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