SIST EN ISO 27874:2008

SLOVENSKI STANDARD
01-november-2008
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Metallic and other inorganic coatings - Electrodeposited gold and gold alloy coatings for
electrical, electronic and engineering purposes - Specification and test methods (ISO
27874:2008)
Metallische Überzüge - Galvanische Gold- und Goldlegierungsüberzüge für elektrische,
elektronische und technische Zwecke - Anforderungen und Prüfverfahren (ISO
27874:2008)
Revêtements métalliques et autres revêtements inorganiques - Dépôts électrolytiques
d'or et d'alliages d'or pour usages électrique, électronique et industriels - Spécification et
méthodes d'essai (ISO 27874:2008)
Ta slovenski standard je istoveten z: EN ISO 27874:2008
ICS:
25.220.40 Kovinske prevleke Metallic coatings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 27874
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2008
ICS 25.220.40
English Version
Metallic and other inorganic coatings - Electrodeposited gold
and gold alloy coatings for electrical, electronic and engineering
purposes - Specification and test methods (ISO 27874:2008)
Revêtements métalliques et autres revêtements Metallische Überzüge - Galvanische Gold- und
inorganiques - Dépôts électrolytiques d'or et d'alliages d'or Goldlegierungsüberzüge für elektrische, elektronische und
pour usages électrique, électronique et industriels - technische Zwecke - Anforderungen und Prüfverfahren
Spécification et méthodes d'essai (ISO 27874:2008) (ISO 27874:2008)
This European Standard was approved by CEN on 13 September 2008.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 27874:2008: E
worldwide for CEN national Members.

Contents Page
Foreword.3

Foreword
This document (EN ISO 27874:2008) has been prepared by Technical Committee ISO/TC 107 "Metallic and
other inorganic coatings" in collaboration with Technical Committee CEN/TC 262 “Metallic and other inorganic
coatings” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by March 2009, and conflicting national standards shall be withdrawn at
the latest by March 2009.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 27874:2008 has been approved by CEN as a EN ISO 27874:2008 without any modification.

INTERNATIONAL ISO
STANDARD 27874
First edition
2008-09-15
Metallic and other inorganic coatings —
Electrodeposited gold and gold alloy
coatings for electrical, electronic and
engineering purposes — Specification
and test methods
Revêtements métalliques et autres revêtements inorganiques — Dépôts
électrolytiques d'or et d'alliages d'or pour usages électrique,
électronique et industriels — Spécification et méthodes d'essai

Reference number
ISO 27874:2008(E)
©
ISO 2008
ISO 27874:2008(E)
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ii © ISO 2008 – All rights reserved

ISO 27874:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Information to be supplied to the electroplater .3
5 Designation . 4
6 Requirements and test methods. 6
7 Sampling. 9
Annex A (normative) Requirements for undercoats. 10
Annex B (normative) Methods of measuring the thickness of gold and gold alloy coatings . 12
Annex C (normative) Adhesion tests . 20
Annex D (normative) Determination of gold content. 22
Bibliography . 24

ISO 27874:2008(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 27874 was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings,
Subcommittee SC 3, Electrodeposited coatings and related finishes.
This first edition of ISO 27874 cancels and replaces ISO 4523:1985, ISO 4524-1:1985, ISO 4524-4:1985 and
ISO 4524-5:1985, of which it constitutes a technical revision.
iv © ISO 2008 – All rights reserved

ISO 27874:2008(E)
Introduction
The engineering uses of electrodeposited gold and gold alloy coatings have expanded with the growth of the
electrical and electronic industries. Low voltages and currents, dry circuits and microwave frequencies require
low-resistance interconnection systems, connectors and waveguides. Non-tarnishing, low-resistance gold
coatings were the logical choice for connectors where the stability of contact surfaces was critical. The need to
improve the wear resistance of gold coatings led to the development of new electroplating solutions containing
controlled amounts of metallic and non-metallic additives that either changed the composition or altered the
crystal structure of the coating. The special needs of the printed-circuit industry led to the development of acid
gold electroplating solutions that contained no free cyanide, yielding coatings that are hard, bright and
solderable. Formulations for high-speed electroplating up to current densities of 200 A/dm were introduced
for continuous strip, stripe or spot gold and gold alloy coatings.
The high cost of gold metal has led to the development of selective and thickness profile plating techniques to
limit the use of the metal to the active areas only of the components, where the gold is required. Designers will
therefore often specify the area requiring gold electroplating as well as the thickness profile, if required, by
reference to suitably marked drawings.
With the introduction of many new gold electroplating formulations and the proliferation of engineering
applications, the need for technical standards that specify the requirements of electrodeposited gold and gold
alloy coatings, as well as the test methods to ensure that the specified requirements are met, is critical.
Composition, appearance, hardness, thickness, purity, porosity, wear resistance, solderability, electrical
contact resistance, infrared reflectivity and other properties must be controlled to produce high-quality gold
and gold alloy coatings for engineering purposes.

