Reliability and Degradation of Bulk and Interfacial Properties in Electronic Packages under Extreme Operating Conditions

Abstract

The durability of electronic packages used in harsh environments is of vital importance to the automotive underhood electronics, aerospace, and high-performance computing industries. Such applications demand materials capable of withstanding long-term exposure to elevated temperatures, humidity, and mechanical stressors without degrading structural integrity and thermal performance. Underfills, thermal interface materials (TIMs), and epoxy mold compounds (EMCs) are key materials that help reduce thermomechanical stresses, enhance structural integrity, and facilitate better heat dissipation in electronic packages. Yet, the materials' deteriorating properties over time result in accelerated stress accumulation, interfacial delamination, and premature failure of packages. The dissertation elaborates on the development of underfill properties under isothermal aging and hygrothermal conditions and examines their influence on packaging's long-term reliability. The development of mechanical and thermal properties of the underfills is assessed using dynamic mechanical analysis (DMA), polarized optical microscopy, and finite element modeling (FEM) to analyze their performance under different environmental conditions. The findings indicate that underfill oxidation has a significant influence on mechanical behavior, including package warpage, stress distribution, and reliability. The research incorporates conventional and non-PFAS underfills, with an emphasis on viscoelastic behavior and oxidation resistance. The comparative study of conventional and non-PFAS underfills highlights the advantages and limitations of novel materials for application in next-generation packaging. The study provides new information on material selection strategies where mechanical property retention and environmental resistance are paramount in determining long-term performance. A competing risk model is established for estimating the collective impact of multiple degradation mechanisms on package failure. The model integrates the non-linear viscoelastic behavior of underfills from DMA tests and linear properties of TIMs into finite element models of FCBGA packages. By considering concurrent effects such as linear and non-linear properties of underfills, the model is a good foundation for reliability prediction. Furthermore, the research investigates the fracture behavior of TIM/copper and EMC/substrate interfaces using experimental fatigue and monotonic test methods. The moisture diffusivity, activation energy, and acceleration factors are extracted to project the long-term stability of these materials under conditions that mimic actual environments. Furthermore, data from accelerated life testing is coupled with predictive models to enhance the knowledge of time-dependent failure mechanisms and thereby connect laboratory experiments to actual operating conditions. Aside from the reliability predictions, actual geometry modeling of QFN packages is accomplished with X-ray Micro-CT. In contrast to conventional idealized models, incorporating actual manufacturing variations in FEM simulations improves accuracy in prediction by taking into account realistic material distributions and defects. Surface Evolver techniques are used for modeling actual solder ball shapes, incorporating the actual geometry in interconnects that influence stress concentrations and fatigue life. The findings of the current study are important for the development of valid predictive models for electronic package reliability and offer fundamental knowledge of underfills, TIMs, EMCs, and interface behavior under harsh operating conditions. By combining experimental characterization, data-driven modeling, and cutting-edge simulation techniques, this research offers a unified platform with the vision of optimizing packaging materials. The platform is employed to guide the pursuit of sustainable and robust solutions for high-performance electronic applications. The outcomes derived from this research will allow design for reliability (DfR) practices for future semiconductor packaging technologies to be improved and therefore facilitate the creation of more reliable and thermally stable electronic products.