What is metal film resistor? Application, Manufacturing and Advantages

What is a metal film resistor

 

A metal film resistor is a resistor widely used in electronic circuits, which is made by depositing a thin metal film on the surface of a substrate. Metal film resistors are characterized by simple structure, small size, high precision, good stability, and small temperature coefficient. Therefore, it is widely used in various electronic devices.

Structure of metal film resistors

 

The structure of metal film resistors is mainly composed of three parts: substrate, metal film and leads.

 

Structure of metal film resistor

 

The first is the substrate, which is the main material on the circuit board, generally glass fiber, epoxy resin, etc. The quality of the base material will affect the performance of the entire circuit board, and it will also affect the service life and stability of the metal film resistor.

 

The second is the metal film, which is the key component of the metal film resistor. A metal film is a thin metal layer that is deposited on the surface of a substrate, generally with a thickness ranging from a few hundred nanometers to several microns. The material of the metal film is generally nickel-chromium alloy, chromium, tungsten, etc., which have excellent electrical conductivity and corrosion resistance.

 

The last is the lead wire. The lead wire of the metal film resistor is generally processed on the metal film by copper plating or nickel plating. Its function is to introduce current from the circuit board to the metal film resistor.

 

Throughout the structure, the metal film acts as a resistor, while the substrate and leads are used to support and connect the metal film.Metal film resistors generally have cap structure, cylindrical structure, chip structure, and leadless structure, as shown in the figure.

 

 

What is the difference between metal film resistors and carbon film resistors

 

Metal film resistors and carbon film resistors are two common resistor devices, the difference between them mainly lies in the different resistor materials.

 

A metal film resistor is a structure in which a metal material (such as nickel chromium, tungsten) is deposited on an insulating substrate to form a thin film, and then a resistive device is formed by photolithography, corrosion and other processes. The resistance value of the metal film resistor is relatively stable, the temperature coefficient is small, and the precision is high, but its durability is poor, and it is easy to be affected by the environment such as moisture and pollution.

 

A carbon film resistor is a structure in which a carbon material (such as graphite) is deposited on an insulating substrate to form a thin film, and then a resistive device is formed by evaporation, corrosion and other processes. Carbon film resistors have better durability, but poor stability of resistance value, large temperature coefficient and low accuracy.

 

Therefore, for application scenarios with high precision requirements and large temperature changes, metal film resistors are generally selected; for scenarios with high durability requirements and low precision requirements, carbon film resistors are selected.

 

The difference between metal film resistors and carbon film resistors

Features	Metal Film Resistors	Carbon Film Resistors
Materials	Metal thin films (nickel-chrome, nickel-chromium alloy, etc.)	Carbon thin films (carbon, titanium oxide)
Temperature Coefficient	±50 ppm/°C (Standard Type)	±500 ppm/°C (Standard Type)
Accuracy	±0.1%	±5%
Power	1/8 W - 5 W	1/16 W - 1/2 W
Resistance Range	1 Ω - 10 MΩ	1 Ω - 10 MΩ
Voltage	100 V - 1 kV	50 V - 200 V
Long-term stability	Good	Fair
Fields of application	High-precision circuits, such as analog circuits, measurement circuits, etc.	General circuits, such as consumer electronics, home appliances, etc.

 

Distinguish between carbon film resistors and metal film resistors

 

1. Appearance distinction

The appearance of carbon film resistors is black or khaki, while the appearance of metal film resistors is white or blue, because the surface of metal film resistors is covered with metal film. Five rings (1%) for metal film and four rings (5%) for carbon film

 

2. Resistance value distinction

You can know the resistance value of the resistor through the resistor color code on the resistor. The resistance value range of carbon film resistors is generally between a few ohms and tens of megaohms, while the resistance value range of metal film resistors is Generally between a few ohms and hundreds of megohms.

 

3. Stability distinction

The stability of metal film resistors is better than that of carbon film resistors, because the surface of metal film resistors is flatter and more uniform, so its temperature coefficient and stability are better than carbon film resistors.

 

4. Long-term durability distinction

The long-term durability of metal film resistors is better than that of carbon film resistors, because the surface of metal film resistors is not easily oxidized or polluted, so its long-term service life is longer.

 

5. Use environment distinction

The high temperature resistance of metal film resistors is better than that of carbon film resistors, so metal film resistors are generally used in circuits that work in high temperature environments. In some ordinary circuits that do not require high resistance accuracy, carbon film resistors can also be used.

 

6. Internal distinction

Scratch off the protective paint with a razor blade, the exposed film color is black, it is a carbon film resistor; the film color is bright white, it is a metal film resistor.

 

 

Characteristics of metal film resistor

 

• Wide precision: 0.25[%], 0.5[%], 1[%], 5[%]
• Wide resistance range: 1Ω～10MΩ
• High stability: metal film resistors use metal film as the resistance material, and the metal film has good chemical stability and thermal stability, so metal film resistors have high stability.
• High precision: metal film resistors have high precision, and usually can meet the precision requirements of 1% or higher.
• Small temperature coefficient: The temperature coefficient of metal film resistors is usually less than 100ppm/°C, so it can maintain good accuracy in environments with large temperature changes.
• Low noise: Metal film resistors usually have low noise and are suitable for circuits that require lower noise.
• Good durability: metal film resistors have good durability and long service life.
• Small size: metal film resistors are small in size, can be made into various specifications and shapes, and are suitable for circuit design in various occasions.
• Moderate price: The price of metal film resistors is moderate, cheaper than other high-precision resistors such as metal foil resistors and precision potentiometers.

 

 

Disadvantages of metal film resistor

 

• The power of metal film resistors is small, and the maximum power is usually below 1/4 watt.
• The resistance range of metal film resistors is limited, usually between a few ohms and several million ohms.
• Metal film resistors have low withstand voltage and cannot withstand high voltage.

 

 

Application of metal film resistor

 

Metal film resistors are a common electronic component that are widely used in various circuits. Its stability, accuracy, temperature coefficient and other characteristics make it suitable for a variety of applications. Following are some applications of metal film resistors:

 

• Analog circuits: The precision and temperature coefficient of metal film resistors make them ideal for use in analog circuits, such as amplifiers and filters.
• Digital circuits: Metal film resistors are also suitable for digital circuits, such as counters and clock circuits.
• Computer and communication equipment: Metal film resistors are also widely used in computer and communication equipment, such as memory, processors and modems.
• Instrumentation and Measurement: Metal film resistors are also used in various instrumentation and measurement applications such as voltage and current measurement, sensors and controllers.