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WS@
05, San Francisco, Feb, 2005
Sn-Zn Based Low Temperature Lead-Free Solder and
Current Status of Lead-Free Soldering in Japan
Katsuaki Suganuma, Keun-Soo Kim (ISIR, Osaka University)
Kenji Toyofuku, Katsumi Yamamoto (Sony)
Kouichi Hagio (Nihon Genma)
Contents
Background and R&D activity
Properties of Sn-Zn lead-free solder
Properties of Sn-Ag-In solder
Other R&D activities
Acknowledgements
This work was partly supported by JIEP and JEITA projects.
Low & High Temperature Solders !
K.Suganuma, ISIR, Osaka University
Pop up cracking of built-up PWB after 3 reflow
In order to finalize lead-free….
Legislations
9 RoHS in EU →
July in 2006
9 Some treatment is required by WEEE for lead bearing products.
WEEE requires marking from August 13, 2005.
9 ELV has already restricted the use of lead from 2003.
9 Chinese RoHS will ban the use of leaded solder from July
2006.
Products still leaded: PWBs and components poor to heat exposure
Low temperature solder is required.
1998
1st roadmap
1999
Lead-free Soldering Projects in Japan
NEDO PJ by
JEIDA-EIAJ/JWES
350 million $
2000
R&D of lead-free soldering
technology and Promotion of
nd lead-free soldering
2
roadmap
Standardization is required
2001
METI Pj by
JWES
100 million $
2002
2003
METI Pj by
JEITA
100 million $
3rdReliability
roadmap
testing methods
for HDP
Testing method for
solders
Basic science is required
Lowering process temperature
IMS Pj
“EFSOT”
200 million
$/year
Low temperature
soldering
Sn-Zn Sn-Bi
Process, Reliability
Hitachi, etc.
R&D of lead-free
soldering
Environmental
impacts
Toxicology
Lowering process
temperature
2004
RoHS and worldwide competition
High temperature
whisker
2005
erosion
RoHS
JIEP-JEITA
solder
2006
Conductive adhesive
2007
2008
2010
JIEP Pj
METI Pj by
JEITA
100 million $
Low temperature
soldering
Sn-Zn Sn-Ag-In SnBi
Lead
-Free Soldering Roadmap
Lead-Free
JEIDA & JIEP
January 30, 1998
1st stage
Lead-free solders:
Reflow : Sn-Ag (Cu or Bi)
Wave : Sn-Ag(-Cu)
Starting from limited commercial production
requiring the establishment of lead-free and
heat-resistant components
2nd stage
Expansion of lead-free components &
Expansion of low temperature solders such as
Sn-Ag with some amount of Bi and
improvement of Sn-Zn
JEITA in 2002-04
Standardization of reliability testing methods
• Thermal/mechanical fatigue/Impact
• Wetting, Lift-Off…..
• Migration
• Whisker
• Sn-Zn working group
JIS standard
IEC standard
METI Project
R & D of Basic Technology for Low Temperature Soldering and
Its Standardization
Period: Oct.2004 – March 2007
9Alloys/pastes developments & process technology
- Solder Materials:Sn-9Zn, Sn-8Zn-3Bi, Sn-Ag-In(-Bi), Sn-58Bi…..
- Plating/electrode: Cu, Sn, Au, Ag …..
- Process :Wetting and Reflow…..
- Recycling
9Reliability evaluation and methods/condition
- Thermal fatigue, humidity exposure, corrosion, migration…..
9Mechanical properties testing method and especially void
effect
- Micro-specimen tensile test method and database
- Influence of void formation on reliability
From basic understanding to practical adaptation
METI Project
R & D of Basic Technology for Low Temperature Soldering and Its Standardization
JEITA
Low Temperature Soldering
Standardization Committee
Suganuma(Osaka Univ.)
& Yamamoto(Sony)
Reliability Testing Method
WG
Honma(Fujitsu) & Matsuoka(NEC)
Reliability Center
for Electronic
Components Japan
Sasaki(RCJ)
Low Temperature Soldering
Process WG
Takeuchi(JVC), Kusakabe(Panasonic)
& Toyofuku(Sony)
Various reliability testing methods and
their standardization
Evaluation of process conditions and
their standardization
Mechanical Property
Evaluation WG
Takahashi(Toshiba) & Nishiyama(Epson)
Kariya(NIMS)
Yu(Yokohama National Univ.)
Development of micro-specimen testing method and
evaluation of void formation on reliability
Low temperature solders: Technical points
Sn-Zn
Productivity is enough?
