Effect of coating thickness on the life of silver-plated contacts

Ag Plated Contacts play a critical role in signal and energy transmission in electronic devices. In practical applications, Silver Plated Electrical Contacts are often affected by fretting wear, which can result in increased contact resistance and even failure. Silver (Ag) is an ideal material for surface coatings on electrical contacts due to its excellent electrical and thermal conductivity, as well as its corrosion resistance. However, the effect of Ag coating thickness on electrical contact life remains a poorly characterized issue. This paper experimentally investigates the electrical life of Ag coatings of varying thicknesses under fretting wear conditions.

2.1 Sample Preparation
The experimental samples were cross-cylindrical Silver electrical contacts constructed from a CuSn4 bronze alloy (containing 4% tin). A 2 μm thick nickel (Ni) layer was electroplated on the substrate surface as a diffusion barrier, followed by four different thicknesses of pure Ag: 1.3 μm, 2 μm, 4 μm, and 5 μm.

2.2 Experimental Conditions
Temperature: 23°C
Relative Humidity: 10%
Frequency: 30 Hz
Normal Force: 3 N

2.3 Test Method
Tests were conducted using a fretting wear tester. The Silver Coated Contact life was determined by monitoring changes in contact resistance. Contact failure was determined when the contact resistance exceeded 10 times the initial resistance.

3.1 Effect of Plating Thickness on Electrical Life
The experimental results show that the thickness of the silver plating layer significantly affects the Bimetal Contacts with Silver Plated life:
1.3 μm plating: The electrical life was the shortest, with approximately 5 × 10⁴ fretting cycles;
2 μm plating: The electrical life was approximately 1 × 10⁵ fretting cycles;
4 μm plating: The electrical life was approximately 2 × 10⁵ fretting cycles;
5 μm plating: The electrical life was the longest, exceeding 3 × 10⁵ fretting cycles.

3.2 Analysis of Coating Wear Mechanisms
Scanning electron microscopy (SEM) observations revealed that the main manifestations of fretting wear on the silver coating are:
Wear failure: wear marks appear on the coating surface, and the silver layer gradually thins until the nickel layer is exposed.
Oxidation failure: an oxide film forms on the silver layer, increasing contact resistance.
With increasing coating thickness, the time to wear failure is prolonged and the impact of oxidation failure is reduced, thereby improving the electrical life.

3.3 Relationship Model between Electrical Life and Coating Thickness
Based on experimental data, a relationship model was established between electrical life (N) and silver coating thickness (t):
N=k⋅tⁿ

where k is the material constant and n is the exponential factor. The fitting results show that n≈1.5, indicating that the electrical life increases nonlinearly with coating thickness.

The thickness of the silver plating layer significantly affects the lifespan of Silver Plated Electrical Contacts; the thicker the silver plating layer, the longer the lifespan.

A quantitative relationship model between plating thickness and electrical lifespan was established, providing a basis for electrical contact design.
In practical applications, it is recommended to select an appropriate silver plating thickness based on reliability requirements to balance cost and performance.