1. MECHANICAL CHARACTERIZATION OF SOLDER
AT THE MICRO-SCALE THROUGH SCANNING
ELECTRON MICROSCOPY AND DIGITAL IMAGE
CORRELATION
Santaneel Ghosh, Konstantin Yamnitski, Ibrahim Guven and
Erdogan Madenci
Department of Aerospace and Mechanical Engineering
The University of Arizona
TECHCON 2005
October 24, 2005

2. 2
Objective
Mechanical Testing of Lead-free
Solder
Specimen Preparation
SEM-DIC
ODIC
Results
Summary
OUTLINE

3. Validation and application of a non-contact
measurement technique utilizing Scanning
Electron Microscope and Optical Setup/Digital
Image Correlation to Characterize Solder
Material at Micro-Scale
OBJECTIVE

4. Specimen Preparation
• V-groove etching
• Encapsulation of copper wire
• Polishing
• Solder reflowing
Testing
• Mechanical testing using SEM-DIC
• Mechanical testing using ODIC
Results
• Tensile test results
• Comparison to the available bulk and small-scale lead-free
solder properties
Mechanical Testing of Lead-free Solder

5. Silicon wafer with V-groove
Silicon Wafer
V Groove
Copper
wires
Solder
balls
Copper wires and solder balls
are placed in the V-groove
Copper wire and solder ball
diameter = 300 µm
Specimen Preparation
Solder balls
Cu wires

6. Encapsulated copper wire End polished copper wire
Copper wire
Specimen Preparation
Wax
Cu wire
section

7. Place glass to:
(a) keep components in place
(b) assist flow of flux
Apply flux
Keep at 250 °C 3 to 4 min.
Heat up to 250 °C
Specimen Preparation
Reflow in progress

8. Solder column is formed
Turn off heater
Remove glass
Remove from hot surface at 85 °C
Wait until room temperature
Remove specimen from V groove
Solder column is formed
Specimen Preparation

9. Specimen Preparation
• Cleaning: All residue & debris is
removed by ultrasonic cleaning
• Sputtering: Gold sputter specimen
to allow SEM imaging of non-
conductive regions
Solder column after reflow
m m

10. DIC identifies features along the
surface of the solder joint
Distance between points 1 and 2 is
(L) in the undeformed configuration
This configuration serves as the
reference image
Mechanical Testing – Application of DIC
Initial (unloaded) configuration

11. Final (loaded) configuration
DIC identifies the same
features by correlating the
undeformed and deformed
images
Distance between points
1 and 2 is (L in the deformed
configuration
This configuration serves as the
object image
Mechanical Testing – Application of DIC

12. • Displacement of each point in
the reference image is
calculated by a DIC software,
ADASIM from Fraunhofer
Institut.
• Strains are calculated
• Stresses are calculated using
L
ε
∆
=
P
A
σ =
Mechanical Testing – Application of DIC
Reference
image Object image
Evaluation of stress–strain relationship

13. SEM image of a test specimen after solder reflow
Mechanical Testing inside SEM

14. Mechanical Testing inside SEM
In-house measurement apparatus

15. Specimen placement in the loading fixture
Mechanical Testing inside SEM
Solder
Cu wire
Cu wire

Groove

16. Point 1 Point 1Point 2 Point 2
Unloaded state Under a load of 3.83 N
Mechanical Testing inside SEM

17. Optical digital image of test specimen after solder reflow
Solder
Cu
Cu
Mechanical Testing using Optical System

18. Unloaded state Under a load of 4.67 N
Region of strain calculations
Mechanical Testing using Optical System

19. SEM-DIC Measurements
Load
(kg-f)
Load
(N)
Stress
(MPa)
Displacement
(pixel)
Displacement
(m)
Strain
(%)
0.00 0.00 0.00 0.00 0.00 0.00
0.15 1.47 17.42 0.21 0.08 0.03
0.23 2.26 26.70 1.56 0.56 0.23
0.30 2.94 34.83 4.18 1.50 0.61
0.38 3.73 44.12 6.01 2.16 0.87
0.44 4.32 51.09 7.18 2.58 1.04
Sample specimen test results (SEM-DIC)
Results

