ASTM B579-73(2004)
(Specification)Standard Specification for Electrodeposited Coatings of Tin-Lead Alloy (Solder Plate)
Standard Specification for Electrodeposited Coatings of Tin-Lead Alloy (Solder Plate)
ABSTRACT
This specification establishes the requirements for mat, bright, and flow-brightened electrodeposited tin-lead alloy coatings on fabricated articles of iron, steel, copper, and copper alloys to protect them against corrosion, to improve and preserve solderability over long periods of storage, and to improve anti-galling characteristics. Sheets, strips, or wires in the unfabricated form, or threaded articles having a specified diameter, are not covered here. The classification notation shall include the type of basis metal, thickness of tin-lead coating required, service condition number indicating the severity of service required, and coating composition. Coatings shall be sampled, tested, and shall conform accordingly to specified requirements as to composition, appearance, thickness, adhesion (to be examined either by burnishing test, quenching test, reflow test, or bend test), and solderability (to be assessed either by non-automated or automated dip test, spread test, globule test, or artificial aging test).
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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Standards Content (Sample)
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Designation: B579 – 73 (Reapproved 2004)
Standard Specification for
Electrodeposited Coatings of Tin-Lead Alloy (Solder Plate)
This standard is issued under the fixed designation B579; 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 Department of Defense.
1. Scope 2. Referenced Documents
1.1 This specification covers the requirements for electrode- 2.1 ASTM Standards:
posited tin-lead coatings on fabricated articles of iron, steel, B183 Practice for Preparation of Low-Carbon Steel for
copper, and copper alloys, to protect them against corrosion Electroplating
(Note 1), to improve and preserve solderability over long B242 Guide for Preparation of High-Carbon Steel for Elec-
periods of storage, and to improve anti-galling characteristics. troplating
B281 Practice for Preparation of Copper and Copper-Base
NOTE 1—Some corrosion of tin-lead coatings may be expected in
Alloys for Electroplating and Conversion Coatings
outdoor exposure. In normal indoor exposure, tin-lead is protective on
B322 Guide for Cleaning Metals Prior to Electroplating
iron, copper, and copper alloys. Corrosion may be expected at disconti-
B487 Test Method for Measurement of Metal and Oxide
nuities (pits or pores) in the coating. Porosity decreases as the thickness is
increased.Aprimaryuseofthetin-leadcoating(solder)iswiththeprinted
CoatingThicknessbyMicroscopicalExaminationofCross
circuit industry as a solderable coating and as an etch mask material.
Section
B499 Test Method for Measurement of Coating Thick-
1.2 This specification applies to electrodeposited coatings
nessesbytheMagneticMethod:NonmagneticCoatingson
containing a minimum of 50 % and a maximum of 70 % tin.
Magnetic Basis Metals
The specification applies to mat, bright, and flow-brightened
B504 Test Method for Measurement of Thickness of Me-
tin-lead coatings.
tallic Coatings by the Coulometric Method
NOTE 2—Tin-lead plating baths are composed of tin and lead fluobo-
B567 Test Method for Measurement of Coating Thickness
ratesandofadditionagentstopromotestability.Thefinalappearancemay
by the Beta Backscatter Method
be influenced by the addition of proprietary brighteners. Without bright-
B568 Test Method for Measurement of Coating Thickness
eners,thecoatingsaremat;withbrighteners,theyaresemibrightorbright.
Flow-brightened coatings are obtained by heating mat coatings to above by X-Ray Spectrometry
the melting point of tin-lead for a few seconds and then quenching; palm
E105 Practice for Probability Sampling Of Materials
oil, hydrogenated oils, or fats are used as a heat-transfer medium at a
E122 Practice for Calculating Sample Size to Estimate,
temperature of 260 6 10°C (500 6 20°F), but other methods of heating
With Specified Precision, the Average for a Characteristic
are also in use. The maximum thickness for flow-brightening is about 7.5
of a Lot or Process
µm (0.3 mil); thicker coatings tend to reflow unevenly. The shape of the
2.2 Other Standards:
part is also a factor; flat surfaces tend to reflow more unevenly than wires
MIL-STD-105 Sampling Procedures and Tables for Inspec-
or rounded shapes (Note 3).
NOTE 3—Volatile impurities in tin-lead coatings will cause bubbling
tion by Attributes
and foaming during flow-brightening resulting in voids and roughness.
MIL-STD-414 Sampling Procedures and Tables for Inspec-
The impurities can arise from plating solution addition agents and from 3
tion by Variables for Percent Defective
improper rinsing and processing.
