The PCD magazine list went down before I could get an
answer to this question, does anyone have experience
with silver and contact switches?

==============================================

Most sources say a silver surface will not be solderable
after a month or so unprotected. (Even in a baggie it will
be okay a year later?)
Anyway, you say it is good for switches, which would solve
some of our hard gold plating problems.

But I would think the "unsolderability" of the aged silver
surface (unprotected in the unit and tarnished?) would
affect the reliability of the switches, wouldn't it?

Jack






Rob Mongey <[log in to unmask]>@freelists.org
4Apr2002 06:08 AM

Please respond to [log in to unmask]

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cc:

Subject:  [pcdlist] Re: Immersion Silver
Retain Until: 05/04/2002 Retention Category: G90 - Information and Reports
Caterpillar Confidential:  Green



Hi all,
     Good to see Immersion Silver is starting to take off. We've been using
it
in here for about two years, and it is now our prefered board finish (We
get silver finish unless we specify differently.) More common useage will
mean that maybe more Far Eastern shops will start supplying it.

     We started to use Silver because it is so adaptable to what we need
our
PCB surface finish to do, namely:

1. Good solderability. (Silver excels at this, ask any vendor).
2. Flatness for fine pitch SMT. (Silver is as flat, if not flatter than
Gold)
3. Mechanical strength for carbon pill switch contacts / Elastomer
contacts. ( Flash Gold is weak, and hard Gold gives SMT solderability
problems)
4. Stability for compression power contacts. (We have power contacts on our
PCBs that mate to battery contacts via a spring compression. We found that
the nickel under gold can cause problems with electrochemical migration
toward our battery contact.)

Immersion silver is the most suitable choice that can do all four. I'd use
gold as an alternative, but we'd have to compromise our designs somewhat.

We specify our Silver finish as 0.1 Microns Min to 0.2 Microns Max, over
bare copper. Anyone else do it differently? Or do we trust our board shops?
:)

                                                      Regards,
                                                           Rob Mongey.
                                                         CAD Technician.

     Robert Mongey <[log in to unmask]>  Tel    : +353 (0)91 774300
     Bio Medical Research                Direct : +353 (0)91 774338
     BMR House,                    Fax    : +353 (0)91 774302
     Parkmore Business Park West,        Mobile : +353 (0)87 2485262
     Galway
     Rep of Ireland.

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