Table Of ContentPreface
Purpose of Publication and Background
Plating technology has existed for more than 2,000 years and has been practiced steadily
over the last two millennia. Modem plating technology is highly advanced, and has
developed to cover a wide range of applications, e.g. in addition to the traditional use for
surface finishing, plating technology can now offer novel processes to fabricate high-
performance films or fine microstructural bodies in the microelectronics industry. This
rapid progress reflects the potential for the electroplating method to become one of today's
leading-edge technologies.
The development of plating technology, however, has been slow due to the lack of a
sound theoretical foundation and has often relied on a method of trial and error to obtain
films with desirable properties. Despite numerous attempts, a unified theory has yet to be
established that can provide this control in a consistent manner.
This book is a compilation of vast amounts of experimental results that we have
obtained in collaboration with our students over the last 34 years. We will introduce the
concept of our new ''Microstructure Control Theory'' for plated films, which is entirely
different from previous theories. We will then describe various experimental results that
prove the validity of our theory. Finally, a large collection of experimental data on plated
metal/alloy systems will be presented with a special emphasis on their microstructure.
In the early days of research, we started modestly with fundamental studies on the
microstructure of electroless films and on epitaxial phenomenon occurring between a
plated film and a substrate. We presented these results as an occasional scientific paper in
technical society meetings. During the course of these studies, we became increasingly
aware of the possibility of producing amorphous films by plating methods. In 1988,
motivated by this curiosity, we proposed a theory that explains why plated films can form
an amorphous phase (cf. /. Surface Finish Soc. Japan 40, 375 (1989)). This theory was
found to be also applicable to crystalline materials, giving us an opportunity to develop a
theory explaining how the microstructure of plated pure metal/alloy films evolves. From
this theoretical exercise, it has become apparent that the microstructure of plated films is
closely connected to their equilibrium phase diagram. This concept finally led to the
establishing of a theory of microstructure control for plated films. In 1999, we found that
the microstructure of plated films can be categorized into 7 types. Each microstructural
type is unique, and thus could be controlled independently (The 2"*^ Thin Film Basic
Seminar, "Plating Methods", Japan Surface Science Society (1999) p. 115; Materia 40,
871 (2001)). Based on this microstructure classification, we are now able to focus on each
individual microstructure type and develop its control theory independently. We believe
that our efforts are finally paying dividends, as if tangled threads are being separated.
vi Preface
It is clear that in recent years much progress on theoretical work dealing with the
microstructural control of plated films has been made. After leading plating technology
discussion groups for the last 10 years, we sensed an urgent need for a specialized book on
the microstmcture control theory among researchers/engineers in the plating industry. For
this reason, we take the liberty to introduce this book although topics described within are
still far from completion. At the same time, we hope that the accomplishments made in
plating technology during the 20^^ century can be conveyed through this book into the 21^^
century.
To describe an effective manner of conducting plating research, we explain research
and experimental methods of plating. We list the microstructures of 53 types of plated pure
metals and alloys, which should serve as a useful database for plated films. The unique
feature of this database is that most of the plating baths are chosen to be simple and contain
no additives. In addition, amorphous materials are used as substrates to avoid the effect of
the substrate structure, and single-crystal substrates are chosen to study the epitaxial
growth phenomenon.
As mentioned above, the coverage in this book is still incomplete. Therefore, our
mission is to continue collecting experimental data to fill the many gaps left in this book.
At an opportune time, therefore, we will update the book accordingly.
We believe that the materials contained within this book represent a crystallization of our
students' efforts in conducting plating experiments over the last 34 years. We wish to express
our sincere thanks to all the students and collaborators involved and list their names below.
Thanks are also due to many companies, which funded, totally or partially, our research
activities over the years. Finally my sincere personal thanks go to Dr. Shohei Nakahara for
his invaluable assistance in the translation of this book from Japanese into English.
Faculty
Professor Emeritus Yoshimi Tanabe, Tokyo Metropolitan University.
Professor Emeritus Nobuyoshi Baba, Tokyo Metropolitan University.
Professor Shohei Nakahara, University of Limerick
Professor Emeritus Ryouichi Urao, Ibaragi University.
Professor Takeshi Nakata, Shibaura Institute of Technology.
Secretary Yoshinari Misaki.
Laboratory Faculty and Senior Associates
Professor Kazuhisa Ishibashi, Tokai University.
