Thick Film LowOhmic Resistors are resistance devices manufactured based on thick film technology, typically ranging from milliohms (m Ω) to several ohms (Ω), designed for current detection, power distribution, and high reliability scenarios. By optimizing material formulations and processes, thick film low resistance resistors have demonstrated advantages in low cost, high power density, and resistance to environmental interference, and are widely used in fields such as automotive electronics, industrial power supplies, and consumer electronics. The following is a detailed analysis of its technical principles, core features, and applications:
1、 Basic Definition and Manufacturing Process
Core structure
Resistance layer: made by mixing conductive paste (such as silver, palladium silver alloy or carbide) with glass adhesive, and coated on the surface of ceramic substrate (such as Al ₂ O3) through screen printing technology, with a thickness of about 10-50 μ m.
Electrode: The end is coated with silver or copper to reduce contact resistance and enhance welding reliability.
Protective layer: Glass glaze or epoxy resin coating, moisture-proof, anti sulfurization and mechanical protection.
Manufacturing process
Substrate preparation: Clean high-purity alumina ceramic substrates.
Printing resistor paste: forming a specific shape of resistor pattern through screen printing.
High temperature sintering: Sintering at 800 ℃~1000 ℃ to bond the slurry with the substrate and form a stable resistor.
Laser resistance adjustment: Fine tune the resistance pattern to achieve the target resistance accuracy (± 1%~± 5%).
Packaging and Marking: Apply a protective layer and print parameter labels (such as resistance and tolerance).
2、 Core Features and Technical Parameters
Low resistance and precision
Resistance range: Typical value of 1m Ω~1 Ω, low resistance can be achieved by adjusting the composition of the paste and the printing area.
Accuracy: ± 1%~± 5%, high-precision models can reach ± 0.5% (such as the Wangquan CR series).
Power carrying capacity
Power density: Surface mount packaging (such as 2512) supports 1W~3W, and direct insertion (such as TO220) can reach 5W~10W.
Heat dissipation design: The ceramic substrate has good thermal conductivity, and the wide electrode design enhances heat dissipation efficiency.
Temperature stability
Temperature coefficient (TCR): ± 100ppm/℃~± 300ppm/℃, better than carbon film resistance but lower than alloy resistance.
Working temperature range: 55 ℃~+155 ℃, meeting the requirements of industrial grade and some vehicle specifications.
Environmental adaptability
Sulfurization and moisture resistance: Glass glaze coating can resist sulfur-containing gas corrosion (such as the Wangquan RL series).
Mechanical strength: Suitable for in vehicle environments through vibration and impact testing (such as IEC 60068 standard).
3、 Thick film low resistance resistor vs. other low resistance resistors
|Features | Thick film low resistance resistor | Surface mount alloy resistor | Metal foil resistor | Wire wound resistor|
|Resistance range | 1m Ω~1 Ω | 1m Ω~100m Ω | 1m Ω~10 Ω | 0.1 Ω~10 Ω|
|Accuracy | ± 1%~± 5% | ± 0.1%~± 1% | ± 0.001%~± 0.1% | ± 0.5%~± 5%|
| TCR | ±100ppm/℃~±300ppm/℃ | ±15ppm/℃~±50ppm/℃ | ±0.2ppm/℃~±5ppm/℃ | ±20ppm/℃~±100ppm/℃ |
|Power density | Medium (1W~10W) | Medium (1W~5W) | High (1W~50W) | High (10W~100W+)|
|Cost | Low | Medium | High | Medium High|
|Typical Applications | Power Modules, LED Drivers, Automotive Electronics | Current Detection, BMS | Precision Measurement, Medical Equipment | High Power Braking, Industrial Heating|
4、 Typical application scenarios
Automotive Electronics
LED car light drive: current detection resistor to ensure constant current output (such as Wangquan CR series).
Body Control Module (BCM): Load current monitoring to prevent circuit overload.
Industrial power and energy systems
Switching mode power supply (SMPS): Output current sampling to achieve overcurrent protection (such as flyback topology).
Photovoltaic inverter: DC side current detection to optimize MPPT efficiency.
Consumer Electronics
Fast charging adapter: current detection in USB PD protocol, triggering protection mechanism.
Home appliance motor control: Current feedback for washing machines and air conditioning compressors.
LED lighting
Constant current driving circuit: Series resistors are used to achieve current balance in LED arrays (such as street lamp driving).
5、 Technical advantages and limitations
Advantages
Low cost: Mature thick film technology, suitable for mass production, and priced lower than alloy or metal foil resistors.
High power density: wide electrode design+ceramic substrate, supporting high current (such as 2512 package carrying 3A continuous current).
Anti environmental interference: Glass glaze coating provides moisture and sulfur protection, suitable for harsh environments.
Limitations
Accuracy and temperature drift: Accuracy and TCR are lower than the resistance of alloy/metal foil, and are not suitable for ultra precision measurement.
High frequency performance: Parasitic inductance is relatively high (about a few nH), and high-frequency switching circuits (such as>1MHz applications) should be avoided.
6、 Selection and Design Points
Matching resistance and power
Formula calculation: Select the resistance value (R=V_drop/Imax) based on the maximum current (I2 max), and ensure that the power P=I ² R ≤ 50% of the rated power (derating design).
Example: When detecting 5A current, a 10m Ω resistor with a voltage drop of 0.05V and a power consumption of 0.25W should be selected, and a model with a rated power of ≥ 0.5W should be chosen.
Packaging and heat dissipation optimization
SMT packaging: 1206/2512 is suitable for compact spaces and requires PCB copper plating for heat dissipation.
Direct insertion package: TO220 with heat sink, suitable for high-power scenarios.
Environmental adaptability design
Wet/sulfur-containing environment: Choose sulfur resistant models (such as Wangquan RL series) or add a three proof paint coating.
High temperature scenario: Priority should be given to models with TCR<± 200ppm/℃, and heat dissipation should be strengthened.
7、 Representative brands and series
RALEC CR Series
Features: Resistance of 1m Ω~1 Ω, accuracy of ± 1%, power of 1W~3W (2512 package), anti humidity design.
Application: Automotive LED driver, industrial power supply current detection.
Yageo TCR Series
Features: Thick film anti sulfurization resistor, TCR ± 200ppm/℃, power 0.5W~2W, suitable for industrial control.
KOA RK73H series
Features: Wide electrode design, power of 1W (2512 package), resistance as low as 5m Ω, used for power modules.
8、 Common Problems and Solutions
Temperature rise causes resistance drift
Solution: Choose models with lower TCR or increase the area of heat dissipation copper foil (such as PCB copper coverage ≥ 80%).
Resistance deviation after welding
Solution: Control the reflow soldering temperature curve (peak<260 ℃) to avoid cracking of the resistance layer caused by high temperature.
High frequency noise interference
Solution: Parallel low ESR capacitors (such as 1 μ F ceramic capacitors) are used to filter out high-frequency ripples.
Thick film low resistance resistors have the core advantages of low cost, high power, and resistance to environmental interference, making them an economical choice for low to medium precision current detection scenarios. Although inferior to alloy or metal foil resistors in terms of temperature drift and high-frequency performance, its wide application in automotive electronics, industrial power supplies, and consumer electronics demonstrates its ability to balance cost-effectiveness and reliability. When selecting, special attention should be paid to resistance accuracy, power margin, and environmental adaptability, combined with heat dissipation design and signal chain optimization to fully unleash its performance potential.