1
It is Time for Low Temperature
- Low Temperature Solders , New
Development, and Their Applications
Dr. Ning-Cheng Lee
Indium Corporation
2
iNEMI 2013 Roadmap Forecast on Solder
Melting Temperature for SMT Assembly
Low Temp Drivers:
Lower cost (energy, materials)
High yield (more thermal warpage due to thin profiles)
High reliability (due to finer pitch)
3
Step Soldering Involving Temperature
Sensitive Components
• Step soldering is the process of attaching
components to a substrate in a series of
steps where each step in the soldering
process uses a lower reflow temperature
than the step before it. Standard
components are attached first and then
temperature sensitive components (like
LEDs) are done last. These temperature
sensitive components reflow at
temperatures less than 180°C.
4
Soldering To MID Plastics
•
Molded interconnect device
(MID) plastics have been around
for many years, but are
becoming more popular in
product design. MID plastics,
which are formed into 3D
shapes to increase the
functionality and reduce overall
weight of each product, are
important in automotive and
medical applications.
Hearing aid
Steeringwheel
Wikipedia:
A molded interconnect device (MID) is an injection-molded thermoplastic part with integrated
electronic circuit traces. The use of high temperature thermoplastics and their structured
metallization opens a new dimension of circuit carrier design to the electronics industry. This
technology combines plastic substrate/housing with circuitry into a single part through selective
metallization.
Key markets for the MID technology are consumer electronic, telecommunication, automotive
and medical. A very common application for MIDs are integrated antennas in cellphones and
other mobile devices including laptops and netbooks
5
Low Reflow Temp To Avoid Thermal
Warpage Induced Defects
the main mechanism of
NWO is the lifting of the
solder paste from the PCB
lands. This stage occurs
when the package
dynamic warpage is fairly
low. However HoP’s main
mechanism is the ball to
paste gap that exist during
reflow when the dynamic
warpage is at the highest
point.
Dudi Amir, Satyajit Walwadkar, Srinivasa Aravamudhan, and Lilia May (Intel), “THE CHALLENGES OF NON WET OPEN BGA
SOLDER DEFECT”, SMTAI proceedings, p684-694, Oct. 14-18, 2012, Orlando, FL
6
Thermal Interface Materials
• Low melting solder systems such as indium are used as
thermal interface materials between flip chip die and lid
(TIM1, for better thermal conductivity), and may also be
used between lid and heat sink (TIM2, for low process
temperature).
7
BiSn + Ag
8
57Bi41Sn2Ag more ductile
than Bi-Sn
Valeska Schroeder, and Fay Hua, “Feasibility Study of 57Bi-42Sn-1Ag Solder”, Apex, San Diego, CA, Jan. 14-18, 2001
9
Isothermal fatigue life: Bi-Sn-2Ag > Sn63 > 58Bi42Sn
Iso-
Valeska Schroeder, and Fay Hua, “Feasibility Study of 57Bi-42Sn-1Ag Solder”, Apex, San Diego, CA, Jan. 14-18, 2001
10
Wetting Performance of 57Bi42Sn1Ag
Solder Paste
• Samples were printed on an OSP finished surface, then
subjected to a humidity chamber (at 76% RH and
90%RH) for 3 hours before being reflowed in air
Indium 5.7LT after 3hr at 76%RH
Indium 5.7LT after 3hr at 90%RH
Indium Corporation technical data on 5.7LT 57Bi42Sn1Ag solder paste
11
After TCT Treatment, Shear Strength of 57.6Bi42Sn0.4Ag and
57Bi42Sn1Ag comparable with BiSn, SnPb, and SAC305
Shear Force After TCT
-45C(30 min)/+125C(30 min)
ALPHA®CVP-520 Solder Paste product guide, 2013
12
Mixed Alloys (57Bi42Sn1Ag & SAC) Drop
& Shear Test DOE
• Material
• Reflow Profile
• Ball
• LT – 176°C (BiSnAg)
• MT – 216°C (SnPb)
• HT – 236°C (SAC)
– BiSnAg, 305, 105, SnPb
• Paste
– BiSnAg, 305, 105, SnPb
• Flux
–
–
–
–
L-140 for BiSnAg
8.9 for SAC
92J for SnPb
446AL for ball bumping
Yan Liu, Joanna Keck, Erin Page, and Ning-Cheng Lee, “Voiding and Reliability of BGA Assemblies with SAC and
57Bi42Sn1Ag Alloys”, SMTAI, Fort Worth, TX, Oct. 13-17, 2013
13Paste-Ball Profile
Shear Test
stress-strain curves of
mounted bumps
All Bi-containing
joints are brittle
Yan Liu, Joanna Keck, Erin
Page, and Ning-Cheng Lee,
“Voiding and Reliability of BGA
Assemblies with SAC and
57Bi42Sn1Ag Alloys”, SMTAI,
Fort Worth, TX, Oct. 13-17,
2013
14
All Bi-containing joints are
brittle.
