This is quite a common phenomenon and is due to the fact that your 
cleaning process is too good. Most cleaning processes leave a monolayer 
of organics over the solder joints, which give a certain amount of 
protection against oxidation. If the cleaning is too good, then this 
monolayer will not exist and, with the temperature of the last rinse, 
you will get a fine layer of oxidation which can appear blue or yellow, 
according to the conditions. It is nothing to worry about.
Brian

On 21/07/2014 17:29, Richard Krug wrote:
> We have recently discovered some CCA's with a distinctive, transparent blue color on the solder joints.  Viewed perpendicular to the solder joint surface, surface looks normal.  The solder surface appears blue when viewed at an angle.  I see no residues at up to 30x magnification.  Boards were wave soldered using Sn63Pb37 solder with ORH1 flux, then in-line water washed with a low concentration of a saponifier as one of our common assembly processes.
>
> Any ideas of what the condition is or what caused it?
>
> Dick Krug, CSSBB, CSMTPE
> Lead Process Engineer
> Sparton Brooksville, LLC
> 30167 Power Line Road
> Brooksville, FL  34602-8299
> p (352) 540-4012  (Internal Ext. 2012)
> [log in to unmask]
>
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