Compatibility with Cu at elevated temperature?
Corrosion to specific atmosphere? e.g., NO2?
High temp./humidity?
Compatibility with precious metals, Au plating?
How about wave soldering?
Sn-Bi
Sn-Ag-In
Poor heat resistance → what applications?
Brittleness
Compatibility with Sn-Pb plating
We need accumulation of reliable database.
R&D activity on low temperature soldering
• JIEP ”Low temperature soldering projects”, ’00-’02
– Productivity, reliability evaluation for Sn-Zn-Bi
– Accumulation of data for Sn-Bi and Sn-Ag-In
• JEITA Standardization Committee, ’01-’02
– Reliability study for Sn-Zn-Bi
• JEITA Sn-Zn Low Temperature Solder Working Group, ’03’05
– Accumulation of information on low temperature solders
– R&D research of low temperature solders, processes and evaluation methods.
JEITA Low Temperature Soldering Projects
K. Suganuma, ISIR, Osaka University
Products with low temperature solders
• Sn-Zn
NEC
Sharp
Fujitsu
Sony
Victor
• Sn-Ag-In
Matsushita
• Sn-Bi
Hitachi, Fujitsu, IBM
Notebook PC
Notebook
LCD
Battery, MD player, etc.
Printer, etc.
MD, DVD, Notebook PC,
….etc.
Computer, etc.
NEC
Fujitsu
Sharp
PC LCD
Sn-Zn products
In market
Tacking force (N)
Properties of commercial Sn-8Zn-3Bi paste
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
Printability
Printability &
& Slump
Slump
Tackiness
Tackiness properties
properties
Printability
new A
(A)
(B)
5
10
15
Exposure time
20
Slump test 160ºC-3min
25
0.3 mm OK
(h)
Voids
Voids
Wettability
Wettability
air
Sn-8Zn-3Bi
N2
230ºC
Sn-3Ag-0.5Cu
230ºC
240ºC
Recommended reflow temperature profile and solder fillets
for New Sn-9Zn paste by Sony & Genma
No Bi & Air reflow
Pb contamination becomes less influential because of absence of Bi.
Shiny face equivalent to Sn-Pb eutectic solder.
Air reflow enables one to adopt low cost production.
Applicable to various components and PWBs that are weak to heat
exposure.
Excellent ductility provides heat shock resistance better than Sn-Pb and
Sn-Zn-3Bi.
……etc.
Basic properties of Sn-8Zn+xBi
Liquidus
ºC
199
Solidus
ºC
199
Density
g/cm3
7.28
Sn-8Zn-1Bi
199
192
7.30
Sn-8Zn-3Bi
197
187
7.34
Sn-8Zn-6Bi
194
178
7.40
Sn-37Pb
183
183
8.64
Alloys
Temperature (ºC)
Sn-9Zn
300
Liquid
250
3Bi 6Bi
200
L + Zn
L + β-Sn + Zn
150 L + β-Sn
β-Sn + Zn
100
β-Sn + Zn + Bi
50 α/β-Sn + Zn
Primary Zn
α-Sn + Zn + Bi
0
0
5
10
15
20
Bi content (wt%)
25
K.Suganuma, ISIR, Osaka Univ.
Thermal reaction
(a)
B
A
Endothermic
Undercooling
3Bi
6Bi
0Bi
Y.-S. Kim, K.-S. Kim, C.-W. Hwang, K. Suganuma
J. Alloys Compounds, 352(1-2) (2003), 237-245.
22
Sn-0.7Cu
1 75
1 80
1 85
1 90
1 95
200
3Bi 1Bi
0Bi
Exothermic
6Bi
205
Undercooling
20
18
16
Sn-3Ag-Bi
14
12
10
8
6
Sn-8Zn-Bi
4
2
0
0
1
2
3
4
5
6
7
8
Bi content (wt%)
1 8 0
1 8 3
1 8 6
1 8 9
1 9 2
1 9 5
1 9 8
Temperature (°C)
Strain rate influence on 0.2% proof stress
⎡ Q ⎤
⎣ RT ⎥⎦
•
0.2% proof stress (MPa)
Power low:
ε = Aσ n exp ⎢−
Typical n value by tensile test
100
Alloys
Sn-8Zn-6Bi
n
Ref.
