techcon 2005
TRANSCRIPT
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 2005October 24, 2005
2
Objective
Mechanical Testing of Lead-free Solder
Specimen Preparation
SEM-DIC
ODIC
Results
Summary
OUTLINE
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
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
Silicon wafer with V-groove
Silicon Wafer
V Groove
Copperwires
Solder balls
Copper wires and solder balls are placed in the V-groove
Copper wire and solder ball diameter = 300 m
Specimen Preparation
Solder balls
Cu wires
Encapsulated copper wire End polished copper wire
Copper wire
Specimen Preparation
Wax
Cu wire section
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
Solder column is formed
Turn off heaterRemove glassRemove from hot surface at 85 °CWait until room temperatureRemove specimen from V groove
Solder column is formed
Specimen Preparation
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
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
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
• 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
P
A
Mechanical Testing – Application of DIC
Reference image Object image
Evaluation of stress–strain relationship
Specimen placement in the loading fixture
Mechanical Testing inside SEM
Solder
Cu wire
Cu wire
Groove
Optical digital image of test specimen after solder reflow
Solder
Cu
Cu
Mechanical Testing using Optical System
Unloaded state Under a load of 4.67 N
Region of strain calculations
Mechanical Testing using Optical System
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
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
Load-displacement response (SEM-DIC)
0
1
2
3
4
5
0 1 2 3 4 5Displacement (Micron)
Lo
ad
(N
)
specimen 5
specimen 6
specimen 7
specimen 8
specimen 9
Results
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 (%)
Str
ess (M
Pa) specimen 7 SEM-DIC
specimen 8 SEM-DIC
specimen 9 SEM-DIC
specimen 5 SEM-DIC
specimen 6 SEM-DIC
specimen 3 ODIC
Results
0
10
20
30
40
50
60
0.0 0.5 1.0 1.5 2.0
Strain (%)
Str
ess
(MP
a)
specimen 5
specimen 6
specimen 7
specimen 8
specimen 9
Stress-strain response from SEM-DIC with error bars
Young’s modulus from SEM-DIC and ODIC
Results
SEM-DICAvg: 30.5 GPaSt 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)
Yo
un
g's
Mo
du
lus
(GP
A)
0
10
20
30
40
50
60
Sn 96
.5 A
g 3.
5
Sn 96
.5 A
g 3.
5
Sn 96
.5 A
g 3.
5
Sn 95
.5 A
g 3.
8 Cu0
.7
Sn 95
.8 A
g 3.
5 Cu0
.7
Sn 95
.5 A
g 3.
8 Cu0
.7
Composition
Yo
un
g's
Mo
du
lus
(G
Pa
)
Young’s modulus for bulk lead-free solder from literature
Results
Avg.: 41.5 GPaSt. Dev.: 10.4 GPa
0
10
20
30
40
50
60
70
Sn 96
.3 A
g 3.
7
Sn 95
.5 A
g 4
Cu0.5
Sn 95
.5 A
g 4
Cu0.5
Sn 96
.5 A
g 3.
5
Sn 99
.3 C
u0.7
Sn 96
.5 A
g 3
Cu0.5
Sn 95
.5 A
g 4
Cu0.5
Composition
Yo
un
g's
Mo
du
lus
(G
Pa
)
Young’s modulus for joint scale lead-free solder from literature
Results
Avg.: 48.4 GPaSt. Dev.: 9.9 GPa
Comparison of Young’s modulus measurement against literature
Results
0
10
20
30
40
50
60
70
Experiments
Yo
un
g's
Mo
du
lus (
GP
A)
Avg.: 30.5 GPaSt. Dev.: 3.6 GPa