High speed selective jet electrodeposition of gold and gold alloys using single circular jets

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High speed selective jet
electrodeposition of gold and
gold alloys using single
circular jets
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• A Doctoral Thesis. Submitted in partial fulfillment of the requirements
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HIGH SPEED SELECTIVE JET ELECTRODEPOSITION OF GOLD AND GOLD
ALLOYS USING SINGLE CIRCULAR JETS
by
C. E. BOCKING FIMF, Grad. IMF (Poly. South Bank)
A Doctoral Thesis
Submitted in fulfilment the
of requirements
for the the degree Doctor Philosophy
award of of of
the Loughborough University Technology
of
of
Supervisor: Dr D. R. Gabe
Institute Polymer Materials Engineering
of and
Loughborough University Technology
of
m by C. Bocking 1994
ABSTRACT
High Speed Selective Jet Electrodeposition (HSSJE) is in
a process which metals and alloys may
be high in fashion for Ile
electrodeposited at rates and a selective without the need masking.
directing high jet be
method consists of a velocity non-submerged of electrolyte at the surface to
between Due flow
plated and passing a current the nozzle and the substrate. to the nature of the
distributioft jet, deposition high but in
and the current within the takes place at rates only the
impingement immediately This has little
and surrounding region. technique seen commercial
7bese
exploitationand onlyasmall numberof papers onthe subject. were concerned withdeveloping
for The
mathematical models the system. purpose of this work was to examine the structural,
bothgold
morphological and metallurgical characteristics of and gold alloy electrodeposits produced
high flow (< Imm) By
undervaried conditionsof electrolyte using small geometry nozzles. relating
factors density, ion
such as electrolyte velocity, current temperature and metal concentration etc
deposits limiting for
to the morphology of the produced, an understanding of the conditions
deposition Results from deposits by HSSJE
maximum rates was ascertained. obtained produced
As
were compared to those made under more conventional conditions. well as examining the
deposits, information factors
to the
attempts were made gain on electrochemical controlling
deposition. 71ese factors,
such as mass transfer characteristics, required the production of
identifying limiting densities Some
the the
polarisation curves current of system under study.
discussed.
the technique
potential applications of are also
ACKNOWLEDGEMENTS
The author would like to thank the following for the invaluable to the
people contribution work
First, DrDavid Gabe, Academic Supervisor,
carried outinthe experimental phaseof thisTbesis. my
who originally suggested that I undertake this 7"hesis and without whom, it would never have been
written. Also, my colleagues at the Hirst Research Centre. Dr Brian Cameron, Group Leader
my
Mr Ian Christie, Laboratory Manager Materials Science Laboratory
and the
of as well as my
Industrial Supervisor, for freedom in
the given to me the pursuit of the aims of the BRITE
from this derived. In I like Dr Brian Cameron
programme which work was addition, would to thank
for carrying out the wear testing of connectors in this study. Mr Alan Vale, for the chemical
deposits
Mr Ian Gunter for
analysis of the electrolytes and produced. the computer control program
jet
that controlled the plating equipment as well as advice and back-up on the electronic control
Mr Colin Dineen, X-Ray Diffraction
systems used. who operated the equipment and provided
enormous expertise in the analysis and interpretation of the results. Mr David Prichard who
the Scanning Electron Micrographs here. Mr Chris Fisher for
produced some of shown the many
interesting discussions had in fathom
varied, and most useful that we trying to the complexities of
the electrochemistry of the system.
At Loughborough University Mr Frank Page,
my thanks go to who produced some stunning and
Scanning Electron Micrographs interesting deposits. Addi-
prize winning of the more visually
Dr Geoff Wilcox for he
tionally, the
assistance provided concerning conventional electrochemical
procedures.
Finally, I like Sue Laura Lewis for during
would to thank my wife and children and their patience
Thesis.
the writing of this
The inthis from BRITE (Basic Research inIndustrial
thesis taken
experimental workdescribed was a
Technology) No. RI I B-304, "The improvement in high
programme the control and attainment of
It Centro Svillupo Materiali,
speed electrodeposition processes". was undertaken with partners
GEC-Marconi Hirst Research Centre Loughborough University Technology. The
the
and of work
HSSJE Hirst Research Centre by
on was carried out solely at the the author except where stated
The different high deposition. As the
above. other partners worked on aspects of speed such,
its For
programme was predetermined prior to commencement. this reason, certain avenues of
interest be due definite
could not pursued to the need to obtain milestones within pre-determined
time
periods.
11
Table Contents
of
CHAPTER 1 INTRODUCTION 1
..........................................................
