On 12/18/2012 11:37 PM, whit3rd wrote:
On Sunday, December 16, 2012 6:24:58 AM UTC-8, Jeff Liebermann wrote:

...
contact preservative, which is just a coating of oil or grease. You
can do as well with almost any thin grease. However, note that all of
them are non-conductive, so adding grease increases the contact
resistance slightly.

Not entirely true; some conductive greases ARE available, including
transparent ones that aren't easy to tell from 'normal' grease

http://store.caig.com/s.nl/it.A/id.1589/.f?sc=2&category=185

...this applies only to tin and
silver contacts, but not gold, which doesn't tarnish, oxidize, or
require lubrication.

If gold really DIDN'T oxidize, it'd weld to itself on contact. There's
no crust of oxide, not even a micron thick layer. But, there's a nanometer
of oxide, all over any gold surface. At elevated temperature and humidity,
even a clean gold/gold connection will fail, because something grows
on that gold surface. We lowered the storage humidity spec and our PC-based
product stopped getting memory and video and PCIe errors at the environment
test lab.

Lubricant might not be irrelevant, after all, on gold contacts.

Gold on boards isn't anything like pure, and the cheap stuff has lots of
gaps in its surface coverage. Depending on the pH, you can get a
monolayer of gold oxide on a surface, or (interestingly) a monolayer of
water, which it turns out forms a _hydrophobic_ surface, since all the
available hydrogen bonding sites are hidden.

(I was going to answer that gold didn't oxidize, but checked first, and
found this interesting paper: http://tinyurl.com/c34olw3 .)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net