The adhesion of the conductive polymers to various surfaces should depends
upon the adhesion promoters they contain. The manufacturer should be able to
include the more appropriate ones for the surfaces involved in an
application. Storage requirements and floor life are valid issues.
Syed.

        -----Original Message-----
        From:   Matthew Park [SMTP:[log in to unmask]]
        Sent:   Monday, June 15, 1998 4:04 PM
        To:     [log in to unmask]
        Subject:        Re: [TN] Conductive Epoxy for Solder termination

        Dear Dr. EC,

        A successful implementation of electrically conductive epoxies
        for SMT application is more than understanding those issues
        you  stated.  And it is NOT definitely a replacement for tin/lead
        solderpaste as some mfg of conductive epoxies claim.    It is not
        very difficult to form fillet with the epoxy.  Simply  epoxies DO
NOT
        form fillets and wet.

        I performed a few sample tests one/two years ago when
        one conductive epoxy mfg claimed it prints like any other
        solderpaste and it is a replacement for solderpaste.  I
        concluded that some fundamental issues have to be addressed
        to make electrically conductive epoxies useful in a SMT
        manufacturing environment,

        - impractical storage/shipping temp, -70'c to-40'c
        - too suceptable to moisure and dry out too quickly
        - do not adhere good to tin/lead surface. A test revealed it
        adhered well to bare copper and solder mask  surfaces.  It is
        proper to have a different metallic finish for SMT component
        soldering terminals and board surface than tin/lead.
        - redesigning  board layout for epoxy application such as pad
        sizes, conductor space req's etc...
        - redesigning component soldering terminals for epoxy
        application.
        - poor performance of printability of epoxy
        - reworkability

        To answer your questions, it is vital to provide only an exact
        amount of epoxy for component terminal area.  A typical printed
        thickness of epoxy should be at 0.1mm.  That is why I believe a
        dispensing option is not suitable.   It won't provide a controlled
        coverage of epoxy for soldering terminals.  There are too many
        parameter variations to control such as epoxy consistency, dot
        size, dot height, placement pressure etc...

        regards
        Matthew
        NII-Norsat International Inc.


        >>> "by Dr. Eden Chen XianSong"
        <[log in to unmask]> June
        14, 1998  8:35 pm >>>
             Dear Sir,

             Some silver-filled conductive epoxies in the market claim to
        be solder
             replacement, but successful use of these material require a
        very good
             understanding of the epoxies properties, the process and
        CTE mismatch.

             The epoxy can be deposited to the pad by stencil printing or
             dispensing,

             Dispensing process has the tailing problem which can cause
        short for
             0402 chip resistor/capacitor.  It is very difficult to form the
fillet
             for epoxy, because the epoxy may have a gap between the
        side of chip
             resistor/capacitor and dot peak of epoxy.  How much should
        the
             placement force be applied and how big should the dot size
        for 0402
             resistor/capacitor?

             I like to discuss the above-mentioned issue in the TECHNET

             Eden

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