Human Factors and Behavioral Science: Membrane Keyboards and Human Performance

Membrane switch technology has become increasingly popular in consumer-oriented products such as pocket calculators and kitchen appliances. Application of this technology to the design of full-size, alphanumeric keyboards has resulted in products that differ markedly from conventional keyboards in terms of keystroke feedback to the user. Membrane switches usually consist of mechanical contacts on two layers of material, separated by a nonconductive third layer of material (see Fig. 1). The upper, membrane layer is usually a thin polyester material with flexible conductors applied to its underside. Graphics may be silk-screened on this surface or on a second surface placed on top of the membrane layer. The substrate may be either a printed circuit board with conductors or a flexible film with printed conductors. This is usually mounted on a rigid, smooth surface. The spacer layer is an insulating material that separates the membrane and substrate layers by 5 to 7 mils. It has holes through which the upper, flexible layer may be depressed, causing contact closure. When pressure on the membrane layer is removed, the resilient, flexible membrane breaks contact with the substrate and returns to its original position. Membrane switch technology has become popular for several reasons. Its production costs are low because there are no key-plunger mechanisms. It also affords considerable design flexibility in terms of panel layout, "key" size and shape, and graphic labels. Good switch enclosure can also be assured for hostile environments and for protection against dust accumulation, spills, and vermin infestation.