ASTM B520-12(2023)

Standard Specification for Tin-Coated, Copper-Clad Steel Wire for Electronic Application

ABSTRACT
This specification covers tin-coated, copper-clad steel wires for electronic applications. The four classes of steel wires considered here are: hard-drawn wires with 30% nominal conductivity (Class T30HS); annealed wires with 30% nominal conductivity (Class T30A); hard-drawn wires with 40% nominal conductivity (Class T40HS); and annealed wires with 40% nominal conductivity (Class T40A). Specimens shall go through tests and shall adhere to specified requirements for dimensions, electrical resistivity, tensile strength, and coating continuity and adherence.
SCOPE
1.1 This specification covers tin-coated copper-clad steel wire for electronic application.  
1.2 Four classes of tin-coated copper-clad steel wire are covered as follows:  
1.2.1 Class T30HS—Nominal 30 % conductivity, hard-drawn,  
1.2.2 Class T30A—Nominal 30 % conductivity, annealed,  
1.2.3 Class T40HS—Nominal 40 % conductivity, hard-drawn, and  
1.2.4 Class T40A—Nominal 40 % conductivity, annealed.  
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3.1 Exception—The SI values for resistivity and volume are to be regarded as standard.  
1.4 The following safety hazards caveat pertains only to the test method portion, Section 6, of this specification: 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. (Warning—Consideration should be given to toxicity and flammability when selecting solvent cleaners.)  
1.5 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.

General Information

• Status: Published
• Publication Date: 30-Sep-2023
• ICS: 29.060.10 - Wires
• Technical Committee: B01 - Electrical Conductors
• Drafting Committee: B01.06 - Bi-Metallic Conductors

Relations

• Replaces: ASTM B520-12(2017) - Standard Specification for Tin-Coated, Copper-Clad Steel Wire for Electronic Application
• Effective Date: 01-Oct-2023

Standards Content (Sample)

