1、BRITISH STANDARD BS EN 14571:2005 Metallic coatings on nonmetallic basis materials Measurement of coating thickness Microresistivity method The European Standard EN 14571:2005 has the status of a British Standard ICS 25.220.40; 17.040.20 BS EN 14571:2005 This British Standard, was published under th
2、e authority of the Standards Policy and Strategy Committee on 3 May 2005 BSI 3 May 2005 ISBN 0 580 45949 7 National foreword This British Standard is the official English language version of EN 14571:2005. The UK participation in its preparation was entrusted to Technical Committee STI/33, Electrode
3、posited and related coatings, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in
4、 the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsib
5、le for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the U
6、K interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 11 and a back cover. The BSI copyright notice displayed in this document indicates
7、 when the document was last issued. Amendments issued since publication Amd. No. Date CommentsEUROPEANSTANDARD NORMEEUROPENNE EUROPISCHENORM EN14571 April2005 ICS25.220.40;17.040.20 Englishversion MetalliccoatingsonnonmetallicbasismaterialsMeasurement ofcoatingthicknessMicroresistivitymethod Revteme
8、ntsmtalliquessurmatriauxnonmtalliques MesuragedelpaisseurdesrevtementsMthode utilisantlamicrorsistivit Metallischeberzgeaufnichtmetallischen GrundwerkstoffenSchichtdickenmessungMikro WiderstandVerfahren ThisEuropeanStandardwasapprovedbyCENon3March2005. CENmembersareboundtocomplywiththeCEN/CENELECInt
9、ernalRegulationswhichstipulatetheconditionsforgivingthisEurope an Standardthestatusofanationalstandardwithoutanyalteration.Uptodatelistsandbibliographicalreferencesconcernings uchnational standardsmaybeobtainedonapplicationtotheCentralSecretariatortoanyCENmember. ThisEuropeanStandardexistsinthreeoff
10、icialversions(English,French,German).Aversioninanyotherlanguagemadebytra nslation undertheresponsibilityofaCENmemberintoitsownlanguageandnotifiedtotheCentralSecretariathasthesamestatusast heofficial versions. CENmembersarethenationalstandardsbodiesofAustria,Belgium,Cyprus,CzechRepublic,Denmark,Eston
11、ia,Finland,France, Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Poland,Portugal, Slovakia, Slovenia,Spain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTANDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG ManagementCen
12、tre:ruedeStassart,36B1050Brussels 2005CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.EN14571:2005:EEN 14571:2005 (E) 2 Contents page Foreword3 1 Scope 4 2 Measurement principle4 3 Factors affecting measurement uncertainty.6 4 Calibration of instrumen
13、ts 7 5 Procedure .8 6 Accuracy requirements.9 7 Test report 9 Annex A (normative) Method for determining the critical current path width.10 Bibliography 11 EN 14571:2005 (E) 3 Foreword This document (EN 14571:2005) has been prepared by Technical Committee CEN/TC 262 “Metallic and other inorganic coa
14、tings”, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by October 2005, and conflicting national standards shall be withdrawn at the latest by October 2005.
15、This document includes a Bibliography. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hunga
16、ry, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EN 14571:2005 (E) 4 1 Scope This document describes a method for nondestructive measurements of the thickness of conductive coa
17、tings on nonconductive base materials. This method is based on the principle of the sheet resistivity measurement and is applicable to any conductive coatings and layers of metal and semiconductor materials. In general, the probe has to be adjusted to the conductivity and the thickness of the respec
18、tive application. However, this document focusses on metallic coatings on nonconductive base materials (e.g. Copper on plastic substrates, printed circuit boards). NOTE 1 This method also applies to the measurement of through-hole copper thickness of printed circuit boards. However, for this applica
19、tion a probe geometry different from the one described in this document is necessary. NOTE 2 This method is also applicable for thickness measurements of conductive coatings on conductive base materials, if the resistivity of the coating and the base material is different. This case is not considere
20、d in this document. 2 Measurement principle The sheet resistivity method uses the so called four-point probe as shown in Figure 1. A row of four spring-loaded metal tips are placed in contact with the surface of the conductive coating. The tip distances between the outer and inner tips S 1and S 3are
21、 equal. Usually a constant current is passed through the two outer contacts (4 and 7). The introduced current penetrates the conductive material of the coating with the resistivity . The resulting voltage drop is measured across the two inner contacts (5 and 6). In general, the flow of the introduce
22、d current is non-uniformly distributed over the cross-section of the coating and is not parallel to the coating (see Figure 2). The current density decreases with increasing distance from the direct line between the contacts 4 and 7 (with depth and width). If the current is effectively limited by th
23、e thickness of the coating, the voltage drop between 5 and 6 is a measure of the thickness. Key 1 Outer contact of the probe 2 Inner contact of the probe 3 Conductive coating 4 Nonconductive base material t Coating thickness Figure 1 Schematic representation of the sheet resistivity method EN 14571:
24、2005 (E) 5 3Key 1 Outer contacts of the probe 2 Inner contacts of the probe 3 Conductive coating 4 Nonconductive base material t Coating thickness Figure 2 Schematic representation of the non-uniformly distributed current within the coating The measured voltage drop depends on the resistivity of the
25、 metallic coating, on the probe geometry (distance of the 4 probe contacts S 1 , S 2 , S 3 ), the applied current and the thickness of the coating. If the resistivity of the coating can be expected to be homogenous and the thickness is sufficiently small, the measured voltage drop is determined only
26、 by the unknown thickness and the applied current. In general, there is no simple and practical equation to calculate the thickness as a function of the material resistivity, the probe geometry and the measured voltage and current. However, there are some well known approximations for practical use
27、in certain cases. Especially in the case of equal tip distances (S 1 =S 2 =S 3 = S) and for a thickness to probe spacing ratio t/s 0,5 the coating thickness, t, in micrometres, can be calculated using the equation: () = 0,5 S t when 2 ln V I t (1) where is the resistivity coating, in ohm.m; V is the
