Metallic coatings on non-metallic basis materials — Measurement of coating thickness — Micro-resistivity method

This document specifies a method for non-destructive measurements of the thickness of conductive coatings on non-conductive base materials. This method is based on the principle of the sheet resistivity measurement and is applicable to any conductive coatings and layers of metal and semiconductor materials. In general, the probe has to be adjusted to the conductivity and the thickness of the respective application. However, this document focuses on metallic coatings on non-conductive base materials (e.g. copper on plastic substrates, printed circuit boards). This method is also applicable to thickness measurements of conductive coatings on conductive base materials, if the resistivity of the coating and the base material is significantly different. However, this case is not considered in this document.

Revêtements métalliques sur matériaux non-métalliques — Mesurage de l'épaisseur des revêtements — Méthode utilisant la micro-résistivité

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Publication Date
03-Nov-2020
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6060 - International Standard published
Start Date
04-Nov-2020
Completion Date
04-Nov-2020
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INTERNATIONAL ISO
STANDARD 14571
First edition
2020-11
Metallic coatings on non-metallic basis
materials — Measurement of coating
thickness — Micro-resistivity method
Revêtements métalliques sur matériaux non-métalliques — Mesurage
de l'épaisseur des revêtements — Méthode utilisant la micro-
résistivité
Reference number
ISO 14571:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 14571:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 14571:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Measurement principle ................................................................................................................................................................................. 1

5 Factors affecting measurement uncertainty ........................................................................................................................... 4

5.1 Range of measurement .................................................................................................................................................................... 4

5.2 Coating resistivity ................................................................................................................................................................................. 4

5.3 Width of the sample............................................................................................................................................................................ 4

5.4 Curvature ..................................................................................................................................................................................................... 5

5.5 Surface roughness ................................................................................................................................................................................ 5

5.6 Temperature .............................................................................................................................................................................................. 5

5.7 Probe contact pressure .................................................................................................................................................................... 5

6 Calibration of instruments ......................................................................................................................................................................... 5

6.1 General ........................................................................................................................................................................................................... 5

6.2 Calibration standards ........................................................................................................................................................................ 6

6.3 Verification ................................................................................................................................................................................................. 6

7 Procedure..................................................................................................................................................................................................................... 6

7.1 General ........................................................................................................................................................................................................... 6

7.2 Width of the sample............................................................................................................................................................................ 6

7.3 Curvature ..................................................................................................................................................................................................... 6

7.4 Number of measurements ............................................................................................................................................................ 6

7.5 Surface cleanliness .............................................................................................................................................................................. 7

8 Accuracy requirements.................................................................................................................................................................................. 7

9 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Method for determining the critical current path width ...................................................8

Bibliography ................................................................................................................................................................................................................................ 9

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 14571:2020(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.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings,

in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/

TC 262, Metallic and other inorganic coatings, including for corrosion protection and corrosion testing of

metals and alloys, in accordance with the Agreement on technical cooperation between ISO and CEN

(Vienna Agreement).

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 14571:2020(E)
Metallic coatings on non-metallic basis materials —
Measurement of coating thickness — Micro-resistivity
method
1 Scope

This document specifies a method for non-destructive measurements of the thickness of conductive

coatings on non-conductive base materials. This method is based on the principle of the sheet resistivity

measurement and is applicable to any conductive coatings and layers of metal and semiconductor

materials. In general, the probe has to be adjusted to the conductivity and the thickness of the respective

application. However, this document focuses on metallic coatings on non-conductive base materials

(e.g. copper on plastic substrates, printed circuit boards).

This method is also applicable to thickness measurements of conductive coatings on conductive base

materials, if the resistivity of the coating and the base material is significantly different. However, this

case is not considered in this document.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Measurement principle

The sheet resistivity method uses the so-called “four-point probe” as shown in Figure 1. A row of

four spring-loaded metal tips are placed in contact with the surface of the conductive coating. The tip

distances between the outer and inner tips, S and S , are equal. Usually, a constant current is passed

1 3

through the two outer contacts (labelled as 1). The introduced current penetrates the conductive

material of the coating with the resistivity ρ. The resulting voltage drop is measured across the two

inner contacts (labelled as 2).

