1、BRITISH STANDARD BS EN ISO 3868:1995 Metallic and other non-organic coatings Measurement of coating thicknesses Fizeau multiple-beam interferometry method The European Standard EN ISO 3868:1994 has the status of a British StandardBSENISO3868:1995 This British Standard, having been prepared under the
2、 directionof the Sector Board forMaterials and Chemicals, waspublished under the authorityof the Standards Boardand comes into effect on 15May1995 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference STI/39 Draft for comment 76/50825 DC ISBN 0 580 23975 6
3、 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee STI/39, Methods of test for metallic and related coatings, upon which the following bodies were represented: Aluminium Federation Aluminium Finishing Association British In
4、dustrial Fasteners Federation British Jewellers Association Institute of Corrosion Institute of Metal Finishing Metal Finishing Association Ministry of Defence NDT Trade Association Royal Society of Chemistry Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd.
5、 No. Date CommentsBSENISO3868:1995 BSI 11-1999 i Contents Page Committees responsible Inside front cover National foreword ii Foreword 2 1 Scope and field of application 3 2 Principle 3 3 Definitions 3 4 Equipment 4 5 Factors affecting the measuring accuracy 4 6 Calibration 6 7 Procedure 6 8 Measuri
6、ng precision 8 Figure 1 4 Figure 2 5 Figure 3 6 Figure 4 7 Figure 5 7 List of references Inside back coverBSENISO3868:1995 ii BSI 11-1999 National foreword This British Standard has been prepared by Technical Committee STI/39, and is the English language version of ENISO3868:1994 Metallic and other
7、non-organic coatings Measurement of coating thicknesses Fizeau multiple-beam interferometry method published by the European Committee for Standardization (CEN). A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for
8、their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theEN ISO title page, pages 2 to 8, an inside back cover and a back cover. This stan
9、dard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 3868 October 1994 ICS 25.220.30 Descriptors: Coatings, metal coatings, dimensional mea
10、surement, thickness, optical measurement, interferometers English version Metallic and other non-organic coatings Measurement of coating thicknesses Fizeau multiple-beam interferometry method (ISO3868:1976) Revtemens mtalliques et autres revtementsnon organiques Mesurage de lpaisseur Mthode base sur
11、 le principedeFizeau dinterfromtrie faisceaux multiples (ISO 3868:1976) Metallische und andere anorganische Schichten Messung von Schichtdicken Fizeau-Vielstrahl-interferenz-Verfahren (ISO3868:1976) This European Standard was approved by CEN on 1994-10-26. CEN members are bound to comply with the CE
12、N/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to
13、 any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions
14、. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation
15、 Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1995 Copyright reserved to CEN members Ref. No. EN ISO 3868:1994 EENISO3868:1994 BSI 11-1999 2 Foreword This European Standard was taken over by the Technical Committee CEN/TC 262, Protection of metallic materia
16、ls against corrosion, from the work of ISO/TC 107, Metallic and other inorganic coatings, of the International Organization for Standardization (ISO). CEN/TC262had decided to submit the final draft for formal vote. The result was positive. This European Standard shall be given the status of a nation
17、al standard, either by publication of an identical text or by endorsement, at the latest by April 1995, and conflicting national standards shall be withdrawn at the latest by April 1995. According to the CEN/CENELEC Internal Regulations, the following countries are bound to implement this European S
18、tandard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, United Kingdom.ENISO3868:1994 BSI 11-1999 3 1 Scope and field of application This International Standard specifies a method for the me
19、asurement of the thickness of thin, highly reflective coatings (up to2m) by the use of Fizeau multiple-beam interferometry. The method described cannot be applied to vitreous enamel coatings. 2 Principle By completely dissolving a small area of the coating without attack of its substrate (or by mask
20、ing before plating), a step is formed from the surface of the coating to that of its substrate. The height of this step is measured with a multiple-beam interferometer. A monochromatic light beam is reflected back and forth between the specimen surface and a superimposed transparent mirror serving a
