Parylene Coating Removal

Parylene coating removal can be broken down into three categories for removal of parylene coating:

1) Chemical Removal: Parylene coatings are sought after primarily for their chemical resistance.  Parylene resists room temperature chemical attacks and are insoluable in all organic solvents up to 150C.  Thus parylene is highly chemical resistant and no chemical can dissolve it at room temperature.

However, Tetrahydrofuran is an organic solvent that can soften the coating, temporarily loosening the adhesion bond between the coating and the substrate so that it can be lifted off, like a mask, with tweezers.  It is not suited to working with specific areas; in the case of rework and repair this is usually desired.  It is highly flammable, caustic and extreme measures must be taken to ensure safe use.

2) Thermal Removal:  All parylene variants demonstrate heat-resistance or "melting point" constraints for removal purposes ranging from 290C for parylene C, the most commonly used variant, to temperatures approaching 500C for parylene D, N, and F.  A high quality soldering iron under a vacuum hood could be used to burn off at the solder points.  This approach might be effective for small repairs though it is not the cleanest method.  Along with residues, discoloration may pose a risk to heat sensitive components or substrates.  

Laser ablation removes material from the surface by irradiating it with a laser beam.  The beam can drill, cut, or mark delicate materials with great precision and repeatability.

Laser ablation removes very precise areas and tends to fit high density difficult to mask parts.  Applications such as microelectronics, electrosurgical devices and implantable elctrodes that require very small, precise and intricate shapes to be free would be ssuited to this approach.  It is less likely to be used for the purpose of general rework as it can be cost restrictive.  

3) Mechanical Removal:  Parylene demonstrates poor resistance to abrasion.  Parylene is a soft polymer and as such physical or mechanical means is the best method for removal.  Using coarse methods such as picking, scraping and cutting can be effective but there is a risk of damage to delicate trace lines, solder pads, components and the substrate itself.

The most common method to remove parylene is via micro-abrasion.  This is the fastest, economic, and ecologically safe method for both spot and whole board parylene coating removal.  Various media from glass beads, plastic beads, sodium bicarbonate, and wheat starch have been tested and used.  Everything from complex to desktop equipment are available and can be used with a hand held stylus directing pressurized air and abrasive media.  

Once the section is repaired, the specific area could be covered with other protective material.  However, for optimum protection the whole board should be recoated with parylene. 

To learn more about the parylene removal process and to learn how you can get started with Diamond MT, please contact us today!

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