Summary
Co-authors and contributors
- Dr Lee Hitchens, Nexus
Parylene conformal coating removal can easily be achieved and can be broken down into three categories.
These are:
- Thermal removal (soldering through)
- Mechanical abrasion by hand
- Machine abrasion
Standard liquid stripping techniques used in the area of liquid conformal coatings tend to be unsuccessful due to the inert nature and high chemical resistance of the Parylene coating.
Thermal removal
The thermal Parylene coating removal technique (including using a soldering iron to burn through the conformal coating) is the least recommended technique of coating removal.
Most conformal coatings require a very high temperature and/or long exposure times.
This, in turn, can cause discoloration, leave residues, and adversely effect solders and/or other materials used in the construction of the board from boards.
Also, temperature-sensitive components may be damaged.
Mechanical removal by hand
Mechanical removal techniques include cutting, picking, sanding or scraping the area of Parylene coating to be removed.
However, the ease of removal will depend on the adhesion of the Parylene coating.
Most types of Parylene coatings are very tough to remove using this method if the adhesion is good and care is needed to ensure no damage to the circuit board.
Machine abrasion (Micro Shot blasting)
The micro abrasive blasting technique is a novel technique.
It is a relatively fast, cost-effective process.
The controls are simple and the process is environmentally friendly as a non-solvent based method to remove conformal coatings.
How does the Micro-Shot Blasting process work with Parylene?
In the micro abrasive blasting process, a precise mixture of dry air or an inert gas and an abrasive media is propelled through a tiny nozzle attached to a stylus.
The stylus is either handheld or mounted on an automated system.
This allows the mixture to be pinpointed at the target area of the Parylene coating to be removed.
A vacuum system continuously removes the used materials and channels them through a filtration system for disposal.
The process is normally conducted within an enclosed anti-static chamber and features grounding devices to dissipate electrostatic potential.
The system can remove Parylene conformal coatings from a single test node, an axial leaded component, a through-hole integrated circuit (IC), a surface mount component (SMC) or an entire printed circuit board (PCB).
Care must be taken where the Parylene coating is of a similar hardness or harder than the components or laminate below.
This is because the eroding material could erode the components as well.
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