| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 95 === The purpose of this study is to investigate the LCF properties of solder joints made of a promising lead-free solder alloy, Sn-3.5Ag-0.5Cu. Displacement-controlled LCF tests were conducted on the solder joint specimens under various loading conditions, including purely axial loading, purely shear loading and mixed-mode loading. The effect of multiaxial loading on the fatigue life and fracture mode was characterized. In addition, the difference in the uniaxial LCF life between solder joints and bulk solders was discussed by making a comparison with a previous study.
Experimental results showed the von Mises equivalent strain was a superior parameter to the maximum normal strain and the maximum shear strain in correlating the LCF life of solder joints under various loading modes. Several fatigue models were applied to describe the LCF lives of the given solder joint specimens subjected to different modes of loading. Among the applied approaches, KBM parameter and the von Mises equivalent strain provided the best unified correlation with the fatigue life of solder joint at all given loading modes through a single power law or a double law relationship.
Although a similar trend of load drop curve to that of the bulk solder was found for the solder joint, the LCF behavior under purely axial loading between the solder joint and bulk solder was different. Based on the fractography analysis results, the loading mode did not have a significant influence on the cracking path of the solder joint, as the fatigue fracture always occurred at the interface between the solder and copper pad for all the given loading modes.
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