1、BRITISH STANDARD BS1872:1984 Specification for Electroplated coatings of tin UDC669.058.7:669.65:621.357.7BS1872:1984 This British Standard, having been prepared under the directionof the Surface Coatings(other than Paints) Standards Committee, was published under the authority ofthe Board of BSI an
2、d comes intoeffect on 29 February 1984 BSI02-1999 First published July 1952 First revision May 1964 Second revision February 1984 The following BSI references relate to the work on this standard: Committee reference SRC/3 Draft for comment 81/50223DC ISBN 0 580 13664 7 Committees responsible for thi
3、s British Standard The preparation of this British Standard was entrusted by the Surface Coatings (other than Paints) Standards Committee (SRC/-) to Technical Committee SRC/3 upon which the following bodies were represented: British Metal Finishing Suppliers Association British Telecommunications El
4、ectronic Components Industry Federation Electronic Engineering Association Institute of Metal Finishing International Tin Research Institute Metal Finishing Association Ministry of Defence Telecommunication Engineering and Manufacturing Association (TEMA) Amendments issued since publication Amd. No.
5、 Date of issue CommentsBS1872:1984 BSI 02-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Information to be supplied by the purchaser to the electroplater 1 4 Coating classification 2 5 Sampling 2 6 Heat treatment of steel 2 7 Undercoats 2 8 Coa
6、tings 2 Appendix A Guidance information 4 Appendix B Determination of undercoat thickness and coating thickness 5 Appendix C Adhesion tests 6 Appendix D Sulphur dioxide porosity test 6 Figure 1 Cabinet with door 8 Figure 2 Hooded cabinet 9 Table 1 Service condition and related recommended coating th
7、ickness 5 Publications referred to Inside back coverBS1872:1984 ii BSI 02-1999 Foreword This British Standard has been prepared under the direction of the Surface Coatings (other than Paints) Standards Committee. It applies to coatings of tin applied by electroplating to fabricated articles of ferro
8、us and non-ferrous metals to protect them from corrosion and to facilitate soldering. It is a revision of the 1964 edition, which is withdrawn, the main changes from which are: a) inclusion, as an appendix, of guidance notes drawing the attention of the user to factors which should be taken into acc
9、ount when electroplating with tin; b) deletion of the post-electroplating heat treatment recommendations for relief of hydrogen embrittlement because tin is now known to be virtually impervious to hydrogen; c) rationalization of the coating thicknesses recommended for different service conditions. T
10、he electroplating processes used are not identified because, if the requirements of the specified tests are met, any of them may be considered suitable. The qualities of suitable chemicals for use in the electroplating of tin are specified in BS1468. Attention is drawn to the legislative requirement
11、s for tin coatings used in the food industry set out, for example, in Statutory Instrument(1972) No.1957. Grade T2 of BS3338 is suitable for this purpose. It is essential, when specifying to BS1872, that the purchaser should state the classification code and the other information listed in 3.1 (and,
12、 if appropriate, 3.2). Merely to ask for the electroplating to be carried out to BS1872 without this information is insufficient. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compl
13、iance 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, pages1 to 10, an inside back cover and a back cover. This Standard has been updated (see copyright date) and may hav
14、e had amendments incorporated. This will be indicated in the amendment table on theinside front cover.BS1872:1984 BSI 02-1999 1 1 Scope This British Standard specifies requirements for electroplated coatings of tin. The coatings may be dull or bright as electroplated, or may be flow-melted by fusion
15、 after electroplating. These coatings are intended for use on ferrous and non-ferrous basis metals and also on printed wiring boards. A classification scheme is included by which the nature of the basis metal and undercoat, if any, and the tin coating thickness can be defined. This standard does not
16、 specify any requirements for the condition, finish or surface roughness of the basis material before electroplating (see A.3). NOTE 1Attention is drawn to BS9760, which specifies capability approval procedure and rules for printed circuits of assessed quality. The standard is not applicable to elec
17、troplating of: a) threaded components (see BS3382-5); b) tin coated copper wire (see BS4393); c) sheet, strip (see BS2920) or wire in the unfabricated form, or of coil springs; d) steels with tensile strengths greater than1000MPa because such steels require hydrogen embrittlement relief after platin
