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A PCB-Embedded 1.2 kV SiC Half-Bridge Module for EV On-Board Charger Applications

Hardware prototype
Fig. 1. The PCB-embedded half-bridge module.
  In this work, the PCB-embedded 1.2 kV SiC MOSFET half-bridge module with integrated gate drive circuitry seen in Fig. 1 was designed and analyzed for use in a 22 kW electric vehicle on-board charger (OBC). The die embedding was performed by AT&S using their PlAnaR Surface-Embedded Component (PARSEC) technique which allows for gate and source electrical connections to be made with copper-filled microvias. The design methodology used to create this module is based on understanding the tradeoffs between thermal and electrical performance in PCB-embedding and using that knowledge to achieve the performance required by this application. To minimize the thermal resistance of the FR4 layers, microvias were used to connect the source-side and drain-side inner layers to their outer layer counterparts. 4 oz and 3 oz copper layers were used for the inner and outer layers, respectively, to balance the tradeoff be-tween heat spreading and gate drive manufacturability. The gate drive circuitry was integrated to reduce loop inductances.

  Following the design and manufacturing, the PCB-embedded half-bridge modules were experimentally tested to measure their performance. The source-side and drain-side junction-to-case thermal resistances were measured to be 0.41 K/W and 0.17 K/W, respectively, using the JEDEC 51-14 standard and a Phase 12 B Thermal Analyzer. Under similar operating conditions, the PCB-embedded half-bridge module achieved 5.6 times lower voltage overshoot during turn-off and 0.5% higher efficiency than a TO-247 package containing the same SiC MOSFET. With the help of soft switching and low loop inductances, the measured peak efficiency and power density of the 22-kW three-phase ac-dc converter prototype with six PCB-embedded half-bridge modules seen in Fig. 2 are 98.2 % and 182 W/in3, respectively.

  The experimental results obtained in this work provide evidence that PCB-embedding is a viable packaging method for use in electric vehicle OBCs. The integrability, power density, and thermal and electrical performance afforded by PCB-embedding makes it a great candidate as a packaging method for SiC MOSFETs. The large-scale adoption of PCB-embedding in power converters hinges on reducing manufacturing costs and gaining a better understanding of the failure mechanisms seen in power and thermal cycling.
Hardware prototype
Fig. 2. A 22-kW three-phase ac-dc converter prototype with six PCB-embedded half-bridge modules plugged into the motherboard containing the PCB winding coupled induc-tors.

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