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what is the oxide film resistor and advantage of it
Oct 30, 2017

Typical Applications

Many properties of metal oxide film resistors are similar to metal film resistors. For basic use, metal film and metal oxide film are currently the predominant resistor types. Compared to carbon film, the prices are just as low. Only for dissipation values above 1 watt combined with reasonable stability, the carbon film resistors are still more cost efficient.

Construction

The metal oxide film is mostly produced with chemical deposition methods. Almost always a ceramic carrier is used as substrate. The deposition process involves the reaction of a pure metal with a gas at high temperature and at a low pressure. A very common metal oxide film is tin oxide. The film is established by heating the resistor body in a tin chloride vapor. Other metal oxide films have usually a different deposition process. Firstly a thin metal film is applied, which is afterwards reacted with oxygen. The desired composition is achieved by measuring the resistance of a test piece.

After the film is applied to the resistor body, the final resistance value is achieved by applying a helical cut. This is usually done by laser cutting, while in the past it was done by grinding or sandblasting. The spiral cut makes the resistance path longer and of smaller cross section, and can increase the resistance value up to thousand times greater than before the cut. The resistance value can be accurately controlled by the cutting. During the cutting process, the resistance is measured to allow for small corrections.

History

Metal oxide film resistors were the first alternatives to carbon composition resistors. They were in the past easier to manufacture than metal film resistors. Nowadays however, their numbers decrease and they are less and less available.



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