Analysis on the selection of automobile wiring harness terminal coating

[Abstract] At this stage, in order to ensure assembly and high integration of vehicle electrical functions, and to meet the development of a new intelligent electrical appliance architecture, the generally selected connector interface has a high degree of integration (not only to transmit high current and high power supply, but also to transmit low-voltage and low-current analog signals), select different levels of connection structures for different functions and different positions to ensure that the service life of the connector should not be lower than the service life of normal vehicles, within the allowable error range The stable transmission of power supply and control signals must be ensured; the connectors are connected through terminals, and the male and female terminals are made of metal conductive materials. The quality of the terminal connection directly affects the reliability of the electrical functions of the vehicle.

The wire harness terminals for current transmission in the vehicle wiring harness connectors are generally stamped from high-quality copper alloys. One part of the terminals should be fastened to the plastic shell, and the other part should be electrically connected to the mating terminals. The copper alloy Although it has good mechanical properties, its performance in electrical conductivity is not satisfactory；In general, materials with good electrical conductivity have average mechanical properties, such as tin, gold, silver, and the like. Therefore, plating is extremely necessary to provide terminals with acceptable electrical conductivity and mechanical properties at the same time.

Due to the different functions of the terminals and the different use environments (high temperature, thermal cycle, humidity, shock, vibration, dust, etc.), the selected terminal plating is also various, usually through the maximum continuous temperature, plating thickness, cost, pairing The suitable plating layer of the mating terminal is to choose terminals with different plating layers to meet the stability of the electrical function.

3.1 Tin-plated terminals
Tin plating generally has good environmental stability and low cost, so it is widely used, and there are many tin plating layers used in different aspects, such as dark tin, bright tin, and hot dip tin. Compared with other coatings, the wear resistance is poor, less than 10 mating cycles, and the contact performance will decrease with time and temperature, and it is generally used in ambient conditions below 125 °C. When designing tin-plated terminals, high contact force and small displacement should be considered to ensure the stability of the contact.

3.2 Silver Plated Terminals
Silver plating generally has good point contact performance, can be used continuously at 150 ° C, the cost is more expensive, it is easy to rust in the air in the presence of sulfur and chlorine, harder than tin plating, and its resistivity is slightly higher than or equivalent to tin , the potential electromigration phenomenon easily leads to potential risks in the connector.

3.3 Gold-plated terminals
Gold-plated terminals have good contact performance and environmental stability, the continuous temperature can exceed 125 ℃, and has excellent friction resistance. Hard gold is harder than tin and silver, and has excellent friction resistance, but its cost is higher, and not every terminal needs gold plating. When the contact force is low and the tin plating layer is worn, gold plating can be used instead. Terminal.

It can not only reduce the corrosion of the terminal material surface, but also improve the insertion force state.

4.1 Reduce friction and reduce insertion force
The main factors that affect the coefficient of friction between terminals include: material, surface roughness, and surface treatment. When the terminal material is fixed, the friction coefficient between the terminals is fixed, and the relative roughness is relatively large. When the surface of the terminal is treated with a coating, the coating material, coating thickness, and coating finish have a positive impact on the friction coefficient.

4.2 Prevent oxidation and rust after the terminal plating is damaged
Within 10 effective times of plugging and unplugging, the terminals interact with each other through interference fit. When there is contact pressure, the relative displacement between the male and female terminals will damage the plating on the terminal surface or slightly scratch it during the movement. Traces lead to uneven thickness or even exposure of the coating, resulting in changes in mechanical structure, scratches, sticking, wear debris, material transfer, etc., as well as heat generation.The more times of plugging and unplugging, the more obvious the scratch marks on the surface of the terminal. Under the action of long-term work and the external environment, the terminal is very easy to fail. It is mainly due to the oxidative corrosion caused by the small relative movement of the contact surface, usually 10~100μm relative movement; violent movement may cause harmful wear between the contact surfaces, slight vibration may cause friction corrosion, thermal shock and environmental influences accelerate the process .

Adding a plating layer to the terminal can not only reduce the corrosion on the surface of the terminal material, but also improve the state of insertion force. However, in order to maximize the function and economy, the plating layer mainly refers to the following conditions of use: it can withstand the actual temperature conditions of the terminal; environmental protection , non-corrosive; chemically stable; guaranteed terminal contact; reduced friction and wear insulation; low cost. As the electrical environment of the whole vehicle becomes more and more complex and the new energy era is coming, only by constantly exploring the manufacturing technology of parts and components can the rapid iteration of new functions be met.