**2. Basic theory**

• the internal insulation problem [15];

76 Design, Simulation and Construction of Field Effect Transistors

For PP IGBTs, the clamping force is a special and very important parameter that many other parameters are correlated with this value, including the electrical and thermal behavior, reliability, and so on. For example, the current and junction temperature distributions are affected by the clamping force distribution a lot [17] through the electrical and thermal contact resistance [18, 19]. Too much clamping force will mechanically damage the silicon chip and too little clamping force will increase the junction temperature caused by the increased thermal contact resistance. Eventually, this leads to the silicon chip thermal damage as shown in **Figure 4** [20]. Therefore, the clamping force distribution within PP IGBTs is quite important that it not only affects both the electrical and thermal behavior but also the long-

There are many factors that may influence the clamping force distribution within PP IGBTs not only during the design process but also in the applications. And the affect factors can be divided into external and internal factors. All the factors that may affect the clamping force distribution within PP IGBTs are shown subsequently and analyzed through the finite element method. For high-power IGBT modules or PP IGBTs, some Fast Recovery Diode (FRD) chips are always connected in anti-paralleled with the IGBT chips to provide the current path while the IGBT chips are turned off. Actually, the matching of the silicon chips, which means the internal layout of IGBT chips and FRD chips within PP IGBTs, will also influence on the clamping force distribution. However, the electrical and thermal behaviors, for example, the collector current and junction temperature distributions, of the PP IGBTs depend on the internal layout or matching of the silicon chips to a large extent. Therefore, the matching of the silicon chips should pay more attention to the electrical and thermal behaviors rather than the

• long-time reliability [16].

time reliability of PP IGBTs.

clamping force distribution.

• external clamping modes

• design of disc spring

**B.** Internal affect factors

• slim plates

• thermal stress

• internal layout

• machining accuracy

• design of electrodes

**A.** External affect factors

**1.3. Clamping force distribution**
