MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
Estimation of Thermal Fatigue Resistances of Sn–Ag and Sn–Ag–Cu Lead-Free Solders Using Strain Rate Sensitivity Index
Ikuo ShohjiKiyokazu YasudaTadashi Takemoto
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2005 Volume 46 Issue 11 Pages 2329-2334

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Abstract

A tensile test was conducted to evaluate thermal fatigue resistances of Sn–Ag and several Sn–Ag–Cu lead-free solder alloys. The test is based on the strain rate change method to obtain a strain rate sensitivity index, m. The m values were investigated at various strains during the tensile test until fracture. The plots of m and strain where m is measured showed a linear relationship. Therefore, the m value at zero strain, m0, and the gradient of the fitting line, k, were obtained by extrapolation. Using m0 and k values investigated, an estimation of the thermal fatigue resistance of the solder joint was attempted. The ranking of the reciprocals of m0 and k in the solders is relatively in good agreement with that of the thermal fatigue resistance of the solder joints, and thus m0 and k can be indexes to develop a new lead-free solder with the excellent thermal fatigue resistance. Moreover, the influences of the aging treatment on m0, k and the microstructure of the solder were also investigated.

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© 2005 The Japan Institute of Metals and Materials
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