Bryan,

If the twisted wires are enamel coated wires, you need to know how was the
enamel coated stripped prior to soldering. Most of the enamel coated, or magnet
wires are solder-strippable, but some of those for high operating temperature
applications must either be mechanically stripped, or, if the wire is too fine,
must be stripped by chemical or molten salt. Chemical or molten salt stripping
give rise to corrosion if the residues are not cleaned properly.

K.K. Chin
Artesyn Technologies,
Fremont, CA
http://www.artesyn.com




Bryan Kerr <[log in to unmask]> on 05/29/99 03:24:46 AM

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cc:    (bcc: KK Chin)

Subject:  [TN] Disappearing Solder ?




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