Difference Between Metal Film and Carbon Film Resistors

Key Difference – Metal Film vs Carbon Film Resistors
 

Most metal film resistors and carbon film resistors have a similar appearance and shape but the key difference between metal film and carbon film resistors is that metal film resistors use a metal film to limit the flow of electric current whereas carbon film resistors use a carbon film to limit the electric current flow.

Resistors are electronic components in circuits. They are used to limit the electric current flow through the circuit. Therefore, these components are very important to regulate the electric current. There are three main types of film resistors named as metal film resistors, carbon film resistors, and metal oxide resistors.

CONTENTS

1. Overview and Key Difference
2. What are Metal Film Resistors
3. What are Carbon Film Resistors
4. Similarities Between Metal Film and Carbon Film Resistors
5. Side by Side Comparison – Metal Film vs Carbon Film Resistors in Tabular Form
6. Summary

What are Metal Film Resistors?

Metal film resistors are a type of resistors that use a thin metal film to limit the electric current flow. The resistor consists of a thin metal layer on a non-conductive material. Metal film resistors are the most common form among thin film resistors.

During the construction of a metal film resistor, a metal film from a suitable metal (antimony, tin, nickel-chromium alloy, etc.) is deposited on a suitable non-conductive material (ceramic with high purity). Then this thin film is made to undergo aging by keeping it for a long time at a low temperature. The aging of the film results in the high accuracy of the resistor.

The stability and the accuracy of the resistor are highly dependent on the thickness of the metal film. For examples, if the thickness is high, the stability of the resistor is high, but the accuracy is low. The ends of the resistor are covered with a metal cover. The metal cover is pressed along with connection leads (terminal points from which the resistor is connected to a circuit). The desired resistance can be obtained by cutting a spiral shaped slot in the metal film using a laser.

The advantages of using a metal film resistor can be listed as below.

• Cheaper than other forms of resistors
• Generates less noise than other types of resistors
• High stability
• Small in size
• High accuracy

What are Carbon Film Resistors?

Carbon film resistors are a form of resistors that use a thin carbon film to limit the electric current flow. The resistor consists of a thin carbon layer on a pure ceramic material. However, when compared with other forms of thin film resistors, carbon film resistors are expensive to produce. These carbon film resistors are better to be used in high voltage and high temperature applications.

Carbon film resistors are produced by a deposition process. Initially, the ceramic portion is kept at a high temperature in the presence of hydrocarbon gases such as methane. The gas undergoes cracking reactions at high temperatures (around 1000°C). Then the crystalline carbon (from pure graphite) deposits on the ceramic. The resistance of the resistor can be controlled by regulating the thickness of the carbon layer.

What are the Similarities Between Metal Film and Carbon Film Resistors?

• Both metal film and carbon film resistors have similar appearance and shape.
• Both are similar in size.
• Both use ceramic as the non-conducting material.
• The resistance of both resistors can be controlled by regulating the thickness of the thin film.

What is the Difference Between Metal Film and Carbon Film Resistors?

Summary – Metal Film vs Carbon Film Resistors

Resistors are components in circuits that are used to regulate electrical current flow through the circuit. The key difference between metal film and carbon film resistors is that metal film resistors use a metal film to limit the flow of electric current whereas carbon film resistors use a carbon film to limit the electric current flow.

Reference:

1. Shaik, Asif. Metal Film Resistor. Physics and Radio-Electronics, Available here.
2. “Metal Film Resistor. Resistor Guide,  Available here.
3. “Carbon Film Resistor, Resistor Guide, Available here.
4. “Types of Resistor Including Carbon, Film and Composition.” Basic Electronics Tutorials, 2 Mar. 2018, Available here.

Image Courtesy:

1. “Resistor metal film 0.5W 1% 82R” By J nestor – Own work (CC0) via Commons Wikimedia
2. “Carbon-film Resistor Construction” By jjbeard – Own work, Made in Inkscape 0.43 (Public Domain) via Commons Wikimedia