Michael,
I will give it a shot.
1) Documented, as in a standard "thou shalt use DI water"? Not really,
no. It would be considered as a Best Manufacturing Practice though. Most
standards and specifications are based on the theory of we don't care how
you clean it, it just has to meet "X".
2) Chloride on electronics is as common as nitrogen in air. The issue is
how much is present and how free is the chloride to react and do its dirty
work. What method did you use to determine chlorine contamination? I
know it takes quite a bit to make gold electromigrate. In your case, ROSE
is worthless, worthless I tell you. You need to have your bare boards
analyzed by ion chromatography in their incoming state, and your
assemblies tested by ion chromatography after your city water cleaning
process. That will tell you where your chlorides are coming from and who
to go after when you arm the villagers with torches and pitchforks. You
can do the same thing on components in the incoming state to see how much
they contribute to the picture.
3) Is 80-100 psi too strong? Depends. Do you want components on the
board when you are done? I would suggest a lower pressure, but a higher
volume. Mike Bixenman of Kyzen Corporation gave an excellent paper on
this at the IPC Cleaning and Coating Conference in December.
Doug Pauls
"Forrester, Michael (H USA)" <[log in to unmask]>
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[TN] PCBA Water Wash
I have three questions I hope someone can help me with:
1) We have a vendor that uses "city water" directly into their SMT
PCA washer. I believe DI water is industry standard.
Does anyone know if it is documented anywhere? Spec?
2) We had an issue where there was Chlorine contamination and gold
dendrites found inside some standard gull-wing 6 pin SMT ICs.
This issue seems to be batch related. The chip manufacturer
claims that chlorine is never used in their process. Should the SMT
process expect to handle the possibility that the wash solution
may get into a part? The PCA vendor uses unfiltered "city water",
with no cleaner, in the wash process and does a ROSE test on one
board of each lot. Since the ROSE test passes, the PCA vendor
is blaming the part manufacturer for having "leaky" parts, since
the thinking is the wash is getting into the part and trapped.
3) One issue I have is the water pressure in the wash is 80-100 psi.
I think this is too strong, and should be half of that? You want to
flood the board with water, not hit the board and bounce off?
Thank you in advance.
Best Regards,
Michael Forrester
Sr. Product Engineer
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