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Printed Circuit Board Assembly & PCB Design Forum

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silkscreen issue

Views: 3462

#40186

silkscreen issue | 4 March, 2006

Something unusual happened yesterday, we reflow soldered two boards with white silkscreen legend, and they came out of the oven with purple silkscreen legend.

Not tan or brown from overheating, but purple. The boards were reflowed on their normal profile.

Anyone out there have this happen before, and what was the root cause? I suspect the silkscreen epoxy material, either wrong type used or the two part epoxy was mixed at an improper ratio.

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#40200

silkscreen issue | 6 March, 2006

Epoxy inks tend to be more resistant to discoloration than the acrylics that are used more widely now. The acrylic-based inks vary in their ability to maintain color after heat cycles. The technical data sheets from the ink supplier should indicate: * Testing has been done. * Limits of exposure to thermal, chemical and mechanical conditions.

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RDR

#40203

silkscreen issue | 6 March, 2006

I have had the purple silkscreen, I don't remember the exact details but it was from either an incomplete cure or a mixing issue. End result was no problems just looked funny.

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#40358

silkscreen issue | 12 March, 2006

Thanks Russ. As it turned out, it was an incomplete cure at the fab house. Rhey sent another fab over from the same lot that had sat for 3 more days, and it came out lavender instead of purple!

have a good one!

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cmiller

#40359

silkscreen issue | 12 March, 2006

We had the same issue on a batch of boards and the board house concluded it was because they did the sikscreen before the imersion gold. (which was done out of house-which is very undesireable). I never knew if this was really the case but thought I would throw it out there. It was more a blueberry than purple. It was ammazing because it was white before reflow, then deep blueberry after.

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RDR

#40377

silkscreen issue | 13 March, 2006

Our PCB also had this process.

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