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August 2002

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Subject:
From:
Earl Moon <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 2 Aug 2002 09:52:54 -0500
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Victor,

As a really old rellic of the stone age, actuall pre-cambrian era, I've
forgotten most what I learned in the late 60's and early 70's. However, I
can tell you in those days platings were much different and much more robust
for just the reason you are seeking answers. In those days, most all
interconnects were effected using card edge connections.

We specified something like .0005" gold over .001" nickel or some such
thickness (when gold was under 32 dollars and ounce. Another important
factor was gold hardness expressed in knoops. We also specified up to 500 or
some such number of insertions/extractions. Speaks volumes doesn't it. No
one I know currently specifies anything like this absurdity.

As for flash or soft, gold, you are right about the number of
insertions/extractions being very minimal. However, I cannot express numbers
here and don't know if anyone else can.

Burndy, an old time card edge connector supplier, used to have what they
called "knife edge" connectors. These were tin lead plated and designed to
be used with tin lead plated board edge connections. This provided a
"gas/air tight" seal and gave some number of insertion/extraction cycles
over flash coatings. This technology was cooked up because, mostly, gold was
selling for around 800 dollars an ounce.

Now we're in an era in which much less reliance is placed on card edge
connections. Other interconnections are much more popular, useful, and
reliable.

So, the answer is there used to be one for your situation but it is not
useful anymore. Without writing another book, I would simply say first check
out your board shop and determine their hard gold capabilities, if any.
Then, contact your connector suppliers and see what they say. Concurrence
here should yield some answers to your question while understanding gold
thickness over nickel thickness, gold hardness expressed in knoops, and
number of insertion/extraction cycles. Most of the old documentation is
contained, probably in some connector supplier's archives and in long ago,
like me, dinosaur, mil specs speaking of which you may still be able to
access as MIL-P-55110, MIL-STD-275, as well as federal metallization
specifications referenced therein as gold, tin, lead, tin/lead, etc.

Another old time guy still in this business is Happy Holden. He often hangs
out on the Circuit Tree forum. He was one of the guys at HP doing serious
gold back in my earlier times. He's a real gold guy. His name appeared on
the technet forum a short time ago as someone was searching for him. It's in
the archives.

Would like to be of more help,

Earl

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