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.
Parylene Coating Requirements FAQ
When parylene is used as a coating on a medical device, does the coating exhibit long-term compatibility with body fluids and tissues? When applied onto the substrate, are there any toxic chemical interactions and/or byproducts that could be harmful to a patient or to the function of the device?
Parylene is 100% biocompatible.
HYDROPHOBIC & HYDROPHILIC CHARACTERISTICS
Does the coating aim for lubricity when dry or wet? (I.e. a cardiovascular catheter that is hydrophilic (slippery when wet) vs. a hydrophobic guidewire that is easy for a cardiologist to grip.)
Parylene is hydrophobic.
Does the coating contaminate the substrate with outgassing from process catalysts, cure agents, solvents or plasticizers?
Parylene is 100% chemically inert
Does the cure temperature of the coating exceed the performance range of the substrate?
Parylene does not require curing of any kind.
Does the curing process degrade or distort the underlying substrate?
Parylene does not require curing of any kind.
Does the coating offer conformability to highly variable surface geometries?
Does the coating maintain conformability at all magnitudes and surface feature sizes, from macro to micro?
Parylene is 100% conformal.
Does the finished coating meet tight dimensional tolerances while maintaining desired physical, chemical, or electrical protection that is free of voids and pinholes?
Parylene coating range is measured in microns and is free of voids and pinholes.
Does the coating perform its function without significantly altering the physical or mechanical properties of the substrate?
Parylene’s micron-thin film does not add a meaningful mechanical load.
RESISTANCE TO FLAKING
Does the coating sufficiently adhere to the substrate to avoid flaking?
Parylene has excellent adhesion to most substrates.
Does the coating withstand the effects of sterilization processes?
Parylene withstands most sterilization processes.
With the continued miniaturization of electronics and their circuitry, the necessity of parylene coating has skyrocketed. However, failure to understand the parylene application process can, unfortunately, lead to avoidable issues. To learn more about the benefits of parylene coatings, coating process, and material properties, visit our Parylene Knowledge Base.