Explicit Finite Element Modeling in Conjunction with Digital Image Correlation Based Life Prediction of Lead-Free Electronics under Shock-Impact
Type of Degreethesis
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Increasing demand for smaller consumer electronics with multi-function capabilities has driven the packaging architectures trends for the finer-pitch interconnects thus increasing chances of failure of the electronic packages under shock and vibration environment. In this work, digital image correlation (DIC) in conjunction with ultra high speed cameras for full-field measurement of transient strain has been investigated. DIC data has been used as input for the finite element models for development of transient strain histories in second-level interconnects. Test boards according to JEDEC standard subjected to shock and vibration at zero horizontal drop orientation were examined. The effect of sequential stresses of thermal aging and shock–impact on the failure mechanism has also been investigated. The thermal aging condition used for the study includes 125°C for 100hrs. Solder alloy system studied include Sn1Ag0.5Cu, Sn3Ag0.5Cu and 96.5Sn3.5Ag. Explicit finite element modeling approaches for second-level package in drop and shock of electronic assemblies have been developed without any assumptions of geometric or loading symmetry. Approaches examined include smeared property with conventional-shell global model, Timoshenko-beam element with continuum shell element global model, node-based explicit sub-model and cohesive zone failure model. Model predictions have been correlated with experimental data. Relative damage-index based on the lead-free interconnect transient strain history and component’s survivability envelope has been developed for life prediction of lead free electronics alloy systems. Damage index based survivability envelope is intended for component integration to ensure reliability in extremely harsh environments.
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