SnPb焊点结构的高周疲劳行为检测与寿命表征方法

Characterization and measuring methods on the high-cycling fatigue behavior of SnPb solder joint

本文对SMT型的SnPb焊点结构(PC基板-SnPb焊料-陶瓷电阻结构)的高周疲劳(2×104～1×106循环次数)失效行为进行了扫描电子显微镜(SEM)原位观测试验和有限元分析.这些结果表明:SMT型SnPb焊点结构的高周疲劳裂纹主要发生在SnPb焊料与陶瓷电阻结合处(趾或踵toeorheel),而高周疲劳裂纹扩展主要在SnPb焊料表面或内部,表面疲劳裂纹扩展方向随基板上施加的应力增大而偏向基板一侧.同时,这些裂纹扩展长度与焊点几何形状相关,一般扩展长度在150μm以内并因为焊料与电阻或焊料与基板的界面开裂出现停顿.此外,用ABAQUS软件分析了基板上外加应力与焊料上响应应力间的比例关系.基于试验和有限元分析计算比较,试验中发现的裂纹萌生源及裂纹扩展方向均与有限元计算得到的最大应力或最大应变集中区域相一致.最后,提出了简便预测这类结构的高周疲劳寿命方法,且预测结果与试验结果吻合较好.

Electric circuits or packages in the large-scale integrated circuits and micro electro-mechanical systems are subjected to various effects of environmental conditions, such as mechanical or thermal fatigue impact loading etc. Therefore, the reliable evaluation technique of electric circuit is necessary to obtain enough experimental data of durability and reliability. The prediction of fatigue life, especially high-cycling fatigue life, of a solder joint is one of the most difficult problems in electronic industry. Successful fatigue life prediction of a solder joint depends on the a- bility of the modeling solder joint accurately. All accurate models have to be validated by experiments and practical applications. In this work, the experimental investigation and simulating analysis for the SnPb solder joint （SMT type） were carried out based on the scanning electron microscopy （SEM） in-situ technology. These results indicate that the fatigue crack initiation occurs at the heel or toe of SnPb solder joint, the fatigue crack propagates along a- bout 20-45° titled to applied stress direction in substrate and the fatigue crack propagation has a small deflection to the applied stress direction with increasing of applied stress. At the same time, the fatigue crack propagation length is limited to within 150 tLm because it is dependence on the geometrical size of solder joint. In addition, the response relation in solder alloy to applied stress in substrate was obtained based on the finite element （FE） analysis. There- fore, the prediction of fatigue life of solder joint was proposed based on the experimental data and simulation analysis and predication results agree good with the experimental data including to other literature.