ASSESSMENT OF ACCRUED THERMO-MECHANICAL DAMAGE IN LEADFREE PARTS DURING FIELD-EXPOSURE TO MULTIPLE ENVIRONMENTS

摘要

Electronic assemblies deployed in harsh environments mayrnbe subjected to multiple thermal environments during thernuse-life of the equipment. Often the equipment may notrnhave any macro-indicators of damage such as cracks orrndelamination. Quantification of thermal environmentsrnduring use-life is often not feasible because of the datacapturernand storage requirements, and the overhead on coresystemrnfunctionality. There is need for tools and techniquesrnto quantify damage in deployed systems in absence ofrnmacro-indicators of damage without knowledge of priorrnstress history. The presented PHM framework is targetedrntowards high reliability applications such as avionic andrnspace systems. In this paper, Sn3.0Ag0.5Cu alloy packagesrnhave been subjected to multiple thermal cyclingrnenvironments including -55 to 125C and 0 to 100C.rnAssemblies investigated include area-array packagesrnsoldered on FR4 printed circuit cards. The methodologyrninvolves the use of condition monitoring devices, forrngathering data on damage pre-cursors at periodic intervals.rnDamage-state interrogation technique has been developedrnbased on the Levenberg-Marquardt Algorithm inrnconjunction with the microstructural damage evolutionrnproxies. The presented technique is applicable to electronicrnassemblies which have been deployed on one thermalrnenvironment, then withdrawn from service and targeted forrnredeployment in a different thermal environment. Testrncases have been presented to demonstrate the viability ofrnthe technique for assessment of prior damage, operationalrnreadiness and residual life for assemblies exposed tornmultiple thermo-mechanical environments. Prognosticatedrnprior damage and the residual life show good correlationrnwith experimental data, demonstrating the validity of thernpresented technique for multiple thermo-mechanicalrnenvironments.