Parylene is the trade name for a variety of chemical vapor deposited poly (p-xylylene) polymers used as moisture and dielectric barriers.
Although Parylene is a conformal coating it is different compared to the standard “wet” liquid conformal coatings in that it is deposited as a gas in a vacuum chamber and it is a dry process.
This method and the material itself give Parylene unique material properties that give it a lot of advantages compared to other traditional conformal coatings.
However, these unique properties also make it an extremely difficult material to remove.
Why is Parylene difficult to remove?
Compared to typical liquid conformal coatings like acrylics and polyurethanes that more easily dissolve in mildly aggressive solvents then Parylene is much tougher to remove.
The reasons are many why but a key point is that the Parylene coating itself is chemically inert. It has a high chemical resistance so the solvents don’t work well.
This means any chemical attack tried with solvents or other liquid chemicals on the Parylene is as much likely to damage the circuit board than remove the actual coating.
So, chemical removal is almost impossible.
This leaves another well know method for Parylene removal that is mechanical abrasion.
Mechanical abrasion of a coating can be done crudely by scraping off the Parylene with a knife or tool. Or, removal can be done with a media blast system that gradually erodes the Parylene coating away.
However, mechanical abrasion is a time consuming process and is highly skilled. Any wrong action could result in irreparable damage.
Further, mechanical abrasion tends to be a localised repair and removal technique. The concept of completely removing all of the Parylene of a circuit by mechanical abrasion is considered almost impossible unless a ridiculous amount of time and effort is injected into the process.
Therefore, a specialist method is required to remove Parylene completely from a whole circuit board.
A new method for completely stripping Parylene from a PCBA
Due to new research two processes have been developed for completely removing Parylene coating from the surface of a circuit.
- A method for <15um thickness of Parylene coating on the board
- A method for >15um thickness of Parylene coating on the board
Removal with <15um thickness of Parylene coating on the circuit
When the Parylene coating is under 15um then the removal from the whole circuit is a relatively simple process.
To successfully remove the Parylene a technique has been developed involving plasma etching.
The plasma-etch process uses a proprietary blend of gasses, and a custom system to mechanically etch off the Parylene. This specially designed alchemy of gasses specifically attacks Parylene rather than the solder mask.
The technique successfully removes the Parylene from all over the board.
Also, the etching process is quick relative to the other mechanical methods. Typically, the circuit can be completely etched of Parylene in under an hour.
Further, the process is safe. It does almost no harm to the circuit and is one of the safest methods for complete removal of Parylene.
Removal with >15um thickness of Parylene coating on the circuit
When the Parylene coating is greater than 15um then the removal from the whole circuit is a little more complex. In fact, it becomes a two-stage process.
First, you can use the plasma etch treatment to loosen the Parylene from the surface of the circuit. Normally the Parylene is bonded well to the surface and this loosening allows for a second stage process.
In the second stage a media blaster like the SWARM system can be used to remove the coating. Since the coating has been loosened it does tend to come off much easier and quicker.
That said it is still a little slow and costs are higher. But, it still can be removed more easily.
Need to find out more?
For further information on Parylene removal then contact us directly and we can help you.
If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.