This
work
Mavoori
This
work
Mavoori
This
This
work
work
This
work
This
This
work
work
This
Plumbridge
work
80
Sn-9Zn
60
Sn-8Zn-3Bi
Sn-8Zn-6Bi
8.2
8.1
14.4
15.0
Sn-3Ag
Sn-3Ag-0.5Cu
Sn-3.5Ag-0.7Cu
Sn-3.9Ag-0.6Cu
12
12.5
9.1
12.5
Sn-0.7Cu
Sn-0.7Cu-0.5Ag
17.4
11.5
Sn-8Zn-3Bi
Sn-9Zn
40
20
10-4
10-3
Strain rate
Y.-S. Kim, K.-S. Kim, C.-W. Hwang, K. Suganuma
J. Alloys Compounds, 352(1-2) (2003), 237-245.
10-2
(/s)
Sn-38Pb
20
K.Suganuma, K.Niihara, T.Shoutoku and Y.Nakamura
J.Mater.Res., 13 (1998), 2859-2865.
γ-Cu5Zn8
111 001
000
β'-CuZn
111
001
000
Cu
100
100 nm
nm
Interface microstructure after reflow
Relative displacement (mm)
Mechanical Fatigue life of various CSP joints
after 125 ºC exposure
30% Load drop
0.01
Sn-Zn-Bi
Sn-Zn-Bi paste
paste
Ball/Paste
SnAgCu/SnZnBi
SnPb/SnZnBi
SnAgCu/SnPb
SnPb/SnPb
SnAgCu/SnZnBi-h
SnPb/SnZnBi-h
SnAgCu/SnAgCu
SnAgCu/SnPb
SnAgCu/SnAgCu-h
SnPb/SnAgCu-h
SnAgCu/SnPb-h
SnPb/SnPb-h
0.005
Sn-Zn-Bi
Sn-Pb
Sn-Pb paste
paste
Cu
Cracking inside Sn-Zn layer
After 110 ºC-300h exposure
0.001
500
1000
5000
10000
Number of fatigue cycles
Stability of interface with Cu
Reaction
½ ž‰w
”
‘ layer
No
reaction
Sn-Zn
Cu
Zn
Reaction
zone
10 µm
½‰
”
ž ‘w layer
Reaction
Sn-8Zn-3Bi/Cu after
135ºC-50h
Sn-Zn
Diffusion constants of elements in Sn at 125ºC
Cu
Cu-Zn
10 µm
Sn-8Zn-3Bi/Cu
after 125ºC-100h
Elements
D (m2/s)
Ref.
64Cu
1.1x10-11
Dyson
65Zn
1.7x10-15
Huang
Humidity influence on shear strength
85ºC/85%RH
Shear direction
S h e a r s tre n g th (M P a )
speed: 500µm/s
Shear strength
MPa
50
40
30
20
10
0
0
200
400
600
Exposure time
h
Sn-Pb plating
800
1000
50
40
30
20
10
Sn-9Zn ■ Sn-8Zn-3Bi
0
0
200
400
600
800
1000
Exposure time h
Sn plating
High temperature & humidity exposure
Pull Strength (kgf)
2.0
1.5
Sn8Zn3Bi
85°C/60%RH
after 500 h
60°C/90%RH
1.0
Sn8Zn3Bi
Sn9Zn
Sn3Ag0.5Cu
SnPb
0.5
0.0
0
250
500
750
1000
Aging time (Hr)
2.0
85°C/60%RH
P u ll S tre n g th (k g f)
1.5
cracking
Sn8Zn3Bi
60°C/90%RH
after 1000 h
1.0
0.5
Sn8Zn3Bi
Sn9Zn
Sn3Ag0.5Cu
SnPb
0.0
0
250
500
Aging time (Hr)
750
How does degradation proceed?
Zn diffuses to surface and interface
with coarsening and is oxidized
Interface/boundaries cracking
100µm
Cracking
85ºC/85RH%
100h
Zn-O
SEM
10 µm
Sn-9Zn solder fillet after 85ºC/85%RH for 1000h
Sn plating
Sn-Pb plating
Influence of high temperature storage
Sn-8Zn-3Bi
After 150°C/1,000H
Sn-8Zn-3Bi
After 120°C/1,000H
150°C
120°C
Sn 8 Z n 3 B i
Sn 3 A g 0 .5 C u
Sn 9 Z n
Sn P b
Sn 8 Z n 3 B i
Sn P b
2 .0
P u ll S t r e n g t h (k g f )
P u ll S t r e n g t h (k g f )
2 .0
Sn 3 A g 0 .5 C u
Sn 9 Z n
1 .5
1 .0
0 .5
1 .5
1 .0
0 .5
0 .0
0 .0
0
250
5 00
A gin g t im e (H r )
750
1 000
0
250
5 00
A gin g t im e (H r )
Sn-8Zn-3Bi & Sn-9Zn lead-free solder
*120°C/1,000H No serious degradation
750
1 000
Printability
Solder balls
Slump
First
Fifth
Initial
Initial
150oC×1 min
24h
Sn-3.5Ag-(3-8)In-0.5Bi
Sn-3.5Ag-(3-8)In-0.5Bi
Tacking
Copper: 235
Copper: 245
Wetting
25oC×65%RH
200
Copper: 255
Oxidized Cu: 235
150
Spreading rate (%)
Force gf
Oxidized Cu: 245
100
50
0
0
1
from Harima Chem.
