Sn-Pb共晶系はんだの引張変形挙動と熱疲労特性

抄録

Tensile deformation characteristics of Sn-Pb eutectic system solder alloys have been investigated using a strain rate changing tensile test to obtain strain rate sensitivity index in order to correlate the behavior to thermal fatigue properties. Mechanical properties such as tensile stress and elongation were also obtained. These properties were compared Sn-Pb eutectic with Sn-Pb alloy containing small amount of Ag and Sb. The addition of small amount of Ag and Sb to Sn-Pb raised tensile strength and slightly decreased elongation. The alloys with elements showed finer microstructure and higher resistance to thermal fatigue than plain eutectic. The solution hardening and dispersion of Ag, Sn would be responsible to the enhanced tensile strength and resistance to thermal fatigue.
Strain rate sensitivity index m was repeatedly odtained during tensile test. The plots between m and the strain where m was measured showed straight relation, therefore, the extrapolated value of m to strain zero (m₀), and the gradient of the line (k) were used as a parameter for the estimation of thermal fatigue resistance. The m₀ decreased with the coarsening of microstructure due to aging at elevated temperature, the value could be used as a measure of coarsening of microstructure. The m₀ and k might be a good measure to estimate the thermal fatigue properties of solder alloys.