There are many international, national and internal company standards for conformal coating processing and inspection.
The role of the standard is to give a guideline for process control and ultimately reliability of the circuit board.
The International inspection standards for conformal coatings used by the majority of companies are the IPC A 610 Acceptability of Electronic Assemblies or the IPC –HDBK-830 Conformal Coating Handbook.
The first gives some minor references that help for specifying acceptance criteria.
The IPC handbook is a compilation of the conformal coating industry’s practical knowledge and will help designers & users of conformal coatings to understand the practical implications of selection, application and inspection, explaining in detail how to achieve the best results.
Alternative conformal coating standards
For conformal coating standards, it’s important to distinguish between application, inspection and selection of the coating, and the qualification and manufacture of the material.
As a general rule the first set of standards are for the user of the end product. They aid with the production process.
The second set of standards is for the manufacturer of the coating. They are guidelines and criteria for achieving a certain quality standard for the material.
There are other standards that exist including the MIL-I-46058C, Underwriters Laboratories (UL) UL 746E and UL94 and IPC-CC-830B but these are not related to inspection but rather materials testing.
The Mil standard for conformal coating has been inactive for new designs since November 1998.
However, the standard is still widely used for independent certification 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 that state MEET the requirements of MIL-I-46058C. It’s highly probable the conformal coating will not have been tested by an independent laboratory to the Mil standard.
Underwriters laboratories (UL)
UL are a global safety certification body for consumer electronics.
For conformal coating, two parts of the standard are important. These are UL 746 and UL94.
This standard 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.
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.
IPC-CC-830B Qualification and performance of electrical insulating compound for printed wiring assemblies
The IPC-CC830 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 standards is that the IPC standard is a self-certification standard and does not require to be completed by independent means.
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