Basic Introduction to Metal Film Resistor

Catalog

Ⅰ Basic introduction

Metal film resistors are a kind of film resistors. Metal film resistors are resistors in which special metals or alloys are used as resistor materials, and the resistor film layer is basically formed on ceramic or glass by vacuum evaporation or sputtering. Because it is a lead type resistor, it is convenient for manual installation and maintenance and is used in most household appliances, communications, and instruments. Metal film resistors are widely used resistors so far, with high precision, stable performance, simple and lightweight structure. It plays an important role in the electronics industry and military aerospace under high-precision requirements.

Ⅱ Thin film resistor

There are mainly four types of thin film resistors

1.Carbon film resistor

Metal film resistors are made by depositing crystalline carbon on the ceramic rod skeleton. Carbon film resistors are low in cost. It has stable performance, a wide resistance range, and low-temperature coefficient and voltage coefficient. It is currently the most widely used resistor.

2.Metal film resistor 

Metal film resistor

Metal film resistors are the main type introduced today. The alloy material is evaporated on the surface of the ceramic rod skeleton by vacuum evaporation. Metal film resistors have higher accuracy, better stability, noise and temperature coefficient calibration than carbon film resistors, and are widely used in instrumentation and communication equipment.

3.Metal oxide film resistor

The feature of a metal oxide film resistor is that a layer of metal oxide is deposited on the insulating rod. Since it is an oxide itself, it is stable at high temperatures, heat shock resistant, and has a strong load capacity.

4.Synthetic film resistor

Synthetic film resistors are made by coating a conductive composite suspension on a substrate, so it is also called paint film resistance. Because its conductive layer presents a granular structure, it has high noise and low accuracy. It is mainly used to make high voltage, high resistance, and small resistors.

Ⅲ Structure of metal film resistor

The production of metal film resistors is to deposit a nickel-chromium alloy on a round base rod to obtain excellent performance. The usual tolerance is ±1%, and tolerances of ±0.1%, ±0.2z5%, and ±0.5% can also be obtained. The temperature coefficient can be as low as ±15ppm/℃. After cycling and aging, the change will not exceed 0.25%. The typical structure is shown in the figure.

Structure of metal film resistor

Metal film resistors are resistors in which special metals or alloys are used as resistance materials, and the resistance film layer is basically formed on ceramic or glass by vacuum evaporation or sputtering. This type of resistor is generally made by a vacuum evaporation process, that is, heating the alloy in a vacuum, the alloy is evaporated, and a conductive metal film is formed on the surface of the porcelain rod. Grooving and changing the thickness of the metal film can control the resistance. Its heat resistance, noise potential, temperature coefficient, voltage coefficient, and other electrical properties are better than carbon film resistors. The manufacturing process of metal film resistors is relatively flexible. Not only can its material composition and film thickness be adjusted, but also the resistance value can be adjusted through grooves, so that a resistor with good performance and a wide resistance range can be made.

Metal film resistors generally have cap structure, cylindrical structure, chip structure, and leadless structure, as shown in the figure

Ⅳ Features of metal film resistor

①Good heat resistance, rated working temperature is 70℃, maximum working temperature can reach 155℃.

②Good voltage stability and small temperature coefficient.

③Wide working frequency range, low noise electromotive force, can be used in high-frequency circuits.

④Under the same power condition, it is much smaller than the carbon film resistor, about half of the carbon film resistor.

⑤It can adjust the precision resistance value by cutting butterfly and pattern method, and the accuracy can reach ±0.5%, ±0.05%.

⑤The resistance range is very wide, and can be made into 1Ω -1000MΩ resistors.

⑦The rated power is 0.125W, 0.25W, 0.5W, lW, 2W, lOW and 25W, etc.

③The pulse load stability is poor, not as good as carbon film resistors.

⑨The application is very wide, suitable for AC, DC, and pulse circuits.

Ⅴ The difference between carbon film resistors and metal film resistors

For carbon film resistors, it uses carbon to be deposited on a magnetic rod or ceramic tube, and at the same time, a layer of the crystalline carbon film is formed on the surface. The thickness of the carbon film and the method of notching the carbon film are used to change the degree of the carbon film resistor and finally, get the required resistance value. The surface is coated with epoxy resin to strengthen the seal. The appearance color is basically khaki, of course, there are other colors, such as pink.

The color band is four bands, the resistance range is 1Ω~10MΩ, the rated power is 0.125W, 0.25W, 0.5W, 1W, etc., the accuracy range: ±10%, ±5%, ±2%. This kind of resistor is universal larger, often used in cheap products, such as power supplies, chargers. It is not recommended for starting resistance, because the impact resistance is relatively defective.

For metal film resistor, it uses vacuum evaporation or burning infiltration to form a metal film on the ceramic tube frame. This film is attached to the surface of the white ceramic. The resistor is cut and adjusted to obtain a more precise resistance. This kind of resistor has high precision, small size, good stability, and high cost. It is usually used in wireless electronic equipment, especially on occasions with higher precision requirements. 

Ⅵ Distinguish between carbon film resistors and metal film resistors

1. According to the temperature coefficient of resistor

We can distinguish the two types of resistors by carbon film resistors with negative temperature coefficient characteristics, and metal film resistors with small positive temperature coefficients, which can distinguish these two resistors well.

2. According to resistance accuracy

The manufacturing process of each type of resistor is different, and the accuracy of the resistor is also different. We know that carbon film resistors are very common resistors, and their accuracy is generally not high. The production requirements of metal film resistors are higher and the resistance accuracy is higher than that of carbon film resistors. It is also an identification method to judge the resistance accuracy.

4. According to resistor color

Common carbon film resistors have low precision and low production costs, so their appearance is mostly khaki or pink, while the appearance of metal film resistors is mostly blue. We can clearly distinguish the two resistors through color.

5. According to resistance painting

Carbon film resistors have a layer of black protective paint on the surface. We can distinguish by looking at the color of the protective paint. Metal film resistors usually use a bright white protective film. Through the protective painting of these two resistors, we can also distinguish the two well.

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