Underwriter’s Laboratories (UL) is a global safety certification company that performs testing on products across many industries and certifies them as fit-for-use. It is very common to see the UL label on consumer goods throughout the world, and this extends to protective coatings for circuit boards. The UL746E Standard comprises a series of tests meant to evaluate whether a conformal coating can withstand sudden electrical surges and maintain its dielectric integrity. The Standard contains three coating designations. Conformal coating is the most difficult designation to achieve and comprises both dielectric and fire retardance testing. Permanent and resist coatings are the other two designations, which constitute only testing for flame retardancy.
For designation as a conformal coating under the 746E standard, coatings must comply with stringent requirements comprising both dielectric and flame retardance testing. For the dielectric testing component, a trace pattern is coated with leads attached. Conductive foil is then placed over the sample and the test vehicle is subjected to a series of high voltage blasts. If voltage is maintained between the electrical leads of the test vehicle the coating insulation is sufficient; however, if the coating is unable to withstand the surge and breaks down, the circuit shorts, and amperage leaks to the conductive foil. Figure 1 (below) illustrates the concept behind the dielectric testing component of UL746E.
Table below lists the specific tests for UL746E Conformal Coating Designation.
|As Received Voltage Transient||sample pulsed with 6kV|
|Environmental Conditioning||Sample exposed to high humidity and then ambient, pulsed with 6kV|
|Humidity Conditioning||Sample exposed to high humidity and immediately pulsed with 6kV|
|Thermal Conditioning||Sample aged for several weeks in thermal chamber, pulsed with 6kV|
|Vertical Burn Test||Burn rate of vertically mounted sample measured for compliance|
For permanent and resist coatings, only the vertical burn test is performed known as the UL94 flammability test.
Coatings that meet the Standard are listed on the UL database and are categorized as conformal coatings, permanent coatings and resist coatings. These products also bear the UL symbol on the product label for easy identification.
MG Chemicals has several UL recognized products:
- Coatings for use on printed writing. See UL File # E203094.
- Plastic Components. See UL File # E334302.
- Metallized Parts—Component. See UL File # E202609.