1、 CEN EN*IS0*3868 94 3404589 0095073 951 = BRITISH STANDARD Metallic and other non-organic coatings - Measurement of coating thicknesses - Fizeau multiple- beam interferometry method The European Standard EN IS0 3868 : 1994 has the status of a ritish Standard BS EN IS0 3868 : 1995 BS EN IS0 3868 : 19
2、95 CEN EN*ISO*3b 94 W 3404589 0095074 898 w This British Standard, having been prepared under the direction of the Sector Board for Materials and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 May 1995 O BSI 1995 The following BSI references relate to
3、 the work on this standard: Committee reference STI/39 Draft for comment 76/50825 DC ISBN O 580 23975 6 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
4、 the following bodies were represented: Aluminium Federation Aluminium Finishing Association British Industrial Fasteners Federation British Jewellerc Association Institute of Corrosion Institute of Metal Finishing Metal Finishing Association Ministry of Defence NDT Trade Association Royal Society o
5、f Chemistry Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd. No. Date Text affected CEN EN*IS0*3BbB 94 3404589 0095075 724 BS EN IS0 3868 : 1995 Contents Page Committees responsible Inside front cover National foreword 11 Foreword 2 Method 1 2 Principle 3 D
6、efinitions 4 Equipment Scope and field of application 5 Factors affecting the measuring accuracy 3 6 Calibration 7 Procedure 5 5 8 Measuring precision 6 i CEN EN*IS0*38b8 94 3404589 009507b bb0 I BS EN IS0 3868 : 1995 National foreword This British Standard has been prepared by Echnieal Committee ST
7、I/39, and is the English language version of EN IS0 3868 : 1994 Metallic and othm non-organic coatings - Measurement of coating thicknesses - Fizeau rnultipk-beam interferometry method published by the European Committee for Standardization (CEN). Compliance with a British Standard does not of itsel
8、f confer immunity from legal obligations. ii CEN EN*ISO*38b8 94 W 3404589 0095077 5T7 EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN IS0 3868 October 1994 ICs 25.220.30 Descriptors: coatings, metal coatings, dimensional measurement, thickness, optical measurement, interferometers English versi
9、on Metallic and other non-organic coatings - Measurement of coating thicknesses - Fizeau multiple-beam interferometry method (IS0 3868 : 1976) Revtemens mtalliques et autres revtements non organiques - Mesurage de l?paisseur - Mthode base sur le principe de Fizeau d?interfromtrie faisceaux multiples
10、 (IS0 3868 : 1976) Metallische und andere anorganische Schichten - Messung von Schichtdicken - Fizeau- Vielstrahl-interferem- Verfahren (IS0 3868 : 1976) This European Standard was approved by CEN on 1994-10-26. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulat
11、e 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 any CEN member. This European Standard exist
12、s 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. CEN members are the national standards bodi
13、es 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 Europisches Komitee fr Normung Central Secre
14、tariat: rue de Stassart 36, B- 1050 Brussels O 1995 Copyright reserved to CEN members Ref. No. EN IS0 3868 : 1994 E CEN EN*IS0*38b8 94 81 3404589 0095078 433 Page 2 EN IS0 3868 : 1994 Foreword This European Standard was taken over by the Rchnical Committee CEN/TC 262, Protection of metallic material
15、s against corrosion, from the work of ISO/Tc 107, Metallic and other inorganic coatings, of the International Organization for Standardization (ISO). CEN/TC 262 had decided to submit the final draft for formal vote. The result was positive. This EuropeanStandard shall be given the status of a nation
16、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 CENKENELEC Internal Regulations, the following countries are bound to implement this European St
17、andard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, United Kingdom. CEN EN*ISO*38b8 94 W 3404589 0095079 37T = Page 3 EN IS0 3868 : 1994 Metallic and other non-organic coatings - Measurem
18、ent of coating thicknesses - Fizeau multiple-beam interferometry method 1 This International Standard specifies a method for the measurement of the thickness of thin, highly reflective coatings (up to 2pm) by the use of Fizeau multiple-beam interferometry. The method described cannot be applied to v
19、itreous enamel coa ti ngs. SCOPE AND FIELD OF APPLICATION 2 PRINCIPLE By completely dissolving a small area of the coating without attack of its substrate (or by masking before plating), a step is formed from the surface of the coating to that of its substrate. The height of this step is measured wi
20、th a multiple-beam interferometer. A monochromatic light beam is reflected back and forth between the specimen surface and a superimposed trans- parent mirror serving as a planar reference plate, so as to produce a pattern of interference fringes observed through a low-power microscope. The referenc
21、e 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 a shift in the fringe pattern. A shift of one full fringe spacing is equivalent to a vertical displace- ment of 1/2 of the wavelengt
22、h 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 filar micrometer eyepiece : A device for observing and measuring an image. It includes an adjustable lens, a hairline that is mov
23、ed 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 to the absolute unit of length. 3.3 Fizeau plate : An optically flat, smooth surface with high reflectivity and low absorpti
24、on. 3.4 fringe lines : The dark lines caused by interference of I ight waves. 3.5 hairlines : The part of the filar eyepiece moved by means of the graduated knob to measure fringe line-spacing and offset. 3.6 offset : The displacement of a fringe line which occurs when it encounters a vertical varia
25、tion on the surface of a specimen. 3.7 spacing : The distance between fringe lines. 4 EQUIPMENT The instrument employs : a) a beam of monochromatic light; b) optics to direct the light through a specially coated Fizeau plate which comes into contact with the specimen at a slight angle and forms an a
