The Tech Blog

Continuing on the types of resistors and where each one shines, let’s look at a few more variations of resistors.

Metal Film Resistor: They are similar to carbon film resistors except a metal film is deposited instead of carbon on a ceramic core. The usual material is nickel chromium. Similar to carbon film they have great precision. Where it shines is in the thermal stability over wide temperature ranges.

Thick Film Resistor: Created by applying a thick paste of conductive material onto a ceramic substrate using the same techniques we use in making T-shirt prints via screen printing. These are the most common resistors you find in SMD resistors and are dirt cheap. The coating thickness would be around 100um(Hence “Thick” film). The only drawback is that you might not get very low resistance values.

Thin Film Resistor: Similar to thick film resistors but use a thinner layer(0.1um) of conductive material. They provide higher precision and lower resistance ranges in manufacturing. The thin layer formed on the ceramic core is created by using vapour deposition. Laser trimming is done to adjust the values post-deposition.

Metal Oxide Resistor: Made by coating a ceramic rod with a layer of metal oxide (typically tin oxide), these resistors are highly durable and can handle high temperatures. Useful in industrial and high-power applications.

Metal Foil Resistor: They are the most precise and stable types of resistors available in the electronics industry. The core element of a metal foil resistor is an extremely thin layer of resistive metal alloy. Metal foil is etched into a specific resistive pattern using photolithography and then laser trimmed to get precision. They are known to get tolerances of ±0.001% range. They have a fast thermal response to changes in temperature and is known for minimal drift in value even after years of use. But they are expensive.

These are the resistor types I found. As a designer, relying on datasheets is often enough to select the resistor, but understanding resistor evolution helps you see why & where each type excels.

Today let’s continue diving into resistors by exploring the different types based on their construction materials. The material used is important to understand its use cases where you might use one over the other.

Carbon/Ceramic Composition Resistor: These are among the oldest resistor types, made by combining carbon powder and a binding material as a cylindrical core. On top, you have a non-insulating cover for protection. Since the entire body core can conduct electricity, they withstand high-energy pulses. So suitable for surge protection and RF circuits. Since it’s a mixture core, tolerance is not great and can’t be tuned that easily.

Wirewound Resistor: As the name suggests, they are made by tightly winding a resistive metal wire, typically nichrome, around a non-conductive ceramic core. The core provides excellent thermal stability, allowing these resistors to handle high power levels and dissipate heat efficiently. The resistance value depends on the resistivity of the wire and thickness so you can get good precision with it. The drawback is their inherent inductance(basically it’s a coiled wire). So for high freq signals, this resistor is not used widely.. There are variations of this resistor with reduced inductance via certain counter-winding techniques to cancel out the inductance. Overall, it is good for high-power DC applications.

Carbon Film Resistor: These are made by depositing a thin layer(film) of carbon on a ceramic substrate. To adjust the resistance value precisely, a helical or spiral groove is cut into the carbon film using lasers. This process effectively increases the length of the resistive path and allows for fine-tuning of the resistance. They provide better stability, precision and lower noise compared to carbon composition resistors. These are some of the common types seen in the through-hole resistor segment.

There are a few more in the list which we need to go over. Because of the word limit, I will explain them in the next post.