Analysis of Automotive Wiring Harness Terminals Plating Technology

In the design of vehicle wiring harnesses that pursue high assembly, functional integration, and intelligent architecture, highly integrated connectors (taking into account both high-power power supply and small signal transmission) have become the mainstream choice. Selecting connectors of different grades according to application scenarios and functional requirements is the basis for ensuring that their lifespan matches the lifespan of the vehicle. However, the core of connector performance lies in the connection quality of its internal male and female metal terminals. It is this end-to-end reliable contact that ensures the stable transmission of power and control signals within the tolerance range, thereby determining the reliability of the vehicle’s electrical functions.

Introduction

Automotive wiring harness terminals need to play a dual role: firmly bond with the plastic housing (mechanical properties) and achieve efficient current transmission with the mating terminal (conductive properties). Although stamped copper alloys have good mechanical strength, their conductivity makes it difficult to meet the optimal requirements; conversely, highly conductive materials such as tin, gold, and silver lack sufficient mechanical strength. In order to solve this inherent contradiction in material properties, applying functional plating on copper alloy terminals is a necessary process to enable them to have both reliable mechanical connection and excellent electrical conductivity.

Types of Coatings

Due to the different functions of Automotive terminals and different use environments (high temperature, thermal cycle, humidity, impact, vibration, dust, etc.), the terminal coatings selected are also various. Usually, automotive wiring harness terminals with different coatings are selected based on the maximum continuous temperature, coating thickness, cost, and coating suitable for the matching end to meet the stability of the electrical function.

• Dark Tin (more commonly used)

1) Manufactured by electroplating technology

2) Usually applied directly on copper alloys, sometimes electroplating is not performed to improve the weldability of the material

3) The coating thickness is generally 2~3μm

• Bright Tin

1) In the same electroplating process, dark tin needs to be quickly melted and cooled at the end of the production line

2) A small amount of quenching can make the coating bright

3) It has lower friction than dark tin

4) It is more expensive than dark tin

5) The coating thickness is generally 2~3μm

• Electroplated Silver

1) Full electroplating on the metal surface, usually cheaper than the selective stripping method

2) Silver has excellent contact electrical properties

3) It is more popular in Europe and also recognized in the United States

4) It is recommended as an anti-rust coating

5) The coating thickness is generally 2-4μm

• Electroplating Hard Gold

1) Reduce the amount of gold by selective stripe electroplating process

2) Usually used on nickel or palladium

3) Usually reinforced gold plating with cobalt or nickel, pure gold is softer

4) Hard gold is prone to cracks during the molding process

5) The plating thickness is generally 0.5-0.75μm

• Gold over Palladium Electroplating

1) Electroplating in the form of stripes

2) Higher temperature resistance than the hardened plating alone

3) The cost is the same as pure gold

4) Smooth surface

5) The plating thickness is generally 0.5~1μm

• Gold overlay

1) Cut a certain groove on the copper alloy coil, a specific contact metal layer is rolled into the groove, and then another metal layer is rolled into the groove

2) Excellent forging performance, high-temperature contact performance

3) Usually more expensive than pure gold plating

4) Usually used in the case of molding in the contact area

Comparison of Plating

• Tin-plated Terminals

Although tin-plating (such as dark tin, bright tin, and hot dip tin) is widely used due to its excellent environmental resistance and economy, its wear resistance is far inferior to other plating (plug-in and unplug cycles <10 times), and the contact resistance is easy to deteriorate with time and temperature (especially when >125℃). Therefore, in the design of tin-plated terminals, ensuring high contact force and using small displacements are the keys to ensuring long-term contact reliability.

•  Silver-plated Terminals

Silver plating generally has good point contact performance and can be used in continuous use conditions at 150℃. It is expensive and easy to rust in the presence of sulfur and chlorine. It is harder than tin plating, and its resistivity is slightly higher than or equivalent to tin. Potential electronic migration phenomenon can easily lead to potential risks in connectors.

• Gold-plated Terminals

Gold-plated terminals have good contact performance and environmental stability; continuous temperature can exceed 125℃, and excellent friction resistance. Hard gold is harder than both tin and silver and has excellent friction resistance. But its cost is high, and not every terminal needs to be gold-plated. When low contact force causes wear of the tin plating, gold-plated terminals can be used instead.

The Significance of Terminal Plating Application

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

•  Reduce friction and reduce insertion force

The main factors affecting the friction coefficient between terminals include materials, surface roughness and surface treatment. Even if the terminal materials are the same, the friction coefficient is not fixed, it will change with the increase of surface roughness. Plating the terminal surface can effectively improve the friction performance. The characteristics of the plating material, the thickness of the plating and the finish of the plating are all key parameters affecting the friction coefficient.

• Prevent oxidation and rust after the terminal plating is damaged

Within the 10 plug-in and pull-out life specified by the connector, the male and female terminals generate contact pressure through interference fit. During the plug-in and pull-out process, the relative movement between the terminals will scratch the contact surface, damage the plating, cause scratches, uneven thickness and even expose the substrate. This will cause changes in the mechanical structure, abrasions, adhesion, wear and material transfer, and accompanied by heat. As the number of plug-in and pull-out times increases, the scratches become more and more significant. Under the influence of long-term work and environmental factors (such as oxidation and corrosion), the terminals are very easy to fail.