21、s a planar reference plate, so as to produce a pattern of interference fringes observed through a low-power microscope. The reference plate is tilted slightly with respect to the surface being inspected, so that the fringe pattern is a series of parallel lines. A step in the specimen surface causes
22、a shift in the fringe pattern. A shift of one full fringe spacing is equivalent to a vertical displacement of1/2of the wavelength of the monochromatic light. The whole and fractional number of fringe spacings occupied by the fringe shift is determined with an eyepiece micrometer. 3 Definitions 3.1 f
23、ilar micrometer eyepiece a device for observing and measuring an image. It includes an adjustable lens, a hairline that is moved with a graduated knob, and a pattern of lines (graticule lines) across the field of view 3.2 filar units the graduations on the micrometer control which are proportional t
24、o the absolute unit of length 3.3 fizeau plate an optically flat, smooth surface with high reflectivity and low absorption 3.4 fringe lines the dark lines caused by interference of light waves 3.5 hairlines the part of the filar eyepiece moved by means of the graduated knob to measure fringe line-sp
25、acing and offset 3.6 offset the displacement of a fringe line which occurs when it encounters a vertical variation on the surface of a specimen 3.7 spacing the distance between fringe linesENISO3868:1994 4 BSI 11-1999 4 Equipment The instrument employs: a) a beam of monochromatic light; b) optics to
26、 direct the light through a specially coated Fizeau plate which comes into contact with the specimen at a slight angle and forms an air wedge. An interference fringe pattern is produced in the air wedge and viewed through a microscope equipped with a filar micrometer eyepiece. The spacing and shape
27、of the fringe lines can be interpreted to determine an extremely accurate contour map of the specimen surface. 5 Factors affecting the measuring accuracy The following factors may affect the accuracy of a coating thickness measurement: 5.1 Reflective overcoat In order to obtain dark, narrow fringe l
28、ines necessary to achieve an accurate measurement, and in order to avoid errors due to different phase shifts, when light reflects over different materials, the test specimen shall be coated with a highly reflective material such as aluminium or silver. If the surfaces at the step are highly reflect
29、ive and the errors due to phase shift are known and corrected for, then the reflective layer can be avoided. 5.2 Step form For specimens with a coating thickness of less than0,3m special fabrication is not normally necessary. If the step being measured is abrupt, so that it is not possible to follow
30、 the fringes across the step, it will not be possible to observe how many full fringe intervals of displacement have occurred. This may be determined by an independent estimate of thickness on the basis of prior knowledge, or on measurements by other techniques such as profilometry, white-light inte
31、rferometry, etc. By the appropriate method the stem can often be made less abrupt so that each fringe can be followed across each step. The optimum angle is normally in the range95to100 . Figure 1 ENISO3868:1994 BSI 11-1999 5 5.3 Reading accuracy Possible backlash errors may be eliminated by always
32、making the final adjustment of the micrometer in the same direction. 5.4 Surface flatness A very flat surface is required, especially for measuring thicknesses between0,001and0,01m, in order to produce lines of good definition when expanded. If the surface is not flat, the fringes may be curved, mak
33、ing accurate measurement more difficult. The loss of accuracy will increase as the radius of curvature decreases. 5.5 Step definition In order to make good thickness measurements, it is necessary to have a good step definition. If the step is poorly defined the fringe lines are not straight and it i
34、s possible to make errors in the superposition of the hairline on the fringe line. Also it may be difficult or impossible to follow the fringes across the step. Poor definition may result from the step preparation method. (If the coating whose thickness is to be measured has been obtained by electro
35、plating, and if masking is done before deposition, there is likely to be a ridge or mound at the edge of the step because of local high current density along the edge. This will show up as a curve in the fringe pattern at the edge. This curve should be ignored or avoided.) 5.6 Roughness Surface roug
