In conformal coating, there are many International, National and internal company standards for manufacture of coating materials, processing and inspection.
The UL standards (and qualification) are used to qualify a conformal coating material to a certain specification. Therefore, it is a material manufacture standard only.
The question of whether a conformal coating actually needs the UL qualification to the standard is down to whether the test regime is relevant to the user of the conformal coating.
What do the UL standards provide for conformal coating?
First, lets understand who and what UL are.
UL stands for Underwriters Laboratories. They are a global safety certification body for consumer electronics.
UL write the standards and provide a 3rd Party test service.
There is no self-certification available for manufacturers of conformal coatings. If you want to qualify to UL, then you have to have the materials tested by UL.
A qualification to UL can be used as a sign of quality control and testing independently of the coatings protective ability.
When do you need UL qualification for a conformal coating?
Sometimes it may be required that the conformal coating needs UL approval before being applied to a printed circuit board.
It may depend on the sector the electronic circuits are used as to whether the UL qualification is required.
However, UL approved coatings can be requested in nearly all areas where conformal coatings tend to be used for protection for electronics including domestic home, industrial controls, telecommunications and aerospace.
What UL standards are used to test conformal coatings?
For conformal coating, there are two parts of the UL standards that are important.
These are:
- UL 94: Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing.
- UL 746E: Standard Polymeric Materials: Industrial Laminates, Filament Wound Tubing, Vulcanized Fibre and Materials Used in Printed-Wiring Boards
The two standards together control the quality of the conformal coating.
UL 94: Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing.
UL 94 is a plastic material flammability standard.
It is used in conformal coating to classify the coating according to how they burn in various orientations and thicknesses.
The standard measures the conformal coating material’s tendency either to extinguish or to spread the flame once the test specimen has been ignited.
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.
The ratings for classifications are as follows:
- 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 classification to show the highest quality.
UL 746E: Standard Polymeric Materials: Industrial Laminates, Filament Wound Tubing, Vulcanized Fibre and Materials Used in Printed-Wiring Boards
This standard 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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