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From [log in to unmask] Tue Jun 25 14: |
00:56 1996 |
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TO: I4235700 IBMMAIL new address for ipc technet 25.6.96
FROM: DSTEWART EX2 D.Stewart - Product Development Manager.
DATE: 25 June 1996
SUBJECT: sulphuric acid and pumice!
REFERENCE: removal of nitric stains
I'm back online again after a 6 month absence due to technical
difficulties - I could read but not write. I am a voice to be heard
again!
We have an issue with nitric acid stains on boards after tin lead
strip - the cause is known and relates to processing thin laminate
cores through outer layer processing, but that's another story.
Prior to soldermask, we cannot remove these stains by standard
pumice, but we can remove them by passing through the 1% H2So4
rinse on our developer prior to pumice. We are obviously trying to
reduce handling and interference with a different process so we are
trying to find an inline method of removing this stain.
Our pumice machine supplier (IS) is not keen on us using sulphuric
in the pumice machine, a nearby friendly shop with the same problem
tried citric in the pumice but it turned the boards yellow! so does
anyone out there have the same problem, or another solution?
Dougal Stewart
Exacta Circuits
Scotland
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