Power Module with Series-connected MOSFETs in Flip-chip Configuration

Power module design is needed for high system performance and reliability, especially in terms of high efficiency and high power density. Low parasitic impedance and thermal management is desired for the lower power loss and device stress. For power module with high efficiency and improved breakdown voltage, this thesis proposes a novel series-connected power MOSFETs module. Three IRF7832 MOSFETs (30 V breakdown voltage) in series are simulated in a chopper circuit. The drain-source voltage sharing in switching off-mode shows that the devices can share voltage within their breakdown ranges. The switching characteristics are studied, and the switching energy losses without parasitic inductance and with 5 nH parasitic inductances are 203.38 μJ and 316.49 μJ, respectively. The critical parasitic inductance is the one connecting the source of the upper MOSFET and the drain of the middle MOSFET. The switching energy loss due to critical parasitic inductance is about 44.4% of the total switching energy loss. The layout is designed for the double-substrates directbond module and wire-bonded module using direct-bond-copper (DBC) substrate. Based on layout dimensions and packaging materials, the packaging module’s parasitic parameters are obtained using Ansoft® Q3D extractor. Using parasitic inductance values from simulation, the switching energy losses of direct-bond module and wire-bonded module are 296.18 μJ and 238.99 μJ, respectively. Thermal management is then studied using Ansoft® ePhysics. The MOSFET junction-to-air thermal resistances of the double-substrate direct-bond module and the single-substrate wire-bonded module are 33C/W and 82C/W, respectively. Hence, by comparing the direct-bond module with a wire-bonded power module, direct-bond module shows lower parasitic impedances and better thermal management.