Dear Darik,

We experienced a similar problem a few years ago, we found that by putting in a caustic pre-dip and changing it out weekly, we problem went away.  When we would try to extend the bath, it would gradually return.  However, usually we could see a reddish color streaking before we pressed it. You might have to look close and angle the layer in a light source.

Hope this help,

Ed Cosper
Director, Quality Assurance and Engineering
Graphic Electronics, Inc.

----------
From:  [log in to unmask][SMTP:[log in to unmask]]
Sent:  Saturday, March 08, 1997 4:22 PM
To:  [log in to unmask]
Cc:  [log in to unmask]
Subject:  Re: Black-oxide layer turned red after pressing

Hello Technetters:

    Recently we are having a problem on our black oxide layer color. 
After pressing (especially for 4 or 6 layer board with thin outer
prepreg, e.g. 2116 single ply), the black oxide around the edge of some
boards seemed to turned red.  This caused particularly low yield
recently.  

    Can anyone knidly give some advice, or have some experience on such
issue?


Darik Leung
Mica-AVA (F.E.) Ind. Ltd. /
Oriental Printed Circuits Ltd. (HK)
Quality Assurance
[log in to unmask]
What do you see after oxide processing before layup?
typically it is caused by two things: Either a temperature issue
          during the run thru or a concentration drop in the oxide
          chemistry.  I have seen two other instances one is
          copper/laminate supplier using too much chromate conversion
          coating and the other was very thick cores.  


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