3-D view of the packaged 650V/300A GaN half-bridge

The key technology involved includes: 1) ceramic insulation. A thin layer of ceramics is sandwiched between two copper layers. In this way, all G, D and S terminals of GaN devices are insulated from the heatsink. The first-layer copper connections are used to internally connect the top-switch S terminal with the D terminal of the bottom switch. The second layer of the copper is directly attached to the heatsink. Thermal grease can be used for better attachement, which however still yields much lower thermal impedance compared to state-of-art TIMs. Silicon gel will be used to fill the package for mechanical support and insulation; 2) smart PCB, which is essentially a multi-layer PCB with the decoupling cap to form the flux cancelling loop to offset the potential parasitic inductance. In addition, the gate-drive circuit of top and bottom switches, including the needed power supply are soldered on this PCB. Only PWM signals for top and bottom switches, i.e., PWM/T and PWM/B are to be provided by the control system. All connectors of this smart PCB will be directly soldered on the external control and power PCBs. Compared to bottom cooled devices using IMS, which essentially is one-layer board introducing high parasitic inductance, the proposed packaging approach adopts the extra multi-layer PCB to realize flux canceling. Compared to discrete switches, soldering dies in one package to form a half bridge yields much higher compactness.