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.