ASTM B579-73(1999)
(Specification)Standard Specification for Electrodeposited Coatings of Tin-Lead Alloy (Solder Plate)
Standard Specification for Electrodeposited Coatings of Tin-Lead Alloy (Solder Plate)
SCOPE
1.1 This specification covers the requirements for electrodeposited tin-lead coatings on fabricated articles of iron, steel, copper, and copper alloys, to protect them against corrosion (Note 1), to improve and preserve solderability over long periods of storage, and to improve anti-galling characteristics. Note 1-Some corrosion of tin-lead coatings may be expected in outdoor exposure. In normal indoor exposure, tin-lead is protective on iron, copper, and copper alloys. Corrosion may be expected at discontinuities (pits or pores) in the coating. Porosity decreases as the thickness is increased. A primary use of the tin-lead coating (solder) is with the printed circuit industry as a solderable coating and as an etch mask material.
1.2 This specification applies to electrodeposited coatings containing a minimum of 50% and a maximum of 70% tin. The specification applies to mat, bright, and flow-brightened tin-lead coatings. Note 2-Tin-lead plating baths are composed of tin and lead fluoborates and of addition agents to promote stability. The final appearance may be influenced by the addition of proprietary brighteners. Without brighteners, the coatings are mat; with brighteners, they are semibright or bright. Flow-brightened coatings are obtained by heating mat coatings to above the melting point of tin-lead for a few seconds and then quenching; palm oil, hydrogenated oils, or fats are used as a heat-transfer medium at a temperature of 260 + 10°C (500 + 20°F), but other methods of heating are also in use. The maximum thickness for flow-brightening is about 7.5 [mu]m (0.3 mil); thicker coatings tend to reflow unevenly. The shape of the part is also a factor; flat surfaces tend to reflow more unevenly than wires or rounded shapes (Note 3). Note 3-Volatile impurities in tin-lead coatings will cause bubbling and foaming during flow-brightening resulting in voids and roughness. The impurities can arise from plating solution addition agents and from improper rinsing and processing.
1.3 This specification does not apply to sheet, strip, or wire in the unfabricated form or to threaded articles having basic major diameters up to and including 19 mm (0.75 in.).
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Designation: B 579 – 73 (Reapproved 1999)
Standard Specification for
Electrodeposited Coatings of Tin-Lead Alloy (Solder Plate)
This standard is issued under the fixed designation B 579; 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 B 183 Practice for Preparation of Low-Carbon Steel for
Electroplating
1.1 This specification covers the requirements for electrode-
B 242 Practice for Preparation of High-Carbon Steel for
posited tin-lead coatings on fabricated articles of iron, steel,
Electroplating
copper, and copper alloys, to protect them against corrosion
B 281 Practice for Preparation of Copper and Copper-Base
(Note 1), to improve and preserve solderability over long
Alloys for Electroplating and Conversion Coatings
periods of storage, and to improve anti-galling characteristics.
B 322 Practice for Cleaning Metals Prior to Electroplating
NOTE 1—Some corrosion of tin-lead coatings may be expected in
B 487 Test Method for Measurement of Metal and Oxide
outdoor exposure. In normal indoor exposure, tin-lead is protective on
Coating Thicknesses by Microscopical Examination of a
iron, copper, and copper alloys. Corrosion may be expected at disconti-
Cross Section
nuities (pits or pores) in the coating. Porosity decreases as the thickness is
B 499 Test Method for Measurement of Coating Thickness
increased. A primary use of the tin-lead coating (solder) is with the printed
by the Magnetic Method: Nonmagnetic Coatings on Mag-
circuit industry as a solderable coating and as an etch mask material.
netic Basis Metals
1.2 This specification applies to electrodeposited coatings
B 504 Test Method for Measurement of Thickness of Metal
containing a minimum of 50 % and a maximum of 70 % tin.
