The production of high-power resistors involves interdisciplinary fields such as materials science, precision machining, and quality control, and its core links directly determine the power carrying capacity, accuracy, and reliability of the product. The core production process of high-power resistors is systematically analyzed from three aspects: process flow, technical difficulties, and quality control
1、 Substrate preparation and surface treatment
Ceramic substrate processing
Material selection: Aluminum oxide (Al ₂ O ∝) or aluminum nitride (AlN) ceramics are the main materials, which need to meet the requirements of high thermal conductivity (AlN thermal conductivity reaches 170W/m · K) and high insulation (volume resistivity>10 ¹⁴Ω· cm).
Precision machining:
Laser cutting: Using femtosecond laser to achieve micrometer level cutting accuracy, ensuring substrate size tolerance<± 0.01mm.
Grinding and polishing: By using chemical mechanical polishing (CMP) technology, the surface roughness Ra is reduced to less than 0.1 μ m, providing a flat substrate for the deposition of resistive films.
Metal substrate processing
Material selection: such as copper molybdenum alloy (CuMo70/30), with a coefficient of thermal expansion (CTE) matching the semiconductor chip (CTE ≈ 6ppm/℃).
Surface treatment:
Electroplated nickel/gold: with a thickness of 3-5 μ m, it enhances oxidation resistance and weldability.
Laser marking: Etching product model, batch number and other information on the substrate surface to ensure traceability.
2、 Deposition and visualization of resistive film
Metal film resistance film deposition
Process selection:
Magnetron sputtering: Deposition of nickel chromium (NiCr) alloy film with a thickness control accuracy of ± 1nm.
Electron beam evaporation: suitable for high melting point materials (such as tantalum nitride) to achieve low stress film layers.
Key parameters:
Deposition rate: 0.1~1nm/s, ensuring the uniformity of the film layer.
Vacuum degree: ＜ 1 × 10 ⁻⁶ Torr, reducing impurity doping.
Thick film resistor paste printing
Slurry preparation:
Ruthenate based conductive paste, with a solid content of 60%~70% and a viscosity controlled between 100~300Pa · s.
Add glass powder (such as borosilicate) and sinter to form a dense conductive layer.
Screen printing:
Screen mesh size: 325-400 mesh, ensuring line width accuracy of ± 5 μ m.
Printing pressure: 0.2~0.4MPa, to avoid slurry penetration.
Photolithography patterning
Photoresist coating:
Rotating glue coating, with a speed of 3000-5000rpm and a film thickness of 1-3 μ m.
Exposure and development:
Using an i-line stepper lithography machine, the resolution reaches 1 μ m.
The precision of developing time control is ± 2s, avoiding over display or under display.
3、 Resistance adjustment and refinement
laser trimming
Equipment requirements:
Picosecond/femtosecond laser, pulse width<10ps, heat affected zone<1 μ m.
Resistance adjustment algorithm:
Real time measurement of resistance based on the four terminal method, and control of laser energy and scanning path through PID algorithm.
Resistance adjustment accuracy: ± 0.1%, capable of wide range adjustment from milliohms to megaohms.
Mechanical refinement
Grinding wheel: used for high-power wire wound resistors, using diamond grinding wheels with a feed rate of 0.1~0.5 μ m/s.
Chemical corrosion: For special materials such as tantalum, a mixture of hydrofluoric acid (HF) and nitric acid (HNO ∝) is used with a corrosion rate of 0.5-1 μ m/min.
4、 Packaging and reliability testing
Process
Plug in packaging:
Wave soldering: The solder temperature is 260 ± 5 ℃, and the soldering time is 3-5 seconds to ensure that the solder joint is full.
Encapsulation: epoxy resin or silicon gel with filling coefficient>90% is used to improve moisture-proof and seismic performance.
Surface mount packaging:
Reflow soldering: peak temperature of 245 ± 5 ℃, heating rate<3 ℃/s, to avoid substrate deformation.
Plasma cleaning: Remove the oxide layer and improve weldability.
Reliability testing
Electrical performance testing:
Resistance measurement: using the four terminal method, with an accuracy of ± 0.01%.
Temperature coefficient (TCR) test: Within the range of -55 ℃~150 ℃, TCR fluctuation is less than ± 10ppm/℃.
Environmental testing:
High temperature aging: Working continuously for 1000 hours at 125 ℃, the resistance change rate is less than 1%.
Temperature cycle: -55 ℃~125 ℃, no cracking or resistance drift after 1000 cycles.
Vibration test: frequency 10-2000Hz, acceleration 50g, continuous for 2 hours, normal function.
5、 Key technical difficulties and solutions
Uniformity control of film layer
Challenge: Uneven film thickness can lead to resistance deviation and local overheating.
Plan:
Adopting a closed-loop control system, real-time monitoring of film thickness and feedback adjustment of deposition parameters.
Introducing Atomic Layer Deposition (ALD) technology to achieve single atomic layer precision control.
Thermal stress management
Challenge: Under power load, mismatched thermal expansion coefficients of materials can lead to cracking.
Plan:
Design gradient material structures, such as CuMo/Cu composite substrates, to alleviate thermal stress.
Optimize the packaging structure and add heat sinks or thermal interface materials (TIM).
Long term stability improvement
Challenge: After long-term work, material aging leads to resistance drift.
Plan:
Select high stability materials (such as NiCr alloy) and optimize the doping ratio.
Introducing self-healing technology, such as adding nano silver particles, can reconstruct local conductive channels after fracture.
6、 Production equipment and production line configuration
Key equipment:
Femtosecond laser (impedance modulation), magnetron sputtering coating machine, screen printing machine, four terminal tester, temperature shock test chamber.
Production line layout:
Cleanroom level: The film deposition and lithography area must reach Class 1000 (0.5 μ m particles<35 particles/ft ³).
Automation level: The automation rate of surface mount resistor production lines is over 90%, while plug-in production lines rely on manual assembly and testing.
The core production process of high-power resistors includes substrate preparation, film deposition, patterning, resistance tuning, packaging, and testing, each of which requires precise control to ensure product performance. The technical difficulties focus on membrane uniformity, thermal stress management, and long-term stability, which need to be solved through advanced equipment, material innovation, and process optimization. With the rapid development of 5G, electric vehicles, aerospace and other fields, the production technology of high-power resistors is evolving towards higher precision, stronger reliability, and more intelligence.