While I have very little experience in the wave solder process, I would
guess the solder spec stuff would be similar to what is used for HASL.
 Check out the levels and types of impurities, esp. other metals.  That may
explain differences between bar types.  Use of 60-40 vs. 63-37 may depend on
tin versus lead usage (sometimes one is used up faster than the other).
 63-37 is closer to the eutetic, but your solder pot is no doubt quite a bit
higher in temp than either solidus point.  Using something other than
eutetic may have some effect when cooling after soldering.

ALWAYS insist on a COA with each shipment.

My two cents!

Patty
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From: Alan Kreplick
To: TechNet
Subject: [TN] Bar Solder