Re: Another scope 7854

Chuck Harris

A really cool thing happens with gold plating, the gold atoms
are huge and the space between them fits all sorts of things,
such as etchant, oxygen, mercury, uranium hexafloride, and
other fun stuff. The gold, if plated too quickly, gets a
little mossy, which is why it appears matte finish rather
than shiny, and makes it even more susceptible to infiltration of
undesirable things. For instance, the electrolyte in batteries
like alkalines and nicads goes right through gold plating...

As a result, the mil specifications for gold plated fingers
requires a thin layer of nickel plating between the copper and
the gold.

I worked at one company, Defense Electronics, Inc (DEI) as a
metal plater, and they routinely flouted the rules on gold
plating. It wasn't so much that they didn't want to follow
the rules, but rather, that they couldn't afford my time, and
their money, to repair/replace their nickel plating tank. So,
they doubled up on the gold plating... at $32/oz, why not?

I later went on to a company called Electro Products, Inc, which
made circuit boards, and they too cheated on the gold plating,
no nickel inter layer.

To be fair, there was a lot of inbreeding amongst the defense
related electronics companies back then...

-Chuck Harris

David @DWH [TekScopes] wrote:

The color was awfully uniform compared to the transparency for that.
It looked a lot like a chemical stain but was difficult to remove; I
just used tin solder, low heat, time, and agitation.

The gold plating was really thick which is no surprise given what
happened. The unit was pretty old and I can probably find it to get
the rough date of manufacturing. I suspect either the problems with
tin solder and gold were obscure at the time or the designer at
Tektronix was just unaware of them.

It still struck me as an odd design mistake and I wonder if Tektronix
originally intended to use a gold compatible solder. Later boards of
the same design used a much thinner gold plating although it still
looks thicker than the flash gold over nickel that is normally used

On Sat, 6 May 2017 01:21:34 +1200 (NZST), you wrote:

The colour of thin films can be misleading in that interference effects in thin films can impart colour to transparent films like soap bubbles, beetle wings, oxide films on steel produced by heat treatment etc.


Posted by: David <@DWH>


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