INTERNATIONAL STANDARD ISO 27874:2008(E)

Metallic and other inorganic coatings — Electrodeposited gold
and gold alloy coatings for electrical, electronic and
engineering purposes — Specification and test methods
WARNING — This International Standard may not be compliant with some countries’ health, safety
and environmental legislations. It calls for the use of substances and/or procedures that may be
injurious to health if adequate safety measures are not taken. This International Standard does not
address any health hazards, safety or environmental matters, or legislation associated with its use. It
is the responsibility of the user of this International Standard to establish appropriate health, safety
and environmentally acceptable practices and take appropriate action to comply with any national,
regional and/or international regulations. Compliance with this International Standard does not, of
itself, confer immunity from legal obligations.
1 Scope
This International Standard specifies the requirements for electrodeposited gold and gold alloy coatings for
electrical, electronic and other engineering applications on metallic and non-metallic substrates. It also
specifies test methods for measuring the properties of the coatings.
Although this International Standard does not specify the condition, finish or surface roughness of the basis
material prior to electroplating, the appearance and serviceability of electroplated gold or gold alloy coatings
depends on the condition of the basis material. It is essential that the purchaser specify the surface finish and
roughness of the basis material in order to conform to the product requirements.
This International Standard does not apply to coatings on threaded articles or to coatings on sheet or strip in
non-fabricated form.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 1463, Metallic and oxide coatings — Measurement of coating thickness — Microscopical method
ISO 2064, Metallic and other inorganic coatings — Definitions and conventions concerning the measurement of
thickness
ISO 2080, Metallic and other inorganic coatings — Surface treatment, metallic and other inorganic coatings —
Vocabulary
ISO 2177, Metallic coatings — Measurement of coating thickness — Coulometric method by anodic
dissolution
ISO 2819, Metallic coatings on metallic substrates — Electrodeposited and chemically deposited coatings —
Review of methods available for testing adhesion
ISO 3497, Metallic coatings — Measurement of coating thickness — X-ray spectrometric methods
ISO 27874:2008(E)
ISO 3543, Metallic and non-metallic coatings — Measurement of thickness — Beta backscatter method
ISO 3868, Metallic and other non-organic coatings — Measurement of coating thicknesses — Fizeau multiple-
beam interferometry method
ISO 3882, Metallic and other inorganic coatings — Review of methods of measurement of thickness
ISO 4516, Metallic and other inorganic coatings — Vickers and Knoop microhardness tests
ISO 4518, Metallic coatings — Measurement of coating thickness — Profilometric method
ISO 4519, Electrodeposited metallic coatings and related finishes — Sampling procedures for inspection by
attributes
ISO 4524-2, Metallic coatings — Test methods for electrodeposited gold and gold alloy coatings — Part 2: Mixed
flowing gas (MFG) environmental tests
ISO 4524-3:1985, Metallic coatings — Test methods for electrodeposited gold and gold alloy coatings — Part 3:
Electrographic tests for porosity
ISO 4524-6, Metallic coatings — Test methods for electrodeposited gold and gold alloy coatings — Part 6:
Determination of the presence of residual salts
ISO 9587, Metallic and other inorganic coatings — Pretreatment of iron or steel to reduce the risk of hydrogen
embrittlement
ISO 9588, Metallic and other inorganic coatings — Post-coating treatments of iron or steel to reduce the risk of
hydrogen embrittlement
ISO 10289, Methods for corrosion testing of metallic and other inorganic coatings on metallic substrates —
Rating of test specimens and manufactured articles subjected to corrosion tests
ISO 10308, Metallic coatings — Review of porosity tests
ISO 12687, Metallic coatings — Porosity tests — Humid sulfur (flowers of sulfur) test
ISO 14647, Metallic coatings — Determination of porosity in gold coatings on metal substrates — Nitric acid
vapour test
IEC 60068-2-20, Environmental testing — Part 2-20: Tests — Test T: Test methods for solderability and
resistance to soldering heat of devices with leads
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 2064 and ISO 2080 and the
following apply.
3.1
gold or gold alloy coating
electrodeposited gold or gold alloy having intentional alloying elements in its composition
3.2
double-layer gold or gold alloy coating
gold or gold alloy coating consisting of two discrete layers of differing gold contents
3.3
multilayer gold or gold alloy coating
gold or gold alloy coating consisting of more than two discrete layers of differing gold contents
2 © ISO 2008 – All rights reserved

