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Baking prior to conformal coat

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cecil

#35652

Baking prior to conformal coat | 20 July, 2005

Does anyone have any input on the need to bake out an assembly prior to the conformal coat process? I understand baking out components/pwb's prior to processing through the reflow or wave solder process if the material shows excess moisture absorbtion using humidity indicators etc.

Just do not understand the need to bake prior to conformal coat, if there is one. Have talked to others in the industry and have received responses that thay do not bake prior to conformal coat and do not see a need to do this. Our QA dept. insists this needs to be done but can not tell me why. Just looking for more input. I have searched the archives and can not find any info on this subject either.

We use Humiseal 1B31 AR coating.

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FW

#35662

Baking prior to conformal coat | 20 July, 2005

Hi! We have both Dip & Spray conformal coating processes & have never done any kind of baking before the process! I am assuming the reason for baking would be the same - ie, remove any moisture on the brds since moisture will create failure of the coat. However, we don't see any moisture issues even though all coated boads are pre-washed thru D/I water. I don't know why your QC dept insists on this & if they can't give a justifiable reason, then they should refrain from giving directions!

Regards, FW

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cecil

#35663

Baking prior to conformal coat | 20 July, 2005

QC dept. refrain from giving direction!! Geez have I died and gone to heaven?

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dougs

#35685

Baking prior to conformal coat | 21 July, 2005

are you going to clean the boards prior to coating?

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#35698

Baking prior to conformal coat | 21 July, 2005

Tell them every action taken with the boards carries risk of damage. Process steps that don't do anything should be avoided because they carry the risk of causing defects. Even inspection causes the occasional defect, and board handling in general should be minumized.

Stephen

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#35699

Baking prior to conformal coat | 21 July, 2005

Stephen,

If you have ever gotten QC to buy into this logic you have a much better QC department than most.

Jerry

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RDR

#35701

Baking prior to conformal coat | 21 July, 2005

This is kind of odd, I am accustomed to the Q.C. dept. verifying that criterias/specs have been met per engineering and contractual requirements and not identifying or implementing these specs. I believe that this philosophy aids in eliminating the "ignorant criterias based upon theory, conjecture, and assumption".

I guess I have been lucky?

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#35833

Baking prior to conformal coat | 1 August, 2005

Hi Cecil,

We using conformal coating in our manufacturing area, we did use to use Humiseal, others have been Bectron and Peters. We recentalt switched all lacquering to Peters, since it is lead free and it is a lot friendly than Humiseal.

To answer your question we do not bake prior to coating, however all our products that are coated are continous lines, so they travel straight from wave or selectice solder to ICT to conformal coating process. So there is very little chance of moisture build up on the PCB.

Is your process similiar or does your products have a long shelf life before they are put through conformal coating process.

Easiest way to prove to QC is to palce a board into coating straight from the line and another which has been shelved for couple of weeks then carry out a humdity test on the two boards for fungal growth.

Cheers

Crishan

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