POWERCONTENT MOULES Versatile IGBT Power Module for Demanding Industrial and Automotive Applications The SKiM63/93 power semiconductor module was launched in 2011 and, owing to its versatility, has become an important IGBT module platform for many applications. Initially the SKiM63/93 module platform used silicon IGBT and diode chips, employing sintering die attach to deliver excellent power cycling capability. By Marco Honsberg and Anastasia Schiller, SEMIKRON INTERNATIONAL GmbH Indeed, with the introduction of AlCu bonding for the top side con- tacts, reliability was further increased and the SKiM63/93 is now a well-established solution for demanding power and load cycling applications that employ the latest technologies. The unique design of the SKiM63/93, based on a laminated busbar structure and multiple connections between the DC-link and the substrate, delivers a very low stray inductance, making the SKiM63/93 suitable for high-speed switching operations utilising SiC chipsets, as required for DC-DC converters, e.g. EV charging stations. This article provides an over- view of the versatile combinations of chipsets and packaging and the resulting performance. Figure 2: The internal structure of the SKiM93 Thermal performance Another important focus during the design stage of the actual SKiM63/93 is the thermal performance. Besides the internal structure, a high performance thermal interface material has been applied, creating an evenly distributed layer of optimal thickness. Furthermore, the choice of a low-inductance dedicated internal busbar structure provides a certain degree of freedom in IGBT and diode chip position- ing. Utilising this flexibility, the IGBT and diode chips are positioned such that the thermal losses are distributed more homogeneously Figure 1: Model design and structure across the substrate. This avoids concentration of local loss density on the ceramic substrate, creating hot spots that can potentially limit An image of the SKiM63/93 module is shown in Figure 1. The module performance. The simulated loss generated in IGBT and free-wheel- design allows the user to simply assemble the driver PCB on top of ing diode chips and the resulting peak junction temperature distribu- the SKiM63/93 and secure the IGBT driver printed circuit board (PCB) tion over the entire ceramic substrate results in fewer hot spots and with a well-positioned set of screws. These screws connect the IGBT allows for the development of more powerful inverter systems that driver with the SKiM63/93 without the use of solder, instead employ- utilise inexpensive heatsink designs. ing SEMIKRON’s tried and tested unique spring technology. This solderless assembly simplifies overall inverter design and enables the The overall design of the baseplate-less SKiM63/93, which features driver to be accessed easily in the event of repair and maintenance, pre-applied high-performance thermal interface material on an even in the field. The internal structure of the SKiM93 is shown in Fig- optimised water-based heatsink-eliminating the additional thermal ure 2. Image A on the left side shows the structure of the low-induc- resistance of a dedicated baseplate found in many off-the-shelf prod- tance laminated busbar and its multiple connections to the substrate. ucts-delivers unprecedented power density that can be yielded from By connecting the power terminals to the Al2O3 ceramic substrate the chipset employed. The performance achieved in an optimised using three individual solid busbars, both static loss and stray induc- configuration such as this is equivalent to the capability of pin-fin tance from terminal to the power semiconductors is reduced. IGBT modules found mainly in automotive applications, but avoids the potential risks of water leakages that are inherent in pin-fin construc- tions as part of a pin-fin IGBT module mounted with a gasket into the designated hole of a water-based heat sink. 28 Bodo´s Power Systems® February 2020 www.bodospower.com POWERCONTENT MOULES Chip technology Reliability Today, the SKiM63/93 IGBT module platform is compatible with a The effect of thermal cycling is frequently mentioned in connection variety of chips. The voltage ranges from 650V to 1200V and 1700V with base plate IGBT modules and addresses the aging effect of blocking voltage. The IGBTs utilised are produced by leading chip the connection between the baseplate of the module itself and the suppliers and achieve different trade-offs between static and turn-off ceramic substrate. Over time, the stresses resulting from changes losses, enabling the user to design the module in line with the specific in temperature produced by the substantially different coefficients of application conditions. The diodes employed are predominantly