ISO 27874:2008(E)
4 Information to be supplied to the electroplater
4.1 Essential information
The following information shall be supplied by the purchaser to the electroplater in writing in the purchase
order or contract, or on engineering drawings:
a) the designation (see Clause 5);
b) the significant surface of the article, indicated, for example, as dimensioned areas on drawings or by the
provision of suitably marked samples;
c) the nature, condition and finish of the basis metal if they are likely to affect the serviceability and/or the
appearance of the coating (see Clause 1);
d) the position on the surface of any unavoidable defects, such as rack marks (see 6.2);
e) the finish required, for example bright, dull or another type, preferably accompanied by approved samples
of the finish (see 6.2);
f) the method of porosity testing to be used and the permitted number and location of acceptable pores
(see 6.4);
g) the tensile strength of the part and the requirements for any heat treatment prior to, or after, electroplating
(see 6.7 and 6.8);
h) sampling methods, acceptance levels and any other inspection requirements if different from those
specified in ISO 4519 (see Clause 7);
i) the requirements for coating thickness, including positions of measurement as indicated on dimensioned
drawings (see 6.3);
j) the requirements for adhesion testing (see 6.9).
4.2 Additional information
The following additional information may be required and, if so, shall be specified by the purchaser in writing,
for example in the contract or purchase order, or on drawings:
a) the composition of the coating and details of intentional alloying elements and undesirable impurities
(see 6.6);
b) any special cleaning procedures to be used;
c) any special requirements for undercoats (see 6.15 and Annex A);
d) any requirements for the composition and thickness of each layer in double or multilayer coatings
(see Clause 3);
e) the electrical properties of the coating and the methods of test to be used (see 6.10);
f) the microhardness of the coating and the test method to be used (see 6.11);
g) any requirements for solderability and the test method to be used (see 6.12);
h) any requirements for wear resistance and the test method to be used (see 6.13);
i) the ductility of the coating and the method of test to be used (see 6.14);
ISO 27874:2008(E)
j) any requirements for the freedom from surface contamination of the finished articles (see 6.16);
k) the agreed mean density of a gold alloy coating if the thickness measurement method requires a density
correction (see Annex B);
l) any requirements for accelerated-corrosion testing (see 6.5);
m) any other requirements, such as a residual-salts test, (see 6.16).
5 Designation
5.1 General
The designation shall appear on engineering drawings, in the purchase order, in the contract or in the detailed
product specification.
The designation specifies, in the following order, the basis metal, the specific alloy (optional), stress relief
requirements, the type(s) and thickness(s) of undercoats (when present), the thickness and composition of the
gold or gold alloy coating or coatings (when double or multilayer coatings are specified), and supplementary
treatments such as heat treatment to reduce susceptibility to hydrogen embrittlement.
5.2 Designation specifications
The designation shall comprise the following:
a) the term, “electrodeposited coating”;
b) the number of this International Standard (ISO 27874);
c) a hyphen;
d) the chemical symbol of the basis metal (see 5.3);
e) a solidus (/);
f) if appropriate, the chemical symbol for an undercoat metal followed, if necessary, by a number giving the
thickness of the undercoat in micrometres (see 6.15 and Annex A);
g) a solidus (/);
h) the chemical symbol for gold, Au, or the standard designation for a gold alloy, including the symbol of the
alloying element and a figure in parentheses giving the mean content of that element expressed as a mass
fraction in percent to one decimal place;
i) a number giving the minimum local thickness requirement for the gold or gold alloy coating in
micrometres;
j) for double and multilayer gold coatings, repeat h) and i), followed by a solidus (/), for each subsequent
gold or gold alloy coating required.
5.3 Designating the basis material
The basis material shall be designated by its chemical symbol or the chemical symbol of its principal
constituent if an alloy, for example:
Fe for iron and steel;
Zn for zinc alloys;
4 © ISO 2008 – All rights reserved

