Thermal management challenges in the passive cooling of handheld devices

This study explores the limits of cooling for handheld devices based on both testing and simulation under various conditions and provides guidelines for maximizing the amount of power that can be dissipated in these small form-factor devices. The factors affecting the maximum possible power dissipation are the available surface area and surface finishes, selection of the outer shell materials, thermal interface materials, heat spreaders and air gaps. In most cases, the limiting factor in the thermal design of these devices is not the temperatures of the internal components but the temperature of the external surfaces since these are in direct contact with the skin of the user. There have been studies that address the maximum allowable comfortable touch temperature of a handheld device. This study presents methods for maximizing the internal power dissipation of these devices while limiting the touch temperatures to the maximum comfortable limits.