Substrate Preparation Design Guide for Coating Parylene
Parylene is the best choice for high quality, uniform, pinhole-free conformal coatings. To ensure that you obtain optimum results, please make certain that all substrate surfaces are clean of organic and other contaminants, including solder flux, oils, etc. For applications where Parylene is to be selectively deposited, please be certain that you use an appropriate masking process. We offer the following recommendations to assist you. Please contact our sales or customer support staff if you require further information.
- Consider using sealed connectors, or back seal the connectors before they are installed on the board. This will reduce the labor cost associated with sealing standard connectors.
- Allow for additional space to work around connectors when they do require masking.
- Card extractors and/or wedge clamps pose a masking problem and should be removed before coating if possible.
- Ejector latches are difficult to mask and can be bound up by the coating. Consider installing ejector latches after the coating process is completed. This will minimize time spent masking and de-masking, reducing your overall cost.
- Consider using male pin headers rather than female/socketed or shrouded headers because they are easier and less expensive to mask.
- Molded connector bodies are typically easier and less expensive to mask than press fit bodies.
- Compliant pin connectors can be put on backplanes after coating without the need to mask.
- Consider attaching long leads or ribbon cables after the coating process if possible. This will reduce the space required inside the coating chamber.
- Power terminals and RTV filled terminals are examples of connectors that do not require masking.
Materials and Surfaces
- Consider using sealed components when adjustable items are needed (potentiometers, switches, etc.)
- Select solder masks that will not have a deleterious effect on adhesion.
- Clean board immediately after soldering operations to eliminate flux residues.
- Allow for coating in areas where it is not required but will not hinder performance. This will reduce additional labor costs associated with masking.
- Some test points may not need to be masked or the masking can be left on and removed only if test is required.
- Offer a wide tolerance on masking parameters when possible.
Metals, Plastics and Rubber
- Surfaces need to be clean and free of cutting oils, mold release or other types of contaminants.
- An etched or roughened surface usually will provide for better adhesion.
- Impregnating or depositing an oxide layer on the surface can also enhance adhesion.
- Coating aluminum can sometimes perform as well as stainless steel and is easier to tool.
- Parylene bonds very well to silicone rubber and neoprene. It is also used to coat other materials like plastic, glass and ceramics.
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