Analysis of the core process of surface mount resistors

Analysis of the core process of surface mount resistors
As the core component of electronic circuits, the performance and reliability of SMD resistors directly depend on material selection, manufacturing processes, and quality control. The core process system is analyzed in depth from three dimensions: material technology, precision machining, and surface treatment
1、 Materials Science and Formula Technology
Substrate material
Aluminum oxide ceramics (Al ₂ O3): mainstream substrate, accounting for over 90%, with high insulation (>10 ¹⁴Ω· cm), high thermal conductivity (24W/m · K), and excellent mechanical strength.
Aluminum nitride (AlN): a high-end application material with a thermal conductivity of 170W/m · K, suitable for high-power scenarios.
Fiberglass reinforced resin (FR-4): a low-cost solution for low precision consumer electronics.
Resistive film material
Metal film: mainly composed of nickel chromium (NiCr) alloy, formed into nanoscale thin films through vacuum sputtering, with an accuracy of ± 0.01%.
Carbon film: Thermal decomposition and deposition of hydrocarbons, with low cost but average stability.
Metal oxides, such as ruthenium oxide (RuO ₂), possess both high-frequency characteristics and pulse resistance.
Thick film paste: Ruthenate based conductive paste, sintered after screen printing, suitable for large-scale production.
Electrode material
Terminal electrode: silver palladium (Ag/Pd) alloy, optimized in proportion (such as 70/30) to balance conductivity and weldability.
Back electrode: Nickel chromium (NiCr) layer to prevent substrate from reacting with solder.
2、 Precision manufacturing process flow
Substrate preparation
Casting molding: Mix ceramic powder and organic binder and cast them into thin sheets, with a thickness control accuracy of ± 1 μ m.
Punching positioning: Laser or mechanical punching forms the resistor area, with an aperture accuracy of ± 2 μ m.
Deposition of resistive film
Vacuum sputtering (metal film): In a vacuum chamber, an ion beam bombards the target material to deposit metal atoms on the substrate, with a film thickness controlled at ± 0.1nm.
Screen printing (thick film): using 325 mesh stainless steel screen, printing accuracy ± 5 μ m, and slurry viscosity controlled between 800-1200cP.
Laser resistance adjustment: By adjusting the thickness of the film layer through laser ablation, the accuracy can reach ± 0.01%, achieving the target resistance value.
Electrode forming
Electroplating process: sequentially plating nickel (Ni, thickness 1-3 μ m) and tin (Sn, thickness 0.5-1 μ m) to improve solderability and corrosion resistance.
End sintering: Sintering is carried out in a nitrogen atmosphere at 850 ℃ to ensure that the bonding force between the electrode and the substrate is greater than 5N.
Cutting and Sorting
Laser cutting: Using picosecond laser, the cutting width is less than 30 μ m, and the edge chipping is ≤ 5 μ m.
Visual inspection: High speed cameras (>1000 frames per second) capture appearance defects, combined with AI algorithms to achieve a 99.98% detection rate.
3、 Key technological breakthroughs
Ultra precision resistance control
Four terminal method: Add detection electrodes at both ends of the resistor to eliminate the influence of lead resistance and achieve ± 0.01% accuracy.
Dynamic compensation: By monitoring temperature and humidity in real-time, adjusting laser resistance parameters, and improving batch consistency.
High frequency characteristic optimization
Low inductance design: Adopting a "U" - shaped electrode structure, the inductance value is reduced to below 0.1nH.
Dielectric matching: Inserting a low dielectric constant layer (such as SiO ₂) between the resistive film and the substrate to reduce parasitic capacitance.
Reliability enhancement
Anti sulfurization technology: The end electrode is gold-plated (Au) or lead-free solder is used to prevent the penetration of sulfur elements.
Thermal shock test: Simulate 1000 cycles from -55 ℃ to+150 ℃, with a resistance change rate controlled within ± 0.1%.
4、 Comparison of Industry Process Routes
Process type, accuracy range, temperature coefficient, typical application scenarios
Thin film sputtering ± 0.01%~± 0.1% ± 1~± 25ppm/℃ for aerospace and medical equipment
Thick film printing ± 1%~± 5% ± 100~± 500ppm/℃ for consumer electronics and power modules
Metal oxides ± 0.1%~± 1% ± 15~± 50ppm/℃ RF circuits, automotive electronics
5、 Future technological trends
Nano scale manufacturing: Atomic layer deposition (ALD) technology achieves single atomic layer precision, driving the evolution of resistance size towards 01005 (0.4 × 0.2mm).
Material innovation: Graphene based composite materials combine high conductivity and flexibility, suitable for wearable devices.
Intelligent resistance adjustment: Integrated MEMS sensors, real-time monitoring and compensation of resistance drift, improving system stability.
Through continuous optimization of the core processes mentioned above, surface mount resistors are developing towards higher precision, smaller size, and stronger environmental adaptability, providing key support for cutting-edge fields such as 5G communication, new energy vehicles, and the Internet of Things.