Thermal design based on surface temperature mapping

Abstract

A method of extracting a conservative thermal model from an existing PCB assembled converter is investigated. This improves upon thermal management by increasing the thermal management contribution of the PCB itself. A thermal calibration loop is proposed in which a given converter is analyzed and data extracted, in order to create a thermal map of the surface temperature from which the component layout and thermal profiles can be estimated. Thermal figures of merit are vital to quantify the thermal adjustments, recorded in this thermal map, which are required during thermal calibration. The thermal figures of merit are also flexible enough to allow for specific optimization objectives such as high power density, or overall reliability. Two graphical means to predict temperature profiles required in the thermal calibration loop have been investigated: a thermal resistor network method with a purely analytical approach, suitable for relatively small systems where the geometry and loss analysis are simple (fewer than ten components), or a more elaborate method using a finite difference method algorithm, implemented in a spreadsheet environment. Both provide flexible means for PCB thermal layout and provide straightforward graphical visualization. A case study illustrates the complete design method.