By optimizing the industrial high-power resistor manufacturing process, manufacturers can improve the resistor's performance and reliability, tolerances, voltage ratings, TCR, stability, and power ratings.
In this article, we will cover the manufacturing process of industrial power resistors. We discuss material selection and production techniques and their potential impact on performance.
A perfect resistor will have a constant resistance value and zero capacitance and inductance throughout its lifetime. Regardless of any external stress, its resistance value will remain the same. These may include overvoltage and surge events, ESD, mechanical stress, temperature changes, humidity levels, and environmental conditions.
In fact, there is no such thing as a perfect resistor. There are trade-offs to provide resistors that meet the required specifications at an acceptable cost. System designers must be aware of these trade-offs when selecting resistors. They should consider:
Power consumption. Rated voltage.
Tolerance. Load-life stability.
Self-heating is also a consideration. It depends on the applied voltage, resistive material, and resistor manufacturing process.
The first step is to deposit a resistive film pattern on a flat substrate, usually alumina. Resistance is a function of track length divided by track width multiplied by ink resistivity.
In screen printing, a metal-oxide mixture is combined with a carrier material and an adhesive is applied to the substrate. The carrier is a mixture of organic solvents and binders (glassy frit). The adhesive holds the resistive material in place after ignition.
After firing a patterned substrate at high temperatures (typically 850°C), the resistance pattern is often worn to provide the desired resistance value. Finally, the resistive element is coated to protect it from environmental influences. This determines the insulation resistance of the device and its dielectric tolerance.
During the high-temperature firing process, the carrier material burns off, the metal oxides combine to form a resistive film, and the glass frit melts to hold the resistive material in place. Manufacturers add layers of resistors in order to create the desired resistance pattern and value.
Optimizing the manufacturing process for thick-film industrial power resistors maximizes performance and reliability. However, it's worth noting that the pursuit of higher performance must be balanced with cost. A more precise manufacturing process can lead to increased production costs.
The power rating of an industrial power resistor is the maximum power that the resistor can safely dissipate (in a given environment) without exceeding its stated temperature limits.
Considering the required power handling capacity, the definition of the operating environment, cooling (if any), and the available space on the system board, resistor manufacturers can make appropriate design choices.
The power dissipation capability of a thick film resistor is affected by the choice of material. Different materials have different thermal conductivity and temperature coefficients. High thermal conductivity materials can handle more power without significant temperature increases.
The high substrate thermal conductivity improves heat transfer and increases the resistor's power handling capabilities. Larger resistors have a larger surface area for heat dissipation, allowing them to handle higher power levels. The shape of the resistor also has an impact on power consumption.
Material selection and design are critical, but so is manufacturing control. For example, the eventual wear and tear of resistive traces can cause the traces to become thinner. This can lead to "hot spots" that can cause the power resistor to fail.
In high-power applications, the resistor's power handling capability is often the primary consideration, but it is also important to consider the maximum voltage rating. Different thick-film resistive materials have different dielectric strengths. This determines the resistor's ability to withstand high voltages without breaking down electrical breakdown.
The substrate material is also a factor to consider. Substrates with high dielectric strength increase electrical insulation and resistance voltage ratings.
As with the power rating, the physical size and shape of the resistor also play an important role. Larger resistors have more space between the conductive elements, which reduces the risk of voltage breakdown.
Tolerance refers to the range in which a resistance value can deviate from its stated value. A change in the resistivity of the resistive material causes a change in the nominal value of the resistor.
Tolerances can also be affected by changes in the manufacturing process. Although manufacturers aim to control these changes, this must be balanced against the cost implications.
Over time, temperature effects, as well as electrical and mechanical stresses, can affect the performance of a resistor. They can affect the resistance value (stability), or cause a complete failure.
The particle structure of resistive films makes them susceptible to thermal, electrical, or mechanical stress. The choice of resistive material can alleviate this problem to some extent, but the trade-off between performance and cost needs to be considered.
A wide range of standard resistor devices are available. Large manufacturers tend to produce equipment suitable for a wide range of applications. They tend to ignore applications with more extreme requirements. A professional EAK thick film resistor manufacturer operates in this field. They offer industrial power resistor devices manufactured in small to medium batches.