ASTM B545-97
(Specification)Standard Specification for Electrodeposited Coatings of Tin
Standard Specification for Electrodeposited Coatings of Tin
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 X5.2 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 A 623M.
1.5 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: B 545 – 97
Standard Specification for
Electrodeposited Coatings of Tin
This standard is issued under the fixed designation B 545; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope A 623 Specification for Tin Mill Products, General Require-
ments
1.1 This specification covers the requirements for electrode-
A 623M Specification for Tin Mill Products, General Re-
posited (electroplated) coatings of tin applied to metallic
quirements (Metric)
articles. Tin coatings are used to provide a low contact-
B 32 Specification for Solder Metal
resistance surface, to protect against corrosion (see 1.2), to
B 183 Practice for Preparation of Low-Carbon Steel for
facilitate soldering, to provide anti-galling properties, and to be
Electroplating
a stopoff coating in the nitriding of high-strength steels.
B 242 Practice for Preparation of High-Carbon Steel for
1.2 Some corrosion can be expected from tin coatings
Electroplating
exposed outdoors. In normal indoor exposure, tin is protective
B 246 Specification for Tinned Hard-Drawn and Medium-
on iron, steel, nickel, copper, and their alloys. Corrosion can be
Hard-Drawn Copper Wire for Electrical Purposes
expected at discontinuities in the coating (such as pores) due to
B 281 Practice for Preparation of Copper and Copper-Base
galvanic couples formed between the tin and the underlying
Alloys for Electroplating and Conversion Coatings
metal through the discontinuities, especially in humid atmo-
B 320 Practice for Preparation of Iron Castings for Electro-
spheres. Porosity increases as the coating thickness decreases,
plating
so that minimum thicknesses must be specified for each
B 322 Practice for Cleaning Metals Prior to Electroplating
application. Parts coated with tin can be assembled safely in
B 374 Terminology Relating to Electroplating
contact with iron and steel, tin-coated aluminum, yellow
B 487 Test Method for Measurement of Metal and Oxide
chromated zinc, cadmium, and solder coatings. (See X5.2 for
Coating Thicknesses by Microscopical Examination of a
oxidation and corrosion properties.)
Cross Section
1.3 This specification applies to electroplated coatings of
B 499 Test Method for Measurement of Coating Thick-
not less than 99 % tin (except where deliberately alloyed for
nesses by the Magnetic Method: Nonmagnetic Coatings on
special purposes, as stated in X5.3) obtained from any of the
Magnetic Basis Metals
available tin electroplating processes (see 4.3).
B 504 Test Method for Measurement of Thickness of Me-
1.4 This specification does not apply to hot-dipped tin or
tallic Coatings by the Coulometric Method
other non-electrodeposited coating; it also does not apply to
B 507 Practice for Design of Articles to be Electroplated on
mill products. For mill products, refer to Specifications A 623
Racks
or A 623M.
B 542 Terminology Relating to Electrical Contacts and
1.5 The values stated in SI units are to be regarded as the
Their Use
standard. The values given in parentheses are for information
B 558 Practice for Preparation of Nickel Alloys for Electro-
only.
plating
1.6 This standard does not purport to address all of the
B 567 Test Method for Measurement of Coating Thickness
safety concerns, if any, associated with its use. It is the
by the Beta Backscatter Method
responsibility of the user of this standard to establish appro-
B 568 Test Method for Measurement of Coating Thickness
priate safety and health practices and determine the applica-
by X-Ray Spectrometry
bility of regulatory limitations prior to use.
B 571 Test Methods for Adhesion of Metallic Coatings
2. Referenced Documents
B 602 Test Method for Attribute Sampling of Metallic and
Inorganic Coatings
2.1 ASTM Standards:
1 2
This specification is under the jurisdiction of ASTM Committee B-8 on Annual Book of ASTM Standards, Vol 01.06.
Metallic and Inorganic Coatingsand is the direct responsibility of Subcommittee Annual Book of ASTM Standards, Vol 02.04.
B08.08.04 on Light Metals. Annual Book of ASTM Standards, Vol 02.05.