1.1 GENERAL BACKGROUND 1
.........................................................
1.2 SCOPE OF THIS STUDY 4
.............................................................
CHAPTER 2 GOLD ELECTRODEPOSITION 6
.......................................
2.1 GOLD PLATING IN THE ELECTRONICS INDUSTRY 6
.....................
2.2 ELECTROLYTE TYPES 8
. .............................................................
2.2.1 Alkaline 8
cyanide electrolytes
. ...................................................
2.2.2 Acid 9
gold electrolytes
.............................................................
2.2.2.1 Pure 9
acid golds
..............................................................
2.2.2.2 Alloy 10
acid golds
.............................................................
2.2.3 Structural deposits 12
characteristics of gold
. .....................................
2.2.4 Ile influence 13
of pulsed current on gold electrodeposition
. .................
CHAPTER 3 SELECTIVE PLATING TECHNIQUES 15
.............................
3.1 DIELECTRIC MASKING 15
................................................ 00 ...... 00 ...
3.1.1 Solvent based lacquers 16
.................................. o .........................
3.1.2 Thick film inks 17
....................................................................
3.1.3 Photo-resists 17
........................................................................
3.1.3.1 Photoresist 18
chemistry
.......................................................
3.1.3.1.1 Positive 18
working resists
.............................................
3.1.3.1.2 Negative 20
working resists
............................................
3.1.3.2 Outline Printed Circuit Board Production Methods 21
of
..........
3.1.4 Pre-formed 23
masks
........................................... o ......................
3.1.5 Controlled depth immersion 25
......................................................
3.2 BRUSH PLATING 25
.................................................... $00 ...............
3.3 ANODE PLACEMENT AND GEOMETRY 27
....... o ............ o .................
3.4 AUTOCATALYTIC (ELECTROLESS) DEPOSITION 29
........................
CHAPTER 4 HIGH SPEED ELECTRODEPOSITION PROCESSES 30
...........
4.1 THEORETICAL ASPECTS 30
..........................................................
4.1.1 Transport diffusion layer 30
mechanisms and the
. ...............................
4.1.2 Realistic limiting densities 32
current
.............................................
4.2 MEASUREMENT OF THE LIMITING CURRENT DENSITY 32
.............
4.2.1 Limiting density 33
current measurement methods
. .............................
4.2.1.1 Galvanodynamic 34
methods
;
. ........... .....................................
4.2.1.2 Potentiodynamic 34
methods
. ................................................
4.2.1.3 Convective 35
control methods
. ..............................................
4.3 PRODUCTION PROCESSES 36
........................................................
CHAPTER 5 ELECTROCRYSTALLISATION AND MORPHOLOGY 39
.......
5.1 SOME FUNDAMENTAL ASPECTS OF ELECTROCRYSTALLISATION
39
*00#0 ... 0 ..... 0 ............ *. 0 ... * ... *0 ......................... 00*00 ..... 00*0 ..... 9009* .... * .... 0....
5.1.1 Electrocrystallisation low densities 42
at current
. ...............................
5.1.2 Electrocrystallisation high densities 43
at current
. ...............................
5.1.3 Mechanisms irregularity 44
of surface amplification
. ...........................
5.1.4 Stability for development 45
theories
roughness
. .................................
5.1.5 Theories dendritic, dense branching (DBM)
of needle, morphology and
fractal 46
growth
. .......................................................................... ...
I
CHAPTER 6 HIGH SPEED JET ELECTRODEPOSITION 53
.......................
6.1 CHARACTERISTICS OF FLUID FLOW WITHIN JETS 53
....................
6.1.1 Flow free jet 54
the
within region
....................................................
6.1.2 Flow impingement 54
the
within region
...........................................
6.1.3 Flow jet 55
the
within wall
. ..........................................................
6.2 MASS TRANSFER CHARACTERISTICS OF IMPINGING JETS 55
.........
lll
6.2.1 Mass in jets
transfer
submerged 55
. ................................................
6.2.2 Mass transfer in the jet
non-submerged 56
........................................
CHAPTER
7 EXPERIMENTAL STUDIES OF HIGH SPEED SELECTIVE
JET ELECTRODEPOSITION
63
...............................................................
7.1. EQUIPMENT USED IN THIS STUDY
63
. ..........................................
7.1.1. Computer
X-Y drive
controlled 63
system
.......................................
7.1.1.1 The
nozzle and substrate mount 64
. .........................................
7.1.1.2 The
pump system 65
. ..........................................................
7.1.1.3 The X-Y Table
65
...............................................................
7.1.1.4 Motion
control system 66
. .....................................................
