ASTM B488-18

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B488 − 11 B488 − 18
Standard Specification for
Electrodeposited Coatings of Gold for Engineering Uses
This standard is issued under the fixed designation B488; 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
1.1 This specification covers requirements for electrodeposited gold coatings that contain not less than 99.00 mass % gold and
that are used for engineering applications.
1.2 Specifically excluded from this specification are autocatalytic, immersion, and vapor deposited gold coatings.
1.3 Gold coatings conforming to this specification are employed for their corrosion and tarnish resistance (including resistance
to fretting corrosion and catalytic polymerization), bondability, low and stable contact resistance, solderability, and infrared
reflectivity. Several types of coatings, differing in gold purity and hardness, are covered by this specification.
1.4 The values stated in SI units are to be regarded as the standard. Values provided in parentheses are for information only.
1.5 The following hazards caveat pertains only to the test methods section, Section 9, 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 safety, health, and healthenvironmental practices and determine the applicability of regulatory
limitations prior to use.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
B183 Practice for Preparation of Low-Carbon Steel for Electroplating
B242 Guide for Preparation of High-Carbon Steel for Electroplating
B253 Guide for Preparation of Aluminum Alloys for Electroplating
B254 Practice for Preparation of and Electroplating on Stainless Steel
B281 Practice for Preparation of Copper and Copper-Base Alloys for Electroplating and Conversion Coatings
B322 Guide for Cleaning Metals Prior to Electroplating
B343 Practice for Preparation of Nickel for Electroplating with Nickel
B374 Terminology Relating to Electroplating
B481 Practice for Preparation of Titanium and Titanium Alloys for Electroplating
B482 Practice for Preparation of Tungsten and Tungsten Alloys for Electroplating
B487 Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
B489 Practice for Bend Test for Ductility of Electrodeposited and Autocatalytically Deposited Metal Coatings on Metals
B499 Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis
Metals
B504 Test Method for Measurement of Thickness of Metallic Coatings by the Coulometric Method
B507 Practice for Design of Articles to Be Electroplated on Racks
B542 Terminology Relating to Electrical Contacts and Their Use
B558 Practice for Preparation of Nickel Alloys for Electroplating
This specification is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.04 on
Precious Metal Coatings.
Current edition approved Oct. 1, 2011Aug. 1, 2018. Published November 2010October 2018. Originally approved in 1968. Last previous edition approved in 20102011
as B488 – 01B488 – 11.(2010)e01. DOI: 10.1520/B0488-11.10.1520/B0488-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B488 − 18
B567 Test Method for Measurement of Coating Thickness by the Beta Backscatter Method
B568 Test Method for Measurement of Coating Thickness by X-Ray Spectrometry
B571 Practice for Qualitative Adhesion Testing of Metallic Coatings
B578 Test Method for Microhardness of Electroplated Coatings
B602 Test Method for Attribute Sampling of Metallic and Inorganic Coatings
B678 Test Method for Solderability of Metallic-Coated Products
B697 Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
B735 Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
B741 Test Method for Porosity In Gold Coatings On Metal Substrates By Paper Electrography (Withdrawn 2005)
B748 Test Method for Measurement of Thickness of Metallic Coatings by Measurement of Cross Section with a Scanning
Electron Microscope
B762 Test Method of Variables Sampling of Metallic and Inorganic Coatings
B765 Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
B799 Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
B809 Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor (“Flowers-of-Sulfur”)
D1125 Test Methods for Electrical Conductivity and Resistivity of Water
D3951 Practice for Commercial Packaging
F390 Test Method for Sheet Resistance of Thin Metallic Films With a Collinear Four-Probe Array
2.2 U.S. Government Standards:
MIL-DTL-45204 Gold Plating, Electrodeposited
MIL-STD-1916 DOD Preferred Methods for Acceptance of Product
2.3 ANSI/ASQC Standard:
ANSI/ASQC Z1.4 Sampling Procedures and Tables for Inspection by Attributes
3. Terminology
3.1 Definitions—For definitions of terms used in this specification refer to Terminologies B374 or B542, B374, and B542.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 significant surfaces—defined as those normally visible (directly or by reflection) or essential to the serviceability or
function of the article. Can be the source of corrosion products or tarnish films that interfere with the function or desirable
appearance of the article. The significant surfaces shall be indicated on the drawings of the parts or by the provision of suitably
marked samples.
