Introduction of Suzhou Maite Technology: How to choose the material of self-locking tuning screw?

As the core tuning component of 5G RF communication equipment (such as cavity filter and resonator), the self-locking tuning screw should take into account the three core requirements of RF performance, mechanical performance and environmental adaptability, and match the design characteristics of the self-locking structure. The specific selection principles and applicable materials are as follows:

Give priority to meeting the requirements of RF signal transmission performance.

5G RF equipment requires extremely high signal loss and electromagnetic shielding, and the screw material should have excellent conductivity and low dielectric loss to avoid interfering with signal transmission or generating stray signals due to its own characteristics.

Red copper (T2/T3 oxygen-free copper): It is one of the first choice materials in the field of radio frequency, with excellent conductivity, extremely low dielectric loss, which can effectively guarantee the stability of signals in the tuning process, and the copper material has good ductility, which is convenient for processing precision threads and self-locking structures (such as gradual pitch and staggered tooth structure). The disadvantage is that the hardness is low, and long-term frequent adjustment is prone to thread wear, which is suitable for scenes with high signal sensitivity and low adjustment frequency.

Brass (H62/H65): The conductivity is slightly lower than that of copper, but it has higher hardness, better wear resistance and relatively lower cost, which is suitable for self-locking tuning screws that need frequent adjustment. The corrosion resistance of brass is better than that of copper, and it can adapt to the mild humid environment of outdoor deployment of base stations. It is the most widely used material in 5G RF equipment.

Phosphor bronze: Adding phosphorus to brass improves the wear resistance and fatigue strength, while maintaining good electrical conductivity. It is suitable for screws that need to bear occlusal stress for a long time in self-locking structure, especially for the high-frequency vibration condition of cavity filter, which can reduce the risk of screw loosening.

Matching mechanical properties and self-locking structure requirements

The core functions of the self-locking tuning screw are "tuning accuracy" and "anti-loosening and self-locking". The material should have enough hardness, strength and deformation resistance to avoid slipping and deformation when the thread is engaged, and at the same time ensure the torque stability during adjustment.

For screws with mechanical self-locking structures such as gradual pitch change and double screw teeth staggered, materials with moderate hardness and good toughness (such as brass and phosphor bronze) should be selected. Too hard materials will easily lead to cracking when the threads are engaged, while too soft materials will easily produce plastic deformation and lose self-locking ability.

If the screw needs to bear large locking torque or long-term high-frequency vibration, the scheme of hard chromium plating/nickel plating on the surface of copper alloy can be selected: the substrate maintains the conductivity of copper, and the coating improves the surface hardness and wear resistance and prolongs the service life of the screw. It should be noted that the coating thickness should be controlled at 5-10μ m. Too thick will affect the thread accuracy and tuning accuracy.

Beryllium copper can be used in some high-precision scenes: it has high strength, high hardness, excellent conductivity and outstanding fatigue resistance, and is suitable for self-locking tuning screws with extremely high requirements, but the cost is high, and it is mostly used in high-end RF equipment.

Meet the environmental tolerance requirements of equipment working conditions.

5G base stations are mostly deployed in outdoor or computer room environment, which needs to cope with humidity, salt spray, temperature difference and other working conditions. The screw material needs to have corrosion resistance and high and low temperature stability.

Outdoor base station scene: brass, phosphor bronze or nickel/zinc plated copper alloy are preferred. The coating can effectively isolate humid air and salt, prevent screws from oxidation and rust, and avoid rust from affecting the RF performance inside the cavity.

High-temperature machine room or high-power equipment scene: materials with good heat resistance should be selected. Pure copper and brass have high melting points (the melting point of pure copper is about 1083℃), which can adapt to the temperature rise of equipment during long-term operation (usually the internal temperature of base station equipment is ≤85℃), and will not cause obvious thermal deformation due to temperature change, thus ensuring the stability of tuning accuracy.

Special corrosive environment (such as coastal areas with high salt fog): Stainless steel (304/316) silver plating scheme can be selected. Stainless steel provides excellent corrosion resistance, and silver plating ensures conductivity. However, it should be noted that the dielectric loss of stainless steel is slightly higher than that of copper, and the signal influence needs to be compensated by structural design, which is only suitable for special scenes with severe corrosion.

Give consideration to processing manufacturability and cost control.

The thread precision and self-locking structure of self-locking tuning screw (such as notch, countersunk table and gradual pitch) require high processing technology, and the material should have good cutting performance and formability.

Brass and copper have excellent cutting performance, and high-precision threads can be machined by CNC lathe with high surface finish, which reduces the friction torque fluctuation during thread occlusion and ensures the adjustment accuracy.

The cutting performance of phosphor bronze is slightly inferior to brass, but precision machining can be realized by optimizing tool parameters, and its fatigue resistance is better, which is suitable for mass production of base station equipment.

Avoid using pure iron, ordinary carbon steel and other materials: poor conductivity, easy to rust, will seriously affect the RF signal, and can not meet the accuracy requirements of self-locking structure.

To sum up, the mainstream materials of self-locking tuning screws for 5G radio frequency communication equipment are brass (H62/H65) and phosphor bronze, which give consideration to conductivity, wear resistance, corrosion resistance and cost advantages. High-end precision scenes can choose copper or beryllium copper; Nickel/silver plated copper alloy or stainless steel can be used in special corrosive environment.