7.1.1.5 The
plating current power supply 66
. .......................................
7.1.1.6 The
computer and control program 67
......................................
7.1.2 Additional
equipment 68
..............................................................
7.2 EQUIPMENT AND METHODS USED FOR DEPOSIT EVALUATION 68
..
7.2.1 Deposit Morphology
68
...............................................................
7.2.2 Deposit
thickness 69
...................................................................
7.2.3 Deposit
structure 69
...................................................................
7.2.4 Deposit hardness
74
...................................................................
7.2.5 Chemical
analysis 74
. .................................................................
7.2.6 Types
of substrate used 74
. ..........................................................
7.3 METHODS USED FOR THE PRODUCTION OF EVALUATION
SAMPLES
75
. .....................................................................................
7.3.1 Pure deposits
gold 75
. .................................................................
7.3.1.1 Electrolyte
composition 76
....................................................
7.3.1.2 Experimental
method 76
.......................................................
7.3.2 Gold deposits
alloy 77
.................................................................
7.3.2.1 Initial for
trials electrolyte selection 78
. ....................................
7.3.2.2 Optimising
the gold/nickel electrolyte 78
. ..................................
7.3.2.3 Experimental
method 79
. ......................................................
7.4 MASS TRANSFER STUDIES
80
. .......................................................
7.4.1 Principles SCPV SVPA
of and 80
. .................................................
7.4.2 The
working electrode/reference 81
electrode assembly
. .......................
7.4.3 The
equipment used 83
. ...............................................................
7.4.4 Experimental
technique 83
. ..........................................................
CHAPTER 8 RESULTS
85
........................................
*.. * ........................
8.1 PURE GOLD DEPOSITS
85
. .............................................................
8.1.1 The effect of nozzle to substrate distance 85
.......................................
8.1.2 The density
effect of current 86
. ....................................................
8.1.2.1 General
observations 86
.......................................................
8.1.2.2 Deposit
topography 88
. ........................................................
8.1.2.3 Deposition
rate 94
...............................................................
8.1.2.4 Cathodic
current efficiency 94
................................................
8.1.2.5 Hardness deposits
of 95
........................................................
8.1.2.6 Selectivity deposit
of the 96
...................................................
8.1.2.7 Crystal
structure and residual strain 97
. ....................................
8.1.3 The
effect of electrolyte velocity 101
................................................
8.1.4 Temperature
effects 101
. ...............................................................
8.1.5 The
influence of the gold concentration 101
. ......................................
8.1.6 The
effect of pH 102
....................................................................
8.1.7 The
role of electrolyte conductivity 102
. ............................................
8.1.8 The influence
of nozzle size 103
. ......................................................
8.1.8.1 Increased
nozzle size 103
. ......................................................
8.1.8.2 Decreased
nozzle size 103
. .....................................................
8.1.9 Pure deposition
gold using pulsed current 104
. ....................................
8.1.9.1 Variation density
of the average current 106
. ...............................
8.1.9.2 Variation
of the on-time 106
. ..................................................
8.1.9.3 The increasing
duty
effect of the cycle 106
. .................................
IV
8.1.9.4 The influence deposition 106
of pulsed on selectivity
. .....................
8.1.10 Examination limiting factors deposition
of the controlling maximum
107
rates
. .........................................................................................
107
8.1.10.1 Mass
transfer studies
. .....................................................
8.1.10.1.1 Sampled Voltage Pulse Amperometry 108
. .........................
8.1.10.1.2 Sampled Current Pulse Voltametry 109
. .............................
ill
8.2 GOLD ALLOY DEPOSITS
. ..........................................................
8.2.1 The influence deposition for the Ronovel N
of parameters electrolyte
112
with no nickel
. .............................................................................
8.2.2 The effect of the addition of nickel to the basic Ronovel N electrolyte. 113
..
8.2.2.1 Relationship between nickel in the deposit, nickel in the electrolyte
113
density
and current
. ...................................................................
115
8.2.2.2 Deposit
topography
. .......................................................
116
8.2.2.3 Deposition
rate
. ..............................................................
117
8.2.2.4 Current
efficienc
117
8.2.2.5 Hardness
of the
120
8.2.2.6 Selectivity the deposits
of
. .................................................
122
8.2.2.7 Crystal
structure
. ............................................................
8.2.3 Sampled current pulse voltammetry of the Ronovel N electrolyte 131
. ........
CHAPTER 9 THE APPLICATIONS OF HIGH SPEED SELECTIVE JET
132
ELECTRODEPOSITION
.......................................................................
