Environmental conditions such as high ambient temperatures, exposure to mechanical shock, and specific drive cycles require special attention to the mechanical and electrical characteristics of IGBT power modules to ensure optimal performance and high reliability throughout their lifespan. This article discusses issues and failure modes related to IGBT power and thermal cycling, material selection, electrical characteristics, etc. [align=center]Schematic diagram of IGBT module architecture including substrate[/align] Various industrial applications typically use up to a dozen different types of Insulated Gate Bipolar Transistors (IGBTs). The purpose of designing IGBT modules is to provide optimal cost-effectiveness and appropriate reliability for a specific application. Figure 1 shows the main components of an existing IGBT power module. The emergence of commercial electric vehicles (EVs) and hybrid electric vehicles (HEVs) has created a new market for IGBT modules. The part of the IGBT power module with the highest reliability requirements in EVs and HEVs is the drivetrain, where the IGBT is located in the inverter, providing power to the motor of the hybrid system. Based on the concept of the drivetrain, the inverter can be placed in the trunk, inside the gearbox, or under the hood near the internal combustion engine; therefore, the IGBT module must withstand severe thermal and mechanical conditions (vibration and shock). To provide automotive designers with highly reliable standard industrial IGBT modules, IGBT designers must be extremely careful in selecting materials and designing electrical characteristics to achieve similar or even better results. Thermal Cycling and Thermal Shock Testing During thermal cycling (TC), the device under test (DUT) is alternately exposed to precisely set minimum and maximum temperatures, resulting in a temperature difference (ΔTC) of 80K to 100K across its casing. The DUT must be stored at the minimum and maximum temperatures for a sufficient time to reach thermal equilibrium (i.e., 2 to 6 minutes). This test focuses on detecting fatigue characteristics at the weld joints. More rigorous testing can also investigate weaknesses in other parts, such as the module frame. Thermal shock testing (TST), also known as two-box testing, is conducted under extended ΔTC conditions, such as from -40°C to +150°C, with a typical storage time of 1 hour. Power Cycling During thermal cycling/thermal shock testing, the DUT is heated externally, while during power cycling (PC), the DUT is actively heated by the load current flowing through the module. Therefore, the temperature gradient inside the module and the temperatures of different material layers are much higher than during thermal cycling. Module cooling is achieved through active load current cutoff and the use of external heat dissipation measures. Water-cooled radiators are most typical, but air-cooled systems are also commonly used. The test setup can stop water flow during the heating phase and restart it after entering the cooling phase. Power cycling allows for the study of the fatigue characteristics of the bonding wire connections and solder joints. IGBT Module Failure Modes In addition to damage caused by exceeding the electrical specifications of the IGBT module (such as overvoltage and/or overcurrent), other failure mechanisms can occur. Some typical failure modes observed in power cycling, thermal cycling, mechanical vibration, or mechanical shock tests will be discussed below. Thermal cycling and specific thermal shock tests can reveal information about the durability of the system solder layer (i.e., the direct-bonded copper layer between the substrate and the ceramic substrate, or DCB). After 600 thermal shock cycles, the standard material combination of copper substrate and Al2O3 ceramic showed delamination of the system solder layer. This result reflects the different coefficients of thermal expansion (CTE) of the selected materials. The greater the difference in thermal expansion coefficients between two materials, the greater the mechanical stress they exert on the intermediate layer (i.e., the solder layer). [align=center]Coefficients of Thermal Expansion (CTE) (ppm/K) for Different Materials[/align] Table 1 shows the coefficients of thermal expansion for different materials. Our goal is to select materials with the smallest possible difference in thermal expansion coefficients for combination. However, not every material is the preferred choice, even if their thermal expansion coefficients are very well matched, because the material cost itself may be too high, or difficult or expensive to process during production. Failure modes caused by power cycling are generally located at the bonding wire connection points. This is typically bonding wire peeling and/or aluminum metallization rebuilding on the chip top. In some cases, cracks can also be observed at the bonding wire base. Mechanical and thermal effects continuously cause the bonding wire to move, leading to cracks, and eventually, material fatigue causes the bonding wire itself to fail. In addition to the internal components of the power module, its housing can also be damaged by extreme external environments and/or operating conditions. For example, the housing frame may crack. In HEVs, depending on the mounting location of the IGBT module, it may be subjected to mechanical vibrations exceeding 5g and mechanical shocks exceeding 30g. If not robust enough, the power terminals can eventually be damaged by