Well, I can't sit quietly through any more of this. As I said earlier, pink
ring is by no means a new phenonmenon, and several articles were written
about 8-10 years ago. They were the ones I listed, plus of course there
were/are others.
Let me just say, some people dealt with pink ring in these ways:
1) Redesign or reconstruct the board so the oxide layer points inward and
you can't see the PR.
2) Use a dark laminate or polyimide, so you can't see the contrast.
3) Use a red oxide, which is much lighter, so you can't see the contrast.
4) Hide it with solder mask.
Some others blamed their electroless and electroplating and sometimes the
oxide suppliers. When I worked for Enthone we learned a lot about
lamination and drilling, etc., in order to determine if it really was a
chemical problem. We spent a lot of time teaching customers how to make
their boards better.
But, also, I don't believe that PR was as much problem prior to that time,
because boards were simpler: there weren't as many layers; the drilled
holes were larger and further apart, plus people didn't drill more than 1 or
2 high because production needs were low; only the "high tech" companies
were making the MLs; and/or (maybe) the FR-4 lamination process in use was a
little more forgiving (i.e., heat-up and cool-down were not rushed to get
out more production).
It gets back to what the articles say, that pink ring is an Indicator of
other process problems, and those problems can begin back as far as the
quality of the pre-preg to be used in lamination. Optimization of the
copper-oxide-resin (C-O-R) bond that is created during lamination (by
optimizing the oxiding, lamination and drill processes) is the key to
reducing or eliminating PR.
The danger of the oxide reduction processes, and other means that hide pink
ring, is that THEY DON'T ADDRESS THE REAL CONCERNS OF A WEAK OR POOR THE
C-O-R BOND. Therefore, if you just try to hide the PR, do you have a good
bond or don't you? So, optimize the processes first, starting with the
first process, and use the amount of PR found as an indicator of how well
you are optimizing. Then, when you have optimized as best possible, and
know you have a strong C-O-R bond, THEN decide if you want to use an oxide
reduction process.
Note: some of the oxide reduction processes may be able to improve the
C-O-R bond beyond what regular oxide can give you. But, as you optimize the
whole manufacturing process, you should be able to determine that.
Patty
----------
From: tgyee
To: TechNet
Subject: Re[5]: Mechanism of Wedge Void Formation
Date: Monday, July 21, 1997 10:19AM
How come chemical vendors almost always emphasize that their oxides
are converted/reduced? Is the reduction process a relatively new
technology?
If so, before the reduction process is available, how did PCB shops
prevent pink ring formation?
The reason I ask is that, since there is a "pink ring" solution -
reduction of oxide, whenever there is pink ring occurence, one would
point at the reduction process by first instinct, forgiving other
possible pink ring causes. We once faced an extremely painful pink
ring crisis, and were able to end it by improving the oxide reduction
process. However, during the crisis, I found out that I can separate
the oxide-coated copper from the prepreg by using a knife. It was that
easy even without thermal-shocking the board. And after the separation
there was not even a bit of oxide seen on the prepreg side. I
considered this as an evidence of poor lamination.
Although we solve the pink ring by oxide reduction, I think may be
we might not have the problem in the first place if the lamination is
in perfect contition.
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