132
9.1 APPLICATIONS WITHIN THE ELECTRONICS INDUSTRY
. ............
9.1.1 The direct Microwave Integrated Circuit Substrates (MICS).
writing of
132
*****'*. ** ... '
5. *i'i*Ee"s*el*ecti*ve*pl*at'i*ng*of*reel"t'o*re*el"co*mpone*n*ts***.
133
134
9.1.3 Bump
plating
. .......................................................................
for boards 134
9.1.4 The direct
writing of etch resist printed circuit
. .................
135
OF THE USE OF HSSJE
9.2 DEMONSTRATIONS
..........................
135
50 lines
9.2.1 Microwave circuit test samples ohm
-
. ........................
136
9.2.2 The
plating of connectors with alloy gold
. .....................................
137
bonding HSSJE
9.2.3 Thermocompression properties of pure gold
. .............
137
9.2.4 The direct boards
writing of printed circuit
. ..................................
139
CHAPTER 10 ANALYSIS AND DISCUSSION
# ...
....................................
139
10.1 GENERAL
..............................................................................
140
MEASUREMENTS
10.2 MASS TRANSFER
..........................................
146
OF DEPOSITION CONDITIONS
10.3 THE INFLUENCE
.......................
146
distance
10.3.1. Nozzle to substrate
:
. ............. .....................................
146
10.3.2. Current density
. ..................................................................
149
10.3.3. Electrolyte
velocity
:. .
. ...........................................................
149
10.3.4. Temperature
. ...................................................................
150
10.3.5. Electrolyte
composition
.........................................................
151
10.3.6. The influence
of nozzle size
. ..................................................
153
10.3.7. The
effects of pulsed current
. .................................................
AND STRUCTURAL PROPERTIES OF PURE
10.4 SOME PHYSICAL
153
GOLD HSSJE DEPOSITS
.......................................... *0-0 .......... so*. *-*...
AND STRUCTURAL PROPERTIES OF GOLD
10.5 SOME PHYSICAL
155
ALLOY HSSJE DEPOSITS
..................................................... 0. *o .... so.
10.6 FLUID FLOW AND ITS INTERACTION WITH THE DEPOSIT 157
........
flow below density 158
10.6.1 Interaction of the the maximum useful current
......
density. 161
flow
10.6.2 Interaction of the above the maximum useful cuff ent
161
10.6.2.1 Nodular deposits
. .....................................
161
10.6.2.2 Needle-ýype deposits
................................. ....
163
10.6.2.3 Field
oriented jet core structures
. .................................
164
10.7 THE GROWTH OF NODULAR DEPOSITS
. ............................
165
10.7.1. Inhibition diffusion
versus mechanisms
......................................
10.8. SUMMARY OF FACTORS CONTROLLING THE MAXIMUM DEPO-
167
SITION RATE
. ...............................................................................
V
REFERENCES
169
...........................................................................................
PHOTOGRAPHS 1-39
174
.................................................................................
TABLES 1-27
198
............................................................................................
ý
VI
NOMENCLATURE
A Amps
A
Lattice
a parameter,
Constant defined in (2 1)
a as equation
Specific
CM2 CM-3
a,. area,
Concentration,
C mol crrr3
& Concentration in bulk
the
electrolyte, mol cm-3
Concentration
CO at the electrode surface, Mol Cm-3
C Coulombs, A
sec-1.
Cf Local friction defined
coeffficient of as
-C.
pU2X12
d diameter
of the nozzle, cm.
d' Radial distance from impingement
centre of zone, cm
D Diffusion
coefficient, mol cm-2sec-I
Deff The for faulting,
effective crystallite size uncorrected
A
Dvw True
crystallite size,
E Electrical
potential, volts
F Faraday's 96,480 C
constant,
Hydrodynamic
9 constant sec-I
H Distance from
of the nozzle the substrate, cm.
Cuff density, A
ent CM-2
Limiting density, A Cm-2
current
io Exchange density, A Cm-2
current
JD
Diffusion flux, Mol CM-2sec-I
k Local
mass transfer coefficient, cm sec-I
K Mass
transfer coefficient, cm sec-I
KL Mass limiting density,
transfer coefficient at the current cm. sec-I
I Litres
Order in hkI
I of reflection, as
M Molar
involved in
Number
n of electrons an electrochemical reaction.
r nozzle radius, cm,
radius of cathode, cm,
r
R Gas 8.314 Joules K-1
constant, mol-I
R Dimensionless distance d/r
ratio,
Re Reynolds defined Ud/v
number as
Re, Local Reynolds defined Ud'/v
number as
Vii