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May 2005

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Subject:
From:
peter blokhuis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, peter blokhuis <[log in to unmask]>
Date:
Wed, 25 May 2005 10:10:32 -0700
Content-Type:
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text/plain (178 lines)
Mr. Munie's comments make sense, (do the testing with
a flux of known activity) but the wetting balance test
will tell you if there is a positive wetting balance,
and with  much greater accuracy than the dip and look
method!

As for SERA, in my experience the SERA accurately
revealed that everything was fine with the metal
phases in a deposit, when our customer told us
everything was definitely not fine.  Wetting balance
tests confirmed our customer's findings.  So, of what
value is SERA in monitoring wettability?  None that I
see.

Peter Blokhuis



--- "Munie, Gregory" <[log in to unmask]> wrote:

> 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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