Several people have forwarded to me a message about reducing rinse water flowrates from the TechNet.  So here is what I know:

At the May 1995 IPC Expo in San Diego, Larry Lemke of Sheldahl (Longmont, CO)
gave a talk on Environmentally Conscious Mfg of PWBs.  During his talk, he
gave out some information about triple-cascade rinsing and some conductivity
requirements.  The cleanest water is injected into the final rinse (cell #3),
and overflows into cell #2, then into cell #1.  The DI water injected into
cell #3 is 1-2 micromho (500,000 ohms to 1 Meg-Ohm).  This injection occurs
when the conductivity of cell #3 reaches 10 micromhos (100,000 ohms).  Cell
#2's conductivity is typically 14 micromhos, and cell #1's conductivity is
16 to 18 micromhos.

Our DI water is normally 16 to 18 Meg-Ohms, which is probably the typical
conductivity (or actually resistivity) of everyone's DI water (that's just
what you get with DI columns).  Larry's work at Sheldahl seems to say that
you can get by with basically Reverse Osmosis-quality water.  Our RO system
upstream of our DI beds puts out 500,000 ohm water.  However, it would be
best to talk to Larry, and see how things are working out with those
conductivity requirements.  At the time of his talk, the Longmont facility
was in low production mode, and maybe the rampup has changed things somewhat.
If you need a copy of the paper that Larry published in the Expo proceedings,
e-mail me back your fax number.

John Sharp
Merix Corporation, Forest Grove, OR
503-359-9300 (ext. 5-4351)
503-359-1040 FAX
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