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September 1999

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Subject:
From:
Pat Kane <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 7 Sep 1999 16:06:02 EDT
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>
>  They need to consider testing the process in accordance with J-STD001B
>  Appendix B (was 001A appendix D)

The numbers are getting mixed.  It should be, in order of progression:
J-STD-001A, Appendix D
J-STD-001B, Appendix D
J-STD-001C, Appendix B (Proposed).

>  This way they can apply some form of  process validation.

Some form yes, but the testing that is in the current version (Appendix D or
the coming Appendix B), is not magical in terms of demonstrating materials
compatibility.  Appendix D/B is ONE way of examining materials compatibility,
but there are dozens of equally valid ways as well.


>  They should also please consider the reliability of the
>  product and process rather than making reference to an empirical
>  "cleanliness" spec..

Absolutely.  You need to be able to define what acceptable and unacceptable
performance first.  Then you figure out what kind of testing best separates
good from bad.  Then, generally through a design of experiments, what kinds
of residues and in what amounts go along with good and bad.

>  No one can answer "How clean is clean?"

Ohhhhhh, I don't know about that..........  I know a lab in Kokomo who is
pretty darn good at it.........

>
>  The only issue I have is that the quoted SIR test method MUST be modified
in
>  light of recent research findings - notably through the UK NPL.  Note that
>  SIR testing is a QUANTITATIVE  not a QUALITATIVE  test method.

SIR as a test tool needs to be improved, no argument, but I think that what
needs developing is SIR as a process validation tool.  Most SIR testing, at
present, goes into the testing of materials and materials compatibility.
There is always that leap of engineering judgement going from lab SIR data to
production hardware field service.

As to Quantitative vs. Qualitative, it can be both, depending on how it is
used.

>
>  These changes involve reducing the test time interval to 20 minutes instead
>  of the present 24 hours. It also means testing at far more sensitive levels
>  and with lower bias voltage more in line with the end product. I will not
>  bore you with comment about the coupon design - but will happily review
this
>  offline if you wish - and there MUST be component over mounting.

Yes, but what kind of component, the footprint, the standoff,,,,,,,,,,,  Yes,
frequent monitoring is the coming thing, but there is still much to do in
relating what a result in SIR testing means to harware reliability.

>
>  What essentially should occur is that you select the desired board, resist,
>  HASL or NiAg finish - the desired flux/paste/wire combo - any other
chemical
>  process steps (underfills, globtops, adhesives etc) and the preferred
>  coating. Test at each process step and in total combination.

Yes, but all these factors on a B-24 board may not mimic what you have in
actual production.  It gets back to an issue of a real-world process
validation substrates testing methods.

>
>  I have just been speaking with a high rel Class 3 customer who was tasked
to
>  "eliminate cleaning in 12 months". That management decision was made
>  (apparently) in January 1998. It is now Sep 99, and they still can't do it!
>

In most of the no-clean evaluations that we have seen, the assembler does not
try to clean off a residue that is designed to be left on the board.  In
general, the assembler will clean for one of three reasons:  to knock off
solder balls, to eliminate visible residues, and to attempt to clean up
assemblies build from contaminated bare boards.  The first is valid, the
second usually the results of paranoid and undereducated customers, and the
third simply does not work.

If you are going to clean a no-clean residue, water cleaning alone, even DI
water, WON'T do it.  I don't care what the flux rep said about the water
washability.  You are going to need a saponifier to get it off.

Doug Pauls

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