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7/23/2019 Resistor Materials Resistor Guide

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Resistor materialsResistor materials

Carbon composition resistor

Carbon film resistor

Foil resistorMetal film resistor

Metal oxide film resistor

Thin and thick film

Wirewound resistor

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Resistors are produced with a wide variety of materials and manufacturing processes. Each resistor material has its

typical properties and specific areas of use. The main types that are used in electrical engineering are summed below.

Wirewound (WW)

These types are made by winding resistance wire in a spiral around a non-conductive core.

The resistance wire is usually a nickel-chromium alloy and the core is often ceramic or

fiberglass. A coating such as vitreous enamel is used for protection. The spiral winding has

capacitive and inductive effects that makes it not suitable for applications higher than 50

kHz. Often other winding techniques are used to reduce the undesired high frequency

effects.Wirewound resistorsare essentially produced for high precision or for high power

applications. They have low noise, are robust, and are temperature stable. Resistance

values are available from 0.1 up to 100 kW, with accuracies between 0.001 and 20%.

Carbon Composition (CCR)

The resistive element is made from a mixture of fine carbon particles and a

non-conductive ceramic material. The substance is pressed in a cylindrical shape and

baked. The resistance value depends on the dimensions of the body and the ratio between

carbon and ceramic material. More carbon means a lower resistance. Carbon composition

resistorsare remarkably reliable, but have a poor accuracy with a maximum tolerance

around 5%. Until the 1960s they were the standard for general applications. They quickly

lost market share as other resistor types came on the market with better properties for

tolerance, voltage coefficient, temperature coefficient, stability and finally cost.However, their ability to withstand high energy pulses and their high reliability makes

them still useful for certain applications. Examples are power supplies and welding controls.

Carbon Film

A thin, purecarbon filmis deposited on an insulating cylindrical core. A spiral cut is made

in the film to increase the resistive path. This increases the resistance value and is also a

way to control the resistance value more precise. Values from 1 up to 10 M are

available. The accuracy is a significant improvement compared to carbon composition,

but metal and metal oxide film have overall better properties and gained therefore more

popularity. In applications that require high pulse stability, special carbon film resistors

are used.

Metal Film

Metal film resistorsare usually made of Nichrome, but also other materials such as

tantalum nitride is used. The resistive film is printed on a cylindrical or flat insulating

substrate. The resistive material is a combination of a Ceramic material and a Metal, and

therefore these resistors are also referred to as Cermet. Just as with carbon film, the

resistance value is adjusted by cutting a spiral pattern in the film. This can be done with

an abrasive or a laser. The stability, temperature coefficient and tolerance are better than

for carbon film. Typical tolerances are between 0.5% and 2% with a temperature

coefficient between 50 and 100 ppm/K. Stability is lower than for wirewound, but the high frequency properties are

better.

Metal Oxide Film

They are similar to metal film with the difference that the resistive material is a metaloxide, such as tin oxide. These durable resistors feature a better reliability and stability

than metal film resistors. Furthermore the operating temperature is higher. Therefore

they are more used in applications requiring a high endurance.

Foil

Thefoil resistor was invented in the 1960s and is still the

most accurate and stable type today. The resistive element

is a thin bulk metal foil that is cemented on a ceramic

substrate. The foil thickness is several micrometers.

Inherent to the mechanical design, they feature a very low

temperature coefficient of resistance. They are used for

applications with high precision requirements.


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2015 Resistor Guide sitemap about contact

1

Key Performance Indicators

The key performance indicators for each resistor material are summarized in the table below.

CharacteristicCarbon

Composition

Carbon

film

Thick Metal

Film

Metal

Film

Precision Metal

Film

Temp. range -40 +105 .55 +155 -55 +130 -55 +125 -55 +155

Max. temp. coeff. 1200 250-1000 100 100 15

Vmax 350-500 350-500 250 200-350 200

Noise (V per volt of applied DC) 4 (100K) 4 (100K) 0.1 0.5 0.1

R Insul. 10000 10000 10000 10000 10000

Solder (change % in resistance

value)2% 0.5% 0.15% 0.2% 0.02%

Damp heat (change % in

resistance value)15% 3.5% 1% 0.5% 0.5%

Shelf life (change & in resistance

value)5% 2% 0.1% 0.1% 0.002%

Full Rating (2000h at 70degC) 10% 4% 1% 1% 0.03%

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resistor materials » resistor guide

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