SAC & SnPb joints are
ductile.
Yan Liu, Joanna Keck, Erin Page, and Ning-Cheng Lee,
“Voiding and Reliability of BGA Assemblies with SAC
and 57Bi42Sn1Ag Alloys”, SMTAI, Fort Worth, TX, Oct.
13-17, 2013
15
Drop Test
• Both coupons are SMD OSP finished Cu
pad.
• To intensify the test condition, the I/O
density was reduced
– pad diameter of 25 mils, pitch of 100
mils, total I/O 100.
• The process on sample preparation is
similar to that of the voiding study.
• Run drop test & shear test
Yan Liu, Joanna Keck, Erin
Page, and Ning-Cheng Lee,
“Voiding and Reliability of
BGA Assemblies with SAC
and 57Bi42Sn1Ag Alloys”,
SMTAI, Fort Worth, TX, Oct.
13-17, 2013
16
Drop No. in proportional with ductility, poor for all Bi-containing joints
Drop No. vs Elongation
Average Void vs Drop No.
800
45
P63/B63
SnPb
40
P105/B105
35
600
30
Drop No.
Elongation at Break (micron)
R² = 0.7858
400
25
P105/B305
P305/B105
20
15
200
10
P305/B305
5
Bi
Bi
0
0
0
10
20
30
Drop No. to Failure
40
50
0
2
4
Average Void (%)
Bi
6
Majority of cracks occurred at the bottom pad on the PCB.
Bi - primary cause of poor drop test resistance
Yan Liu, Joanna Keck, Erin Page, and Ning-Cheng Lee, “Voiding and Reliability of BGA Assemblies with SAC and
57Bi42Sn1Ag Alloys”, SMTAI, Fort Worth, TX, Oct. 13-17, 2013
8
17
BiSn + In, Ni
18
58Bi42Sn+In or Ni
• Sn-58Bi-0.5In, Sn58Bi-1In, Sn-58Bi0.5Ni, Sn-58Bi-1Ni
• Solder paste 88%
metal load, 12% flux.
• Substrate Cu
• Paste print
thickness: 200
microns
• Reflow 100C (150
sec)/170C (60
sec)/N2
• Thermal aging at
80C for 168, 504,
1008 hrs
Omid Mokhtari, Hiroshi Nishikawa (Osaka Univ.), “Effect of minor alloying additive on the shear strength of Sn-58Bi solder joint”,
IMAPS 2013, p.100-103, Sept. 30-Oct. 3, 2013, Orlando, FL
19
After reflow
Sn-Bi
0.5In
0.5Ni
After 80C/1008 hrs
Sn-Bi
0.5In
0.5Ni
Coarsening: Ni (worst) > Sn-Bi > In (best)
Omid Mokhtari, Hiroshi Nishikawa (Osaka Univ.), “Effect of
minor alloying additive on the shear strength of Sn-58Bi solder
joint”, IMAPS 2013, p.100-103, Sept. 30-Oct. 3, 2013, Orlando,
FL
20
As reflow
After reflow, all samples
showed similar IMC thickness.
After 80C aging, 0.5In and
0.5Ni showed thinner IMC than
Sn-Bi
Sn-Bi
80C/1008 hrs (42D)
Sn-Bi
1In
1Ni
0.5In
0.5Ni
0.5In
Omid Mokhtari, Hiroshi Nishikawa (Osaka Univ.),
“Effect of minor alloying additive on the shear strength
of Sn-58Bi solder joint”, IMAPS 2013, p.100-103,
Sept. 30-Oct. 3, 2013, Orlando, FL
0.5Ni
21
(80C)
In
Shear Strength:
In > Sn-Bi > Ni
Ni
(80C)
Omid Mokhtari, Hiroshi Nishikawa (Osaka Univ.), “Effect of minor alloying additive on the shear strength of Sn-58Bi solder joint”,
IMAPS 2013, p.100-103, Sept. 30-Oct. 3, 2013, Orlando, FL
22
BiSn + Sb, Zn, Ag
23
• Sn-Bi + 0.5Sb
– showed improved drop test resistance. But,
the improvement of drop test performance on
Cu diminished upon thermal aging. This is
attributed to brittle Bi-rich layer near IMC layer
on Cu.
