Electric & Hybrid Vehicle Technology - July 2021
The SiC-IGBT solution (Kerafol)
2021-07-20 03:25:05
To meet the automotive industry’s ambitious targets, the challenges for semiconductors and thermal interface materials are becoming greater
In the field of switching technology, the insulated-gate bipolar transistor (IGBT) is the most mature solution. It is a power semiconductor that is built on a standard silicon wafer and can handle voltages as high as 1700V. The Si-IGBT has advantages such as reliability and cost efficiency, and this technology has been successfully used for both industrial and automotive applications for many years.
Nevertheless, the switching speed of the Si-IGBTs is limited to around 15kHz which means higher losses and bigger passive components. New materials with a wider band gap like SiC and GaN can be used at higher frequencies and the size of other electric components can be reduced, which saves space. For example, the power losses of SiC-MOSFETS – both switching and conduction losses – are very low and the total efficiency is higher in comparison to Si-IGBTs.
SiC has been used for more than 25 years in power converters for solar, wind energy and industrial applications. Now, more automotive applications are following this trend for the inverter, onboard charger and DC-DC converter. As well as the already highlighted advantages in comparison to Si-IGBT, it is estimated that SiC semiconductors increase the range of electric vehicles by approximately 6%. Now, also the costs are becoming lower, and the production process is increasingly stable.
Despite the semiconductor material, the power density in power electronic components is continuously increasing. This high level of generated heat and temperature requires smart thermal transfer from the electronics to the heat sink, such as the cooling plate or alumina housing. Next to the thermal parameters, the voltage level in the used concepts of the described automotive applications is also continuously increasing, which means a reliable electrical isolation between the electronics and housing is crucial.
To combine these two counter-rotating properties of thermal conductivity and electrical isolation is the job of thermal interface materials. The success of reaching the target comes from usage of tapes, gap pads, double sided adhesives, graphite tapes and liquid solutions such as pastes or Gap Filler Liquids (GFL).
Whereas in the past it was mainly tapes and pads that were used, these days liquid materials are being considered more often. Tapes and pads have the advantage they can be applied easily by hand, which is especially useful in the prototyping stage. Those materials are approved, widely used and a reliable solution for IGBTs.
For higher quantities, GFLs are becoming state-of-the-art. The material price and total price per part is lower due to the faster production time and higher material utilization thanks to the fact there is no waste material. The thermal conductivity of pads and GFL is in a similar range of up to 6W/mK, but the total thermal resistance in the application is lower for GFL, due to the better compensation of the surface roughness.
When it comes to applying the materials in the serial production line, the GFL has an additional advantage. The dispensing equipment ensures a reliable and cost-effective solution by having a short cycle time. In many applications there are different electronic parts with different gaps and tolerances that must be connected. To solve this efficiently, it means that it is possible to use just one GFL instead of different pads with various geometries.
Kerafol’s technical center has first-hand experience in the dispensing process.
Its experience has shown that two-component low volatile silicone elastomers are the best solution to meet the requirements of automotive applications. These kinds of materials are characterized by high temperature resistance, long lifetime and resistance against vibrations and mechanical stress which is caused by the different kind of thermal expansion factors of the involved materials.
More electronic devices are being introduced in the automotive market, particularly the applications for electric and hybrid vehicles that are used for the battery and power conversion such as the inverter, DC/DC converter, onboard charger. As the applications become more complex, it is important to focus on overlapping R&D. It is not only about one single part, it is about the whole concept which means the interaction of the semiconductor, thermal interface material and automation in the production line which dictates the final success.
Gap Filler Liquids are increasingly trending as the favorite solution for the automotive industry, but there are still plenty of solutions where new tapes and pads are required.
FREE READER INQUIRY SERVICE
To learn more about Kerafol, visit: www.magupdate.co.uk/PEHV
©MAB - Aviation & Auto. View All Articles.