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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