How to choose the material of self-locking tuning screw suitable for 5G filter?
Choosing the material of self-locking tuning screw suitable for 5G filter needs to be comprehensively judged around the four core dimensions of filter's application frequency band, deployment environment, mechanical conditions and RF performance requirements, combined with the key characteristics of the material, such as electrical conductivity, thermal expansion coefficient, hardness and corrosion resistance. The following are the selection methods and principles of sub-scenarios:
1. Core selection basis: match the performance and working condition requirements of 5G filter.
Priority of RF performance: The frequency band difference of high-conductivity 5G filter in high frequency band (millimeter wave) directly determines the electrical conductivity requirements of screw materials, and high-frequency signals are extremely sensitive to skin effect loss and passive intermodulation (PIM).
Millimeter wave band (28GHz/39GHz): Beryllium copper/phosphor bronze+thick silver plating (5–8 μ m) is preferred. Silver is the metal with the highest conductivity, and the thickness of the coating should be ≥5μm to reduce the high frequency loss; Beryllium copper substrate has high hardness and toughness, which can maintain thread accuracy, ensure the stability of central frequency after tuning, and inhibit PIM (which needs to meet ≤-165dBc).
Sub-6G medium and high frequency band (3-5μmGHz/4.9GHz): phosphor bronze+silver plating (3–5 μ m) can be selected, which gives consideration to both conductivity and cost and meets the requirement of insertion loss ≤0.3dB.
Sub-6G low frequency band (below 2.6GHz): The requirement for RF loss is low, so 316 stainless steel (without plating) or ordinary brass+nickel plating can be selected to reduce the material cost.
Mechanical working conditions are preferred: the mechanical reliability of screws made of high hardness and fatigue resistance should match the vibration intensity and debugging frequency of the base station to avoid thread wear and self-locking failure.
High vibration scene (wind power base station, roadside base station): priority is given to quenched beryllium copper (hardness 35–45hrc), which has excellent fatigue resistance, does not crack under tens of thousands of alternating vibrations, and the elastic self-locking structure can continuously maintain pre-tightening; The thread can be designed as a triangular tooth structure to strengthen the locking effect.
Frequent debugging scenes (production line calibration, operation and maintenance re-adjustment): Beryllium copper/316 stainless steel with high hardness can avoid thread slipping caused by repeated screwing; It is forbidden to use ordinary brass (hardness is only 8–12 HRC), otherwise it is easy to cause tooth deformation.
Low vibration/fixed scene (indoor machine room filter): ordinary brass+nickel plating can be selected, which has low cost and good processability and meets the requirements of basic machinery.
Environmental adaptability is preferred: corrosion-resistant 5G base stations are mostly deployed outdoors in harsh outdoor environments, and environmental factors such as salt fog, humidity and temperature difference directly affect the life of screws, so the selection should be targeted.
Coastal high salt fog environment: 316 stainless steel (containing molybdenum, salt fog resistance test ≥1000h) or phosphor bronze+nickel plating is preferred to avoid thread corrosion and sticking; It is forbidden to use uncoated brass (it is easy to produce patina and destroy the self-locking structure).
High-cold/high-heat temperature difference scene (-40℃ to+85℃): Phosphor bronze is selected, and its thermal expansion coefficient (CTE ≈ 17× 10/℃) is highly matched with the aluminum alloy cavity of the filter (CTE ≈ 23× 10/℃), which is synchronous in expansion and contraction under temperature cycle and will not cause structural stress to loosen; Excellent toughness, not brittle at low temperature.
Dry inland environment: optional brass+silver plating, giving consideration to conductivity and corrosion resistance, with moderate cost.
Second, the comparison and recommendation scheme of different material selection
Matters needing attention in adapting the core advantages of material scheme to the scene
Quenched beryllium copper+thick silver plated millimeter wave filter with high conductivity, high hardness and excellent fatigue resistance, and high vibration outdoor base station have high cost, so it is necessary to control the tightening torque (0.8–1.5 nm) to avoid deformation.
Phosphor bronze+silver plating has good thermal expansion matching, good toughness, low PIM, moderate and high frequency, and moderate wear resistance in severe temperature difference scenes, so frequent debugging should be avoided.
316 stainless steel is salt fog resistant and its thread strength is stable. Coastal base stations, low-frequency filters and scenes with low requirements for conductivity have low conductivity, so it is not suitable for high-frequency bands.
Ordinary brass+nickel plating has the advantages of low cost, good machinability, indoor fixed filter and low hardness in low vibration scene, so it is forbidden to be used in high vibration/frequent debugging conditions.
Third, the principle of type selection and supplement
The plating process can not be ignored: the silver plating layer should be uniform and void-free, otherwise local oxidation will occur; The thickness of nickel plating layer should be ≥2μm to improve the surface hardness and corrosion resistance.
Torque matching material characteristics: high-hardness materials (beryllium copper, stainless steel) can bear higher torque, while low-hardness materials (brass) need to reduce the torque (0.5–0.8 nm) to prevent tooth slipping.
Give priority to the mature scheme: give priority to the material combination verified by the base station on site to avoid the reliability risk caused by insufficient testing of new materials. How to choose the material of self-locking tuning screw suitable for 5G filter?
