Study on Thermal Fatique Life Prediction of Micro Soldered Joints

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Torsional fatigue tests and creep tests were carried out on a 60Sn-40Pb solder. In both tests three temperatures (303-333K) were used, and in the fatigue test five cycling frequencies (0.001-5.0Hz) were used. An evaluation method for the solder fatigue life under relatively high temperature or low cycling frequency was proposed from the test results, nothing that the characteristics of fatigue under the above mentioned conditions were similar to the creep characteristics. Furthermore, this evaluation method was applied to the estimation of the crack initiation life of through-hole-type joints. By comparing the estimated values with the experimental ones it was clarified that this method was valid for the assessment of the crack initiation life of solder joints.To predict the fatigue life of soldered joints owing to the cyclic bending of the substrates when carrying movable electronic equipments, we conducted the fatigue tests by bending the substrates cyclically. As a result of the fatigue tests, it was shown that the fracture life was predicted well by Manson-Coffin's law using the equivalent plastic strain ranges as parameters and the life prediction equation was determined. Furthermore, the easier prediction method that the fracture life was about five times the crack initiation life was obtained.Finally, the state of the art of the research on fatigue life prediction of micro soldered joints was reported.