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April 1997

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Subject:
From:
Ed Cosper <[log in to unmask]>
Date:
Wed, 23 Apr 1997 13:53:45 -0500
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Joef,

I used to have the same "inconsistencies"  when I worked for a military shop. I found that by baking panels after drilling reduced the variation of the etchback. As for the gouging, this is probably drill quality. The baking after drill seemed to provide a more even "cure" of the laminate and the epoxy residue that was melted due to the heat generated by the drill. I don't know if you bake after drill but if you don't it is something to try.

Ed Cosper
Graphic Electronics,
Tulsa OK

----------
From:  joef[SMTP:[log in to unmask]]
Sent:  Friday, April 18, 1997 12:43 PM
To:  [log in to unmask]
Subject:  FAB: Etchback & NaMnO4 bath life

     
     How does one determine when (if) a sodium permanganate bath is spent??
     
     Problem: Our previously calibrated [Mil-class] etchback cycles for 
     various epoxies are now requiring 2-3 cycles; sections show too much 
     variability from .0005"-.0013"; lots of "gouging" into glass-rich 
     regions with lowest etchback at the copper interface.
     
     Conditions are as follows:
     - All chemistries (solvent swell, permanganate, glass etch) are within 
       vendor specs.
     - NaOH normality: 1.2-1.3
     - NaMnO4 concentration: 60-70 g/l 
     - MnO3 conc. 9 -12 g/l
     - S.G.: 1.13
     - 180 gal tank with 500A continuous electrolytic regeneration
     - swell temp: 175 degF,  permanganate temp: 185 degF
     
     Vendor's tech service won't touch this one - if you want to do 
     chemical etchback "you're on your own"...
     
     Any ideas out there before I dump this bath?
     
     Thanks, Joe Felts 
     PC World, Toronto

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