To:        D. Stewart
     From:      Richard Denier  - Facilities / Maintenance Mgr
     Re:        Sulphuric acid & pumice
     
        We have had a Pumiflex in operation at our plant for over 12 years 
     and have experienced the same problem you are having.  I.S. did not 
     recommend using sulphuric and neither did our other suppliers at the 
     time. Although it may be a band-aid, it is still practiced here.  The 
     main slurry tank holds approximately 50 litres and in that, we add 9 
     kg of pumice / 250 ml of sulphuric acid and fill the rest with water.
     
     Caution:
     
     1.  Make sure that the core material from your brush manufacturer is  
     a high grade stainless steel, otherwise the acid will eat through the 
     core.  This will occur within 36 hours of production and may upset 
     your maintenance staff ( slightly ) when they have to peel the brushes 
     out of there! 
     
     2.  Do not exceed 250 ml of acid, or it will also attack the cotton 
     socks that cover the pinch rollers.  This will defeat the purpose of 
     the pinch rollers and cause excessive dragout into your rinse section. 
     
        I don't know if this is what you had in mind, but I figured you 
     should know that your not alone!  We have had good results over the 
     years with this method.  Please call me if you wish to go into further 
     detail. ( 416-299-4000 ext#314 )
     
     Regards, Richard Denier
              PC World, Toronto, Canada
               
     


______________________________ Reply Separator _________________________________
Subject: sulphuric acid and pumice!
Author:  donb at PCWORLD
Date:    6/25/96 3:45 PM


    \0
   TO:         I4235700 IBMMAIL   new address for ipc technet 25.6.96
     
   FROM:       DSTEWART EX2       D.Stewart        - Product Development
Manager.
     
   DATE:       25 June 1996
   SUBJECT:    sulphuric acid and pumice! 
   REFERENCE:  removal of nitric stains
     
    I'm back online again after a 6 month absence due to technical 
    difficulties - I could read but not write. I am a voice to be heard 
    again!
     
    We have an issue with nitric acid stains on boards after tin lead 
    strip - the cause is known and relates to processing thin laminate 
    cores through outer layer processing, but that's another story. 
    Prior to soldermask, we cannot remove these stains by standard 
    pumice, but we can remove them by passing through the 1% H2So4 rinse 
    on our developer prior to pumice. We are obviously trying to reduce 
    handling and interference with a different process so we are trying 
    to find an inline method of removing this stain.
     
    Our pumice machine supplier (IS) is not keen on us using sulphuric 
    in the pumice machine, a nearby friendly shop with the same problem 
    tried citric in the pumice but it turned the boards yellow! so does 
    anyone out there have the same problem, or another solution?
     
    Dougal Stewart
    Exacta Circuits
    Scotland