Test method of coating thickness

The test method of coating thickness can be divided into three categories: chemical method, electrochemical method and physical method according to the basic principle of test method. Among them, the chemistry method includes chemical dissolution analysis method, chemical solution weighing method and chemical solution flow timing method. The electrochemical method includes electrochemical anodic method (coulomb method); The physical method includes direct measurement and instrument measurement (magnetic, non-magnetic, X-ray and electron microscopy).
The test method of coating thickness can also be divided into two categories: breaking and non-breaking. Among them, the damage method includes the drop method, liquid flow method, electric charge method and metallographic method. The non-destructive method includes measuring method, The quality of method and instrument measurement.
This paper introduces the method of coating thickness test for several electroplating plants.
X ray method [test principle] X-ray spectrometry method to measure the thickness of the cover layer is based on the interaction of a strong and narrow multichromatic X ray with the matrix and the covering layer. This interaction produces secondary radiation of discrete wavelength and energy, and these secondary radiation has the characteristics of covering layer and matrix elements. There is a relationship between The quality of coverage (if The density is known, and The thickness of The cover layer) and The secondary radiation intensity. The relationship is first calibrated by The standard block calibration of The coverage of The quality of known units. If the density of the coating material is known and the actual density is given, then the standard block can give a linear thickness of the covering layer.
[test instrument]
The scope of the test is wide and applicable to the thickness of the metal covering which needs to be analyzed in the electroplating and electronic circuit board. Including: gold (Au), silver (Ag), Sn (Sn), copper (Cu), nickel (Ni), chromium (Cr), etc. It is suitable for the coating structure that does not contain the coating element in the base material. For example, the electric Chrome plate on the base of stainless steel is not suitable for the thickness of the X-ray method, because the stainless steel also contains the chromium element, and the test error is very large.
The advantages and disadvantages of the test method are that the scope is wide, the test is accurate and fast, and the coating is not damaged. The disadvantage is that it is necessary to purchase dedicated X-ray coatings with special price.
3 magnetic magnetic testing principle 】 【 thickness gauge measurement due to exist between permanent magnet and the matrix metal layer caused by the change of the magnetic attraction, or the measure through the coating and substrate metal magnetic resistance of magnetic path.
Test instruments:
[test range] suitable for measuring non-magnetic coating on magnetic metal.
The advantages and disadvantages of the test method are relatively small, which can only be used to measure the non-magnetic coating on the magnetic metal, such as galvanized coating.
4 coulomb method testing principle 】 【 coulomb method thickness is part of the metal coating to be measured for local anodic dissolution by anodic oxidation coating to achieve material substrate for coating thickness measurement of potential change. Coulomb's law thickness, the metal coating to be tested as anode, electrolysis and put in the electrolyte, the dissolution and through the current amount of metal and dissolved time is proportional to the product, is proportional to the consumption of electricity.
[test instrument]
[the test range] is suitable for measuring the thickness of a single layer and multi-layer metal covering layer thickness of the anode, including the measurement of the multi-layered system, such as Cu/Ni/Cr, and the thickness of the alloy covering layer and the alloying diffusion layer. It can not only measure the coating thickness of flat sample, but also measure the thickness of the covering layer of the cylinder and wire, especially for the metal and its potential difference of the multi-layer nickel coating. The types of plating are Au, Ag, Zn, Cu, Ni, dNi, Cr.
The advantages and disadvantages of the test method are that the multi-layer continuous coatings (such as the electroplated copper nickel chromium plating layer) can be tested. The downside is that it is a destructive test.
5 metallographic method [test principle] used metallographic microscope to detect cross section, and directly measured the local thickness of metal covering layer and oxide film layer.
[test instrument]
[test range] the average thickness test needs to be greater than 1um to ensure that the measurement results are within the margin of error. The larger the thickness, the smaller the error.
The advantages and disadvantages of the test method are that the test results in the applicable coating range are especially accurate and the error is very small, which can be chosen as the method of arbitration in dispute. The disadvantage is that the process of preparing the coating thickness test is time-consuming.
1. In order to ensure the accuracy and accuracy of the test, all tests should always calibrate the test instruments with standard samples.
2. The selection of test methods firstly takes the electroplating substrate and the product category of the plating layer as the first consideration, and selects the method for scientific application of accurate and fast; Secondly, we can consider the specific shape of the electroplating, whether it can be damaged, whether it is necessary to get the test data quickly and the actual condition of the electroplating plant to consider the applicable and practical methods.
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References:
1. GB/T 6462-2005 metal and oxide coating thickness measurement microscopy
2. ASTM b487-85 (2007) Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section
3. ASTM b764-04 Standard Test Method for Simultaneous Thickness and Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)
4. GB/t4955-1997 metal covering layer thickness measurement
5. GB/t16921-2005 metal covering layer thickness measurement of X-ray spectrometry
6. ASTM b568-98 (2004) Standard Test Method for Measurement of Coating Thickness by X-ray Spectrometry
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