Date: Mon, 20 Jul 1998 10:49:07 -0400
From: Bill Page <[log in to unmask]>
Subject: An aqueous cleaning question
Hey, folks,=20
I should know where to find this, but my brain is getting old.
We recently changed the lower limit for our H2O processing (for washing OA
= fluxes) from 200KOhms to not less than 1 megOhm. Obviously, when the
beds = are new, we run in the 10 meg range.=20 So one of our customers
wanted to know how we set 1 meg as the lower = limit...our answer, of
course, was that it was based on experience and = what other folks are
doing...
Can anyone give me a better (i.e., more supportable) answer that I can =
give to my (45% of my business) customer?
Thanks,=20
Bill
Actually, there is no valid reason for any setpoint except experience. Most
water recycling systems will run in the 6-20 ppm range even thought the original
specification was 1 megohm or something like that. It is not real. Changing
from 200 kohm to 1 meg ohm means that you changed your spec from .6 ppm
HCl to .015 ppm or from 2 ppm NaCl to .4 ppm or from 11 ppm CO2 to .7. It
depends on what is the contaminant. If 2 ppm salt is really a contaminant
problem, you must be doing wafers. The real contaminant problem is what you
try to rinse off the panel, and don't get rid of. 2 ppm should rinse the panel just
as well as .1 ppm when you have it covered with flux and salts. If you are
having problems, you might want to experiment with spray bar angles, flow
rates, pressures, etc.
What is the absolute limit? I doubt if anyone know or can know. It is all
experience. It will change with machine set up and THE TEST FOR
CONTAMINANTS that is performed on the finished panel.
You will get more contamination from your hands just handling the panel than
you will from a 2 ppm rinse. Are you a white glove operation?
It isn't what the water puts on the panel that is usually the problem, it is what it
doesn't take off and this is mostly machine setup.
Best Regards,
Bob Mesick
Remco Engineering
Water and Wastewater Treatment Systems
http://www.remco.com
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