The reasons why alloy resistors are difficult to achieve high resistance values (such as 1 Ω or more) can be summarized into the following five points, involving the comprehensive effects of material characteristics, process limitations, and market demand:
The natural limitation of material resistivity
The resistivity of commonly used materials for alloy resistors, such as nickel chromium alloys, manganese copper, and constantan, is usually in the range of 10 ⁻⁶~10 ⁻Ω· m, significantly lower than that of thick film resistors (10 ⁻⁴~10 ⁻Ω· m) or carbon film materials. For example:
Nickel chromium alloy resistivity: approximately 1.1 × 10 Ω· m
Manganese copper resistivity: about 4.3 × 10 Ω· m
Physical constraint formula:
Resistance value \ (R=\ rho \ cdot \ frac {L} {A} \)
(\ (\ rho \) is the resistivity\ (L \) is the length of the conductor\ (A \) is the cross-sectional area)
To achieve high resistance, it is necessary to significantly increase (L) or decrease (A), but it is limited by the following process bottlenecks.
Contradiction between process accuracy and reliability
Difficulty in cross-sectional area control: Alloy resistors often form conductive paths through etching or stamping. If a resistance value of over 1 Ω needs to be achieved, the width of the conductor needs to be compressed to the micrometer level (e.g. width<50 μ m in surface mount resistors), but a conductor that is too thin can easily lead to:
Decrease in processing yield (increase in defect rates such as wire breakage and burrs)
Insufficient mechanical strength (susceptible to thermal stress or mechanical vibration damage)
Length limitation: Increasing the conductor length requires more complex zigzag design, but the packaging size of surface mount resistors (such as 0603/0805) is difficult to accommodate excessively long paths.
Risk of deterioration in temperature stability
The core advantage of alloy resistors is low-temperature drift (TCR<50ppm/℃), but high resistance design may disrupt this characteristic:
Higher requirements for material uniformity: finer alloy proportion control is needed to increase resistance, and local compositional deviations can lead to TCR nonlinearity.
Decreased heat dissipation efficiency: The cross-sectional area of high resistance conductors is smaller, and the power density per unit volume increases. Local temperature rise may exacerbate resistance drift.
Mismatch between application scenarios and market positioning
Power carrying requirements: Alloy resistors are mainly used in high current and high power scenarios (such as current detection and power diversion), with a typical resistance range of 0.001 Ω~0.1 Ω. High resistance applications such as signal conditioning and high impedance voltage division typically require thick/thin film resistors with lower power consumption and smaller volume.
Cost economy: The precision machining cost of alloy resistors is high, while thick film technology is more cost-effective in the high resistance field (such as 1 Ω thick film resistors, which can cost less than 1/10 of alloy resistors).
Mature competition of alternative solutions
In response to the high resistance demand, there are already better technological routes available:
Thick film resistor: By adjusting the composition of the paste (such as containing ruthenium oxide), it is easy to achieve resistance values ranging from Ω to M Ω.
Thin film resistor: Using vacuum sputtering technology, it can accurately control the thickness of nanoscale thin films, balancing high resistance and low temperature drift.
Wire wound resistance: Although it can achieve high resistance, its volume and frequency characteristics are poor, limited to specific industrial scenarios.
The limitations of alloy resistors in the high resistance field are essentially the result of a comprehensive balance between material properties and process costs. Its core value lies in the precision and power density advantages in the low resistance range, while the high resistance demand has been more efficiently covered by other technologies. If breakthroughs are needed in the future, it may rely on innovations in new high resistivity alloys (such as amorphous metals) or micro nano processing technologies, but the market driving force is insufficient in the short term.