Shigeo Urai, Toyama National College of Technology.
Shouzo Asano, Senju Metal Co., Ltd.
Visiting Professors and Scientists
Wei-Ping Yu (China), Dr. Goran Holmbom (Sweden), Dr. Torben Tang (Denmark),
Preface vii
Dr. Xin-Tan Hu (China), Su-Wei Yao (China), Dr. Imre Bakonyi (Hungary) and
M.Sc. Anett Alsted Rasmussen (Denmark).
Research Students (Domestic)
Shinji Katou, Kazuo Shimizu, Suguru Abe, Yasutaka Mogi, Dr. Susumu Arai,
Hiroko Furusawa, Katsuhiko Tashiro, Hiroshi Tsukamoto, and Hirokazu Takagi.
Trainee (Foreign)
Yin-Qi Zhang.
Company Doctor Course Graduates
Motonobu Onoda (Nippon Piston Ring Co., Ltd) and Kiyoshi Itoh.
Doctor Course Graduates
Tokyo Metropolitan University
Seiji Kamasaki, Yasuo Shimizu, Masayuki Kakegawa, Hisakazu Ito, Hisashi
Fumy a, and Naoki Fukumuro, and Feng Wang.
Shibaura Institute of Technology
Koichiro Inoue.
Master Course Graduates
Tokyo Metropolitan University
Ken Tone, Hiroshi Matsubayashi, Toshihisa Sudo, Hiroki Shimizu, Hiroshi
Ikebuchi, Hiroyasu Kojima, Hideo Suda, Hiroshi Imai, Yukio Numakura, Yoshiaki
Ikeda, Naoya Hasegawa, Akira Narita, Hiroyuki Yamaguchi, Norimoto Usuzaka,
Satoru Katsumata, Kazuyoshi Arai, Kenji Takahashi, Akira Suzaki, Hai-Ying
Liang, lo Mizushima, Toshie Murai, Naoyuki Igarashi, Isao Satou, Kei Imafuji, and
Takayuki Ikeda. Yuuichiro Miura and Shouji Matsuda.
Shibaura Institute of Technology
Takanobu Kanayama, Kenji Ikejima, Ichiro Wada, and Hideki Kotsuji. Tomoya
Teshigawara, Takako Terakado, Yuki Makino, and Nobuto Sasaki.
Undergraduates
Tokyo Metropolitan University
Toshiaki Ogura, Toshiie Kurihara, Minoru Kanda, Hiroshi Nakajima, Isao Kawaida,
Mitsuru Kasahara, Kouhei Kitukawa, Akiyuki Kuniyoshi, Masao Soranishi, Kenzou
Matsui, Yukio Matsumoto, Isao Ikegaya, Minoru Uehara, Hiroshi Takashio, Fumiaki
Komatsu, Takakazu Fukuchi, Fujio Kawashima, Zenzaburo Naito, Kazuo Hoso-
kawa, Hideo Tomita, Mamoru Arai, Nobuyuki Kataigi, Takashi Inoue, Kazuo
Fukuda, Satomi Inoue, Takashi Eguro, Yoshio Kubota, Kazuyoshi Nishizawa,
viii Preface
Minom Odaka, Masaya Naoi, Satoru Shinohara, Nobuo Tomizawa, Susumu
Morohashi, Shinji Tobita, Yukihisa Hiroyama, Takayuki Anma, Jun Tanaka, Takuya
Naoe, Keiichi Nozawa, Tetsuo Sakamoto, Wakana Wasa, Takeshi Hirose, Hiroyuki
Hoshina, Toshiko Kitagawa, Naoyuki Kanami, Yoshiaki Fukuda, Tomokazu
Takasaka, Shusuke Minami, Shinichi Miyazaki, Saeko Yoshioka, Hroo Sawanobori,
Mari Tomita, Megumi Osada and Yuji Hanaie.
Shibaura Institute of Technology
Atushi Mituo, Jun Kubo, Sadanori Tanemura, Junko Hirose, Kenji Asada, and
Kazuyuki Koide. Akihiro Inami.
Current Students (2004)
Doctor Course
Tokyo Metropolitan University
Takashi Sugizaki (Meltex Inc.), Naoki Okamoto.
