A figure of merit for mobile device thermal management

With mobile devices available in various sizes and shapes, it is challenging to think in a consistent and comparative manner about the effectiveness of the thermal management solutions that they employ. Here we define a universal thermal figure of merit - a dimensionless Coefficient of Thermal Spreading (CTS) - calculated using either numerical simulations or IR surface temperature imaging and can be used to compare the thermal design effectiveness of many mobile devices and power levels. Heat spreading at the mobile device surface becomes an important factor that impacts the overall device performance. In order to meet the various performance specifications (skin and junction limit temperatures), the processors have to be throttled to reduce the amount of power and avoid exceeding the temperature limits, which in turn reduces the device overall performance. The proposed CTS Figure of Merit quantifies the effectiveness of heat spreading within the device by means of the uniformity of the surface temperature, and addresses a long-time need to quantify the thermal design effectiveness of various mobile devices which are skin temperature limited. The CTS indicates how much a phone or other mobile device can be improved for the given shape and size/form factor. This paper includes details on the CTS Figure of Merit definition and governing equations, will quantify the design targets and how the CTS can be tested and improved.