28、 potential difference across the inner probe tips, in Volts; I current passed through outer probe tips, in amps; S is the equal probe tip spacing (S=S 1 =S 2 =S 3 ). Usually the supplied current I is held constant. Therefore, the coating thickness is inversely proportional to the measured voltage :
29、EN 14571:2005 (E) 6 V C t = (2) where C is a the constant 0,221 I Equation (2) is the basis for many applications in the above case. In general suitable correction functions for Equation (2) are necessary if the prerequisite of a ratio t/s0,5 or an equal probe tip spacing is not satisfied. Because t
30、he introduced current decreases with increasing penetration depth, a sufficiently thick coating does not limit the current and the coating appears to be infinite to this method. The wider the probe spacing the deeper the current penetrates into the conductive material. Consequently, the measurement
31、range is determined by the probe spacing for a given coating material. The probe geometry (tip spacing) has to be adjusted with respect to the conductivity and the expected thickness range of the application of interest. Furthermore, the sensitivity of this method decreases with increasing thickness
32、. The application of Equation (2) is also limited by very thin coatings because the resistivity is expected to be constant and not a function of the thickness. However, for very thin thicknesses the resistivity starts to increase and below a critical thickness this increase of the resistivity is str
33、ongly pronounced. Typical values of this critical thickness are in the range of approximately 10 nm to 300 nm for metals. For measurements in this range and below this critical thickness a special calibration or additional correction functions are necessary. Because the introduced current decreases
34、with increasing distance in width, the current flow is not affected by a sample width wider than a critical width. Therefore, the sample width has to be wider than this critical width. Otherwise, the measured thickness becomes a function of the sample width and the sample width has to be considered
35、in addition. The probe spacing also determines the value of the critical width for a given coating material. 3 Factors affecting measurement uncertainty 3.1 Range of measurement The measurable thickness range is determined by the probe geometry (tip distance) and the conductivity of the coating. The
36、 probe geometry has to be adjusted to the thickness range of interest. Usually the manufacturer provides the uncertainty of the respective probe for the recommended thickness range. 3.2 Coating resistivity Measurements will be affected by the resistivity of the coating if the resistivity of the coat
37、ing differs from the resistivity of the calibration standard(s) used to calibrate the instrument. A 5 % difference in resistivity will result in a 5 % error unless this difference is accounted for in the calibration procedure. Furthermore, a homogenous resistivity throughout the coating is expected
38、for this method. The measurement will be affected by a resistivity variation of the coating. This can be caused by composition variation of the coating, by coating defects (e.g. cracks, porosity, voids, inclusions) or by a surface preparation or contamination. 3.3 Width of the sample Below a critica
39、l width, determined by probe design (tip spacing) and to a lesser degree on the electrical conductivity of the metallic coating, the coating thickness measurement becomes dependent upon the width of the electrical current path (e.g. conductive track width of printed circuit boards). The instrument s
40、hall therefore be calibrated using calibration standards of the width to be measured or appropriate correction functions shall be used. EN 14571:2005 (E) 7 NOTE 1 An exact positioning of the probe in the middle of the sample (e.g. conductive track) and parallel to its direction is necessary to avoid
41、 measurement errors. Usually special probe positioning systems or probe guides are provided by the manufacturers. NOTE 2 If the critical path width is not known, or for some reason is unobtainable, it may be obtained using a number of reference standards having the same thickness (made from the same
42、 piece of uniform material), but of different known widths (see Annex A). 3.4 Curvature Sharp or small radii of curvature will greatly affect the thickness measurement. This effect is minimised if the probe is placed on the surface so that its axis is parallel to that of the curved surface. Alternat
43、ively, calibration standards of the same curvature can be used. The influence decreases with increasing radii of curvature. 3.5 Surface roughness Measurements are affected by surface topography of the metallic coating. Rough surfaces can cause thickness measurement errors. In such cases it is strong
44、ly recommended to perform a sufficient number of measurements at different locations on the sample and using the mean together with the standard deviation as a representative thickness value of the coating. 3.6 Temperature A temperature change between calibration and measurement causes errors of the
45、 measured thickness because the resistivity of the coating varies with temperature. This temperature influence is important especially if the resistivity temperature coefficient of the coating material is high (e.g. Cu : =0,0039 K -1 ). Therefore, the temperature of the sample should be measured and
46、 the thickness should be corrected with respect to temperature. Some manufacturers provide instruments with a temperature sensor and an automatic temperature correction for this purpose. 3.7 Probe contact pressure The pressure with which the probe contacts are applied to the test specimen can affect
47、 the instrument readings. The applied pressure should therefore be made constant and as low as possible to minimise sample damage but still steady to ensure a good repeatability (reliable contact to the coating). This is achieved in practice by using a constant pressure probe having tips supported b
48、y adapted springs. The shape of the tips can be sharpened or rounded with respect to the coating material to achieve a reliable contact. The current through the two outer tips should applied only if the contact of the tips is established in order to avoid possible damages of the surface. 4 Calibration of instruments 4.1 General Before use each instrument shall be calibrated in accordance with the manufacturers instructions, using suitable calibration standards. Appropriate attention shall be given to the factors listed in Clause 3 and to t
