High Reliability Reed Switches with Rhodium Plated Contacts

Cross section of the reed blades (a) and structure of the reed switch (b)

Fig.1 Cross section of the reed blades (a) and structure of the reed switch (b)

Variation of the contact resistance

Fig.2 Variation of the contact resistance

Micrograph of contact surface at 10[sup]6[/sup] operations (a) and X-ray microanalysis of carbon (b)

Fig.3 Micrograph of contact surface at 106 operations (a) and X-ray microanalysis of carbon (b)

  This technology is on the realization of the high reliability reed switch with rhodium plated contact which has a stable operating contact resistance.

  As semiconductor circuits are getting popular, reed switches are used in many application area, at the low level lord circuits (less than several volt, μA-mA), not only as a relay element driven by coil but a magnetic sensor device driven by the magnetism. Rhodium is very excellent contact material for reed switches. Rhodium has high hardness, high melting point and resists abrasion. But the rhodium plated contact has the defect of an occasional increase in contact resistance in early stage of operation. This is caused mainly by the phenomena of the surface adsorption and catalysis by Rhodium. Various organic compounds and other impurities are adsorbed on the surface of the rhodium contact. When mechanical operations are applied, some organic compounds are formed catalytically and by the collision energy of mutual contacts. These organic compounds make the contact resistance increase.

  Toshiki Yokokawa and Chihiro Kawakita studied this failure mechanism in detail. And they developed the oxygen treatment at high temperature (about 450 °C). This new surface treatment is an effective way of preventing adsorption and catalysis on the surface of the rhodium contacts, thus enabling the production of high-reliability reed switches with stable contact resistance.



Publications

[1] Toshiki Yokokawa and Chihiro Kawakita、High Reliability Reed Switches with Rhodium Plated Contacts、1973、Proceeding of 21st Annual National Relay Conference, Oklahoma State University, May 1,2 1973
[2] Toshiki Yokokawa and Chihiro Kawakita、Stabilization of Contact Resistance of Reed Switch with Rhodium Contacts in Low Level Lord、1985、IEICE Transaction, Vol.J68-C, No.2, pp.124-130. 1985/2
[3] Toshiki Yokokawa, Takao Yano, Chihiro Kawakita, Kunio Hinohara, and Akira Nagai、A Study on the Surface Deactivation Treatment of Rhodium-Plated Contact Reed Switches、1986、IEEE Transactions on Component, Hybrid, and Manufacturing Technology, Vol.CHMT-9, No.1, March 1986

Related Researches

Category

Electronics & Devices
(Fundamental Technology)

Events in World

1974
Politician Eisaku Sato received the Nobel Peace Prize.
1974
Shigeo Nagashima of professional baseball team Yomiuri Giants retired as a player.
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