Development of Micro-displacement and low-load fatigue tester and fatigue-strength estimating method for micro structures

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With the increasing need for high mount density, the BGA (Ball Grid Array) or CSP (Chip Size Package) soldering became the main trend of the electronics mount technology. As a result, the evaluation of the fatigue life of BGA solder joints is one of the most important problems to study the reliability of BGA packages. In this study, a micro-displacement and low load fatigue tester for the micro-structures was developed. Using the tester, the fatigue life of BGA CSP solder joints was studied, and fatigue reliability assessment method was established.The results of this study are shown as follows ;(1) A new testing machine suitable for fatigue testing for the micro-structures such as BOA or CSP solder joints was proposed, by utilizing a piezoelectric translator (PZT) for the main push/pull actuator and twin PZTs for measuring the load without dislocation.(2) Based upon the proposed concept, a new fatigue tester was developed.(3) Using this tester, the fatigue lire of BGA CSP solder joints were investigated, and the results of fatigue tests were used to develop a fatigue reliability assessment method for all kinds of BOA solder joints. Furthermore, three-dimensional FEA were carried out to get the associated fracture parameter, inelastic equivalent strain range. Based upon the experimental and analytical results, an estimation criterion for fatigue life of the solder joints was developed.