Thanks for all the responses regarding the use of silver epoxy and solder
coated parts... obviously, not the way to go!
I'm still trying to understand the mechanism for increased DC resistance,
though.  From what I have learned, silver oxides are conductive, so this
isn't it.  The tin seems to migrate into the epoxy, I assume leaving a
lead-rich zone.  Is it that the lead oxidizes?  Are lead oxides conductive?
Can anyone explain?
Thanks again,
Jim Marsico
EDO Electronic Systems Group
[log in to unmask] <mailto:[log in to unmask]>



        -----Original Message-----
        From:   Mike Fenner [SMTP:[log in to unmask]]
        Sent:   Wednesday, January 24, 2001 1:52 PM
        To:     TechNet E-Mail Forum.; Marsico, James
        Subject:        Re:      [TN] silver epoxy & solder coated parts

        I would avoid it.

        Conventionally:
        Epoxy has poor adhesion to tin and its alloys
        The tin/silver interface will give an inter-reaction at the bondline
        leading to electrical opens although you may retain mechanical
        adhesion. One/Two years is a long time in this situation especially
if
        you have mechanical stress/vibration or any temperature swings in
        service.
        This is very well documented in the literature and you should see
        something in the Technet archives.

        More open mindedly:
        There are some companies working on this and there are now products
        which claim to have solved this problem, either by using a sort of
        halfway house product (adhesive with a fusible metal filler
basically)
        or by special undisclosed ingredients/formulations.
        Contact suppliers for the latest



        Mike


         ----- Original Message -----
        From: "Marsico, James" <[log in to unmask]>
        To: <[log in to unmask]>
        Sent: Tuesday, January 23, 2001 8:34 PM
        Subject: [TN] silver epoxy & solder coated parts


        > Hello, Technet...
        >
        > Here is an unusual situation.  We have to assemble a surface mount
        assembly
        > using silver epoxy.  Some of the components will be solder coated.
        I know,
        > don't bother asking... this is the way it has to be.  The good
thing
        is that
        > this assembly is a prototype for bench-top laboratory use only.
        There is no
        > harsh environment and needs to operate 1, maybe 2, years.  The
        question is
        > does anyone foresee any problems?  What happens when one mixes toe
        two
        > technologies?
        >
        > Thanks,
        > Jim Marsico
        > EDO Electronic Systems Group
        > [log in to unmask] <mailto:[log in to unmask]>
        >


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