Conformal Coating Standards: MIL-I-46058C, UL 746E & More
Posted by Sean Horn
Tuesday, August 14, 2012 7:38
@ 7:38 AM
The Conformal Coating Standards that currently exist can be considered from two points of view. First, there are the standards that are used by the manufacturers of conformal coatings to qualify the products, whether that is done by self-certification or completed by independent testing. Second, the standards are a method for users to determine the quality of the conformal coatings they are considering to select.
The four standards to consider are:
- MIL-I-46058C Mil Standard
- Underwriters Laboratories (UL) UL 746E and UL94
- IPC-CC-830B Qualification and Performance of Electrical Insulating Compound for Printed Wiring Assemblies
- IEC 61086-1 edition 2.0 Coatings for loaded printed wire boards (conformal coatings) – Part 1: Definitions, classification and general requirements
Each is considered independently below with a brief description.
The Mil Standard for conformal coating has been inactive for new designs since November 1998 and is INDEPENDENT TESTING. However, the standard is still widely used for independent certification of all types of conformal coatings. All companies tested to the Mil standard are listed on a Qualified Product List (QPL). Conformal coatings listed on the QPL will have been through rigorous 3rd party testing.
Caution should be shown when examining conformal coating datasheets which state MEET the requirements of MIL-I-46058C since the conformal coatings will likely not have been tested by the independent laboratory.
UL 746E & UL94
Underwriters Laboratories (UL) are a global safety certification body for consumer electronics. For conformal coating, two parts of the standard are important, being UL 746E and UL94 and both require INDEPENDENT TESTING.
UL 94 measures conformal coating material’s tendency either to extinguish or to spread the flame once the test specimen has been ignited. The first program is described in UL 94. This is now harmonized with IEC 60707, 60695-11-10 and 60695-11-20 and ISO 9772 and 9773.
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.
The IPC-CC-830B Qualification and Performance of Electrical Insulating Compound for Printed Wiring Assemblies was originally written as an alternative to MIL-I-46058C and is used in conformal coating all over the world. The major difference between the IPC standard and the Mil and UL standard is that the IPC standard is self-certification and not completed by independent means.
IEC 61086-1 ed2.0
The IEC 61086-1 ed2.0 Coatings for loaded printed wire boards (conformal coatings) – Part 1: Definitions, classification and general requirements standard gives the definitions, classification and general requirements for electrical insulating materials suitable for application as coatings for loaded printed wire boards (conformal coatings). This standard excludes requirements for compatibility between such coatings and printed wire boards, this characteristic being evaluated in individual applications.
This was a guest post by Dr. Lee Hitchens from Nexus3C.