carbonfilm

Carbon film, in electronics often referred to as a carbon film resistor, is a fixed resistor in which a thin layer of carbon is deposited on an insulating ceramic substrate to form the resistive element. The film is patterned and trimmed to achieve the desired resistance, and it is mounted with end caps and leads to make electrical connections. The outer body is typically cylindrical or rectangular and often color-coded to indicate resistance, tolerance, and sometimes temperature coefficient.

Manufacture and structure: The carbon film is deposited on the substrate by a thermal or chemical process and then processed to set the resistance. The final device is then encapsulated and tested. Variants of carbon film resistors may use different substrate materials and film deposition methods, but the basic principle remains a carbon-based resistive layer integrated into a compact package.

Electrical characteristics: Carbon film resistors cover a wide value range, from a few ohms to several megohms. Tolerances are commonly 5%, with tighter tolerances (1–2%) available on precision parts. The temperature coefficient is typically negative, in the range of about −50 to −350 ppm/°C, meaning resistance tends to decrease as temperature rises. Power ratings commonly range from 1/8 W to 1 W in common axial packages, with higher-power variants available in larger formats. They generally exhibit higher noise and drift than metal film resistors but offer low cost and good performance for many applications.

Applications and history: Introduced as a cost-effective alternative to carbon composition resistors, carbon film resistors became widely used in consumer electronics, audio equipment, and general-purpose circuits during the mid-to-late 20th century. They remain common in many legacy designs and budget applications, though metal film and thin/thick film technologies have become dominant for precision and stability in modern circuitry.

See also: resistor, carbon composition resistor, metal film resistor.