Sustained damage and remaining useful life assessment in leadfree electronics subjected to sequential multiple thermal environments

Field deployed electronics us often subjected to a combination of thermal aging and thermal cycling. The thermal cycle magnitudes may vary over the lifetime of the product. Long-life systems may be re-deployed several times over the use life of the product. Aging has been previously shown to effect the reliability and constitutive behaviour of second-level leadfree interconnects. Often the equipment may not have any macro-indicators of damage such as cracks or delamination. The ability to identify impending failures in systems and their sub-components has great potential to mitigate the risks of unanticipated failures and reduce the support costs. The presented approach in this paper is intended to address the need for tools and techniques for prognosticating the prior accrued damage and the remaining useful life of the product prior to redeployment. Leadfree assemblies with Sn3Ag0.5Cu solder have been subjected to various duration-combinations of thermal aging at 125°C, thermal cycling from -40°C to 125°C and thermal cycling from 0°C to 100°C. The presented methodology uses leading indicators of failure based on micro-structural evolution of damage to identify accrued damage in electronic systems subjected to sequential stresses of thermal aging and thermal cycling. Leading indicators studied in this paper include the phase growth parameter and the intermetallic thickness. Damage equivalency relationships have been developed to map damage accrued in thermal aging to the reduction in thermo-mechanical cyclic life based on damage proxies. Accrued damage between different thermal cyclic magnitudes has also been mapped for -40°C to 125°C and 0°C to 100°C thermal cycles. The presented method for interrogation of the accrued damage for the field deployed electronics, significantly prior to failure, may allow insight into the damage initiation and progression of the deployed system. The expected erro- with interrogation of system state and assessment of residual life has been quantified.