[Elecraft] Solder rot?

[Don Wilhelm]

  Brian,

Is there any chance that you used a lead-free solder on that board?  
Your description certainly sounds like that may have been the case.  The 
white residue could be the start of "tin whisker" formation, but could 
also be caused by flux removal attempts.

Attempts to remove flux can result in future failures.  Rosin flux 
itself is non-conductive, and will do no harm, but many removal attempts 
will actually create future conductive paths.  I don't know what it is 
about rosin flux and flux cleaners, but there is some reaction that 
causes problems "down the road".

Use a cored solder with mildly reactive flux and there will be little 
visible residue.  A highly reactive flux (such as Kester 44) is OK, but 
will leave quite visible flux residue - that is OK unless you attempt to 
remove it.  Professional flux removal - i.e. assembly line washing will 
completely remove the flux, but attempts to remove flux by "home" 
methods will leave some compound behind.

My recommended correction at this point - remove the existing solder 
with solder wick or a de-soldering tool, and then resolder.

73,
Don W3FPR

On 3/9/2011 7:50 AM, Brian Jones wrote:
> Anyone got any thoughts - my K2 has been playing up with the serial
> connection so I investigated and ...
>
> The entire serial board is no longer the neat bright solder joints that were
> there when I made it. Instead almost every joint is a dull matt grey and in
> many places there are bits of white dusty solder around the base of the
> joint, in several places joints are connected by this 'dust'. It's almost as
> if the solder has rotted.
>
> I do have several different spools of solder and, who knows, which one I
> used 8 years ago. However they are all traditional 60/40 Sn/Pb flux cored
> from reputable manufacturers so ought be OK. It is only this one board that
> has the problem, all the others still show nice shiny joints.
>
> No problem it's just a few hours work to remove, clean and then replace all
> the components (and a joy to do since I get chance to use my new retirement
> gift of a Metcal solder station) I'm just curious as to the cause, bad
> solder, a board that hadn't been cleaned of flux properly, anything else?
>
> Brian G0UKB
>