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| Date: | Mon, 11 Oct 1999 15:16:24 -0400 |
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I've run into this problem several times. You are setting up a
galvanic reaction between the gold and copper causing the copper to
etch faster. I've solved this two ways.
1. If possible tape the tabs or gold area completely. This prevents
the reaction but involves a good deal more in handling. There is also
the tape residue.
2. Preclean the panels utilizing a non acidic cleaner. I use a Hyoki
with an aluminum oxide grit. Test your panels to determine best speed
and pressure as well as to see if the boards hold up.Clean your panels
then go into whatever process you are doing.
I have found the 2nd method to work the best. Even with soft gold I've
had no problems with reducing the gold thickness.
______________________________ Reply Separator _________________________________
Subject: [TN] Micro-etch attacking copper when gold tabs are involved
Author: Franklin <[log in to unmask]> at smtplink-hadco
Date: 10/8/99 2:51 PM
Okay brainiac's, here's a stumper.
We are witnessing micro-etch attacking exposed copper circuitry only on boards
with gold tabs.
This occurs right at the copper to gold demarcation point.
This only just started, within two days.
No significant process changes have occurred. (normal replenishments, all data
looks nominal)
We first noticed it after we stripped off some poor white tin for rework. When
we inspected the boards before
the second trip through immersion tin, we saw reduced circuits, some to the
point of non-existing, pads etched away far beyond anything the micro-etch
should be capable of in the seconds we keep product in this bath.
From our supplier, they believe the gold is reacting with chemistry in the
micro-etch bath??????
Has anyone else witnessed this? And how'd you resolve it?
Thanks,
Franklin
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<DIV><FONT color=#000000 size=2>Okay brainiac's, here's a stumper.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>We are witnessing micro-etch attacking exposed
copper circuitry only on boards with gold tabs.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>This occurs right at the copper to gold
demarcation point.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>This only just started, within two
days.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>No significant process changes have occurred.
(normal replenishments, all data looks nominal)</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>We first noticed it after we stripped off some
poor white tin for rework. When we inspected the boards before</FONT></DIV>
<DIV><FONT color=#000000 size=2>the second trip through immersion tin, we saw
reduced circuits, some to the point of non-existing, pads etched away far beyond
anything the micro-etch should be capable of in the seconds we keep product in
this bath.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>From our supplier, they believe the gold is
reacting with chemistry in the micro-etch bath??????</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>Has anyone else witnessed this? And how'd you
resolve it?</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>Thanks,</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>Franklin</FONT></DIV></BODY></HTML>
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