3.2.2 underplating—a metallic coating layer between the basis metal or substrate and the topmost metallic coating. The
thickness of an underplating is usually greater than 1 μm (40 μin.), in contrast to a strike or flash, which is thinner.
4. Classification
4.1 Types of Coatings—A coating shall be specified by a combination of the following:
4.1.1 Type, characterizing minimum purity in accordance with 4.2.1,
4.1.2 Code, designating Knoop hardness in accordance with 4.2.3, and
4.1.3 a numeral designating thickness in micrometres micrometers (μm) in accordance with 4.3.
4.2 Purity and Hardness:
4.2.1 Purity—The 2001 issue of this standard establishes a established new ASTM Type designation,designations, which isare
identical to the original standard (MIL-G-45204, which is now MIL-DTL-45204), established for electrodeposited gold and is they
are outlined in the following table.
Mass Percent Gold, Minimum, New ASTM MIL-DTL- Old ASTM
Excluding Potassium, Carbon & Type 45204 Type Type
Nitrogen
99.70 I I 2
99.00 II II 3
99.90 III III 1
NOTE 1—It is commonly accepted that a gold purity of 99.7 % is defined as no more than 0.3 % of total codeposited metallic components, excluding
potassium and sodium. Likewise, 99.9 % purity is recognized to mean no more than 0.1 % of total codeposited metal impurities, excluding potassium
and sodium. Almost all gold electrodeposits will contain potassium, carbon, and nitrogen that are occluded or precipitated in the deposit. In the case of
6,7
Type I gold, the occludedco-deposited potassium has been shown to improve durability and is desirable for that reason.
The last approved version of this historical standard is referenced on www.astm.org.
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://dodssp.daps.dla.mil.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Whitlaw, K. J., Souter, J. W., Trans. Inst. Metal Fin., “The Role of Codeposited Elements in Gold Plated Contacts,” 1984, 62(1), pp. 29–31.Whitlaw, K. J., Souter, J.
W., “The Role of Codeposited Elements in Gold Plated Contacts,” Trans. Inst. Metal Fin., Vol 62, No. 1, 1984, pp. 29–31.
B488 − 18
4.2.2 Gold purity is calculated by subtraction of the sum of all non-gold metals in mass %, excluding potassium (K) and sodium
(Na), from 100 %. The presence of Carbon (C), Nitrogen (N), Hydrogen (H), Na, and K contained in the electrodeposit are not
included in the calculation.
4.2.3 Hardness—Hardness values shall be specified by ASTM Code. The military standard designation of Grade is included for
reference.
Knoop Hardness Range ASTM Code MIL-DTL-
45204 Grade
90 HK maximum A A
91–129 HK B B
90–200 HK (see Note 2) . . .
130–200 HK C C
>200 HK D D
NOTE 2—ASTM Code B has previously been specified for hardness grade 90–200. This hardness grade has been eliminated and replaced with hardness
grade 91–129 in accordance with MIL-DTL-45204.
4.2.4 Relationship Between Purity and Hardness—The following combinations of purity and hardness ranges are representative
of good commercial practice:
New ASTM Type Old ASTM Type Code
I 2 A, B and C
II 3 B, C and D
III 1 A only
4.3 Thickness—Thickness shall be specified by an Arabic numeral that designates the minimum linear thickness in micrometres.
micrometers (μm). Examples of commonly specified thicknesses are shown in Table 1.
4.3.1 See 7.4.2 for thickness tolerances.
4.3.2 Instead of specifying the thickness in micrometres,micrometers, the purchaser may specify the mass of gold per unit area
(coating weight) in milligrams per square centimeter. Unless otherwise specified, the density of gold is assumed to be 19.3 g/cm
for Type III and 17.5 g/cm for Type I and Type II.
3 3
NOTE 3—The density of Type III gold coatings will be less than or equal to 19.3 g/cm , but not less than 18.5 g/cm .
NOTE 4—When significant surfaces are involved on which the specified thickness of deposit cannot readily be controlled, such as threads, holes, deep
recesses, bases of angles, and similar areas, the purchaser and the supplier should recognize the necessity for either thicker deposits on the more accessible
surfaces or for special racking. Special racks may involve the use of conforming, auxiliary, bipolar electrodes, or nonconducting shields.
5. Ordering Information
5.1 To make the application of this standard complete, the purchaser needs to supply the following information to the supplier
in the purchase order or other governing document.
