| Research Abstract |
On the thermal fatigue strength evaluation method, the result that thermal fatigue strength in the solder micro joining division can be evaluated by the Manson-Coffin rule is mainly reported. Therefore, thermal fatigue strength evaluation was carried out by the Manson-Coffin rule in Lead-Free solder in this study. The Lead-Free solder as an object was Sn-3.5Ag-0.75Cu, Sn-2Ag-7.5Bi-0.5Cu, Sn-3.5Ag-5Bi 3 types. Solder material generally melting point is low (around 200℃). And, the effect of the creep is considered, because the temperature rises to 125℃ in this test. However, the finite element analysis result showed that the effect of the creep was very little. And, the finite element analysis result showed that a material has the dependence of the strain rate. Next mechanical fatigue testing method would be selected as an acceleration test of the thermal cycling fatigue test method, and the test was carried out. And, the finite element analysis was carried out in order to clarify what kind of stress strain behavior has been generated in the soldered joints division. From those results, it was possible to carry out fatigue strength evaluation in the Lead-Free solder micro joining division by the Manson-Coffin rule. And, the thermal cycling test was carried out, and the result was compared with fatigue life curve given by the mechanical fatigue test. As the result, both agreed well. And that mechanical fatigue testing method is effective as an acceleration test of the thermal cycling test method. In addition, fatigue life strength in the Lead-Free solder micro joining and eutectic solder micro joining division was compared. In comparison with the eutectic solder, the result showed that fatigue life strength of the way of the Lead-Free solder might be excellent a little. From this fact, it was proven that the Lead-Free solder seemed to be effective as substitution metal that changes for the eutectic solder.
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