Application of Electrolytic Thickness Tester in Quality Control of Precision Electroplating Layers

How it works:

Electrolytic thickness gauge is a precision measuring device based on the principle of electrochemical dissolution. The core working process is to delineate a small measured area of a known area on the surface of the coating to be measured, and use a specific electrolyte to form an electrolytic cell with the outside world. By applying a constant DC current, the coating dissolves quantitatively as an anode. According to Faraday's law of electrolysis, the mass of the dissolved metal is directly proportional to the amount of electricity that passes through. The instrument accurately monitors voltage abruptness to determine the end point at which the coating is completely dissolved, and then accurately calculates the average thickness of the coating by combining the known current value, energization time, dissolution area, and electrochemical equivalent of the metal. Its basic calculation formula can be expressed as:

δ = (K * Q) / (ρ * A)

where δ represents the thickness of the coating, K is the comprehensive constant related to the electrochemical equivalent of the metal, Q is the total amount of electricity consumed during the dissolution process, ρ is the density of the metal in the coating, and A is the area of the measured area. This method realizes the absolute measurement of the coating thickness, does not rely on the calibration standard, and has high theoretical accuracy.

In the field of precision electroplating, such as the manufacturing of electronic components, connectors, aerospace components, and high-grade decorative parts, coating thickness is a key parameter that directly affects product conductivity, corrosion resistance, weldability, mechanical strength, and appearance. Electrolytic thickness measurement technology is unique in this type of quality control. First of all, the measurement results are highly accurate, traceable to basic physical quantities such as current and time, which is suitable for arbitration methods and high-precision comparison in laboratories. Second, it can measure the thickness of a single metal layer in a multi-layer coating system, such as non-destructive bottom measurement of the gold coating on the nickel substrate, which is critical for the quality control of functional composite coatings. Finally, the method is insensitive to the slight unevenness of the measurement surface, and can provide the average thickness in the measurement area, and the data is stable and reliable.

Application Practice

In the actual quality control process, the application of electrolytic thickness gauges requires careful planning. Before measurement, the matching electrolyte is strictly selected according to the type of plating metal (e.g., gold, silver, nickel, tin, and its alloys) to ensure selective dissolution and protection of the underlying material. The selection of measurement points should cover the high current density zones, low current density zones, and key functional surfaces of the workpiece to comprehensively evaluate the uniformity of the coating distribution. During operation, it is necessary to ensure that the measurement area is well sealed to prevent electrolyte leakage and inaccuracy of the measurement area.

In order to effectively monitor the status of the production line, it is recommended to combine electrolytic thickness measurement with production batch sampling to establish a thickness control chart. The following is an example of a typical multilayer coating quality control sampling measurement scheme:

At the same time, it is important to note the limitations of this method: it is a destructive measurement, and the measurement point will leave a tiny mark; The measurement speed is relatively slow; For extremely thin (typically less than 0.1 μm) or loosely porous coatings, end-point judgment can be challenging. Therefore, it is often used in complementary use with non-destructive methods such as X-ray fluorescence thickness measurement.

Modern electrolytic thickness gauges have made great progress in automation and intelligence, realizing the programmatic control of the measurement process, automatic judgment of the end point and direct output of data, and reducing human operation errors. In terms of standard compliance, this method has been adopted by many international and domestic standards as one of the reliable methods for measuring coating thickness. For example, standards such as ISO 2177 and ASTM B764 detail the instruments, procedures, and requirements for electrolytic thickness measurement. Measuring according to these standards ensures that test results are globally comparable and credible, providing a solid technical basis for quality agreements in the supply chain.

Conclusion

Electrolytic thickness gauges play a key role in the quality control system of precision electroplating layers with their rigor of principle and high accuracy of measurement. It is particularly suitable for applications where high-precision, traceable measurements and multi-layer coating analysis are required. Through scientific application planning, combined with other measurement methods, and strict compliance with relevant technical standards, this technology can effectively ensure the performance and reliability of electroplating products and support the development of the manufacturing industry in the direction of high quality and high consistency.

References

ISO 2177: Metallic coatings Measurement of coating thickness Anode-dissolved coulomb

ASTM B764: Standard Test Method for Simultaneous Measurement of Thickness of Layers of Multilayer Coatings (Coulomb Method)

GB/T 4955: Metal overlay - Measurement of overlay thickness - Anode dissolution coulomb method