5.1.1 The name, designation, and date of issue of this specification.
5.1.2 Classification: Type, Code, and thickness (or mass per unit area) (see Section 4).
5.1.3 Presence and thickness of underplating, if required (see 3.2.2).
5.1.4 Significant surfaces shall be specified (see 3.2.1).
5.1.5 Requirement, if any, for performance testing such as porosity testing (see 9.6), solderability testing (see Appendix X4),
ductility testing (see 9.7), etc.
5.1.6 If the substrate is one that requires a nickel underplating (see 6.5.1 and Appendix X6).
5.1.7 Whether or not stress relief has been or is to be done, whether embrittlement relief bake is to be done (steel parts only).
5.1.8 Sampling plan employed (see Section 8).
6. Manufacture
6.1 Any process that provides an electrodeposit capable of meeting the specified requirements is acceptable.
6.2 Substrate:
TABLE 1 Coating Thickness
Class Minimum Thickness, μm
0.25 0.25
0.50 0.50
0.75 0.75
1.0 1.0
1.25 1.25
2.5 2.5
5.0 5.0
th.
Whitlaw, K. J., Souter, J., Wright, I.S., Nottingham, M., Electrical Contacts, “Wear Properties of High Speed Gold Electrodeposits,” (1984), 30 pp. 33–45.Whitlaw,
th.
K. J., Souter, J., Wright, I.S., Nottingham, M., “Wear Properties of High Speed Gold Electrodeposits,” Electrical Contacts, 30 , 1984, pp. 33–45.
B488 − 18
6.2.1 The surface condition of the basis metal should be specified and should meet this specification prior to the plating of the
parts.
6.2.2 Defects in the surface of the basis metal such as scratches, porosity, pits, inclusions, roll and die marks, laps, cracks, burrs,
cold shuts, and roughness may adversely affect the appearance and performance of the deposit, despite the observance of the best
plating practice. Any such defects on significant surfaces shall be brought to the attention of the purchaser.
6.2.3 The basis metal shall be subject to such cleaning procedures as are necessary to ensure a satisfactory surface for
subsequent electroplating (see Practices B183, B242, Guide B253, Practices B254, B281, B322, B343, B481, B482, and B558).
6.2.4 Proper preparatory procedures and thorough cleaning of the basis metal are essential for satisfactory adhesion and
performance of these coatings. The surface must be chemically clean and continuously conductive, that is, without inclusions or
other contaminants. They must be smooth and as free of scratches, gouges, nicks, and similar imperfections as possible.
NOTE 5—A metal finisher can often remove defects through special treatments such as grinding, polishing, abrasive blasting, chemical treatments, and
electropolishing. However, these may not be normal in the treatment steps preceding the plating and a special agreement is indicated.
6.3 If required by the purchaser (see 5.1.7), steel parts with a hardness greater than 31 HRC shall be given a suitable stress relief
heat treatment prior to plating. Such stress relief plating, and an embrittlement relief bake after plating. Such relief baking shall
not reduce the hardness to a value below the specified minimum. Acid pickling of high strength steels shall be avoided.
6.3.1 The coating shall be applied after all basis metal heat treatments and mechanical operations on significant surfaces have
been completed.
6.4 Racking—Parts should be positioned so as to allow free circulation of solution over all surfaces. The location of rack or wire
marks in the coating shall be agreed upon between the purchaser and the supplier.
6.5 Plating Process:
6.5.1 Nickel Underplating—For thickness Classes except 5.0, a nickel underplating shall be applied before the gold coating
when the product is made from copper or copper alloy. Nickel underplatings are also applied for other reasons (see Appendix X6).
NOTE 6—When the thickness of the nickel underplate has a detrimental impact on the mechanical properties or bondability of the substrate, the nickel
thickness may be reduced to a non-detrimental level as specified by the purchaser.
NOTE 7—In certain instances in which high-frequency analog signals are employed, such as in wave guides, the magnetic properties of nickel may
attenuate the signal.
NOTE 8—In applications in which forming or flaring operations are to be applied to the plated component, a ductile nickel electrodeposit should be
specified.
6.5.2 Strikes—It is recommended to apply a gold strike to the underplate or substrate, except if the latter is silver or platinum,
prior to applying the gold top coating.
6.5.3 Plating—Good practice calls for parts to be electrically connected when entering the gold plating solution. A minimum
of 0.5 V is suggested.
