2011-10-24 by Charles R. Patton
In the very early days of SMT parts, the terminations were pure silver.
Not magnetic, but the silver dissolved rapidly leaving the part with no
terminations, hence the solders with silver content. Later terminations
often had a nickel layer. Much more robust, but also magnetic.
Capacitors and resistors were made with copper wire. That has long ago
ceased for cost savings. So today all those kind of parts use plated
iron wire.
Cheap tweezers (Harbor Freight imports and the like, are carbon steel
with residual magnetism.) Even several varieties of stainless steel are
magnetic enough. I would be suspicious of your Wiha de-magnetizer.
Often they use permanent magnets to "de-magnetize". Not really, they
just make shorter poles or magnetize through the cross section rather
than lengthwise of a tool like a screwdriver. This will reduce the
available 'pick-up' power, but not remove it entirely. The better
solutions are the AC powered demagnetizers -- the AC field will get the
part to almost zero remnant field. Or as has already been mentioned,
Titanium. Titanium is non-magnetic and also almost un-solderable, so if
using your tweezers while soldering, they don't get soldered to the
part/board. The other way is to use ESD plastic tweezers as was also
mentioned. I was trying to go that route when I purchased a couple of
plastic tipped tweezers from Harbor Freight. Don't waste your money.
The plastic tips are thermo-plastic that melts instantly on contact with
a hot soldering iron. I had hoped they would be Teflon -- no such luck.
So glancing at the Digikey site, the cheapest titanium tweezers are over
$23. I have some old tungsten TIG-arc rod and think I'll try brazing
that on a cheap carbon steel tweezer. Should be as good as titanium --
non-magnetic and un-solderable.
Just some musings,
Regards,
Charles R. Patton
On 10/24/2011 5:45 AM, Leon Heller wrote:
>
> On 24/10/2011 13:05, Steve wrote:
> > Thanks all for the advice.
> >
> > I'm using Wiha 44523 and 44529 tweezers, which the Wiha web site lists
> > as ESD safe and anti-magnetic. Not sure what anti-magnetic means. The
> > dental pick is just "normal" steel as far as I can tell.
> >
> > I have one of those magnetize/demagnetize gadgets (made by Wiha I think)
> > that you pass a screwdriver through one side to magnetize and the other
> > side to demagnetize. I'll try passing the tweezers and dental pick
> > through the demagnetize side and see what happens (this evening
> after work).
> >
> > Never gave much thought to SMD components such as resistors and
> > capacitors having enough ferrous material in them to be attracted to a
> > magnet. As well as IC's, they stick to the tools as well.
>
> I don't think I've noticed it with SMD parts. Rs and Cs with leads are
> often magnetic, though. I've had them or cut-off leads sticking to
> loudspeakers.
>
> Leon
> --
> Leon Heller
>
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