Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


LeeAnne

#12848

conformal coating after rework | 22 January, 1999

I have boards coated with Humiseal 1B73. At a late point mfg. site we need to remove a series of 0603 resistors for optioning purposes. I have been trying to determine the fastest, easiest way to re-coat the pads after removal. Drying time of the coating will slow up production on the line. Does anyone know of a substance, possibly a pen type applicator, which dries within seconds and is non-conductive?

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Dave F

#12849

Re: conformal coating after rework | 22 January, 1999

| I have boards coated with Humiseal 1B73. At a late point mfg. site we need to remove a series of 0603 resistors for optioning purposes. I have been trying to determine the fastest, easiest way to re-coat the pads after removal. Drying time of the coating will slow up production on the line. Does anyone know of a substance, possibly a pen type applicator, which dries within seconds and is non-conductive? | Hey LeeAnne!!! How are you??

Good ol� 1B73 is an acrylic. You can speed-up its cure time with heat. Alternately, try applying:

1 A drop of cyanoacrylate - "super glue" to each pad, keeping your fingers away from the pad until the glue is dry 2 A drop of UV curable adhesive to each pad and cure it with a hand-held UV lamp 3 A UV conformal coating 4 A dab of hot melt glue to the pads, if you can live with those "hairs" that you end-up with from the glue

TTYL

Dave F

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Graham Naisbitt

#12850

Re: conformal coating after rework | 23 January, 1999

| I have boards coated with Humiseal 1B73. At a late point mfg. site we need to remove a series of 0603 resistors for optioning purposes. I have been trying to determine the fastest, easiest way to re-coat the pads after removal. Drying time of the coating will slow up production on the line. Does anyone know of a substance, possibly a pen type applicator, which dries within seconds and is non-conductive? | LeeAnne,

1B73 brush applied should cure tack free within 15 minutes. If the operator is doing this job under a UV light and ventilated booth, then the production could be "batched" with many coated and left drying within a short time frame? Could that suit you?

Please bear in mind that using a different coating type to the original, will compromise MIL Spec qualification which may be important.

Using a fundamentally different coating, such as a UV, will influence flexibility and may well give you TCE mismatch.

If there is anything else I can help with, call me

Graham

Graham.Naisbitt@concoat.co.uk

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Chris Fontaine

#12851

Re: conformal coating after rework | 27 January, 1999

| | I have boards coated with Humiseal 1B73. At a late point mfg. site we need to remove a series of 0603 resistors for optioning purposes. I have been trying to determine the fastest, easiest way to re-coat the pads after removal. Drying time of the coating will slow up production on the line. Does anyone know of a substance, possibly a pen type applicator, which dries within seconds and is non-conductive? | | | LeeAnne, | | 1B73 brush applied should cure tack free within 15 minutes. If the operator is doing this job under a UV light and ventilated booth, then the production could be "batched" with many coated and left drying within a short time frame? Could that suit you? | | Please bear in mind that using a different coating type to the original, will compromise MIL Spec qualification which may be important. | | Using a fundamentally different coating, such as a UV, will influence flexibility and may well give you TCE mismatch. | | If there is anything else I can help with, call me | | Graham | | Graham.Naisbitt@concoat.co.uk | Graham is right about the 15 minute cure time for CC touch up with 1B73. If you need to speed the process up further you can do so by baking the boards. A general rule of thumb is a doubling of cure rate for every 10 deg C temperature increase. Be careful though, speeding up the cure can cause solvent entrapment, and lead to a bubbling of the coating. 1B73 cures by solvent evaporation, and this early in the cure the faster solvents are flashing off. This could leave you prone to bubbling and foaming of the coating if you choose too high a cure temp. We cure all of our 1B73 coatings for 10 minutes at room temp before baking to avoid this.

Chris Fontaine Christopher.P.Fontaine@lmco.com

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