Keishiro Okamoto, Kenji Nomura, Shuichi Doi, Toshiya Akamatsu, Seiki Sakuyama, and Keisuke Uenishi (Fujitsu), “Effect of Sb and
Zn Addition on Impact Resistance Improvement of Sn-Bi solder joint”, IMAPS 2013, p.104-108, Sept. 30-Oct. 3, 2013, Orlando, FL
24
Sn-57Bi + Sb, Zn, Ag
100 balls on electrolytic NiAu, with Au
0.05µ, and Ni 2-5µ; 0.45mm pitch.
BGA assembled with 180C peak
temp/N2, using pastes on OSP board
1.Sn-57Bi-0.5Sb-0.5Zn
2.Sn-57Bi-0.5Sb
3.Sn-57Bi-1Ag
4.Sn-58Bi
After reflow, boards soaked at 45, 85,
125C for 250 hrs, followed by drop
test with max. distortion 2000µƐ of
PCB around the corner of chip.
Failure criteria: 1000 ohm, or stopped
at Max. drop no. 40
K. Okamoto, K. Nomora, S. Doi, T. Akamatsu, S. Sakuyama, and K. Uenishi (Fujitsu Laboratories, Osaka Univ.), “Effect of Sb and
Zn addition on Impact Resistance Improvement of Sn-Bi Solder Joints”, IMAPS 2014, Sept. 30-Oct. 3, 2013, Orlando, FL, USA.
25
As reflowed
Drop Impact Resistance:
Sb-Zn (> 40 drops)
> 3X of Sb (13 drops, R increase)
> 10X of Ag, Sn-Bi (4 drops)
Sn-Bi
Ag
Sb
Sb-Zn
K. Okamoto, K. Nomora, S. Doi, T. Akamatsu, S. Sakuyama, and K. Uenishi (Fujitsu Laboratories, Osaka Univ.), “Effect of Sb and
Zn addition on Impact Resistance Improvement of Sn-Bi Solder Joints”, IMAPS 2014, Sept. 30-Oct. 3, 2013, Orlando, FL, USA.
26
Adding Sb: Sub-micron sized SnSb (Sn3Sb2?) IMC particles
precipitated at grain boundaries of near Sn phase, refined
grain size. Ductility improved significantly.
Adding Zn: Zn was depleted from solder by forming Cu-Zn
IMC at interface.
K. Okamoto, K. Nomora, S. Doi, T. Akamatsu, S. Sakuyama, and K. Uenishi
(Fujitsu Laboratories, Osaka Univ.), “Effect of Sb and Zn addition on Impact
Resistance Improvement of Sn-Bi Solder Joints”, IMAPS 2014, Sept. 30-Oct. 3,
2013, Orlando, FL, USA.
High ductility
Bi
Sn
Hardness of Sn-Bi-Sb-Zn at IMC
layer is lower than that of Sn-Bi-Sb,
thus serve as an effective stress
relaxation and suppressed crack
formation at drop test
27
Sn-Bi
Average grain
size
Sn-Bi-Sb
Sb cause grain size refined
K. Okamoto, K. Nomora, S. Doi, T. Akamatsu, S. Sakuyama, and K. Uenishi (Fujitsu Laboratories, Osaka Univ.), “Effect of Sb and
Zn addition on Impact Resistance Improvement of Sn-Bi Solder Joints”, IMAPS 2014, Sept. 30-Oct. 3, 2013, Orlando, FL, USA.
28
Sn-Bi
Ag
Sb
Sb-Zn
K. Okamoto, K. Nomora, S. Doi, T. Akamatsu, S. Sakuyama, and K. Uenishi (Fujitsu Laboratories, Osaka Univ.), “Effect of Sb and
Zn addition on Impact Resistance Improvement of Sn-Bi Solder Joints”, IMAPS 2014, Sept. 30-Oct. 3, 2013, Orlando, FL, USA.
29
Sn-Bi, Ag, Sb failed within 2 drops
Sn-Bi
Ag
Sb
Sb-Zn
Electrical resistance increase < 10%
K. Okamoto, K. Nomora, S. Doi, T. Akamatsu, S. Sakuyama, and K. Uenishi (Fujitsu Laboratories, Osaka Univ.), “Effect of Sb and
Zn addition on Impact Resistance Improvement of Sn-Bi Solder Joints”, IMAPS 2014, Sept. 30-Oct. 3, 2013, Orlando, FL, USA.
IMC of
SnBiSbZn
changed
from
Cu6Sn5 to
Cu5Zn8,
avoided Sn
depletion,
thus
avoided
forming
brittle Birich layer,
the joint is
more crack
resistant
after high
temp aging.
