ASTM B545-97(2009)
(Specification)Standard Specification for Electrodeposited Coatings of Tin
Standard Specification for Electrodeposited Coatings of Tin
ABSTRACT
This specification covers the requirements for electrodeposited tin coatings applied to metallic articles to provide a low contact resistance surface, to protect against corrosion, to facilitate soldering, to provide anti-galling properties, and to be a stop-off coating in the nitriding of high-strength steels. This specification does not cover hot-dipped tin or other non-electrodeposited coatings, and mill products. Coatings shall be grouped into six service classes, which is based on the minimum thickness and severity of service required for the coating, and three surface appearance types, which is based on the type electroplating process employed. The surface appearance types are matte tin electrodeposits, bright tin electrodeposits, and flow-brightened electrodeposits. Coatings shall be sampled, tested and conform accordingly to specified requirements as to appearance, purity, local and mean thickness, integrity (including gross defects, mechanical damage, and porosity), adhesion, solderability, and hydrogen embrittlement relief.
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 A623M.
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:B545 −97(Reapproved2009)
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.Anumber 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 Department of Defense.
1. Scope 2. Referenced Documents
1.1 Thisspecificationcoverstherequirementsforelectrode- 2.1 ASTM Standards:
posited (electroplated) coatings of tin applied to metallic A623Specification for Tin Mill Products, General Require-
articles. Tin coatings are used to provide a low contact- ments
resistance surface, to protect against corrosion (see 1.2), to A623MSpecification for Tin Mill Products, General Re-
facilitatesoldering,toprovideanti-gallingproperties,andtobe quirements [Metric]
a stopoff coating in the nitriding of high-strength steels. B32Specification for Solder Metal
B183Practice for Preparation of Low-Carbon Steel for
1.2 Some corrosion can be expected from tin coatings
Electroplating
exposed outdoors. In normal indoor exposure, tin is protective
B242Guide for Preparation of High-Carbon Steel for Elec-
oniron,steel,nickel,copper,andtheiralloys.Corrosioncanbe
troplating
expectedatdiscontinuitiesinthecoating(suchaspores)dueto
B246Specification for Tinned Hard-Drawn and Medium-
galvanic couples formed between the tin and the underlying
Hard-Drawn Copper Wire for Electrical Purposes
metal through the discontinuities, especially in humid atmo-
B281Practice for Preparation of Copper and Copper-Base
spheres. Porosity increases as the coating thickness decreases,
Alloys for Electroplating and Conversion Coatings
so that minimum thicknesses must be specified for each
B320Practice for Preparation of Iron Castings for Electro-
application. Parts coated with tin can be assembled safely in
plating
contact with iron and steel, tin-coated aluminum, yellow
B322Guide for Cleaning Metals Prior to Electroplating
chromated zinc, cadmium, and solder coatings. (See X5.2 for
B374Terminology Relating to Electroplating
oxidation and corrosion properties.)
B487Test Method for Measurement of Metal and Oxide
1.3 This specification applies to electroplated coatings of
Coating Thickness by Microscopical Examination of
not less than 99% tin (except where deliberately alloyed for
Cross Section
special purposes, as stated in X6.3) obtained from any of the
B499Test Method for Measurement of CoatingThicknesses
available tin electroplating processes (see 4.3).
by the Magnetic Method: Nonmagnetic Coatings on
Magnetic Basis Metals
1.4 This specification does not apply to hot-dipped tin or
other non-electrodeposited coating; it also does not apply to B504Test Method for Measurement of Thickness of Metal-
lic Coatings by the Coulometric Method
mill products. For mill products, refer to Specifications A623
or A623M. B507Practice for Design ofArticles to Be Electroplated on
Racks
1.5 The values stated in SI units are to be regarded as the
B542Terminology Relating to Electrical Contacts andTheir
standard. The values given in parentheses are for information
Use
only.
B558Practice for Preparation of Nickel Alloys for Electro-
1.6 This standard does not purport to address all of the
plating
safety concerns, if any, associated with its use. It is the
B567Test Method for Measurement of Coating Thickness
responsibility of the user of this standard to establish appro-
by the Beta Backscatter Method
priate safety and health practices and determine the applica-
B568Test Method for Measurement of Coating Thickness
bility of regulatory limitations prior to use.
