Thick film resistors combine cost-effective manufacturing with superior performance characteristics in high-voltage and high-power applications. In this article, we discuss the main technical advantages of thick film resistor technology that make it a practical choice for demanding circuit applications. These include:
Cost-Effectiveness
Thick film resistor technology is widely regarded as the most cost-effective solution for high-voltage and high-power applications.
The thick film manufacturing process is less complex than other resistor technologies and utilises relatively low-cost materials. It is well suited to high-volume manufacturing, which helps drive down component costs.
Compact Size – High Power Handling
Thick film resistors deliver high power density. Hence, for a given power rating, they are significantly smaller than wirewound equivalents. The planar structure of thick film resistors provides a large surface area relative to their volume.
Thick film resistor materials have excellent heat dissipation properties. The resistive element is typically screen-printed onto substrates such as alumina, aluminium nitride, or beryllium oxide, which possess high thermal conductivity.
High Resistance Values
The resistive element of a thick film resistor consists of metal oxides and glass frits. When fired, this mixture creates a granular structure with inherently high resistivity.
The screen-printing process facilitates the creation of various serpentine or meander patterns. These extend the current path within a compact area, delivering high resistance values.
Low Inductance
All conductors exhibit self-inductance when carrying time-varying currents. The inductance value depends on factors including the conductor material and geometry, the configuration of the circuit, and the operating frequency.
The flat cross-section of a thick film resistor track minimises inductance compared to resistor wire.
High Voltage Capability
Thick film resistors are manufactured by screen-printing a conductive layer onto an insulating (typically alumina) substrate. These substrates possess excellent insulating properties and high dielectric strength and can withstand high voltages without breakdown.
If the resistive element is arranged in a serpentine or meandering pattern, it increases the effective length of the resistive path. This reduces the electric field intensity for a given applied voltage and improves the resistors voltage-handling capacity.
Thick film resistors can deliver high resistance values. This limits current flow for a given voltage, reducing power dissipation and the risk of thermal damage. These characteristics make them particularly suitable for high-voltage applications.
Robustness
The thick film resistor manufacturing process (firing a screen-printed conductive paste on an insulating substrate) produces an integrated device with high resistance to vibration and shock. A protective coating shields the device from moisture and environmental factors.
Thick film resistor substrates (usually alumina, Al₂O₃) exhibit excellent thermal conductivity and stability. They offer low thermal expansion coefficients and maintain performance under thermal stress.
Heat Dissipation
The materials and manufacturing process combine to provide excellent heat dissipation properties. Thick film resistor substrates tend to have high thermal conductivity and remain stable under thermal stress.
The resistor’s conductive paste forms a stable, thermally conductive thick film. Tight bonding between the film and substrate minimises thermal resistance, facilitating rapid heat transfer.
The flat surface of thick film resistor substrates enables direct bonding to thermally conductive substrates, heatsinks, or circuit boards, enhancing their heat dissipation capabilities.
Moisture Resistance
Although thick film resistors are not inherently moisture-resistant, they can be protected by conformal coatings, encapsulation, or hermetic sealing to ensure reliable long-term operation.
Customisation
Compared to alternative resistor technologies, thick film resistor technology is highly customisable. Design or resistance value modifications can be implemented quickly and economically. Adjusting patterns or resistances usually doesn’t require expensive tooling, making thick film resistors cost-effective to customise in small to medium volumes.
The screen-printing manufacturing process allows engineers to adjust resistor patterns, shapes, and sizes (and hence resistance values) by modifying screens or printing masks.
Altering the composition of metal-oxide paste mixtures and firing conditions allows manufacturers to achieve a broad spectrum of resistance values. The thick film printing process makes it possible to create custom resistor shapes and sizes, optimising component layouts for specific applications.
Resistor Technology Comparison
Different resistor technologies offer distinct advantages for specific applications. Comparisons between thick film and thin film resistors, thick film vs wirewound, thick film vs ceramic, and thick film vs metal foil resistors can be found elsewhere on this blog.
The technical advantages of thick film resistors mean they are used in a diverse range of applications. Their manufacturing scalability and customisation capabilities make them particularly valuable for projects requiring performance at the lowest viable cost.