Some possibles you may wish to check on:
1. Solder joint cooling rate: slow cooling will result in large crystals
(coarse grain structure) of the solder alloy components, resulting in a 'dull'
look. See paper by Livingstone & Weed given at NWC, China Lake on this issue.
This work done on military pwas that were vapor phase soldered using rosin
fluxes. Accelerating the cooling rate gave smaller grain structure, thus
'shiny' joints.
2. Use a mild alkaline pre-wash/wash to neutralize any residual acidic flux
residues to prevent 'micro-etching' of the solder surface. See paper by Cala
on this subject given at NEPCON West.
Bill Kenyon
Global Centre Consulting
3336 Birmingham Drive
Fort Collins, CO 80526
Tel: 970.207.9586 Cell: 970.980.6373
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