NOTE 9—For rack and barrel plating processing, residual plating salts can be removed from the articles by a clean, hot (50 to 100°C) water rinse. A
minimum rinse time of 2.5 min (rack) or 5 min (barrel) is suggested. Best practice calls for a minimum of three dragout rinses and one running rinse
with dwell times of 40 s in each station when rack plating and 80 s when barrel plating. Modern, high-velocity impingement-type rinses can reduce this
time to a few seconds. This is particularly useful in automatic reel-to-reel applications in which dwell times are significantly reduced.
7. Coating Requirements
7.1 Nature of Coating—The gold deposit shall meet the appropriate purity requirements as put forth in the following:
7.1.1 Type I coatings shall contain at least 99.70 mass % gold, excluding potassium, sodium, carbon and nitrogen. For Type I
Code A (“soft”) coatings only, metallic hardening agents such as nickel, cobalt or iron combined, shall be less than 0.05 mass %
and none of these three elements shall be present in an amount greater than 0.03 mass %. All other metals excluding potassium
and sodium are considered impurities and shall not be present in amounts greater than 0.05 mass % combined. For Type I Code
B and C coatings, metallic hardening agents such as nickel, cobalt or iron combined shall be equal to or less than 0.3 mass %. All
other metals are considered impurities and shall not be present in amounts greater than 0.05 mass % each, 0.1 % combined. The
gold purity shall be calculated by determining the content of all non-gold metals in mass % (except potassium and sodium) and
subtracting this value from 100 %.
7.1.2 Type II coatings shall contain at least 99.00 mass % gold, excluding potassium, sodium, carbon and nitrogen. Type II
coatings may contain metallic hardening agents, such as nickel, cobalt or iron, which may be present in amounts greater than 0.3
mass %. All other metals, excluding potassium and nitrogen, shall be considered impurities and shall not be present in amounts
greater than 0.1 mass % each. The gold purity shall be calculated by determining the content of all non-gold metals in mass %
(except potassium and sodium) and subtracting this value from 100 %.
7.1.3 Type III coatings shall contain at least 99.90 mass % gold, excluding potassium, sodium, carbon and nitrogen. Individual
metal impurities shall not be present in a quantity greater than 0.04 mass %. Iron, nickel and cobalt combined shall be less than
0.05 mass %, and none of these three elements shall be present in an amount greater than 0.03 mass %. All non-gold metals,
excluding potassium and sodium, are considered impurities and shall not be present in amounts greater than 0.1 mass % combined.
The gold purity shall be calculated by determining the content of all non-gold metals in mass % (except potassium and sodium)
and subtracting this value from 100 %.
B488 − 18
7.2 Hardness—The gold coating shall have a Knoop hardness within the specified range as shown in 4.2.3 when tested in
accordance with 9.2.
7.3 Appearance—Gold coatings shall be coherent, continuous, and have a uniform appearance to the extent that the nature of
the basis metal and good commercial practices permit.
7.4 Thickness:
7.4.1 The gold coating shall have a thickness on the significant surfaces in accordance with 4.3 unless otherwise specified.
NOTE 10—Where Type I (Code B or C) or Type II (Code B or C) gold is specified, improved protection of the underlying metals can be obtained by
applying a duplex gold composite coating consisting of an underlying layer of Type III (Code A) gold. Typical thicknesses of the Type III gold underlayer
are 10 to 30 % of the total specified thickness. However, care must be taken to ensure that the thickness of the Type I or Type II gold topcoat is sufficient
so as not to compromise wear properties. When measuring the total gold thickness of duplex composite coatings, a density of 17.5 g/cm should be
employed (see 9.4).
7.4.2 The thickness of the gold coating shall be equal to or exceed the specified thickness throughout the significant surface (see
3.2.1). When plated parts are used in mating applications, the maximum thickness shall not exceed the tolerance specified for the
part on its engineering drawing. It is customary that allowance for plated coatings be included within the part tolerance.
NOTE 11—The coating thickness requirement of this specification is a minimum requirement: that is, the coating thickness is required to equal or exceed
the specified thickness throughout the significant surfaces, while conforming to all maximum allowed thicknesses created by part dimensional tolerances
given in the engineering drawing. Variation in the coating thickness from point to point on a coated article is an inherent characteristic of electroplating
processes. Therefore, the coating thickness at any single point on the significant surface will sometimes have to exceed the specified value in order to
ensure that the thickness equals or exceeds the specified value at all points. Hence, most average coating thicknesses will be greater than the specified
value; how much greater is largely determined by the shape of the article (see Practice B507) and the characteristics of the plating process. In addition,
the average coating thickness on articles will vary from arti
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