Reliability Optimisation and Lifetime Modelling of micro-BGA Assemblies in Harsh Environment Applications

A micro-Ball Grid Array ($\mu$BGAs) is a Chip Scale Package (CSP) architecture that becomes increasingly deployed by electronics manufacturers and used in applications ranging from consumer electronics to high-reliability and high-value equipment operated in harsh environments. In the latter case, design engineers of high-reliability electronics must develop and adopt novel assembly design solutions and new assembly materials that enhance the reliability of such commercial off-the-shelf components. This paper details the results from a comprehensive reliability test program on assessing the thermal fatigue life of $\mu$BGA board-level interconnects (quaternary alloy SnPbAgCu solder composition) and from the related physics-of-failure thermo-mechanical modelling. Several package-board assembly designs developed with rigid and compliant printed circuit board (PCB) materials, and with/ without resin application are investigated and discussed. The thermo-mechanical simulation results are used to provide insights into the solder joint physics of failure. The findings confirmed that the reliability of $\mu$BGAs can be significantly impacted through assembly design alterations, and lifetime of solder joints can be increased by factor 10X and more. The modelling predictions for solder joint damage and the experimental failure data are used to develop a lifetime model for the thermal fatigue life of $\mu$BGA and similar CSP architectures.