**1. Introduction**

#### **1.1. Opportunities for PP IGBTs**

Nowadays, the challenges such as globally increasing demand of electrical energy, the stringency of conventional energy resources (such as oil, gas, and coal), and so on are arising in the field of electrical energy supply [1]. The high-voltage direct current (HVDC) transmission

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

system, especially the flexible HVDC transmission system with voltage source converters (VSC), is an innovative solution because of its advantages of the ability to supply the power to the passive power grid (i.e., islet), the independent control of the active and reactive power, and the flexible operation modes [2]. The most important parts of the flexible HVDC transmission system are the converter valve and HVDC breaker, which are based on Insulated Gate Bipolar Transistors (IGBTs), briefly shown in **Figure 1**.

The flexible HVDC transmission system has been successfully applied in the developed countries for many years, and it is prosperous in China in the recent years. More and more projects with higher voltage and higher capacity ratings are developing to meet the requirements and the reliability as the most important issue. This high-voltage and high-reliability application has greatly promoted the development of IGBTs. There are two packaging styles for high-power IGBT devices: typical wire-bonded IGBT modules and press pack IGBTs (PP IGBTs). The highpower IGBT module of 3300 V/1500 A had been widely used in the flexible HVDC transmission system. While with the growing demand of capacity, the IGBT module cannot meet the increasing voltage and capacity requirements, and PP IGBTs are gradually applied with its advantages of higher-power density, easy to connect in series, and short-circuit failure mode [3].

The first PP IGBTs used in the converter valve of the flexible HVDC transmission system in China is 4500 V/1500 A. After this, PP IGBTs of 3300 V/2000 A, 3300 V/3000 A, 4500 V/2000 A, and 4500 V/3000 A are required in the future flexible project because of the higher capacity demand, for example, the 4500 V/3000 A is needed in the 500 kV/3000 MW or 800 kV/3000 MW flexible project.

## **1.2. Challenges for PP IGBTs**

The press pack packaging style for high-voltage and high-power density IGBT can be divided into StakPak (**Figure 2**) and press pack (**Figure 3**). The original motivation in most cases was the poor power-cycling capability of early versions of wire-bonded modules and their explosion behavior [5]. The StakPak packaging style is patent protected by ABB, and the research on the StakPak is very limited. The press pack is widely used by Poseico, Fuji, Westcode, and Toshiba because of the experience with the packaging of high-power devices, such as gate turn-off thyristors, diodes, IGCT, and so on [6], and many researches are based on this packaging style. Therefore, the PP IGBTs discussed in this chapter are the press pack style as shown in **Figure 3**.

**Figure 3** shows that the PP IGBTs have a multilayered structure. The electrical and thermal paths for the silicon chips are supplied by the collector and emitter copper electrodes. Furthermore, the needed clamping force also should be applied on the two electrodes to make all components to contact well. The recommended clamping force for applications in

instructions from manufacturers [8, 9]. Two molybdenum plates surrounding the silicon chips are to uniform the clamping force distribution and reduce the thermal expansion/contraction between the molybdenum plates and silicon chips when the press pack IGBT undergoes hightemperature variations. A silicon chip subassembly is consisted of a silver shim plate, together with a silicon chip and two molybdenum plates. Many silicon chip subassemblies connected in parallel to form a press pack IGBT and the current rating is determined by the paralleled

With the increasing demand of higher voltage and current ratings, more and more silicon chip subassemblies are needed to connect in parallel. Therefore, there are many challenges in the packaging technology, especially the long life time reliability when applied in the flexible

is ideal according to mounting

Clamping Force Distribution within Press Pack IGBTs http://dx.doi.org/10.5772/intechopen.75999 75

a datasheet is a range, and a clamping pressure of 1.2 kN/cm<sup>2</sup>

**Figure 3.** Press pack packaging style from Westcode [7].

number.

