**4. Internal affect factors**

Those factors that mainly existed in PP IGBTs or during the design process are defined as the internal affect factors. The internal factors that may affect the clamping force distribution should be analyzed and optimized because it is quite important for the structure design of PP IGBTs. There are five parameters that may affect the clamping force distribution within PP IGBTs a lot: slim plates, thermal stress, machining accuracy, internal layout, and the design of electrodes. Among those affect factors, thermal stress is not a structure parameter that can be changed during the structure design. But this factor is quite important because it will influence the layout or the matching of silicon chips.
