Hi Neil and Bob,

There are even more three gold finishes,
The oldest one was electroplating gold over electroplated nickel barrier, E=
NEG for short. This is usually used now only for edge connectors where thic=
kness of gold is important for reliability of the connection (when gold nee=
d to be thicker than the 3 microns of a standard gold flash).
The two newest ones are ENIG (Electroplating Ni and Immersion Au) and INIG =
(Immersion Ni and Immersion Au).
INIG has become mainstream now, and prices are reasonable for production.

For contact finish, you can also use selective organic finish that will dep=
osit a thin carbon layer on the PCB.

My $0,02,
Jean-Paul
AC9GH



> On Nov 23, 2014, at 11:30 AM, Bob Blick <bobblick@ftml.net> wrote:
>=20
> Hi Neil,
>=20
> There's two different gold finishings for PCBs, immersion gold or hard
> gold. Immersion gold is usually good enough and it's pretty cheap. Maybe
> the scary quote you got was for hard gold.
>=20
> Cheerful regards, Bob
>=20
> On Sun, Nov 23, 2014, at 06:17 AM, Neil wrote:
>> I'm not familiar with conductive epoxy, so will investigate that.
>>=20
>> Silver (which I can get from the PCB house at much lower cost) will=20
>> tarnish relatively quickly (few months) so won't be a good choice for=20
>> the membrane-switch pads.
>>=20
>> Cheers,
>> -Neil.
>>=20
>>=20
>> On 11/23/2014 1:34 AM, RussellMc wrote:
>>> On 23 November 2014 at 18:37, Neil <picdude3@narwani.org> wrote:
>>>=20
>>>> I'm looking for a conductive carbon coating that I can apply to PCBs
>>>> myself, for conductive membrane switches.  Or something else
>>>> ...
>>>>=20
>>>=20
>>> Just some ideas.
>>> I do not know how suitable any of these would be.
>>> I've never tried  them. Each should have level of conductivity needed.
>>> May have degree of wear resistance needed.
>>>=20
>>> - Conductive epoxy.
>>>=20
>>> - Silver-loaded track repair lacquer which does not conduct unti 'set'.
>>> As carrier liquid evaporates silver particles produce conductive strip.
>>> I've used this for repair of fractures in flexible carbon tracked keybo=
ard
>>> tails.
>>>=20
>>> - Stick layer of eg butyl rubber (carbon loaded) to board surface in
>>> contact with a conductor.
>>>=20
>>>=20
>>>=20
>>>       Russell
>=20
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>=20
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