Sorry, Plato maintains that a carefully controlled dip test, as I
described, can be just as objective as a WB test. It just provides
numbers which may be different from those from a WB, but it provides
verifiable numbers - and a physical proof that can be archived and
referred to.
I've worked more than a bit on WB and I know darn well that if you split
a batch of doubtful components between a number of operators, you will
obtain different results (e.g., caused by variation of time between
fluxing and testing, oxidation of solder etc.), so it is also, to some
extent, subjective. And the test piece is useless for archiving; all you
have is a piece of paper with a squiggly line drawn on it, and a
subjective interpretation as to whether it is acceptable or not.
So my summary is this:
A. Dip test = OK, especially useful for dewetting
B. WB test = OK, especially useful for wetting
Both: different tests, serving different purposes (the dip test is
useless for SMDs): both have a mix of objectivity and subjectivity.
Neither: gives an entirely objective answer.
Brian
The two tests are different
Ingemar Hernefjord (KC/EMW) wrote:
> The defence speek by Socrates?
> Well, we are going to blow the dust off our WB and try to find a person who
> is interested in continuity use for many years.
> I'm trying to understand the discussion that has been on TN.
> Ain't the summary this?
> A. dip test=subjective test
> B. WB = objective test
>
> I know an old electrician who checked the existence of voltage simply by
> making a touch with the finger on the line. He could tell there was voltage
> present on the line.
> Myself, I preferred a Fluke. I could tell how much voltage.
>
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of David D. Hillman
> Sent: den 4 juni 2005 01:10
> To: [log in to unmask]
> Subject: Re: [TN] Wetting balance
>
>
> 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"
> <[log in to unmask]
> M> To
> Sent by: TechNet [log in to unmask]
> <[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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