18、g (seeclause 6). This standard does not apply to coatings applied by other processes, e.g. autocatalytic, immersion or “electroless” processes. NOTE 2The titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this standard, the
19、following definitions, together with those given for other terms in BS5411-1, apply. 2.1 significant surface the part of the article covered or to be covered by the coating and for which the coating is essential for serviceability and/or appearance 2.2 flow-melting a process by which a coating is me
20、lted in order to impart desirable properties, such as brightness or improved solderability NOTE 1Less preferred terms applicable to this definition are “fusing”, “flow-brightening” and “reflowing”. NOTE 2See A.6. 3 Information to be supplied by the purchaser to the electroplater 3.1 Essential inform
21、ation. The following information shall be supplied by the purchaser to the electroplater: a) the number of this standard, i.e. BS1872; b) the nature of the basis material; c) the classification code of the coating required (see clause 4); d) the significant surface of the article to be electroplated
22、, indicated, for example, by drawings or by the provision of suitably marked samples; e) which method of adhesion testing from Appendix C is to be used (see 8.3); f) the sampling procedure to be adopted (seeclause 5); g) the positions where unavoidable contact marks and other defects are acceptable
23、(see 8.1); h) requirements, where they exist, regarding the purity of the coating. 3.2 Additional information. The following additional information may be required, and if so, shall be specified by the purchaser, if necessary in consultation with the electroplater: a) whether any heat treatment, wit
24、h the exception of that specified in clause 6 for certain steels, is required before electroplating; b) whether, for coatings whose minimum thickness is 10m or greater, the porosity test of Appendix D is to be applied (see 8.4), and if so: 1) the type, number, shape and dimensions of the test specim
25、ens to be used and whether cut edges to test specimens are to be protected; 2) the total exposed surface area of the specimen or specimens to be tested at one time, and the angle of inclination of flat test specimens, if other than that specified in D.4; c) whether solderability testing is required,
26、 and if so, the test methods and conditions to be applied (see 8.5); d) undercoats: 1) for a basis material of copper alloy, containing zinc as an alloying constituent, and where solderable properties are required, which method is to be used to determine the required undercoat thickness; 2) whether
27、an undercoat (or undercoats) is required for basis materials other than described in item d)1) above, and if so: i) its nature and minimum local thickness (see A.3 and A.4);BS1872:1984 2 BSI 02-1999 ii) which method is to be used to determine the required undercoat thickness; e) which method is to b
28、e used to determine the required coating thickness (see 8.2); f) whether any special pretreatment is required. If necessary, the purchaser shall supply a sample showing the required finish. 4 Coating classification Coatings shall be classified by a code consisting of five parts, each of which shall
29、be separated by an oblique stroke, as follows: a/b/c/d/e where Example. Fe/Ni/Sn/5/f represents a ferrous basis metal with a nickel undercoat, tin electroplated to a coating thickness of 5m and flow-melted. 5 Sampling The method of sampling shall be selected from the procedures given in either BS600
30、1 or BS6041. NOTEThe acceptance levels should be agreed between the purchaser and supplier. 6 Heat treatment of steel Severely cold-worked steel parts shall be stress-relieved before electroplating by either: a) heating for1h at a temperature of 190C to230C; or b) where treatment as in item a) would
31、 impair some steels which have been carburized, flame-hardened or induction-hardened and subsequently ground, heating at a lower temperature, e.g. at 170C for not less than1h. NOTEHydrogen embrittlement relief after electroplating. Because diffusion of hydrogen through tin coating is very slow, heat
32、 treatment for hydrogen embrittlement relief after electroplating is impractical. 7 Undercoats 7.1 General. If the basis material is a copper alloy containing zinc as an alloying constituent, and solderable properties are required, a nickel or copper undercoat of minimum local thickness2.5m shall be
33、 applied. In other cases where an undercoat is specified, its nature and minimum local thickness shall be specified by the purchaser (see A.3, A.4 and A.5.2). 7.2 Thickness. The thickness of any undercoat (or undercoats) shall be determined by either: a) one of the methods given in Appendix B, as sp
34、ecified by the purchaser; or b) any other method that the purchaser specifies, provided that it can be demonstrated to have an accuracy of 10% or better of the true local thickness, or is as good as or better than the methods given in Appendix B for the particular application. The method specified s
