Membrane Switch Definition - 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)

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