Thermal Interface Materials in Electronic Packaging

Abstract

With the continual increase in cooling demand for electronic packaging, there has been an increased focus within the microelectronics industry on developing high performance thermal solutions. Thermal interface materials (TIMs) play a key role in thermally connecting various components of the thermal solution. As electronic assemblies become more compact and there is an increase in processing bandwidth, escalating thermal energy has become more difficult to manage. The major limitation has been nonmetallic joining using poor TIMs. The interfacial, versus bulk, thermal conductivity of an adhesive is the major loss mechanism and normally accounts for an order magnitude loss in conductivity per equivalent thickness. The next generation TIM requires a sophisticated understanding of material and surface sciences, heat transport at submicron scales, and the manufacturing processes used in packaging of microelectronics and other target applications. Only when this relationship between bond line manufacturing processes, structure, and contact resistance is well understood on a fundamental level, will it be possible to enhance interfacial thermal conductance and advance the development of miniaturized microsystems. TIMs are widely needed to improve thermal contacts for facilitating heat transfer in electronic packaging, such as that associated with the flow of heat from a microprocessor to a heat spreader or a heat sink in a computer. A TIM is commonly in the form of paste, solder, or a resilient sheet that serves to fill a gap between the two adjoining surfaces. The resiliency helps the conformability. The performance of a TIM is enhanced by conformability of the interface material to the topography of the mating surfaces because the air residing in the valleys in the surface topography is thermally insulating and should be displaced by the interface material. This chapter will discuss interfacial conduct mechanism and review current status and future trends of commercial and advanced TIMs, including metallic, organic, graphite, hybrid, and nanotechnology-based TIMs.