Table Of ContentHUMIDITY AND ELECTRONICS
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Woodhead Publishing Series in Materials
HUMIDITY AND
ELECTRONICS
CORROSION RELIABILITY ISSUES
AND PREVENTIVE MEASURES
R A
AJAN MBAT
K P
AMILA IOTROWSKA
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Contents
Preface vii
1. Humidity and electronics: corrosion perspectives 1
1.1 Scopeofthisbook 1
1.2 Historyofelectronics 6
1.3 Useofmaterialsinmodernelectronics 13
1.4 Electronicsandcorrosionreliabilitytoday 15
References 18
2. Basic theory of corrosion and important failure mechanisms
connected to corrosion in electronics 19
2.1 Definitionofcorrosion 19
2.2 Corrosioninelectronicsversusconventionalcorrosionscenario 21
2.3 Electrochemicalcorrosionofmetalsunderwetconditions 24
2.4 Corrosionfailuremodesforelectronicsandrelatedmechanisms 48
References 88
3. Factors determining water film buildup on surfaces and
relevance to corrosion in electronics 93
3.1 Characteristicsofmoisture 94
3.2 Interactionofhumiditywithelectronics 103
References 138
4. Importance of PCBA cleanliness in humidity interaction with
electronics 141
4.1 Natureoftheresidueandhumidityinteraction 143
4.2 ContaminationoriginatingfromthePCBAmanufacturingprocess 147
4.3 Contaminationrelatedtooperatorhandling 181
4.4 Contaminationoriginatingfromtheuserenvironment(servicelife) 182
References 191
v
vi
Contents
5. Materials and processes for electronic devices and components: how
they contribute to corrosion reliability? 197
5.1 Manufacturingprocessofbareprintedcircuitboard 199
5.2 Componentassembling,mounting,andsolderingprocesses 214
5.3 Electroniccomponents 225
References 249
6. Examples of corrosion failures in electronics: summary of case
studies 251
6.1 Failuresduetoprocess-relatedcleanlinessissuesasamainfactor 251
6.2 Failurescausedbycorrosivegasesandhumidity 259
6.3 Failuresduetomaterialcombinationsandenvironment 271
6.4 Failuresofhigh-powerelectronicsystemsduetoenvironmentalconditions 278
References 281
7. Preventive measures for corrosion in electronics: intrinsic and
extrinsic strategies 285
7.1 Intrinsicmethodsforcorrosionmitigationinelectronics 286
7.2 Extrinsicmethodsforenhancingthehumidityrobustness 300
References 336
8. Corrosion reliability testing, standards, and failure analysis 339
8.1 TestingofPCBAcleanlinessandcontaminationlevel 341
8.2 Testsinvestigatingthecleanlinessandcorrosioneffects 350
8.3 Methodologyofacceleratedtestingofelectronicequipment 374
8.4 Spectroscopicandmicroscopicmethods 376
References 379
Index 381
Preface
Today, electronics is used everywhere as a part of industrial systems
and as consumer electronics, while the intended use of electronic sys-
tems will be exponentially increased in the future. The focus of 21st-
century technological development is oriented toward sustainability.
Today’s three main global challenges are energy, clean water, and clean
air, and electronics is an integral part of this development, while, on the
other side, the everyday life of a person is closely connected to the use
of several electronic gadgets and their performance. Efficient electrical
energy production, distribution, and utilization are the most important
aspects for sustainable development, especially considering the growth
in the renewable energy sector within the next 20 years, and reliable
electronics are thekey components.
The effect of exposure climate on the robustness and reliability of
electronicsismoresignificanttodaythanbeforeduetotheirwidespread
use exposing them to all types of climatic conditions. Although humid-
ity is the key factor contributing to the robustness and reliability issues,
other atmospheric conditions such as the presence of aerosol and gas-
eous contaminations also influence the device performance. All result in
several corrosion failure modes causing intermittent or permanent fail-
ures at the component-, Printed Circuit Board Assembly (PCBA)-, or
system level. There exist other inherent factors related to the electronic
systems contributing to these increased robustness and reliability issues
such as the multimaterial usage, miniaturization, electrical aspects, or
process-related issues, all while the systems are expected to perform in
mild to harsh climatic conditions without failure occurrence. Such pro-
blems will increase significantly in the future due to the enhanced inte-
gration of electronics as part of all technological sectors, for example, in
connection with a green transition and e-mobility. Today, the knowl-
edge on corrosion reliability issues of electronics and how to tackle
them are limited among those involved in developing and using the
electronics.