ISO 27874:2008(E)
Cu for copper and copper alloys;
Al for aluminium and aluminium alloys.
In the case of non-metallic materials, the letters NM shall be used.
A specific alloy shall be identified by its standard designation, for example its UNS number or the local,
national, equivalent placed between the symbols < >.
For example, Fe is the UNS designation for a particular high-strength steel (see Reference [5] in
the Bibliography).
5.4 Designation of heat treatment requirements
The heat treatment requirements shall be in brackets and designated as follows:
a) the letters SR for stress relief heat treatment prior to electroplating, the letters ER for hydrogen
embrittlement relief heat treatment after electroplating, and the letters HT for heat treatment for other
purposes;
b) in parentheses, the minimum temperature, in °C;
c) the duration of the heat treatment in hours, for example SR(210)1 designates stress relief heat treatment
at 210 °C for 1 h.
When heat treatment prior to or after electrodeposition is specified, the requirements shall be included in the
designation as shown in the examples (see 5.5).
The structure and composition of gold and gold alloy coatings may be modified and the coating properties
substantially altered by heat treatment. Designers should be aware of these effects before specifying gold
coatings on high-tensile-strength basis material.
5.5 Examples
A pure gold coating, Au, with a minimum thickness of 5 µm on nickel-electroplated steel, Fe/Ni, will have the
following designation:
Electrodeposited coating ISO 27874 – Fe/Ni/Au5
An alloy coating containing 98,0 % gold and 2 % silver, AuAg(2,0), with a minimum thickness of 5 µm on a zinc
alloy, Zn, with copper and nickel undercoats will have the following designation:
Electrodeposited coating ISO 27874 – Zn/Cu/Ni/AuAg(2,0)5
An alloy coating containing 99,5 % gold and 0,2 % nickel, AuNi(0,2), with a minimum thickness of 0,5 µm
deposited over a pure-gold coating, Au, with a minimum thickness of 1 µm on a Cu alloy will have the
following designation:
Electrodeposited coating ISO 27874 – Cu/Au1/AuNi(0,2)0,5
A pure-gold coating with a minimum thickness of 5 µm, Au5, deposited over a copper undercoat that is 5 µm
thick, Cu5, on a steel that has an ultimate tensile strength of 1 200 MPa and is heat-treated prior to electroplating
for stress relief at 200 °C for 3 h, SR(200)3, and after electroplating to reduce the risk of hydrogen
embrittlement at 190 °C for 12 h, ER(190)12, will have the following designation:
Electrodeposited coating ISO 27874 – Fe/SR(200)3/Cu5/Au5ER(190)12
The designation describes the heat treatment and electroplating steps in the order in which they are
performed. The standard designation of the basis material could be placed after the chemical symbol, Fe, in
the above example. It is especially important to know the standard designation of a metal or alloy that is
difficult to prepare for electroplating and that is susceptible to hydrogen embrittlement.
ISO 27874:2008(E)
6 Requirements and test methods
6.1 General
Gold and gold alloy coatings normally consist of a single layer of gold metal, usually with a strike undercoat of
unspecified thickness, but double or multilayer coatings may be specified by the purchaser [see 4.2 c)].
6.2 Appearance
Although this International Standard does not specify the condition, finish or surface roughness of the basis
material prior to electroplating, the appearance of electroplated gold and gold alloy coatings depends on the
condition of the basis material (see the Bibliography for surface preparation methods). Over the significant
surface, the electroplated article shall be free from clearly visible blisters, pits, roughness, cracks and
uncoated areas other than those that arise from defects in the basis material. The electroplated article shall be
free from extraneous soil and mechanical damage. On articles where a contact mark is unavoidable, its
position and extent shall be specified by the purchaser [see 4.1 d)].
In the case of selectively plated articles, the degree and extent of discoloration at the boundary between the
areas that have been electroplated and those that are not electroplated shall be specified on the product
drawing.
If required, a preliminary sample with the required standard of finish shall be supplied or approved by the
purchaser [see 4.1 e)].
The types of article which are selectively electroplated with gold are commonly also selectively electroplated
with other metals, such as a nickel undercoat or solderable tin alloy coating. Agreements on visual standards
will thus extend to all such areas and boundaries. It is therefore essential that such parameters be specified
on the product drawing.
6.3 Thickness
The thickness of the coating specified in the designation shall be the minimum local thickness. The minimum
local thickness of the coating shall be measured within the reference area or at a site specified on the
component drawing. The minimum thickness of the gold or gold alloy coating shall be that specified by the
purchaser.
One or more of the methods given in Annex B shall be used to measure the thickness of the gold or gold alloy
coating.
A profile of the minimum-thickness distribution may alternatively be specified on suitably prepared drawings.
Thicknesses of gold and gold alloy coatings commonly specified for electrical, electronic or engineering
applications are given in Table 1.
Table 1 — Examples of commonly specified thicknesses of gold and gold alloy coatings
for various applications
Minimum thickness
Application
µm
Solderability retention, low-reliability electrical contacts 0,1
Medium-reliability electrical connector and switch contacts 0,25
(electroplated acid gold alloy)
Semiconductor bonding (pure gold) 0,5
High-reliability consumer electrical contacts 0,75
High-frequency devices and waveguides (pure gold) 1,0
High-reliability electrical contacts for safety-critical applications 2,5 or 5,0
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ISO 27874:2008(E)
The thickness values given are approximate only. The thickness which a designer specifies for an application