Choosing the material of self-locking tuning screw suitable for 5G filter needs to be comprehensively judged around the four core dimensions of filter's application frequency band, deployment environment, mechanical conditions and RF performance requirements, combined with the key characteristics of the material, such as electrical conductivity, thermal expansion coefficient, hardness and corrosion resistance. The following are the selection methods and principles of sub-scenarios:
1. Core selection basis: match the performance and working condition requirements of 5G filter.
Priority of RF performance: The frequency band difference of high-conductivity 5G filter in high frequency band (millimeter wave) directly determines the electrical conductivity requirements of screw materials, and high-frequency signals are extremely sensitive to skin effect loss and passive intermodulation (PIM).
Millimeter wave band (28GHz/39GHz): Beryllium copper/phosphor bronze+thick silver plating (5–8 μ m) is preferred. Silver is the metal with the highest conductivity, and the thickness of the coating should be ≥5μm to reduce the high frequency loss; Beryllium copper substrate has high hardness and toughness, which can maintain thread accuracy, ensure the stability of central frequency after tuning, and inhibit PIM (which needs to meet ≤-165dBc).
Sub-6G medium and high frequency band (3-5μmGHz/4.9GHz): phosphor bronze+silver plating (3–5 μ m) can be selected, which gives consideration to both conductivity and cost and meets the requirement of insertion loss ≤0.3dB.
Sub-6G low frequency band (below 2.6GHz): The requirement for RF loss is low, so 316 stainless steel (without plating) or ordinary brass+nickel plating can be selected to reduce the material cost.
Mechanical working conditions are preferred: the mechanical reliability of screws made of high hardness and fatigue resistance should match the vibration intensity and debugging frequency of the base station to avoid thread wear and self-locking failure.
High vibration scene (wind power base station, roadside base station): priority is given to quenched beryllium copper (hardness 35–45hrc), which has excellent fatigue resistance, does not crack under tens of thousands of alternating vibrations, and the elastic self-locking structure can continuously maintain pre-tightening; The thread can be designed as a triangular tooth structure to strengthen the locking effect.
Frequent debugging scenes (production line calibration, operation and maintenance re-adjustment): Beryllium copper/316 stainless steel with high hardness can avoid thread slipping caused by repeated screwing; It is forbidden to use ordinary brass (hardness is only 8–12 HRC), otherwise it is easy to cause tooth deformation.
Low vibration/fixed scene (indoor machine room filter): ordinary brass+nickel plating can be selected, which has low cost and good processability and meets the requirements of basic machinery.
Environmental adaptability is preferred: corrosion-resistant 5G base stations are mostly deployed outdoors in harsh outdoor environments, and environmental factors such as salt fog, humidity and temperature difference directly affect the life of screws, so the selection should be targeted.
Coastal high salt fog environment: 316 stainless steel (containing molybdenum, salt fog resistance test ≥1000h) or phosphor bronze+nickel plating is preferred to avoid thread corrosion and sticking; It is forbidden to use uncoated brass (it is easy to produce patina and destroy the self-locking structure).
High-cold/high-heat temperature difference scene (-40℃ to+85℃): Phosphor bronze is selected, and its thermal expansion coefficient (CTE ≈ 17× 10/℃) is highly matched with the aluminum alloy cavity of the filter (CTE ≈ 23× 10/℃), which is synchronous in expansion and contraction under temperature cycle and will not cause structural stress to loosen; Excellent toughness, not brittle at low temperature.
Dry inland environment: optional brass+silver plating, giving consideration to conductivity and corrosion resistance, with moderate cost.
Second, the comparison and recommendation scheme of different material selection
Matters needing attention in adapting the core advantages of material scheme to the scene
Quenched beryllium copper+thick silver plated millimeter wave filter with high conductivity, high hardness and excellent fatigue resistance, and high vibration outdoor base station have high cost, so it is necessary to control the tightening torque (0.8–1.5 nm) to avoid deformation.
Phosphor bronze+silver plating has good thermal expansion matching, good toughness, low PIM, moderate and high frequency, and moderate wear resistance in severe temperature difference scenes, so frequent debugging should be avoided.
316 stainless steel is salt fog resistant and its thread strength is stable. Coastal base stations, low-frequency filters and scenes with low requirements for conductivity have low conductivity, so it is not suitable for high-frequency bands.
Ordinary brass+nickel plating has the advantages of low cost, good machinability, indoor fixed filter and low hardness in low vibration scene, so it is forbidden to be used in high vibration/frequent debugging conditions.
Third, the principle of type selection and supplement
The plating process can not be ignored: the silver plating layer should be uniform and void-free, otherwise local oxidation will occur; The thickness of nickel plating layer should be ≥2μm to improve the surface hardness and corrosion resistance.
Torque matching material characteristics: high-hardness materials (beryllium copper, stainless steel) can bear higher torque, while low-hardness materials (brass) need to reduce the torque (0.5–0.8 nm) to prevent tooth slipping.
Give priority to the mature scheme: give priority to the material combination verified by the base station on site to avoid the reliability risk caused by insufficient testing of new materials.
