Design and characterization of nanowire array as thermal interface material for electronics packaging

To allow electronic devices to operate within allowable temperatures, heat sinks and fans are employed to cool down computer chips. However, cooling performance is limited by air gaps between the computer chip and the heat sink, due to the fact that air is a poor heat conductor. To alleviate this problem, thermal interface material (TIM) is often applied between mating substrates to fill air gaps. Carbon nanotube (CNT) based TIM has been reported to have excellent thermal impedance; however, because it is non biodegradable, its potential impact on the environment is a concern. In this thesis research, two types of TIMs were designed, synthesized, and characterized. The first type, Designed TIM 1, consisted of anodic aluminum oxide (AAO) templates with nanochannels (pore size=80nm) embedded with copper nanowires by electrodeposition. This type of nanostructure was expected to have low thermal impedance because the forest-like structure of copper nanowires can bridge two mating surfaces and efficiently transport heat one dimensionally from one substrate to the other. The second type, Designed TIM 2, was fabricated by sandwiching Designed TIM 1 with commercially available thermal grease to further reduce thermal impedance. It was expected that the copper nanowire structures would secure the thermal grease in place, thus preventing grease pump-out under contact pressure, which is a common problem associated with the usage of thermal grease. The morphologies of the two designed TIMs were studied using scanning electron microscopy (SEM), and their thermal properties were determined using ASTM D5470-06, the standard method for testing thermal transmission properties of thermally conductive materials. Experiments were conducted to evaluate the proposed TIMs, as well as commercially available TIMs, under different temperature and pressure settings. Experimental results suggest that the thermal impedance of TIMs can be reduced by increasing contact pressure or reducing thickness. Designed TIM 2 yielded 0.255?-cm2/W, which is lower than thermal grease and other available TIMs at the operating temperature of 50 to 60?. Considering the application limitations and safety issues of thermal grease, phase change material, and CNT-based TIMs, our designed TIMs are safe and promising for future applications.