will be the minimum necessary for satisfactory performance in porosity and/or wear tests.
6.4 Porosity
When specified by the purchaser, the parts shall be subjected to one or more of the environmental and
porosity tests given in ISO 4524-3, ISO 10308, ISO 12687 or ISO 14647. The method to be used and the
acceptable number and location of pores shall be specified by the purchaser.
The electrographic tests given in ISO 4524-3:1985, Clauses 2 to 5, can be used for articles with flat surfaces.
The tests given in ISO 12687 and ISO 14647 involving gas exposure and the electrographic test given in
ISO 4524-3:1985, Clause 6, can be used for articles with curved surfaces.
6.5 Accelerated-corrosion testing
Where the corrosion resistance of the coated articles is important and accelerated-corrosion testing is specified,
one of the tests given in ISO 4524-2 shall be used. The acceptable corrosion rating after testing shall be
specified by the purchaser in accordance with ISO 10289.
The duration and results of accelerated-corrosion tests may bear little relationship to the service life of the
coated article and, therefore, the results obtained are not to be regarded as a direct guide to the corrosion
resistance of the tested coatings in all environments where these coatings may be used.
Accelerated-corrosion tests are frequently used as part of the qualification testing of electrical subassemblies
containing gold or gold alloy electroplated components. Such operational tests typically involve multiple
operations of the assembly followed by exposure to a corrosive atmosphere. Qualification depends upon the
satisfactory results of electrical tests, such as contact resistance measurements, conducted before and after
the operational tests. Corrosion testing on its own is not to be used as a guide to performance in qualification
tests.
6.6 Composition
When required, the minimum gold content of the coating shall be specified by the purchaser in the designation.
Where alloy coatings are required, the gold and alloyed-metal contents shall be specified. The nature and
amount of non-metallic inclusions may be specified, especially in the case of electrical and electronic
applications. The properties of the coating may be significantly affected by the presence of non-metallic
inclusions.
If specified by the purchaser, the gold content of the coating shall be determined by the method given in
Annex D.
Pure-gold coatings or gold alloy coatings electroplated from sulfite-containing solutions produce deposits with
a tendency to cold welding. They are not recommended for use as finishes for connector or switch contacts.
6.7 Stress relief heat treatment prior to electroplating
When specified by the purchaser, steel parts that have an ultimate tensile strength equal to or greater than
1 000 MPa and that contain tensile stresses caused by machining, grinding, straightening or coil-forming
operations shall be given a stress relief heat treatment prior to cleaning and metal deposition. The procedures
and classes for stress relief heat treatment shall be as specified by the purchaser or the purchaser shall
specify appropriate procedures and classes from ISO 9587 [see 4.1 g)].
Steels with oxide or scale shall be cleaned before application of the coatings. For high-strength steels
(strength equal to or greater than 1 000 MPa), non-electrolytic alkaline and anodic alkaline cleaners as well as
mechanical cleaning procedures are preferred to avoid the risk of inducing hydrogen embrittlement during
cleaning.
ISO 27874:2008(E)
6.8 Hydrogen embrittlement relief heat treatment after electroplating
Steel parts having an ultimate tensile strength equal to or greater than 1 000 MPa as well as surface-hardened
parts shall receive hydrogen embrittlement heat treatment in accordance with the procedures and classes of
ISO 9588 or as specified by the purchaser.
The effectiveness of the hydrogen embrittlement relief heat treatment may be determined by test methods
specified by the purchaser or by test methods described in International Standards (see the Bibliography).
The properties of some gold alloy coatings may be changed by heat treatment procedures. It is, however,
unlikely that high-strength steels of strength equal to or greater than 1 000 MPa will be used for any such
application.
6.9 Adhesion
Coatings shall pass one or more of the adhesion tests (see ISO 2819) given in Annex C, as specified by the
purchaser. The individual layers shall not separate when tested by the methods given in this International
Standard.
Aluminium alloys may be given a post-plating heat treatment at 130 °C to improve the adhesion of the coating.
This treatment is not recommended for alloys which could suffer deterioration at or above this temperature.
The preparation of sectioned metallographic specimens for the microscopical determination of thickness may
give an indication of poor adhesion because grinding and polishing of the specimen may cause separation of
the coating from the substrate which can be observed in the microscope. Misleading results may also be
obtained if grinding or polishing are not properly carried out during metallographic preparation.
6.10 Electrical properties
If the electrical properties are important to the function of the coating, those properties shall be specified by
the purchaser, along with the methods of assessing the properties [see 4.2 e)].
6.11 Microhardness
If the microhardness of the coating is specified, it shall be measured by one of the methods given in ISO 4516.
Typical microhardness ranges for gold and gold alloy coatings are given in Table 2.
Table 2 — Microhardness ranges for gold and gold alloy coatings for various uses
Knoop microhardness range
Type of coating and typical applications
HK25
90 maximum Pure gold for semiconductor bonding and microwave applications
91 to 130 Alloyed acid gold coatings for sliding contacts and connectors
91 to 200 Alloyed-gold coatings from neutral or alkaline plating solutions for
switches or heavy-duty connectors
> 200 Other applications requiring wear resistance