35、hall be the one that is expected to yield the most reliable results considering such factors as shape of component, size of component, undercoat material, basis material,etc. In the case of dispute, the microscopical method referred to in B.1.1 shall be used. 8 Coatings 8.1 Appearance. When examined
36、 by normal or corrected vision without other aid, the significant surface(s) of the electroplated article shall be clean, free from visible defects such as blisters, pits, roughness, nodules, cracks or unplated areas and shall not be stained or discoloured. Where fused, the surface shall be free fro
37、m de-wetted areas. The acceptability of defects on non-significant surfaces and the position of unavoidable contact marks shall be specified by the purchaser. If necessary, a sample showing the required finish shall be supplied or approved by the purchaser. 8.2 Thickness. The minimum thickness of th
38、e tin coating shall be specified in the coating classification code (see 3.1 c), clause 4, and A.8) from within the range 5m to 30m and the preferred thickness values shall be 5m, 10m, 20m and30m. a indicates the chemical symbol for the basis metal (or for the main constituent if an alloy); b indica
39、tes the undercoat, by the symbol “Ni” or “Cu” in the case of nickel or copper, or by the symbol “u” where other undercoat materials or systems are required see3.2 d), or by the symbol “z” where an undercoat is not required; c indicates the chemical symbol “Sn” for tin; d indicates the minimum coatin
40、g thickness, inm; e indicates the surface finish, by the symbol “m” if the coating is matt, or “b” if it is bright electroplated, or “f” if it is flow-melted.BS1872:1984 BSI 02-1999 3 The thickness of the coating shall be measured over a reference area (see BS5411-1) on any part of the significant s
41、urface that can be touched with a20mm diameter ball. In the case of articles having a significant surface area of100mm 2or greater, the minimum thickness shall be regarded as the minimum value of local thickness. In the case of articles having a significant surface area of less than100mm 2 , the min
42、imum thickness shall be regarded as the minimum value of average thickness (see A.5.2). In the case of printed wiring boards with electroplated-through holes, the measurements shall also be carried out on the surfaces within the holes, and not only the areas that can be touched with a20mm diameter b
43、all. In the case of flow-melted coatings, the measurements shall be carried out on the as-electroplated condition, prior to flow-melting (seeA.6). The thickness of the coating shall be determined by either: a) one of the methods given in Appendix B, as specified by the purchaser; or b) any other met
44、hod the purchaser specifies, provided that it can be demonstrated to have an accuracy of 10% or better of the true thickness, or is as good as or better than the methods given in Appendix B for the particular application. The method specified shall be one that is expected to yield the most reliable
45、results considering such factors as coating thickness, shape of component, size of component, coating material, basis material,etc. In the case of dispute, the microscopical method referred to in B.1.1 shall be used. 8.3 Adhesion. Coatings shall be subjected to one of the adhesion tests described in
46、 Appendix C, when there shall be no evidence of poor coating adhesion. 8.4 Porosity. If specified by the purchaser, coatings having a minimum thickness of10m or greater shall be subjected to a porosity test as follows: a) for ferrous basis material, the test given in BS5466-1; b) for non-ferrous bas
47、is material, the test given in Appendix D. In either case, there shall be no evidence of corrosion of the substrate when viewed with a magnification of 3 (see A.2.1). 8.5 Solderability 8.5.1 General materials and piece parts. If specified by the purchaser, solderability testing on general materials
48、and piece parts shall be carried out in accordance with method1 of test Ta of BS2011-2.1T:1981, using non-activated flux. If accelerated ageing is specified, the steam-ageing procedure (ageing1 of test Ta of BS2011-2.1T:1981) shall be used but the exposure time shall be24h. 8.5.2 Printed wiring boar
49、ds. If solderability testing is required on printed wiring boards, they shall be tested in accordance with test Tcof BS2011-2.1T:1981. If accelerated ageing is specified, the purchaser shall prescribe either a steam/oxygen or damp heat procedure.BS1872:1984 4 BSI 02-1999 Appendix A Guidance information A.1 General. The information in this appendix is intended to draw the attention of the user to: a) certain properties of tin which, if not appreciated, may lead to inappropriate use of the coating; b) properties and preparation of the basis material; c) ele
