PVD coating thickness and inspection
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Coating thickness refers to the outer surface of the coating and the distance to the substrate surface under the coating, generally in 0 ~ 15um, there are many detection methods, the following introduces the current application of the more common methods: cross section method, spherical mark method and non-destructive detection method.
1. method of section
Section method is a destructive detection method, the workpiece may not be used again.It will test the workpiece or sample along the coating section cut, under the microscope 1000 ~ 10000 times larger for measurement, the larger the magnification factor, the smaller the impact of human factors, the higher the precision.The boundary between the coating and the substrate is very obvious and it is convenient to measure by the scale in sem.The distance between the ruler's starting and ending points is the thickness of the coating.Whether the measurement is accurate or not is to correctly judge the boundary between the coating and the substrate, otherwise it will bring errors.If the interface between the coating and the substrate is fuzzy, it is best not to use this measurement method.In general, this measurement method is intuitive and accurate.In addition, when this method is used for measurement, it is better to observe the section, which should be relatively flat. Otherwise, manual processing should be carried out to make the section even for observation and measurement.
Oil mirror can also be used to observe the coating section for measurement. The cut sample is placed in plastic powder for pressing, burning and forming into a block sample, and then the tested surface is grinded, and the tested surface is grinded and leveled. During the measurement, the air pumped from the oil is measured between the objective lens and the measured surface to reduce interference.
Ball mark method is to use a certain diameter of steel ball on the surface of the coating grinding, coating and matrix grinding out a pit, ball grinding instrument section for an arc. The grinding operation requirements are the same as those of the ball mark test, which measures the adhesion of the coating. After ball grinding, the image is observed under the microscope through the imaging system and under the monitor.
The appearance of the workpiece will be damaged by the ball mark method. If the detection point is not in the functional area, it usually will not affect its reuse. However, in order to avoid errors, it is necessary to discuss with and obtain the consent of the artifact owner before testing with this method.
Nondestructive testing method is to detect the coating thickness on the workpiece without damaging the workpiece. There are many types of NDT methods, in general, nondestructive tests need to provide the substrate and the coating composition, or provide coating sample piece to analyze benchmark data, in the test, will be measured and coating composition composition compare with master sample blocks to deduce the theory of the coating thickness, so, for different substrate and coating composition analysis, make measuring program, and then to the actual measurement. Of course, some instruments can be directly measured without making sample blocks, but the error is large. This section mainly introduces X-ray fluorescence (XRF).
XRF instrument is mainly composed of X-ray excitation source and detection system.X ray tube produce X-ray based rays) (radiation or hit workpiece to be measured, each element of the workpiece to be measured is motivated, secondary X rays emitted and secondary rays emitted by the different elements with specific energy characteristics (that is, according to the energy feature of secondary rays types and content of elements can learn).The detection system measures the energy and amount of these excited secondary rays. The detection system software converts the detected energy and amount information into corresponding elements and content, so that the type and content of the elements in the workpiece under test can be detected.Using X-ray fluorescence principle, every element in the periodic table can be measured theoretically.However, in practical application, the effective elemental measurement range is from element 11, sodium (Na), to element 92, uranium (U).
According to the above principles, when measuring the coating thickness of the sample, XRF analyzes the element composition of the matrix and coating respectively. Generally, the element composition of the coating is very different from that of the matrix. Therefore, the calculation software can calculate the thickness of the coating. If the element composition of various substrates and coatings is detected separately in advance and stored in the computer database as a standard, when XRF detection, the detected element composition is compared with the standard to find the corresponding matrix and coating type, and judge the interface between the coating and the substrate, so as to measure the thickness of the coating more accurately.