UL

Co-Authors and contributors

  • Dr Lee Hitchens, Nexus

Underwriter Laboratories (UL) is a global safety certification body for consumer electronics.

They test conformal coating materials as part of this service.

They are a 3rd Party test service. There is no self certification available.

For conformal coating, two parts of the standard are important.

These parts are UL94 and UL 746E.

UL 94

UL 94 is the Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing.

It is a plastic material flammability standard.

The standard classifies plastics according to how they burn in various orientations and thicknesses.

UL 94 measures conformal coating material’s tendency either to extinguish or to spread the flame once the test specimen has been ignited.

Classifications

For conformal coatings they are normally tested Horizontally (HB).

HB: slow burning on a horizontal specimen; burning rate < 76 mm/min for thickness < 3 mm or burning stops before 100 mm

  • V-2 burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
  • V-1: burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
  • V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.

Most conformal coatings aim to achieve V-0 status (top result).

Tests

Tests are normally conducted on coupons of the minimum approved thickness with different types of laminate. The conformal coating thickness range also is normally specified.

UL 746E

UL 746E is the Standard Polymeric Materials: Industrial Laminates, Filament Wound Tubing, Vulcanized Fiber and Materials Used in Printed-Wiring Boards

UL 746E measures the ignition resistance of the conformal coating to electrical ignition sources.

The conformal coating material’s resistance to ignition and surface tracking characteristics is described in UL 746E.


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