In general, the flow of the introduced current is non-uniformly distributed over the cross-section of the

coating and is not parallel to the coating (see Figure 2). The current density decreases with increasing

distance from the direct line between the outer contacts labelled as 1 (with depth and width). If the

current is effectively limited by the thickness of the coating, the voltage drop between the inner

contacts labelled as 2 is a measure of the thickness.
© ISO 2020 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO 14571:2020(E)
Key
1 outer contacts of the probe
2 inner contacts of the probe
3 conductive coating
4 non-conductive base material
t coating thickness
Figure 1 — Schematic representation of the sheet resistivity method
2 © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 14571:2020(E)
Key
1 outer contacts of the probe
2 inner contacts of the probe
3 conductive coating
4 non-conductive base material
t coating thickness

Figure 2 — Schematic representation of the non-uniformly distributed current within the coating

The measured voltage drop depends on the resistivity of the metallic coating, on the probe geometry

(distance of the four probe contacts S , S , S ), the applied current and the thickness of the coating. If

1 2 3

the resistivity of the coating can be expected to be homogenous and the thickness is sufficiently small,

the measured voltage drop is determined only by the unknown thickness and the applied current.

In general, there is no simple and practical equation to calculate the thickness as a function of the

material resistivity, the probe geometry and the measured voltage and current. However, there are

some well-known approximations for practical use in certain cases. Particularly in the case of equal tip

distances (S = S = S = S) and for a thickness to probe spacing ratio t/S < 0,5, the coating thickness, t, in

1 2 3
micrometres, can be calculated using Formula (1), when t/S < 0,5:
ln 2
I ()
t=ρ (1)
V π
where
ρ is the resistivity of the coating, in μΩ⋅m;
V is the potential difference across the inner probe tips, in volts;
I is the current passed through the outer probe tips, in amperes;
S is the equal probe tip spacing (S = S = S = S ).
1 2 3
© ISO 2020 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO 14571:2020(E)

Usually the supplied current I is held constant. Therefore, the coating thickness is inversely proportional

to the measured voltage:
t= (2)
where C is a constant 0,221 ρI.

Formula (2) is the basis for many applications in the above case. In general, suitable correction functions

for Formula (2) are necessary if the prerequisite of a ratio t/S < 0,5 or an equal probe tip spacing is not

satisfied.

Because the introduced current decreases with increasing penetration depth, a sufficiently thick

coating does not limit the current and the coating appears to be of infinite thickness to this method. The

wider the probe spacing the deeper the current penetrates into the conductive material. Consequently,

the measurement range is determined by the probe spacing for a given coating material. The probe

geometry (tip spacing) has to be adjusted with respect to the conductivity and the expected thickness

range of the application of interest. Furthermore, the sensitivity of this method decreases with

increasing thickness.
The application of Formula (2) is also limited by very t
...

DRAFT INTERNATIONAL STANDARD
ISO/DIS 14571
ISO/TC 107 Secretariat: KATS
Voting begins on: Voting terminates on:
2020-01-21 2020-04-13
Metallic coatings on nonmetallic basis materials —
Measurement of coating thickness — Microresistivity
method

Revêtements métalliques sur matériaux non-métalliques — Mesurage de l'épaisseur des revêtements —

Méthode utilisant la microrésistivité
ICS: 25.220.40
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
FAST TRACK PROCEDURE
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 14571:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO 2020
---------------------- Page: 1 ----------------------
ISO/DIS 14571:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/DIS 14571:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Measurement principle ................................................................................................................................................................................. 1

5 Factors affecting measurement uncertainty ........................................................................................................................... 4

5.1 Range of measurement .................................................................................................................................................................... 4

5.2 Coating resistivity ................................................................................................................................................................................. 4

5.3 Width of the sample............................................................................................................................................................................ 4

5.4 Curvature ..................................................................................................................................................................................................... 5

5.5 Surface roughness ................................................................................................................................................................................ 5

5.6 Temperature .............................................................................................................................................................................................. 5

5.7 Probe contact pressure .................................................................................................................................................................... 5

6 Calibration of instruments ......................................................................................................................................................................... 5

6.1 General ........................................................................................................................................................................................................... 5

6.2 Calibration standards ........................................................................................................................................................................ 5

