Parylene Design Guidelines
Parylene coatings are a unique type of coating that is applied directly onto surfaces as a vapor. It provides excellent dielectric strength and exceptional resistance to moisture, chemicals and extreme temperatures. Because of its vapor coating method, parylene can be applied very thin and still provide excellent circuit board protection. Below we share things to consider when working with parylene to save you money, time and heartache.
Parylene vapor is highly intrusive and will penetrate the smallest of openings to coat everything in its path. Parylene repair and removal is often a difficult and costly process to implement. The masking process is therefore critical to the success of coated parts. Whenever possible, developing the coating process in parallel with the product development results in the most effective and efficient process.
Design the board to make it efficient to mask and de-mask the areas to be free of Parylene. For example, flat solder pads are easier to mask when associated components are not yet attached creating complex 3D topographies.
Ensure there is space between components to allow masking materials to be applied efficiently and ensure secure coverage. For example, placing small resistors adjacent to a connector that will require masking may result in the resistor not being parylene coated thoroughly.
Parylene offers a truly conformal coating without bridging, peeling, or pooling. As a result, choose to mask only when absolutely needed. For example, un-plated holes and other low points will not pool. Heat sinks, dependent on coat thickness, may not meaningfully impact heat dissipation as there is no bridging between individual fins.
When selecting components for your board, emphasis should be placed on ‘vapor-friendly’ connectors. Doing so can drastically reduce the amount of masking required. Choose sealed connectors, switches, and relays that have a closed back or bottom without vent holes or alignment pinholes.
Sealing connectors prior to arriving at the masking stage will reduce overall process cost. Choose silicone or epoxy material to seal connector bases and openings.
Where applicable, choose male pin type connectors for your board design. Male connectors simplify the masking process by mating with a simple boot to seal. Female sockets require careful and time-consuming masking.
Cables and wires
Parylene is deposited inside a vacuum chamber of fixed size. To make efficient use of chamber’s space constraints avoid cables and wires that protrude from your board. Selecting shorter cable and wires will increase density per batch reducing cost.