All standard toroidal cores, composite toroid cores, rectangular toroidal cores and balun cores are provided with a protective coating. In addition a number of other geometries will come standard with coating on non-mating surfaces. The geometries with protective coating on nonmating surfaces include bus bar cores, HC/IC and HD/ID cores. Please refer to the individual part datasheet for information if core finish is included as well as coating type.
Toroid sizes with outside diameter of 0.20in./5.1mm (“T20” part prefix) and smaller are typically coated under vacuum with Parylene C. The larger cores are coated with a two color epoxy finish with colors being used to identify material. It is important to note Parylene C is not compliant with European Union Directive 2002/95/EC on Restriction of Hazardous Substances (ROHS) for Halogens. It may be possible to substitute to RoHS compliant parylene coating, please contact the factory or local representative for further details.
The epoxy coated parts are RoHS compliant and UL approved for Flame Class UL94V-0 per file #E140098 (S). A copy of the Yellow card can be provided upon request or located on the UL website.
All finishes have a minimum dielectric strength of 500 Vrms at 60 Hz. Toroidal cores can be double or triple coated for greater dielectric strength. Plastic core caps are available for “T400” and “T520” part series for very heavy gauge wire or when greater dielectric strength is required. Parts can also be supplied without coating. Contact local sales assistant for further details.
All finishes resist most cleaning solvents, however, extended exposure to certain solvents may have detrimental effects. All coatings will tolerate elevated temperatures for a limited time for Reflow solder, IR or Vapor Phase soldering operations. The typical solder temperatures encountered are 200°C to 240°C for up to 25 seconds of exposure time. Parylene coated parts are most susceptible to damage if exposed too long to elevated temperature. The coating can soften and possibly “blister” under worst case exposure. The epoxy coated parts will tolerate solder temperatures for up to 2 minutes and not suffer any long-term damage.
Uncoated cores may be subject to surface oxidation. Micrometals recommends that all uncoated cores should be sheltered from high humidity or moisture. It is suggested that bare cores are handled with gloves in order to avoid formation of surface blemishes. Surface oxidation or discolorations are cosmetic and will not affect core performance.
Further details about prolonged exposure to high temperatures can be at the Temperature Considerations section of this website.