Actuation Force –
The force required to collapse the web of a rubber keypad in conjunction with polydome, metal dome, mechanical switch or rubber only.
Air Channel –
A flexible layer within a membrane switch’s air path(s) on the bottom of rubber keypads that allows for air passage/venting when switch is depressed. Switches should be vented on at least two sides.
Alignment Hole –
Through-hole in rubber keypad that is used to position keypad in enclosure.
Base Matte –
Silicone sheet material that joins all keys/switches on a rubber keypad. Also known as mat or apron. Typically, 1-2mm thick.
Bezel –
The faceplate or cover, typically plastic or metal, used to secure a keypad to a printed circuit board or switch. The bezel also aligns the keypad during the final assembly and protects the keypad base material from contact with human hands.
Bosses –
Small posts used for positive alignment of rubber keypad in bezels or assemblies.
Compression Set –
The measurement of a material’s ability to recover its original size and shape after compression under prescribed conditions.
Conductive Rubber –
Silicone keypad impregnated/coated with conductive material.
Colour Matching –
The visual and electronic analysis of a mixed silicone rubber material compared to a supplied colour sample.
Diaphragm / Web –
The thin hinged area that permits a rubber key to flex.
Contact Force –
The force required to maintain the rubber switch contact closure.
Contact Rating –
The electric power handling capability for rubber contacts under strictly controlled laboratory conditions.
Durometer –
A measurement range of hardness for silicone rubber.
Key Height –
The measured distance from the bottom of a keypad (base matte) to the top surface of a key.
Legend –
Printed graphic (symbol, letter or number) on the top of the rubber surface.
Life –
The number of actuations realised before the rubber diaphragm/web ruptures.
Membrane –
The non-conductive hinge that permits a rubber key to flex and is responsible for the tactile feel realised (also called flexing web or web).
Reversed-Out Graphics –
Graphics that allow rubber colour or masking colour to be seen through top surface printing on keypad. Also called Negative Image Graphics.
Positive-Image Graphics –
Single or multi-colour printing on top of the key surface.
Return Force –
Force created by switch membrane as it returns the key to a non-actuated position.
Snap Ratio (A-C)/A – Tactile Response:
F = Return Force
A = Actuation force
C = Contact force
Snap Ratio = (A-C)/A
Example: A = 350 grams C = 230 grams
Snap Ratio = (350-230)/350
=0.343
= 34.3%
Keypads with snap ratios of 40 – 60% have an excellent tactile feel and a relatively long life, while keypads with snap ratios below 40% have a relatively weak tactile feel, but longer life.
Stroke/ Travel –
Distance from the contact surface on a rubber switch to an electrode pattern on a printed circuit board.
Swell –
The increase in volume of rubber when in contact with petrochemicals for a determined period.
Tactile Feel –
The response of rubber while depressing. For tactile rubber keypads, it is a critical function of the diaphragm web geometry.
Tear Strength –
The tear strength is a measure of the resistance of rubber to tear forces. The tear strength is calculated by dividing the maximum force load by the thickness of the rubber.
Wear or Abrasion Resistance –
The resistance of a particular ink or coating to manual wearing. The testing process typically uses an RCA Abrasion tester, which is widely used as a standard for many silicone key pad and membrane switch manufacturers.