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From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 3 Jun 2005 18:09:55 -0500
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Hi folks! Ok, I have sat back long enough and need to square up some
mis-information - Greg, you and I really need to talk. The JSTD-002/003
committees have taken your 1996 testing and advanced it a tremendous
distance.

1) Gauge R&R of the Wetting Balance: The JSTD-002/003 committees ran a
series of round robin tests which resulted in the demonstration that the
Wetting Balance equipments could meet industry Gauge R&R expectations. The
wetting balance test methodology/standard testing procedures were
completely revised (based on the Munie, National Physics Laboratory, and
NIST investigations). However, additional investigative efforts were needed
to be completed before the committee felt that testing efforts to develop
acceptance/rejection criteria could be initiated.

2) The JSTD-002/003 solderability test specification's purpose is to test
the robustness of a finish for wettability. Tooooo many people attempt to
use and/or believe the specifications are designed to mimic production
conditions (this is best described as soldering-ability). Although the
committees attempts to have the specifications reflect soldering-ability
concerns, it is not possible or practical in terms of testing methodology
to mimic production. There are so many flux/process combination that the
specifications would cease to be of value (the specifications would be huge
and contain a multitude of variations). The test parameters contained in
the specifications are designed to have some safety margin in terms of
demonstrating the solderability of a surface - a test which gives either a
false positive or false negative result is not of value to the industry.

3) The JSTD-002/003 committees completed the round robin on revising the
solderability test flux just last year. The old "R" flux was not applicable
to the newer finishes on the market (eg. OSP or palladium/nickel) and a
new, standardized flux with a specific level of activation was qualified.
The new flux improved the overall test variability over the results
obtained using the "R" flux for a wide variety of finishes the industry
was/is using.

4) Those folks who actually believe that the Dip & Look methodology has a
respectable Gauge R&R would be in for an extreme shock. The "active
wetting" information that George W. described and the solderability test
parameter improvements that the committee has implemented have improved the
situation for the industry but we still have room for improvement. The
committees have voted that no new solderability test methods will be
introduced into the specifications without a demonstrated, industry
acceptable Gauge R&R value.

5) The JSTD-002/003 committee is actually one of the largest joint
committees at IPC - we have EIA, JEDEC, IPC and IEC representation which
means we don't move real fast but we get a tremendous industry
cross-section input/review which overall makes the drive for one global
solderability specification very real activity.

6) The JSTD-003 committee completed a Gauge R&R study on the SERA testing
methodology which demonstrated the SERA equipments to be industry
acceptable. However, the committee has not undertaken the round robin
testing for SERA acceptance/rejection criteria because of other
specification priorities. Many companies use SERA methodology for surface
characterization very successfully (the IPC-TM-650 method is in progress)

7) And finally, the JSTD-002/003 has been working diligently on test
confirmation of a set of solderability test parameters applicable to Pbfree
solderability testing - more "news at 11:00" but the specification
proposals should be going out for industry ballot shortly.


Dave Hillman
JSTD-002/003 Committee Chair
[log in to unmask]



             "Munie, Gregory"
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             M>                                                         To
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             <[log in to unmask]>                                          cc

                                                                   Subject
             05/25/2005 08:17          Re: [TN] Wetting balance
             AM


             Please respond to
              TechNet E-Mail
                   Forum
             <[log in to unmask]>
             ; Please respond
                    to
             "Munie, Gregory"
             <[log in to unmask]
                    M>






Luigi

You didn't say what flux you were using. I assume it's the flux called out
in the spec.

My experience at AT&T (and resulting contributions to the IPC wetting
balance test) are that if you use ANY flux but water white rosin (WWR) the
results you get in production will NOT equal the results of the wetting
test. The test will always look better.

I and my co-workers published this as a reliability study at the SMI
conference in San Jose, CA in 1995.

I have heard the arguments that wetting balance is inherently too noisy to
provide good repeatable data from site to site if one uses WWR. Yup! A
little activation in the flux definitely improves the repeatability: It
makes everything good. And when that happens, from an assembly standpoint,
you're the loser.

I suggest a simpler alternative: use the "dip and look" test with WWR and
the wetting balance to control immersion depth and speed. But only accept
the parts if the area wetted exceeds the area dipped. Why? Simple! In
production you want the solder to wet "up" the part/wet "over" the lead.
When you put the part in the solder with WWR and the solder climbs up the
lead you know it's good! If all the solder does is wet the immersed area .
.
. well, on my desk I have some carbon fiber bundles that exhibit good
"wetting" per the current test. They're well covered with SnPb over the
area
immersed. But I defy anyone to actually make good connections in production
with leads like that. (Years ago John Devore, if I remember correctly,
would
show people a solder surface that was well wetted. Then he'd hand it to
them. It was a wood toothpick with solder adhered to part of the wood. Sure
looked it'd solder per the spec!)

So, per my opinion, WWR and demonstrated active wetting of the parts are
the
only way to go in solderability testing.

Greg Munie



-----Original Message-----
From: Luigi Cantagallo [mailto:[log in to unmask]]
Sent: Wednesday, May 25, 2005 2:00 AM
To: [log in to unmask]
Subject: [TN] Wetting balance


Hello Technetters,

I have questions about wetting balance.
We intend to use a wetting balance not to accept/reject supplied SMD's (Our
SMD's are 1 to 5 years old) but to minimize the risk of solderability
defects in production (Low volume, SnPb technology).
So we don't apply J-STD-002D criterium but we try to find them to
corroborate wetting balance and production results.
On some tests (Wetting balance calibrated and in order, same type of flux,
same alloy) on same component lots, we have not a perfect correspondence
between wetting balance and visual inspections results in production (Vapor
phase soldering). One of the case is "Good at the solderability test/Defect
in production" and this one is the most risky.
Somebody have experience with that kind of problem?
What actions have you made ?

Thanks for answers.

Best regards,

CANTAGALLO Luigi

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