Re: Correct Silver solder

Chuck Harris
 

The tektronix specified alloy is tin lead silver, with about
4% silver.

They also specify that you can solder using 60/40 several times,
but after too many times, and the ceramic will lose hold of the
silver plated terminals while soldering.

A curious feature of alumina ceramic is pure silver will soak
into the surface, and wet the ceramic, just like solder will wet
compatible metals, like copper. Several other metals and alloys
will also wet the ceramic, notably gold, and indium. Any alloy
containing tin or lead will not wet the ceramic at all.

Silver likes to alloy with tin and lead, more than it likes to
wet ceramic, so ordinary tin/lead solder leaches the silver out of
the silver fired contacts on the ceramic barrier strips, and the
ceramic can no longer retain the leads you are connecting.

There are two ways of preventing this from happening:

The first is to use a highly silver bearing solder, that already
has enough silver, so there is little tendency for the silver to
migrate from the barrier strips into the solder.

The second is to keep the heat, and accumulated soldering time,
to the minimum that will do the job.

Every time you heat up the joint, it will be one step closer to
failing, regardless of what solder you use.

Any solder with 2-4% silver content will work ok, but only if it
doesn't overheat the strips.

I use what is called SN62 silver bearing solder. It contains
62% Sn, 2% Ag, and 36% Pb.

Another comment that needs to be said. These barrier strips really
suck away the heat from your iron. You need a high wattage, 70W
is good, temperature controlled iron (600F) with a screwdriver tip.
A big screwdriver tip, 1/8" at the point is about right.

Do *NOT* put the soldering iron tip into the notch in the barrier
strip, doing so will break the strip *EVERY TIME*.

Instead, follow the instructions shown in the manual, and heat the
component lead, with the side of the iron leaning into the side of
the barrier strip.

-Chuck Harris


greenboxmaven via Groups.Io wrote:

I am beginning restoration on a 555 I got a few months ago. What is the correct alloy
of solder for the ceramic tie strips? I have found both tin/lead/silver and
lead-free, both with 2% silver content . Are these satisfactory? Is 2% silver
enough, or is a richer alloy needed? Thanks, Bruce, KA2IVY




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