Guy,
When I read the first sentence in your last paragraph it sounds like you have components with immersion silver plated leads. Is that correct? Or do you have immersion silver plated boards and/or components with silver plating?
Regards,
George
George M. Wenger (908)-546-4531
Reliability Engineer
RF Power Amplifier Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059
[log in to unmask]
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Thursday, July 17, 2003 8:41 AM
To: [log in to unmask]
Subject: Re: [TN] High temp pastes for wave soldering...
Why do we care what the wetting angles are? (Indirect overhead question)
SnPb on SnPb finish yields solder contact angles we expect, we infer
that certain process outputs exist because of the appearance of the
solder joint.
With Pb free finishes and SnPb finishes we still expect the same
appearance but is the inference still true?
Now, add Pb-free solder to the mix. Why would we expect the contact
angels and solder joint geometries to be the same. The process inputs
are different.
I feel the more important, and largely unanswered question, remains.
Given the variety of lead and board finishes, and variety of Pb-Free
solder alloys, changes in performance from small shifts in alloy
composition . . . Can we expect to have a single visual acceptance
criteria, acceptance criteria that are data driven and performance
based.
I have observed that SnAgCu solder wets Immersion silver plated leads
quite differently than PdNi finishes. What looks "normal" on the latter
would definitely be a defect on the former. And neither of these would
come close to what we call "target" today.
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of
> Dave Hillman
> Sent: Wednesday, July 16, 2003 1:15 PM
> To: [log in to unmask]
> Subject: Re: [TN] High temp pastes for wave soldering...
>
>
> Hi Mel and crew! Sorry for the lack of response - been
> chasing alligators in the swamp and they seem bigger than
> normal this week. Mike F. and Gebbard hit the nail on the
> head - because of the higher temperatures of a Pbfree
> soldering process the thermal stability of many of the
> current fluxes is pushed to the limit (and/or over the
> cliff). We are going to need to rely on the flux supplier's
> expertise in reformulating our fluxes to have better thermal
> stability and hopefully have the same level of
> noncorrosivitivity. The NIST webpage/database has a good
> listing of Pbfree surface tension values if anyone is
> interested in alloys properties type information. One
> industry concern which has been expressed in a number of
> conferences is what changes in our expectations of "assembly
> cleanliness" do we need to be prepared for as the flux
> formulations are adjusted. If we expect to achieve the same
> wetting angles and solder joint geometries we'll have to make
> adjustments in our assembly materials.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
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