6.3 Verification ................................................................................................................................................................................................. 6

7 Procedure..................................................................................................................................................................................................................... 6

7.1 General ........................................................................................................................................................................................................... 6

7.2 Width of the sample............................................................................................................................................................................ 6

7.3 Curvature ..................................................................................................................................................................................................... 6

7.4 Number of measurements ............................................................................................................................................................ 6

7.5 Surface cleanliness .............................................................................................................................................................................. 6

8 Accuracy requirements.................................................................................................................................................................................. 7

9 Test report ................................................................................................................................................................................................................... 7

Annex A (normative) Method for determining the critical current path width ......................................................8

Bibliography ................................................................................................................................................................................................................................ 9

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/DIS 14571:2020(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.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 14571:2020(E)
Metallic coatings on nonmetallic basis materials —
Measurement of coating thickness — Microresistivity
method
1 Scope

This document describes a method for nondestructive measurements of the thickness of conductive

coatings on nonconductive base materials. This method is based on the principle of the sheet resistivity

measurement and is applicable to any conductive coatings and layers of metal and semiconductor

materials. In general, the probe has to be adjusted to the conductivity and the thickness of the respective

application. However, this document focusses on metallic coatings on nonconductive base materials

(e.g. Copper on plastic substrates, printed circuit boards).

NOTE 1 This method also applies to the measurement of through-hole copper thickness of printed circuit

boards. However, for this application a probe geometry different from the one described in this document is

necessary.

NOTE 2 This method is also applicable for thickness measurements of conductive coatings on conductive base

materials, if the resistivity of the coating and the base material is different. This case is not considered in this

document.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Measurement principle

The sheet resistivity method uses the so called four-point probe as shown in Figure 1. A row of four

spring-loaded metal tips are placed in contact with the surface of the conductive coating. The tip

distances between the outer and inner tips S and S are equal. Usually a constant current is passed

1 3

through the two outer contacts (4 and 7). The introduced current penetrates the conductive material of

the coating with the resistivity ρ. The resulting voltage drop is measured across the two inner contacts

(5 and 6).

In general, the flow of the introduced current is non-uniformly distributed over the cross-section of the

coating and is not parallel to the coating (see Figure 2). The current density decreases with increasing

distance from the direct line between the contacts 4 and 7 (with depth and width). If the current is

effectively limited by the thickness of the coating, the voltage drop between 5 and 6 is a measure of the

thickness.
© ISO 2020 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO/DIS 14571:2020(E)
Key
1 Outer contact of the probe
2 Inner contact of the probe
3 Conductive coating
4 Nonconductive base material
t Coating thickness
Figure 1 — Schematic representation of the sheet resistivity method
2 © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/DIS 14571:2020(E)
Key
1 Outer contacts of the probe
2 Inner contacts of the probe
3 Conductive coating
4 Nonconductive base material
t Coating thickness

Figure 2 — Schematic representation of the non-uniformly distributed current within the coating

The measured voltage drop depends on the resistivity of the metallic coating, on the probe geometry

(distance of the 4 probe contacts S , S , S ), the applied current and the thickness of the coating. If the

1 2 3

resistivity of the coating can be expected to be homogenous and the thickness is sufficiently small,

the measured voltage drop is determined only by the unknown thickness and the applied current. In

general, there is no simple and practical equation to calculate the thickness as a function of the material

resistivity, the probe geometry and the measured voltage and current. However, there are some well

known approximations for practical use in certain cases. Especially in the case of equal tip distances

(S =S =S = S) and for a thickness to probe spacing ratio t/s < 0,5 the coating thickness, t, in micrometres,

1 2 3
can be calculated using the equation:
ln 2
I () t
 
t = ρ when <0,5 (1)
 
V À S
 
where
ρ is the resistivity coating, in ohm.m;
V is the potential difference across the inner probe tips, in Volts;
I current passed through outer probe tips, in amps;
S is the equal probe tip spacing (S=S =S =S ).
1 2 3

Usually the supplied current I is held constant. Therefore, the coating thickness is inversely proportional

to the measured voltage :
t = (2)
where C is a the constant 0,221ρI
© ISO 2020 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO/DIS 14571:2020(E)
Equation (2) is the basis for many applications in the above case. In genera
...

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