Thermal Fatigue Life Estimation for Lead - Free Solder Joints

在热疲劳强度评估方法方面，主要报道了采用Manson-Coffin准则对焊料微连接区域进行热疲劳强度评估的结果。因此，本研究采用Manson-Coffin准则对无铅焊料进行了热疲劳强度评估。无铅焊料为Sn3.5Ag-0.75Cu型、Sn2Ag7.5Bi0.5Cu型、Sn3.5Ag5Bi3型三种。焊料的熔点一般较低(约200℃)。同时，考虑了蠕变的影响，因为在本试验中，温度上升到了125℃。然而，有限元分析结果表明，蠕变的影响很小。有限元分析结果表明，材料具有应变率依赖性。接下来，选择机械疲劳试验方法作为热循环疲劳试验方法的加速试验，并进行了试验。并对焊点进行了有限元分析，明确了焊点区域产生了什么样的应力应变行为。根据这些结果，可以根据Manson-Coffin准则对无铅焊料微连接分区进行疲劳强度评估。并进行了热循环试验，并与机械疲劳试验给出的疲劳寿命曲线进行了比较。结果，双方都很好地达成了一致。机械疲劳试验方法作为热循环试验方法的加速试验是有效的。此外，还比较了无铅焊料微连接和共晶焊料微连接的疲劳寿命强度。结果表明，与共晶焊料相比，无铅焊料的疲劳寿命强度可能略有提高。从这一事实证明，无铅焊料似乎是有效的替代金属的共晶焊料。

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.