Transient Liquid Phase (TLP) Bonding and Sintered Silver Paste for

Transcription

Transient Liquid Phase (TLP) Bonding
and Sintered Silver Paste for
Die‐attach/Substrate‐attach
in High‐power, High‐temperature Applications
Avishesh
A
i h h Dh
Dhakal*
k l*
Graduate Student, IML
Yuihin Tseung*, Brian Patterson*, Srikanth Kulkarni*, Venkata Seetha Gona*
Fredd Barlow
l †, Aicha
A h Elshabini
lh b †
Department of Electrical and Computer Engineering,
*Student Members, †Faculty Members
Idaho Microelectronics Laboratory
University of Idaho
[email protected]
10/20/2011
SPONSORS:
1
Outline
• Extreme Environment
Extreme Environment
• HEV/PHEV Application
• Challenges
• Past Work
• Sinter Silver Paste
‫ ۔‬Comparison w/ Solders
p
‫ ۔‬Goal of Experiment
‫ ۔‬Characterization
‫ ۔‬Metallization
‫ ۔‬Process Optimization
‫ ۔‬Process Development
‫ ۔‬Preliminary Experiment
10/20/2011
‫ ۔‬DOE
‫ ۔‬Result
‫ ۔‬Summary
• Diffusion Bonding
Diffusion Bonding
• TLP Bonding
‫ ۔‬IMC Properties
‫ ۔‬Test Procedure
‫ ۔‬Bonding Issues
‫ ۔‬Conclusions and Future Directions
Conclusions and Future Directions
IDAHO MICROELECTRONICS LAB
2
• Challenges
• Past Work
‫۔‬
Comparison w/ Solders
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
Process Optimization
‫۔‬
Process D
Development
l
t
‫۔‬
Preliminary Experiment
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
Applications with Extreme Environment Conditions
• Extreme environment conditions entail •
temperature, humidity, stress, and vibrations
•
• Extreme Temperature due to heat Extreme Temperature due to heat
generated during operation and ambient temperature
• HEV/PHEV
HEV/PHEV applications applications – temperature
temperature of of
the coolant is higher when shared between engine and power module
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Higher thermal resistance in the g
path of heat dissipation
Junction temperature of power module with shared coolant ≈ module with shared coolant 200°C
K
K (W/m‐K) t(mm) A(mm²) Rɵ (°C/W)
Si Die
153
0.30
Solder
50
0.05
Cu
390
0.30
AlN
170
0 30
0.30
Cu
390
0.30
Solder
50
0.05
Base Plate
390
3.00
Grease
1
0.05
Cold Plate
Total Thermal Resistance
100
100
100
100
800
2000
4000
4000
0.020
0.010
0.007
0 015
0.015
0.023
0.000
0.002
0.500
0.020
0.597
Figure 1. A typical Power Module
Table 1. Module Thermal Resistance
3
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
HEV/PHEV Application
• HEV/PHEV (Plug‐in Hybrid Electric Vehicle) require two coolant loop for Si /
( g
y
) q
p
based electronics (≈ 168⁰C)
• Goal: Use one single coolant loop for both power electronics and internal combustion engine using SiC power electronics (
combustion engine using SiC
power electronics (≈ 200
200⁰C)
C)
• Power electronic packaging reliability on extreme temperature (‐40⁰C ‐ 200⁰C) No data!
