ASTM B545-22

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B545 − 13 (Reapproved 2021) B545 − 22
Standard Specification for
Electrodeposited Coatings of Tin
This standard is issued under the fixed designation B545; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope Scope*
1.1 This specification covers the requirements for electrodeposited (electroplated) coatings of tin applied to metallic articles. Tin
coatings are used to provide a low contact-resistance surface, to protect against corrosion (see 1.2), to facilitate soldering, to
provide anti-galling properties, and to be a stopoff coating in the nitriding of high-strength steels.
1.2 Some corrosion can be expected from tin coatings exposed outdoors. In normal indoor exposure, tin is protective on iron, steel,
nickel, copper, and their alloys. Corrosion can be expected at discontinuities in the coating (such as pores) due to galvanic couples
formed between the tin and the underlying metal through the discontinuities, especially in humid atmospheres. Porosity increases
as the coating thickness decreases, so that minimum thicknesses must be specified for each application. Parts coated with tin can
be assembled safely in contact with iron and steel, tin-coated aluminum, yellow chromated zinc, cadmium, and solder coatings.
(See X5.1 for oxidation and corrosion properties.)
1.3 This specification applies to electroplated coatings of not less than 99 % tin (except where deliberately alloyed for special
purposes, as stated in X6.3) obtained from any of the available tin electroplating processes (see 4.3).
1.4 This specification does not apply to hot-dipped tin or other non-electrodeposited coating; it also does not apply to mill
products. For mill products, refer to Specifications A623 or A623M.
1.5 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information
only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
This specification is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.06 on Soft
Metals.
Current edition approved May 1, 2021Nov. 15, 2022. Published May 2021December 2022. Originally approved in 1971. Last previous edition approved in 20132021 as
B545 – 13.B545 – 13(2021). DOI: 10.1520/B0545-13R21.10.1520/B0545-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B545 − 22
A623 Specification for Tin Mill Products, General Requirements
A623M Specification for Tin Mill Products, General Requirements [Metric]
B32 Specification for Solder Metal
B183 Practice for Preparation of Low-Carbon Steel for Electroplating
B242 Guide for Preparation of High-Carbon Steel for Electroplating
B246 Specification for Tinned Hard-Drawn and Medium-Hard-Drawn Copper Wire for Electrical Purposes
B281 Practice for Preparation of Copper and Copper-Base Alloys for Electroplating and Conversion Coatings
B320 Practice for Preparation of Iron Castings for Electroplating
B322 Guide for Cleaning Metals Prior to Electroplating
B374 Terminology Relating to Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
B499 Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis
Metals
B504 Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
B507 Practice for Design of Articles to Be Electroplated on Racks
B542 Terminology Relating to Electrical Contacts and Their Use
B558 Practice for Preparation of Nickel Alloys for Electroplating
B567 Test Method for Measurement of Coating Thickness by the Beta Backscatter Method
B568 Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
B571 Practice for Qualitative Adhesion Testing of Metallic Coatings
B602 Guide for Attribute Sampling of Metallic and Inorganic Coatings
B659 Guide for Measuring Thickness of Metallic and Inorganic Coatings
B678 Test Method for Solderability of Metallic-Coated Products
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B762 Guide of Variables Sampling of Metallic and Inorganic Coatings
B765 Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
B809 Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor (“Flowers-of-Sulfur”)
B849 Specification for Pre-Treatments of Iron or Steel for Reducing Risk of Hydrogen Embrittlement
B850 Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement
B851 Specification for Automated Controlled Shot Peening of Metallic Articles Prior to Nickel, Autocatalytic Nickel, or
Chromium Plating, or as Final Finish
D3951 Practice for Commercial Packaging
3. Terminology
3.1 Definitions:
3.1.1 Many of the terms used in this specification are defined in Terminology B374 or B542.
3.1.2 rack-plating—rack-plating, n—an electrodeposition process in which articles to be coated are mounted on racks or other
fixtures during the process.
3.1.3 significant surface—surface, n—that portion of the surface of a coated article at which the coating is required to meet all of
the requirements of the coating specification for that article; significant surfaces are usually those that are essential to the
serviceability or function of the article, or that can be a source of corrosion products or tarnish films that interfere with the function
or desirable appearance of the article; significant surfaces shall be indicated on the drawings of the parts or by the provision of
suitably marked samples.
3.1.4 undercoating (see 3.1.5)—), n—also called an underplate in the electronics industry.
