Mr. Krup:

Whether you want to use pH or conductivity to replenish a resist stripper
depends on the pH that you want to maintain.   If the resist stripper is
Caustic (NaOH, or KOH) based, you will want to maintain a pH of greater than
13, and frankly, measuring pH at that high is iffy, and inexact, and
concentration and pH do not correlate well at that range, so you would want to
use conductivity.

However, if you are using a Monoethanolamine based stripper you will likely be
running in the pH =10 +/-- range, and conductivity does not work well in that
range, but pH is a great control, some of our customers are controlling using
pH, and loving life.

The iffy one is Choline, or Tetra Methyl Ammonium Hydroxide based strippers.
These strippers will want to run at pH = 12.5, or so, and this is at the high
end of the pH control range, and at the low end of the conductivity control
range.  I would make measurements using both, if I were in this situation.
Conductivity has a GREAT advantage over pH, because the "probe" does not have
to touch the solution, it can be a ring around a pipe/manifold intake.  (These
are called Toroidal controllers), but if it cannot keep the stripper constant
in performance, it is not worth much.

The thing about controlling at pH above 12, is that standardizing becomes a
real science.  You really must use pH 10 buffer, and even pH 12 buffer.  And
these buffers are not real stable, and should be used once, and thrown out.
You cannot even buy pre-made up pH 12 buffer, it comes in capsule form, and
must be dissolved.  So, using pH for high pH measurement has its own
challenges.

Have you had more help from any other competitors in a while?

Best regards,

Rudy Sedlak
RD Chemical Company

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################