Lowering Nitrogen Levels to burn off flux residue

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I am currently building boards which have to be conformal c... - Aug 11, 2000 by

GJ: If your supplier uses a conformal coating that "must be... - Aug 12, 2000 by davef

#3329

Lowering Nitrogen Levels to burn off flux residue | 11 August, 2000

I am currently building boards which have to be conformal coated (done by an outside source) in a no clean process. The conformal coating however, must be applied to a clean surface. The flux residue left from the paste has come into question. I have been adviced to reduce the Nitrogen content during reflow. It will supposedly aid in burning off more flux during reflow. However, to my knowledge, the addition of Nitrogen is supposed to aid in less flux residue. So which is it?

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davef

#3330

Re: Lowering Nitrogen Levels to burn off flux residue | 12 August, 2000

GJ: If your supplier uses a conformal coating that "must be applied to a clean surface," then you are using the wrong supplier and no amount of twiddling with your N2 levels will change this.

NC fluxes are inherently "dirty" and nothing aside of cleaning will change that. Generally, these "dirty" NC flux residues are not the type that affect the long term reliability of most boards.

Some conformal coatings are compateable with some NC fluxes. You and your supplier must determine the correct combination.

Playing with N2 levels has a minor effect on NC flux residues. Flux choice, reflow profile, and cleanliness of in-bound boards and components each have a far greater effect on flux residues.

Good luck

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