LOL
perhaps you should add some rum to your Diet Dew.
Mirka
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, October 22, 2002 2:43 PM
To: [log in to unmask]
Subject: Re: [TN] Cleanliness Testing - When is it clean enough?
To answer your question - how clean is clean enough:
Your assemblies are clean enough, when they function in the end-use
environment with the stated MTBF of the product or for the design life of
the product, with no failures attributable to electrochemical failure
mechanisms.
There, now that we have solved that burning question for the industry,
let's go do lunch
<Hmmmmmm, dum de dum de dummmmmm>
Oh, you would like to know how this is done? Wouldn't we all!!!!!!!
First you have to understand electrochemical failure mechanisms. Then you
have to understand your end use environment. Then you have to understand
how your material sets interact in the end-use environment. Then you have
to understand residue classification and quantification. Then you have to
understand how residues affect end item performance. Then (and you should
be approaching retirement by now) you have to correlate the results of the
residue assessment with the life predictions from accelerated stress tests.
Once you have done all this, then you will have the beginnings of wisdom
and understanding of how clean is clean enough. Then you go retire to
Cyprus and raise oranges, or kumquats, or figs, or whatever Brian grows
these days.
To bring myself down from a Diet Dew crazed haze:
The white residue that you are seeing is most likely abietic acid from the
RMA that did not get cleaned off in the batch cleaner. I have found that
assemblies at the outer portion of a batch cleaner do not get as clean as
those in the inner portion. Most of the time when I have seen white
residue from an RMA, it is harmless and is more of a process indicator.
But, that all depends on how much activator is retained in the white
residue. Another possible drawback is that it may be an amalgam of
residual flux and cleaning agent. How do your assemblies do in
environmental stress testing.
If you go back through the Technet Archive, search on either my name or
Brian Ellis'. We have talked about this topic numerous times in the past.
Doug Pauls
Advanced Operations Engineering
Rockwell Collins
P.S. Have flipped 23 matches into a bucket of Diet Dew and so far, no
explosions.............
Virgil Lenton
<lenton@SEDSYSTEM To: [log in to unmask]
S.CA> cc:
Sent by: TechNet Subject: [TN] Cleanliness Testing - When is it clean enough?
<[log in to unmask]>
10/22/02 09:55 AM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to Virgil
Lenton
We have recently had some cleanliness testing issues.
We are washing SMT CCA's with RMA solderpaste in a batch washer (AQ400RU)
with Armakleen E2001A saponifier. The CCA's are being cleanliness Tested
with an Omega Meter Model 600 SMD without heat.
Cards that easily pass cleanliness testing at the 14uGNaCl/in squared
acceptance level refered to in MIL-P-28809 have visible traces (under
magnification) of whitish flux residue under and around many of the SMT
components.
I do understand that the cleanliness tester is not meant to be an
analytical tool, but is a tool to be used for process control.
Here are my questions.
What do others in the industry do to decide when CCA's are clean enough?
Do you come up with your own acceptable cleanliness test level using SPC
techniques?
Any other comments?
Many thanks in advance
Virgil
Virgil Lenton - Manufacturing Engineering
SED Systems - A Division of Calian
Saskatoon, Saskatchewan
Canada
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