Philip Pemberton <philpem <at> dsl.pipex.com> writes:

> 
> In message <v.z.dx <at> gtdg.qmkun>
>           Peter <plp <at> actcom.co.il> wrote:
> 
> > You can't re-attach the conductive plastic strips without the specified 
> > adhesive, and you will need a jig to keep things in place and a stencil 
> > for the adhesive.
> 
> So I couldn't just buy a tube of conductive epoxy and use that? Any reason in
> particular why it wouldn't work?
> What about low-melting-point metal alloy (I've got some indium-bismuth-lead
> LMP alloy somewhere that melts at about 100C)?
> 
> BTW, it looks like these are "heat seal" connectors, which explains the
> Sellotape on the cable. The backside of the cable is bare - the tape is there
> to stop it getting torn off the board and also to protect the carbon
> strips.
> 
> That just leaves the problem of removing the strip without tearing the carbon
> off (or finding a way to remove the rather sticky plastic tape - same
> problem).

Conductive assembly has nothing whatsoever to do with heat, excepting that
soldering requires a certain temperature to achieve the melting and wetting of
the metals involved.

The conductive epoxy would have to be able to grip the ITO on the glass and the
carbon loaded plastic on the strip, and afaik it won't. Heat is not needed and
may be bad. The softening point of the plastic carrier is often only 65 deg. C.
A stencil is needed to get the conductive adhesive where it needs to be so it
does not bridge circuits when pressed home by the jig. 

Typical cure time for such an adhesive is between 1 hour and 24 hours. The
problem is price. You can't buy the supplies in small quantities and they do not
keep. So the cost of making one of those things is enormous. You have to make
several thousands to start thinking about breaking even, even if you disregard
the high cost of labor and tooling.

There is a reason why these things are exclusively made in the Far East.

I made a one-off hookup to glass for a prototype, *once*. I made a custom pcb to
match the strips on the glass 1:1 physically at the edge, mounted the glass and
the pcb on a carrier with adhesive, facing each other, and about 1 mm apart, and
attached about 50 80um wires to the glass and pcb, each with a single drop of
epoxy on each end, using a microscope. The protoype lasted about two weeks in
the lab, enough to check out things. It took more than two days to make (the
epoxy does not always stay where intended and needs to be cleaned off and put on
again several times until there are no shorts and everything is connected).

Peter

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