Hi Peter - the ANSIJ-STD-003 is a solderability test specification and not
the solder alloy composition requirements specification. You should be
getting your solder alloy composition requirements from one of two
documents depending on your operation: either ANSIJ-STD-006 or
ANSIJ-STD-001B.  A "mix of Sn63/Pb37 and Sn60/Pb40" will be a specific
alloy of solder and not a mixture as inferred. Many technologists would
agree that using the exact eutectic alloy of 61.9 tin-lead (and that is a
debatable value too!) is ideal but in the real world you will get solder
alloy variations as printed wiring assemblies are processed and introduce
small composition changes. Thus having a tolerance (+/- 1%) on the solder
alloy composition is a process practicality. Most PCB customers I am
familiar with use the ANSIJ-STD-006 document or any of the PCB fabrication
specifications with take the ANSIJ-STD-006 values and apply PCB fabrication
tolerances.  You can buy  the eutectic alloy of 61.9% tin-lead but I
imagine it will be higher in cost than the typical Sn63/Pb37 or  Sn60/Pb40.
Good Luck.

Dave Hillman
Rockwell Collins
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[log in to unmask] on 01/30/98 08:08:34 AM

Please respond to [log in to unmask]; Please respond to [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: David D Hillman/CedarRapids/Collins/Rockwell)
Subject:  [TN] HASL solder specs




Here are two problems I see with solder standards:
The most exact standard I can find is ANSI/J-STD-003 (1992) which calls out
"plus or minus 1% of nominal". (nominal being 63% tin in a 63/37 bar)  Well
what if you change your "nominal" to be a mix of 60/40 and 63/37 to follow
whatever tin concentration happens to be in your HASL pot?
Further:  the eutectic composition of tin/lead is 61.9%, which should be
optimal from a wetting perpective.  However this  'ideal' concentration is
actually out-of-
spec according to the above standard.
So: what do PCB customers actually require on a finished board?
Peter Blokhuis
Circuits DMA
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