Temperature(°C)
Si devices SiC devices
Si devices
• State of art solder alloy usually have low
State of art solder alloy usually have low
208.73
SiC/Si DIE
168.73
melting/degradation temperature
solder
165.64
205.64
• Lead free solder required in Europe
Cu
164.07
204.07
(US
(US in consumer products)
in consumer products)
AlN
162.85
202.85
≈ 208⁰C
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
1/28/2010
Figure 2. Schematic of an inverter module in a d l
HEV/PHEV
Solder
Die (SiC)
Cu Cu
160.08
200.08
solder
158.86
198.86
base plate
base plate
157 29
157.29
197 29
197.29
grease
147.03
187.03
cold plate
≈ 105⁰C
65.00
105.00
4
Table 2. Temperature at levels of module
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
Solder
• Desirable features (ideal solder material)
(
)
‫ ۔‬Low processing temperature
‫ ۔‬High melting point
‫ ۔‬High electrical conductivity
Hi h l t i l
d ti it
‫ ۔‬High thermal conductivity
‫ ۔‬Low modulus of elasticity
‫ ۔‬Matching Coefficient of Thermal Expansion (CTE)
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
1/28/2010
5
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Challenges in High Temperature Packaging
• Die Attach
Die Attach
‫ ۔‬High Reflow Temperature
‫ ۔‬Low Void Fraction
‫ ۔‬Low Modulus of Elasticityy
• Wirebonding
‫ ۔‬Formation of Intermetallics
‫ ۔‬Shape of Wirebonds‐‐ball, wedge, and ribbon
‫ ۔‬Diameter, Number of Wires
‫ ۔‬Materials employed
• Substrates
‫ ۔‬High Electrical Conductivity
‫ ۔‬Low Thermal Resistance
‫ ۔‬High Mechanical Strength
High Mechanical Strength
• Encapsulation
‫ ۔‬High Operating Temperature
‫ ۔‬High Breakdown Voltage
‫ ۔‬Low Modulus of Elasticity
• Path of electrical conduction must have low resistance and inductance
• Heat spreading in the package must be good
• Package must offer low thermal resistance between the devices and the heat P k
t ff l th
l it
b t
th d i
d th h t
sink and impedance matching
6
• The package must be mechanically reliable from strength point of view
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Past Work
• Developed suitable die attach, p
, • Current Challenges and Potential g
encapsulation, and housing Solutions
material for high temperature • Lead‐Free die attach
environments
Sinter Silver Paste
‫ ۔‬Lead Based Die Attach : Solder • Transient Liquid Phase (TLP) 92.5Pb/5.0In/2.5Ag
diffusion bonding
‫ ۔‬Encapsulate : NuSIL GEL 8100
Encapsulate : NuSIL GEL 8100
‫ ۔‬Housing : Torlon 5030
• Verified encapsulation slightly weakens wirebond strength when weakens wirebond
strength when
thermally aged
• Assembled three‐phase inverter module with above mentioned d l ith b
ti
d
materials
7
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
Sinter Silver Paste
• What is Sinter Silver Paste?
‫ ۔‬A new lead free alternative die attachment material similar to solder
‫ ۔‬Micro‐silver particle (<20μm) mixed with organic solvents (to avoid agglomeration)
‫ ۔‬Decrease surface energy by decreasing particle size ‐ Require less energy to sinter silver particles
particles together
together
‫ ۔‬Can be cured in low temperature (<3000C) and approach solid silver (9510C melting point)
Ag
Dispersant
Ag
Ag
Ag
Ag
Ag
Ag
Ag
Binder
Before Sinter (silver particle with organic solvents)
Ag
After sintered organic solvents Af
i
d
i
l
are burnt out
Thinner
Ag
Ag
Ag
Ag
Paste agglomerate and becomes P
l
db
solid silver
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Figure 4. Various components of a silver paste and the structure at different phases of the sintering process
8
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Sinter Silver Paste ‐ Lead Free Solder Comparison
• Why not others lead free solders?
‫ ۔‬Low thermal and electrical conductivity
‫ ۔‬Hard solder alloys tend to have higher stress and high processing temperatures
• Why Sinter Silver?
y
‫ ۔‬Low sintering temperature (300⁰C)
‫ ۔‬High subsequent reflow temperature (961⁰C)
‫ ۔‬Lead Free
Lead Free
‫ ۔‬High thermal and electrical conductivity
‫ ۔‬Resulting porous materials have lower stress • Why Heraeus
Wh H
Si t Sil
Sinter Silver Paste?
P t ?