30
Cu5Zn8
Cu6Sn5
Cu6Sn5
Bi-rich zone
Only small cracks
seen
K. Okamoto, K. Nomora, S. Doi, T. Akamatsu, S. Sakuyama, and K. Uenishi (Fujitsu Laboratories, Osaka Univ.), “Effect of Sb and
Zn addition on Impact Resistance Improvement of Sn-Bi Solder Joints”, IMAPS 2014, Sept. 30-Oct. 3, 2013, Orlando, FL, USA.
31
Wetting of Sn-Bi-X Alloys
Addition of 1.0 wt.%Cu or 1.0 wt.%Sb has little effect on the spread
area, but addition of Zn significantly reduced spread area.
Solder
58Bi-42Sn
60Sn-40Bi
63Sn-37Pb
Alloy Element
Spread Area (mm2)
Water Sol.
No-Clean
None
40±1
35±2
Cu
37±1
36±4
Zn
26±3
30±2
Sb
39±1
33±1
None
43±2
38±1
Cu
41±1
38±1
Zn
28±3
27±3
Sb
42±1
38±2
None
53±2
110±5
Ref: L.E. Felton, C.H. Raeder, and D.B. Knorr, "The properties of Sn-Bi alloy solders", JOM,
p.28-32 (Jul. 1993).
32
BiSn + Proprietary Dopants
SnBi + certain additives
• In this category are alloys that can be used in reflow
soldering temperatures from 170°C to 210°C, resulting in
lower thermal stresses and defects such as warping
during assembly.
• In the case of the Sn42-Bi58 eutectic alloy, it was
observed that its thermal-mechanical fatigue properties
can be improved by small Ag additions. For example,
Sn42-Bi57.6Bi-Ag0.4 alloy has been commercialized,
resulting in improved mechanical and thermal
properties.
Morgana Ribas, Sujatha Chegudi, Anil Kumar, Sutapa Mukherjee, Siuli Sarkar, Ranjit Pandher, Rahul Raut, Bawa Singh (Alpha),
33
“LOW TEMPERATURE ALLOY DEVELOPMENT FOR ELECTRONICS ASSEMBLY – PART II”, SMTAI 2013, MFX5-P2.
34
Dopants improve elongation moderately
Ag addition and Ag+X addition of C1-C result in higher tensile strength than
Sn42-Bi58. Yield strength of Sn42-Bi57.6-Ag0.4 and C1-C is also slightly higher
than Sn42-Bi58. C1-A and C1-B have lower yield strength. As expected, Ag
addition results in higher ductility, especially in C1-A and C1-C.
(12% > BiSn)
(37% > BiSn)
Morgana Ribas, Sujatha Chegudi, Anil Kumar, Sutapa Mukherjee, Siuli Sarkar, Ranjit Pandher, Rahul Raut, Bawa Singh (Alpha),
“LOW TEMPERATURE ALLOY DEVELOPMENT FOR ELECTRONICS ASSEMBLY – PART II”, SMTAI 2013, MFX5-P2.
35
Dopants slightly improve impact energy
2.6% >
1.7% >
3.3% >
3.3% >
Sn42-Bi57.6-Ag0.4
absorbs slightly more
impact energy as
compared to Sn42
Bi58. Nonetheless,
secondary alloying
additions of C1-A, C1B and C1-C resulted in
further toughness
improvement.
Morgana Ribas, Sujatha Chegudi, Anil Kumar, Sutapa Mukherjee, Siuli Sarkar, Ranjit Pandher, Rahul Raut, Bawa Singh (Alpha),
“LOW TEMPERATURE ALLOY DEVELOPMENT FOR ELECTRONICS ASSEMBLY – PART II”, SMTAI 2013, MFX5-P2.
