1. Terminal material
The following characteristics are important to consider when selecting terminal materials:
①The mechanical properties of the material. Strength, ductility, yield strength, hardness, etc.;
②The electrical conductivity and thermal conductivity of the material. There is a proportional relationship between the electrical conductivity and the thermal conductivity. The electrical conductivity is related to the electrical conductivity of the terminal and the size of its own resistance.
③ Stress relaxation resistance. The terminal is divided into a crimping part and a connecting part. The elastic-plastic deformation of the crimping part causes stress between the terminal and the wire. If the stress relaxes, the contact between the terminal and the wire will become unstable. If the connection part of the terminal is To communicate through plug deformation, stress relaxation and fatigue issues need to be considered.
2. Terminal plating
Electroplating on the terminal surface is a process method to solve the metal oxidation and corrosion of the terminal surface, strengthen the terminal conductivity and reduce the contact resistance. The most commonly used terminal plating is tin plating, in addition to gold plating, silver and nickel or chromium.
Gold itself has high chemical stability, strong corrosion resistance, high temperature resistance, easy welding, strong electrical conductivity, and certain wear resistance. However, because the metal is used for cathodic coating, the price is also relatively expensive. Due to the thin gold coating and insufficient process technology, the coating has pores in actual production, which will cause microporous corrosion, which affects the protective performance. Therefore, it is often used in terminals. connection part to reduce the contact resistance of the connection.
Silver itself also has high chemical stability, is not easy to corrode in the air, has good welding performance, and has good electrical and thermal conductivity. However, its disadvantage is that it will be halogenated or sulfided when exposed to the air containing halides and sulfides, the surface of the silver coating will be discolored, and the electrical conductivity will decrease. In addition, microporous corrosion will also occur in case of moisture, so it is often used in the terminal connection part like gold to reduce the contact resistance of the connection.
Tin has good chemical stability, high ductility, and is difficult to change color in the atmosphere. And because the tin plating layer is relatively soft, it can improve the running-in effect on the sliding parts of the machine. Therefore, tin plating can improve solderability and prevent nitridation. It is commonly used in electronic products and is a common terminal plating process.
In addition, there are nickel plating and chromium plating. When the thickness of nickel plating is less than 25 microns, there are more pores. In addition, the solderability of nickel plating is deteriorated due to passivation. The hardness, wear resistance and heat resistance of chromium plating are good. Chrome plating is mainly used for decorative plating and functional purposes.
It can be seen that there are many kinds of plating layers of terminals. The plating layer of the crimping part of the terminal is generally tin-plated, and the plating layer of the connecting part of the plug-in terminal is gold-plated, silver-plated, and multi-plated. required coating.
3. Influence of terminal design parameters
The design parameters of the terminal generally refer to the parameters of the crimping part, mainly referring to the inner and outer diameter of the terminal, the engagement length, and the depth, number and arrangement of the dents.
①Internal and external diameters.
The inner and outer diameter of the terminal determines the thickness of the terminal. The smaller the bending radius, the greater the relative elongation of the outer metal. When the relative elongation of the outer metal reaches the ultimate elongation of the material, that is, the bending radius reaches the minimum value, the material will have a bending crack. The selection of terminal thickness needs to be determined according to the wire diameter of the crimped wire.
② Mesh length.
The influence of the engagement length on the pull-off force of the terminal: the longer the engagement length, the larger the contact area between the terminal and the wire, and the stronger the contact between the terminal and the wire under the same crimping degree, the greater the pull-off force.
The influence of meshing length on the contact resistance of the terminal: the longer the meshing length, the larger the contact area between the terminal and the wire, and the smaller the contact resistance of the crimped terminal under the same crimping degree.
③ Depth, number and arrangement of dents
Indentations are generally present on the inner surface of the crimp portion of the terminal as a way to increase the mechanical and electrical properties of the terminal. The depth, number and arrangement of the dimples have different effects on the performance of the terminals.