This is cut and dry response, but you'll get the jest of it.
     
     I've used pH and titration methods in the past, but with using KCO^3 
     and not KOH.  The pH method worked well, provided the following was 
     monitored and maintained PROPERLY.  I can not stress enough how it 
     must be maintained PROPERLY.  The Titration method was questionable.  
     I could never get the right percentage of weight by volume of KCO^3.  
     
     As some have mentioned you need a pH meter.  Ensure the location of 
     the meter is near the bleed or overflow.  A Flow Valve is also 
     recommend (furthest from the overflow) on the Stripper Unit, if not, 
     acquire one.  Remember to pre-mix the stripper prior to dumping into 
     the daytank or feed and bleed tank.  There were too many cases at many 
     different companies the unmixed KCO was added to the feed tank.  Add a 
     pump and heater to the feed tank and while your at it some defoamer.  
     The ball valve should be set as low as possible 1~2 gallons/min to 
     ensure proper filling of the process tank.  Any greater will be 
     solution waste and the hysteresis of the pH meter will be over shot.  
     The pH should be maintained at about 10.4~10.7, with a ±0.05.
     
     These comments are of my own and do not reflect my companies view 
     points.
     
     John Gulley - Process QE
     INET Inc.
     1255 W. 15th Ste 600
     Plano, TX 75075


______________________________ Reply Separator _________________________________
Subject: Re: [TN] automatic replenishment of resist stripper.
Author:  Ted Stern <[log in to unmask]> at Internet
Date:    9/25/98 9:00 AM


Dear Mr. Kurup:
     
I believe the applicability of pH control applied to automated resist 
stripping is dependent upon the chemistry.  I have had success with some 
types of resist strippers (typically formulations which employ a strong 
bas) and failures with others.  Unlike developing, the speed and 
performance of many resist stripper formulations appears dependent on 
more variables than the pH; and it was observed changes in the pH were 
not directly proportional to changes in other stripping factors, hence 
control by pH alone proved insufficient.
     
Also, if you are free to share the information, I would be interested in 
learning about your experience with conductivity control.
     
Regards,
Ted Stern
     
Lenny Kurup wrote:
>
> Hello Technetters,
>
> Anyone out there using pH control for automatic replenishment of resist 
> stripping chemistry. Conductivity control works fine, but I wonder if
> anyone has been able to optimize pH control. 
>
> Thanks for all anticipated responses. 
>
> Lenny Kurup
> EMX Enterprises Ltd.
> 905-475-8000 ext 240.
>
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