3.1.5 underplating—underplating, n—application of a metallic coating layer between the basis metal or substrate and the topmost
metallic coating or coatings. The thickness of such an undercoating is usually greater than 0.8 μm (30 μin.). 0.8 μm (30 μin.). This
is in contrast to strikes or flashes, whose thicknesses are generally much smaller.
4. Classification
4.1 General—Orders for articles to be plated in accordance with this specification shall specify the service class (4.2) (and
underplating, if required), indicating the severity of service required for the coating. Other coatings variations, such as surface
appearance type (4.3) or alloy composition (Appendix X6), are optional.
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4.2 Service Class:
Class Minimum Thickness Typical Applications
A 2.5 μm (100 μin.) Mild service conditions, particularly where the
significant surface is shielded from the
atmosphere (as in electronic connector
housings). To provide corrosion and tarnish
resistance where greater thicknesses may be
detrimental to the mechanical operation of the
product (for example, small electrical spring
contacts and relays). Class A is often used for
tin coatings that are not to be soldered, but
must function as low-resistance electrical
contact surfaces.
B 5 μm (200 μin.) Mild service conditions with less severe
requirements than Class C (below).
Applications are as follows: precoating on
solderable basis metals to facilitate the
soldering of electrical components; as a surface
preparation for protective painting; for
antigalling purposes; and as a stopoff in
nitriding. Also found on baking pans after
reflow.
C 8 μm (320 μin.), Moderate exposure conditions, usually indoors,
(10 μm (400 μin.) but more severe than Class B. Examples are
for steel substrates) electrical hardware (such as cases for relays
and coils, transformer cans, screened cages,
chassis, frames, and fittings) and for retention
of the solderability of solderable articles during
storage.
D 15 μm (600 μin.) Severe service, including exposure to
(20 μm (800 μin.) dampness and mild corrosion from moderate
for steel substrates) industrial environments. Examples are fittings
for gas meters, automotive accessories (such
as air cleaners and oil filters), and in some
electronic applications.
E 30 μm (0.0012 in.) Very severe service conditions, including
elevated temperatures, where underlying metal
diffusion and intermetallic formation processes
are accelerated. Thicknesses of 30 to 125 μm
(0.0012 to 0.005 in.) may be required if the
coating is subjected to abrasion or is exposed
to slowly corrosive liquids or corrosive
atmospheres or gases. Thicker coatings are
used for water containers, threaded steel
couplings of oil drilling strings, and seacoast
atmospheres. Coatings subject to mild etchants
are included.
F 1.5 μm (60 μin.) Similar to Class A, but for shorter-term contact
applications and short shelf-life requirements,
subject to purchaser approval.
4.3 Surface Appearance Type (Electroplating Process):
4.3.1 Matte Tin Electrodeposits—Coatings with a matte appearance are obtained from tin plating baths (stannate, sulfate,
methylsulfonate, and fluoborate) used without the addition of any brightening agents. However, all matte baths (except for stannate
baths) do require the addition of grain-refiners, and often of other additives in order to produce the desired matte finish.
4.3.2 Bright Tin Electrodeposits—Bright coatings are obtained when proprietary brightening agents are used in specific bright tin
plating baths.
4.3.3 Flow-Brightened Electrodeposits—Flow-brightened coatings are obtained by heating the matte coating above the melting
point of tin for a few seconds, followed by quenching; palm oil and hydrogenated oils and fats are used as heat-transfer medium
at a temperature of 240 to 260°C260 °C (464 to 500°F),500 °F), but other heating methods also are in use, such as hot air. The
maximum thickness for flow-brightening is, in most cases, approximately 8 μm (300 μin.). 8 μm (300 μin.). The shape of the part
is also a factor; flat surfaces dewet more readily than wires or rounded shapes.
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NOTE 1—Terms commonly used in soldering, such as dewet, are described in soldering textbooks (1) or reviews of solderability testing (2). Some
examples are given in Appendix X6.
5. Ordering Information
5.1 In order to make the application of this specification complete, the purchaser must supply the following information to the
seller in the purchase order and drawings:
5.1.1 Title, ASTM designation number, and year of issue of this specification;
5.1.2 Deposit by classification (4.1), including thickness or service class (4.2);
5.1.3 Composition and metallurgical condition of the substrate to be coated (6.1);
5.1.4 Additional underplating, if required (6.8);
5.1.5 Surface-appearance type (for example, matte, flow-brightened, or bright), if required (4.3 and 6.2);
5.1.6 Location of significant surfaces (3.1.3);
5.1.7 Hydrogen embrittlement relief, if required (Supplementary Requirement S2); and
5.1.8 Any other items needing agreement (for example, 6.5.2, 8.4 and 8.5).
6. Coating Requirements
6.1 Substrate—The metal substrate shall be subjected to such surface preparation, cleaning, and electroplating procedures as are
necessary to yield deposits with the desired quality.
