The thickness of the electroplating layer is one of the important indicators to measure the quality of the plating layer. The thickness of the coating directly affects the corrosion resistance and electrical conductivity of the workpiece, which greatly affects the reliability and service life of the product.
There are many methods for measuring the thickness of the coating, which can be divided into non-destructive and destructive methods according to whether the coating is damaged by the test. Destruction methods include: dissolution method, liquid flow method, drop method, coulometric method (electricity method), metallographic microscope method, profilometer method, interference microscope method, etc. Non-destructive methods include: gravimetric method, magnetic method, eddy current method, ray reflection method and ray fluorescence method, double-beam microscope method, mechanical measuring tool method, etc. Various methods are described below.
This method does not determine the local thickness of the coating, but the average thickness of the entire coating. The measurement error is generally less than 5%. However, when the substrate and the plating layer contain the same metal, the error increases and it is difficult to measure accurately.
When measuring, soak the sample in an appropriate solution to dissolve the coating or base metal, and then compare the weight of the sample before and after dissolution to determine the quality of the coating. Or after the coating is dissolved, use chemical analysis to measure the quality of the coating. According to the mass, density and sample area, calculate the average thickness of the coating on the sample.
1. Preparation of samples
Degrease the sample with an organic solvent before dissolving. It was then washed with water, dehydrated with alcohol and dried, and stored in a desiccator for weighing.
2. Test solution
See Table 7-2-1 for the test solution used in thickness measurement by dissolution method. The reagents used should be chemically pure, and the solutions are prepared with distilled water, which can be used many times.
① See GB 9799-99 ② See GB 12599-90 ③ See GB 12307.1-90
3. Calculation of average thickness
The average thickness of the coating can be calculated by the following formula
In the formula:
h - the average thickness of the coating (μm:);
m1——the mass of the sample when the coating is not dissolved (g);
m2——the mass of the sample after the coating is dissolved (g);
S——the surface area of the coating on the sample (cm2);
d——the density of the coating metal (g/cm3).
