|Ask the Experts|
June 21, 2021
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.
Principal Materials and Process Engineer
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.
Technical Expert Sales Support
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.
Engineering and Operations Management
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