36、hness such that the fringe lines become irregular causes uncertainty in measurement of coating thickness by making the fringes less sharp, very diffuse, and poorly defined. 5.7 Cleanliness To achieve the best results it is necessary that the surface has no residues from manufacturing, fingerprints,
37、oil, etc. Specimen areas having visible defects shall be avoided in making measurements. 5.8 Preparation of step If the step is formed by masking and dissolution of the coating substrate or incomplete dissolution of the coating will lead to an erroneous measurement. Figure 2 ENISO3868:1994 6 BSI 11-
38、1999 6 Calibration The measurement obtained by multiple-beam interferometry is absolute and calibration is not required. 7 Procedure 7.1 Step preparation 7.1.1 Masking before plating 7.1.1.1 Mask a portion of the surface before plating. 7.1.1.2 Plate the unmasked portion of the surface. 7.1.1.3 Comp
39、letely remove the masking material. NOTEThe mask area should be as small as possible to minimize edge build-up. 7.1.2 Masking after plating 7.1.2.1 Mask all of the coating surface except that part to be dissolved. 7.1.2.2 Dissolve a small area of the coating. 7.1.2.3 Remove the masking material. NOT
40、E 1The preparation of the step shall be such that the top of the step is not marred or attacked in any way, the bottom of the step is free of all traces of the coating, and the coating is removed without any attack whatsoever of its substrate. NOTE 2The step shall slope so that the fringe displaceme
41、nt can be followed across the step. This requirement may be ignored if the step height or coating thickness is already known accurately enough to determine how many fringe spacings are covered by the fringe displacement. 7.2 Measuring procedure To obtain a fringe-line pattern the following procedure
42、 shall be observed: 7.2.1 Adjust the object focus and place the step in the field of the microscope. 7.2.2 Adjust the angle between the Fizeau plate and the specimen to obtain a fringe-line pattern. Adjust the angular position of the specimen so that the fringes are perpendicular to the step. 7.2.3
43、Adjust the brightness, field size and eyepiece focus to obtain optimum definition of the fringes. 7.2.4 Adjust the focus of the object again for maximum clarity. 7.2.5 Measure the displacement of a fringe across the step and the spacing between fringes with a filar micrometer. The coating thickness
44、is given by where %N is the number of fringes or fraction traversing the step; 2 is the incident light wavelength. In practice when making measurements with the filar eyepiece the fringe line offset method is used (seeFigure 3). Figure 3 d %N 2 2 - =ENISO3868:1994 BSI 11-1999 7 The coating thickness
45、 is calculated, with the fringe spacing and offset in filar units, in the following way: For the measurement of thin coatings on smooth substrates an improvement can be made by using the fringe-line width method. This procedure is particularly useful for measuring surface variations between0,002and0
46、,01m but this technique also has general application. A very smooth specimen is necessary to obtain well-defined lines in order to retain good definition when expanded as shown in Figure 4 and Figure 5. The procedure is as follows: 1) adjust the Fizeau plate tilt to spread the fringe line pattern un
47、til only two lines are in view (Figure 4); 2) calculate the actual line width: 3) adjust the Fizeau plate tilt to spread the fringe line pattern until only one broad fringe is in view (Figure 5); Figure 4 Figure 5 ENISO3868:1994 8 BSI 11-1999 4) calculate the coating thickness: The line width with a
48、 very smooth surface is about0,006m. Accuracy is0,003m, i.e. 50%. Thus a film thickness of0,002m can be measured with an accuracy of 0,001m. The fringe-line width method is dependent on the fringe lines being of uniform width. The uniformity of line width should be verified experimentally or with th
49、e instrument manufacturer. 8 Measuring precision The multiple-beam interferometer provides an absolute measure of the microscopic vertical surface variation ranging from0,002to2m. Precision is normally 0,001m in the range0,002to0,01m using the “fringe-line width method”, while it is normally 0,003m in the range0,01to2m. * as calculated in step 2.BSENISO3868:1995 BSI 11-1999 List of references See national foreword.BS EN ISO 3868:1995 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution B
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