20. Optical DIC (ODIC) Measurements
Load
(kg-f)
Load
(N)
Stress
(MPa)
Strain
(%)
0.00 0.00 0.00 0.00
0.09 0.88 12.49 0.06
0.19 1.86 26.37 0.13
0.30 2.94 41.64 0.22
0.39 3.83 54.13 0.45
0.47 4.61 65.23 0.69
Sample specimen test results (ODIC)
Results

21. Load-displacement response (SEM-DIC)
0
1
2
3
4
5
0 1 2 3 4 5
Displacement (Micron)
Load(N)
specimen 5
specimen 6
specimen 7
specimen 8
specimen 9
Results

22. Stress-strain response from SEM-DIC and ODIC
Results
Stress - Strain Diagram for SEM and OPTICAL DIC
0
10
20
30
40
50
60
0 0.5 1 1.5 2
Strain (%)
Stress(MPa)
specimen 7 SEM-DIC
specimen 8 SEM-DIC
specimen 9 SEM-DIC
specimen 5 SEM-DIC
specimen 6 SEM-DIC
specimen 3 ODIC

23. Results
0
10
20
30
40
50
60
0.0 0.5 1.0 1.5 2.0
Strain (%)
Stress(MPa)
specimen 5
specimen 6
specimen 7
specimen 8
specimen 9
Stress-strain response from SEM-DIC with error bars

24. Young’s modulus from SEM-DIC and ODIC
Results
SEM-DIC
Avg: 30.5 GPa
St Dev. : 3.6 GPa
0
5
10
15
20
25
30
35
40
Specimen 9
(SEM-DIC)
Specimen 8
(SEM-DIC)
Specimen 7
(SEM-DIC)
Specimen 6
(SEM-DIC)
Specimen 5
(SEM-DIC)
Specimen 3
(ODIC)
Young'sModulus(GPA)

25. 0
10
20
30
40
50
60
Sn
96.5
Ag
3.5Sn
96.5
Ag
3.5Sn
96.5
Ag
3.5
Sn
95.5
Ag
3.8
C
u0.7
Sn
95.8
Ag
3.5
C
u0.7
Sn
95.5
Ag
3.8
C
u0.7
Composition
Young'sModulus(GPa)
Young’s modulus for bulk lead-free solder from literature
Results
Avg.: 41.5 GPa
St. Dev.: 10.4 GPa

26. 0
10
20
30
40
50
60
70
Sn
96.3
Ag
3.7
Sn
95.5
Ag
4
Cu0.5
Sn
95.5
Ag
4
Cu0.5
Sn
96.5
Ag
3.5
Sn
99.3
Cu0.7
Sn
96.5
Ag
3
Cu0.5
Sn
95.5
Ag
4
Cu0.5
Composition
Young'sModulus(GPa)
Young’s modulus for joint scale lead-free solder from
literature
Results
Avg.: 48.4 GPa
St. Dev.: 9.9 GPa

27. Comparison of Young’s modulus measurement against literature
Results
0
10
20
30
40
50
60
70
Specim
en
9
(SE
M
-D
IC
)
Specim
en
8
(SE
M
-D
IC
)
Specim
en
7
(SE
M
-D
IC
)
Specim
en
6
(SE
M
-D
IC
)
Specim
en
5
(SE
M
-D
IC
)
Specim
en
3
(O
D
IC
)
W
iese
-JointScale
D
arveaux
-JointS
caleW
ein
-Bulk
Lin
-Bulk
Experiments
Young'sModulus(GPA)
Avg.: 30.5 GPa
St. Dev.: 3.6 GPa

28. Summary
• Joint scale lead-free solder specimen
preparation technique implemented
successfully
• Performed tensile tests within the SEM and
using the Optical Setup
• Both SEM-DIC and ODIC measurements for
Young’s modulus are lower than those
reported in literature