Wang S.^*; Sun W.; Ma B.; Chen Y.; Huang Y.; Ke L.

来源：Rare Metal Materials and Engineering, 2020, 49(11): 3822-3827.

• Aging
• Microstructure evolution
• Pb content
• Shear strength
• Ultra-low temperature

The Ni/solder/Cu sandwich solder joints were prepared with four kinds of mixed soldering alloys with different Pb contents (0, 4.67, 22.46, 37, wt%), and the effects of Pb content and aging time on the microstructure, the evolution of intermetallic compounds (IMC), and mechanical properties were investigated by putting the solders into the -196℃ liquid nitrogen with different aging time of 10 d, 20 d and 30 d. The results indicate that Pb element accumulates gradually with the increase of Pb content in solder; moreover, the Pb-rich phase continuously coarsens with the increase of aging time. The nominal chemical composition in IMC layer does not alter during ultra-low temperature aging treatment, while some microcracks and holes occur gradually accompanied with the transformation of the scallop-like IMC into lamellar IMC. At the same time, the Pb element accumulates along the IMC interface near the solder, and a Pb-rich layer is formed, even some Pb-rich phases extend inside the IMC layer. With the prolongation of aging time, the fracture mode of the solder joint is transformed from ductile fracture to ductile-brittle mixed fracture. The shear strength is improved with appropriate Pb content; however, it will be decreased when the Pb content exceeds 22.46%.