Thank you Dave, you have once again succinctly nailed it! Of course my
customer is looking for a report that substantiates your answer and it
sounds like that's still a ways off with CALCE and NASA/DOD.
Thanks again, you da man!
KennyB
-----Original Message-----
From: David D. Hillman [mailto:[log in to unmask]]
Sent: Wednesday, August 15, 2007 5:26 AM
To: [log in to unmask]
Subject: Re: [TN] SAC Soldered With SnPb
Hi Technet! Pbfree component finishes - a very cool subject that gives
all
of us ulcers! I have no doubt there will be a Dilbert strip some day
showings an engineer rambling about the "old days" when all we had were
tin/lead surface finishes. It is easier to cover the topic of Pbfree
component finishes if we break it up into a couple of segments.
Area Array Components (BGAs, CSPs, FCs) - there are a couple of industry
camps: those folks who solder a Pbfree BGA in a tin/lead solder process
with a reflow temperature that achieves good solderpaste/solderball
mixing
and those folks who rebump the BGA with tin/lead solderballs. There is
plenty of industry data which shows that a nonhomogeneous area array
solder joint has poor integrity so the industry folks has been focused
on
getting a uniform solder joint. The industry camp that raises the reflow
temperature has to deal with the potential temperature impact on the
other
components on the assembly. The industry camp that rebumps the BGA has
to
deal with the potential impact on the BGA integrity. Great discussion
topic to exchange beers over!
Other Components - there is a persistent myth that Pbfree component
surface finishes can not be used in a tin/lead solder process. I wish we
could put that myth in the ground and forget about it sometime in the
near
future. In a tin/lead solder process we diffuse a non tin/lead surface
finish into the solder joint, we don't melt them into the solder joint.
The industry is very good at doing this - we have utilized gold,
nickel/palladium/gold, tin, palladium silver, etc., for many years
making
solder joints with good integrity. Due diligence is needed on
understanding that you don't have some weird metallurgical issue result
from a component surface finish/solder joint combination but combining
Pbfree component finishes with a tin/lead soldering process is very
simple
and not rocket science.
As for Ken's question: What about a SAC component surface finish? Well,
its a Pbfree surface finish that has a high tin content. Hummm, sounds
like a matte tin finish with a little bit of silver added and the
industry
solders matte tin surface finishes all of the time. There will be a
pretty
decent industry data set on this topic by APEX. The gang at CALCE has
SAC
surface finishes under test, the NASA DoD consortia (formerly the
JCAA/JGPP group) has SAC surface finishes going into test and a number
of
other organizations/investigators are chasing the topic. My opinion is
that a SAC component surface finish is not a solder joint integrity
issue
if the reflow solder process uses adequate time/temps. If the industry
is
competent with soldering matte tin surface finishes, then a SAC finish
should not be any greater issue (and yes, I didn't mention tin whiskers
on
purpose!).
Enough said - time to find a Diet Coke and harass Doug!
Dave Hillman
Rockwell Collins
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bloomquist, Ken
Sent: Tuesday, August 14, 2007 4:51 PM
To: [log in to unmask]
Subject: [TN] SAC Soldered With SnPb
We are a Class 3 manufacturer and are looking at the different lead
finishes that can be soldered successfully with SnPb. One that we are
having a hard time finding information on is SAC lead finish soldered
with SnPb. I know that it's not good practice for BGA's but what about
SMT and through-hole parts?
Thanks in advance,
KennyB
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