by X-Ray Spectrometry
This specification is under the jurisdiction of ASTM Committee B08on
Metallic and Inorganic Coatingsand is the direct responsibility of Subcommittee
B08.06 on Soft Metals. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Sept. 1, 2009. Published December 2009. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ε1
approved in 1971. Last previous edition approved in 2004 as B545–97 (2004) . Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/B0545-97R09. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B545−97(2009)
B571Practice for Qualitative Adhesion Testing of Metallic 4.2 Service Class:
Coatings
Class Minimum Thickness Typical Applications
B602Test Method for Attribute Sampling of Metallic and
A 2.5 µm (100 µin.) Mild service conditions, particularly where the
Inorganic Coatings
significant surface is shielded from the
B659Guide for Measuring Thickness of Metallic and Inor-
atmosphere (as in electronic connector
housings). To provide corrosion and tarnish
ganic Coatings
resistance where greater thicknesses may be
B678Test Method for Solderability of Metallic-Coated
detrimental to the mechanical operation of the
Products
product (for example, small electrical spring
contacts and relays). Class A is often used for
B697Guide for Selection of Sampling Plans for Inspection
tin coatings that are not to be soldered, but
of Electrodeposited Metallic and Inorganic Coatings
must function as low-resistance electrical
B762Test Method of Variables Sampling of Metallic and
contact surfaces.
B 5 µm (200 µin.) Mild service conditions with less severe
Inorganic Coatings
requirements than Class C (below).
B765GuideforSelectionofPorosityandGrossDefectTests
Applications are as follows: precoating on
for Electrodeposits and Related Metallic Coatings solderable basis metals to facilitate the
soldering of electrical components; as a surface
B809Test Method for Porosity in Metallic Coatings by
preparation for protective painting; for
Humid Sulfur Vapor (“Flowers-of-Sulfur”)
antigalling purposes; and as a stopoff in
B849Specification for Pre-Treatments of Iron or Steel for nitriding. Also found on baking pans after
reflow.
Reducing Risk of Hydrogen Embrittlement
C 8 µm (320 µin.), Moderate exposure conditions, usually indoors,
B850GuideforPost-CoatingTreatmentsofSteelforReduc-
(10 µm (400 µin.) but more severe than Class B. Examples are
ing the Risk of Hydrogen Embrittlement for steel substrates) electrical hardware (such as cases for relays
and coils, transformer cans, screened cages,
B851Specification for Automated Controlled Shot Peening
chassis, frames, and fittings) and for retention
of MetallicArticles Prior to Nickel,Autocatalytic Nickel,
of the solderability of solderable articles during
storage.
or Chromium Plating, or as Final Finish
D 15 µm (600 µin.) Severe service, including exposure to
D3951Practice for Commercial Packaging
(20 µm (800 µin.) dampness and mild corrosion from moderate
for steel substrates) industrial environments. Examples are fittings
for gas meters, automotive accessories (such
3. Terminology
as air cleaners and oil filters), and in some
3.1 Definitions: electronic applications.
E 30 µm (0.0012 in.) Very severe service conditions, including
3.1.1 Many of the terms used in this specification are
elevated temperatures, where underlying metal
defined in Terminology B374 or B542.
diffusion and intermetallic formation processes
are accelerated. Thicknesses of 30 to 125 µm
3.1.2 rack-plating—an electrodeposition process in which
(0.0012 to 0.005 in.) may be required if the
articles to be coated are mounted on racks or other fixtures
coating is subjected to abrasion or is exposed
during the process. to slowly corrosive liquids or corrosive
atmospheres or gases. Thicker coatings are
3.1.3 significant surface—that portion of the surface of a
used for water containers, threaded steel
couplings of oil drilling strings, and seacoast
coatedarticleatwhichthecoatingisrequiredtomeetallofthe
atmospheres. Coatings subject to mild etchants
requirements of the coating specification for that article;
are included.
significant surfaces are usually those that are essential to the
F 1.5 µm (60 µin.) Similar to Class A, but for shorter-term contact
applications and short shelf-life requirements,
serviceability or function of the article, or that can be a source
subject to purchaser approval.
of corrosion products or tarnish films that interfere with the
function or desirable appearance of the article; significant
4.3 Surface Appearance Type (Electroplating Process):
surfaces shall be indicated on the drawings of the parts or by
4.3.1 Matte Tin Electrodeposits—Coatings with a matte
the provision of suitably marked samples.
appearance are obtained from tin plating baths (stannate,
3.1.4 undercoating (see 3.1.5)—also called an underplate in
sulfate, methylsulfonate, and fluoborate) used without the
the electronics industry. addition of any brightening agents. However, all matte baths
(except for stannate baths) do require the addition of grain-
3.1.5 underplating—application of a metallic coating layer
refiners, and often of other additives in order to produce the
between the basis metal or substrate and the topmost metallic
desired matte finish.
coating or coatings. The thickness of such an undercoating is
usually greater than 0.8 µm (30 µin.). This is in contrast to 4.3.2 Bright Tin Electrodeposits—Bright coatings are ob-
strikes or flashes, whose thicknesses are generally much tained when proprietary brightening agents are used in specific
smaller.
bright tin plating baths.
