IEC TR 62866:2014

IEC TR 62866 ®
Edition 1.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
Electrochemical migration in printed wiring boards
and assemblies – Mechanisms and testing

Migration électrochimique dans les cartes a circuits imprimés et assemblages –
Mécanismes et essais
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IEC TR 62866 ®
Edition 1.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
Electrochemical migration in printed wiring boards

and assemblies – Mechanisms and testing

Migration électrochimique dans les cartes a circuits imprimés et assemblages –

Mécanismes et essais
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XD
ICS 31.180 ISBN 978-2-8322-1559-3

– 2 – IEC TR 62866:2014 © IEC 2014
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Electrochemical migration . 10
2.1 Operation failure of electronic and electric equipment . 10
2.2 Name change of migration causing insulation degradation and nature of the
degradation. 11
2.2.1 History of naming with migration causing insulation degradation . 11
2.2.2 Process of degradation by migration . 11
2.3 Generation patterns of migration . 11
3 Test conditions and specimens . 13
3.1 Typical test methods . 13
3.2 Specimens in migration tests . 14
3.2.1 Design of test specimens . 14
3.2.2 Specifications and selection of specimen materials . 19
3.2.3 Remarks on the preparation of specimens . 20
3.2.4 Storing of specimens . 20
3.2.5 Pretreatment of the specimen (baking and cleaning) . 20
3.2.6 Care to be taken in handling specimens . 21
3.3 Number of specimens required in a test . 21
3.3.1 Specifications given in JPCA ET 01 . 21
3.3.2 Number of specimens in a test . 22
3.3.3 Number of specimens for the different evaluation purposes of a test. 22
4 Test methods . 23
4.1 General . 23
4.2 Steady state temperature and humidity test and temperature-humidity cyclic
test . 23
4.2.1 Purpose and outline of the test . 23
4.2.2 Test profile . 24
4.2.3 Test equipment . 27
4.2.4 Remarks on testing . 28
4.3 Unsaturated pressurized vapour test or HAST (highly accelerated temperature
and humidity stress test) . 30
4.3.1 Purpose and outline of the test . 30
4.3.2 Temperature-humidity-pressure profile . 31
4.3.3 Structure of and remarks on the test equipment . 32
4.3.4 Remarks on performing HAST . 34
4.4 Saturated and pressurized vapour test . 36
4.4.1 Purpose and outline of the test . 36
4.4.2 Test profile . 36
4.4.3 Remarks on test performing . 36
4.5 Dew cyclic test . 37
4.5.1 Purpose and outline of the test . 37
4.5.2 Dew cycle test temperature-humidity profile . 37
4.5.3 Structure of the test equipment . 38
4.5.4 Remarks on the test method . 38

4.5.5 An example of migration in the solder flux from the dew cycle test . 41
4.6 Simplified ion migration tests . 43
4.6.1 General . 43
4.6.2 De-ionized water drop method . 43
4.6.3 Diluted solution method . 45
4.7 Items to be noted in migration tests . 46
5 Electrical tests . 49
5.1 Insulation resistance measurement . 49
5.1.1 Standards of insulation resistance measurement . 49
5.1.2 Measurement method of insulation resistance . 49
5.1.3 Special remarks on insulation resistance measurement . 52
5.2 Measurement of dielectric characteristics . 55
5.2.1 General . 55
5.2.2 Dielectric characteristics of board surface . 55
5.2.3 Migration and dielectric characteristics of the printed wiring board surface
5.2.4 Evaluation of migration by AC impedance measurement . 59
6 Evaluation of failures and analysis . 60
6.1 Criteria for failures . 60
6.2 Data analysis . 61
6.2.1 Analysis of experimental data . 61
6.2.2 Relationship of the parameters in the experimental data and an example
of the analysis . 63
6.2.3 Electric field strength distribution . 64
6.3 Analysis of specimen with a failure, methods of analysis and case study . 65
6.3.1 General . 65
6.3.2 Cross section. 66
6.3.3 Optical observation . 70
6.3.4 Analysis methods . 72
6.3.5 Defect observation and analysis . 72
6.4 Special remarks on the migration phenomenon after the test . 77
Annex A (informative) Life evaluation . 80
A.1 Voltage dependence of life . 80
A.2 Temperature dependence of life . 80
A.3 Humidity dependence of life . 80
A.3.1 General . 80
A.3.2 Relation between temperature (°C), relative humidity ( %RH) and vapour
pressure (hPa) . 81
A.4 Acceleration test of life and acceleration factor . 81
A.5 Remarks . 82
Annex B (informative) Measurement of temperature-humidity . 83
B.1 Measurement of temperature and humidity . 83
B.1.1 General . 83
B.1.2 Commonly used temperature-humidity measurement systems and their
merits . 83
B.1.3 Requirements for the humidity measurements in a steady-state
temperature-humidity test chamber . 83
B.2 Typical methods of temperature and humidity measurement . 83
B.2.1 General . 83