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.
Designation: B520 − 12 (Reapproved 2023)
Standard Specification for
Tin-Coated, Copper-Clad Steel Wire for Electronic
Application
This standard is issued under the fixed designation B520; 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 2. Referenced Documents
2.1 The following documents of the issue in effect on date
1.1 This specification covers tin-coated copper-clad steel
of material purchase form a part of this specification to the
wire for electronic application.
extent referenced herein:
1.2 Four classes of tin-coated copper-clad steel wire are
2.2 ASTM Standards:
covered as follows:
B193 Test Method for Resistivity of Electrical Conductor
1.2.1 Class T30HS—Nominal 30 % conductivity, hard-
Materials
drawn,
B258 Specification for Standard Nominal Diameters and
1.2.2 Class T30A—Nominal 30 % conductivity, annealed,
Cross-Sectional Areas of AWG Sizes of Solid Round
1.2.3 Class T40HS—Nominal 40 % conductivity, hard-
Wires Used as Electrical Conductors
drawn, and
B452 Specification for Copper-Clad Steel Wire for Elec-
1.2.4 Class T40A—Nominal 40 % conductivity, annealed.
tronic Application
1.3 The values stated in inch-pound units are to be regarded 2.3 National Institute of Standards and Technology:
as standard. The values given in parentheses are mathematical NBS Handbook 100 Copper Wire Tables
conversions to SI units that are provided for information only
3. Ordering Information
and are not considered standard.
1.3.1 Exception—The SI values for resistivity and volume 3.1 Orders for material under this specification shall include
the following information:
are to be regarded as standard.
3.1.1 Quantity of each size.
1.4 The following safety hazards caveat pertains only to the
3.1.2 Wire size (see 5.3 and Table 1),
test method portion, Section 6, of this specification: This
3.1.3 Class of wire (see 1.2),
standard does not purport to address all of the safety concerns,
3.1.4 Package size and shipping (see 7.1.7 and Section 9),
if any, associated with its use. It is the responsibility of the user
packaging inspection if required (see 9.3.3),
of this standard to establish appropriate safety, health, and
3.1.5 Special package marking, if required, and
environmental practices and determine the applicability of
3.1.6 Place of inspection (see 9.1).
regulatory limitations prior to use. (Warning—Consideration
should be given to toxicity and flammability when selecting
4. Material
solvent cleaners.)
4.1 The basis material shall consist of copper-clad steel wire
1.5 This international standard was developed in accor-
conforming to the product description, quality and specifica-
dance with internationally recognized principles on standard-
tion requirements of Specification B452.
ization established in the Decision on Principles for the
4.2 The tin-coated wire shall consist of the basis wire coated
Development of International Standards, Guides and Recom-
with tin. The tin used for coating shall be commercially pure
mendations issued by the World Trade Organization Technical
(Note 1). For purposes of this specification, the tin shall be
Barriers to Trade (TBT) Committee.
considered“ commercially pure” if the total of other elements,
1 2
This specification is under the jurisdiction of ASTM Committee B01 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Electrical Conductors and is the direct responsibility of Subcommittee B01.06 on contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Bi-Metallic Conductors. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Oct. 1, 2023. Published October 2023. Originally the ASTM website.
approved in 1970. Last previous edition approved in 2017 as B520 – 12 (2017). Available from National Institute of Standards and Technology (NIST), 100
DOI: 10.1520/B0520-12R23. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B520 − 12 (2023)
TABLE 1 Wire Sizes
5.2 Resistivity—The electrical resistivity at a temperature of
Diameter Cross-Sectional Area at 20 °C (68 °F) 20 °C shall not exceed the values prescribed in Table 2. See
2 2
in. mm cmil in. mm Note 2 for calculating electrical resistance.
0.0720 1.8129 5180 0.00407 2.63
NOTE 2—Relationships that may be useful in connection with the values
0.0641 1.6128 4110 0.00323 2.08
of electrical resistivity prescribed in this specification are shown in Table
0.0571 1.450 3260 0.00256 1.65
2 2
3. Resistivity units ⁄58 Ω · mm /m and 0.15328 Ω · g/m at 20 °C are
0.0508 1.290 2580 0.00203 1.31
respectively the international equivalent of volume and weight resistivity
0.0453 1.151 2050 0.00161 1.04
0.0403 1.024 1620 0.00128 0.823 of annealed copper equal to 100 % conductivity. The latter term means