NOTE 2—Careful preparation of metal surfaces is necessary in order to assure good adhesion and quality. For suitable methods, see Practices B183, B242,
B281, B320, B322, and B558. Also see 6.6.
6.2 Electroplating shall be applied after all basis metal heat treatments and mechanical operations have been completed.
6.3 Appearance—Tin coatings shall have the characteristic appearance, including surface texture (4.3), for the process used. The
appearance shall be uniform throughout, insofar as the basis metal will permit. They shall be adherent and visually free of blisters,
pits, peeled areas, cracks, nodules, and unplated areas. They shall not be stained or discolored. Flow-brightened coatings shall be
free of dewetted areas and beads. All surfaces shall be substantially free of grease or oil used in the flow-brightening process.
6.4 All tin-coated articles shall be clean and undamaged. When necessary, preliminary samples showing the finish shall be
supplied to and approved by the purchaser. Where a contact mark is inevitable, its location shall be subject to agreement between
the supplier and the purchaser.
6.5 Thickness of Coatings—Tin coatings on articles shall conform to the thickness requirements specified in 4.2 as to the minimum
thickness on significant surfaces.
6.5.1 Local Thickness—The thickness values specified in 4.2 are the minimum local thicknesses measured by one or more of the
methods given in Practice B659 at any number of desired spots on the significant surface.
6.5.2 Mean Thickness—When specified by the purchaser, instead of being a local minimum requirement, the thickness requirement
can be a minimum (arithmetic) mean thickness.
NOTE 3—Specification of the coating thickness in terms of the mean is normally made when the coated articles are small and relatively simple, such as
connector pins and terminals.
The boldface numbers in parentheses refer to the list of references at the end of this specification.
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NOTE 4—Thickness of electrodeposited coatings varies from point to point on the surfaces of a product (see Practice B507). The thickness is less in interior
corners and holes. Such surfaces are normally exempt from the thickness requirement. If the full thickness is required on these surfaces, the electroplater
will have to use special techniques that probably will increase the cost of the process.
NOTE 5—When articles are plated by mass plating techniques (such as barrel plating), such measurement methods as “strip and weigh” or “weigh before
and after plating” may be used to determine the mean thickness.
6.6 Adhesion—Adhesion of the coating shall be tested by one of the methods given in Practice B571. The coating should adhere
to the basis metal when subjected to the agreed test; flaking or blistering of the coating is to be taken as evidence of unsatisfactory
adhesion.
6.7 Integrity of the Coating:
6.7.1 Gross Defects/Mechanical Damage—Coatings shall be free of visible mechanical damage and similar gross defects when
viewed at up to 4× magnification. For some applications, this requirement may be relaxed to allow for a small number of such
defects (per unit area), especially if they are outside of or on the periphery of significant surfaces (also see 6.7.2), as allowed by
the purchaser.
6.7.2 Porosity—Almost all as-plated electrodeposits contain some porosity. The amount of porosity in the coating that may be
tolerable depends on the severity of the environment that the article is likely to encounter during service or storage. If the pores
are few in number, or away from significant surfaces, their presence can often be tolerated. Such acceptance (or pass-fail) criteria,
if required, should be part of the product specification for the particular article or coating requiring the porosity test. See 8.5 for
porosity testing.
6.8 Underplating:
6.8.1 For tin coatings in Class A and Class F (4.2) that will not be exposed to solder temperatures (especially those that must
function as electrically conductive surfaces), a nickel underplate or undercoating of at least 1.3 μm (50 μin.) 1.3 μm (50 μin.) shall
be applied before tin plating.
6.8.2 To prevent zinc migration and impairment of solderability during service or storage, substrates of brass or other copper alloys
containing more than 5 % zinc must have a copper undercoating of at least 2.5 μm 2.5 μm (100 μin.), μin.), or a nickel undercoating
of at least 1.3 μm (50 μin.), 1.3 μm (50 μin.), prior to tin plating. A thicker coating of nickel may be required in some situations
for additional retardation.
