Pressure-Free Phenomenon in Top Layer of Chip Body Under Local Pressure and Design of Channel-Free Flat-Packaged IGBT

This letter investigates the magnitude and direction distributions of stress on an insulated gate bipolar transistor (IGBT) die when local pressure is applied to the chip surface. The results show that the pressure needs a certain thickness to spread uniformly all over the entire chip area. At the top of the chip, the stress concentrates right below the pressure contact region while the other region is pressure-free. Deeper into the die, the pressure becomes uniform vertical stress. This phenomenon is used to design the channel-free flat-packaged IGBT with little stress in the channel region by keeping the pressure contact region a safe distance away from the channel region. This improves the effective area of flat-packaged IGBT without destroying the reliability.