What’s the difference between Thin Film Resistors and Thick Film?
When looking at these two types of resistors side by side, they may appear to be similar. The main differences of these two products are the construction, thickness, and application usage of the resistive element itself (hence the descriptions of “thick” and “thin” film resistors). Thick film resistive elements are typically 10 ~ 50 uM in thickness, while thin films are 10 to 200 nM in thickness. Thick films are applied using a very simple screening process while thin films use a much more sophisticated vacuum process technique that applies the element on a molecular level. Let’s take a look this in detail.
The base material of a thick film resistor element is a Ruthenium Oxide (RuO₂) paste that is screened onto a ceramic substrate. After this process, the thick film resistors are then fired causing these layers to become glass-like which helps protect the resistive film and makes them less susceptible to failures due to the infiltration of moisture and other contaminants. Thick film resistor processes can be referred to as an additive process; this means that it consists of layers (resistive element, protective coating, and electroplated terminations) added to the substrate. The thin film resistor element consists of a combination of nickel and chromium (also known as Nichrome) that is applied to a ceramic substrate using a high-voltage, vacuum sputtering process. A serpentine pattern is then etched into the Ni/Cr element using a photolithographic process. An epoxy layer is screened onto the element to protect it from moisture and other contaminants. This thin film process can be referred to as a subtractive process, meaning unwanted material being etched away in the photo etching process.
Both thick film and thin film resistors are laser trimmed to their final resistance value. But in general, thin films overall thickness is literally thinner because of the subtractive process. Keep in mind that thick and thin film resistors are also application specific. That is, the application and circuit design will determine what type of resistor is utilized. Thick film resistors are ideal for low cost, economical applications and are also better suited for higher power and high ohmic value requirements. Thin film resistors, on the other hand, offer tighter tolerances for precision applications.