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Design007-Jan2022

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JANUARY 2022 I DESIGN007 MAGAZINE 39 Heat Generation With high current, heat is generated on the boards and results in power loss while devices are working. Miniaturization, where densifica- tion of components are installed in close prox- imity, can save space, but results in intensifying this problem. Temperature may also be further increased by the introduction of a new power semiconductor technology. Today's commonly used semiconductors are silicon based. is semiconductor material is approaching its performance and efficiency limits. e upcoming new power semiconduc- tor generation for the electrical powertrain will be based on silicon carbide (SiC), which is part of the wide band gap semiconductors family. Energy loss is reduced using SiC chips in comparison to silicon-based semiconduc- tors which makes the electronic devices work more efficiently. More energy is available and thus the driving range is increased. Higher switching frequen- cies and e.g. faster charging of batteries is pos- sible. ese are some of the advantages of SiC chips. 2,3 Due to the lower heat losses, SiC chips can operate at higher junction temperatures (Tj) up to 175°C or even beyond 4 . e over- all increase in temperatures of the electronic devices the designer must deal with, will lead to the use of different active or passive cooling technologies. ermal management and heat spreading become necessary. Common FR-4 type base materials that are usually used in PCB production tempera- tures around 150°C are already challenging. e new FR15.1/0 material category defined by UL should help to identify materials with increased thermal stability and offer a choice of materials for these thermally demanding applications. Temperatures levels up to 175°C make it necessary to develop a new base material solu- tion so that cost of intensive cooling or ther- mal management systems for the components can be reduced. Benzoxacine is an example for an innovative resin system that was devel- oped to withstand operating temperatures up to 175°C. is resin system shows an increased thermal stability compared to the common epoxy resins, but at the same time has the advantage of a FR-4 similar behavior during PCB production. Standard manufacturing processes can be used, and the resin system enables higher operating temperatures up to 175°C while still having the advantage of FR-4 similar processing. Automotive electrification is pushing the boundaries of the base material. Increased voltages make high voltage CAF resistance of base material necessary. Increased cur- rent flows and the resulting use of heavy cop- per requires a base material with appropriate resin filling behavior. e material offering must include very high resin content prepreg to ensure proper filling of the heavy copper structures. And finally, the base material must withstand the increased thermal load. Stan- dard FR-4 materials are reaching their limit when it comes to high voltage applications and new base materials should be selected for these applications. DESIGN007 References 1. ZVEI—German Electrical and Electronic Manu- facturers' Association, Voltage Classes for Electric Mobility, December 2013. 2. MTI Instruments Inc., "Silicon Carbide Versus Silicon in EV Power Electronics;" AZoM, April 19, 2021. 3. Murray Slovick; "Making the Jump to Wide Bandgap Power;" Electronic Design, December 2017. 4. B. Wrzecionko, J. Biela, J.W. Kolar; "SiC Power Semconductors in HEVs: Influence of Junction Tem- perature on Power Density, Chip Utilization and Effi- ciency;" IEEE, 2009. Michael J. Gay, is director of High Performance Products with Isola. He has been with Isola for 20 years and has 25 years of experience in the lami- nate and PCB manufacturing industries.

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