Abstract
Recently, reliability assessment on the micro-joining for electronic apparatus attracts major attention of engineers and researchers in this field. Failure problems of the micro-joining have to be investigated from an interdisciplinary point of view, for the failure phenomena are caused not only by a mechanical effect but also by a metallurgical and/or electrochemical effect. For example, construction of brittle intermetallic compounds at Au wire/Al pad interface of ball bonding is a problem of metallurgical aspect, and electro-migration induced between soldering parts on high density printed circuit board is problem of electrochemical aspect. Though there are several micro-joining methods such as thermo-compression, ultrasonic bonding, micro-soldering and so on, a majority of micro-joining applied in electronic apparatus is micro-soldering. Therefore, it is an urgent problem to establish a valid evaluation method for solder joint performance under service conditions. A typical problem on this point is the solder cracking induced by temperature cycling, depending on the mismatch of thermal expansion coefficients of structural elements. In order to clear the failure problem of solder joint, fatigue failure mechanism of solder itself must be systematized.
The main purpose of the present study is to investigate the fatigue strength and strain behaviors of 60Sn/40Pb solder plate specimen under several repeated load conditions including impact load carried out at room temperature. And furthermore, room temperature creep tests were also carried out to discuss the correlation between cyclic fatigue and static fatigue of the solder.
The results of this study revealed a clear dependence of the fatigue life on the stress patterns; the lower was the frequency of stress cycle the lower was the fatigue strength. And the strength in impact fatigue showed the highest value. Then, the evaluation from the viewpoint of cumulative loading time indicated that the fatigue life of the solder could be well estimated by the cumulative loading time regardless of the type of stress pattern. And furthermore, the relationship of the stress vs. the cumulative loading time in cyclic fatigue well coincided with the creep rupture curve.