‫ ۔‬Nano silver paste cannot print >25µm thickness
‫ ۔‬Microscale particle size (<20µm) allows for thicker paste
‫ ۔‬Lower cost than nano silver
‫ ۔‬No pressure required
P
Property
UNIT
Coefficient of Thermal Expansion (CTE)
ppm/°C
Thermal Conductivity
at 25 °C W/m‐°C
Maximum Service (Reflow)Temperature
°C
High Heraus Ni‐Sn Lead Silver Paste Metal Solder (LTS116)
Alloy
29
19
8.65
26
240
19.6
300
961
400
Electrical Resistivity at 25 °C
Ω‐cm
2.01E‐07 6.67E‐08
2.85E‐07
Electrical Conductivity
Tensile Strength
Shear Strength
Solid Content
S/m
MPa
MPa
%
3.51E+06
Viscosity
Processing Temperature (lowest)
cPs
4.98E+06 1.50E+07
29
55
15.4
10‐20
89
35000‐
50000
⁰C
300
Processing Time (correspond to Processing Temp)
to Processing Temp)
min
Print Thickness
µm
Shelf Life (at 4⁰C)
Month
220
250
50
40‐150
6
Table 3. Property Comparison
9
• Challenges
• Past Work
Goal of the Experiment
• Find out the characteristics of sinter silver paste
p
‫۔‬
• Find out the suitable die and substrate metallization for sinter silver paste
‫۔‬
Goal of Experiment
‫۔‬
Characterization
p
gp
p
• Develop a sintering process for sinter silver paste
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Ideal Cases!
d l
!
15
10
5
Series1
0
0
500
Number of Thermal Cycle
1000
Ideal Result of High Thermal Storage Test
Shear Sttrength (kgf)
• TLP Bonding
Ideal Result of Thermal Cycling Test
Shear Sttrength (kgf)
• Develop a statistical experiment to evaluate any present degradation of shear strength using sinter silver paste after 1000 hours of thermal cycling range from 40⁰C to 200⁰C and 1000 hours of High Temperature Storage
range from ‐40⁰C to 200⁰C and 1000 hours of High Temperature Storage (HTS) at 200⁰C
15
10
5
Series1
0
0
500
1000
Number of hours
10
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
Sinter Silver Paste ‐ Characterization
• Characterization of sinter silver paste (Differential Scanning Calorimetry / Thermogravimetric
Analysis TG)
‫ ۔‬Sintering Point: 210⁰C
• Sintering Profile Optimization
‫ ۔‬Time (10mins / 30mins)
‫ ۔‬Temperature (200⁰C / 250⁰C / 300⁰C)
(
⁰ /
⁰ /
⁰ )
• Sintering Process:
‫۔‬
‫۔‬
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
‫۔‬
‫۔‬
Dispense paste on ¼” x ¼” substrate then scrub in 4mm x 4mm Si die
then scrub in 4mm x 4mm Si die
Sinter based on optimization profiles in convection oven
Samples are then glued on plastic holder and sheared
Initial testing done on Si substrate
Si die
Metallization
Silver Paste
Metallization
Si Substrate / DBC
11
• Challenges
• Past Work
Testing of Metallization on Sinter Silver Paste
• Three metals were considered and tested (Al, Cu, Ag)
( , , g)
• Al fail in adhesion to Sinter Silver Paste
• Cu and Ag results in consistent shear strength
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
Metal Layer
Metal Layer
‫۔‬
Silver Paste
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
2mm x 2mm Si Die
Metal Layer
0.25”x0.25”(6.35mm x 6.35mm)Silicon Substrate
Al‐Al
Cu‐Cu
Ag‐Ag
Mean Shear Strength on Al‐Al vs Cu‐Cu vs Ag‐Ag
Shear Strength (kgf)
8
6
Al Al M
Al Al Mean
4
Cu Cu Mean
2
Ag‐Ag Mean
0
Al Al Mean
Cu Cu Mean
Ag‐Ag Mean
12
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Optimization of Sintering Process
•
•
•
•
Two sets of time are tested: 10 and 30 minutes
Three sets of temperature are tested: 200 ⁰C, 250 ⁰C, and 300 ⁰C
DBC substrate and Cu die were used
10 i @ 300 ⁰C l t d b d
