Abstract
With the need to further reduce the size of electronic devices, securing the solder joint reliability of CSPs (Chip Scale Packages) is becoming important. There is a demand for an improvement in design technology that includes not only the average of the mounting lifetime but also the dispersion of the lifetime. However, the cause of the dispersion of the lifetime is extremely complicated and the analysis requires serious and difficult study. In this study, we paid attention to that tendency which is different from the Weibull distribution of the lifetime of the solder bump connection under thermal shock fatigue testing. From this, we propose a way of extracting different destruction modes from the sample group to explain each tendency. Moreover, we could clarify the main influences on the destruction mode from the correlation between the change of the inclination and the dispersion factor. This correlation shows that the dispersion in the solder resist opening diameter of the CSP solder joint caused the change of the mode of the fatigue destruction in this research, and brought about the large dispersion begin the fatigue lifetime. Moreover, the relation between the organized dispersion factor and the destruction mode could be verified using a fatigue crack developing simulation technology.
