GW-DEC-1: A New DEC Prototyping Board

[Paul Koning]

> On Aug 16, 2019, at 2:43 PM, systems_glitch via cctalk <cctalk at classiccmp.org> wrote:
> 
> 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.

	paul

> On Fri, Aug 16, 2019 at 2:27 PM ben via cctalk <cctalk at classiccmp.org>
> wrote:
> 
>> On 8/16/2019 12:13 PM, systems_glitch via cctalk wrote:
>>> Dwight,
>>> 
>>> I spot check boards. I lack sufficiently sensitive instruments to measure
>>> actual thickness (even on a surface plate, it's the same for ENIG as hard
>>> gold with an 0.0001" indicator) but ENIG won't stand up to a few swipes
>>> with an ink eraser, whereas hard gold will stand up to it no problem. The
>>> main issue I've seen, in buying other people's products and projects, is
>>> board houses passing off ENIG as hard gold (and charging for it!) or
>>> claiming they're using "extra heavy ENIG" -- which of course isn't a
>> thing,
>>> because ENIG is an ion swap!
>>> 
>>> Thanks,
>>> Jonathan
>> 
>> Is gold plating the best thing? I thought that gold plating only works
>> best when matching other gold connections.
>> Ben.
>> 
>>