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June 1999

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Sat, 5 Jun 1999 07:18:01 EDT
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I guess that you are using a no clean wire for which the supplier recommends
a low bit (US tip) temperature. However as you are soldering transformer wire
(aka magnet wire, self fluxing wire) you need a high temperature to
successfully burn off, thermally decompose if you prefer, the insulation.
Probably what you are looking at is some complex of part used flux part
decomposed insulation spattered around a joint which is actually a simple
dewet. The cure will depend on  geography and how you can police materials on
line. ie if you can dunk the joint into a tiny bench solder pot, or use a
different iron/csw combo for one joint and so on.

Mike Fenner

In a message dated 29/05/99 11:26:06 GMT Daylight Time, [log in to unmask]
writes:

> Hi Netters
>  I've had an incident where two fine wires twisted and soldered together in
a
> transformer assembly have gone open circuit. When the assembly is stripped
> down the twisted wires appear to have a residual solder coverage but
> insufficient to provide a proper solder joint. there is also a light
powdery
> residue all over. It's as if the wires were soldered OK originally and some
> chemical reaction has stripped the majority of the solder away and left a
> corrosion product. The joint is within a sealed assembly, is covered
locally
> in a protective tape and the transformer is impregnated before wiring. Does
> anyone have any history or knowledge of any reaction between transformer
> varnish and solder ? I appear to remember some problems with phenolic fumes
> attacking metals however I've never seen solder attacked in this way.
Perhaps
> David Copperfield's been in town !!
>  Any feedback appreciated.
>  Bryan Kerr
>  Alenia Marconi Scotland
>

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