Models for thermal contact resistance metal polymer interface models for friction and heat transfer for microchannels

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Advances in functionality, speed, and performance of all microelectronic devices such as cell phones, notebooks, and high end servers have resulted in significant increases in heat which is produced at the device level. The heat must cross many interfaces formed by different materials (e.g. metal/metal, metal/polymer, polymer/polymer) before it is dissipated into the ambient through heat sinks. To ensure continuous functionality, the temperature of the devices must be maintained below certain critical levels. This requires the overall thermal resistance from the device to the ambient to be reduced and maintained at low levels over long periods of time. The overall resistance consists of several spreading-constriction and contact resistances in series arrangement. The thermal resistance of the heat sink is an important part of the overall resistance budget. Experimental research is being done to reduce the thermal resistance and the pressure drop of heat sinks by novel designs, and the use of new materials and cooling fluids. It is proposed to replace the conventional heat sinks with a system of microchannels of noncircular cross section such as trapezoidal or double trapezoidal which are etched into silicon. The hydraulic diameter of the microchannels is about 100 micrometers and the length may be several millimeters. Preliminary experimental results for microchannels show that they can outperform pin fin heat sinks by a factor of 2-3. However, little is known about the underlying transport mechanisms and whether the friction and heat transfer correlation equations developed for macrochannels are applicable for microchannels. All Canadian microelectronics companies are facing these severe thermal and hydraulic problems. The proposed experimental and modeling research has two parts: 1) Research on thermal spreading and contact resistances with different metal/polymer interfaces will yield accurate data, correlations and models for predicting the interface resistances. The data and correlations can be used by industries to rank the polymers. 2) Research on fluid flow and heat transfer in microchannels will produce thermofluids models and correlations to predict friction factor, pressure drop, and heat transfer correlations.