MOSFET Packaging for Low Voltage DC/DC Converter : Comparing embedded PCB packaging to newly developed packaging

Abstract: This thesis studies the options of using PCB embedding bare die power MOSFET and new packaging of MOSFET to increase the power density in a PCB. This is to decrease the winding losses in an isolated DC/DC converter which, according to "Flex Power Modules", can be done by improving the interleaving between the layers of the transformer and/or decreasing the AC loop. To test the MOSFET packaging two layout are made from a reference PCB, one using embedded MOSFET and the other using the new packaging. The leakage induction and winding losses are simulated and if they are lower compared to the reference PCB prototypes are manufactured. The simulated result is that PCB embedded MOSFET decrease the leakage induction but the winding loss is higher. With the new packaging the leakage induction is higher and the winding loss has linear characteristics. Only the PCB with the new MOSFET packaging is made because the MOSFET die gate pad is too small for the PCB manufacturer to make a via connection to it. The PCB is tested that it operates as a DC/DC converter with a 40-60 V input and a 12 V output. The PCB is put on a test board in a wind-tunnel to test its characteristics under different wind speeds, input voltage and loads. The result is that the PCB has a higher efficiency than the reference PCB but it has worse thermal resistance. Further development of the design needs to be made to improve the thermal resistance. Using new packaging is a way to continue the development of power converter with lower efficiency but embedding MOSFET needs a less complicated manufacturing process before there is any widespread usage.