Steve, just got around to reading your post. Are these the same kind of
boards that you have been processing? Some time back I had boards that would
not pass cleanliness test. Checked everything in our cleaning system, all
good. Found that the more we washed them and the longer they were in the
Ionograph the worse they were. Turned out that the soldermask was leaching
something. The board vendor of course said that was impossible but baking the
assemblies overnight fixed the problem.
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Thursday, February 26, 2004 12:36 PM
To: [log in to unmask]
Subject: [TN] Conductivity and Resistivity Correlation
Hi All!
Is there any chart, formula, or conversion that I can use to correlate a
conductivity reading to a resistivity reading?
The reason I'm asking is that I have a new batch cleaner that has been up and
running the last three weeks or so. One of the neat things with the cleaner
is that during the rinse cycle, it monitors the rinse water resistivity to a
setting that you program in the machine. If it reaches that pre-programmed
resistivity setpoint before completing the number of rinse cycles that you
program,
it will terminate the rinse cycles and go into the dry cycle. If it never
reaches the resistivity setpoint within the number of rinse cycles that
you've
programmed, it will display "FAILED" on the touch screen. You can then run
another cycle, or start trying to figure out why the boards didn't come
clean.
Well, everything has been going fine with the cleaner up until yesterday.
Every batch of boards I ran failed the resistivity setting I had in the
machine.
The manual recommends a setting between 350-750 kohms, I've had my setting at
550 kohms from the beginning, and everything has been fine. I've had to lower
the setting to 400 kohms so the batches would pass. It's still within the
350-750 kohm range, but I'm curious why all of a sudden things won't pass at
550
kohm like it's been doing the few weeks.
So I called tech support for the cleaner, and they feel that my input DI
water may be going bad. I have a US Filters reverse osmosis filtering system
that
dumps that water into Ion exchange columns and that water goes directly to my
cleaner. The DI system displays the conductivity of the output water in µS
(micro-siemins). I want to correlate that to resistivity to see if my DI
water is
truly going bad.
Thanks!
-Steve Gregory-
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