The microhardness of electroplated gold and gold alloy coatings is dependent on the solution formulation and
how the process is controlled and operated. In general, variation in microhardness is achieved by the addition
of alloying elements and organic additives.
8 © ISO 2008 – All rights reserved

ISO 27874:2008(E)
6.12 Solderability
If specified, the solderability of the gold or gold alloy coating shall be measured by the method described in
IEC 60068-2-20, or by an alternative test method specified by the purchaser. The type of test and any
artificial-ageing treatment carried out before testing shall be specified [see 4.2 g)].
The formation of brittle joints and the loss of solderability of thin, porous gold coatings during storage is
possible. Soft-soldered joints on gold coatings may contain intermetallic compounds that are hard and brittle
and may lower shear, fatigue and impact resistance. The risk of developing brittleness becomes greater with
increase in soldering temperature or gold thickness and may be greater with some alloy coatings. If the
thickness exceeds 1,5 µm, special soldering techniques will need to be used. When thin coatings are
specified, the loss of solderability that may occur in storage may be avoided by specifying a suitable
undercoat.
6.13 Wear resistance
If the wear resistance of the coating is important to the function of the component, the purchaser shall specify
the wear resistance and its method of measurement [see 4.2 h)].
6.14 Ductility
When ductility is important, the ductility required, and its method of test, shall be specified by the purchaser
[see 4.2 i)].
6.15 Undercoats
Undercoats applied prior to electroplating with gold or gold alloy coatings may be specified to improve
corrosion resistance, adhesion and solderability; to prevent interdiffusion between the basis metal and the
coating; to prevent contamination of electroplating solutions; or to reduce surface roughness or porosity.
Typical undercoats include copper, nickel, palladium, palladium-nickel, palladium-cobalt and combinations of
these undercoats. When undercoats are specified, they shall meet the requirements given in Annex A.
6.16 Freedom from contamination
If specified by the purchaser, the articles shall be subjected to the residual-salts test specified in ISO 4524-6.
An increase in conductivity of not more than 150 µS/m, as measured by that test, shall be acceptable.
Articles electroplated with gold or gold alloy coatings shall be thoroughly rinsed after each electroplating
process. It is preferable to use de-ionized water for each rinse and to dry the plated articles thoroughly after
the final rinse.
7 Sampling
A random sample of the size specified in ISO 4519 shall be selected from the inspection lot. The articles in the
sample shall be inspected for conformance to the requirements of this International Standard. The lot shall be
considered conforming or non-conforming for each requirement, in accordance with the sampling plans in
ISO 4519 [see 4.1 h)].
ISO 27874:2008(E)
Annex A
(normative)
Requirements for undercoats
A.1 Thickness requirements and measurement
The minimum thickness requirement for an electrodeposited undercoat applied prior to gold or gold alloy
electroplating is given in Table A.1 for different basis materials. The minimum thickness of the undercoat shall
be that given in Table A.1. The thickness of any undercoat, when specified, shall be determined by the
microscopical method (ISO 1463) or the coulometric method (ISO 2177) or, when local thickness determination
is required on selectively plated articles, by the X-ray spectrometric method (ISO 3497).
Table A.1 — Thickness requirements for undercoats for various basis materials and applications
Minimum thickness
Basis material Application Undercoats
µm
Copper Interdiffusion Nickel 2
prevention
Copper alloys (notably those Copper or nickel Specified by the purchaser
containing lead)
a
Ferrous materials (other than Corrosion Nickel 10
austenitic stainless steel) prevention
a
Copper plus nickel 10 of Cu plus 5 of Ni
(i.e. Cu10/Ni5)
c
Austenitic stainless steel Adhesion An acid nickel strike (Woods bath) Thin, not normally specified
b
will normally be required .
a
Zinc and its alloys Adhesion, Copper plus nickel 8 of Cu plus 10 of Ni
corrosion (i.e. Cu8/Ni10)
protection
a,d
Aluminium and its alloys Adhesion, Nickel 20
corrosion
protection
Other basis materials with Adhesion, Nickel or copper may be required. Specified by the purchaser
soldered or brazed joints interdiffusion
prevention
Non-metallic basis materials Adhesion, Copper and/or nickel will be Specified by the purchaser
strength, required.
conductivity
a
Ductile, low-stress nickel undercoats may be essential.
b
If gold-electroplated austenitic stainless steel is to be used in a chloride environment, a substantial nickel undercoat will be necessary
and its thickness shall be specified.
c
An initial copper coating may be used under the nickel coating, but the thickness of the nickel shall not be reduced.
d
Aluminium alloys are given post-plating heat treatment at 130 °C to improve adhesion of the coating. This treatment is not
recommended for alloys, which could suffer deterioration at or above this temperature.

