Ask the Experts
June 27, 2024 - Updated
April 16, 2014 - Originally Posted

Question About J-STD-001

We have a requirement to conformal coat a PCB assembly that is processed using a no clean flux. The customer is asking for the product to meet J-STD-001. Can we apply conformal coating over boards processed with no-clean flux and meet the requirements of J-STD-001?


Expert Panel Responses

The short answer is yes. J-STD-001, in both the present Rev E and the proposed Rev F (nearing finalization) there is no linkage between flux usage or low solids flux residues, and conformal coating.

The coating film has to go where it says on the drawing, not go where it says to not go in the drawing, and have good adhesion. It is now, and has always been on the OEM to determine if the selected coating on the selected assembly with the selected material set is adequate.

Doug Pauls
Principal Materials and Process Engineer
Collins Aerospace
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.

You will hear a common phrased answer, "It all depends."

You have not specified the final application of your assemblies. Therefore I would be hesitant to accept a definitive yes answer without doing a thorough evaluation.

If the exercise of running a DOE with adhesion, thermal shock or other performance tests is too daunting of a task then based off my experience I would advise to thoroughly clean the assembly of all flux residues.

So going back to the phrase "It all depends." Many of my customers who build assemblies for aerospace, medical, automotive and military cannot afford to take the risk of a system failure that can be traced back to a no clean PCB assembly. So all the flux must be removed. The cost to wash the flux is cheaper than a product recall.

If you are not equipped to wash your PCB's at this time feel free to contact me for assistance in this matter.

Charlie Pitarys
Technical Expert Sales Support
Kyzen Corporation
Charlie Pitarys has over thirty years of industry experience and has been with KYZEN for twenty-one years. Charlie is a former Marine and a retired Sargent First Class in the Army Reserves. His previous employers include Hollis and Electrovert. Charlie continues to use his expertise on cleaning processes and machine mechanics to help KYZEN customers and partners improve their cleaning operations.

Without running a DOE it is very difficult to assess the risks involved with this. A rule of thumb is that if an assembly is going to be coated, it has to be clean(that implies that all flux residues need to be removed prior to the coating application).

The no clean flux residues can be removed - I recommend you to get the suppliers involved in this (the solder paste supplier and the chemicals supplier). They can come up with the best solution for your cleaning process.

Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at

Reader Comment
Bottom line is the flux should be removed. Any flux, can and will absorb water from the atmosphere. If you coat over the flux you entrain the moisture and that leads to many potentials for failure. The 'rules' such as J-STD-001, many allow coating over flux but if you want the best product and few failures, just wash the boards first. Now, it is important to was the boards within 24 hours of soldering for the following reason: mitigation or prevention of Dendrite ( AKA 'Whisker' ) growth.

A top American manufacturer of solder paste and solder products advised me that, with SAG, if the flux is removed within 12 hours then statically, no dendrites will form. However after 48 hours, dendrite growth can start, and once they do start, no subsequent cleaning will stop them. We changed our process to include same-day wash after soldering and at the same time our Dendrite issues were totally eliminated. We then follow with WR coating. So, following the rules is permitted. But for the best result, just wash the boards and sleep well at night knowing you have done the best possible.
Jaye Waas, Renkus-Heinz

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