Prognostics and Health Management of Lead Free Electronics Subjected to Single Steady-State and Multiple Cyclic Thermal Environments
Type of Degreethesis
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Requirements for system availability for ultra-high reliability electronic systems such as implantable biological systems, avionics and space are driving the need for advanced heath monitoring techniques for early detection of onset of damage. There are various state of the art diagnostics techniques like BIST, fuses and canaries currently in use today but they all provide very limited visibility into system reliability and remaining useful life of the system. In order to provide more insight into these aspects a different approach called Prognostics and Health Management (PHM) has been presented in this thesis. PHM resides in the pre-failure-space of the electronic-system, in which no macro-indicators such as cracks or delamination exist. The presented PHM methodologies enable the estimation of prior damage in deployed electronics by interrogation of the system state based on damage proxies. Prognostics Health Management approach presented in this thesis is used to estimate the residual life on an electronic system subjected thermo-mechanical loading. Health management and interrogation of systems state based on leading of failure has already been studied by Lall [2004, 2005, 2006, 2007, and 2008]. Data has been collected for leading of failure (Intermetallic growth in this case) for alloy system 99Sn0.3Ag0.7Cu second-level interconnects under the application of Isothermal Loading at 125°C. A non linear least square method called Levenberg-Marquardt algorithm is used for determining prior damage history. Further this PHM methodology is extended to cover electronics subjected multiple thermal environments. Electronic assemblies which are deployed in harsh environments may be subjected to multiple thermal environments during the use-life of the equipments. Often the equipment may not have any macro-indicators of damage such as cracks or delamination. So in order to access the damage caused to these electronics system there is need for tools and techniques to quantify damage in deployed systems. In this thesis a PHM based methodology has been presented that can be used for residual life calculation of electronics subjected to multiple thermal environments. For this study, Sn3.0Ag0.5Cu alloy packages have been subjected to multiple thermal cycling environments including -55°C to 125°C and 0° to 100°C. Assemblies investigated include area-array packages soldered on FR4 printed circuit cards. A damage-state interrogation technique is based on the Levenberg-Marquardt algorithm in conjunction with the microstructural damage evolution proxies has been used. The presented technique is applicable to electronic assemblies which have been deployed on one thermal environment, then withdrawn from service and targeted for redeployment in a different thermal environment. Different test cases have been presented to demonstrate the viability of the technique for assessment of prior damage, operational readiness and residual life for assemblies exposed to multiple thermo-mechanical environments. The correlation demonstrates that the presented leading indicator based PHM technique can be used to interrogate the system state in multiple environments and thus estimate the residual life of a component.