Current edition approved Oct. 10, 1997. Published February 1998. Originally Annual Book of ASTM Standards, Vol 02.03.
published as B 545 – 71. Last previous edition B 545 – 92. Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
B 545
B 659 Guide for Measuring Thickness of Metallic and
Class Minimum Thickness Typical Applications
A 2.5 μm (100 μin.) Mild service conditions, particularly where the
Inorganic Coatings
significant surface is shielded from the atmo-
B 678 Test Method for Solderability of Metallic-Coated
sphere (as in electronic connector housings). To
Products
provide corrosion and tarnish resistance where
greater thicknesses may be detrimental to the
B 697 Guide for Selection of Sampling Plans for Inspection
mechanical operation of the product (for ex-
of Electrodeposited Metallic and Inorganic Coatings
ample, small electrical spring contacts and re-
B 762 Method of Variables Sampling of Metallic and Inor- lays). Class A is often used for tin coatings that
4 are not to be soldered, but must function as
ganic Coatings
low-resistance electrical contact surfaces.
B 765 Guide to the Selection of Porosity Tests for Elec-
B 5 μm (200 μin.) Mild service conditions with less severe require-
trodeposits and Related Metallic Coatings ments than Class C (below). Applications are
as follows: precoating on solderable basis met-
B 809 Test Method for Porosity in Metallic Coatings by
als to facilitate the soldering of electrical com-
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
ponents; as a surface preparation for protective
painting; for antigalling purposes; and as a sto-
B 849 Specification for Pre-Treatments of Iron or Steel for
4 poff in nitriding. Also found on baking pans after
Reducing the Risk of Hydrogen Embrittlement
reflow.
B 850 Specification for Post-Coating Treatments of Iron or
C 8 μm (320 μin.), Moderate exposure conditions, usually indoors,
(10 μm (400 μin.) but more severe than Class B. Examples are
Steel for Reducing the Risk of Hydrogen Embrittlement
for steel substrates) electrical hardware (such as cases for relays
B 851 Specification for Automated Controlled Shot Peening
and coils, transformer cans, screened cages,
of Metallic Articles Prior to Nickel, Autocatalytic Nickel,
chassis, frames, and fittings) and for retention
of the solderability of solderable articles during
or Chromium Plating, or as a Final Finish
storage.
D 3951 Practice for Commercial Packaging
D 15 μm (600 μin.) Severe service, including exposure to damp-
(20 μm (800 μin.) ness and mild corrosion from moderate indus-
3. Terminology
for steel substrates) trial environments. Examples are fittings for gas
meters, automotive accessories (such as air
3.1 Definitions—Many of the terms used in this specifica-
cleaners and oil filters), and in some electronic
tion are defined in Terminology B 374 or B 542. applications.
E 30 μm (0.0012 in.) Very severe service conditions, including el-
3.1.1 rack-plating—an electrodeposition process in which
evated temperatures, where underlying metal
articles to be coated are mounted on racks or other fixtures
diffusion and intermetallic formation processes
during the process. are accelerated. Thicknesses of 30 to 125 μm
(0.0012 to 0.005 in.) may be required if the
3.1.2 significant surface—that portion of the surface of a
coating is subjected to abrasion or is exposed
coated article at which the coating is required to meet all of the
to slowly corrosive liquids or corrosive atmo-
spheres or gases. Thicker coatings are used for
requirements of the coating specification for that article;
water containers, threaded steel couplings of oil
significant surfaces are usually those that are essential to the
drilling strings, and seacoast atmospheres.
serviceability or function of the article, or that can be a source
Coatings subject to mild etchants are included.
F 1.5 μm (60 μin.) Similar to Class A, but for shorter-term contact
of corrosion products or tarnish films that interfere with the
applications and short shelf-life requirements,
function or desirable appearance of the article; significant
subject to purchaser approval.
surfaces shall be indicated on the drawings of the parts or by
the provision of suitably marked samples. 4.3 Surface Appearance Type (Electroplating Process):
3.1.3 undercoating (see 3.1.4)— also called an underplate
4.3.1 Matte Tin Electrodeposits—Coatings with a matte
in the electronics industry.
appearance are obtained from tin plating baths (stannate,
3.1.4 underplating—application of a metallic coating layer
sulfate, methylsulfonate, and fluoborate) used without the
between the basis metal or substrate and the topmost metallic
addition of any brightening agents. However, all matte baths
coating or coatings. The thickness of such an undercoating is
(except for stannate baths) do require the addition of grain-
usually greater than 0.8 μm (30 μin.). This is in contrast to
refiners, and often of other additives in order to produce the
strikes or flashes, whose thicknesses are generally much
desired matte finish.
smaller.
4.3.2 Bright Tin Electrodeposits—Bright coatings are ob-
tained when proprietary brightening agents are used in specific
4. Classification
bright tin plating baths.
