>From the EMPF HelpLine in Indianapolis, prepared by Tim Crawford:
Nancy,

The Ionograph works on what they call a "dynamic" process as opposed to an
Omegameter (for example) that works on a static process.  If you want to
know the difference I can send you a very good description, but what you
need to know now is that the static system will deionize the solvent to a
very "clean" (pure) conductivity/resistivity value prior to testing.  The
test speciman is then dropped into the solvent where the ionic residues
disolve into the solvent.  As the residue dissolves, the
conductivity/resistivity changes.  When testing is complete, the starting
conductivity/resistivity is compared with the final conductivity/resistivity
and the change is then equated to a level of sodium chloride (NaCl).  The
reason I told you this is that with this process you can start and stop at
any time because "change" is "change".  If you don't think your
conductivity/resistivity is going to change any more you can stop and
measure that start to stop difference.

With the dynamic process (ionograph),  solvent is still deionized to a very
"clean" (pure) conductivity/resistivity value prior to testing and the test
speciman is still dropped into the solvent where the ionic residues disolve
into the solvent.  But unlike the static process that measure the difference
from start to finish, the dynamic system deionizes and tests at the same
time.  What happens is conductivity (in the case of the Ionograph)
increases, but since the solvent is also being deionized, the conductivity
will peak, then return to the baseline that it started from (forming a bell
curve).  The Ionograph then integrates the area under that curve and equates
that to a NaCl equivelant.  If you stop the test in the automatic mode it
has not formed that curve yet.  Running the system in manual mode is a way
of making sure all of the ionic material is dissolved and measured.  MAnual
mode is generally used to EXTEND the time of the test, not shorten.   If you
have any more questions feel free to call me at (317) 226-5634.

>
>In the past we have operated the Ionograph tester in manual mode for 10
>minutes with an accept/reject criteria of 20 ugNaCl/sq.in..  However, we
>discovered that this is not the proper method, that in fact, it should be
>operated in automatic mode.  The problem with automatic mode is many tests
>run for 20 to 60 minutes before detecting a levelling off of contamination.
> I have studied many test files and find a significant correlation between
>the contamination measured at 10 min. vs. the final contamination.
>
>With a high degree of confidence, if the contamination level is less than
>8.5 ugNaCl/sq.in. within the first 10 min. the raw PCB will meet the accept
>criteria.  I would like the ability to run the equipment in auto mode,
>observe the contamination level at the 10 min. mark, if less than 8.5 then
>shut the test down, yet still retain the test record.  I am told this is not
>possible.  Is there a solution to this?  Can the software be changed to
>allow for retention of tests terminated prior to the equipment auto mode
>shutdown?
>
>One recommendation I received was to run in manual mode for 10 min..  If the
>contamination level is above 8.5, pull a second sample and run in auto mode.
> This is an unacceptable alternative because 55% of the tests run in
>automode shut off by 2 minutes.  In manual mode it would run the full 10
>minutes and not shutdown prior if a levelling off was determined.  So on one
>hand I am eliminating the long 20-60 minute auto mode tests, but on the
>other hand running 55% of the tests 8 minutes longer than necessary.
>
>Anyone with answers or suggestions please contact me via e-mail at:
>[log in to unmask] or by phone at (414)751-3573.
>Thank you.
>Nancy Diehl.

                      Jack Crawford
                  HelpLine Manager
    Electronics Mfg. Productivity Facility
                     317.226.5616
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