16 Aug
2019
16 Aug
'19
5:55 p.m.
That *is* surprising, HP sometimes gold plated the whole thing!
In any case, I will continue to run edge connectors with the superior
albeit more expensive selective hard gold process :P
Thanks,
Jonathan
On Fri, Aug 16, 2019 at 5:46 PM Brent Hilpert via cctalk <
cctalk at classiccmp.org> wrote:
On 2019-Aug-16, at 11:56 AM, systems_glitch via cctalk
wrote:
On Fri, Aug 16, 2019 at 2:53 PM Paul Koning
<paulkoning at comcast.net>
wrote:
>
>> On Aug 16, 2019, at 2:43 PM, systems_glitch via cctalk <
>>
>> I'm sure DEC wouldn't have bothered with hard gold plating if their
>> connectors were metallurgically incompatible :P The few busted DEC
>> connectors I've replaced did indeed have selective gold plating on the
>> contact surfaces. Most quality edge connector slots are similarly
>> constructed.
>
> It's been a while and I never looked in depth, but it most definitely is
> not true that gold is only compatible with gold.
>
> From what I remember, the detailed analysis involves an "electrochemical
> series", which has metals like sodium at one end, copper closer to the
> middle, and gold at or near the other end. Metals are compatible if
their
> potential value differs by less than a limit.
The limit depends on the
> environment; in an office you can have a larger limit than on a ship
where
> you have salt spray, or a tire factory with
lots of SO2 in the air.
>
> There are also some twists; I think stainless steel is compatible with
> many things thanks to the alloy ("stainless") properties. In fact, I
think
> the subject came up in connection with
failure analysis of coin cell
> battery holders. The battery cases are stainless steel; the question is
> what contacts are acceptable. Gold is; there may be others but some
things
> that are used in the market are not good
choices.
You can look it up in an electronegativity chart
for a quick "will these
ruin each other" check.
I think a lot of this comes from the SIMM era in PCs, where folks were
told
to only use gold-flash SIMMs in gold sockets, and
only tin plated SIMMs
in
tin plated sockets.
I've seen pieces of HP high-end lab equipment from thru the 60s that used
tin plating on the PCB edge fingers, mating into gold-plated edge
connectors on the backplane.
Never quiet understood it, they (HP) were doing gold-plated edge fingers
on other equipment at the same time.