Investigations on Damage Mechanics and Life Prediction of Fine-Pitch Electronics in Harsh Envirorments

Abstract

Increased use of sensors and controls in automotive applications has resulted in significant emphasis on the deployment of electronics directly mounted on the engine and transmission. Increased shock, vibration, and higher temperatures necessitate the fundamental understanding of damage mechanisms which will be active in these environments. Electronics typical of office benign environments uses FR-4 printed circuit boards.

In this dissertation, damage mechanics and prognostication techniques for thermo-mechanical reliability of fine-pitch electronics in harsh environments have been studied. The research encompasses investigations on 63Sn37Pb, 62Sn36Pb2Ag leaded and 95.5Sn4Ag0.5Cu leadfree solder alloy systems in conjunction with high Tg metal-backed laminate assemblies. Damage relationships have been developed on plastic packages, with predominantly NSMD pads. The focus on lead free solder alloys (95.5Sn4.0Ag0.5Cu) is motivated by legislation that mandates the banning of lead in electronics, due to environmental and health concerns.

In addition, electronic-system prognostication methodologies have been developed and demonstrated with data on leading indicators of failure for accurate assessment of product damage significantly prior to appearance of any macro-indicators of damage. The focus of prognostication techniques and models is thermo-mechanical loads typical of automotive underhood applications. The current state-of-art in managing system reliability is geared towards the development of predictive models for un-aged pristine materials. The research is targeted at need for methods and processes which will allow interrogation of complex systems and sub-systems to determine the remaining useful life prior to repair or replacement. Damage proxies have been correlated to measures of damage progression.