b'Automotive | Engineer Innovationautomated driving functions. This encompasses all of the vehicles electronic chassis and safety systems to optimum driver assistance in all driving systems. A typical current generation ADCU us shown in Figure 1. Figure 1 shows aspects of the cooling solution, being a finned metal enclosure, typically bolted to the chassis of the vehicle to conduct heat from the system. Most of the components seen would be represented directly within the thermal model. A typical mounting arrangement is shown in Figure 2 for a similar unit, which reveals further aspects of the thermal design, through the use of gap pads between key components and the enclosure, andFigure 2: Slice through Assisted & Automated Driving Control Unit showing mountingconduction from the edge of the PCB. modeler for geometry handling, so we The thermal design in such systems iscan directly transfer a clean error-free very challenging for a number ofCAD model of the entire board assembly reasons. The system has to withstand awhile retaining all the assembly, part maximum underhood temperature ofand feature information. This allows us 80C as its ambient condition. Theto easily attach materials and boundary orientation of the system often cannotconditions for the thermo-mechanical be guaranteed, which is why the unitsimulation. shown in Figure 2 uses a pin fin arrangement for the heatsink. However,The thermo-mechanical simulations we the most challenging aspect of theperform can also include the stiffening design is that the thermal design needseffect of the components on the board, to ensure the thermo-mechanicalwhich have an effect on the prediction reliability of the unit. While componentsof the effective, i.e. von-Mises stress, have to be kept sufficiently cool, theand the out-of-plane deflection of the high underhood temperatures meanboard, shown in Figure 3. that the electronics are subjected to far more thermo-mechanical stress due toUsing a lumped treatment for the the temperature changes during a driveboard can significantly under or over-cycle than would be experienced by, forpredict the magnitude and location of example, most consumer electronicsthe maximum deflection. Using a products. For automotive applications,lumped representation of the board the thermal and thermo-mechanicalalso totally fails to capture the variation design go together hand-in-hand.in von-Mises stress shown in Figure 3. Our preferred approach is to performThe high level of geometric detail we the thermal design in Simcenterare able to work to in Simcenter Flotherm XT software. This softwareFlotherm XT also contributes to the allows us to build a thermal model thataccuracy of the stress and deflection takes into account all the componentspredictions we are able to make, as we on the board, usually using 2-Resistorget a finer grain resolution of models, plus the board layers with layertemperature throughout the structure. copper detail, this information is needed for a highly-accurate thermalGenerally it is impossible to replicate simulation using a geometricthe CFD simulation thermal results representation of the board assemblydirectly in finite element software, as that can be used directly for ourthe CFD simulation predicts thermo-mechanical stress simulations.temperatures throughout the solid and An advantage of using Simcenterfluid regions, and the local surface heat Flotherm XT is that it uses a solidtransfer rate, which typically varies 53'