In this post, we compare the performance of ceramic vs thick film resistors in power applications. We cover the construction of each type of resistor before comparing their electrical performance characteristics.
Resistor construction comparison
Although ceramic resistors are one of the oldest resistor technologies, they do still have some advantages. They are based on a mix of carbon granules, alumina and ceramic clays. The ratio of carbon granules to ceramic determines the resistance.
The mix of materials is first pressed into a cylindrical shape then fired in a kiln. The electrical connection is via wires attached to each end of the cylinder. The assembly is then coated with a protective film. The wire leads construction is not compatible with surface mount applications.
Ceramic resistors are also known as carbon resistors as carbon is the conductive element. However, they should not be confused with carbon film resistors. These devices use a different manufacturing process. As a result, they also have a different set of electrical and mechanical characteristics.
The thick film resistor manufacturing process is discussed in detail elsewhere on this blog. Unlike a ceramic resistor, a thick film resistor has two main parts, a substrate and a resistive film. These two elements bond together during the manufacturing process. The substrate material is usually ceramic, but other substrate materials are available.
Comparing the performance of ceramic and thick film resistors
Ceramic resistor devices do not use a wire or track as the resistive element. The conductive path is between carbon granules in a bulk ceramic material. Hence they have low inductance and excellent overload and pulse energy characteristics.
As the base materials are low cost and the manufacturing process relatively simple, ceramic resistor devices are low cost. However, they do have performance limitations when compared to thick film resistor devices.
Comparing the key resistor parameters:
- Resistor tolerance is 5% at best for ceramic resistors compared to 0.5% for thick film resistors.
- Resistance values of up to 1MOhm are available for ceramic devices. Thick film resistance values can exceed 100MOhm.
- The power rating of ceramic resistor devices is between 1W and 1KW compared to in excess of 2KW for thick film.
Unlike thick film, ceramic resistors do not perform well in high-temperature applications and are generally not suitable for heatsinking applications. The power watt density (amount of heat dissipated per unit area) of a thick film power resistor is far superior to ceramic.
Ceramic resistors temperature coefficient of resistance (TCR) is poor and generally exceeds 300ppm. This compares to 50ppm and below for thick film.
In summary, therefore, thick film resistors have superior performance to ceramic in most applications. Their power handling capabilities, resistance to external stresses, good TCR, small size and surface mount capability often makes them the first choice.
Ceramic resistors are reserved for a more limited range of applications. These may include applications where cost rather than performance is the main concern. Or applications where surge survivability is a key issue.