Master Course
Tokyo Metropolitan University
Jin-Song Qiu, Sayaka Doi, Kaori Hosoiri, Atushi Kondo and Mituhisa Funatu.
Shibaura Institute of Technology
Takuya Yoshihara Takahiro Makino and Miki Yachidate.
Undergraduate (Senior)
Tokyo Metropolitan University
Keigo Hoshina and Satoko Shoda.
Shibaura Institute of Technology
Kyohei Komori, Shinya Okahara, and Kazuya Kitazawa.
Companies that Provided Research Funds
Alps Electric Co., Ltd.
Nippon Piston Ring Co., Ltd.
Nihon Steel Corp.
Sumitomo Metal Industries, Ltd.
Hitachi Ltd.
Sumitomo Heavy Industries, Ltd.
Ebara-Udylite Co., Ltd.
Asahi Glass Co., Ltd.
Mitsui Mining & Smelting Co., Ltd.
N. E. Chemcat Corp.
Mitsubishi Aluminum, Ltd.
Mitsubishi Materials Co., Ltd.
Preface ix
Kyocera Corp.
Electroplating Engineering of Japan Ltd.
Hitachi Cable Ltd.
Limited Liability Company Taw
Konika Technology Center Corporation
Toppan Prating Co., Ltd.
Fuji Electric Co., Ltd
This book was originally published in Japanese in February 2003. The title was
"FINE PLATING: Microstructure Control and Analysis Methods for Plated Films"
published by Technical Information Association, Co., Ltd. This book is an English
version.
Dr. Tohru Watanabe
Department of Applied Chemistry
Graduate School of Engineering
Tokyo Metropolitan University
Minami-ohsawa, Hachioji-shi, Tokyo, 129-0397
Japan
Chapter 1
Microstructure Control Theory of Plated Film
1.1. Introduction 3
1.2. Research process of plating technology 4
1.3. Review of previous TMC and practical plated films 7
1.4. Theory of microstructure control for plated films 10
1.4.1 Metallurgical structure (crystalline, solid-solution, intermetallic
compound, meta-stable phase, amorphous phase, mixed phases) 10
1.4.2 Surface morphology (leveling, brightness, surface irregularities/
form, dendrite, etc.) 14
1.4.2.1 Surface morphology change with increasing film
thickness 14
1.4.2.2 Surface morphology change with current density
(overpotential) 24
1.4.2.3 Surface morphology change with the type of anions 29
1.4.2.4 Surface morphology change with solution temperature 32
1.4.2.5 Surface morphology change with solution agitation 32
1.4.2.6 Surface morphology of alloy films 32
1.4.2.7 Summary of the formation principles of surface
irregularities 36
1.4.2.8 Formation of dendrites 37
1.4.2.9 Effect of brighteners 38
1.4.3 Grain size (grain size, granular, spherical, columnar, needle-like,
etc.) 39
1.4.3.1 Grain size of pure metal deposits 39
1.4.3.2 Grain size of alloy deposits 41
1.4.4 Preferred orientation (texture) (film normal/film plane direction
and assembled structure) 46
1.4.4.1 Experimental methods for determining the texture of
plated films 50
1.4.4.2 Relationship between the texture of various plated films
and plating conditions 50
1.4.4.3 Effect of plating conditions on the film texture 57
1.4.4.4 Texture of electroless films 66
1.4.4.5 Summary 68
1.4.5 Bonding with substrate and crystallographic matching (epitaxy) 68
Nano-Plating
.4.6 Residual stress (compressive, tensile stresses, cracks) 74
.4.7 Anomalous morphology 79
1.4.7.1 Nodules 79
1.4.7.2 Pits 82
1.4.7.3 Cracks 82
1.4.7.4 Formation of layer structure 83
1.4.7.5 Initial layer 88
1.4.7.6 Whisker 91
References 91
Chapter 1
Microstructure Control Theory of Plated Film
1.1 INTRODUCTION
The ultimate goal of conducting research in the electroplating technology field is to
investigate how to produce plated films with desirable mechanical, physical, and chemical
properties that meet particular application requirements.
In the past, a vast number of papers have been published in the field of electroplating
technologies, and their primary emphasis has been placed on electrochemical studies. At the
same time, various attempts have been made to establish a unified theory that allows one to
control both the microstructure and properties. Attempts to establish such a theory have
been unsuccessful due to the complexities in achieving controlled experimental conditions.
