August 2003

Detailed, board-level thermal simulations were carried out at the beginning of the design process, before fixing the locations of the key components on the board. Thermal engineer Marc Iliozer states “It was vital for me to work closely with the electronic engineers at this early stage, so that thermal solutions such as adding copper layers or thermal vias to reduce the temperature of critical components could be investigated and decided while there was still time to influence the component layout and board design. Working this way, we quickly arrived at a final solution which was acceptable from both electronic and thermal viewpoints.”

Throughout the design process, thermal simulations and measurements were combined, with infrared camera and thermocouple measurements being used to check and calibrate the thermal model predictions, and vice-versa.

Excellent correlation between IR measurements and thermal simulations were observed, even on such details as the copper tracks at the surface of the PCB (which are subject to a non-linear heating phenomenon known as “Joule heating”) and in the components themselves, where the thermal conductivity changes with temperature. Marc Iliozer states, “These comparisons confirmed the temperatures predicted by Flotherm, and gave us full confidence that the prototype motor control unit complied with thermal specifications. At the same time, the simulations allowed us to speed up and optimise the design, minimizing the weight of the product and therefore the costs of manufacturing. For mass-market products such as control units for cars, these cost savings can be huge.”