Coatings by the Coulometric Method
The specification applies to mat, bright, and flow-brightened
B 567 Test Method for Measurement of Coating Thickness
tin-lead coatings.
by the Beta Backscatter Method
NOTE 2—Tin-lead plating baths are composed of tin and lead fluobo-
B 568 Test Method for Measurement of Coating Thickness
rates and of addition agents to promote stability. The final appearance may 2
by X-Ray Spectrometry
be influenced by the addition of proprietary brighteners. Without bright-
E 105 Practice for Probability Sampling of Materials
eners, the coatings are mat; with brighteners, they are semibright or bright.
E 122 Practice for Choice of Sample Size to Estimate the
Flow-brightened coatings are obtained by heating mat coatings to above
Average Quality of a Lot or Process
the melting point of tin-lead for a few seconds and then quenching; palm
oil, hydrogenated oils, or fats are used as a heat-transfer medium at a 2.2 Other Standards:
temperature of 260 6 10°C (500 6 20°F), but other methods of heating
MIL-STD-105 Sampling Procedures and Tables for Inspec-
are also in use. The maximum thickness for flow-brightening is about 7.5 4
tion by Attributes
μm (0.3 mil); thicker coatings tend to reflow unevenly. The shape of the
MIL-STD-414 Sampling Procedures and Tables for Inspec-
part is also a factor; flat surfaces tend to reflow more unevenly than wires
tion by Variables for Percent Defective
or rounded shapes (Note 3).
NOTE 3—Volatile impurities in tin-lead coatings will cause bubbling
3. Classification and Service Condition
and foaming during flow-brightening resulting in voids and roughness.
The impurities can arise from plating solution addition agents and from 3.1 Orders for articles to be plated in accordance with this
improper rinsing and processing.
specification shall specify, in addition to the ASTM designation
number and year of issue, the classification notation indicating
1.3 This specification does not apply to sheet, strip, or wire
the basis metal and thickness of tin-lead coating required, or
in the unfabricated form or to threaded articles having basic
the service condition number indicating the severity of service
major diameters up to and including 19 mm (0.75 in.).
required for the coating. In addition, when specifying a tin-lead
2. Referenced Documents
coating composition, the first number shall refer to the tin
content in percent.
2.1 ASTM Standards:
1 2
This specification is under the jurisdiction of ASTM Committee B-8 on Annual Book of ASTM Standards, Vol 02.05.
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee Annual Book of ASTM Standards, Vol 14.02.
B08.08.04 on Light Metals. Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
Current edition approved March 29, 1973. Published June 1973. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B 579
3.1.1 Classification Notation: factory adhesion and corrosion performance of the coating.
Accordingly, it is suggested that the following Practices for the
Symbol Classification
Fe/ Iron or steel basis metals
preparation of various basis metals for electroplating be
Cu/ Copper or copper alloy basis metals
followed when appropriate: B 183, B 242, B 281, and B 322.
/Sn-Pb Tin-lead coating and its composition number, when re-
5.4 When necessary, preliminary samples showing the finish
quired; for example, Sn60-Pb40
Number Minimum coating thickness in micrometres
shall be supplied to and approved by the purchaser. Where rack
(5 to 50)
marks are inevitable, their location shall be the subject of
Suffix Letter agreement between supplier and purchaser.
f flow-brightened
b bright
6. Physical Composition
m mat
6.1 Composition—The tin-lead coating composition shall
be as follows (Note 7):
An example of complete classification notation is as follows: Cu/Sn60-Pb40/5F
Element Weight, %
3.1.2 Service Condition Number: Tin (Sn) 50 to 70
Lead (Pb) remainder
No. Service Condition
6.1.1 The tin percentage is calculated as follows:
4 very severe exposure
3 severe exposure
Tin, % 5 134.1 3 ~L/A 2 1! (1)
2 moderate exposure
1 mild exposure
where:
NOTE 4—See Appendix X1 for additional description of exposure
L = weight of lead coating, g, and
conditions and examples of typical end uses. The coating thicknesses
A = weight of alloy coating, g.
given for each service condition are guidelines and are not intended to be
absolute values.
