LCD Interconnection; Elastomers,
Pins, & Heatseals
This section primarily pertains to the interconnection methods of Liquid
Crystal Display Glass
to the rest of the world. These methods are used in standalone LCD
applications, as well as LCD Module assembly processes. We give examples of the three three primary
methods here:
Elastomers
Elastomers
are silicon strips of alternating conductors and insulators. These materials
are generally soft and compliant and can be easily compressed between the
Liquid Crystal Display and circuit board. Elastomers require a bezel to squeeze the display
and circuit board together. This method will yield a higher conductor
interconnection than pins, potentially less costly than pins, but requires a
specialized compression bezel.
Pins
Pins
are attached to the display to allow the user to either mount the display in
a socket or solder it directly into a circuit board. From an end user
standpoint, pins are the easiest to use since there is no requirement for a
compression bezel or expensive heat seal bonding equipment.
The pins are attached to the glass with a structural epoxy on the back. On
the top, we apply an electrically conductive epoxy with an RTV overcoating.
Pins are the most reliable connection method, they are also the easiest to
deal with for prototyping and smaller production runs. However, of all
three methods, they have the lowest number of interconnects per inch.
Heat Seals
Heat seals
are similar to flexible circuit boards with the difference being that the
interface tabs are made of a conductive hot melt adhesive. Generally,
particles such as carbon, gold, or silver are added to the adhesive to make
it conductive. The pads of the heat seal are aligned with the pads of the
display and a hot bar is brought down under pressure and the conductive
adhesive is melted and bonded to the display. The adhesive is allowed to
cool and an electrical bond is made with the display. This method is the
most cost effective for the higher volume applications, but due to the
expensive setup and equipment required in this process, Heat Seals are
typically not
used for lower volume / low interconnection density requirements..