10 © ISO 2008 – All rights reserved

ISO 27874:2008(E)
A.2 Chemical symbols for common undercoats
For common undercoats, the chemical symbols in Table A.2 shall be used in the coating designation when
required.
Table A.2 — Chemical symbols of common undercoats applied prior to gold electroplating
Chemical symbol Undercoat
Ni Nickel
Cu Copper
Cu/Ni Nickel applied over copper

ISO 27874:2008(E)
Annex B
(normative)
Methods of measuring the thickness of gold and gold alloy coatings
B.1 Uncertainty of thickness measurements
The methods given below have adequate precision, that is the uncertainty in the measurement is less than
10 % when the method is properly used with standard thickness reference materials. If a referee method is
required, it shall be specified by the purchaser and shall be selected from the test methods given in
Clauses B.3, B.4 and B.5. The most reliable method (see ISO 3882) shall be selected taking into
consideration the expected coating thickness, the shape and size of the components, the nature of the coating
material and the nature of the basis material.
B.2 Density and thickness calculations
For those thickness test methods where a value of the density of the coating is required, the true density of
the gold or gold alloy coating should be used. If the true density is not known, use a suitable arithmetically
calculated value. For example, an alloy coating containing 60 % gold (by mass) and 40 % silver (by mass)
would have the following calculated density, in g/cm :
ρ = 100/[60/19,3 + 40/10,5] = 14,5
where
ρ is the calculated density of the alloy coating, in g/cm ;
19,3 is the density of pure gold, in g/cm ;
10,5 is the density of pure silver, in g/cm .
A value of the density is required for the beta backscatter, X-ray spectrometric, coulometric, gravimetric and
chemical analytical methods described in Clauses B.3, B.4 and B.5. If a density is calculated or assumed, the
uncertainty in the measurement is likely to be greater than 10 %.
The suppliers of proprietary gold electroplating solutions may be able to estimate the density of the gold
coating electrodeposited from their particular solutions, but variations can arise in practice due to different
operating conditions, ageing of the solution, poor bath maintenance or inclusions of organic matter.
The true values of density for gold coatings electrodeposited from different solutions are compared to values
calculated from deposit purity in Table B.1. Table B.1 illustrates the fact that calculated density values ma
...