Please see embedded comments below.
Dick
-----Original Message-----
From: allisonp_at_world.std.com <allisonp_at_world.std.com>
To: classiccmp_at_classiccmp.org <classiccmp_at_classiccmp.org>
Date: Monday, March 13, 2000 11:12 AM
Subject: Re: Red Erasors
>> PCB's were gold-plated. Since the eraser always left a clean gold plated
>> edge connector, I quickly concluded it was dirt and not corrosion that
was
>> accumulating at the interface between PCB and backplane. I found much
less
>> of this occurring in clean environments where dust didn't accumulate in
the
>
>Actually it can be corrosion. Good gold plated fingers are gold over
>nickel over copper and have excellent resistance to wear, corrosion and
>metal migration. Many however cheap out and do gold over copper, very
>bad. This gold over copper tends to have problems with the copper ions
>migrating to the gold surface and turning a bluish-green.
Being "chromatically challenged" (can't tell either blue or green from grey
or pink) to such extent that the corrosion or dirt was just a dark smudge, I
never considered that it might result form low quality boards.
Thanks for explaining this.
>Attacking that
>with abrasives or solvents are temprorary solutions at best ans the
>copper ions will continue to migrate. This is why the layer of nickel is
>needed to keep the gold clean. This also depends on the connector being
>gold/nickle/copper as well or the metal migration happens from the
>otherside (connector). Adding to that boards with tin(solder) plated
>connectors and you can effectively posion the connector system. My altair
>and later replacement WAMCO backplanes suffered this fate from the mixed
>plated connectors and boards. It showed up after about two years in the
>slightly salty humid LongIsland air, symptoms were boards must be pulled
>and plugged back in before the system would run if powered off for more
>than a few days. I would have to use goldwipes and M50 solvent every
>few weeks to make it only somewhat stable. Even a film of silicone oil
>only helped somewhat.
>
>Oh, add oil vapor (machine shops), tobacco smoke or other pollutants and
>the reliability and surface accumulations can be far worse.
>
>
>Allison
>
>
Received on Mon Mar 13 2000 - 12:35:44 GMT