Hi Jim! The industry camps don't seem as divided on the "flip side" of the
issue, although it will be a period of time before there is an industry
consensus (at least for the High Performance - IPC Class 3 - use
environment folks). The reason the "flip side" is not as dramatic is that
the overall metallurgy of the resulting solder joint is dominated by solder
application method - for reflow its the paste deposit and for wave its the
alloy in the solder pot. The amount of "metallurgical additions"
contributed to the overall solder joint by either the component leads or
the printed wiring board surface finish is pretty small as compared to the
solder application method contribution. I should mention (if for no other
reason to avoid getting turned into a crispy critter) that under many
conditions, it doesn't take a lot  of "metallurgical contamination" to
degrade a solder joint's performance. Some of the studies documenting the
possible impact of Bismuth poisoning in a Tin/Lead system is one  example.
Unfortunately we are still lacking a good share of needed knowledge in
terms of metallurgical reactions but with all of the ongoing testing we
should have some of the answers we need in the short term. Isn't changing
an industry's entire materials knowledge base fun! Have a good weekend!

Dave



                      Jim Kittel
                      <harold.j.kittel@        To:       [log in to unmask]
                      L-3COM.COM>              cc:
                      Sent by: TechNet         Subject:  Re: [TN] Lead-free components in SnPb processes
                      <[log in to unmask]>


                      03/05/2004 02:31
                      PM
                      Please respond to
                      "TechNet E-Mail
                      Forum."; Please
                      respond to
                      harold.j.kittel







Dave,
What about the 'flip side' of this issue?  Is there any concern about
alternative component lead coatings (e.g. Tin-Lead-Silver) with the use of
Eutectic solder attachment?
Thanks,
Jim Kittel
L-3 Communications

-----Original Message-----
From: Dave Hillman [mailto:[log in to unmask]]
Sent: Friday, March 05, 2004 7:15 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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