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| About Membrane Switch | ||||||||
Membrane Switch Definition
--Five Conditions
--Five Layers
--Specification
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Membrane Switch Difinition-5 Layers
Every membrane switch must contain a Membrane Layer & a Static Layer in order to satisfy the definition (as stated in the conditions). There are many other components and options available to the membrane switch design engineer, for example;
embossing, tactile response, materials, colors, backlighting etc. However, the basic construction can be described with five basic layers, two of which must exist , the
1. Graphic Layer: Decoration of a membrane switch is conventionally accomplished with thin, screen printed, polyester or polycarbonate. Elastomer is also a method of decorating a switch assembly and an attractive and functional alternative especially when a three dimensional look and feel is desired. The graphic layer options are:
a. Polyester
b. Polycarbonate
c. Elastomer
2. Membrane Layer: As discussed above the Membrane Layer is thin & pliable and carries at least one of the poles of the switch or carries a conductive shorting pad. The following list are examples of membrane layers along with their associated conductive material. Note the "Poly-Graphic Layer" (poly referring to either polyester & polycarbonate) can also be the Membrane Layer if it contains the switch shorting pad.
a. Polyester, opaque conductor - silver or carbon.
b. Polyester, transparent conductor - ITO.
c. Metal Dome, metal conductor.
d. Elastomer, conductive pill - carbon or metal.
e. Poly-Graphic Layer, (polyester or polycarbonate) - opaque conductor.
3. Tactile Layer: There are several ways to create a tactile response, some are a result of forming another layer. For example a dome embossed polyester overlay means the graphic layer is also the tactile layer. If a polyester dome is formed in the membrane layer means it doubles as the tactile layer. Obviously if the tactile layer is absent, you have a non-tactile membrane switch.
a. Metal Dome.
b. Polyester Dome: thermally formed dome in the membrane layer.
c. Dome Emboss: formed dome in the graphic layer.
d. Packaged Membrane Switch: small momentary switch module that, by itself, satisfy the definition of a membrane switch. They are used in membrane switch assemblies and provide a tactile response.
e. Elastomer Keypad: An elastomer keypad can provide the tactile response if the internal web surrounding the key is designed to collapse and return to its original position after release.
4. Static Layer: As discussed above the Static Layer is rigidly supported and carries at least one of the poles of the switch or carries a conductive shorting pad. Polyester and Polyimide is a thin flexible material and in order to be static must be laminated to a rigid backer. The following list are examples of static layers along with their associated conductive material.
a. Polyester, opaque conductor - silver or carbon ink.
b. Polyester, transparent conductor - ITO.
c. Polyimide, copper conductor (flexible PCB).
d. Printed Circuit Board, copper conductor (rigid PCB).
e. Packaged Membrane Switch, internal (unspecified) conductor.
f. Glass, transparent conductor - ITO.
5. Rigid Backer: If the static layer is made from a flexible material it must be laminated to a rigid material. Many membrane switches are purchased without a rigid backer and the static layer does not become truly static until it is attached permanently to the instrument housing. Materials that are used as a rigid backer:
a. Aluminum
b. Steel
c. Plastic
d. Glass
e. Fiberglass (PCB)