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There are three primary methods to
connect the LCD with its control circuitry.
Elastomers (Zebra Strips)
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. Other Types of Connection
FPC (Flexible Print Circuit) is a circuit substrate
of patterning Cu electrode with Polyimide film as a base. Usually offers
more flexibility than Flexible Flat Cables. FFC
(Flexible Flat Cable) is a cable with two smooth or corrugated, but
essentially flat, surfaces. Attached to the PCB by soldering or plugging
into a zero insertion force connector. Very reliable. |
