Interrogation of System State of Lead-Free Electronics Subjected to Mixed Sequential Steady-State and Cyclic Thermal Environments
Type of Degreethesis
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Electronic assemblies deployed in harsh field environments may be exposed to single and multiple thermal environments during their service life. In real world setting it is often required to know during the service life of the system what is the amount of life consumed well before the actual failure occurs to schedule maintenance well in advance. The thermal conditions can change according to the change in the usage profile or also during redeployment from one field environment to another. For example in case of defense applications, military equipments come back from a particular field environment and are redeployed in different field environments after certain time intervals. Or in case of space missions the electronic systems embedded in the space equipments have to undergo different operational temperatures depending on the field conditions. It is important to note that different field environments have different magnitudes of damage incursions on electronic systems. Also electronic systems are often stored for a very long time before they are deployed in the intended environment. It is extremely important to quantify the expended life during storage especially for electronic systems used in mission critical applications. Although ambient temperature storage does not lead to any macro indicators of failure like cracks or de-lamination but it is well known that aging has an adverse effect on the life of electronics. Modern day electronic systems perform well when exposed to such multiple harsh environments and often times may not fail before their designed service life however the latent damage incurred at each stage can not be neglected and has to be taken in to account to avoid catastrophic failures and system down time in the field. Quantification of thermal environments during use-life is often not feasible because of the data-capture and storage requirements, and the overhead on core-system functionality. Thus there is a growing need to develop and demonstrate technologies that can monitor and predict the remaining useful life (RUL) of electronics in single thermal environments and also assess operational readiness of the electronic system during redeployment. Proposed prognostic models are based on physics-of-failure based damage-proxies of second level solder interconnects found in today’s commercially available high I/O packaging architectures. Test vehicles have been carefully selected for the development and implementation of the models so that they are relevant to the current packaging trends. Prognostic framework involves the use of condition monitoring devices for gathering data on damage pre-cursors at periodic intervals. The presented Prognostic Health Management (PHM) framework lies in the pre-failure space without any knowledge of prior stress histories i.e. in the absence of macro-indicators like cracks or de-lamination. In this thesis, test cases have been presented to demonstrate the viability of the approach for assessment of prior damage, operational readiness, cyclic life reduction due to long-term storage and residual life for electronic assemblies exposed to single and multiple thermal environments.