Lars,

Testing for ionic contamination must be performed in a special way, since the
alcohol and water combination is actually used to strip aqueous solder masks.


Your tester must be capable of plotting the level of contaminates detected,
as well as a continuous time recording, in real time. Start your test, along
with the plot. You should see a rapidly changing curve, at the start of the
test. The degree of change should diminish over time. When the curve appears
to have appreciably flattened out, stop the test. Record the amount of time
it took to reach 90% of the curve, just prior to the flattening of the curve.
This is the time that you may use for product with the same board area. If
you have another board, with a different area, you must recalculate the time.

The problem with the automatic testers is that they are quite sensitive, and
respond to very low levels of ionics. Since the alcohol/water combination
actually breaks down the ionic content of the mask, the tester will continue
the test until ionics are no longer detected. Which for all intents and
purposes, until the mask has been removed. 

On boards that have very large areas, expect the mask to soften a bit. 

In summary, there is no standard test time, that can be applied to the test.
It must be based on the product area and how long it takes to flatten out the
curve. Small boards are easily tested in an automatic mode. Large boards will
have to utilize the calculation method.

Regards,

Gary Ferrari
Executive Director
IPC Designers Council


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