Membrane Switch Industry Glossary of Terms

Ability to resist surface wear.

Force required to collapse the walls of a rubber keypad, metal or polyester dome.

A substance capable of bonding two surfaces together. The adhesive applied to the rear surface of a membrane switch to attach to the customer application surface, normally between .002-.005 thick. Adhesives are often activated by pressure and/or heat.

A printed display prepared on transparent material that can be illuminated from the rear to enhance attention value.

The process of illuminating transparent artwork or screen printed transparency film from behind.

•  FIBER OPTIC BACKLIGHTING - Illuminating device employed to light large areas. Strands of clear fiber are woven and bundled, after polishing the fiber ends are illuminated by an LED or Halogen lamp
• LIGHT EMITTING DIODE or LED - A semiconductor device that emits incoherent light formed by the P-N junction. The light intensity is roughly proportional to electrical current flow
• LCD - Liquid crystal display
  

Mechanical and thermoforming of graphic features, providing a raised feature for accenting key surfaces, logo’s, and to allow for embedding of surface mount LED’s within the switch.

• RACETRACK, RIM or RAIL - Creates a raised ridge around the perimeter of the key area, usually .010” to .015 high
• PLATEAU or PILLOW - Creates a raised surface in the graphic overlay over the entire key area, usually .010” to.015”high
  

Membrane touch switch resists damage from pens, pencils, screwdrivers, and other sharp objects. The unit's front switch can be constructed from aluminum, stainless steel, or film (polycarbonate up to .060" and other film material as identified). Unique tamper-resistant, patented design provides unparalleled protection – even in the most hostile or abusive applications. Switch elements are completely sealed to protect against environmental contaminants. An economical and reliable alternative to piezo switches. Thick polycarbonate overlays can double as protective display lenses.

• CHEMICAL RESISTANCE - The ability of a material to resist deterioration when in contact with chemical substances

• SOLVENT RESISTANCE - The ability of a product to resist the deteriorating action of specific liquids such as: water, ethanol, MEK, acetone, ammonia, etc.
  

Decoration of a membrane switch is conventionally accomplished with thin, screen printed, polyester or polycarbonate layers. Elastomer is also a method of decorating a membrane switch assembly and an attractive and functional alternative especially when a three dimensional look and feel is desired. The graphic layer options are:

1. Polyester

2. Polycarbonate

3. Elastomer

    

The IP Code defined in international standard IEC 60529 classifies the level of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water. It consists of the letters IP (for "international protection rating", sometimes also interpreted as "ingress protection rating") followed by two digits and an optional letter.

The digits ('characteristic numerals') indicate conformity with the conditions summarized in the tables below. Where there is no protection rating with regard to one of the criteria, the digit is replaced with the letter X.

For example, an electrical socket rated IP22 is protected against insertion of fingers and will not be damaged or become unsafe during a specified test in which it is exposed to vertically or nearly vertically dripping water. IP22 or IP2X are typical minimum requirements for the design of electrical accessories for in-door use. The standard aims to provide users more detailed information than vague marketing terms such as "waterproof".

FIRST DIGIT

The first digit indicates the level of protection that the enclosure provides against access to hazardous parts (e.g., electrical conductors, moving parts) and the ingress of solid foreign objects.

Level	Object size protected against	Effective against
0	-	No protection against contact and ingress of objects
1	>50 mm	Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part
2	>12.5 mm	Fingers or similar objects
3	>2.5 mm	Tools, thick wires, etc.
4	>1 mm	Most wires, screws, etc.
5	Dust protected	Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact
6	Dust tight	No ingress of dust; complete protection against contact

SECOND DIGIT

Protection of the equipment inside the enclosure against harmful ingress of water.

Level	Protected against	Details
0	Not protected	-
1	Dripping water	Dripping water (vertically falling drops) shall have no harmful effect.
2	Dripping water when tilted up to 15°	Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position.
3	Spraying water	Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.
4	Splashing water	Water splashing against the enclosure from any direction shall have no harmful effect.
5	Water jets	Water projected by a nozzle against enclosure from any direction shall have no harmful effects.
6	Powerful water jets	Water projected in powerful jets against the enclosure from any direction shall have no harmful effects.
7	Immersion up to 1 m	Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).
8	Immersion beyond 1 m	The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. NOTE: Normally, this will mean that the equipment is hermetically sealed. However, with certain types of equipment, it can mean that water can enter but only in such a manner that produces no harmful effects.

 

A keypad is a set of buttons arranged in a block which usually bear digits and other symbols but not a complete set of alphabetical letters. If it mostly contains numbers then it can also be called a numeric keypad. Keypads are found on many alphanumeric keyboards and on other devices such as calculators, combination locks and telephones which require largely numeric input.

The ASTM subcommittee on Membrane Switches defines a membrane switch as: "A momentary switch device in which at least one contact is on, or made of, a flexible substrate"

To be more specific, all of the following conditions or features must be met in order to truly be classified as a membrane switch:

1. Direct (Ohmic) Contact: the poles of the switch must make physical contact, i.e. can not be non-contact type like capacitive, ferrite core, or hall effect.
2. Momentary Action: Upon release, the poles immediately separate as the flexing membrane returns to its original position.
3. Low Voltage Application: A membrane switch is designed to be used in low voltage, DC logic-level-signal, applications.
4. Membrane Layer: A thin pliable layer and carries one pole, both poles or that flexes during switch operation used to short both switch poles together. See figures 2 & 3

Figure 2	Figure 3

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:

Figure 3

The adhesive applied to the rear surface of a membrane switch to attach to the customer application surface, normally between .002-.005 thick.

NEMA stands for the National Electrical Manufacturers Association has established a range of standards for electrical equipment enclosures. For more detailed and complete information, NEMA Standards Publication 250. You can reach the National Electrical Manufacturers Association at: http://www.nema.org/

NEMA defines standards for various grades of electrical enclosures typically used in industrial applications. Each is rated to protect against designated environmental conditions. A typical NEMA enclosure might be rated to provide protection against environmental hazards such as water, dust, oil or coolant or atmospheres containing corrosive agents such as Acetylene or gasoline.

NEMA 4 - Type 4 enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose-directed water; and to be undamaged by the formation of ice on the enclosure. They are not intended to provide protection against conditions such as internal condensation or internal icing. 

Adhesive materials which bond with the application of pressure alone and do not require activation by heat or solvents

• PSA - Pressure Sensitive Adhesive