There are various key actuation methods for remote control.
Rubber Keypad
? The most common and simple method
? It provides adequate key actuation feeling to user.
a) Contact area type
? Metal dome
? most reliable and best contact conductivity.
? Expensive.
? For industrial or medical grade product use.
? Contact life to be 1000K cycles Min.
? Carbon pill
? more reliable and good conductivity.
? Higher cost and limited contact key shape.
? Contact life to be 1000K cycles.
? It can be identified with some texture on carbon surface.
? Carbon paste
? More versatile for different key contact
? Comparable reliable quality at moderate pricing.
? It needs equipment setup for the carbon dipping process.
? Contact life to be 500K cycles Min.
? It forms a slight convex shape on contact surface.
? Carbon silk screen printing
? use in low-cost product, such as calculator and toy.
? Lowest cost.
? contact life to be 100K cycles
b) Additional Keycap
? Rubber can assemble with polydome as contact surface sheet or plastic keycap
to form a sub-assembly part.
? When assemble with plastic keycap, it is termed P+R (Plastic + Rubber) type.
c) Material and Fabrication
? Most common use is Japanese brand Shin-Etsu for best quality. Dow Chemical
is another choice.
? Local China brand is mature and available at relative lower cost.
? There are two types of key color mixing method when different color keys are
required.
? Key color mix during molding
? Low cost
? Easy spread different color to adjacent keys if key height and key pitch
distance is not enough for as rubber material will flow and spread during
molding.
? It is difficult to handle and human costly if more colors are used in one
same keypad.
? Color insert key
? Color insert key is pre-formed by using another single key tooling.
? The color insert key is then put in the designated key cavity of the master
tooling for fabrication.
? It is easier control as rubber color will not spread during molding.
? Higher initial cost for additional insert key tooling and key insertion fixture.
? It needs careful consideration either mixing rubber base material for color
key or apply different color on key top surface by silk screen printing.
? Silk screen printing need time curing after each color printed, so if more color,
it needs longer process time.
? Mixing rubber base color is not encouraged if key height is low or key distance
is small, as it creates more yield loss.
d) Keypad Decoration
? Silk screen printing
? Use normal silk screen printing method for legend printing.
? Add transparent overcoat printing to protect printed legend if longer life is
expected.
? Use mixing base color for different key base colors OR add a color legend
on keytop for differentiation.
? PU spray
? PU spray is use to protect the printed legend for longer durability.
? Rubber surface becomes smooth after spraying.
? Epoxy potting
? Epoxy is added on key top surface for decoration and protective purpose.
? Higher cost as cost is counted per keys.
? Laser Etch
? Laser etch process is best used for backlight key
? Keypad is originally formed in translucent color and spray in black, dark
grey or silver color, then use laser beam to etch the required legend on key
surface. Then cover the surface with PU protective spray.
? Plastic keycap (P+R) can also use laser etch.
Polydome
? It uses sheet plastic, normally PET, to form dome shape
? Carbon-Silver paste is applied on the sheet bottom for conductive contact
purpose.
? It provides better tactile feeling than rubber keypad at a shorter travel distance.
? Contact life to be 300K-500K cycles.
Metal Dome
? It uses sheet plastic, normally PET or PC, to form dome shape and then apply
metal dome disc as the contact area on the bottom side.
? It provides better tactile feeling than polydome and rubber keypad at a much
shorter travel distance.
? It is more reliable contact than polydome.
? The metal contact sound may be noisy to user.
? Contact life to be 500K-1000K cycles depends on dome shape.
Membrane keyboard
? Flat surface touch and dust proof
? Need soldering or use connector on PCB.
? No tactile feeling
? Contact life can be over 1000K cycles depends on the contact type.
Mechanical switch
? Bulky in construction but most reliable contact.
? Normal use in industrial grade product.
? General design is metal dome key with external mechanical support.
? Contact life to be 1000K –3000K cycles depends on switch type.
? Select to use when less keys on product.
? Higher unit cost but no tooling cost.
Touch panel
? Transparency contact panel add over LCD area for user access corresponding
functions on LCD.
? Glass plate as base layer with a poly sheet on top.
? Normal is provided in flat type panel and curved touch panel is possible.
? Relative expensive and require tooling. Some LCD manufacturer provide LCD
module with touch panel.
? Two types: resistive and capacitance type. Resistive type is cheaper and capacitance
type is widely use on smartphones.
? Contact life can be up to 1000K cycles.
Capacitance Sensing keyboard
? Use capacitance change for sensing human touch or movement through nonconductive
material.
? No mechanical movement for contact but need a rigid PCB (or FPC) below the
contact surface.
? Completely sealed product can be achieved for aesthetic and waterproof consideration.
? Require Capsense controller IC and sensing key array layout.
? It can combine with glass panel for LCD touch panel.
? Key contact life to be same as product service life.
? Module cost is expensive including IC and PCB.