System Level Thermal Optimization of an Automotive Lightning Module Incorporating Several Power Devices

The conjugate thermal performance of microelectronics module incorporating several power packages and additional passive components in a custom environment is evaluated and further optimized using numerical simulation and experimental validation. The automotive industry deals on a daily basis with multiple packaging and module-level thermal issues when reducing the size of components for a lightning system in a car, while managing the routing of very high current. The study provides a better understanding of the strengths and weaknesses of the IC incorporation into a system module level, for both present and future product development. The reference design is evaluated at a system level, and several improvements are identified to enhance the overall thermal performance of the lightning system. The main concern is related to the possibility of exceeding the thermal budget for a large system incorporating several PQFN (Power Quad Flat No-Lead Package) packages with additional heat dissipation devices in an enclosure, at an external ambient temperature of 85°C. Due to the compactness of the device, there are only limited solutions to extract the heat from the high power dissipation system. The impact on the thermal balance of the trace dissipation, the location and size of the pins connecting the two boards (motherboard and daughter board) forming the system, the header heating and other passive components under various powered conditions are evaluated. A revised model includes additional pins (reduced diameter), modified motherboard and harness structures and their locations; the impact of additional heater traces on both top and bottom surfaces of the motherboard, and a modified daughter board design, is also evaluated. The resulting peak temperatures range from 118.3°C to 137.3°C and the corresponding junction-to-ambient thermal resistances (Rja) vary from 8.4°C/W to 8.8°C/W. Rja is defined as the temperature difference between the peak device and ambient divided by the total power dissipation of the PQFN packages. An optimized design is further evaluated, with lowered thermal resistance from the motherboard, the board-to-board pins, the junction box board, and the wiring harness. The thermal budget is satisfied, as the peak temperatures reached by the two designs are below the 150°C limit. Additional experimental results are used to benchmark the simulation results, within 1–6% accuracy.