IEC TR 61191-9:2023

IEC TR 61191-9
®

Edition 1.0 2023-06
TECHNICAL
REPORT

colour
inside


Printed board assemblies –
Part 9: Electrochemical reliability and ionic contamination on printed circuit
board assemblies for use in automotive applications – Best practices
IEC TR 61191-9:2023-06(en)

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IEC TR 61191-9

®


Edition 1.0 2023-06




TECHNICAL



REPORT








colour

inside










Printed board assemblies –

Part 9: Electrochemical reliability and ionic contamination on printed circuit

board assemblies for use in automotive applications – Best practices

























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 31.180; 31.190 ISBN 978-2-8322-7028-8




  Warning! Make sure that you obtained this publication from an authorized distributor.


® Registered trademark of the International Electrotechnical Commission

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– 2 – IEC TR 61191-9:2023 © IEC 2023
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions related to management . 9
3.2 Technical terms and definitions . 9
3.3 Abbreviated terms . 10
4 Failure mode electrochemical migration . 10
4.1 Background of electrochemical migration . 10
4.2 Complexity of electrochemical migration . 12
4.3 Conductive anodic filament (CAF) and anodic migration phenomena (AMP) . 13
4.4 Creep corrosion . 14
5 Electrochemical migration and relevance of ionic contamination . 15
5.1 General aspects . 15
5.2 Background of ionic contamination measurement . 15
5.3 Restrictions and limitations of ionic contamination measurement for no-clean
assemblies . 17
5.4 Restrictions and limitations of Ionic contamination measurement for cleaned
products . 28
5.5 How to do – Guidance to use cases . 37
5.6 Examples for good practice . 40
6 Surface insulation resistance (SIR) . 43
6.1 SIR – An early stage method to identify critical material combinations and
faulty processing . 43
6.2 Fundamental parameters of influence on SIR . 43
6.3 Harmonization of SIR test conditions for characterization of materials for
automotive applications . 51
6.4 Different steps of SIR testing . 51
7 Comprehensive SIR testing – B52-approach . 55
7.1 General aspects . 55
7.2 The main B52 test board . 56
7.3 The test patterns . 57
7.4 Processing of B52 boards . 59
7.5 Sample size for SIR testing of B52 test coupons . 59
7.6 Preparation for SIR testing . 59
7.7 Sequence of SIR testing . 60
7.8 Evaluation . 62
8 Example for good practice . 62
8.1 Methodology for material and process qualification, process control . 62
8.2 Step 1 – Material qualification . 62
8.3 Step 2 – Product design verification and process validation . 64
8.4 Step 3 – Definition of process control limits . 65
Annex A (informative) SIR measurement for SMT solder paste – Representative
example . 67
A.1 Purpose . 67
A.2 Equipment . 67

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IEC TR 61191-9:2023 © IEC 2023 – 3 –
A.3 Example of an instruction how to perform the test . 67
Bibliography . 70

Figure 1 – Principal reaction mechanism of ECM . 11
Figure 2 – Uncertainty in local conditions determines ECM failures . 11
Figure 3 – Occurrence of ECM failures during humidity tests . 12
Figure 4 – VENN diagram showing the factors influencing ECM . 13
Figure 5 – Occurrence of CAF and AMP . 14
Figure 6 – Creep corrosion caused by corrosive gases . 15
Figure 7 – Ionic contamination measurement . 16
Figure 8 – Principal operation mode (fluid flow) of ROSE . 17
Figure 9 – Effect of solvent composition on the obtained ROSE results . 18
Figure 10 – Effect of solvent composition on the obtained ion chromatography result . 18
Figure 11 – Comparison of ROSE values with different solvent mixtures and material
variations of the CBA . 21
Figure 12 – Variation in ROSE values depending on technology used . 22
Figure 13 – Destructive action of solvent on resin matrix . 23
Figure 14 – Comparison of the resin change . 23
Figure 15 – Destructive action of solvent on resin matrix and chipping effect . 24
Figure 16 – Assembly manufactured with 2x SMT and 1x THT process for the
connector . 28
Figure 17 – Comparison of SPC-charts from 1-year monitoring of different CB
suppliers and two different iSn final finish processes . 29
Figure 18 – Differences in ROSE values for unpopulated CBs depending on the
extraction method . 30
Figure 19 – Reduction of ionic contamination on bare CBs (state of delivery from CB
supplier) by leadfree reflow step without solder paste or components . 32
Figure 20 – Influence of components on the ionic contamination based on
B52‑standard . 33
Figure 21 – Formation of a white veil or residue on MLCCs during active humidity test . 34
Figure 22 – Chromatogram derived from ion chromatography measurement of a
cleaned CBA . 36
Figure 23 – Approach for achieving objective evidence for a qualified manufacturing
process in the automotive industry . 41
Figure 24 – ROSE as process control tool . 42
Figure 25 – View on SIR measurement . 44
Figure 26 – Principal course of SIR curves . 45
Figure 27 – Response graph concerning stabilized SIR-value after 168 h from a DoE
with B53-similar test coupons (bare CB) . 45
Figure 28 – SIR measurement with B24-CB, no-clean SMT solder paste . 46
Figure 29 – Increase in ECM propensity depending on voltage applied (U) and Cu-Cu
distances (d) of comb structures . 48
Figure 30 – Layout of B53 test coupon . 49
Figure 31 – B53 with solder mask, partially covered and fully covered comb structures . 53
Figure 32 – B52 CBA after SMT process, layout slightly adapted to fulfil company
internal layout rules . 56

