Hi Bev! Yep, and then there is a Sandia report which shows little solder
joint degradation from 0% to 8% Pb additions for two different Pbfree
solder alloys. The Sandia report also shows that both a chemistry effect
(what types of metallurgical phases are formed) and a physical effect (what
shape are the phases and how do they interact with stress/strain) can be
found. Life was pretty good with only three elements (Sn, Pb, Cu)  for
worry about - having 3 element systems (Sn, Ag, Cu) plus having other
metallurgical contributions from component leads and pwb surface finishes
creates many new "opportunities" to consider. Throw in the possible
contributions of solder joint cooling rate impact of metallurgical phase
formation/growth and we can start to make heads spin! I think everything is
solvable provided we have the time to investigate.

Dave



Dave,
You hit on it at the end of your message - it appears to depend on HOW MUCH
lead.  One of Tom Woodrow's papers shows that less than 1% lead isn't going
to get us and there is a Swedish report, highlighted on the front page of
the latest NPL circular, that suggests that around 2% is bad and above and
below that is OK.  I don't know the details.  Worth looking into.

Bev Christian
Research in Motion

-----Original Message-----
From: Dave Hillman [mailto:[log in to unmask]]
Sent: March 5, 2004 9:15 AM
To: [log in to unmask]
Subject: Re: [TN] Lead-free components in SnPb processes


Hi Scott! There appears to be two distinct industry camps on the topic of
Pb contamination of Pbfree solder joints. One camp is of the opinion that
the presence of Pb is detrimental to Pbfree solder joints and significantly
reduces the thermal cycle fatigue life. The opposing camp is of the opinion
that the presence of Pb does not impact or only slightly degrades a Pbfree
solder joint thermal cycle fatigue life. Lots of data, lots of good
discussion - most folks are concern with the issue in relation to how to
deal with "legacy product" processes. There will be some pretty good data
available later this year - the JGPP consortia study and NEMI consortia are
working on the issue. There were a couple of papers presented at APEX on
the topic too but I haven't had the chance to read them yet. IMHO the issue
of Pb contamination may boil down to understanding how much lead (i.e. what
percentage) can a Pbfree solder joint tolerate before metallurgical
reactions result in degradation.

Dave Hillman
Rockwell Collins
[log in to unmask]



                      03/04/2004 11:12
                      AM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to Scott
                      Lefebvre



I would like to add a concern that I have on this issue of Pb Free
components.

What is the industry doing about cross contamination of Pb Free components
be soldered with SnPb solder as well as SnPb components soldered with Pb
Free solder.  I know of a few concerns about cross contamination but I
would like to hear what all the techneters have to say on this issue.

Scott
 -----Original Message-----
From:   Dave Hillman [mailto:[log in to unmask]]
Sent:   Wednesday, March 03, 2004 4:56 PM
Subject:        Re: Lead-free components in SnPb processes

Hi Blair! One issue to consider with the industry move toward Pbfree
soldering processing is that a number of component fabricators are moving
to matte tin as a component lead finish. Matte tin is not as robust in
terms of solder process and shelf life solderability in comparison to a
tin/lead component lead finish (matte tin oxidizes must faster). The use of
a nitrogen reflow environment and possible changes in your flux formulation
are two possible avenues of investigation to increase your reflow process
window . Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]



                      03/03/2004 09:28 AM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to "Blair
                      K. Hogg"



Hi Technetters,

We've been seeing increasing problems in our SMT processes with wetting of
component leads and I am wondering if our processes which were designed
around all SnPb materials now need to be updated as I have a strong
suspicion that we are seeing components with lead-free terminations.

Are lead-free components drop-in replacements in SnPb processes? Has anyone
here had to adjust processes due to lead-free component terminations?

Thanks,

Blair

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