Difficulty inunderstandingthecorrosion reliability issues ofelectron-
icsisalsorelatedtotheinterdisciplinarynatureofthissubjectcompared
to the conventional corrosion topics. Although the fundamental basis of
the failure mechanisms of corrosion in electronics is centered on electro-
chemical or chemical aspects, the resulting effect on the product is man-
ifested as electrical functional issues. Additionally, behavior of the
vii
viii
Preface
materials(individuallyorincombinationduetothemultimaterial usage
and manufacturing process-related issues) plays a key role. For exam-
ple, PCBA as a whole corroding substrate is too complex to understand
as it does not involve only the material- and corrosion-related features,
but also corrosion mechanisms that interact with the electrical and elec-
tronic functionality of thesystem.
This book attempts to provide a discussion on these topics at a basic
level with an intention to cover the readers from across the interdisci-
plinary areas, while providing a more detailed discussion on topics
with well-referenced coverage of literature—all to build the knowledge
from a basic to the application level. The book contains a mix of aca-
demic and industrial relevance, making it suitable for a detailed under-
standing of the humidity-related issues in electronics, both for the
materials and corrosion experts and for electronics and electrical
experts. Our ambition is for the book to be useful for researchers, aca-
demics, and the industrial community involved in materials, corrosion,
and electronics reliability aspects. The methodology used in the book is
based on a proactive-design-prevention perspective. To the best of
author’s knowledge, this is the first book in this area comprehensively
discussingthese topics.
Today,manyfailuresinelectronics arenotidentifiedduetocorrosion
because of two factors: (1) difficulty in locating the humidity-related
failures as the traces of failure could disappear during disassembling
and (2) lack of knowledge on the corrosion failures and related factors
among those involved in failure analysis, therefore, compromising the
quality of the failure evaluation. Lack of knowledge also influences the
possibilityofimplementingthepreventivemeasures,asthereisnocom-
prehensive knowledge on steps that could be taken to instill the corro-
sion reliability perspective from the production stage. This book tried to
fill this gap by attempting to show a number of intrinsic and extrinsic
possibilities for preventing the occurrence of corrosion failures in elec-
tronic devices.
The limitation of any book is related to the difficulty in covering all
relevant subtopics in detail. Our aim is to provide a broad coverage
encompassing all required topics in relation to the title of the book;
however, this meant cutting short on certain topics depending on their
relative importance. To address this issue, chapters are well referenced
for providing additional information to thereader. We strongly urgethe
readers to further explore the topics using the references provided at
theendof each chapter.
All books are expected to contain some errors due to the massive
nature of the work. We expect the same to be true for this book despite
the repeated reading and editing exercises. If you find any mistakes or
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Preface
discrepancies, please inform us so that they can be corrected in the
future.
There are many people that we owe our sincere thanks in connection
with preparing this book. Many topics covered in it contain a summa-
rized knowledge from a number of research activities and published
work from the CELCORR research group based at DTU. In this respect,
we are indebted to several students and researchers who have contrib-
utedtotheseactivitiesinthelast15years,although,duetospacelimita-
tions, all names cannot be mentioned. Our foremost appreciation goes
to Daniel Minzari, Umadevi Rathinavelu, Vadimas Verdingovas, Helene
Conseil-Gudla, Morten Jellesen, Feng Li, Salil Joshy, Simone Lauser,
Ioannis Mantis, Sajjad Bahrebar, Anish Rao, Abhijeet Yadav, and Peter
Westermann. We are also indebted to the collaborators from our indus-
trial partners, namely, Danfoss, Grundfos, Vestas, Eltek, Volvo, Widex,
Inventec, Wevo, and Bosch, who have contributed to generating the
knowledge relevant to this book. Many other research and industrial
partner’s contributions, through their participation in various research
programs during the last 15 years, are also acknowledged, although
their namesarenot mentioned. Additionally, wewouldlike to acknowl-
edge Mathilde Buret (Inventec), Chris Hunt (GEN3 systems), and Lutz
Muller (Bosch) for providing pictures for illustrations. We are also
grateful to the staff of Elsevier for a great collaboration and profession-
alism during this project.
Finally, we would like to thank our family members Indu, Deepthi,
Tina, Hanna, Ryszard, and Hristo for providing enough time for us to
sparefor this work, which otherwisebelongs to them.
Rajan Ambat and Kamila Piotrowska