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– 4 – IEC TR 61191-9:2023 © IEC 2023
Figure 33 – Pattern of B52 CB, layout slightly adapted to fulfill company internal layout
rules . 57
Figure 34 – Positive example of comprehensive SIR tests obtained for qualification of
a SMT process . 61
Figure 35 – Negative example of a contaminated B52-sample, tested by the sequence
of constant climate and cyclic damp heat climate . 61
Figure 36 – SIR test coupon, similar to B53, for principal material qualification . 63
Figure 37 – SIR test with constant climate and cyclic damp heat condition . 63
Figure 38 – B52 test board and example of SIR curve . 64
Figure 39 – Example of the product that was realized by the released materials and
process . 64
Figure 40 – Ionic contamination test results from 4 repetitions of PV samples . 65
Figure 41 – Results of ionic residue testing and calculation of upper control limit (UCL) . 65
Figure 42 – Run chart derived from 2 samples per month during mass production . 66

Table 1 – List of ions based on IPC-TM650, 2.3.28 [21] . 26
Table 2 – Fingerprint after ion chromatography of no-clean assembly shown in
Figure 16 . 27
Table 3 – Fingerprint after ion chromatography of bare CBs (state of delivery) . 31
Table 4 – Fingerprint after ion chromatography of a bare CB and the respective PBA in
uncleaned and cleaned condition . 35
Table 5 – Fingerprint after ion chromatography of an uncleaned CBA compared to the
cleaned CBA and after removing the components . 37
Table 6 – Common test conditions for basic material evaluation . 51
Table 7 – Recommended SIR test conditions for basic material- and process release
for the outer layer manufactured by a CB supplier. 55
Table 8 – List of materials for components with recommendations for minor
adaptations . 58
Table 9 – Sequence for SIR testing of B52-CBAs for general material- and process
qualification . 60

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IEC TR 61191-9:2023 © IEC 2023 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

PRINTED BOARD ASSEMBLIES –

Part 9: Electrochemical reliability and ionic contamination on
printed circuit board assemblies for use in automotive applications –
Best practices

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC TR 61191-9 has been prepared by IEC technical committee 91: Electronics assembly
technology. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
91/1811/DTR 91/1825A/RVDTR

Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.

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– 6 – IEC TR 61191-9:2023 © IEC 2023
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 61191 series, published under the general title Printed board
assemblies, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

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IEC TR 61191-9:2023 © IEC 2023 – 7 –
INTRODUCTION
The document applies to electronic and electromechanical automotive circuit board assemblies.
It describes current best practices for dealing with electrochemical reactions like migration or
corrosion and ionic contamination on the surface of a printed circuit board as one failure mode
under humidity load.
This document is an informative document which serves to illustrate the technically feasible
options and provide a basis for customer and supplier agreements. It is not intended to be
regarded as a specification or standard.
Related standards are gathered in the Bibliography.