NOTE 7—Only the tin content need be determined. Lead is usually
determined by difference. A sample of the deposit can be obtained by
4. Significant Surfaces
plating on a stainless steel panel from which the coating can be peeled or
4.1 Significant surfaces are defined as those surfaces nor-
by employing any recognized stripping method. The alloy composition of
mally visible (directly or by reflection) that are essential to the the deposit can be determined by methods such as gravimetric or
volumetric analysis, density measurements, atomic absorption spectropho-
appearance or serviceability of the article when assembled in
tometry, X-ray fluorescence, and beta backscatter.
normal position; or those surfaces that can be the source of
In addition, the alloy composition produced by a plating solution may
corrosion products that will deface visible surfaces on the
be obtained by comparing the weight of a tin-lead coating deposited by a
assembled article. When necessary, the significant surfaces
given number of ampere-hours to the weight of lead coating produced in
shall be indicated on the drawing of the part, or by the
a lead fluoborate coulometer in series with the plating bath.
provision of suitably marked samples.
6.2 Appearance—The tin-lead coating shall be smooth, fine
NOTE 5—When significant surfaces include areas on which the speci-
grained, continuous, adherent, and shall be free of visible
fied thickness of deposit cannot readily be controlled, such as threads,
blisters, pits, nodules, indications of burning, excessive build-
holes, deep recesses, bases of angles, and similar areas, the purchaser and
up, staining, and other defects. Flow-brightened coatings shall
the manufacturer should recognize the necessity for either thicker deposits
not have dewetted areas or beads, and shall be free of the oil
on the more accessible surfaces or for special racking. Special racks may
used in the fusion process.
involve the use of conforming, auxiliary bipolar electrodes, or noncon-
6.3 Thickness—The thickness of the coating on significant
ducting shields.
surfaces shall conform to the requirements in Table 1 and Table
5. Materials and Manufacture
2.
6.3.1 Thickness Measurements—Tin-lead alloy thickness
5.1 Defects in the surface of the basis metal, such as
measurements shall be made on those areas of the significant
scratches, porosity, nonconducting inclusions, roll and die
surfaces where the coating would be expected to be thinnest.
marks, cold shuts, and cracks, may adversely affect the
The method of determining the thickness shall be agreed upon
appearance and the performance of coatings applied thereto
by the manufacturer and purchaser. Several methods are
despite the observance of the best plating practices. Accord-
ingly, the plater’s responsibility for defects in the coating
resulting from such conditions shall be waived, except when he
TABLE 1 Tin-Lead Alloy Coatings on Steel
is also in the position of prime contractor supplying plated
Minimum
Service Classification
parts. Thickness
Condition Number
μm mil
NOTE 6—In order to minimize problems of this sort, the specifications
A
covering the basis material or the item to be plated should contain SC4 Fe/SnPb 30 30 1.2
A
SC3 Fe/SnPb 20 20 0.8
appropriate limitations on such basis metal conditions.
SC2 Fe/SnPb 10 10 0.4
SC1 Fe/SnPb 5 5 0.2
5.2 When required the basis metal shall be subjected to such
B
SC1 Fe/SnPb 5f 5 0.2
polishing or buffing operations as are necessary to yield
A
An undercoat of 2.5 μm (0.1 mil) copper is recommended for SC3 and SC4.
deposits with the desired final appearance (Section 6).
B
f = flow brightened or
5.3 Proper preparatory procedures and thorough cleaning of
m = mat or
the basis metal surface are essential in order to assure satis- b = bright
B 579
A
TABLE 2 Tin-Lead Alloy Coatings on Copper, Copper Alloys ,
9. Test Methods
B
and Nonmetals
9.1 Thickness:
Minimum
9.1.1 To meet the thickness specifications of the coatings,
Service Classification
Thickness
Condition Number
the plater is advised to:
μm mil
9.1.1.1 Maintain regular control of all solutions,
SC4 Cu/SnPb 30 30 1.2
9.1.1.2 Inspect the equipment at regular intervals, and
SC3 Cu/SnPb 15 15 0.6
SC2 Cu/SnPb 8 8 0.3
9.1.1.3 Check thickness at periodic intervals.
SC1 Cu/SnPb 5 5 0.2
9.1.2 The following ASTM methods are acceptable for
C
SC1 Cu/SnPb 5f 5 0.2
measuring local thickness of the coating: B 487, B 499, B 504,
A
If the basis metal is a brass containing more than 15 % zinc, the tin-lead
B 567, and B 568.
