Charles Barker@I-O INC
01/29/98 04:56 PM

Richi,

A few questions:
1. You said your are pcb manufacturers. Are you a raw board maker or an
assembler of parts onto raw boards? I think you are the latter.
2. Are all of these problem boards from the same PWB vendor?
3. Do you process any other boards from that same vendor?
4. What is the underlayment material and thickness beneath the gold flash?
5. Do you have a means of verifying the thickness of the gold?
6. Can you see any sort of blemishes on the fingers prior to reflow?
7. Could you have some contamination on the bottom of your stencils for
this board?
8. Has anything changed in you stencil cleaning or stenciling process?

Just a few things that came to my mind. Hope this might help.

Good luck.
Charlie B.




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Subject:  [TN] Solder spots on gold fingers




We are PCB manufacturers and seem to be having a enigmatic problem on one
of
our boards we manufacture for one of our customers.
The board is a double sided 0.062" SMOBC board with flash gold goldfingers(
1-3 microinches). The assembly process consists of screen printing of
solder
paste, pick and place SMT machines , Reflow, manual insertion of through
hole
components and finally wave solder. The problem manifests itself after IR
reflow. There are tiny silverish/grey spots on the goldfingers. Suspecting
that the spots were caused by solder paste particles which were either
deposited because of contaminated equipment or degassing from the PTH
causing
splattering of solder paste we ran the next batch of boards using Kapton
tape
on the gold fingers. Unfortunately we saw the same spots again. The straw
which broke the camels back was when a recent datecode boards fresh out of
the
cartons were run without Kapton tape and exhibited the same symptoms.
Our dilemma:
We manufacture 30 P/Ns for this customer. The problem is only on this P/N.
The
same lines are used to run all the boards.
We have manufactured thousands of these boards without any problem and now
suddenly we have this issue.
The same assembly line used to assemble this board is used to run other
boards
we manufacture and no other P/N exhibits this problem.
Hope somebody has seen such a manifestation and can advise.
Thank you.
Richi
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