This is most likely due to having a cleaning process that is almost too 
good! Most commonly seen after some kind of aqueous cleaning, followed 
by drying at temperatures above 60-70°C. The cleaning will leave 
unprotected metal (if it were solvent cleaning, it would leave a 
protective monolayer on the metal). The metal will then oxidise during 
the drying. I've seen this hundreds of times.

Brian

On 12/08/2011 21:56, Gumpert, Ben wrote:
> Technetters,
>
> I seem to remember this coming up previously, but I couldn't find it in the archives... What causes solder joints to have a blue tint?
>
> I have a card where most of the solder joints across the assembly have a blue tint to them. It's Sn63Pb37 solder on a SnPb HASL board and a variety of part finishes - but the pads that weren't pasted don't exhibit the blue color. This is the only card in the lot that has this condition, but I don't know what process it may have seen differently from the others.
>
> Some kind of oxide?
>
> Thanks in advance,
> Ben
>
>
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