BS EN 13603-2021 pdf free download.Copper and copper alloys — Test methods for assessing protective tin coatings on drawn round copper wire for electrical purposes
4.2.5.3 Electrolysis (Dissolution of the unalloyed tin coating)
The electrolyte (4.2.2.1) and test piece shall be introduced into the cell so that a known area is exposed to the electrolyte. Efforts shall be made to ensure that no gas bubbles occur on the measuring area by use of the agitation mechanism. The electrical connections shall be made and the agitator operated. Electrolysis shall be continued until dissolution of the unalloyed tin coating is complete, as indicated by a sharp change in the anode potential or cell voltage, or by the operation of the automatic cut-out. After completion of the test, the test piece shall be removed from the cell, rinsed with water and examined to ensure that complete removal of the unalloyed tin coating has occurred over the measuring area (see 4.2.5.4.9).
4.2.5.4 Factors affecting the measuring accuracy
4.2.5.4.1 Coating thickness
The optimum accuracy is achieved with coating thicknesses in the range 0,2 μm up to 50 μm.
4.2.5.4.2 Current variation
For instruments using the constant current and time measuring technique, current variation will cause errors. For instruments using a current-time integrator, too large a change in current can change the anode current efficiency or interfere with the end-point, causing an error.
4.2.5.4.3 Area variation
The accuracy of the thickness measurement will be no better than the accuracy to which the measuring area is known. Area variations due to electrolyte level (excessive agitation), can lead to measurement errors. In some cases it can be advantageous to measure the length after electrolysis is complete and re-calculate the area.
4.2.5.4.4 Agitation
Agitation (i.e. the rate of stirring) shall be sufficient to remove any gas bubbles formed during the test, which can adhere to the test piece or cathode. Excessive agitation shall be avoided to prevent interference with the length of test piece submerged.
4.2.5.4.5 Condition of the test piece surface
Oil, grease, paint, corrosion products, staining or other surface chemical treatments can interfere with the test.
4.2.5.4.6 Cleanliness of the cell
Deposition of tin can take place on the cathode in some electrolytes. This deposit can alter the cell voltages. It is, therefore, essential to keep the cathode clean.
4.2.5.4.7 Cleanliness of the electrical connections
In the case of instruments other than the constant current type, if the electrical connections are not clean, the current/potential relationship will be disturbed and false end-points obtained.
4.2.5.4.8 Calibration standards
Measurements made using calibration standards are subject to the additional error of the calibration standards.
4.2.5.4.9 Non-uniform dissolution
If the rate of dissolution is not uniform over the measuring area, a premature end-point can be obtained and yield low results. Examination of the surface shall be made after the test (see 4.2.5.3) to verify that most of the coating has dissolved.
The presence of other matter in the coating, the roughness of the coating surface and the presence of porosity in the coating can cause fluctuation of the cell voltage. Such fluctuation can affect the end-point.
4.2.5.4.10 Electrolyte efficiency
The determination of tin thickness by this method depends upon the efficiency of the electrolyte K being at least 98 %. The value of K should be determined periodically (see 4.2.5.6).
4.2.5.5 Measurement uncertainty
The test equipment and the procedure shall be such that the coating thickness can be measured to
within a 5,0 % uncertainty under the following conditions:
— the electrical current shall be controlled within 10 mA;
— the time shall be controlled within 1 s;
— the area shall be controlled within the accuracy given in 4.2.5.2;
— the efficiency of the electrolyte K shall be greater than 98 % (see 4.2.5.6).
4.2.5.6  Determination of electrolyte efficiency
Where a manufacturer of apparatus recommends the use of a particular electrolyte for determining tin thickness on copper wire, the control of electrolyte efficiency shall be in accordance with the manufacturer’s instructions. In other cases, the value of K shall be determined periodically using the following procedure:
a) a suitable test anode shall be manufactured comprising wire in the range of diameter 0,5 mm up to and including 2,00 mm, of suitable length, coated with pure, unalloyed tin (4.2.2.2) to a thickness of at least 4 μm;
b) the test anode shall be accurately weighed and its mass recorded;
c) the test anode shall be immersed in the cell containing the electrolyte using either the same length as that recommended by the instrument manufacturer or used in the routine determination of
tin thickness;
d) the current shall be either that recommended by the instrument manufacturer or used in the routine determination of tin thickness;BS EN 13603 pdf download.