Completely removing Parylene from a circuit board- How to do it successfully and be cost effective
Parylene coating removal from a circuit board is not easy. In fact it is a hard process to do well!
Compared to typical liquid conformal coatings like acrylics and even urethanes that use more easily dissolve in mildly aggressive solvents then it is much tougher.
The problems are many 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.
This leaves another well know method for Parylene. That is mechanical abrasion.
Mechanical abrasion 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.
Also, it tends to be a localised repair and removal technique. The concept of completely removing all of the Parylene off a circuit by mechanical abrasion is considered almost impossible unless a ridiculous amount of time and effort is injected into the process.
The concept of completely removing Parylene from a printed circuit board assembly is considered almost impossible unless a large amount of time and effort is used in the process.
An alternative method for completely stripping Parylene from a circuit board
Due to our research recently on methods for removing Parylene we have developed a process for completely removing the coating from the surface of a circuit.
However, there are two methods.
- 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 we have developed a special process in-house involving plasma etching.
The plasma-etch process uses a proprietary blend of gasses developed by us, 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.
Further, the etching process is quick relative to the other mechanical methods. Typically, the circuit can be completely etched of Parylene in under an hour.
Also, 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, we use the plasma etch treatment to loosen the Parylene from the surface of the circuit. Due to our processes we have normally bonded the Parylene well to the surface and this loosening allows us to prepare for the next stage.
Second, we use a media blaster like the SWARM system 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.