Influence of Terminal Plating on Design of Automobile Harness

At present, the wiring harness terminals used in automobile connectors are mainly stamped with high-quality copper alloy. For the purpose of protecting the terminal base materials from corrosion and optimizing the surface performance of the terminals, different surface treatments such as fog tin, reflowing bright tin, tin-lead, silver, gold and palladium-nickel flash gold are usually carried out on the terminals, which is what we often call terminal surface plating, namely terminal plating.

What is the influence of terminal plating on automotive wire harness design?

We know that the terminals play two main roles in wiring loom connection, one is to fasten the plastic shell, and the other is to form electrical connection with the mating terminals. Although copper alloy has good mechanical properties, its performance in electrical conductivity is not satisfactory. Generally, the materials with good electrical conductivity have average mechanical properties, such as tin, gold and silver.

Therefore, plating is extremely necessary for the terminal to have both acceptable electrical conductivity and mechanical properties.

Tin-plated terminals can generally achieve good environmental stability in use, and because of its low cost, it is widely used in the market. The main surface treatment methods are dark tin, bright tin and hot dipping tin. However, its shortcomings are also obvious. First, compared with other coatings, its wear resistance is poor, and the number of plugging and unplugging cycles is less than 10 times. Second, its contact performance will decrease with time and temperature, and it is generally used in environmental conditions below 125℃. When designing tinned terminals, high contact force and small displacement should be considered to ensure the contact stability.

Silver-plated terminals have the advantages of good point contact performance and can be used continuously at 150℃, but they are expensive, easy to rust in the air with sulfur and chlorine, harder than tin, and slightly higher than or equal to tin in resistance coefficient. Potential electronic migration phenomenon easily leads to potential risks of connectors.

Gold-plated terminals have the good contact performance and environmental stability of tin-plated and silver-plated terminals, and have excellent friction resistance. It is accompanied by its higher cost price among the three, but in fact, not every terminal needs gold plating. When the tin-plated terminal will be worn due to low contact force, we can use gold-plated terminal instead.

With the rapid development of automobile industry and the requirements of new energy and intelligence, the requirements of intelligence, refinement and reliability are put forward for all kinds of functional components inside the automobile, and the automobile connectors are gradually developing towards the direction of high reliability, high density, miniaturization, high speed, standardization, integration and modular. Miniaturization means putting more needles in a limited space, that is, realizing the high density of products. Therefore, in the design of connectors, we have to consider the design of plugging force, which not only affects the difficulty of connector assembly and disassembly, but also relates to the electrical performance of connectors.

The application of the terminal coating can not only reduce the corrosion of the terminal material surface, but also improve the state of insertion force. To reduce the insertion force, it is necessary to reduce the friction force, and there are three main factors that affect the friction coefficient between terminals: material, surface roughness and surface treatment. The minimum surface roughness of different coating types is reflowed bright tin, and the maximum is silver. The largest insertion force of terminals with different surface treatments is tin-lead and the smallest is gold, which is the comprehensive result of surface hardness and surface roughness. From this, it can be seen that the insertion force of gold is better, while tin-lead is relatively poor. However, the pull-out force of different electroplating is also good for gold, but poor for tin and lead.

Therefore, the plating layer of the terminal not only protects the surface of the terminal material from corrosion, but also improves the state of insertion force. However, considering the cost performance of functionality and economy, besides the design of plugging force, we should also refer to the following operating conditions to select the appropriate terminal coating:

① Can withstand the actual temperature of the terminal working conditions;

② Environmental protection and non-corrosiveness;

③ Chemical stability;

④ Ensure terminal contact;

⑤ Wear insulation to reduce friction;

⑥ Low cost.

With the increasing complexity of the electrical environment of the whole vehicle and the arrival of the new energy era, only by continuously exploring the manufacturing technology of parts can we meet the rapid iteration of new functions.