Hi Ken,
If you are trying to look for electrochemical (ECM) failures as a result of
the flux, then you may wish to consider doing SIR testing per IPC-TM-650,
method 2.6.3.7. The conditions used in this method (40 C / 93% RH with a 10
VDC bias and test for 7 days using continuous monitoring) have been shown to
be more stringent than using higher temperatures with high humidity (i.e. 70
C / 95% RH), especially for low solids fluxes (i.e. no cleans). Part of the
drawback of using higher temperature / humidity test environments, is that
you often cook off the very residues you are trying to observe. Work done
by Dr. Chris Hunt of NPL showed that lower temperatures with high humidity
and lower biases was better for evaluating the potential for ECM events due
to flux residues.
All that said, I would suggest evaluating the flux residues using the above
method with a test board that is designed for SIR and has components to
mimic modern assemblies. The IPC-B-52 board comes to mind.
I would highly recommend that you obtain the Gerbers for the board you
choose and have them made by your preferred supplier with your preferred
materials and surface finish. This may cost you a bit more, but it gives
you an apples to apples comparison.
Secondly, it would be a good idea to compare the residues from your current
materials against the Indium material using ion chromatography. This will
give you some important additional data and provide a baseline to compare to
the SIR data and to the performance of your current paste / flux material.
Anyway, I hope this helps.
Best Regards,
Joe Russeau
----- Original Message -----
From: "Chafin, Ken G." <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, November 12, 2008 1:13 PM
Subject: [TN] Flux Qualification
We are trying to qualify a no-clean flux to be used in our wave solder
process.
The flux in question is Indium #9942.
After wave soldering our boards are conformal coated with polyurethane
coating Conathane CE-1164.
We have done some baking of a test sample at 70 degrees C and and have
tested per IPC-TM-650 2.6.7.1--thermal shock test.
This testing was done primarily to evaluate the adequacy of the adhesion
of the conformal coating.
We are interested in further evaluating this flux to determine if it
contributes to corrosion development or other undesirable effects.
We are considering "soaking" a sample in a chamber at 70 degrees C at
95% relative humidity for four or five days.
I am interested in any recommendations for further
testing--standards-related tests, nonstandards-related tests that may
reveal undesirable properties in the flux, etc.
Thanks
Kenneth Chafin
Quality Compliance Leader
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