Hi folks! Guy - Mel did a much better response than I was going to put
together! You are right - having a great wetting angle(s) is not end-all
evidence that a good solder joint has been formed, just as having a bright
and shiny solder joint does not always indicate good solder joint
formation. However, many folks use the combination of wetting angles,
solder joint geometry, and surface topography as a set of solder joint
formation indicators. The Pbfree soldering process(es) will need to be
evaluated to understand if the same criteria we use today to "measure"
solder joint formation is going to still be valid. The 610 and 001
committees are working diligently to answer that question. We may need to
recalibrate ourselves - the introduction of immersion surface finishes has
force the industry to rethink having complete solder flow on a surface pad
as the HASL finishes have better flow but the overall solder joint quality
is the same. Lots of work ahead of us!
Dave
|---------+---------------------------->
| | Mel Parrish |
| | <mparrish@SOLDERI|
| | NGTECH.COM> |
| | Sent by: TechNet |
| | <TechNet@listserv|
| | .ipc.org> |
| | |
| | |
| | 07/17/2003 09:05 |
| | AM |
| | Please respond to|
| | "TechNet E-Mail |
| | Forum."; Please |
| | respond to Mel |
| | Parrish |
| | |
|---------+---------------------------->
>------------------------------------------------------------------------------------------------------------------------------|
| |
| To: [log in to unmask] |
| cc: |
| Subject: Re: [TN] High temp pastes for wave soldering... |
>------------------------------------------------------------------------------------------------------------------------------|
Guy,
We are in the process of looking at the criteria for 610 and 001.
Some thoughts-and discussion.
Much of the content and criteria for filleting accomplished to a
termination
is based upon physical properties of the termination or attachment. A case
in reference is the lack of requirement for a toe fillet in Gull Wing leads
per 001C, but the specification of a fillet in the Heel area even though
it's minimal. If in fact we did not have a heel fillet, the lead geometry
could contribute to a separation failure, even with adequate fillet
transition of the termination in other areas. Consider that all of the lead
configuration dimensions and design attributes commonly used today were
created for performance with SnPb alloys. We don't have lead designs
created
for Pb free specifically, and even if we did there is certainly a
significant number of combinations that would be necessary to cover the
field.
This being the case, fillets where fillets were required in the past should
still be required unless and until we have design definitions for each of
the lead/board/solder combinations that fall within Lead Free.
Surface appearance of the solder connection criteria went out of the
standards 20 years ago, so that should not be an issue except for education
of inspection when "it looks different" becomes an issue.
Fillet transition (commonly wetting) is still another issue. We have used
Sn96 in production soldering for as many years as I've been in the industry
with success based upon the standardized criteria. It is a Lead Free
alloy.
Should we, at this transition time, eliminate the criteria to say that
wetting to the terminations is not required? I certainly hope not. In the
exception cases where fillets do perform in operation even though they
don't
wet to the surface (such as when Inert atmosphere is not employed or Flux
performance is minimal) there may be justification for exception to
standard
requirements, but at this time that might require sample testing to
determine the success of the metallurgy within the attachment. Barring
that
we have the appearance of a fillet transition (wetting) to determine
success
of the process to attach to the surfaces involved. It's still a good
indication for the ability of the surface to accept the metallurgical bond.
Best regards,
Mel
Mel Parrish
[log in to unmask]
www.solderingtech.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Guy Ramsey
Sent: Thursday, July 17, 2003 7:41 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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