TECHNICAL INFORMATION - STRUCTURE OF LAYERS
Overlay / Front
Foil:
It is the superficial layer in the Membrane
Keypad. It includes all graphic design features to allow operating the keypad
correctly.
In Membrane Switching manufacturing the
materials regularly used in Overlays and Front Foils are Polyester and
Polycarbonate. We offer materials highly resistant to chemical solvents,
scratching, temperature, UV, moisture environments, etc; this material also
allow embossment.
There are a wide range of possibilities for
finishing. Our vast experience in silk-screen printing and digital printing will
help you out in your project; offering the Artwork and finishing that you like.
Dome retainer:
The function of this is structural layer is to
keep the domes in the right position ensuring correct keypad operation while
pressing keys.
If your project does not include Metal Domes,
it would not be necessary to include this layer in the structure of the
membrane keypad.
Spacer:
This layer helps to adjust the thickness in the
membrane keypad. Its function is to ensure correct LEDs and metal domes
operation.
This layer is usually built in laminated layers
of polyester and adhesive.
Circuit:
The electrical circuitry of membrane keypads is
printed on this flexible layer. Illumination LEDs and metal domes are also
mounted on it.
The in the circuit tracks can be made in cooper
or using silk-screen printing techniques with conductive inks, mainly silver
conductive inks. CRESPO assists you to find the best solution in your membrane
keypad project according with the application.
The circuit always includes a dielectric
coating for protecting the tracks.
It is possible to include different types of
finishing for protecting conductive contacts in the circuit of the membrane
keypad or for protecting the contacts in the flex tail of the circuit. We offer
finishing in: graphite, Lead free Tin or Flash-Gold.
Components:
LEDs:
The LEDs are the electronic component that
allows illumination in the membrane keypad. CRESPO mounts SMD LEDs in different
colors (Green, Yellow, Orange, Red, White and Blue), bi-clour (Red / Green) or
tri-colour (Red / Green / Blue).
Backlighting in Membrane Keypads can be
achieved using electroluminescence (EL), fiber optics and embedded LEDs.
Electroluminescence (EL) is the result of
applying an electric current to a specially silk-screened layer of glass
phosphors. This layer is embedded between two conductive layers. Even though it
offers an attractive result, Electroluminescence (EL) is a complex and
expensive option with short shelf life cycle.
Backlighting with fiber optics is achieved by
light transmission through fibers connected to a source of illumination. As in
the previous alternative Backlighting offers an attractive result, however, it
adds complexity in design and manufacturing to membrane keypad projects. This
would mean higher manufacturing and maintenance costs.
In CRESPO we are working on a way to offer
backlighting with embedded illumination SMD LEDs at a low price; without adding
complexity or additional systems to the membrane keypad. We are constantly
innovating!
Metal Domes:
Metal Domes are components of membrane keypads
that increase the tactile feeling while operating the keys in the switch. In
CRESPO we offer a wide range of possibilities in shape, actuation force, sizes
and finishes according to each application.
Connectors:
The circuit in the membrane keypad is connected
to the PCB through a flex “tail”. Features and characteristics of this tail are
not standard and are different in each project.
In CRESPO we offer different distance between
tracks (pitch): 1,00mm, 1,27mm pitch or 2,54mm. We have the possibility to
assemble plastic housings (female connector) in circuits made with 1,27mm or
2,54mm pitch.
Rear adhesive:
This layer make possible to stick the membrane
keypad to the surface of a carrier or housing in the device. The type of
adhesive to use on each project depends on the surface, environment exposure,
chemical attack, etc.
CRESPO MS - Structure of layers.pdf