HVDC transmission system as follows:

**Figure 2.** StakPak packaging style from ABB.

• current distribution among silicon chips [10];

• clamping force distribution among silicon chips [11–13];

• junction temperature distribution among silicon chips [14];

**Figure 1.** Two most important components in the flexible HVDC transmission system: (a) converter valve station and (b) schematic diagram for HVDC breaker [4].

**Figure 2.** StakPak packaging style from ABB.

system, especially the flexible HVDC transmission system with voltage source converters (VSC), is an innovative solution because of its advantages of the ability to supply the power to the passive power grid (i.e., islet), the independent control of the active and reactive power, and the flexible operation modes [2]. The most important parts of the flexible HVDC transmission system are the converter valve and HVDC breaker, which are based on Insulated

The flexible HVDC transmission system has been successfully applied in the developed countries for many years, and it is prosperous in China in the recent years. More and more projects with higher voltage and higher capacity ratings are developing to meet the requirements and the reliability as the most important issue. This high-voltage and high-reliability application has greatly promoted the development of IGBTs. There are two packaging styles for high-power IGBT devices: typical wire-bonded IGBT modules and press pack IGBTs (PP IGBTs). The highpower IGBT module of 3300 V/1500 A had been widely used in the flexible HVDC transmission system. While with the growing demand of capacity, the IGBT module cannot meet the increasing voltage and capacity requirements, and PP IGBTs are gradually applied with its advantages

of higher-power density, easy to connect in series, and short-circuit failure mode [3].

The first PP IGBTs used in the converter valve of the flexible HVDC transmission system in China is 4500 V/1500 A. After this, PP IGBTs of 3300 V/2000 A, 3300 V/3000 A, 4500 V/2000 A, and 4500 V/3000 A are required in the future flexible project because of the higher capacity demand, for example, the 4500 V/3000 A is needed in the 500 kV/3000 MW or 800 kV/3000 MW flexible project.

The press pack packaging style for high-voltage and high-power density IGBT can be divided into StakPak (**Figure 2**) and press pack (**Figure 3**). The original motivation in most cases was the poor power-cycling capability of early versions of wire-bonded modules and their explosion behavior [5]. The StakPak packaging style is patent protected by ABB, and the research on the StakPak is very limited. The press pack is widely used by Poseico, Fuji, Westcode, and Toshiba because of the experience with the packaging of high-power devices, such as gate turn-off thyristors, diodes, IGCT, and so on [6], and many researches are based on this packaging style. Therefore, the PP IGBTs discussed in this chapter are the press pack style as shown in **Figure 3**.

**Figure 1.** Two most important components in the flexible HVDC transmission system: (a) converter valve station and (b)

Gate Bipolar Transistors (IGBTs), briefly shown in **Figure 1**.

74 Design, Simulation and Construction of Field Effect Transistors

**1.2. Challenges for PP IGBTs**

schematic diagram for HVDC breaker [4].

**Figure 3.** Press pack packaging style from Westcode [7].

**Figure 3** shows that the PP IGBTs have a multilayered structure. The electrical and thermal paths for the silicon chips are supplied by the collector and emitter copper electrodes. Furthermore, the needed clamping force also should be applied on the two electrodes to make all components to contact well. The recommended clamping force for applications in a datasheet is a range, and a clamping pressure of 1.2 kN/cm<sup>2</sup> is ideal according to mounting instructions from manufacturers [8, 9]. Two molybdenum plates surrounding the silicon chips are to uniform the clamping force distribution and reduce the thermal expansion/contraction between the molybdenum plates and silicon chips when the press pack IGBT undergoes hightemperature variations. A silicon chip subassembly is consisted of a silver shim plate, together with a silicon chip and two molybdenum plates. Many silicon chip subassemblies connected in parallel to form a press pack IGBT and the current rating is determined by the paralleled number.

With the increasing demand of higher voltage and current ratings, more and more silicon chip subassemblies are needed to connect in parallel. Therefore, there are many challenges in the packaging technology, especially the long life time reliability when applied in the flexible HVDC transmission system as follows:

