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Switch technology undergoing key changes
Rick Hampton, President, E-Switch, Brooklyn Park, MN -- Design News, June 18, 2001
Rick Hampton has spent nearly all of his three-decades long career in the electromechanical component industry in distribution, representation, and manufacturing. He was named president of E-Switch last year. He spends much of his time directing the efforts of the company's product development and marketing initiatives, and is interested in helping educate engineers on how they can more effectively apply switch technology within their designs.
Miniaturization, SMT, high-temperature materials, and low-power logic-level switching are key changes within the switch world. The terms miniaturization, subminiature, ultra-miniature have been redefined many times over to describe products ever smaller than before.
Design News: You've been in the electromechanical component industry your entire career. How far have we come?
Hampton: When I first started in the industry, receiving tubes were in use for radio and television circuitry. The transistor radio was in its infancy with six or eight transistor AM radios available. The best communication was by mail or telephones, which were all rotary dialing; no cell phones. The Russian Sputnik satellite had just been launched. The fax had not been invented so paper transfer was done by Telex paper tape readers. Copies of important documents were made by using carbon paper and inventories were managed using manual card systems (no computers available) and Olivetti paper tape calculators. Digital calculators would not be readily available for another ten years.
Q: What impact has the advent of tactile switches had on product design?
A: Tactile switches are replacing standard pushbutton switches due to low cost, lower power circuitry, board space (real estate) considerations, variety, and surface mount requirements. These switches continue to fall within the definition of mechanical switch products but are rapidly replacing standard switches used over the past three decades. Faster and faster chip technology sets the pace of change within switch technology. Faster speeds generate more heat, requiring lower level switching current. A by-product is lower battery drain in a world of handheld wireless technology.
Q: What are some other important product developments in the switch arena?
A: The trend toward printed circuit board and enclosure size reduction, as well as logic-level circuitry has driven the development of smaller size switching devices. The tactile switch is well suited for the purpose. Low power (dry circuit) applications, until quite recently, were defined as power levels less than 300 milliamps, but probably greater than 10 milliamps @ 0.3V. We are now seeing a need for switching consistently below that level (measured in micro amps). These new products must be gold plated both on the fixed and movable contacts to insure low contact resistance; a requirement in this newly defined region of dry circuit.
Q: How can engineers design with switches successfully?
A: Mechanical design engineers should relate their switch need to power requirement, size, mode of actuation (right-angle), life, surface mount, sealed, surge requirement, number of poles required, agency approvals, temperature (in-process and environmental), current level, and the lowest number of actuations during a six-month period. Problems can arise if the wrong switch is selected for the application. Engineers specify a low power switch with silver plating for a low power circuit. If that switch has a butt contact, as in the case of a tactile switch, a silver-oxide film may prevent proper logic level signal transfer. Gold is the recommended solution. Use of a switch with wiping action may also solve the problem. However, we often run into the problem where the application requires few actuations, if any, on an annual basis. Once again, gold is the material recommended as the oxidation build up during non-use may cause failure until it is removed by repeated actuations. These problems do not surface in high-power applications as the oxidation is removed during the electrical switching cycle.
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