Thermal Performance and Reliability of Thermal Interface Materials: A Review

Interface thermal resistance minimization has been identified as a critical issue for the thermal management of electronic systems by the NEMI 2004 technology roadmap [1]. In current high-performance air-cooled microelectronic applications, the component-to-heat sink interfacial contact thermal resistance can be comparable to that of the actual heat sink [2]. Consequently, improved thermal interface materials are now the focus of much on-going research [2]–[4]. Typically, TIM applications are categorized as either die-to-heat spreader (TIM 1), die-to-heat sink (TIM 1.5), heat spreader-o-eat sink (TIM 2), or die-to-die carrier (die attach). An overview of thermal interface technologies is given in [4]–[6]. The majority of TIMs are polymeric-based materials, such as adhesives, greases, phase change materials (PCMs) and thermal pads. The thermal performance of such systems is constrained by their bulk thermal conductivity and interfacial thermal contact resistance. The bulk thermal conductivities of newly developed silver-filled or carbon fiber-loaded epoxy resin die attach adhesives, which are intended for power ICs, are claimed to exceed those of eutectic solders. However, to fully exploit the potential of such materials, the die attach assembly process (adhesive deposition, curing) requires careful optimization to ensure good structural integrity of the bulk adhesive (maximum surface area coverage, minimum voiding) and optimum bond line thickness [7]. Apart from progress in manufacturability, thermal interface minimization also requires new modeling techniques for micro/nano resistance across hard/soft interfaces, and an understanding of fatigue-induced failures in bonded interfaces.