Applying and Inspecting Conformal Coatings
APPLICATION METHODS
There are multiple ways to apply conformal coatings to printed circuit boards, but the appropriate method to use depends on some key criteria including the type of material used, cost, and number of boards that require processing. Common application methods include automated selective application, automated spraying, brushing, curtain coating, manual spraying, and dipping. Below is a brief overview of each method and some of their benefits and disadvantages.
Automated Selective Application
* Repeatable process for functional topside surface coverage
* Moderate to high-volume applications
* Higher systems cost than spray application
* Designed for repeatability
* Suited for medium-volume applications
* Can be applied for in-line operations with curing
* Best suited for short-run, prototype, and touch-up after repair/rework
* Also works for high-topography assemblies
* Low-cost initially, but difficult to achieve uniform coverage
* Material falls continuously as the board passes underneath on a conveyor
* Good for coverage on complex shapes and low-volume production
* Viscosity should be closely monitored
* Fastest method for applying conformal coatings
* Stable viscosity with reliable, consistent results
* Masking is required, but implementation costs are reasonable
Dipping
* PCBs are dipped into the conformal coating and then hung to dry
* Good for coating small components
* Streaking, inconsistent thicknesses, and uneven finish can occur
Note: Dipping is almost never practical for light-cure conformal coatings as it requires an elaborate equipment setup.
Contact Electronic Coating Technologies (ECT), Dymax’s preferred partner, for assistance with conformal coating application services. ECT has 25+ years of experience protecting critical electronics for manufacturers throughout Canada and the United States.
INSPECTION METHODS
Once a printed circuit board has been conformally coated, it requires careful quality inspection to ensure there are no flaws in the coating. There are a few ways this can be achieved.
All industry approved conformal coatings fluoresce upon exposure to black light. Off-the-shelf black lights or 365 nm LED lamps may be used. The glowing appearance helps the operator or vision system detect coating presence and voids. Most conformal coatings fluoresce blue. Manual inspection is often the most common method. Simple vision systems may be used for 100% in-line inspection. Newer 3-D laser measurement systems are available as well and are used for high reliability applications.
The development of new technologies, such as Ultra-Red® fluorescing, has allowed PCB manufacturers the enhance bond-line inspection processes and product authentication. Coatings formulated with Ultra-Red® remain clear until exposed to low-intensity UV light at which point they fluoresce bright red. This is particularly effective while bonding substrates that naturally fluoresce blue, such as PVC and PET. Ultra-Red® technology also produces a unique spectral signature that can be used by manufacturers for product authentication. Read a case history about how this fluorescing agent helped verify if an adhesive was being used.