state- thermal expansion of the metal base plate and the ceramic substrate of-the-art SEMIKRON CAL4 diodes that deliver unprecedented perfor- will deteriorate the quality of the thermal connection. This is caused mance with regard to static and dynamic losses. Silicon carbide diode by the interconnection material used, in many cases solder. For a populated SKiMs as a part of the portfolio are ideal for high frequency module family such as the SKiM63/93 that has been designed without switching applications. baseplate, this failure mode has been eliminated entirely. Owing to the variety of available chips and chip combinations, the Furthermore, any reliability enhancing technology developed for SKiM module can be tailored to meet the needs of the given applica- SEMIKRON IGBT modules can be adopted in the SKiM63/93. The tion, delivering superior performance in certain applications than sintering process introduced to SEMIKRON’s process portfolio more off-the shelf modules. The figures below compare the performance of than 10 years ago, for example, offers huge potential to significantly modules that use standard types of silicon chips with those with dedi- improve the reliability of the connection between the back side of the cated chipsets based on different Hybrid Silicon Carbide (HSiC) chip chip and the substrate. For most IGBT modules based on an Al2O3 selections. The main differences under identical application conditions substrate, this connection is one of the common causes of premature are shown accordingly. module failure. Figure 3: Standard silicon IGBT/ silicon diode chipset versus the same converter utilising a SKiM93 Figure 3 shows a performance comparison between a converter operating at fc=20kHz, VDC=600V, cos phi = 0.8, using a SKiM93 based on a standard silicon IGBT/ silicon diode chipset and the same converter utilising a SKiM93 equipped with silicon IGBT and SiC Figure 5: Sintered modules are approximately six times more robust diode on the substrate. than soldered modules For more demanding application conditions such as operation at Figure 5 shows that sintered SKiM63/93 modules are approximately cos(φ) of -1, the SKiM63/93 provides the flexibility to optimise the six times more robust than soldered modules for a temperature swing populated diode space accordingly. The result of optimisation for of 80K. This optional sinter technology thus makes the SKiM63/93 far operation at fc=20kHz, VDC=600V is shown in Figure 4. more robust to load cycles than industry standard modules, making it the preferred choice for large servo motor applications, lift and eleva- Figure 4: The result of optimisation for operation at fc=20kHz, VDC=600V Figure 6: Cross-section of an AlCu bond wire 30 Bodo´s Power Systems® February 2020 www.bodospower.com POWERCONTENT MOULES tor applications, electric vehicle (EV) applications as well as for wind Accessories: turbine generator converter applications. A gate drive adapter board developed for the SKiM63 and the SKiM93 is shown in Figure 9. The SKiM63/93 is also available with AlCu bonding for applications with increased power cycling stresses where more robust compo- nents are required. Figure 6 shows a cross-section of an AlCu bond wire where the inner copper wire is covered entirely by an outer aluminium sheath. Such aluminium cladded copper wiring along with carefully chosen wire bonding process parameters has proven to be 4 times more robust under power cycling at ∆T =80K, as shown in Figure 7. Figure 9: Gate drive adapter board developed for the SKiM63 and the SKiM93 The SKiM63/93 housing concept features a main PCB, which is screwed on to supporting plastic domes, providing the electrical connections between the contact spring system in the module and the driver PCB. Indeed the main PCB holds the IGBT drivers in place and provides mounting space for gate resistors. Matching with the re- Figure 7: State-of-the-art robustness and ruggedness quired gate driving performance of the IGBT utilised in the SKiM63/93 the industrial standard SKYPER42 LJ driver employing state-of-the- art mixed signal ASICs to reduce the number of overall components Combining these core technologies, the SKiM63/93 platform deliv- is well suited to safely control and protect the SKiM modules in typical ers state-of-the-art robustness and ruggedness under demanding applications. This SKYPER42 LJ is shown in Figure 9 on top of the changes in load conditions, outperforming industry standard modules. main PCB. Product overview: A wide range of chip technologies and processes are available for the SKiM63/93 platform. Figure 8 shows the standard options for this www.semikron.com platform: Figure 8: Standard options for this platform 32 Bodo´s Power Systems® February 2020 www.bodospower.com.