4.3.3 Flow-Brightened Electrodeposits—Flow-brightened
4. Classification
coatings are obtained by heating the matte coating above the
melting point of tin for a few seconds, followed by quenching;
4.1 General—Orders for articles to be plated in accordance
palm oil and hydrogenated oils and fats are used as heat-
with this specification shall specify the service class (4.2) (and
transfer medium at a temperature of 260 6 8°C (500 6 14°F),
underplating, if required), indicating the severity of service
required for the coating. Other coatings variations, such as but other heating methods also are in use, such as hot air. The
maximum thickness for flow-brightening is, in most cases,
surface appearance type (4.3) or alloy composition (Appendix
X6), are optional. approximately 8 µm (300 µin.); thicker coatings tend to dewet.
B545−97(2009)
The shape of the part is also a factor; flat surfaces dewet more more of the methods given in Practice B659 at any number of
readily than wires or rounded shapes. desired spots on the significant surface.
6.5.2 Mean Thickness—When specified by the purchaser,
NOTE 1—Terms commonly used in soldering, such as dewet, are
instead of being a local minimum requirement, the thickness
described in soldering textbooks (1) or reviews of solderability testing
(2). Some examples are given in Appendix X6.
requirement can be a minimum (arithmetic) mean thickness.
5. Ordering Information
NOTE 3—Specification of the coating thickness in terms of the mean is
normally made when the coated articles are small and relatively simple,
5.1 In order to make the application of this specification
such as connector pins and terminals.
complete,thepurchasermustsupplythefollowinginformation
NOTE 4—Thickness of electrodeposited coatings varies from point to
to the seller in the purchase order and drawings:
point on the surfaces of a product (see Practice B507). The thickness is
5.1.1 Title,ASTM designation number, and year of issue of
lessininteriorcornersandholes.Suchsurfacesarenormallyexemptfrom
this specification; the thickness requirement. If the full thickness is required on these
surfaces,theelectroplaterwillhavetousespecialtechniquesthatprobably
5.1.2 Deposit by classification (4.1), including thickness or
will increase the cost of the process.
service class (4.2);
NOTE 5—When articles are plated by mass plating techniques (such as
5.1.3 Composition and metallurgical condition of the sub-
barrelplating),suchmeasurementmethodsas“stripandweigh”or“weigh
strate to be coated (6.1);
before and after plating” may be used to determine the mean thickness.
5.1.4 Additional underplating, if required (6.8);
6.6 Adhesion—Adhesion of the coating shall be tested by
5.1.5 Surface-appearance type (for example, matte, flow-
one of the methods given in Appendix X2.The coating should
brightened, or bright), if required (4.3 and 6.2);
adhere to the basis metal when subjected to the agreed test;
5.1.6 Location of significant surfaces (3.1.3);
flakingorblisteringofthecoatingistobetakenasevidenceof
5.1.7 Hydrogen embrittlement relief, if required (Supple-
unsatisfactory adhesion.
mentary Requirement S2); and
5.1.8 Any other items needing agreement (for example,
6.7 Integrity of the Coating:
6.5.2 and 8.5).
6.7.1 Gross Defects/Mechanical Damage—Coatings shall
be free of visible mechanical damage and similar gross defects
6. Coating Requirements
whenviewedatupto4×magnification.Forsomeapplications,
6.1 Substrate—The metal substrate shall be subjected to
thisrequirementmayberelaxedtoallowforasmallnumberof
such surface preparation, cleaning, and electroplating proce-
such defects (per unit area), especially if they are outside of or
dures as are necessary to yield deposits with the desired
on the periphery of significant surfaces (also see 6.7.2).
quality.
6.7.2 Porosity—Almostallas-platedelectrodepositscontain
NOTE 2—Careful preparation of metal surfaces is necessary in order to
some porosity. The amount of porosity in the coating that may
assure good adhesion and quality. For suitable methods, see Practices
betolerabledependsontheseverityoftheenvironmentthatthe
B183, B242, B281, B320, B322, and B558. Also see 6.6.
article is likely to encounter during service or storage. If the
6.2 Electroplating shall be applied after all basis metal heat
pores are few in number, or away from significant surfaces,
treatments and mechanical operations have been completed.
their presence can often be tolerated. Such acceptance (or
6.3 Appearance—Tin coatings shall have the characteristic
pass-fail) criteria, if required, should be part of the product
appearance, including surface texture (4.3), for the process
specification for the particular article or coating requiring the
used. The appearance shall be uniform throughout, insofar as
porosity test. See 8.5 for porosity testing.
thebasismetalwillpermit.Theyshallbeadherentandvisually
6.8 Underplating:
freeofblisters,pits,peeledareas,cracks,nodules,andunplated
areas.Theyshallnotbestainedordiscolored.Flow-brightened 6.8.1 For tin coatings in ClassAand Class F (4.2) that will
coatingsshallbefreeofdewettedareasandbeads.Allsurfaces not be exposed to so
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