Decades ago, I specified 5 µm of nickel and 3 µm of hard gold for wiping
switch contacts and 3 + 1 µm for edge connectors, which don't get the
same wear. The gold was fairly bright but I forget the composition of
the bath.
I would, however, refer you to a book Gold Plating Technology by Frank
H, Reid and William Goldie, Electrochemical Publications, 1974, It is
pre-ISBN, but is a mine of info (630 pages) with chapters on wear,
friction, lubrication, contact properties, porosity, density, contact
resistance testing, hardness, stress, ductility etc., despite its age.
After writing above, I did a web search and found it available at
http://elchempub.com/epfiles/ep11.htm with an a posteriori ISBN 0
901150 02 9.
Brian
Jack Olson wrote:
> ya know, every time I think I know enough about a particular subject,
> something comes along to make me realize there is more to it....
>
> I need to order some boards using a fabrication drawing that hasn't been
> updated in over fifteen years.
> We need Hard Gold Electroplating for a rotary switch contacts.
> One of the notes calls for gold knoop hardness 200-300, thickness 130-230
> uin. 93.7% purity
> The last FAI report showed gold thickness of 160 uin. All other historical
> records are lost in the shifting sands of time
>
> Our vendor has knoop hardness 150, 99.7% purity and says gold requirement is
> too thick.
>
> IPC says knoop 150, gold minimum 31.5 uin. for edge connector fingers, which
> I assume is the same for contacts (doesn't seem to be addressed)
>
> Printed Circuits Handbook says knoop 150, thickness 25-50 uin for
> non-military, 99.8% gold purity
>
> Has gold plating changed that much since then?
> Is there a danger of wear-out if I get 50uin. gold plating when our old
> boards were 160 uin.?
>
> surfin' the learnin' curve,
> Jack
>
>
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