A detailed transient thermal study for a Remote Keyless Entry System with dynamic heat sources is performed using numerical simulations. The SmartMOS-type device is packaged in a 54 lead SOIC (small outline IC) package with an exposed copper slug. The package is attached to a 4-layer PCB with thermal vias embedded in the board. The challenge resides in the transient thermal interaction between several dynamic heat sources (channels), activated in a sequential fashion following different powering profiles and patterns. The main purpose of the device is to wirelessly provide a communication path between the remote and the receiver placed in the car, so the distance and the signal strength between the two are paramount for an optimal operation. The signal strength is directly associated with the voltage (and associated powering) levels. Several operating scenarios are evaluated by modifying the system design (thermal via pattern) and varying both power dissipation and duration levels. The study starts with just one channel dissipating power, followed by activating the entire dynamic system comprised of six channels dissipating each powers reaching up to 22W at different time intervals. The transient thermal behavior of each source is analyzed during the process. Results indicate that the system dissipating over 14V exceeds the thermal budget (150C) after only 3 powering cycles. Based on the analysis of the complex temperature fields for the multiple dynamic source system, the authors identify alternative power profiles to improve the thermal performance of the overall wireless system, by splitting the power in selective channels and by modifying the power sequence. Several additional cases are further investigated, and the optimized power profiles indicate that they satisfy the thermal budget under various operating conditions and several multiple cycles, while still maintaining the device voltage at 14V levels. A thorough study of the transient patterns and needed system improvements are included.

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