Re: 2% Silver
Chuck Harris <cfharris@...>
A little background information:toggle quoted messageShow quoted text
Tektronix made its own ceramic terminal strips. Before
they made them, they made their own micarta strips with
riveted turret posts.
I'm guessing that one of the workers, possibly one of the
women on the assembly line, had some experience making
ceramic pottery, and got the idea. It is an obvious thought
progression: plastic insulates, but burns when soldered, need
something that doesn't burn... wait! Ceramic doesn't burn...
They found that they could with very little effort, mass
produce the ceramic strips more quickly, and at a much lower
cost than the riveted turret strips, so they economized.
One of the interesting characteristics of silver metal is
it will fuse with alumina ceramic at high temperature.
Tektronix molded the terminal strips, and then painted each
notch with a flaked silver metal paint. When they fired
the ceramic, the binder in the paint burned away, and the
silver metal "tinned" the ceramic, just like solder tins
Nature abhors a vacuum. When ordinary 60:40 tin/lead solder
(the standard for electronics assembly at the time) is used
to solder the strips, the molten solder dissolves a little
of the silver into solution, forming a tin/silver/lead alloy
that is very similar to the alloy of tin/silver/lead that
tektronix used in their factory.
If the tin/lead reaches the ceramic, the silver will instantly
be rejected from the ceramic, and you lose your mechanical
attachment of the parts to the terminal strip.
You can use ordinary 60:40 tin lead solder to rework a joint
on the terminal strips, but each time you heat the joint, and
apply more tin/lead solder, more of the silver will alloy with
the solder, and quicker than you would like, it will no longer
stick to the ceramic, as tin/lead/silver can not "tin" alumina
The whole idea behind using tin/silver/lead alloy solder is that
it already has quite a lot of silver in it, and will not leach
away the silver on the ceramic terminals as quickly as it would
if it had no silver already in the alloy.
But mark my words, even if you do use the correct silver solder,
if you dawdle with a hot iron on the joint, you can still
destroy the bond of the silver to the ceramic.
So, use a high wattage (50-70W), temperature regulated to 600-700F
iron with a flat sided chisel tip, and get in, get done, and get
out of the joint.
And, do not ever put the chisel tip in the notch, trying to heat
the lead that way, it will crack the ceramic every time. Put
one of the flats of the chisel tip on the side of the terminal
strip, and let the adjacent flat, or the tip, touch the lead,
and heat the joint that way. Stay out of the notch!
David Kuhn wrote:
"The tektronix solder is definitely not lead free, and you definitely