Metal film resistor

 
Metal film resistor

Metal film resistors Metal film resistors have a thin metal layer as resistive element on a non-conducting body. They are amongst the most common types of axial resistors. Other film type resistors are carbon film and thick and thin film resistors. In most literature referrals to metal film, usually it is a cylindrical axial resistor. However, thin film chip resistors use the same manufacturing principle for the metal layer. The appearance of metal film resistors is similar to carbon film resistors, but their properties for stability, accuracy and reliability are considerably better. Metal film resistor definition Metal film resistors are axial resistors with a thin metal film as resistive element. The thin film is deposited on usually a ceramic body. Construction The resistive element is a thin metal layer that is usually sputtered (vacuum deposition) on a cylindrical high purity ceramic core. Sometimes other techniques than sputtering are used. The deposited metal is artificially aged by keeping it for a long period at a low temperature. This results in a better accuracy of the resistor.  The resistance material is often nickel chromium (NiCr), but for special applications also other alloys are used such as tin and antimony, gold with platinum and tantalum nitride. The stability and resistance are strongly dependent on the thickness of the metal film (50-250 nm). A larger thickness of the layer results in a better stability and a lower resistance value. On both ends a metal cover is pressed with the connection leads.  After this, the desired resistance is achieved by cutting a spiral shaped slot in the thin metal layer. This is usually done by lasers, while in the past sandblasting and grinding techniques were used. Carbon film resistors use the same technique to trim the resistance. The resistor is covered with several coating layers [… read more]