Re: Lead-free Solder ( continued ... )

Arfa Daily <arfa.daily@xxxxxxxxxxxx> wrote in message
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"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@xxxxxxxxxxx> wrote in
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Arfa Daily wrote:
Trouble with that philosophy, is that the jury is still out on whether you
can reliably mix leaded and non-leaded solder. Some solder manufacturers
say
that you can, whilst others say that you can't. A number of independant
metalurgical experts are of the opinion that by mixing the two solders,
the
long term integrity of the joint will be compromised. There is actually no
requirement in the legislation to repair equipment that was originally
manufactured with leaded solder, with anything other than leaded solder.
Somewhere around the shop, I have an old reel of leaded high melting point
solder that I used to use for that sort of thing, but haven't in a long
time. It was originally for resoldering those spring-off resistors -
remember them ?

Just as an aside, after this morning's NAD, this afternoon I had a Sony
home
cinema - one of the DAV series - I dunno, a 300 or 500 or some such. It
had
the usual problem of thinking that it was in headphone mode, but instead
of
the common bad connector, this time, it was yet more lead-free bad joints
on
the power amp PCB. As well as the ones on the bottom of the connector that
were causing the headphone problem, it also had cracked-around joints on
just about all of the six channels' output filter chokes, a problem which
you've probably all seen more than once on these, and also on the output
relays. Now these are problems that have developed, as the boards are old
enough that if they were original production drys, they would have showed
long ago. I accept that drys also 'develop' with leaded solder on certain
components that suffer high levels of thermal cycling in use, but the
amount
of drys on this one board, all on components that are either fairly large,
or subject to mechanical vibration stress ( the relays ) rather than
thermal
issues, leads me to believe that there is a different failure mechanism at
work here, possibly related to the lack of ductility of lead-free compared
to leaded solder.

As far as the suggestion of manufacturers having to hand work bunches of
components as the boards roll off the line, I can't imagine any way that
this could be accomplished in a practical or cost-effective way.

Arfa



Another failure mode I've come across ove rthe years is where the component
sourcing changes, but the board layout/drilling remains the same and the new
comps have smaller diameter pins. The solder bridges the gap ok for a few
years and then cracks, not even heat stressed, just room temp changes
probably. How would the non Pb/Sn stuff fare with that situation in
comparison.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



.

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