Hi Jim,
not knowing more than that we sometimes see the same phenomenon. Our
chemist says you can get spots within the adhesive joint that do not
cure properly. The reason may be many: unsufficient stirring before
dispensing, catalyst problems, reaction with aluminium, humidity
absorption, passed storage time etc. It's a mystery that so few papers
take up this issue. The best we could do was to speak with Ken Gilleo at
Alpha Metals ("father of silver epoxies"). His e-mail is
[log in to unmask]  Good Luck!
                                  Regards / Ingemar



> Hi all,
>
> I need some help on understanding conductive adhesive.  I have an
> application that involves a membrane switch made of polyester.  We
have a
> resistor in line with one of the traces that is attached by the
conductive
> adhesive.  The problem I see is possibly the resistor pulling away
from the
> adhesive causing intermediate readings.  Since the polyester is
flexible, we
> had the company that makes the switch apply a thicker piece of
polyester to
> act as a stiffener.  But I believe this may not be good enough to
support
> the resistor.  I looked under a microscope and saw that there was a
small
> gap between the resistor and the adhesive and I used a tool to push on
the
> adhesive and was surprised that it was soft in texture.  Does all
conductive
> adhesive remain soft or is there others that would harden?  Maybe with
the
> polyester being so flexible you need the same from the adhesive.
Also, the
> switch company applies the resistor by hand and basically the adhesive
gets
> smashed out under the switch.   How good is conductive adhesive when
it
> comes to adhering to the resistor?  It's nothing like solder that
flows to
> create a good bond.  I'm not sure how I can tell if I have a good
> connection.  If any of you have any insight on this subject I would
> appreciate your help.  Thanks for your time.
>
> Regards,
>
>
> Jim West
> Manufacturing Engineer
>