2
4
Time
8
15
24
100
95
90
85
80
75
70
65
60
55
50
Oxidized Cu: 255
84
85
87
85
85
PS37BR-600A-MP3
84
Microstructure
Sn
ζ-Ag3In + γ-InSn4
K. Suganuma, ISIR Osaka University
Sn-3.5Ag-0.5Bi
Ag3Sn
Interfaces as soldered
Sn-3.5Ag-8In
Sn-3.5Ag-4In-0.5Bi
10 µm
ζ-Ag-In
Sn-3.5Ag-8In-0.5Bi
Cu6Sn5
Cu
10 µm
100 ºC
150 ºC
125 ºC
0In 4In 8In
Shear test data of
various solder joints
JEITA Action on Urgent Four Concerns
• Prevention of whiskers
• Erosion of solder bath
• 0.1 % Pb contamination & detection
• Low temperature soldering
METI project(’04-’06)
Erosion of Solder Bath
9Stainless steel reacts with lead-free solders
9Type 316 is better than type 304?
9Reaction mechanism?
9Prevention methods…..
Effects of Pb contamination in soldering
Enhancing defect formation by expanding pasty range.
Lift-off, Solidification cracking, Segregation
Formation of low temperature phase, e.g., Sn-Bi-Pb….
Undesirable reaction proceeds rapidly
Weakening interfaces, grain boundaries?
Boundary cracking
Enhancing diffusion?
Undesirable reaction proceeds rapidly
….. etc.
Whiskers
Static growth
9 Whiskers grow much faster for Cu lead frames
than for Ni plated or Fe-Ni lead-frames in
ambient temperature.
9 Driving force of whisker growth is compressive
stress in Sn plating layer, which is influenced by
the spontaneous growth of Cu6Sn5.
9 Whisker grows faster for thin plating than thick.
9 Thermal treatment before of pleated leadframes is effective for suppression.
Thermal cycle growth
9 Thermal expansion mismatch between Sn plating and substrates enhances
whisker growth during thermal cycles.
9 Maximum length of whiskers reaches 50 µm for thick plating.
Connectors
9 Higher contact stress makes longer whisker growth.
9 Stiffness of flexible substrate influences on whisker growth.
9 Whisker becomes severe in the order of Sn-Cu>Sn>Sn-Bi Sn-Ag reflowed
Sn>Sn-Pb.
Technology issues in lead-free soldering
9 Lift-off/Land-lifting mechanism and
prevention
9 Whisker : mechanism/prevention
9 Low temperature soldering
9 High temperature solder
9 Erosion of solder bath
9 Database/reliability evaluation
9 Standardization of evaluation/analysis
methods
Current research targets of us
9 Lead-free solder interfaces & solidification defects
9 Whiskers
9 Low temperature solders & diffusion & corrosion
9 Developments of high temperature solders
9 Reliability aspects & Improvements of conductive
adhesives
9 Nanopastes & IJ printing
9 Technology transfer of lead-free soldering in
industries
9 ….etc.
Microstructure
Solidification
Interface
Lift-off
Joint strength (MPa)
Compatibility of Sn plating with conductive adhesive
Cu joint heat-exposed at 150 ºC
70
60
Without plating
Initial Sn-Pb/Ni coating
Adhesive
50
40
Cu
10 µm
30
20
With Sn-10Pb/Ni plating
300 h
10
0
0
200
400
600
800
1000
Gap
Adhesive
Cu
Exposure time (h)
Stopping Sn diffusion !
Void
10 µm
Thank you!
Katsuaki Suganuma
ISIR, Osaka University
e-mail: suganuma@sanken.osaka-u.ac.jp

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