Irga

• membrane keyboard - electric circuit is realized by the tracks imprinted on the foil, while using silver paints as a typical laminate PCB tile. Electric junction is provided by silver layers or silver plates. Keys descriptions are printed on the front foil (from the inside, that ensure print durability)

• micro switch keyboard - electric circuit is a typical PCB tile. In that tile micro switch is a contact element situated there by soldering. Keys description is placed on the heating foil, that mask micro junction and also often masks elements that secure PCB in the casing.

• silicone keyboard - electric circuit is placed on PCB or silver paint printed on the foil. Pastille made of rubber, that conduct electric current is the junction element. It's glued under the silicone mat, which provides simultaneously mechanical(in case of springing) and decorative(keys description) function

Our company makes membrane keyboards on the PCB basis, foil that mask micro switch keyboards, as well as complete panels that are used to assembly micro switch keyboards.

Those examples above are typical construction schemes. In addition, two additional types of keyboards enter the market. They are impossible to discern by the user, still having totally different technology in the realization aspect:

That kind of implementation requires a special driver, that can record these physical effects and generate logic signals.

2. Versions of membrane keyboards

There are many subtypes of membrane keyboards. Every one of them is different.Those differences can be pick out, when we are looking at the technology, that was used during realization of this keyboard. Thereupon cost and durability in the final adaptation are different.

"Purely" foil keyboard:

All the layers are made on polyester foils using screen printing method (also conductive layers). In this activity special paste is used. It's made of silver micro particles, that are hanged in the resin binders. Switching is realized trough upper foil deflection, that causes that two silver fields contact on the two silver foils. Top cover contains any graphics with a keys description.

Foil keyboard with blades

That type of keyboard it's a previous model modification. It's created to improve electric junction durability. Contact between foils and silver paste is realized through steel blade that springs ( usually gilded, nickel plated in cheaper solutions).

Keyboard on PCB layer with foil contacts.

Structures on the PCB layer are previous model expansions. Laminate with metallic copper cover is used instead of foil layer. This allows to create much thinner paths, that have better conductivity (copper resistivity 1,7*10E-8[Ωm], silver paste about 40*10E-8[Ωm] and practically junction final resistance independence from the inside keyboard connection grid. Junction element is made using carbon or a sliver paste in a form of a copper comb. It's joined together by a silver field printed on a foil. That solution is cheaper in production than using plates.

Keyboard with plates, on the PCB basis:

Using PCB and contact plates(gilded) together, definitively eliminates foil keyboard disadvantages that are connected with the use of the silver paste(oxidation, connection grid - resistance dependence, leading out tape unreliability). Copper connection field can be protected from corrosion with an low-ohm coal layer, that improves skid of the working spring or when there is need to obtain minimal final resistance.

Both versions of the keyboard on the PCB basis allow to solder LED instead of gluing them to the silver paste, which is more resistant in case of abnormal assembly and mechanical injury. In addition, the underside of the keyboard may also contain whatsoever electronic elements that are soldered there. That's very useful when you have to make miniaturization of a device.

Production of PCB keyboards is the main branch of our company. We project graphics designs and electric sets. Further LED mounting and applications of the electric lead out is also a part of our company actions. Thick layer resistors are also produced in our company. We provide modules that are already prepared to use. You need only to mound it in a case(glue or screw on) and connect it to your own project electronics.

3. Micro switch keyboard with decorative foil

Despite the slightly more difficult mechanical application, micros joint keyboards are still very popular. Especially low series designers like this solution and all those who are planning device evolution.(adding new features, case lifting). Because of the fact, that next versions will need new PCB plate project, it is not good to be attached to separately designed membrane keyboard circuit.

Our company serve clients also in the application field of that solutions. We make not only masking foils, but also buttons. Furthermore we mill holes in cases and produce complete panels ( on the metal or material field) that are ready to suspend on micro switch modules.

4. Comparison of construction - the advantages and disadvantages

The following table contains fundamental differences between the types of keyboards discussed. Consideration of the possibilities and limitations of each technology is quite often more important, than production costs. So it's reason to choice proper solution.

 

	keyboard
	foli	on the PCB basis	microswitch
conductor	silver paste	metallic copper	metallic copper
materials	polyester foils	polyester foils copper-polyester laminates steel contact blades (gold-plated)	plastics steel contact blades (gold-plated or nickel)
electrical lead-out	foil tapes with copper tracks	foil tapes with copper tracks solder cable bunch any type PCB coupling (SMD or thru-hole)
mechanical durability of the switching element	10e6 cycles	10e6 cycles	n/d 1
SMD elements application (LED, resistors)	glue	solder	n/d 2
thru-hole elements application (LED,resistors,display units etc.)	n/d	solder	solder
other electronic elements application	n/d	solder	solder
keyboard as mechanical carrier	n/d 3	PCBs (thickness from 2.0 to 3.0 mm)	usual PCBs 1.5 mm thick