Ask the Experts
February 18, 2019
Removal of Coatings from PCBs
What the best way to remove coatings from assembled PCBs. Can you point me to some type of guide?
Expert Panel Responses
It will depend on the coating type for the right approach and if you want specific areas removed or total board removal. Dynaloy Corp. makes a variety of chemical stripping agents.
President/Senior Technical Consultant
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.
The short answer to this question is "use the materials and process recommended by the coating manufacturer." It truly is always best to look at the coating material manufacturer's data and select chemistry based on their recommendations. That said, in general acrylic coatings can be removed fairly easily without damage to the PWB.
Silicones are a little tougher to deal with, but usually can be removed. Urethane coatings can be extremely difficult to remove, and the chemistry used to strip them will leave ionic residues that are very hard to remove. I recommend removing this type of coating only in small areas, not across an entire board.
In fact, it is a good general rule to avoid wholesale removal of any coating where possible. In some cases, rework can be performed without any removal (burn through the coating). If you do this, use very good ventilation that draws away from the operator.
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
IPC-7711/7721B has a multitude of information including how to identify and remove coatings from a circuit board. To begin, the IPC-7711/7721B has a procedure for identification of the coating and the best method for removal. Procedure 2.3.1.
Once you have identified the coating, there are 5 different methods for removing the coating. Then there are 2 methods of coating replacement!
Manager of Assembly Technology
Kris Roberson has experience as a machine operator, machine and engineering technician and process engineer for companies including Motorola, and US Robotics. Kris is certified as an Master Instructor in IPC-7711 / 7721, IPC A-610 and IPC J-STD 001.
The best way to remove conformal coating depends on the coating that is to be removed, how hard that coating is, how thick that coating is, and whether or not you are removing it from a small area of the board for rework purposes, or trying to globally strip the coating from the assembly.
The coating manufacturer can recommend the best chemical stripping agent and the optimal parameters. Companies that make chemical strippers,such as Dynalloy, may also be able to provide guidance.
Mechanical means of stripping, using specialized media blasting such as Crystal Mark's Swamblaster or CCRD are good for localized removal of coating, especially the more rigid kinds like Parylene and Urethanes.
The various methods are covered in greater depth in the IPC-HDBK-830, Rev A, Conformal Coat Handbook. Available from the IPC. A valuable reference tool for anyone who has to work with conformal coatings.
Principal Materials and Process Engineer
Doug Pauls has a bachelors in Chemistry & Physics, Carthage College, BSEE, Univ of Wisc Madison. He has 9 years working experience for US Navy - Materials Lab, Naval Avionics Center Indianapolis. 8 years Technical Director, Contamination Studies Laboratories. 11 years Rockwell Collins Advanced Operations Engineering.
Coating removal from a PCB depends on several factors: 1) type of coating, 2) type of substrate, 3) type of materials on the board.
Generally, your Type of Coating is going to be a) water soluble, b) solvent soluble, or c) impossible to remove by chemistry. Your Type of Substrate will probably be either a) G10 epoxy-based, b) polyimide, or c) ceramic. The Type of Materials on the Board are is very critical assuming that you actually wish to reuse the board. Be careful of sensitive plastics such as polycarbonate or Lexan, connector inserts (ZZR765 red rubber silicone, or others) ... So, in order to guide you more info is needed; there is not a simple guide.
If you are simply looking for information on "what dissolves what",you should get a copy of this book by Allan Barton and learn about Hildebrand Parameters, "Handbook of Solubility Parameters and Other Chohesion Parameters" CRC Press.
It will help you to understand what solvents dissolve which polymers.
Rick Perkins is a chemical engineer with more than 33 years of Materials & Processes experience. He has worked with Honeywell Aerospace in high-reliability manufacturing, as well as with several oil-field manufacturing companies. He also has a good understanding of environmental, health, and safety regulations.
How about laser ablation? You can use a laser beam to remove the coating in some areas whilst keeping the coating in others. There is no residue and one can also avoid damage to the layers underneath. Other components won't be impacted. The spatial resolution is in the 10s of micro-meter range.
Dirk Mueller, Coherent