Consumer electronics, particularly the portable variety, require advanced components that combine miniaturisation with ruggedness. These design objectives can be difficult for engineers to meet without sacrificing performance, functionality or operating life.
Author: Jerome Smolinski, Senior Product Manager, C&K
Highly reliable miniature switches can play a major role in today’s advanced electronic devices that require significant space and weight reductions, while 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 required from harsh environmental conditions they encounter.
Miniature switch functionality
The significant size constraints associated with handheld and portable devices has 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 specific ergonomics. 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 available on the market today are offered in package sizes as small as 3.0x4.0x0.55mm, not including the height of the actuator.
Flexibility in design
The flexibility of switch components is instrumental in their ability to meet application-specific requirements of consumer devices, particularly handheld devices such as mobile phones, wearables 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, which provide greater flexibility and create the ability to configure the switch for application-specific needs.
Reliability is another major requirement that switch manufacturers must take into account when designing for consumer electronic devices, particularly handheld devices that are constantly exposed to severe environmental conditions, such as violent impacts against the ground, vibration, moisture, humidity, dust and other contaminants.
Designing switches with or without plating is a consideration for switch manufacturers. Plating the stainless steel contacts with gold or silver to resist corrosion requires the deposition of a nickel underlay to chemically prepare the surface to accept the plating; however, 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 as Parylene or other hydrophobic material. Many critical devices require 'zero defect' components, given the nature of the application, and in portable equipment used in the field there is no room for device failure.
The KMT0 Series switches from C&K are designed without plating, sealed with Teflon films and adhesives to prevent the ingress of fluids and provide maximum reliability.
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 10-500Hz and an operating temperature of -40 to 85˚C.
The miniaturisation trend of mobile and handheld devices continues to be a driving factor in the development of innovative switches. Ultra-miniature 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.