– 4 – IEC TR 62866:2014 © IEC 2014
B.2.2 Checking procedure for temperature measurement . 84
B.2.3 Checking procedure for humidity measurement . 85
B.2.4 Derivation of temperature in a chamber . 86
B.2.5 Definition of relative humidity in HAST . 87
Bibliography . 89

Figure 1 – Main causes of insulation degradation in electronic equipment . 10
Figure 2 – Generation patterns of migration . 12
Figure 3 – Basic comb pattern . 14
Figure 4 – Comb type fine pattern . 15
Figure 5 – ECM group comb type pattern (mm) . 16
Figure 6 – Comb pattern for insulation resistance of flexible printed wiring board. 16
Figure 7 – Insulation evaluation pattern for through-holes and via holes . 17
Figure 8 – Details of the insulation evaluation pattern of Figure 7 (cross section of 4
and 5) . 18
Figure 9 – Test pattern of the migration study group . 18
Figure 10 – Recommended profiles of increasing temperature and humidity . 24
Figure 11 – Humidity cyclic profile (12 h + 12 h) . 25
Figure 12 – Profiles of combined temperature-humidity cyclic test . 26
Figure 13 – Structure of steady state temperature-humidity test equipment . 27
Figure 14 – Specimen arrangement and air flow in test chamber . 29
Figure 15 – Effective space in a test chamber . 30
Figure 16 – HAST profile . 31
Figure 17 – Two types of HAST equipment and their structures . 32
Figure 18 – Difference in failure time among different test laboratories . 33
Figure 19 – Colour difference of specimen surface among different laboratories

°C/85 %RH/DC 50 V) . 34
(130
Figure 20 – Resistance and pull-strength of cables used in HAST (130 °C 85 %RH) . 35
Figure 21 –Difference between unsaturated and saturation control of PCT equipment
(relative humidity and average failure time) . 37
Figure 22 – Temperature-humidity profile of dew cycle test . 38
Figure 23 – Structure of dew test equipment . 39
Figure 24 – Dew-forming temperature and dew size . 40
Figure 25 – Board surface at the best dew formation condition . 41
Figure 26 – Surface state before test . 42
Figure 27 – Surface state after 27 h . 42
Figure 28 – SEM image of specimen surface after the test . 42
Figure 29 – Element analysis of the surface after the test . 43
Figure 30 – Circuit diagram of water drop test . 44
Figure 31 – Migration generated in the water drop test . 44
Figure 32 – Electroerosion test method using the diluted solution . 45
Figure 33 – Current and concentration of electrolytic solution . 46
Figure 34 – Precipitation on a specimen and its element analysis . 46
Figure 35 – An example of insulation resistance measurement outside of the chamber . 50

