June/July 2021

14 PCIM EUROPE 2021 www.pcim.mesago.com Issue 3 2021 Power Electronics Europe www.power-mag.com Embedding Technology, means integration of WBG-devices into PCB material, is reflected in the working group of Automotive Qualification Guideline (AQG- 324) by implementation of this technology. Losses in half bridges The effect of stray inductances has been analyzed considering the MOSFET’s non-linear junction capacitance. The results show that the source capacitance L S affect the switching transient more than the others inductances - even small values produce significant negative effects. For this reason, during the design phase, the source connection is crucial to reduce the switching losses. On the other hand, the drain inductance L D affect less than the waveforms, but it is responsible for the overshoot on V DS . Therefore L S must be kept low to avoid that V DS let reach values higher than the breakdown voltage. As shown in Figure 1 the parasitic of a Si half-bridge are affecting the switching losses. Especially the source inductance L S , which is evident on High-side as well on Low-side MOSFT is critical for increasing electrical losses. The embedding technology is well known as an enabler to reduce electrical losses and improve performance of modules with embedded Si devices. One reason for this is the direct interconnection realized by galvanic copper deposition. As shown in Figure 2 the R DSon values can be reduced with an embedded concept by using the same Si MOSFET in a SMT package and an embedded in PCB as bare die. With the capability of miniaturization using embedding technology the dimensions of the packages and modules are shrinking. Because embedded constructions are much thinner than conventional multilayer and SMT packaged components, the loop inductance is reduced drastically. For the characterization of the switching behavior of the demonstrator, the double-pulse-measurement is an established method. Figure 3 shows the switching-off behavior of the SMT benchmark module, Figure 4 of the embedded module. In general, the embedded module shows good switching behavior, especially in comparison to the SMT benchmark module. This is realized by low inductive layouts for embedded circuits (short paths). The over-voltage and the swinging of the Drain-Source-voltage can be reduced which results in less switching losses. By reducing the switching losses the switching on and off time can also be improved and a faster switching is possible. Embedded SiC half-bridge A major benefit of WBG devices is their ability to switch faster, thereby increasing switching frequency and reducing passive component size. Embedding of IGBTs and Diodes up to 1,2 kV has been shown on demonstration level with the potential of loop inductance reduction. Furthermore, SiC-modules with embedded MOSFETs show even lower loop inductance values. Embedding die allows a design for short power and gate loops, if the circuitry is integrated into the same PCB, but only a few modules have explored this advantage. An embedded half bridge module with integrated SiC-MOSFETs has ben designed by Virginia Tech. This module operates at 1,2 kV and offers excellent cooling capabilities. On the topside of the module DC-link capacitors are mounted to reduce the loop inductance below 3 nH which is about 5 times LEFT Figure 1: Test circuit used to estimate the power losses in a half-bridge Figure 2: SMT R DSon (left) vs. AT&S embedded concept Figure 3: Switch-off behavior of SMT module Figure 4: Switch-off behavior of embedded module