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. > > >