that a copper wire 1 m in length and weighing 1 g would have a resistance
0.0359 0.912 1290 0.00101 0.653
of 0.15328 Ω. This is equivalent to a resistivity value of 875.20
0.0320 0.813 1020 0.000804 0.519 2
Ω·lb/mile , which signifies the resistance of a copper wire 1 mile in length
0.0285 0.724 812 0.000638 0.412
weighing 1 lb. It is also equivalent, for example, to 1.7241 μΩ/cm of
0.0253 0.643 640 0.000503 0.324
length of a copper bar 1 cm in cross section. A complete discussion of this
0.0226 0.574 511 0.000401 0.259
subject is contained in NBS Handbook 100. The use of five significant
0.0201 0.511 404 0.000317 0.205
figures in expressing resistivity does not imply the need for greater
accuracy of measurement than that specified in Test Method B193. The
0.0179 0.455 320 0.000252 0.162
0.0159 0.404 253 0.000199 0.128 use of five significant figures is required for complete reversible conver-
0.0142 0.361 202 0.000158 0.102 sion from one set of resistivity units to another.
0.0126 0.320 159 0.000125 0.0804
5.3 Dimensions and Permissible Variations—The wire sizes
0.0113 0.287 128 0.000100 0.0647
0.0100 0.254 100 0.0000785 0.0507 shall be expressed as the diameter of the wire in decimal
fractions of an inch to the nearest 0.0001 in. (0.003 mm) (Note
0.0089 0.226 79.2 0.0000622 0.0401
3). For diameters under 0.0100 in. (0.254 mm), the wire shall
0.0080 0.203 64.0 0.0000503 0.0324
0.0071 0.180 50.4 0.0000396 0.0255
not vary from the specified diameter by more than plus
0.0063 0.160 39.7 0.0000312 0.0201
0.0003 in. (0.008 mm) and minus 0.0001 in. (0.003 mm) and
0.0056 0.142 31.4 0.0000246 0.0159
for diameters of 0.0100 in. (0.254 mm) and over, the wire shall
0.0050 0.127 25.0 0.0000196 0.0127
not vary from the specified diameter by more than plus 3 % and
0.0045 0.114 20.2 0.0000159 0.0103
minus 1 %, expressed to the nearest 0.0001 in. (0.003 mm).
0.0040 0.102 16.0 0.0000126 0.00811
0.0035 0.089 12.2 0.00000962 0.00621
NOTE 3—The values of the wire diameters in Table 1 are given to the
0.0031 0.079 9.61 0.00000755 0.00487
nearest 0.0001 in. (0.003 mm) and correspond to the standard sizes given
in Specification B258. The use of gauge numbers to specify wire sizes is
not recognized in this specification because of the possibility of confusion.
An excellent discussion of wire gauges and related subjects is contained
in “Copper Wire Tables” NBS Handbook 100.
exclusive of copper, does not exceed 1 %. Notwithstanding the
5.4 Continuity of Coating—The tin coating shall be continu-
previous sentence, chemical analysis of the tin coating or of the
ous. The continuity of coating on the wire shall be determined
tin used for coating shall not be required under this specifica-
on representative samples taken before stranding or insulating.
tion. Adequacy of the tin coating is assured by the continuity of
The continuity of tinning shall be determined by the hydro-
coating and adherence of coating requirements (see 5.4 and
chloric acid-sodium polysulfide test in accordance with 6.2.
5.5). The quality of the tin-coated wire shall be such that the
finished product meets the properties and requirements in this
5.5 Adherence of Coating—The tin coating shall be firmly
specification.
adherent to the surface of the copper-clad steel wire. The
adherence of coating on the wire shall be determined on
NOTE 1—It is necessary that the coating of the tin on the wire be
continuous. The test in the sodium polysulfide is for the purpose of representative samples taken before stranding or insulating.
determining whether or not the wire carries a continuous envelope of pure
The adherence of coating shall be determined by the wrapping
tin. The thickness of the tin coating is necessarily varied. Under the same
and immersion test in accordance with 6.3.
conditions of tinning, the coating on all sizes of wire, excepting on fine
wire, is approximately the same. The coating on fine wire is in general
relatively heavier than that on coarse wire. It is not, therefore, correct to
apply a larger number of cycles in the test on coarse wire than is applied
to fine wire. It is probable that one cycle of the dip test would be sufficient TABLE 2 Resistivity, max at 20 °C
to discover defects in tinned wire, but in order to make certain that no
Nominal Diameter, in.
Class of Wire Ω·mm /m
partially covered spots may escape attention, provision has been made for
(mm)
two cycles. It has been found that the tin coating on copper wire consists
T30HS 0.0720 (1.829) to 0.06743
of two parts, an envelope of pure tin on the outside, with an intermediate
0.0201 (0.511) incl (0.067427)
layer of copper-tin alloy. This tin alloy, as well as the amount of tin
and under 0.0201 (0.511) to 0.07315
