2.1.2 Hybrid Integration and Intelligent Power Modules

Medium- and high-power applications have been implemented using hybrid integration. Hybrid integration covers a large range of power electronics. IPM (intelligent power modules) or ASIPM (application specific intelligent power modules) are used for voltage ratings up to 600V from a current rating from a fewA up to 100A, and the standard power modules for current ranges greater than 100A and voltages over 1200V.

High-power requirements (currents from 100A to 2000A and voltages up to 3000V) can be implemented with standard power modules using conventional system designs. In general integration of standard power modules is restricted to parallel construction of IGBT (or power MOSFET) dies in order to increase the current rating including free-wheeling diodes. There is no control or protection circuitry inside the modules. These modules use classical assembly technologies like solder mount on the backside of the die and ultrasonic bonding of aluminum wires for the top side contacts. They are limited in terms of reliability, thermal performance, and voltage performance (blocking voltage and insulation voltage of the overall module). As an example of the reliability requirements in railway traction applications these modules will have to ensure about 10 million power cycles during their life time. One can see serious thermal fatigue in the modules, which is due to the stress on the solder resulting from the use of different materials which expand and contract at different rates during the thermal cycle. The bonding wires which are connected to the aluminum metalization on the top side of the power device are particularly sensitive to the thermal cycling. Innovative package design using new materials such as aluminum nitride (AlN) or silicon nitride (SiN) ceramics can enhance the thermal capabilities and reliability of high-power modules. Improvements in high-voltage IGBTs, with a new structure design such as trench IGBTs, can also give better electrical characteristics.

Figure 2.4: Cross section view of the IGBT and MOSFET module package.

Figure 2.4 shows the construction of the IGBT and MOSFET module. Integrating of the base plate can considerably improve the thermal resistance, and further improvements are possible by associating the use of new ceramic materials with the heat sink design. Pressure contact assembly is also another solution which enhances the reliability of high-power devices. In many applications, like the production of converters delivering several $\mathrm{kW}$, the integration of electromagnetic components is a fundamental requirement to reduce size and weight. This leads to a hybrid technology where power semiconductor devices are integrated on a planar substrate with other planar components.

Figure 2.5: Concept of IPM and ASIPM.

The use of inverters in motor drive and servo applications has been increasing in recent years. The main purpose of the IPM and ASIPM is to introduce power devices and peripheral circuitry in the same package. These solutions allow power transistors (generally IGBT and power MOSFET) to be integrated with the drive circuits and protection functions as well as with the power supply in a single package. The drive circuits and internal logic in the IPM enables efficient control of the gate driver which provides large output currents to charge and discharge the gate capacitance of the IGBT or power MOSFET. These define the on and off time of the power devices. The gate driver includes unintentional switching and desaturation failure protection circuits together with over-temperature and under-voltage protection circuitry. These features help to increase the safe operating area of power devices. Therefore, IPMs or ASIPMs are becoming the most obvious choice for inverters because of their many attractive advantages. IGBT or MOSFET gate drive and protective functions are provided by power integrated circuits. With the help of the level shifter included in the high-voltage IC (HVIC), ASIPMs provide its user with the advantage of optocoupler-less control interface. The DC isolation of the gate signals allows the module to be directly driven from a microcontroller. The power part contains an IGBT (or power MOSFET) and a soft recovery free-wheeling diode. These ASIPMs are only a step away from system integration. However, temperature limitations of these modules (including power devices with ICs and power ICs in the same package) tend to limit their use in medium-power applications.