Material Property Evolution of Underfills Encapsulants, Electronic Molding Compounds, Thermal Interface Materials and Magnetic ACAs

Abstract

The evolution of material properties in electronic packaging plays a critical role in the reliability of semiconductor devices operating in harsh environments. This dissertation investigates the thermo-mechanical behaviors of underfill encapsulants, epoxy molding compounds (EMCs), thermal interface materials (TIMs), and magnetically oriented anisotropic conductive adhesives (ACAs), emphasizing their viscoelasticity, thermal stability, and interfacial integrity under high-temperature aging. Underfill materials, critical in flip-chip technology, were characterized for their ability to mitigate coefficient of thermal expansion (CTE) mismatches between silicon dies and organic substrates. Accelerated aging tests revealed the degradation mechanisms affecting their mechanical properties and thermal reliability. DMA analyses identified changes in storage modulus, loss modulus, and glass transition temperature (Tg), demonstrating their temperature-dependent viscoelastic behavior. For EMCs, long-term aging studies highlighted the influence of filler content and microstructure on thermal and mechanical properties. High silica filler concentrations, exceeding 80%, contributed to superior thermal stability but introduced challenges in fatigue performance. Finite element modeling elucidated stress distributions at the wire interface, correlating material aging with increased stress accumulation. TIMs were evaluated for their efficiency in reducing thermal resistance between microelectronic components. Conventional greases and phase-change materials demonstrated limitations in high-power applications due to viscosity-induced reliability issues. Novel TIM formulations incorporating carbon-based fillers, such as carbon nanotubes and graphene, exhibited superior thermal conductivities, though their widespread adoption remains constrained by cost considerations. Magnetically oriented ACAs were explored for their potential in flexible and stretchable electronics. By aligning conductive particles under a magnetic field, these materials achieved directional conductivity and robust mechanical performance. Experimental and finite element studies demonstrated enhanced interconnect reliability under mechanical and thermal cycling. This work provides valuable insights into material design and selection strategies for electronic packaging, addressing challenges posed by elevated temperatures and mechanical stresses. The findings contribute to the advancement of packaging technologies, enabling reliable performance in applications ranging from consumer electronics to automotive and aerospace systems.