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→Porosity
The primary requirement on an electroplated deposit is its thickness, since a series of other properties such as porosity, hardness and ductility, are depending on the layer thickness. A widely used method for thickness measurement is the microscopical evaluation of a mounted micro
section. Because of optical resolution limits however, layer thicknesses below 0.5 μm cannot be measured with sufficient accuracy. For low coating
thicknesses the x-ray fluorescence method is used, which often is integrated for quality assurance into the manufacturing process, for example in selective reeltoreel-to- reel electroplating plating lines. In this process, the returned characteristic x-ray impulses of the coating material and the substrate, generated by the primary x-rays, are detected and counted and then converted into material thickness by a computerized indicator or recording and control unit.
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During the electrolytic test, a sample is immersed into an electrolyte, containing an indicator solution. After passing electrical current, the pores are visible as colored spots.
Frequently a SO test at higher concentrations (100 ppm) and high humidity (2 levels, 95% RH at 40°C) is used. One advantage of this method is, that the severity level can be increased easily by varying the concentration of SO<sub>2</sub>. Besides these, other corrosive gas mixtures of H<sub>2</sub>S, SO<sub>2</sub>, and NO<sub>2</sub> are used in porosity tests (i.e. tests according to ASTM B735 and B 799).
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