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July 1997

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From:
"Goldman, Patricia J." <[log in to unmask]>
Date:
Mon, 21 Jul 97 12:53:00 PDT
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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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