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What is Carbon Film Resistor and its Advantages?

A carbon film resistor is an evolved form of the carbon composition resistor; it is smaller in size and capable of providing much better performance. It is a type of fixed resistor that uses carbon film to restrict an electric current to a certain level. It is constructed by using a ceramic carrier rod onto which a thin layer of pure carbon is deposited as a film. This thin carbon film acts as the resistive element. The ceramic substrate acts as the insulating material to heat or electricity. 

A helical cut is made into the film to enable the carbon film resistor to have the correct resistance. This helical cut increases the length of the path of the current while reducing the width of the resistive element— the path length, width, and thickness of the carbon film all govern the resistance that is present. The use of pure carbon means that these resistors can operate in higher temperatures and sustain functionality as opposed to their predecessor, the carbon composition resistor. The desired resistance value can be obtained by selecting the proper layer of thickness and cutting an applicable helix. By decreasing the pitch of the helix, the length of the resistive path increases, correlating to an increased resistance value. A fine-tuned cut can have a higher accuracy of resistance value. Their manufacturing process plays a crucial role in its capabilities.

Carbon film resistors are manufactured using a deposition process. The ceramic rod is placed in an environment where temperature and pressure are high. Hydrocarbon gas is passed over the rods at over 1000 degrees Celsius. The gas naturally breaks down and a thin film of carbon is placed into the rods. After the rods have been obtained, end caps are installed onto the rods to connect to the carbon film, and a helical cut is performed. The resistors are then coated in resin to shield them from moisture, contaminants, and handling. Alas, the carbon film resistor is built and ready to use. Typical applications for carbon film resistors include power supplies, radars, x-rays, and lasers.

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