You might want to consider looking at the same sort of soldreing
temperture for rework as would be used for using lead-free components in
manufacturing a board with a lead-free BGA, i.e. raise the temperature
of the leaded solder by about +20C over what you would have used for
leaded rework to insure a good intermetallic bond between the materials
and insure that you have at least 3% or greater lead in the mix.
cheers,
chuck...
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Dennis Fritz
Sent: Tuesday, February 17, 2009 11:53 AM
To: [log in to unmask]
Subject: Re: [LF] mixing solder
Pearl,
Your hand soldering dilema is very close to the repair scenario our
"Crane Depot Repair Team" faces in advising US military installations
about repair.? Since we do not have XRF instruments to determine the
finish on incoming parts, nor the solder used on the original assembly
(fortunately mostly all legacy tin/lead assemblies), Crane has written a
Lead-Free Control Plan to outline that eutectic tin lead solder must be
used for repair.? Of course, this does involve some risk for mixed
solder joints, but predominantly tin-lead solder joints have shown
reasonable thermal cycle, drop shock, and vibration resistance in past
tests like the JCAA-JGPP testing.?
To determine a better answer, Crane is participating now in the ongoing
NASA/DoD study? where we are "repairing" many components?on lead-free
assemblies up to two times with eutectic solder.??Repair is?followed by
military specified thermal cycle, drop shock, and vibration testing.?
Results are just beginning to come in on the first data - drop shock,
and of course, the thermal cycle data may take as long as a year to be
complete.? In addition, we are funding a graduate student looking at the
mechanical properties of 1%, 5%, and 20% lead in "SAC"?solder balls on
simulated BGAs to again simulate lead solder repair. ? Again, that data
is just beginning to come in.?
Right now, we are saying the use of tin-lead solder in a mixed
environment is the "least bad" alternative.? And, we hope to prove it is
a "good" alternative.? It will never be the "best" alternative, but then
who wants to use seven kinds of solder paste or seven different wire
solders on a job, anyway.?
Denny Fritz
SAIC, Inc.
-----Original Message-----
From: pearl petras <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, 17 Feb 2009 11:22 am
Subject: [LF] mixing solder
We have a big debate going on right now.
We make a mix of products, some are RoHS, some are not, because they are
legacy
and they are sold into markets not RoHS (ie US).
We have a new product in development, geared only to US.? There are
BGA's on it,
only available in leadfree.? So we are using leadfree solder paste at
the CM
stage.? However, there are also hand-installed components - some are low
value
commodity parts only available out of Asia, that we cannot confirm RoHS
status.?
Others are whatever we can find, leaded or RoHS, due to production
pressures.?
Caps, connectors, etc.
The debate is whether to build with leaded or leadfree solder on the
floor.? I
don't want them using leadfree solder stations, because of the potential
for
them to think these stations are RoHS compliant.? They may become
"contaminated"
by the components used.? If the tools are then used for RoHS product,
they could
contaminate those products.
Others don't want to use leaded solder, because they think mixing solder
types
will cause reliability issues.?
I completely understand their concerns when it involves something like
installing a BGA in a?reflow process, but this is hand soldering
processes.? is
there still a reliability issue in that type of circumstance?
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Search previous postings at: http://listserv.ipc.org/archives
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