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– 8 – IEC TR 61191-9:2023 © IEC 2023
PRINTED BOARD ASSEMBLIES –

Part 9: Electrochemical reliability and ionic contamination on
printed circuit board assemblies for use in automotive applications –
Best practices



1 Scope
This part of IEC 61191, which is a Technical Report, applies to electronic and electromechanical
automotive circuit board assemblies and describes current best practices for dealing with
electrochemical reactions like migration or corrosion and ionic contamination on the surface of
a circuit board as one failure mode under humidity load. This document deals with the evaluation
of materials and manufacturing processes for the manufacturing of electronic assemblies with
focus on their reliability under humidity loads. The electrical operation of a device in a humid
environment can trigger electrochemical reactions that can lead to short circuits and
malfunctions on the assembly. In this context, a large number of terms and methods are
mentioned, such as CAF (conductive anodic filament), anodic migration phenomena, dendrite
growth, cathodic migration, ROSE (resistivity of solvent extract), ionic contamination, SIR
(surface insulation resistance), impedance spectroscopy, etc., which are used and interpreted
differently. The aim of the document is to achieve a uniform use of language and to list the
possibilities and limitations of common measurement methods. The focus of the document is
on the error pattern of electrochemical migration on the surface of assemblies with cathodic
formation of dendrites.
Evaluation of different test methods of control units under high humidity load are not part of this
document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
IEC 60194-1, Printed boards design, manufacture and assembly – Vocabulary – Part 1:
Common usage in printed board and electronic assembly technologies
IEC 60194-2, Printed boards design, manufacture and assembly – Vocabulary – Part 2:
Common usage in electronic technologies as well as printed board and electronic assembly
technologies
3 Terms, definitions and abbreviated terms
For the purposes of this document, the terms and definitions given in IEC 60194-1, IEC 60194-2
and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp

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IEC TR 61191-9:2023 © IEC 2023 – 9 –
3.1 Terms and definitions related to management
3.1.1
design authority
individual, organization, company, contractually designated authority, or agency responsible for
the design of electrical/electronic hardware, having the authority to define variations or
restrictions to the requirements of applicable standards, i.e., the originator/custodian of the
applicable design standard and the approved or controlled documentation
3.1.2
manufacturer
individual, organization, or company responsible for the assembly process and verification
operations
3.1.3
production part approval process
PPAP
procedure in accordance to IATF 16949 [1] to regulate the sample submission process within
the supply chain, primarily used for the series release of new parts
Note 1 to entry: The main objective of the procedure is the regulated start-up assurance with regard to quality and
quantity of mass production.
3.1.4
user
individual, organization, company, or agency responsible for the procurement of
electrical/electronic hardware and having the authority to define any variation or restrictions to
requirements
EXAMPLE Originator/custodian of the contract detailing the requirements.
3.2 Technical terms and definitions
3.2.1
conductive anodic filament
CAF
migration which occurs along the monofilament of reinforcing material such as glass cloth in an
inner layer part of a printed wiring board
3.2.2
no-clean
produced with a no-clean solder material and optimized process parameters throughout the
entire process chain (e.g. design, printing, soldering), for which flux residues are usually not
critical and removal of these residues is not necessary
Note 1 to entry: There could be additional requirements of customers.
3.2.3
resistivity of solvent extract
ROSE
analytical method to determine the integral contamination load on a CB or CBA causing
electrical conductivity
3.2.4
surface insulation resistance
SIR
electrical resistance of an insulating material between a pair of contacts, conductors or
grounding devices in various combinations, which is determined under specified environmental
and electrical conditions

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– 10 – IEC TR 61191-9:2023 © IEC 2023
3.3 Abbreviated terms
AIT assembly and interconnect technology
AMP anodic migration phenomena
CB circuit board
CBA circuit board assembly
DI-water deionized water
ECM electrochemical migration
ECU electronic control unit (CBA with housing)
IC ion chromatography
ICont ionic contamination
iSn immersion tin
OSP organic surface protection
PB printed circuit board (bare board as delivered by PB manufacturer)
Note 1 to entry: This abbreviated term is not preferred.
PBA printed circuit board assembly (unit without housing)
Note 1 to entry: This abbreviated term is not preferred.
PCB printed circuit board (bare board as delivered by CB manufacturer)
Note 1 to entry: This abbreviated term is not preferred.
PCBA printed circuit board assembly (populated CB without housing)
Note 1 to entry: This abbreviated term is not preferred.
SMD surface mounted devices
SMT surface mounting technology
THR through hole reflow
THT through hole technology
WOA weak organic acid

4 Failure mode electrochemical migration
4.1 Background of electrochemical migration
The electrochemical migration on electronic assemblies is understood as the migration of
metallic ions such as Ag, Cu, Sn, Ni in a water film on the assembly. The ions are released at
the anode (the positive pole of the assembly, e.g. terminal 30), migrate by a diffusion controlled
mechanism in the water film to the cathode (the negative pole, e.g. ground, GND) and are
deposited there again by reduction with dendrite formation (electrocrystallisation). The dendrite
can then grow back towards the anode and create an electrical short circuit. This process can
only take place if there is a closed water film between the anode and cathode and if there is a
corresponding pot
...