Difficult to tell you more, Patrick. The top finger shows the finish has 
never been fused, is soft, thick and plated. I would say the first thing 
you should do is to send a sample of the peeled metal to a lab to find 
its composition, so that you can chemically remove all that remains on 
the connector. If it contains lead, you will need to use fluoboric acid 
(nasty stuff: get a chemist to do it if you are not qualified), making 
sure only the edge connector is immersed. IMHO, do not use abrasives; 
you will implant solid abrasive particles into the copper. These will 
cause dewetting if you subsequently hot-tin the fingers and may wear the 
gold of the socket, certainly causing an increased contact resistance. 
Rinse copiously with DI water.

Once you have the connector down to bare, clean, copper, give it a short 
dip in an ammonium persulfate solution to activate the surface: the 
copper should now have a rose colour. Rinse copiously with DI water and 
thoroughly dry with a low temperature hair dryer or similar.

My preference then would be to solder carefully a thin copper wire 
across all the fingers, adjacent to the solder mask, making sure the 
solder doesn't flow down the fingers. You can then electroplate 3-5 µm 
of nickel followed by 1 ± 0.2 µm of hard gold (but not over the wire; 
you have plenty of real estate where the socket contacts do not reach 
this high, so you will be able to unsolder it at the end). Do not think 
of ENIG, as you would probably strip off the gold on the first insertion 
in the socket, which appears brutal from your photo. If you want to do 
the best job, replace the socket, as well, because the plating on the 
contacts cannot be guaranteed to be tin-free.

The alternative, but 2nd choice, finish would be an air-levelled or 
braid-removed hot tinning, followed by a good flux removal. Possibly 
easier but not as good!

Hope this helps

Brian

On 17.02.2014 10:25, [log in to unmask] wrote:
> Brian,
>
> Yes the board is that old about 1980 vintage, replacement is not an
> option since these things work out to be about 200K a pop, and they are
> very scarce.    Here is a picture of the edge, we can re-flow copper
> plating using a hand plating process, we have the salts.   We can
> electroclean or abrative clean the fingers.    I think the board is too
> new for the solder to be 40-60, so my guess is 63-37, the mating
> contacts are gold plated an have a very high contact pressure.  I assume
> the reason for the tin/lead pad is to ensure positive contact.
>
>
> -------- Begin forwarded message --------
> Subject: Emailing: eptboard.jpg
> Date: 2/16/14 10:36:20 PM
> From: "Goodyear, Patrick" <[log in to unmask]>
> To: [log in to unmask], "Goodyear, Patrick" <[log in to unmask]>
>
>
> Your message is ready to be sent with the following file or link
> attachments:
>
> eptboard.jpg
>
>

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