Solder joint testing and failure analysis

Adhesively bonded joints within most electronic devices are constantly subjected to a complex combination of tensile-shear loading. These devices are also likely to undergo thermo-mechanical cycling during device processing and service and therefore, the joints are likely to have existing low-cycle fatigue cracks, which might adversely affect the joint mechanical integrity under various loading situations. A compact mixed mode (CMM) fracture specimen will be used in this report to study the effect of mix-modes on its failure mechanism and mechanical integrity. In this report, 2 types of specimens, namely SAC 387 solder bonded joint specimen without pre-crack, SAC 387 solder bonded joint specimen with pre-crack would be tested at room temperature at varying angles using an Instron tensile machine with a constant strain rate of 0.01/s. The SAC387 solder alloy is being chosen as it is a suitable candidate for the replacement of lead-bearing solder alloy used in the present electrical and electronics industry. In the case of SAC387 solder alloy, both the solder bonded joint specimens with and without pre-crack were found to sustain a mixture of brittle and ductile failure at the solder-copper (IMC) interface for mixed mode loading at 22.5o and 67.5o. It was suggested that the fracture could have propagate from the ductile bulk solder to the brittle IMC interface or vice versa. Both the solder bonded joint specimens with and without pre-crack were tested at 2 other different strain rates of 0.001/s and 0.1/s. Comparing all 3 strain rates, for solder bonded joint specimens without pre-crack, it was found that work hardening effect is present in between loading angles of 0o to 45o. With a higher strain rate, the load was also found to be higher. In all, the CMM fracture specimen had proven to have successfully generated the effect of mode-mixity on its failure mechanism and the understanding of joint integrity at different conditions.Bachelor of Engineering (Mechanical Engineering