It is often the case that while fixing one parameter, others change uncontrollably, i.e. all
the experimental parameters cannot be fixed at the same time. Furthermore, not all the
chemical reactions occurring during electrodeposition processes are well understood.
Because of these experimental difficulties and uncertainties, a reliable theoretical work
that attempts to find a link to electroplating technologies has been largely hindered.
From our extensive electrodeposition research in the past, we have come to the
conclusion that all the physical properties of electroplated films must originate from their
microstructure.
For example, in deriving the microstructure-alloy composition relationship in electro
plated alloy films, we found that the microstructural details provided more relevant infor
mation than the knowledge of the chemical reactions occurring during electrodeposition.
If we realize that "electroplated films are metallurgical materials and thus their
properties are closely related to their equilibrium phase diagram", "we can explain the
microstructure logically using a metallurgical concept".
Understanding of the microstructure led to the development of a theory that suggests a
way of controlling the microstructure of plated films. This theory will be called a theory of
microstructure control (TMC). Other physical properties, such as the surface morphology,
grain size and texture, can also be controlled independently in a similar manner. Based on
our previous studies as well as reports from the literature, we constructed seven categories
of microstructures in plated films, as depicted in Figure 1.1. Once the TMC is fully
developed for each microstructural category, we will be able to control the physical
properties of all categories of films.
In this book, we will attempt to explain the TMC concept and discuss the validity of the
theory using microstructural data for various plated films.
Nano-Plating
1) Metallurgical structure crystal, amorphous,
(Crystal, Amorphous, Solid solution, intermetalic compound, etc.
Metastable, Mixture)
\^yWy/y Substrate yCyy/A
W///////////////////A
2) Surface morphology
(smooth, rough, dendlight, glossness)
3) Crystal size, Crystal shape
(Size, round shape, Columnar,
needle, etc.)
4) Crystalographic orientation
(parallel, perpendicular, texture)
5) Contact with substrate
epltaxai
(adhesive, epitaxial, coherent, misfit
dislocation. Misfit twin)
///// ' SSuubbssttrraattee :Y ////A
y////////////////////A
p.^^.^.^-^^—^^ tension
6) Remaining stress
(tensile stress, compression, crack)
77I 7c7o7m77p7re7s7s7i7o7n; ^ |
y//7 Substrate ^^////A
y//yyyyyyyyyy////////yA
7) Unusual shape
(pit, nodule, whiskers, etc.)
77777777777777
y/yy Substrate y/////A
v//yyy/yyy/yyyy/////yA
Figure 1.1. Seven microstructure types observed in plated films.
1.2 RESEARCH PROCESS OF PLATING TECHNOLOGY
A process diagram describing electrodeposition research is summarized in Figure 1.2. In
the past, most of research has been conducted by varying plating conditions by a trial and
error method based on an empirical rule stemming from a large number of experimental
Microstructure Control Theory of Plated Film
Physical properties
Physical properties
(electrical properties, magnetic properties, etc.)
Chemical properties
(anti-corrosion, catalytic properties, etc.)
Mechanical properties (hardness, plastisity, tensile strength, etc.)
Crystal
Crystallographic structure (phase, crystal size, orientation, stress, etc.)
Amorphous
(uniformity, emblio, etc.)
Composition
Pure metal
Alloy
Impurity
Reaction on electrode
Electronic double layer
A
Diffusion layer
Adhesion
Discharge
etc.
Ion, Aqua-ion,
Reaction in solution
Complex ion.
Dissociation, Diffusion,
Reaction velocity, etc
Plating conditions Bath composition
(kinds of metal salt, concentration)
pH, Kinds of anion, Addition, Reduction,
Orver voltage, Current density. Pulse
Agitation,Temperature,
Electrode
etc.
Figure 1.2. A process diagram for conducting electrodeposition research.
results. The properties of the resulting film were then matched with the properties of
interest, applicable to a specific research objective. The problem with this approach is that
the numbers of plating conditions are extremely large, as described below. The possible
variables to be considered prior to plating include:
(a) Substrate material (metal, non-metal (ceramics, plastic)).
(b) Pre-treatment of substrate materials (deoxidation, degreasing, washing, drying).
(c) Type of metals (pure metal, alloy).
(d) Solution concentration (concentration, alloy composition).
(e) Type of metallic salts (effect of anion type).