Figure 36 – Circuit diagram of insulation resistance measurement . 51
Figure 37 – Examples of leakage current characteristics . 52
Figure 38 – Relationship insulation resistance with charging time of capacitor mounted
boards . 53
Figure 39 – Comparison of insulation resistance measurement inside and outside a test
chamber . 53
Figure 40 – Relative humidity and insulation resistance . 54
Figure 41 – Effect of interruption of measurement on insulation resistance (variation of
insulation resistance with the time left in atmospheric environment) . 55
Figure 42 – Frequency response of dielectric characteristics of printed wiring board . 57
Figure 43 – Temperature response of dielectric characteristics of printed wiring board . 57
Figure 44 – Changes of static capacitance and tan δ of a specimen through a
deterioration test . 58
Figure 45 – Test procedure of a dielectric characteristics test . 59
Figure 46 – Comparison of dielectric characteristics of two types of flux . 59
Figure 47 – Measurement principle of EIS (Electrical Insulation System) . 60
Figure 48 – Gold (Au) plating, non-cleaning . 60
Figure 49 – Bath tub curve . 61
Figure 50 – Relation between the variation of insulation resistance and the weight
changes by water absorption . 64
Figure 51 – Distribution of electric field between line and plane . 65
Figure 52 – Distribution of the electric field between lines . 65
Figure 53 – Different observations of the same dendrite according to different cross
section cutting planes . 66
Figure 54 – An example of angle lapping . 68
Figure 55 – Structure analysis of an angle lapped solder resist in the depth direction . 69
Figure 56 – Observed images of dendrite with different illumination methods (without
solder resist) . 73
Figure 57 – EPMA analysis of migration (dendrite) on a comb type electrode . 73
Figure 58 – EPMA analysis of migration (dendrite) in the solder resist . 74
Figure 59 – 3D shape measuring system . 75
Figure 60 – Electrodes which migration was generated . 75
Figure 61 – 3D observation of electrodes before and after the test . 76
Figure 62 – 3D observation of dendrite . 77
Figure A.1 – Temperature and saturated vapour pressure . 81
Figure B.1 – Specification of sensors used in the test and their shapes . 85
Figure B.2 – Calculation method of the average temperature (humidity), the average
maximum temperature (humidity) and the average minimum temperature (humidity) . 86
Figure B.3 – Relative humidity in a pressurized chamber . 88

Table 1 – Standards for migration tests . 13
Table 2 – Standard comb type pattern (based on IPC-SM-840) . 15
Table 3 – Comb fine pattern (based on JPCA BU 01) . 15
Table 4 – Dimension of insulation evaluation pattern for through-holes . 18
Table 5 – Surface pretreatment to printed wiring board . 21

– 6 – IEC TR 62866:2014 © IEC 2014
Table 6 – Number of specimens (JPCA ET 01) . 22
Table 7 – Approximate number of specimens required depending on the purpose of the
test 22
–6
Table 8 – Ionic impurity concentration of wick (10 ) . 29
Table 9 – Insulation covering materials for cables for voltage application . 34
Table 10 – Dew cycle test condition . 38
Table 11 – Dew formation condition and dew size . 41
Table 12 – Dew cycle test condition . 41
Table 13 – Water quality for test . 47
–6
Table 14 – Water quality change in steady-state temperature-humidity test (10 ) . 47
–6
Table 15 – Ionic impurities in voltage applying cables (10 ) . 48
Table 16 – Standards of insulation resistance measurement . 49
Table 17 – Criteria of migration failure by insulation resistance . 61
Table 18 – Various methods for optical observation of failures . 70
Table 19 – Various methods for defect analysis . 72
Table 20 – Board specification and test conditions . 77
Table 21 – Effect of the overlap of electrodes . 78
Table 22 – Effect of the area of the conductor . 78
Table 23 – Effect of the shape of the tip of the electrodes . 79
Table A.1 – Vapour pressure at test temperature and relative humidity . 81
Table B.1 – Merits of and remarks on various humidity measuring methods (applicable to
steady state temperature-humidity tests) . 84
Table B.2 – Derivation of relative humidity from dry-and-wet bulb humidity meter . 87

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROCHEMICAL MIGRATION IN PRINTED WIRING BOARDS
AND ASSEMBLIES – MECHANISMS AND TESTING

