This is a reminder that Doug has made available a set of informative
papers and articles with general discussion on cleaning. I've zipped
them all together into a single file (>4MB) that you can download using
a web browser.
In the address line put: http://216.203.210.37 and that will open in our
public FTP site. You'll see a folder called "CleaningBoards"; the
download file is inside. I think I remember that all the papers are in
.pdf.
Some of the reports have had a birthday or two but there's good info
available to the determined reader.
Thanks again to Doug for sharing.
Jack Crawford
Director, Professional Development and Assembly Technology
[log in to unmask]
847-790-5393
fax 847-504-2393
APEX 2003 March 31-April 2 Anaheim CA
www.goapex.org
IPC Printed Circuits EXPO March 25-27 Long Beach CA
http://www.ipcprintedcircuitexpo.org/
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, October 22, 2002 1:43 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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