10mins @ 300 ⁰C selected based on the optimization tests
th
ti i ti t t
DBC‐Cu
Shear Strength of DBC(0.25"x0.25")‐
Cu(4mmx4mm)
8
4mm x 4mm Si Die
Ti/Cu
Silver Paste
Cu Layer
0.25”x0.25”(6.35mm x )
6.35mm)DBC Substrate
Cu Layer
S
Shear Strength (
(N/mm^2)
7
6
5
4
200⁰C
3
250⁰C
2
300⁰C
1
0
0
10
20
30
Sintering Time (min)
40
13
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
Process Development
Warm up the Sinter Silver Paste for 30 mins at room temperature and preheat oven
Dispense spe se
Paste
Clean the substrate using alcohol
Dispense the Sinter Silver Paste with pressure time dispenser
Attach Dies
Attach the die
Sinter in Oven
Put samples to the oven for sintering process
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Shear the sample after sintering process
Shear
14
• Challenges
• Past Work
‫ ۔‬Die Attach
‫ ۔‬Encapsulation
‫ ۔‬Housing
‫ ۔‬TGA & DSC
‫ ۔‬Summary
• Wirebonding
‫ ۔‬Known Issues
‫ ۔‬Objective & Plan of Experiment
‫ ۔‬Sample Preparation
‫ ۔‬Sample Treatment
‫ ۔‬Sample Testing
• Substrates
Wafer Preparation
f
i
•
•
•
•
•
Double side polished SiC wafer was used in the process. Metal deposition on the wafer was done by sputtering process in a Kurt J Lesker PVD system
On the SiC
h
wafer, 300Å of Ti was deposited followed by 1500Å of Al and annealed.
f
Å f
d
d f ll
db
Å f l d
l d
Another 300Å of Ti followed by 1500Å of Al was sputtered on the top side of the wafer
The wafer was annealed by resistive heating in an atmosphere of forming gas
1000
35
Anneal Profile
30
800
300 Å Ti / 1500 Å Al 25
600
20
15
400
10
Pressure (PSIa)
• Future Work F t
W k
Sample Preparation
Temperature (°C
C)
• Applications
200
5
0
0
0
1/28/2010
100
200
300
400
500
Time (sec)
600
700
800
15
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Preliminary Experiment for Sample Size Calculation
• 10 samples were made to determine p
sample size
• DBC substrates and Ag metallized dice were used
were used
• 95% confidence level was selected Sample (Substrate‐Die) 04/01/2011
Value (kgf)
DBC‐Ag 1 (040101)
DBC‐Ag 2 (040102)
DBC‐Ag 3 (040103)
DBC‐Ag 4 (040104)
DBC‐Ag 5 (040105)
DBC‐Ag 6 (040106)
DBC‐Ag 7 (040107)
(
)
DBC‐Ag 8 (040108)
DBC‐Ag 9 (040109)
DBC‐Ag 10 (040110)
5.588018
6.847297
6.274248
7.449623
8.080512
5.33452
6.800168
7.100795
5.631934
6.592014
Mean μ
Variance σ^2
Confidence Level Z(α/2) ‐ 95%
Tolerable Error
Tolerable Error
Sample Size
Total Samples Need
6.5699129
0.6925618
1.96
1
2.6605456
45
Table 4. Statistical analysis of sample size calculation
16
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
Design of Experiment (DOE)
Sample size = 5 (total=75 samples)
p
(
p )
Latin square design was used
Process variations were eliminated
TST (Thermal Shock Test) Test Point
TST (Thermal Shock Test) Test Point
• 100, 250, 450, 700, 1000 cycles
• HTS (High Temperature Storage) Test Point
• 100, 250, 450, 700, 1000 Hours
100 250 450 700 1000 H
2mm x 2mm SiC Die
Ti/Ni/A Layer
Ti/Ni/Ag
L
Silver Paste
Cu Layer
‫۔‬
IMC Properties
‫۔‬
Test Procedure
0.25”x0.25”(6.35mm x 6.35mm)DBC Substrate
‫۔‬
Bonding Issues
Cu Layer
‫۔‬
Conclusion
10/20/2011
Control
25
1
samples
•
•
•
•
HTS
25
2
samples
TST
25
3
samples
DBC‐Cu Shear Stregth Result (04/21/2011)
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
Batch 2
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
Batch 3
Batch B
t h
1
10
Shear Strength (kgf)
8
6
DBC ‐
Ag
4
2
0
DBC Ag 1 (042101)
DBC Ag 2 (042102)
DBC Ag 3 (042103)
Sample No.