FOREWORD
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all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected data
of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 62866, which is a technical report, has been prepared by IEC technical committee 91:
Electronics assembly technology.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
91/1102/DTR 91/1128/RVC
Full information on the voting for the approval of this technical report can be found in the report
on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 8 – IEC TR 62866:2014 © IEC 2014
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• reconfirmed,
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INTRODUCTION
Electronic products including components nowadays are designed to satisfy the demands for
miniaturization, high functionality and environmentally friendly products. Various types of
degradation occur in the electronic products used in the field. Appropriate measures are
required to mitigate such degradation from the standpoint of reliability assurance. A study has
been carried out to develop the understanding of the phenomenon and has proposed test
methods for electrochemical migration with the purpose of suppressing the migration in products
used in the field.
This Technical Report is related to electrochemical migration including conductive anodic
filament (CAF). Specifically, it explains:
• the preliminary test: the steady state temperature humidity test, the temperature humidity
cycle test, the unsaturated pressurized vapor test, the saturated pressurized vapor
pressure test, the dew condensation cycle test and the water drop test;
• the insulation resistance measurement method: manual measurement, automatic
measurement, a dielectric characteristics method, and an AC impedance method. Moreover,
the difference between the measurement while the specimen is kept in the testing
environment and not taken out of the chamber for measurement, and the measurement of
the resistance of a specimen while it is taken out of the test chamber, and the merit of an
automatic measurement are also described;
• the equipment used for analysis, the observation method of a failure part, and examples
which are used for analysis.
This Technical Report generates a number of benefits for the user:
Usefulness the user can examine the electrochemical migration test in a short
time, and can use it as an indicator of exact analysis.
Test method selection since for the user the test method which responds to the operating
condition of the equipment or the purpose is clearly demonstrated,
comparison of test condition becomes easy. Compared to the
measurement resistance of a specimen while it is taken out of the
test chamber after the test chamber is return to the standard
atmosphere condition, the measurement in the test chamber by
automatic measurement does not experience the environmental
change of a specimen at the time of measurement, and since
continuous measurement can be carried out, the resistance change
and failure time can be grasped correctly.
Avoidance of trouble by observing the notice on the test, the user can avoid a trouble and
carry out test and analysis efficiently.

– 10 – IEC TR 62866:2014 © IEC 2014
ELECTROCHEMICAL MIGRATION IN PRINTED WIRING BOARDS
AND ASSEMBLIES – MECHANISMS AND TESTING

1 Scope
This Technical Report describes the history of the degradation of printed wiring boards caused
by electrochemical migration, the measurement method, observation of the failure and remarks
to testing in detail.
2 Electrochemical migration
NOTE Electrochemical migration is sometimes called ion migration. In this technical report electrochemical
migration/ion migration will be referred to as migration.
2.1 Operation failure of electronic and electric equipment
It is known that failures caused by various degradation phenomena occur in electric and
electronic products while they are used in the field. Causes of such failures are classified in
Figure 1. The causes may be classified into: electric, thermal, mechanical and electrochemical
origins. They are entwined with each other. The environment in which equipment is used also
affects the generation of failures.
Growth of an electrically conducting filament caused by migration will short-circuit two
conductors when a bias voltage is applied between them and will lead to a malfunctioning in the
equipment.
Electric
Partial discharge
Electrical treeing
Water treeing
Electrochemical migration
Tracking
Arc
Chemical and thermal
Environmental Electrochemical
Whisker
Corrosion
Crack
Chemical treeing
Interfacial
-separation
Mechanical
IEC  1272/14
Figure 1 – Main causes of insulation degradation in electronic equipment