26、ir 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 of the fringe lines can be interpreted to determine an extremely accurate contour map of the specimen surface. 5 FACTORS AFFECTING TH
27、E MEASURING ACCU- RACY The following factors may affect the accuracy of a coating thickness measurement : 5.1 Reflective overcoat In order to obtain dark, narrow fringe lines necessary to achieve an accurate measurement, and in order to avoid errors due to different phase shifts, when light reflects
28、 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 reflective and the errors due to phase shift are known and corrected for, then the reflective layer can be avoided. CEN EN*ISO*3868 94 34
29、04589 0095080 091 Page 4 EN IS0 3868 : 1994 5.2 Step form For specimens with a coating thickness of less than 0.3 pm special fabrication is not normally necessary. If the step being measured is abrupt, so that it is not possible to follow the fringes across the step, it will not be possible to obser
30、ve how many full fringe intervals of dis- placement 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 interferometry, etc. By the appropriate method the stem can ofte
31、n be made less abrupt so that each fringe can be followed across each step. The optimum angle is normally in the range 95 to 100“. Substrate Coating Reflective overcoat FIGURE 1 I I I Reflective coat Film edge for coatings lea than 0,3 pm thick - Coating Ref I ect ive overcoat Film edge for coatings
32、 over 0.3 pm thick FIGURE 2 CEN EN*IS0*38b8 79 3409589 0095081 T28 ai 5.3 Reading accuracy Possible backlash errors may be eliminated by always making the final adjustment of the micrometer in the same direct i on. 5.4 Surface flatness A very flat surface is required, especially for measuring thickn
33、esses between 0,001 and 0.01 pm, in order to produce lines of good definition when expanded. If the surface is not flat, the fringes may be curved, making accurate measurement more difficult. The loss of accuracy will increase as the radius of curvature decreases. 5.5 Step definition In order to mak
34、e good thickness measurements, it is necess- ary to have a good step definition. If the step is poorly defined the fringe lines are not straight and it is 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 acr
35、oss the step. Poor definition may result from the step preparation method. (If the coating whose thickness is to be measured has been obtained by electroplating, 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 den
36、sity 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 roughness such that the fringe lines become irregu- lar causes uncertainty in measurement of coating thickness by making the fringes less sharp, very d
37、iffuse, and poorly defined. 5.7 Cleanliness To achieve the best results it is necessary that the surface has no residues from manufacturing, fingerprints, 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
38、 and dissolution of the coating substrate or incomplete dissolution of the coating will lead to an erroneous measurement. 6 CALIBRATION The measurement obtained by multiple-beam interfero- metry is absolute and calibration is not required. 7 PROCEDURE 7.1 Step preparation 7.1.1 Masking before platin
39、g 7.1.1.1 Mask a portion of the surface before plating. Page 5 EN IS0 3868 : 1994 7.1 .I .2 Plate the unmasked portion of the surface. 7.1 .I .3 Completely remove the masking material. NOTE - The mask area should be as small as possible to minimize edge buildup. 7.1.2 Masking after plating 7.1.2.1 M
40、ask 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. NOTES 1 The 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 t
41、races of the coating, and the coating is removed without any attack whatsoever of its substrate. 2 The step shall slope so that the fringe displacement can be followed across the step. This requirement may be ignored if the step height or coating thickness is already known accurately enough to deter
42、mine how many fringe spacings are covered by the fringe displacement. 7.2 Measuring procedure To obtain a fringe-line pattern the following procedure 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 a
43、nd the specimen to obtain a fringe-line pattern. Adjust the angular position of the specimen so that the fringes are perpen- dicular to the step. 7.2.3 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 max
44、imum clari ty . 7.2.5 Measure the displacement of a fringe across the step and the spacing between fringes with a filar micrometer. The coating thickness is given by h d=AN- 2 where AN is the number of fringes or fraction traversing the step; A is the incident light wavelength. CEN EN*IS0*3868 94 34
45、04589 O095082 964 Page 6 EN IS0 3868 : 1994 In practice when making measurements with the filar eye- piece the fringe line offset method is used (see figure 3). FIGURE 3 The coating thickness is calculated, with the fringe spacing and offset in filar units, in the following way : fringe offset (fila
46、r units) A fringe spacing (filar units) 2 x-= height of surface variation 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 between 0,002 and 0.01 pm but t
47、his 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 figures 4 and 5. The procedure is as follows : 1) adjust the Fizeau plate tilt to spread the fringe line pattern until only two li
48、nes are in view (figure 4); FIGURE 4 2) calculate the actual line width : relative line width (filar units) h X-= actual line width line spacing (filar units) 2 3) adjust the Fizeau plate tilt to spread the fringe line pattern until only one broad fringe is in view (figure 5); Relative line width Of
49、fset -IL- FIGURE 5 4) calculate the coating thickness line offset (filar units) actual line - film relative line width width“ thickness (filar units) - X The line width with a very smooth surface is about 0,006 prn. Accuracy is 0,003 pm, .e. tr 50 %. Thus a film thickness of 0,002 pm can be measured with an accuracy of ? 0,001 pm. 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 the instrument manufacturer. 8 MEASURING PRECISI
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