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@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 <paulkon...@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.
>
>
>
