Heat spreaders and heat sinks for mixed convection electronic cooling.

摘要

This dissertation involves the development and experimentation/analysis of heat spreaders and heat sinks for the thermal management of electronics. Attention is focused on low-velocity cooling and high-conductivity substrates. The dissertation divides into three parts: Establishment of a test laboratory; experiments/analysis of a standard electronic package and an idealized heater-on-substrate; and the comparative testing of novel heat sinks.; The experimentation was conducted in a Thermal Measurement Laboratory established as part of this dissertation. The laboratory's equipment includes a rotatable wind tunnel, in-plane and through-thickness conductivity meters, a thermocouple fabrication/calibration station, a hot-wire anemometer calibration unit, and a data acquisition/control system.; Experiments are reported on low-velocity cooling of a plastic quad flat package (PQFP) and a three-dimensional heater-on-substrate geometry. The thermal effects of combined buoyancy and forced convection, orientation, substrate sizes, and thermal conductivity are investigated. The limits of mixed convection for the horizontal orientation, and of orientation effects from buoyancy-opposing to assisting conditions are identified. For velocities greater than 2.5 m/s, for all orientations, the thermal resistance of the PQFP shows a steep decrease, which is attributed to restarting of the boundary layer on the package.; An approximate analytical solution for the thermal resistance of an axisymmetric heater-on-substrate is presented for a substrate with a direction dependent conductivity. The solution reveals substrate geometries with low maximum temperatures which are mapped for typical Biot numbers. The effects of varying the radial and axial conductivity are investigated. In general, radial conductivity enhancement is beneficial for thin substrates desirable for electronic packaging. The approximate solution is adapted for the three-dimensional heater-on-substrate with the surface cooling coefficients estimated using heat transfer correlations.; Heat sinks with novel geometric fin arrangements are developed for natural and low-velocity convection. Seven novel fin arrangements are considered based on the principles of pressure drop minimization, boundary layer interruption, and flow deflection. The measured thermal performance of the novel heat sinks is compared with that of longitudinal-plate and pin-fin heat sinks. The pin-fin heat sink performs the best. This dissertation documents the modest heat transfer enhancement of the novel heat sinks, and reports their thermal performance in a comparative record.