Metal domes evolve to meet new demands.
Dome switches are fabricated from steel pre-formed into a dome shape. When depressed, the dome closes and makes electrical contact while providing a tactile feedback to the user. According to Paul Griffiths, product manager of ITT Industries, Cannon, the benefits of this type of switching system include a low profile, a minimum use of space on a PC board, and low cost. It is also suitable for automated or manual assembly.
"The wireless market has largely been responsible for driving the changes and requirements for the dome," Griffiths says. "Increased demand created by the wireless boom in the late '90s led to increased automation, forcing assembly operations to embrace automotive-style control systems such as Six Sigma. This was in stark contrast to early dome array assembly, which was often a manual task that required an operator to pick the individual dome and, by means of accurate jigging, locate each one in the correct position."
Griffiths says processes became more stable and robust after the shift to automated manufacturing techniques, satisfying the more stringent requirements set down by phone manufacturers. The leading dome suppliers quickly ramped up from manufacturing tens of thousands per month to hundreds of thousands per month. In addition, the mobile phone market has not stood still, and dome manufacturers have had to respond by producing tighter tolerance devices.
"Power, size, and life are the main drivers for mobile phones," Griffiths says. "How thin can a phone be? How long can the batteries last? And, how many operations can a dome reliably make?"
The shape of a dome determines its tactile feedback, its trip force, and how many operations it can make. Nowadays, domes are capable of over 500,000 cycles. With many mobile phones being used as game platforms, the life requirement is often in excess of 1.5 million cycles. These kinds of expectations have forced dome manufacturers to get busy creating even more powerful devices.
OEMs have been stretching the boundaries of what's possible in regards to size. Greater component density on PC boards has led to shrinkage in dome diameter, but these ever-tightening space restrictions have not been at the expense of the dome's retaining life and tactile characteristics. However, as the dome diameter reduces, so too does the area of the dome that can be operated and still give an acceptable tactile feedback.
Consequently, it is still advisable to fit the largest dome possible to achieve maximum performance as required for the given application.
When choosing the dome best suited to any application, an engineer must consider the conditions of use and the interface with other components such as the keypad or PC board," Griffiths advises. "Correct material selection is vital. High grade stainless steel, such as 301, is a pre-requisite because it negates the requirement for plated domes. The size, length, and material of the actuator will affect the operation of the dome and the feedback felt by the user."
Although the cellular phone sector has driven dome producers to constantly innovate and develop their products, other key applications benefiting from the technological improvements in domes include PDAs and global positioning systems.
More information on metal dome arrays is available by contacting ITT Industries, Cannon, 57 Stanley Ave., Watertown, MA 02472, calling 800-635-5936, visiting www.itt.com, writing in 300 on our reader service card, or replying online at www.pddnet.com.