DBC Ag 4 (042104)
Final Test Structure
17
• Challenges
Sinter Silver Initial Results
Average Shear Strength
• Past Work
‫۔‬
6
7
‫۔‬
Goal of Experiment
6
‫۔‬
Characterization
5
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
7
8
‫۔‬
9
5
Kgf
Kgf
4
4
3
3
2
2
1
1
0
0
0
100
200
300
400
500
600
700
Hours
A
Average Shear Strength Sh
S
h
(High Temperature Storage)
800
900
1000
0
100
200
300
400
500
600
700
800
900
1000
Cycles
A
Sh
S
h
(Thermal Shock Test)
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
18
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
SEM/EDAX analysis for a sheared sample p
after 1000hrs of HTS top of the substrate shown in the picture
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
19
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
SEM/EDAX analysis for a sheared sample after 1000hrs of HTS (bottom of the die shown in the picture)
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
20
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Summary: Sintered Silver Paste
Electronic packaging
• Demand for improvement on high power electronic packaging for SiC device
Lead Free Solder
• Sinter Silver Paste has superior electrical and thermal conductivity compare to lead base solder
Sinter Process
• Sinter process is simple and can easily be integrated to manufacturing process
Experimental Design
• Sintering process has been designed
• Test Structure has been created
Future Work
• Elimination of process variation and repeat accelerated ageing test
• Consistent thickness (screen printing)
21
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Diffusion Bonding
HM Metal
HM Metal
LM Metal
IMC
• Background
HM Metal
HM Metal
HM Metal
HM Metal
‫ ۔‬Solid liquid interdiffusion bonding
Graphical representation of the Diffusion Bonding Process
‫ ۔‬Pb‐free technology based on isothermal solidification
TLP
Processing
Processing Remelt Combination
bi i
Temperature
Time
i
Temperature
‫ ۔‬Low melting metal sandwiched between high melting metal layers
‘Cu‐Sn
280°C
4 min
>415°C
‫ ۔‬Heated under small applied S A
250°C
60 i
60 min
>600°C
600°C
pressure to form IMC (Intermetallic f
IMC (I
lli Sn‐Ag
Compound)
‘Sn‐Ni
300°C
6 min
>400°C
‫ ۔‬IMCs shows a drastic change in Cu‐In
180°C
4 min
>307°C
thermal electrical and mechanical
thermal, electrical, and mechanical Ag‐In
175°C
120 min
>880°C
behavior • Transient Liquid Phase (TLP) Bonding Au‐Sn
260°C
15 min
>278°C
‫ ۔‬Diffusion Bonding without the Diffusion Bonding without the
Au‐In
200°C
0.5 min
>495°C
application of pressure
Table 5. Diffusion bonding pairs with process parameters
22
• Challenges
TLP Bonding ‐ DBC as Die‐attach
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Sn‐Cu and Ni‐Sn binary phase diagrams
SiC
Ni
Sn
C
Cu
Graphical representation of
representation of the TLP pairs for die attach application
SiC
Ni
Sn
Ni
C
Cu
ASM Handbook Vol. 3 Alloy Phase Diagrams, ed. By H. Baker, ASM International, Materials Park, Ohio (1992).