present, has an effect on the resistivity of the wire. Since the relative
0.0113 (0.287) incl (0.073148)
amount of tin coating and alloy is greater on the small wire than it is on
T30A under 0.0113 (0.287) to 0.07642
0.0031 (0.079) incl (0.076423)
the coarser wire, the resistivity of the wire increases as the size decreases.
This also accounts for the decrease in elongation due to tinning soft wire.
T40HS 0.0720 (1.829) to 0.04874
0.0201 (0.511) incl (0.048742)
5. General Requirements
and under 0.0201 (0.511) to 0.05162
0.0113 (0.287) incl (0.051618)
5.1 Tensile strength and elongation of the tin-coated wire
T40A under 0.0113 (0.287) to 0.05328
shall conform to the requirements of Specification B452 for the
0.0031 (0.079) incl (0.053280)
applicable size and class of copper-clad steel wire.
B520 − 12 (2023)
TABLE 3 Equivalent Resistivity Values
Volume Resistivity Equivalents at 20 °C
Conductivity
Class and Size, in. (mm) Volume Mass
at 20 °C
2 2 2
% IACS Ω·mm /m Ω·c mil/ft μΩ·in. μΩ·cm Ω·lb/mile Ω·g/m
T30A and T30HS 0.0720
25.570 0.067427 40.56 2.6546 6.7427 3137.9 0.54953
(1.829) to 0.0201 (0.511)
Under 0.0201 (0.511) to
23.570 0.073148 44.00 2.8799 7.3148 3404.1 0.59616
0.0113 (0.287)
Under 0.0113 (0.287) to
22.560 0.076423 45.97 3.0088 7.6423 3556.5 0.62285
0.0031 (0.079)
T40A and T40HS 0.0720
35.372 0.048742 29.32 1.9190 4.8742 2268.3 0.39725
(1.829) to 0.0201 (0.511)
Under 0.0201 (0.511) to
33.401 0.051618 31.05 2.0322 5.1618 2402.2 0.42069
0.0113 (0.287)
Under 0.0113 (0.287) to
32.359 0.053280 32.05 2.0977 5.3280 2479.5 0.43423
0.0031 (0.079)
TABLE 4 Limiting Number of Test Specimens for Coating Tests
5.6 Joints—Necessary joints in the wire and rods prior to
Maximum Number of Specimens to be
final coating and drawing shall be made in accordance with
Nominal Diameter, in. (mm) Tested for Two Cycles in
good commercial practice. Joints made after coating shall not
180 mL of Acid Solution
be allowed to remain in the final product.
0.0720 (1.829) to 0.0501 (1.273) 6
incl
5.7 Finish—The coating shall consist of a smooth, continu-
Under 0.0501 (1.273) to 0.0381 10
ous layer, firmly adherent to the surface of the copper. The wire
(0.968) incl
shall be bright and free from all imperfections not consistent
Under 0.0381 (0.968) to 0.0301 12
(0.765) incl
with good commercial practice.
Under 0.0301 (0.765) to 0.0031 14
(0.079) incl
6. Test Methods
6.1 For tensile strength, elongation, resistivity, dimensional
measurement and the quality of the basis wire, the latest issue
of Specification B452 shall apply and the tests shall be
performed on the tin-coated wire.
excess of sulfur after the solution has been allowed to stand for
at least 24 h. The test solution shall be made by diluting a
6.2 Continuity of Coating:
portion of the concentrated solution with distilled water to a
6.2.1 Specimens:
specific gravity of 1.142 at 15.6 °C (60 °F). The sodium
6.2.1.1 Length of Specimens—Test specimens shall each
polysulfide test solution should have sufficient strength to
have a length of about 6 in. (150 mm). They shall be tagged or
blacken thoroughly a piece of clean untinned copper wire in
marked to correspond with the coil, spool, or reel from which
5 s. The test solution used for testing samples shall be
they were cut.
considered exhausted if it fails to blacken a piece of clean
6.2.1.2 Treatment of Specimens—The specimens shall be
copper as described above.
thoroughly cleaned by immersion in a suitable organic solvent
for at least 3 min, then removed and wiped dry with a clean,
NOTE 4—It is important that the polysulfide solution be of proper
soft cloth. (Warning—See 1.4.) The specimens thus cleaned
composition and strength at the time of test. A solution which is not
shall be kept wrapped in a clean, dry cloth until tested. That
saturated with sulfur or which has been made from decomposed sodium
sulfide crystals may give a false indication of failure. Therefore, the
part of the specimen to be immersed in the test solution shall
requirement that the solution be tested by observing its blackening effect
not be handled. Care shall be taken to avoid abrasion by the cut
on a bright copper wire is significant. Significant also is the requirement
ends.
that the solution be saturated with sulfur by allowing the solution to stand
6.2.2 Special Solutions:
at least 24 h after preparation. Attention is called also to the necessity for
6.2.2.1 Hydrochloric Acid Solution (sp gr 1.088)—
the use of sodium sulfide which has not deteriorated through exposure to
air; and if exposure has occurred, the crystals should be tested for purity.
Commercial HCl (sp gr 1.12) shall be diluted with distilled
The
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