Title
Conformal coating: in house or contract assembly? Bob Willis
Conformal coating: in house or contract assembly?
There are two options when design engineering requires the benefits of a conformally coated board assembly. The boards can be coated on site after the assembly process which will require the investment of time, equipment and factory space. There is also the need to learn about the whole coating process, which can take considerable time. Alternatively if the product is being built by a contract assembly service they may already provide the service. If not, he may wish to contract out the service to a specialist company. If that is the case, the design and quality engineers must be aware of this off site service and be involved in agreeing on the manufacturing criteria. Otherwise if things go wrong it can be difficult to sort out problems with the three companies involved. The following brief checklist covers
the issues to consider when setting up an onsite coating facility or the benefits of contracting out the service to a specialist service provider. Always look at all the costs; there are many hidden costs to costs to contracting out a service
Conformal coating processing requirements—production factory requirements þ Dedicated area of factory—Floor space suitable to station the systems, the operators and the PCBs being processed.
þ Temperature, humidity and suitable cleanliness—The environment constraints can be crucial. For example, temperature and humidity affect the application of the coating, and contamination from airborne particles can completely ruin a coating finish.
þ Ventilation and extraction—More critical to solvent-based coatings in
volume.
þ Drying area or cabinet—For storage of wet coated PCBs to minimise contact with particulates either from operators or airborne whilst drying.
þ Curing system, IR/convection or UV inline or batch—If high speed processing is required, or the coating demands a certain cure process, then accelerated drying and curing may need to be considered.
Figure 1. Perfect example of board after a conformal coating process, under UV inspection.
terms of extraction for health & safety, ventilation and airflow are also crucial since stagnant airflows inhibit factors such as drying.
þ Material storage facility—Storing volumes of volatile & flammable coating on site can be a critical factor, as can the temperature at which the coating is stored.
þ Material disposal—Most coatings, and the waste generated from the process, including extracted solvent in large volume cases, cannot be disposed of casually, and this must be considered.
þ Health and safety information—The right knowledge is important since most coatings are harmful in some way to operators, equipment and the environment.
Conformal coating equipment/ facilities
þ Coating application—Specification of suitable coating equipment from selective robotic systems to simple homemade inspection boxes for brushing. The requirement will depend on the material, specification and
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þ Inspection equipment/rework area— Having understood the inspection requirements, an area is required where either manual or automated inspection can take place to measure and provide feedback for the process. This could simply be a UV inspection booth with a single operator or more sophisticated options.
In-house conformal coating service Advantages • No lead times on shipment to an external source.
• No packaging/transport costs to protect the product during transport.
• Continual monitoring of quality of the external source.
• Additional service to customers by coating in house.
Disadvantages • Factory space and operator/staff requirement—may be the wrong time for investment.
• No previous experience in coating— Coating can have a steep learning curve in terms of scrap product.
• Training requirement—This can minimise the learning curve but can be costly.
• Emissions and material disposal—VOC emissions are being a big factor in
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