GW-DEC-1: A New DEC Prototyping Board

[Brent Hilpert]

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.