coating shall be preceded by an undercoat of at least 2.5 μm (0.1 mil) of copper
and nickel to prevent the diffusion of zinc into the tin-lead. The same undercoating 9.2 Adhesion:
shall also be applied when the basis metal is beryllium copper to assure adhesion
9.2.1 Burnishing Test—Rub an area of not more than 630
of tin-lead coating.
2 2
B mm (1 in. ) of the coated surface, selected at the discretion of
Nonmetals shall be suitably sensitized and metalized prior to tin-lead coating.
C
f = flow-brightened or
the inspector, rapidly and firmly for 15 s with a smooth metal
m = mat or
implement. A suitable burnishing implement is a copper or
b = bright
steel disk used edgewise and broadside. Maintain a pressure
sufficient to burnish the coating at every stroke, but not so great
available depending upon the thickness of coating, the shape of
as to cut it. Poor adhesion will be shown by the appearance of
the article, and the basis metal. They include beta backscatter,
a loose blister which grows as burnishing is continued. If the
coulometric, magnetic, microscopical, and X-ray fluorescence
quality of the coating is poor also, the blister may crack and the
test methods. The methods are outlined in 9.1.
coating peel away from the basis metal.
NOTE 8—Thicknesses determined by beta backscatter, coulometry, and
9.2.2 Quenching Test—Heat the coating article in an oven
X-ray fluorescence are a function of the composition as well as the
for a sufficient time to reach 150 6 10°C (3006 20°F) and
thickness of the coating.
quench in room-temperature water. The adhesion is inadequate
6.4 Adhesion—The adhesion of the coating shall be ad-
if the coating blisters, cracks, or peels.
equate to pass the tests described in 9.2.
9.2.3 Reflow Test—Parts may be evaluated by immersion in
6.5 Solderability:
a bath of palm oil at a temperature of 205–260°C (400–500°F)
6.5.1 When specified by the purchaser, the coating shall be
until the deposit melts. A bright coating completely covering
tested by one of the methods described in 9.2. The results shall
the significant surfaces indicates adequate adhesion.
be evaluated in accordance with each procedure described in
9.2.4 Bend Test—Bend a sample, with the coated surface
that section.
away, over a mandrel until its two legs are parallel. The
6.5.2 When specified by the purchaser, the coating on
mandrel shall have a diameter equal to the thickness of the
copper and copper alloys shall, before solderability testing, be
sample. Examination at 43 magnification should show no
subjected to the preliminary artificial aging treatment described
evidence of peeling or cracking.
in 9.3.6 to determine if they may be expected to retain their
9.3 Solderability:
solderability during periods of storage.
9.3.1 General:
NOTE 9—See Appendix X2 for design considerations that have an effect
9.3.1.1 Methods for testing the solderability of tin-lead
on the selection of thickness of the coating and, ultimately, on the
coated articles are based on the measurement of the extent of
solderability of the electrodeposits.
wetting by molten solder or the determination of the minimum
time required to produce full or perfect wetting by solder.
7. Hydrogen Embrittlement
9.3.1.2 The extent of wetting can be observed by manual or
7.1 High-tensile strength steels, and severely cold-worked
automatic immersion in molten solder under controlled condi-
steels, are susceptible to embrittlement by hydrogen in both
tions.
cleaning and plating operations. The embrittling hydrogen
9.3.1.3 Determine the minimum wetting time by carrying a
shall be removed by heat treatment. Procedures for ba
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