Thoughts?

I was prepared to spend the 50$ on a new financial calculator so I just tried this with a hair drier =D.

THANKS AGAIN!!

First the conductive anisotropic adhesive used
is typically thermosetting rather than thermo-
plastic. Meaning you will have limited to
no success functionally re-plasticizing it via
heat. Even if you do succeed to soften the
adhesive of the defective connection you’ll
also be doing so to the adjacent connections
as well given the broad stroke of the heat
gun being used.

The principle by which anisotropic conductive
heat seal adhesives function is to create an
electrical connection between surfaces via
microscopic conductive particles embedded in
the adhesive base. These conductive particles
are either fully metallic or metal plated
glass/plastic forced into conduction between
surfaces under tension established by heat
set of the adhesive while the joint is held
under pressure. This is usually accomplished
during manufacture via a resilient hot bar
fusing device which holds the entire joint
under pressure until the adhesive has set.

By reheating such a broad area there is risk
of relaxing unintended adjacent conductors as
well causing them to fail. While the above
technique may well succeed in some limited
scenarios, it can as easily do more damage than
good. Particularly given the low mass of the
flex cable and the unregulated output of the
heat gun.

The typically recommended technique to repair a
defective heat seal connection is to heat the
joint and remove the entire flex conductor,
solvent remove the remaining adhesive on the
mating glass/flex surfaces, apply a new film
of anisotropic adhesive, *accurately* realign
the surfaces, tack them in place temporarily
(a modest temp soldering iron will do here) and
re-weld the joint with the above hot bar
mechanism.

That said, if the household hot bar fuser isn’t
available I’d recommend trying more localized
heat + pressure to repair the failed connection.
I’d avoid the use of hot air altogether as it
is difficult to control where the heat is being
applied in this case. Rather I’d place a small
metallic object such as a bare metal thumbtack
head-down over the suspect joint ideally
separated from the flex cable by a scrap of
paper. Heat the exposed underside of the tack
with moderate heat from a soldering pencil and
keep the tack moving and pressed against the
flex. Initially the adhesive thermosets is the
150*C ballpark so you don’t want to exceed this
by too much otherwise the risk of degrading (or
outright melting) of the flex cable exists.
Once the tack is up to temperature I’d remove
the heat and keep the tack in pressure and motion
over the joint. You can grasp the stem with a
pair of tweezers to do so. I’d recommending
starting off conservatively in terms of heat
and retry with increased temperature if the
initial attempts fail to reestablish the joint.

I’ve just fixed 2 of my 3 cheap DECT phones that all suffered this problem.

The third one still has characters missing, maybe I’ll try to heat it one more time later…