At MicroCare, we often are asked about reworking conformal coatings on PCBs. These coatings are very important for PCBs that operate in a harsh environment. Conformal coatings are used on electronics that near the ocean, outdoors, in aviation, in dusty cities and dirty factories. For example, the PCBs that control gas station pumps and traffic lights are almost always coated to help them endure their harsh environment. Coatings keep water, dust, salt and dirt from touching delicate components and degrading the performance of the boards.
If rework is required, alcohol is not the best choice. While alcohol is inexpensive and widely available, it lacks the solvent “muscle” to dissolve coatings and often requires long soaking times to dissolve the coatings. This is an expensive waste of time and money.
There are four types of conformal coatings: acrylic, silicone, urethane and epoxy. In chemistry, there is a saying that “like dissolves like.” The best way to dissolve any contamination is to use a cleaning fluid with a chemical composition similar to the contamination. So to remove a coating, get a cleaning fluid that is chemically similar to the coating itself.
Here’s a brief list of some popular choices for reworking and cleaning coatings:
To remove silicone coatings, use the No Clean Flux Remover – VeriClean™ (#MCC-DC1) or the VOC-Free Flux Remover — UltraClean™ (#MCC-VOC). These are unsurpassed at silicone coatings, inks and adhesives.
To remove acrylic coatings, good choices would be General Purpose Flux Remover (#MCC-FRC), the Heavy Duty Flux Remover – SuprClean™ (#MCC-SPR) and the best-selling Lead-Free Flux Remover — PowerClean™ (#MCC-PW2).
These last two products may attack soft plastic components. Almost nothing removes epoxy coatings and urethane coatings. Epoxies are problematic: when cured, the molecules “cross-link” to form an unbreakable bond. Only a mechanical action, like sand-blasting, can remove epoxies, and that will damage the board.