3. Classification and Service Condition
1.3 This specification does not apply to sheet, strip, or wire
in the unfabricated form or to threaded articles having basic
3.1 Orders for articles to be plated in accordance with this
major diameters up to and including 19 mm (0.75 in.).
specificationshallspecify,inadditiontotheASTMdesignation
1 2
This specification is under the jurisdiction of ASTM Committee B08 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
B08.08.04 on Soft Metals. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2004. Published April 2004. Originally the ASTM website.
approved in 1973. Last previous edition approved in 1999 as B579–73 (1999). DOI: AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700
10.1520/B0579-73R04. 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.
B579 – 73 (2004)
number and year of issue, the classification notation indicating 5.2 Whenrequiredthebasismetalshallbesubjectedtosuch
the basis metal and thickness of tin-lead coating required, or polishing or buffing operations as are necessary to yield
the service condition number indicating the severity of service deposits with the desired final appearance (Section 6).
requiredforthecoating.Inaddition,whenspecifyingatin-lead 5.3 Proper preparatory procedures and thorough cleaning of
coating composition, the first number shall refer to the tin the basis metal surface are essential in order to assure satis-
content in percent. factory adhesion and corrosion performance of the coating.
3.1.1 Classification Notation: Accordingly, it is suggested that the following Practices for the
preparation of various basis metals for electroplating be
Symbol Classification
Fe/ Iron or steel basis metals
followed when appropriate: B183, B281, and B322 and Guide
Cu/ Copper or copper alloy basis metals
B242.
/Sn-Pb Tin-lead coating and its composition number, when re-
5.4 Whennecessary,preliminarysamplesshowingthefinish
quired; for example, Sn60-Pb40
Number Minimum coating thickness in micrometres
shallbesuppliedtoandapprovedbythepurchaser.Whererack
(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
An example of complete classification notation is as follows: Cu/Sn60-Pb40/5F
be as follows (Note 7):
Element Weight, %
3.1.2 Service Condition Number:
Tin (Sn) 50 to 70
No. Service Condition Lead (Pb) remainder
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
NOTE 4—See Appendix X1 for additional description of exposure
where:
conditions and examples of typical end uses. The coating thicknesses
L = weight of lead coating, g, and
given for each service condition are guidelines and are not intended to be
A = weight of alloy coating, g.
absolute values.
NOTE 7—Only the tin content need be determined. Lead is usually
4. Significant Surfaces
determined by difference. A sample of the deposit can be obtained by
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
appearance or serviceability of the article when assembled in
volumetricanalysis,densitymeasurements,atomicabsorptionspectropho-
normal position; or those surfaces that can be the source of
tometry, X-ray fluorescence, and beta backscatter.
corrosion products that will deface visible surfaces on the
In addition, the alloy composition produced by a plating solution may
assembled article. When necessary, the significant surfaces be obtained by comparing the weight of a tin-lead coating deposited by a
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
themanufacturershouldrecognizethenecessityforeitherthickerdeposits
on the more accessible surfaces or for special racking. Special racks may
not have dewetted areas or beads, and shall be free of the oil
involve the use of conforming, auxiliary bipolar electrodes, or noncon-
used in the fusion process.
ducting shields.
6.3 Thickness—The thickness of the coating on significant
surfacesshallconformtotherequirementsinTable1andTable
5. Materials and Manufacture
5.1 Defects in the surface of the basis metal, such as
TABLE 1 Tin-Lead Alloy Coatings on Steel
scratches, porosity, nonconducting inclusions, roll and die
Minimum
marks, cold shuts, and cracks, may adversely affect the
Service Classification
Thickness
appearance and the performance of coatings applied thereto
Condition Number
µm mil
despite the observance of the best plating practices. Accord-
A
SC4 Fe/SnPb 30 30 1.2
ingly, the plater’s responsibility for defects in the coating
A
SC3 Fe/SnPb 20 20 0.8
resultingfromsuchconditionsshallbewaived,exceptwhenhe
SC2 Fe/SnPb 10 10 0.4
is also in the position of prime contractor supplying plated
SC1 Fe/SnPb 5 5 0.2
B
SC1 Fe/SnPb 5f 50.2
parts.
A
An undercoat of 2.5 µm (0.1 mil) copper is recommended for SC3 and SC4.
