Essential Guide to the Identification and Removal of Conformal Coating
WHAT ARE THE DIFFERENT TYPES OF CONFORMAL COATING?
IPC-CC-830 has superseded MIL-46058 as the primary specification for conformal coatings on printed circuit assemblies. This covers the following conformal coating types:
• Type AR – Acrylic Resin
• Type SR-- Silicone Resin
• Type UR—Polyurethane resin
• Type ER—Epoxy Resin
• Type XY—Parylene
These coatings can be grouped into two categories—those able to be removed by chemical solvents and those which cannot:
Can be removed by solvent - conformal coatings made of acrylic are ideally suited for chemical removal. Silicone and polyurethane are also suitable materials, but may require manual agitation.
Cannot be removed by solvents - Those coatings made of Epoxy and Parylene require physical (scraping, abrasion) rather than solvent removal methods.
HOW TO IDENTIFY THE TYPE OF CONFORMAL COATING?
In order to identify the appropriate coating removal procedure you must first identify the coating employed. During manufacture, this is known and can be specified. Labels may be present on the assembly, which should conform to Standards such as IPC-1066 (superseded by IPC/JEDEC J-STD-609) and IPC/JEDEC J-STD-609.
These labels are not always available or visible, but with simple observation and testing you can identify the coating characteristics sufficient to select the proper removal procedure. The generic or commercial identification is not necessary.
The following approaches will assist your identification:
• Hardness: Perform a penetration test in a non-critical area. If it is medium hard or soft, it is suitable for chemical solvent. If it is hard, it is not.
• Transparency: Transparent coatings are usually more suitable for removal than opaque coatings. Removal methods used with opaque coatings must be far more controlled to prevent damaging covered component and board elements.
• Solubility: In a small noncritical area, brush isopropyl alcohol and observe. Do not immerse printed board assemblies in harsh solvents in testing; some solvents can damage components.
• Visual Inspection: Inspect or use small tools to determine if the surface is glossy or dull, if it adheres strongly to the board, and\or is susceptible to chips, peeling or flaking, scratches or tears, or if it stretches.
Other tests can be performed for alternative removal methods, including thermal removal and stripability. Many of these tests in isolation do not identify whether chemical solvent is a suitable removal method, but may assist if you need to know the specific coating for other purposes. Refer to the IPC 7711/7721.2.3.1 standards.
The following is a summary of how to identify specific coating types:
• Acrylic Resin (AR) – Glossy surface, reacts to heat, strong bond, and readily dissolves with common solvents. glossy surface.
• Silicone Resin (SR) – Semi-gloss rubbery surface, and soft so easily scraped off.
• Polyurethane resin (UR) – Glossy hard surface that is more solvent resistant than AR.
• Epoxy Resin (ER) – Glossy hard surface that is solvent resistant.
• Parylene (XT) – Matte hard surface that is solvent resistant. Because it is applied by vapor deposition, it will be much more even over all surfaces and component corners.
LINK:https://www.techspray.com/essential-guide-to-the-identification-and-removal-of-conformal-coating
