Resistors are passive two-terminal electrical devices that are equipped with electrical resistance as a circuit element. These components find use in street lighting, fan speed controllers, temperature sensors, and more, limiting the flow of electrical current of such apparatuses. More than that, they are available in varying types, all of which serve a diverse set of industrial applications. One such type includes a metal film resistor. Serving as one of the most widely used resistor types, metal film resistors outperform their counterparts. As such, this blog will cover metal film resistors, their uses, and importance.
As their name suggests, metal film resistors are axial leaded resistors that are made from a thin film of metal that is positioned inside a ceramic rod. The film works similarly to a resistance wire with adjustable specifications. As their thickness, width, and length can be accurately controlled, metal film resistors can be designed with a high tolerance. Due to their stability, accuracy, reliability and noise reduction characteristics, metal film resistors are selected over carbon composition, carbon film, and other various resistor types for many applications.
Metal film resistor construction and manufacturing consists of a few integral steps. First, the resistor is manufactured by vacuum depositing a metal layer onto a high purity ceramic cylindrical rod. It is important to note that the thicker the metal being deposited onto the rod, the more stable the resistor value will be. In most cases, film thickness ranges between 50 and 250 nm as these values typically provide long term stability. There are a number of techniques that can be used to achieve this, the most common being sputtering. Furthermore, the metal that is deposited is normally Chromium, NiCr, gold with platinum, or tantalum nitride. Once the film has been deposited onto the rod, a metal end cap is placed on the end.
The next step in the manufacturing process necessitates special attention to trimming the resistance value to the required figure. This can be achieved through the use of lasers that cut a helix into the metal film that will extend the length of the metal element. The helix reduces the width of the current carrying track while also keeping the deposited material thickness within an ideal range for long term stability. Laser trimming offers many benefits, one of which includes the accuracy it produces. With this in mind, tolerances of 0.1%, 0.25%, 0.5%, 1%, and 2% are feasible.
Additionally, metal film resistors maintain a good temperature coefficient of resistance with values falling between 50 and 100 ppm/°K. The last step of the manufacturing process requires the resistor be covered in a protective coating and markings. The coating is usually a resin while the markings are just values that are added to the resistor. Beyond their design, metal film resistors have many uses while also offering countless advantages. The biggest benefits metal film resistors offer include their low-price points, reliability, and accuracy. However, metal resistors are not suitable for applications that may experience surges, making carbon composition resistors a better option in such instances.
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