Automotive electrical validation thermal tests analysis

The scope of electrical validation thermal tests is to check the parameters of each electric signal from the ECU (Electronic Control Unit) design and ensure it is within the specified range in all temperature conditions.A special setup must be created to collect all relevant electric signals from the PCB (Printed Circuit Board) to perform these tests in a thermal chamber. It is necessary to remove the ECU housing to access the test points easily. The oscilloscope probes are not qualified for the automotive temperature range (-40°C up to 85°C). Because of this, they need to be connected outside the thermal chamber via a port adaptor that facilitates the connection between oscilloscope probes and PCB test points. The connections via the port adaptor shall be as short as possible; therefore, the PCB must be placed as close as possible to the port adaptor, respectively, to the outside.If the housing is used, either one or more holes are needed in the housing, or the wires need to be taken out by the connector slot. Testing with housing will require longer wires, and this solution is less reliable. Longer wires affect the precision measurements more than the accepted tolerance.When using ECU housing, the heat is removed from the critical hot spots, from the top of the electronic components to the housing via thermal paste. Metal housing acts as a heatsink of components with thermal paste, significantly reducing their temperature. On the other hand, components without thermal paste metal housing bring additional heat, increasing their temperature.Different heat transfer paths from the main heat sources to the ambient are created when the ECU housing is removed. Critical electrical components will not transfer heat to the housing via thermal paste, and their temperature will increase more than in case the housing is in place. In this case, electrical components without thermal paste will have a lower temperature than in case the housing is in place. These differences mean different junction temperatures for electrical components, which leads to different current consumption, which leads to different power losses than reality.The current paper highlights the thermal behavior of both categories of components, with and without thermal paste, in two different cases, with and without housing, and shows examples of how electrical validation thermal test results should be analyzed.If a housing test is not possible, the heatsink solution shall be considered. A PCB-only solution is not recommended; it will provide false results, and overengineering solutions might be considered.