This type of conformal coating is used in products that are exposed to outdoor elements such as moisture and heat. If the products are coated they do not get damaged when there is reduction of thermal and mechanical stress or if they are installed or handled roughly. The dielectric strength is increased between the conductors. PCBs can be designed to look small and compact as a result and the components and circuitry are protected from solvents and abrasions.
The product has a clear shiny look when coated. Sometimes the texture can be a little rubbery or hard. If it is examined under a UV light some coating display a greenish white marker that proves that the coating has been properly done on the product.
The cost of this type of military conformal coating was high and therefore used only on medical and life products. However, in the recent years, new processes and material have been developed to enable coating of all electronic consumer products. Since these electronic components and circuitries are being introduced in smaller sizes and dimensions, this type of coating will soon become a norm.
The repair and rework issues of this type of military conformal coating should be considered carefully before use on products. The requirement for performing this type of rework or repair of conformal coating arises after assemblies go through difference process and completed. Several important considerations should be placed on the requirements of component replacements and product and the selection of the coating chemistry.
The method that is not generally recommended is the thermal removal method that uses soldering irons. This is because conformal coatings require exposure for long hours and very high temperatures. This can cause residues to be left behind, discolorations and solder joints and other components/materials that are used for fabricating assemblies can be affected.
It is essential to monitor the process and ensure that de-lamination, lifting of pads or overheating of devices that are sensitive and lying around does not occur as a result of excess temperatures. Toxic vapors are emitted sometimes when conformal coating is burned which can be dangerous and therefore this type of method should be done with extreme caution.
Here is a list of the different types of coating that can be used with chemical removal methods.
Many types of solvents are available that can be selected that offer different ranges of speed. Depending on the application anyone of the following can be used:
Solvents such as alkaline activators and methanol base provide selectivity and a range in the power of dissolving. Solvents that are alkaline activators or ethylene glycol are fast and least selective.