NOTE 6—In order to minimize problems of this sort, the specifications B
f = flow brightened or
covering the basis material or the item to be plated should contain
m = mat or
appropriate limitations on such basis metal conditions. b=bright
B579 – 73 (2004)
2. testing of lots of coated items. In order that the manufacturer
6.3.1 Thickness Measurements—Tin-lead alloy thickness (plater) may know the quality standard he is expected to meet,
measurements shall be made on those areas of the significant the plan selected should be made part of the purchase contract.
surfaces where the coating would be expected to be thinnest. 8.2 General information on sampling procedures is given in
The method of determining the thickness shall be agreed upon Recommended Practices E105 and E122. Standard sampling
by the manufacturer and purchaser. Several methods are plans are suggested in Military Standards MIL-STD-105 and
availabledependinguponthethicknessofcoating,theshapeof MIL-STD-414.
the article, and the basis metal. They include beta backscatter,
9. Test Methods
coulometric, magnetic, microscopical, and X-ray fluorescence
9.1 Thickness:
test methods. The methods are outlined in 9.1.
9.1.1 To meet the thickness specifications of the coatings,
NOTE 8—Thicknesses determined by beta backscatter, coulometry, and
the plater is advised to:
X-ray fluorescence are a function of the composition as well as the
9.1.1.1 Maintain regular control of all solutions,
thickness of the coating.
9.1.1.2 Inspect the equipment at regular intervals, and
6.4 Adhesion—The adhesion of the coating shall be ad-
9.1.1.3 Check thickness at periodic intervals.
equate to pass the tests described in 9.2.
9.1.2 The following ASTM methods are acceptable for
6.5 Solderability:
measuring local thickness of the coating: B487, B499, B504,
6.5.1 When specified by the purchaser, the coating shall be
B567, and B568.
tested by one of the methods described in 9.2.The results shall
9.2 Adhesion:
be evaluated in accordance with each procedure described in
9.2.1 Burnishing Test—Rub an area of not more than 630
that section. 2 2
mm (1 in. ) of the coated surface, selected at the discretion of
6.5.2 When specified by the purchaser, the coating on
the inspector, rapidly and firmly for 15 s with a smooth metal
copper and copper alloys shall, before solderability testing, be
implement. A suitable burnishing implement is a copper or
subjectedtothepreliminaryartificialagingtreatmentdescribed
steel disk used edgewise and broadside. Maintain a pressure
in 9.3.6 to determine if they may be expected to retain their
sufficienttoburnishthecoatingateverystroke,butnotsogreat
solderability during periods of storage.
as to cut it. Poor adhesion will be shown by the appearance of
a loose blister which grows as burnishing is continued. If the
NOTE 9—SeeAppendixX2fordesignconsiderationsthathaveaneffect
on the selection of thickness of the coating and, ultimately, on the qualityofthecoatingispooralso,theblistermaycrackandthe
solderability of the electrodeposits.
coating peel away from the basis metal.
9.2.2 Quenching Test—Heat the coating article in an oven
7. Hydrogen Embrittlement
for a sufficient time to reach 150 6 10°C (300 6 20°F) and
7.1 High-tensile strength steels, and severely cold-worked
quench in room-temperature water.The adhesion is inadequate
steels, are susceptible to embrittlement by hydrogen in both
if the coating blisters, cracks, or peels.
cleaning and plating operations. The embrittling hydrogen
9.2.3 Reflow Test—Parts may be evaluated by immersion in
shall be removed by heat treatment. Procedures for baking to
a bath of palm oil at a temperature of 205 – 260°C (400 –
minimize embrittlement before and after plating are covered in
500°F) until the deposit melts. A bright coating completely
Sections 2 and 7 of Guide B242.
covering the significant surfaces indicates adequate adhesion.
9.2.4 Bend Test—Bend a sample, with the coated surface
8. Sampling
away, over a mandrel until its two legs are parallel. The
8.1 Test methods are time consuming and often destructive;
mandrel shall have a diameter equal to the thickness of the
therefore 100 % inspection is usually impractical. The pur-
sample. Examination at 43 magnification should show no
chasershouldselectasuitablesamplingplanfortheacceptance
evidence of peeling or cracking.
9.3 Solderability:
A
TABLE 2 Tin-Lead Alloy Coatings on Copper, Copper Alloys , 9.3.1 General:
B
and Nonmetals
9.3.1.1 Methods for testing the solderability of tin-lead
Minimum coated articles are based on the measurement of the extent of
Service Classification
Thickness
wetting by molten solder or the determination of the minimum
Condition Number
µm mil
time required to produce full or perfect
...
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