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Solder rot?

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Brian Jones-13

Solder rot?

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
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Don Wilhelm-4

Re: Solder rot?

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
>

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David Gilbert

Re: Solder rot?

Tin whiskers form in the presence of moisture and high electric fields,
and I doubt there are high enough E-fields in a K2 to do that ...
especially at the circuit board level. Plus, tin whiskers usually have
a spider web appearance.

A whitish powder, on the other hand, is much more likely to be lead
oxide. It forms in the presence of moisture, especially at warm
temperatures. If only one board shows it, it is likely that there was
some residual reactive agent (probably the flux in one of the rolls of
solder) that accelerated its formation. Resoldering the joints is
probably a good idea, but I'd also do my best to clean the board with
something ... not sure what since I don't know what the reactive agent
might be. I'm not familiar with the K2 boards but if most of the parts
are on one side of the board you may be able to clean the side with the
solder joints with mild soap and water, rinsing profusely afterward and
then drying it.

In any case, I certainly wouldn't leave the board as it is.

I'd also try to figure out which roll of solder was used so I could
throw it away. Worst case throw them all away and buy a new roll.

73,
Dave AB7E

On 3/9/2011 6:09 AM, Don Wilhelm wrote:

> 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
>>
> ______________________________________________________________
> Elecraft mailing list
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> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>