vibrations and shocks. Failures occur at the bends in the assembled terminals, where microcracks create damaged bends. Pre-formed terminals improve robustness, preventing damaged areas from appearing at the bend edges, thus resulting in higher reliability. Therefore, all Infineon power modules for HEVs are designed using this approach. High-Reliability IGBT Power Modules for HEVs All IGBT modules developed for HEVs share a specific goal: to provide excellent reliability, suitable electrical characteristics, and optimal cost. Based on extensive research into IGBT power module development, significant investment in new material combinations and assembly technologies, and the use of modern power semiconductor chips, Infineon has developed two module series specifically for HEVs: HybridPACK1 and HybridPACK2. Both models are based on Infineon's leading IGBT channel gate field-termination technology, providing the lowest conduction and switching losses. The selected 600V third-generation chip can operate at a junction temperature Tj,op of 1501°C (absolute maximum Tj,max = 1751°C). The HybridPACK1, capable of housing up to 400A of 600V IGBT3 and EmCon3 diodes in a six-package configuration, is suitable for air-cooled or cryogenic liquid-cooled inverter systems. These modules feature a 3mm copper substrate and an improved Al2O3 DCB ceramic substrate, offering optimal reliability and cost; they are ideal for peak 20kW power levels (single module) and full HEV applications, and can achieve even higher power ratings through parallel connection. The HybridPACK1 module series employs the following special measures to achieve optimal cost-effectiveness while providing high reliability: (1) A combination of copper substrate and improved Al2O3 ceramic is used to reduce delamination, which also offers a cost advantage compared to the AlSiC/Si3N4 combination; (2) Spacing material is used to further mitigate delamination; (3) Independent DCB ceramic is used for each phase to achieve optimized thermal coupling and thermal diffusion characteristics; (4) Improved bonding wire process enhances power cycling capability; (5) Appropriate plastic materials and optimized process parameters are selected to avoid cracking under large temperature fluctuations; (6) Pre-formed power terminals prevent microcracks from occurring during production. The HybridPACK2 is specifically developed for inverter systems with high-temperature liquid cooling and HEV applications. As a power module with direct liquid cooling, it can operate at temperatures up to 105°C. This module series integrates finned heat sinks directly inserted into the liquid cooling medium on the AlSiC substrate. This module features a maximum configuration of six 600V/800A IGBT3 packages. The HybridPACK2 module series employs the following special measures to achieve optimal cost-effectiveness while providing high reliability: (1) An optimized combination of AlSiC substrate and Si3N4 ceramic provides the lowest delamination effect (best-in-class solution); (2) The use of spacers further mitigates the delamination effect; (3) Independent DCB ceramics are used for each phase to achieve optimized thermal coupling and thermal diffusion characteristics; (4) Directly cooled substrate provides the lowest thermal resistance between the power semiconductor and the heat dissipation medium. This approach reduces Tj by more than 30K (depending on load conditions and chip configuration); (5) Improved bonding wire process enhances power cycling capability; (6) Selection of appropriate plastic materials and optimized process parameters prevent cracking under large temperature fluctuations; (7) Pre-formed power terminals prevent microcracks during manufacturing. High-power electric vehicles such as E-Busses and E-Trucks require robust and reliable IGBT modules. For these applications, the PrimePACK series of modules is an ideal choice. They are available in two different package forms and feature a maximum half-bridge configuration of 1200V/1400A and 1700V/1000A using Infineon's state-of-the-art IGBT4 chip technology (Tj,op=1501C, Tj,max=1751C). The PrimePACK module series employs the following special measures to achieve optimal cost-effectiveness while maintaining high reliability: (1) Optimal combination and manufacturing process of copper substrate and improved Al2O3 ceramic substrate to reduce delamination effect; (2) Use of spacers to further mitigate delamination effect; (3) Optimized chip layout provides the lowest thermal resistance, reducing thermal resistance by 30% compared to the previous generation (i.e., IHM) high-power devices; (4) Improved bonding wire process enhances power cycling capability; (5) Selection of appropriate plastic materials and optimized process parameters to prevent cracking under large temperature fluctuations; (6) Internal stray inductance is reduced (up to 60% compared to IHM); (7) Ultrasonic welding is used for power terminal connections at the DCB ceramic to improve mechanical strength. Summary Due to the highest reliability requirements for power semiconductor modules in automotive applications such as HEVs, today's suppliers must guarantee and meet these market demands. For these applications, Infineon has launched the HybridPACK and PrimePACK series of power semiconductor modules with optimized performance and cost. In addition, Infineon will further invest in the research and development of future IGBT modules that can provide higher reliability under more demanding power densities and ambient temperatures.