6.9 Hydrogen Embrittlement Relief—High-tensile strength steels and severely cold-worked steels are susceptible to embrittlement
by hydrogen in both cleaning and electroplating operations. See Supplementary Requirements S1 and S2 for details.
6.10 Deposit Purity—The tin coating shall be not less than 99 % 99 % tin, when tested in accordance with 8.1. Deliberate alloying
for special purposes shall only be allowed when specifically agreed upon between the purchaser and seller (see X6.3).
7. Sampling
7.1 The sampling plan used for inspection of a quantity of the coated articles shall be as agreed upon between the purchaser and
the supplier.
NOTE 6—The procedure for sampling is accomplished by selecting a relatively small number of the finished articles at random. These articles (the
inspection lots) are inspected and classified as complying or not complying with the requirements of the specification. The size of the sample and the
criteria of compliance are determined by the application of statistics. The procedure is known as sampling inspection. Three standards, Test Method B602,
Guide B697, and Test Method B762, contain sampling plans that are designed for the sampling inspection of coatings.
Test Method B602 contains four sampling plans, three for use with tests that are non-destructive and one for use when they are destructive. The buyer
and seller may agree on the plan or plans to be used. If they do not, Test Method B602 identifies the plan to be used.
Guide B697 provides a large number of plans and also provides guidance in the selection of a plan. When Guide B697 is specified, the buyer and seller
must agree on the plan to be used.
Test Method B762 can be used only for coating requirements that have a numerical limit, such as coating thickness. The test must yield a numerical
value, and certain statistical requirements must be met. Test Method B762 contains several plans and also provides instructions for calculating plans to
meet special needs. The buyer and seller may agree on the plan or plans to be used. If they do not, Test Method B762 identifies the plan to be used.
7.2 An inspection lot shall be defined as a collection of coated articles that meet the following requirements: they are of the same
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kind; have been produced to the same specifications; have been coated by a single supplier at one time, or at approximately the
same time, under essentially identical conditions; and are submitted for acceptance or rejection as a group.
7.3 Special Test Specimens—It may be preferable to use special test specimens to represent product in process control or in
acceptance inspection when, for example, destructive tests are used and it is desirable not to destroy product or if the test specimen
is better adapted to the test. The use of special test specimens, their number, the material from which they are made, their size and
shape, and the conditions of their coating shall be as agreed upon by the purchaser and the seller.
8. Test Methods
8.1 Deposit Purity—Atomic absorption or energy dispersion spectrophotometry, or any other methods with a demonstrated
uncertainty of less than 10 % of the component measured, may be used to determine impurities. Initial scanning should be
conducted for all elements in order to detect any unknown or unexpected impurities. Determine deposit purity by subtracting the
total impurities from 100 %.
NOTE 7—Deposit purity is best determined on samples of the actual product (see Section 7). If special test specimens are used (7.3), care must be taken
to arrange the specimens so as to electroplate them under the same conditions as typical production pieces.
8.2 Thickness:
8.2.1 Standard Thickness—The coating thickness shall be measured at locations on significant surfaces by one of the following
test methods: Test Methods B487, B499 (magnetic substrates only), B504, B567, and B568. Practice B659 may be consulted to
determine the most appropriate test method.
8.2.1.1 When Methods B504 and B568 are used with tin platings that have been alloyed with more than 0.5 % of lead, bismuth,
or antimony to reduce whiskering (see X6.3.2.5), the standard shall have the same composition as the coating. When Test Method
B567 is used to measure these types of coatings, the measuring instrument shall be calibrated with thickness standards that have
the same substrate and same composition of coating as the product.
8.2.2 Mean Thickness—If the entire surface of the article is a significant surface, the mean thickness can also be determined by
the method described in Appendix X1. Also see Note 5.
8.3 Adhesion—Adhesion of the coating shall be tested by one of the recommended methods of Practice B571 (see Appendix X2).
8.4 Solderability—For coatings that must be solderable, the method by which solderability is tested shall be specified. Three test
methods are described in Appendix X3, while a simple dip test is given in Test Method B678. The purchaser shall specify whether
the tested articles are to receive an artificial aging treatment, such as that given in Test Method B678, so as to demonstrate whether
the articles may be expected to retain their solderability during long storage periods.
8.5 Porosity and Gross Defects Testing:
8.5.1 Coatings on articles of steel (or iron) having a local thickness of 10 μ (0.4 mil) 10 μ (0.4 mil) or greater should be subjected
to the test given in Appendix X5.
8.5.2 Fo
...