GW-DEC-1: A New DEC Prototyping Board

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.