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June 27, 2018

Cleaning Military Circuit Boards Contaminated with Sand

We are repairing military electronic equipment that has been in the field. The circuit boards are contaminated with sand, dirt, grime, sometimes oils, etc. The boards had been conformal coated with acrylic and urethane coatings.

We were considering processing the boards through an aqueous spray cleaner, but have not found a detergent that is compatible with the acrylic coating and can be used in high pressure spray equipment. Any ideas on the best way to clean these boards, especially the removal of sand, without removing the conformal coating.


Experts Comments

Cleaning of this type can effectively be done with a low pressure (25 PSI) wash system with a weak 1% saponifier (either the Kyzen or EnviroGold saponifier) at 125 F wash and ambient rinse a belt speed of 4-5 ft/min and rinse with DI water at low pressure.

By using the weak saponifier the surface tension is lowered and has a bit of cleaning energy but not enough to attack the acrylic coating. By using low pressure in wash and rinse will remove the residue but not ablate the surface of the coating. If you want to run ten test boards through this set up please contact me at Foresite.

We have been removing field residues on military hardware and removing military and avionic coatings for repair for 8 years give us a call and we can help you set up the appropriate approaches to coating removal and cleaning. 
Terry Munson
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.

Acrylic conformal coatings are "thermoplastic" coatings which are used if the coating has to be removed easily or if through-soldering repair should be possible. Acrylic systems can be removed very easy by some solvent especially at higher temperatures as they are thermoplastics. So you have to use a cleaning agent which is not solvent based or which has a very low solvent content and the temperature should be as low as possible. Products that we would recommend would be from the Atron and Vigon product range.

Umut Tosun
Application Technology Manager
Zestron America
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".

This is a tough question, because most of the cleaners strong enough to remove heavy oils and grime will also begin to damage the conformal coatings.

To my mind, the spray wash is taking the solution in the wrong direction. You're going to use lots of water and water-treatment machinery, lots of electricity to wash and then dry, and quite often have problems with quality of the result. Unless you already have the equipment to use, this is a slow and expensive way to clean these boards.

My suggestion would be to look at a vapor degreasing option, using a milder solvent that will remove the oils but not damage the conformal coatings. You could, if desired, enhance the cleaning with ultrasonics -- the general prohibition on ultrasonics and PCBs has faded into history as the myth it was. The boards will come out clean, dry and with relatively short cycle times (especially when compared to water-cleaning) which will boost through-put.

For solvents, I suggest you check with 3M Novec or DuPont's Vertrel (the
latter of which we sell, so my bias is strong).

For cleaning machinery, Branson Ultrasonics (818) 707-7001, and Ultronics (800) 553-7881, make excellent machines, as does Tiyoda Serec, 502-212-9226.

Mike Jones
Vice President
Micro Care
Mr. Jones is an electronics cleaning and stencil printing specialist. Averaging over one hundred days a year on the road, Mike visits SMT production sites and circuit board repair facilities in every corner of the globe, helping engineers and technicians work through the complex trade-offs today's demanding electronics require.
I would try a very weak Saponifier solution bubbled through a cleaning tank to remove the sand and other residues. This technique removes solder powders very efficiently and should be safe on the coatings
Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
I think to remove the sand/grime/loose debris, I would use a very low pressure source (dry) such as nitrogen or even a commercial nonflammable "duster" using 134a or the new HFO 1234ze. This would avert damaging the coating since low pressure is used and would avoid the blasting effect.

To further clean without damaging the coatings (acrylics are more easily damaged than urethane), I would recommend a very mild non-alkaline detergent in a batch cleaner. Many aqueous formulas, generally used for defluxing etc, are highly alkaline and can strip acrylics either by a saponifier or other included solvents (often glycol ethers).

Many detergents are also alkaline as well as high foaming. A low foaming surfactant solution can quite possibly clean the remainder of the oils etc as well as any other particulate debris not previously removed. I would be glad to speak with anyone concerning this issue and am always ready to resolve these types of cleaning problems.
Pierce Pillon
Laboratory Mgr.
Pierce Pillon is the Laboratory Manager and lead formulations chemist at Techspray, a division of Illinois Tool Works (ITW) and a leading manufacturer of chemical products for the electronics industry.
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