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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