In a message dated 98-01-19 22:00:54 EST, you write:

>  There is many archived "tech-letters" that address the issues of "how to",
"
> what to do", and "the theory of" SIR testing.  But what can be done in
> practical terms in a production process situation, to address "borderline"
> SIR results.   This with city water rinses, at both pumice preclean (prior
to
> coat) and post HASL cleaner. HASL with the use of no-clean flux.

SIR is affected by many factors.  For what you describe, if you are getting
"borderline" SIR results, it means you either have technique related problems,
or residues which adversely affect SIR, such as halides or polyglycols.  The
latter is more likely.  As such, you need to improve the cleanliness of your
assemblies.

1.  Don't use city water.  It often has chloride and sulfates added to control
bacteria.  Lots of other garbage too.  Many have acheived better cleaning
through the use of RO or DI (recommended) water.

2.  Use a small amount of a good saponifier.  A good saponifier will decrease
the surface tension of water, allowing better cleaning under low standoff
components.  It should also remove polyglycol residue (from HASL) that cannot
normally be detected by most analytical methods.  You might contact me off
line for what I consider to be good and bad saponifiers (wouldn't want any
commercials here, would we?!)

3.  Use slower speeds through the cleaner.  The pressure is always on to push
more product through faster.  It only increases the overall residue load.

4.  Do you check the cleanliness of your incoming boards?  By any other method
than ROSE testing?  Consider it.  No clean processes are held hostage to the
cleanliness of incoming boards.  A no-clean manufacturer has not eliminated
the need for cleaning, he/she has only moved it farther upstream to the
fabricator.

5.  The issue of what constitutes "borderline" SIR depends on the
specification and who you talk to.


>  Is there a cleaner, chemical change, etc... that has made the difference to
> others that may enhance our SIR results in the future?

There are lots of factors that impact overall residue levels.  From the
failure analysis work we do, we have a pretty good feel for what are good
residues and what are bad residues for differing levels of technology.  If you
have a cleanliness problem in house, and have cleaning capabilities, I can
recommend some materials.  If not, then I know of some good contract cleaners
you can try.  It would be worthwhile though to make sure it is a problem with
the assemblies, and not with your SIR test technique.

Doug Pauls
Technical Director
Contamination Studies Laboratories
[log in to unmask]
765-457-8095

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