**Neil, having a long history with the test methods, I will attempt to
answer.
We recently discovered a difference in procedure for extraction of salts
for ion chromatography. After soaking in IPA at 80°C for an hour, what
should be done with the sample?
IPC-TM-650 2.3.28 doesn't specifically state that the PCB should soak in
the IPA solution while cooling. The extraction described in IPC-TM-650
2.3.25.1 requires that the PCB remain in the Kapak bag for half an hour
while cooling.
**I would suggest that you leave the sample in the solution till it cools
to room temperature. Early research by CSL showed that the 60 minute 80C
extraction removed all surface contaminants and some subsurface ones, and
after one hour you had very little added to the extract solution, so
letting it cool down in the bag should not be a significant change in
results, provided you have a quality solder mask. In my own work here, I
let it cool to room temperature. The important thing is to develop a
consistent process, since the test method does say one way or the other.
If you want to make sure that the cool down time does add ionics to the
extract solution, then pull it out right away. If you are trying to
reproduce the data from another site, do it the way THEY did it. Again, be
consistent.
Should the solution be shaken or otherwise agitated?
**I would suggest that you gently agitate the bag so that you get a
homogenous mixture. In most of my analyses here, I only retain 5-10 ml of
extract solution and the rest is waste, so you want to make sure that what
you retain is representative of the bulk extract solution.
IPC-TR-583 would suggest that a static extraction is less efficient.
**Now you are mixing apples and Kumquats. The 583 refers to static and
dynamic ROSE testing, and has nothing to do with IC testing. Dynamic ROSE
tests do have a better removal efficiency for the low temperature
extractions, but the high temperature extraction of the IC method gets the
ionic material without the need for agitation or sprays.
In the situation I'm in, these additions resulted in significantly
different results.
**Same IC system? Same methodology? How different is "significantly
different"?
The tests were requested in order to troubleshoot a solderability problem
so the procedural question is more academic.
**Solderability problem? Hell boy, yur going after bass with a deer rifle
(I'm studying to be a Texan). Very seldom, except in cases of the grossest
contamination, will IC testing ever give you insights into solving a
solderability problem. You need to use a tool like SERA for that. SERA
identifies the oxide structures. The second most common cause of
solderability problems is an organic residue, and IC does not identify
those. YOu need a tool like FTIR for that.
I'd just like to know if my methods are inconsistent with accepted
practices.
**No, you identify a need for more clarification in the test method, and
methods currently under development at the IPC. Renee Michalkiewicz of
Trace Labs leads that group. I would recommend that you leave the items in
the extract solution for either the half hour or until room temperature.
That's what I do, and of course, that is naturally the correct way to do
things ......
(fail-safe ego fuse engaging, shutting down cognitive functions now......)
Doug Pauls
Rockwell Collins
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