Meeting shrinking design objectives

Double-action tactile switches combine miniaturization with increased functionality

BY JEROME SMOLINSKI
C&K Components, Newton, MA
www.ck-components.com

Consumer electronics, particularly the portable variety, require advanced components that combine miniaturization with increased functionality. These design objectives can be difficult for engineers to meet without sacrificing performance and/or operating life.

Highly reliable miniature switches can play a major role in advanced electronic devices that need significant space and weight reductions along with increasing performance and device longevity. New tactile switch designs not only meet the size requirements of portable consumer devices, but also the functionality, performance, and durability to withstand harsh environments.

Miniature switch functionality

The significant size constraints associated with handheld and portable devices have forced switch manufacturers to develop miniature electromechanical switches with increased functionality. Low-profile double-action double-tactile switches are now being designed into handheld and portable electronic devices that require a specific ergonomics, such as a focus and shutter release on a digital camera or mobile phone. The advanced double-action double-tactile switches provide fast, repetitive action in these handheld consumer electronics applications. The increased functionality from the miniature double-action double-tactile switches can enable designers to eliminate components from their designs, decreasing the weight and size of an end product.

Some miniature double-action double-tactile switches on the market today are offered in package sizes as small as 2.6 x 3.0 x 0.7 mm, including the height of the actuator.

Flexibility in design

The flexibility of switch components is instrumental in their ability to meet application-specific needs of consumer devices, particularly handheld devices such as mobile phones, MP3 accessories, and Bluetooth headsets. Tactile switches are inherently smaller and more flexible than many other switch technologies, such as pushbuttons. These types of switches afford the capability of multiple mounting and actuation configurations, providing greater flexibility along with the ability to configure the switch for application-specific needs.

Reliability

Reliability is another major requirement for switch manufacturers designing consumer electronic devices, particularly handheld devices that are constantly exposed to severe environmental conditions, such as vibration, violent impacts against the ground, and contaminants such as moisture, humidity, and dust.

Designing switches with or without plating is another decision. Plating the stainless-steel contacts with gold or silver to resist corrosion requires depositing a nickel underlay to chemically prepare the surface to accept the plating, but this degrades the stainless steel itself, downgrading the overall capacity of the product to resist corrosion. As a result, designing the switch without plating could be much more effective.

Unfortunately, without plating, the switch exhibits extremely high and variable contact resistance, which is not compatible with the current levels seen in many handheld consumer devices, and thus has the potential to compromise the switch design. With all of these considerations in mind, the most effective solution is to seal the switch using Teflon films with either acrylic or silicon adhesives. This provides a robust solution with sealing to up to IP68 specifications, and doesn’t allow perspiration or other liquids to corrode the switch. It also allows the designers to apply conformal coating on its board such Parylene or other hydrophobic material. Many critical devices require “zero defect” components, given the nature of the application, and portable equipment used in the field have no room for device failure.

Fig. 1: The KMT0 series switches are designed without plating, sealed with Teflon films and adhesives to prevent the ingress of fluids, and provide maximum reliability.

Life expectancy

Standard pushbutton switches have a typical life cycle of around 30,000 actuations, while typical tactile switches can reach a range of 100,000 and 300,000 actuations, respectively, with a target goal of up to 600,000 for future tactile switch designs. A long operating life is due in part to a resistance to shock and vibration of 10 to 500 Hz and an operating temperature of 40 to 85C.

The miniaturization trend of mobile and handheld devices continues to be a driving factor in the development of innovative switches. Ultraminiature double-action switches provide a nice tactile feel and are an ideal solution for applications requiring a small footprint and good tactile feedback on both actions. Because electrical and mechanical specifications in consumer applications are critical tolerances are extremely tight and product profiles are small and development cycles and lead time requirements are short, switch manufacturers that develop flexible and reliable devices are at a distinct advantage for design wins. ■