BiSn + Proprietary Dopants
New Progress at Indium Corp
Ductility of new alloys much higher than BiSn
Eutectic Sn58Bi for control
757-38-1
Eu SnBi + dopants
Ave. 101%
169% > BiSn
757-41-1
Eu SnBi + dopants
Ave. 114%
203% > BiSn
Internal data of Indium Corporation
Ave. 37.6%
37
BiSn + Proprietary Dopants
SEM images show that a lot of extremely fine Bi grain size (~1um) spreading in tin-rich zones,
which gives good explanation of excellent mechanical strength improvement
BiSn (reference)
BiSn -D1
BiSn -D2
BiSn -D3
Internal data of Indium Corporation
38
Rework Solution Using Low Melting
77.2Sn20In2.8Ag Alloy Solder Paste
For Better Reliability
P. Snugovsky, S. Bagheri, Z. Bagheri, M. Romansky (Celestica), “The New Lead Free Assembly Rework Solution Using Low
Melting Alloys”, APEX, 2007.S24-01,
39
Ning-Cheng Lee, James A. Slattery, John R. Sovinsky, Iris Artaki, and Paul T. Vianco, “A Drop-In Lead-Free Solder Replacement”,
Surface Mount International, p.463-472, San Jose, CA, August 30 – September 1, 1994
40
Ning-Cheng Lee, James A. Slattery, John R. Sovinsky, Iris Artaki, and Paul T. Vianco, “A Drop-In Lead-Free Solder Replacement”,
Surface Mount International, p.463-472, San Jose, CA, August 30 – September 1, 1994
Rework Board and Alloys
• Alloy A – Sn77.2In20Ag2.8
• Alloy B – Bi58Sn42
due
• Alloy C – In52Sn48 (excluded
to cost)
41 P. Snugovsky, S. Bagheri, Z. Bagheri, M. Romansky (Celestica), “The New Lead Free Assembly Rework Solution Using Low
Melting Alloys”, APEX, 2007.S24-01,
42
There was no portion of initial solder ball visible at the cross-sections of reworked
solder joints. It shows that solder balls were fully dissolved in liquid solder paste
during reflow.
SnInAg
BiSn
InSn
(excluded due
to cost)
P. Snugovsky, S. Bagheri, Z. Bagheri, M. Romansky (Celestica), “The New Lead Free Assembly Rework Solution Using Low
Melting Alloys”, APEX, 2007.S24-01,
43
Weibull plots showing the difference in fatigue lives at 0°C to 100°C for
as-assembled pure SAC405 (1) and reworked CBGA937 using Incontaining Alloy A (2) and Bi-containing Alloy B (3).
BiSn
SnInAg
SAC
P. Snugovsky, S. Bagheri, Z. Bagheri, M. Romansky (Celestica), “The New Lead Free Assembly Rework Solution Using Low
Melting Alloys”, APEX, 2007.S24-01,
44
Thank You
45
46
Summary (I)
• Low melting solders needed for SMT assembly or
special applications.
• In-Sn is softer, much weaker, more ductile, much lower
in creep resistance & stress rupture life than Sn63. Low
in thermal fatigue resistance. Good on fatigue at low
cyclic isothermal strain rates. In alloys are slow in crack
propagation. High cost & low supply. Wetting at low
temperature a challenge.
• Bi expand upon solidification, reduce surface tension. BiSn brittle, coarsen extensively. Pb contamination forms
eutectic 8Sn-52Pb-40Bi melt at 95C. Higher in UTS,
shear strength, stress rupture time, creep resistance,
lower in thermal fatigue resistance (20C/110C) than
Sn63. Wetting sensitive to impurity. Helped by Pb, hurt
by Sb, P, & As.
47
Summary (II)
• Bi-Sn improvements were made through addition of
minor elements.
– Ag increase ductility, & TCT performance. Still poor
on drop test performance
– In reduce coarsening, increase shear strength,
reduce IMC thickness.
– Cu slow down coarsening.
– Co aggravate coarsening
– Ni reduce IMC thickness & shear strength, increase
coarsening. Wetting a challenge.
– Sb refine grain size, improve drop test performance
– Zn maintain drop test improvement of Sb even with
high temp aging on Cu, but hurt wetting
48
Summary (III)
• New progress at Indium Corporation on BiSn
modification made significant improvement in ductility.
• SnInAg medium low melting temperature provided high
reliability and good processability. SAC assembly
reworked with SnInAg solder paste rendered joints with
reliability higher than SAC joints.
49
The criteria for rework parameter optimization were: proper shape of solder joint after rework, minimized
voiding, uniform microstructure, and absence of or reduced low melt fractions in the crystallized mixtures of
solder paste and solder ball.
Alloy C was excluded from the experimental matrix after the first step because of the high solder paste price
precluding its use in most processes.
CBGA937
SnInAg
InSn
BiSn
PBGA196
P. Snugovsky, S. Bagheri, Z. Bagheri, M. Romansky (Celestica), “The New Lead Free Assembly Rework Solution Using Low
Melting Alloys”, APEX, 2007.S24-01,
50
Reworked Joint Using SnInAg Paste
CBGA937
PBGA196
P. Snugovsky, S. Bagheri, Z. Bagheri, M. Romansky (Celestica), “The New Lead Free Assembly Rework Solution Using Low
Melting Alloys”, APEX, 2007.S24-01,