23
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
TLP Bonding ‐ IMC Properties
• P
Processing time and i ti
d
metal cost/availability limited intermetallic selection
• Nickel‐Tin‐Nickel
sandwich picked for i iti l t t
initial test
Property
Cu
Sn
Ni
Density (g/cm3)
8.9
7.3
8.9
Young’s Modulus (GPa)
117
41
213
Shear Modulus (GPa)
Cu6Sn5 Cu3Sn Ni3Sn4
8.28
8.9
85.56 108.3 133.3
50.21 42.41
Toughness (MPa∙m‐1/2) 8.65
45.0
1.4
1.7
1.2
Vickers Hardness (kg/mm2)
30
100
15
378
343
365
Electrical Resistivity (µΩ∙cm)
1.7
11.5 7.8
17.5
8.93
28.5
0.67 0.905
34.1
70.4
19.6
Thermal Conductivity (W/(m∙K))
3.98
Thermal Diffusivity (cm2/s)
Specific Heat (J/(kg∙K))
0.145
286
326
272
16 3
16.3
19 0
19.0
13 7
13.7
Table 6. Comparison between some common metals and intermetallic compounds
24
Thermal Expansion (10
Thermal
Expansion (10–6/K)
0.385 0.227 0.439
0.24 0.083
17 1
17.1
23
12 9
12.9
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
TLP Bonding – Test Procedure
• Full Scale Test Issues:
– Surface roughness in common substrate materials such as DBC
materials such as DBC
– Clean interface before processing
Diffusion Bonding Process
• Initial
Initial Test Process
Test Process
– A thin Ni strike layer was sputtered and patterned on a 5” diameter Si wafer
– 5 µm of Ni followed by 5 µm of Sn were electroplated on the wafer
– Wafer was diced to produce 4mm x 4mm dice and ¼” x ¼” substrates
– Graphite tooling was used to hold the die attach assembly in place during reflow
25
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
TLP Bonding – Issues
• Attachment inconsistencyy
– Processing time
– Temperature
– Surface cleanliness
S f
l
li
– Surface roughness
– Curing profile
– Thermal stress developed
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Diffusion Bonding Process
26
• Challenges
• Past Work
‫۔‬
‫۔‬
Goal of Experiment
‫۔‬
Characterization
‫۔‬
Metallization
‫۔‬
‫۔‬
Process D l
Development
t
‫۔‬
‫۔‬
DOE
‫۔‬
Result
‫۔‬
Summary
• TLP Bonding
‫۔‬
IMC Properties
‫۔‬
Test Procedure
‫۔‬
Bonding Issues
‫۔‬
Conclusion
10/20/2011
Conclusions
•
•
•
•
Evaluating two lead‐free die attachment methods: sintered silver & TLP
Sintered silver shows significant potential on some surfaces: silver & copper
Thermal shock testing and HTS will be completed by November 2011
TLP is more complex, but Ni‐Sn system shows significant potential as well
•
The use of plated Ni and Sn is likely the most economical approach
•
Key challenges are substrate surface roughness & camber Future Directions
Future Directions
• High Temperature Storage (HTS) and Thermal Shock Test (TST) for Cu‐Sn and y
Ni‐Sn TLP systems
• Partial sintering of sinter silver paste to prepare preform or screen printing for thickness consistency
27
Acknowledgement
O group iis grateful
Our
f l to II-VI
II VI foundation
f d i for
f supporting
i our work.
k
I thank Professor Fred Barlow, Professor Aicha Elshabini, and Professor
Gabriel Potirniche
for their valuable guidance throughout the project
I thank Dr. Tom Williams from the Electron Microscopy Center and Triratna
Shrestha from the Department of MSE for their invaluable support and
suggestions.
suggestions
I thank Micron Inc. for supporting my undergraduate project as well as II-VI
F d ti for
Foundation
f supporting
ti my graduate
d t studies.
t di
1/28/2010
28

Transient Liquid Phase (TLP) Bonding and Sintered Silver Paste for

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