Conformal coatings were originally developed for military, aerospace, and marine applications but have been increasingly used in a broader base of telecommunication, computer, automotive, consumer, industrial, and instrumentation applications to increase product quality and performance.
Printed Circuit Board (PCB) rework may be necessary for high-value boards. Conformal coatings should be removable with minimal to moderate effort and easily repairable off-line. Ease of rework and removal are directly linked to the resilience of a coating to specific factors in the operating environment. In general, solvent-based, non-cross-linked coatings will be relatively easy to remove with solvents. UV light-curable and cross-linked materials, with their enhanced environmental and chemical resistance, will be more challenging to remove.
It’s important to consider the effect of the rework/removal method on solder masks, components, and assembly materials prior to choosing the appropriate method. The three most common techniques for removal are chemical, thermal, and mechanical.
Removing cured conformal coatings by chemical treatment requires immersion of the coated board or treating localized areas with the chemical stripping solution. Several companies manufacture materials that dissolve/attack conformal coatings
Thermal Heat Removal
Two techniques are possible to remove a cured conformal coating depending upon the temperature sensitivity of the components located on the printed circuit board.
1) Heat the entire board to 150°C [300°F] and strip the coating once it softens (while still hot).
2) Use a hot-air de-soldering tool or a solder gun to remove spot areas of the coating. Apply the heat source to the treated area and remove the coating as it softens. Exercise care not to damage heat-sensitive components or traces. These methods are useful when the surrounding area does contain heat-sensitive components since it directs the hot air to one spot. When heat sensitivity is not a factor, a heat gun capable of 200-230°C [400-450°F] may be used to heat the area.
Scraping or cutting the conformal coating may be an option for some applications and is easier with thicker, more flexible coatings. Pressurized abrasive systems - like micro-abrasive blasting - are often used to safely remove cured coatings. The abrasive is easily separated from the surfaces without danger to the components or reworking process. This technique is fast, cost-effective, and environmentally clean. It also enables you to selectively remove the coating from a specific targeted area, while causing no damage to the surrounding components.