**4.5. Design of electrodes**

Many factors that affect the clamping force distribution within PP IGBTs have been analyzed before because it is known that most of those factors lead to warping the electrode. Therefore, the design of the collector electrode is also quite important for the clamping force distribution


**Table 5.** Average clamping force comparison for different internal layouts.

of PP IGBTs. A step has to be designed in the electrode to form a flange to make the PP IGBT a confined space to protect the silicon chips out of environment disruption. Two important parameters in this part are shown in **Figure 16** and are explained.

Where *A* is the diameter of the electrode and *B* is the equivalent diameter of the pedestals. The parameter *A* is the most important parameter because it is used to conduct the current, heat flux, and the clamping force. And furthermore, the equivalent diameter *B* is also very important that the clamping force is transmitted through the pedestals. Whether the value of *A* is matched with *B* or not will affect the clamping force to a large extent. The finite element model used in this section consists of 40 IGBT chips and 20 FRD chips, and this model is axial symmetry. Only half of this model is simulated to save time, and then the results can be expanded to the whole model. Firstly, the electrode diameter of 125 and 141 mm is simulated and the pressure on the surface of the silicon chips is shown in **Figure 17**.

Where the value of 125 mm is smaller than the equivalent diameter of pedestals and 141 mm is larger than that value. The simulation results show that the pressure will concentrate in the center of the PP IGBT when the diameter of the electrode is smaller than the equivalent diameter of pedestals. And the pressure will concentrate in the boundary of the PP IGBT when the diameter of the electrode is too large. The reason is that the electrode undergoes a different direction warpage under those two conditions. Then, different electrode diameters as 125, 127, 131, 135, 139, and 141 mm are simulated based on this finite element model and the average clamping force of each silicon chip is extracted. The clamping force error of each silicon chip is shown in **Table 6** with half model.

As it is seen in the results, the majority of the IGBT chips have plus deviation/error when the electrode diameter is smaller than 135 mm and they have minus error when the diameter is

**Figure 16.** Explanation for important parameters.

Proposal I is the circular electrodes with the square internal layout; proposal II is the square electrodes with the square internal layout, and proposal III is the circular electrodes with the circular internal layout. The different internal layouts lead to some distinction in the warpage of the electrodes and then affect the clamping force distribution. The average clamping force

From the clamping force distribution of three different internal layouts, it is shown that it is relatively uniform and the error is acceptable. Considering the difference between the IGBT chips and FRD chips, proposal II is better than I and III with a relatively lower error between the IGBT chips and FRD chips of 4.3% (2.65% to (−1.65%)). The error of those two proposals is 14.98 and 15.75%, respectively. Considering the difference among IGBT chips or FRD chips, proposal III is better because all the IGBT chips or FRD chips are located in the same circular and have the same deformation. However, the error among IGBT chips or FRD chips of proposal II is also relatively low with a value of 0.9 and 0.39%, respectively. In conclusion, proposal II is better than those two proposals because the electrode undergoes little deformation when the PP IGBT is clamped.

Many factors that affect the clamping force distribution within PP IGBTs have been analyzed before because it is known that most of those factors lead to warping the electrode. Therefore, the design of the collector electrode is also quite important for the clamping force distribution

IGBT1 1129 1172.5 1119.2 1068.9 3.85 −0.87 −5.32 IGBT2 1129 1179.3 1111.9 1069.5 4.46 −1.51 −5.27 IGBT3 1129 1176.5 1111.2 1069.6 4.21 −1.58 −5.26 IGBT4 1129 1168.1 1119.8 1069.5 3.46 −0.81 −5.27 IGBT5 1129 1168.1 1120.0 1069.6 3.46 −0.80 −5.26 IGBT6 1129 1026.2 1110.8 1068.5 −9.11 −1.61 −5.36 IGBT7 1129 1024.6 1110.4 1069.5 −9.25 −1.65 −5.27 IGBT8 1129 1162.5 1120.5 1070.0 2.97 −0.75 −5.23 IGBT9 1129 1010.3 — 1069.3 −10.5 — −5.29 IGBT10 1129 1004.9 — 1070.0 −11.0 — −5.23 IGBT11 1129 1136.6 — — 0.67 — — FRD1 1161 1207.2 1191.8 1281.1 3.98 2.65 10.39 FRD2 1161 1198.9 1186.1 1281.6 3.26 2.16 10.36 FRD3 1161 1189.9 1187.2 1281.3 2.49 2.26 10.35 FRD4 1161 1192.3 1190.8 1281.2 2.70 2.57 10.28 FRD5 1161 1182.1 — 1280.3 1.82 — 10.34

**I II III I II III**

**No Rated (N) Average clamping force (N) Error (%)**

**Table 5.** Average clamping force comparison for different internal layouts.

of each silicon chip is extracted and listed in **Table 5**.

88 Design, Simulation and Construction of Field Effect Transistors

**4.5. Design of electrodes**

**Figure 17.** Pressure distribution on the surface of the silicon chips: (a) diameter of 125 mm and (b) diameter of 141 mm.


and the simulation results are well presented and explained. Based on the simulation results, we know that we should pay more attention to the thermal stress, machining accuracy, internal layout, and electrode design during the structure design process, especially the thermal stress. The disc spring is very important for the PP IGBT application, and this factor also should be considered during the mechanical simulation. The slim plate can be omitted in the mechanical simulation that it is too thin and its contribution to the clamping force distribution is very limited. The clear classification and analysis of all the factors that affect the clamping force distribution can give a guideline not only for the semiconductor manufacturers to optimize the structure

Clamping Force Distribution within Press Pack IGBTs http://dx.doi.org/10.5772/intechopen.75999 91

The work presented in this chapter has been supported by the National Key R&D Program of China (2016YFB0901800) and the State Key Laboratory of Alternate Electrical Power System with Renewable Energy Source, North China Electrical Power University (Grant No.

[1] Dorn J, Huang H, Retzmann D. Novel voltage- sourced converters for HVDC and FACTS applications. Keynote In: International Council on Large Electric Systems (CIGRE'2007).

[2] Gao Q, Lin Y, Huang L. An overview of Zhoushan VSC-MTDC transmission project.

[3] Wakeman F, Hemmings D, Findlay W, Lockwood G. Pressure Contact IGBT, Testing for

[4] Häfner J, Jacobson B. Proactive hybrid HVDC breakers—A key innovation for reliable HVDC grids. The Electric Power System of the Future Integrating Super Grids and

Micro-grids International Symposium; Bologna, Italy: IEEE, 2011. pp. 264-273

and Yongzhang Huang1

design but also for users to take full advantages of the PP IGBTs.

, Jinyuan Li<sup>2</sup>

2 Global Energy Interconnection Research Institute, Beijing, China

\*Address all correspondence to: dengerpinghit@163.com 1 North China Electric Power University, Beijing, China

Power System & Clean Energy. 2015;**31**(2):33-38

Reliability. Westcode Semiconductors Ltd.; March 2012

**Acknowledgements**

LAPS17003).

**Author details**

**References**

Erping Deng1,2\*, Zhibin Zhao1

Osaka, Japan; 2007

**Table 6.** Average clamping force errors among silicon chips with half model (unit: %).

larger than 135 mm. And the clamping force distribution among IGBT chips is uniform. For FRD chips, there exists some difference among those chips but this is acceptable. Therefore, the electrode diameter of 135 mm is the best among those diameters, and this value is close to the equivalent diameter of pedestals. That is to say, the best way to improve the clamping force distribution within PP IGBTs is to match the electrode diameter with the equivalent diameter of pedestals during the electrode design process.
