超低温下不同Pb含量焊点组织演变规律研究

Microstructure evolution of solder joints with different Pb content at ultra-low temperature

摘要:

通过自制四种不同Pb含量(0，4.67%，22.46%，37%)混装钎料制成Ni/钎料/Cu三明治焊点，置于-196℃超低温环境进行0、10、20和30天时效处理，研究Pb含量及超低温时效对焊点内部组织、IMC层演变规律以及力学性能的影响。结果表明，Pb含量的增加会促使焊点内部Pb相不断聚集，并随着时效时间的增加进一步粗化。超低温时效不会改变IMC层成分，但会促进IMC层缓慢向层状转变，并逐渐产生微裂纹与空洞，促使聚集的Pb相不断朝界面处转移形成隔离区，甚至部分镶嵌于IMC层内。随着时效时间的延长，焊点断裂方式由韧性断裂逐渐转变为韧脆性混合断裂，而适量的Pb含量对于焊点剪切强度具有提高作用，但当含量超过22.46%时再增加Pb含量则会降低焊点抗剪切强度。

Abstract:

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%), 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 times of 10 days, 20 days and 30 days, respectively. 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 will occur gradually by accompanied with the transformation of the scallop-like IMC into lamellar IMC. At the same time, the Pb element accumulates alone the IMC interface near the solder, and a Pb-rich layer will be 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 will be improved with appropriate increased of Pb element, however, it will be decreased as exceeding to 22.46% of Pb content.