4.1 General—Orders for articles to be plated in accordance
4.3.3 Flow-Brightened Electrodeposits— Flow-brightened
with this specification shall specify the service class (4.2) (and
coatings are obtained by heating the matte coating above the
underplating, if required), indicating the severity of service
melting point of tin for a few seconds, followed by quenching;
required for the coating. Other coatings variations, such as
palm oil and hydrogenated oils and fats are used as heat-
surface appearance type (4.3) or alloy composition (Appendix
transfer medium at a temperature of 260 6 8°C (500 6 14°F),
X5), are optional.
but other heating methods also are in use, such as hot air. The
4.2 Service Class:
maximum thickness for flow-brightening is, in most cases,
approximately 8 μm (300 μin.); thicker coatings tend to dewet.
The shape of the part is also a factor; flat surfaces dewet more
Annual Book of ASTM Standards, Vol 15.09. readily than wires or rounded shapes.
B 545
NOTE 1—Terms commonly used in soldering, such as dewet, are
requirement can be a minimum (arithmetic) mean thickness.
described in soldering textbooks (1) or reviews of solderability testing
NOTE 3—Specification of the coating thickness in terms of the mean is
(2). Some examples are given in Appendix X6.
normally made when the coated articles are small and relatively simple,
such as connector pins and terminals.
5. Ordering Information
NOTE 4—Thickness of electrodeposited coatings varies from point to
5.1 In order to make the application of this specification
point on the surfaces of a product (see Practice B 507). The thickness is
complete, the purchaser must supply the following information
less in interior corners and holes. Such surfaces are normally exempt from
to the seller in the purchase order and drawings:
the thickness requirement. If the full thickness is required on these
5.1.1 Title, ASTM designation number, and year of issue of surfaces, the electroplater will have to use special techniques that probably
will increase the cost of the process.
this specification;
NOTE 5—When articles are plated by mass plating techniques (such as
5.1.2 Deposit by classification (4.1), including thickness or
barrel plating), such measurement methods as “strip and weigh” or “weigh
service class (4.2);
before and after plating” may be used to determine the mean thickness.
5.1.3 Composition and metallurgical condition of the sub-
6.6 Adhesion—Adhesion of the coating shall be tested by
strate to be coated (6.1);
one of the methods given in Appendix X2. The coating should
5.1.4 Additional underplating, if required (6.8);
adhere to the basis metal when subjected to the agreed test;
5.1.5 Surface-appearance type (for example, matte, flow-
flaking or blistering of the coating is to be taken as evidence of
brightened, or bright), if required (4.3 and 6.2);
unsatisfactory adhesion.
5.1.6 Location of significant surfaces (3.1.2);
6.7 Integrity of the Coating:
5.1.7 Hydrogen embrittlement relief, if required (Supple-
6.7.1 Gross Defects/Mechanical Damage— Coatings shall
mentary Requirement S2); and
be free of visible mechanical damage and similar gross defects
5.1.8 Any other items needing agreement (for example,
when viewed at up to 43 magnification. For some applications,
6.5.2 and 8.5).
this requirement may be relaxed to allow for a small number of
6. Coating Requirements
such defects (per unit area), especially if they are outside of or
6.1 Substrate—The metal substrate shall be subjected to
on the periphery of significant surfaces (also see 6.7.2).
such surface preparation, cleaning, and electroplating proce-
6.7.2 Porosity—Almost all as-plated electrodeposits contain
dures as are necessary to yield deposits with the desired
some porosity. The amount of porosity in the coating that may
quality.
be tolerable depends on the severity of the environment that the
article is likely to encounter during service or storage. If the
NOTE 2—Careful preparation of metal surfaces is necessary in order to
pores are few in number, or away from significant surfaces,
assure good adhesion and quality. For suitable methods, see Practices
their presence can often be tolerated. Such acceptance (or
B 183, B 242, B 281, B 320, B 322, and B 558. Also see 6.6.
pass-fail) criteria, if required, should be part of the product
6.2 Electroplating shall be applied after all basis metal heat
specification for the particular article or coating requiring the
treatments and mechanical operations have been completed.
porosity test. See 8.5 for porosity testing.
6.3 Appearance—Tin coatings shall have the characteristic
6.8 Underplating:
appearance, including surface texture (4.3), for the process
6.8.1 For tin coatings in Class A and Class F (4.2) that will
used. The appearance shall be uniform throughout, insofar as
not be exposed to solder temperatures (especially those that
the basis metal will permit. They shall be adherent and visually
must function as electrically conductive surfaces), a nickel
free of blisters, pits, peeled areas, crack
...
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