Removal Process of Conformal Coatings— 24 / 06 / 2021
What are Conformal Coatings?
Conformal coatings are a protective chemical coating of polymeric material applied in thin layers to printed circuit boards (PCBAs) and electronic assemblies. Its purpose is to provide environmental and mechanical protection to significantly improve the longevity and reliability of the components and circuitry. There are five primary conformal coating materials: parlyene, acrylic, urethane, acrylic, and parlyene. Each of these coatings presents its own set of advantages, limitations, and challenges, along with different application methods.
PARYLENE Conformal Coating Features:
- Fully biocompatible. Parylene has been FDA-approved (with USP XXII Class VI biocompatibility rating) and is safe for use within the human body. Parylene coatings protect a wide array of devices and components, including stents, pacemakers, defibrillators, and more.
- Chemically inert. Parylene is chemically and biologically inert and stable, does not readily react with any other substance or chemical, and make excellent barrier materials.
- Non-toxic. Parylene is routinely used in medical and bio-medical applications.
- Clean, clear, and sterile. Parylene does not promote the growth of biologics. Its surface is unsuitable for the proliferation of bacteria and other pathogens.
- Exceptional electrical isolation. Parylene possesses exceptional electrical properties, notably its low dielectric constant and high dielectric strength.
- Superior protection. Parylene films provide superior protection against moisture, chemicals, salt water, corrosion, fumes, gases and widely varying environmental conditions as well as being Mil-l-46058C approved.
- Chemical resistance. Parylene resists attacks and is insoluble in all organic solvents and is resistant to and permeation by most solvents with the exception of aromatic hydrocarbons.
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ACRYLIC Conformal Coating Features
- Ease of rework
- User friendly
- Simple drying and curing process
- Good moisture resistance
- High florescence level for ease of inspection
- Excellent, smooth, durable, and crystal clear finish
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Urethane Conformal Coating Features
- Good moisture, chemical, and solvent resistance
- Abrasion resistance and mechanical strength
- Resistant to mold growth
- Excellent adhesion under all climatic conditions
- Exceptional dielectric properties
- UV traceable for inspection purposes
- High level of flexibility, even at low temperaturesProperties of Urethane (UR) Conformal Coatings
- Moisture and oil resistant
- Good flexibility
- Can be thinned to achieve a chosen viscosity
- Typically brushed sprayed or dipped
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SILICONE Conformal Coating Features:
- Stability over a temperature range of usually -40°C to 200°C
- Soft and flexible, providing minimal impact protection
- High dielectric strength
- Good moisture, humidity, and UV sunlight barrier
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EPOXY Conformal Coating Features:
- Useful to temperatures up to 150°C
- Very rigid, offering a superior abrasion resistance
- Moisture resistance along with good chemical resistance
- High dielectric strength
- Very robust and difficult to remove.
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Why do you need removal when it’s meant to be permeant?
Every now and then conformal coatings need to be removed for reworking. Reworking could be for a number of reasons, such as electrical or functional failures that require rework, circuit board malfunctions, initial design process issues, etc. Whatever the reason may be, the first step in the removal process is to determining which coating material we are working with, as this will help determine the process we will be using to remove the coating.
Conformal Coating Removal Techniques
After identifying your coating, the next step is to choose the removal technique. Popular methods that can be used are:
Typically used for silicone or thick rubber coatings. This method uses a dull blade or knife to slit the coating material and peel it off.
Chemical Solvent Method
This process is very effective for removing urethane, acrylic, and silicone coatings. The area is prepped with high-temperature tape and then solvent is applied using a foam swab.
Grinding, Scraping Method
This removal technique can grind away thin, hard coatings with a micro motor tool or soft coatings with a rotary brush.
Using low-temperature heat, we can gently burn and melt the coating material off.
Micro Sandblaster Method
This technique involves projecting a fine abrasive powder onto the coating to flake off the material.
Which Removal Technique is Best for My Conformal Coating Material?
Grinding / scraping method, solvent method, or micro-blasting method
Thermal removal method, chemical solvent method, scraping and grinding method, or micro-blasting method
Thermal removal method, grinding and scraping method, or micro-blasting method
Grinding and scraping method, micro-blasting method, chemical solvent method, or thermal method
Parylene coatings are often harder to remove, but you can typically use the micro-blasting method, grinding and scraping method, or thermal method.