2.2 Name change of migration causing insulation degradation and nature of the
degradation
2.2.1 History of naming with migration causing insulation degradation
Migration causing insulation failure had been called “ion migration” in Japan. A change of the
definition of the phenomenon resulted in a change of name to “electrochemical migration”, but
the name of “ion migration” is sometimes still used. The following description is the history of the
change of name.
The first report on insulation failure was made in 1955, where the failure caused by the migration
of silver atoms was reported and the phenomenon was called “silver migration”. It was also
found that other metal atoms, including Pb and Cu, caused similar insulation failures, and so the
phenomenon was called “metal migration”. The term “electromigration” was used as a general
term for the phenomenon, and has been used for a long time in the IPC test method,
IPC-TM-650:1987, 2.6.14A.
It was found since the latter half of the 1960s that interconnection failures in semiconductor
devices were serious problems as the current flowing through a conductor significantly
increased. This phenomenon was also called “electromigration”. The opening of a conductor
was caused by the movement of metal atoms due to an increased current density, which
produced dense and sparse layers within the conductor and resulted in a break of the conductor.
IPC changed the name of the phenomenon to “electrochemical migration” in its technical report
IPC-TR-467A, and developed a new test method, IPC-TM-650:2000, 2.6.14C, which
ISO adopted as ISO 9455-17. IEC 60194 which provides the terms and definitions for printed
board design, manufacture and assembly, still uses the term “electromigration”. However, the
name should be changed in the near future.
NOTE IPC-9201A uses and defines both electromigration (EMg) and electrochemical migration (ECMg).
References: 1) KOHMAN G. T., et al. Silver migration in electrical insulation, BSTJ 34 299, 1955
2) POURBAIX, M., Atlas d’Equilibres Electrochimiques, Gauthier-Villars et Cie ed., 1963
2.2.2 Process of degradation by migration
Good insulation between electrodes may be maintained in the application of DC voltage
between electrodes on a printed wiring board of electronic equipment, as long as the electrodes
are isolated by an insulating material of a high resistivity. If the insulating material absorbs
moisture and the insulation resistance decreases, residual ionic contaminants in the insulating
material or ions in the absorbed moisture will become active and metal atoms in the material will
be ionized. Metal ions dissolve from the metal electrodes, either from an anode or a cathode,
into the moistened electrolyte. Ions are transferred through the electrolyte by the electric field
force. Metal ions (migration) move to an electrode and then educe in the form of dendrite. The
dendrite bridges the neighbouring conductor electrode. The generation of (electrochemical)
migration is described in 2.3.
2.3 Generation patterns of migration
Migration begins in the anode by dissolving as metal ions by an electrochemical reaction. There
are two cases of this phenomenon as shown in Figure 2. In the first case, the reduction of ions
into metal atoms or chemical compound molecules occurs somewhere in between the electrodes.
In the second case, the reduction of metal ions occurs when the ions reach the cathode.
The first case is observed when the insulating material still maintains a high resistance to the
order of 10 Ω or higher. The second case is often observed in HAST (highly accelerated
temperature and humidity stress test), where the insulation resistance is reduced by the
presence of dew, solder resist or cover layer on the insulation surface.
The difference in these two cases of migration seems due to the difference in the degree of
easiness of movement of the metal ions. The second type of migration becomes dominant when

– 12 – IEC TR 62866:2014 © IEC 2014
the apparent resistance decrease exists and the metal ions can move more easily than in the
first case, while the first case is dominant when metal ions resolve from the anode but cannot
move easily in the insulation. The change of one mechanism to the other in the migration is not
an independent phenomenon but is simply due to the difference in insulation resistivity of the
electrolyte material between electrodes.
Reduction of metal ions left from the anode into
metal atoms or reduction of ions to form chemical
compounds in insulation
Reduction of metal ions reaching to the cathode and
receiving electrons to become metal ions
Anode
Cathode
IEC  1273/14
Figure 2 – Generation patterns of migration

3 Test conditions and specimens
3.1 Typical test methods
the main test method for migration is shown in Table 1.
Table 1 – Standards for migration tests
Items Humidifying conditions Duration and bias Document no.
Steady state IEC 60068-2-78
40 °C ± 2 °C +24
168 h
Temperature/ 0
93 % ± 3 %RH
humidity test
500 h ± 48 h
1 000 h ± 96 h
60 °C ± 2 °C IEC 60068-2-78
+24
168 h, 500 h ± 48 h
+2
93 %RH
1 000 h ± 96 h
−3
IEC 60068-2-67
85 °C ± 2 °C
+24
168 h, 500 h ± 48 h
85 % ± 3 %RH
1 000 h ± 96 h
Temperature/ Relative humidity: 90 % to As agreed between user and IEC 60068-2-38
humidity cycle test 98 % supplier
80 % in rising and falling Abou
...