Phase Change Materials as an Alternative to Thermal Grease for Networking Applications - a technical comparison of Thermal Interface Materials in networking applications. Presented jointly by Juniper Networks and Honeywell Electronic Materials.

1. Phase Change Materials:
Alternative to Thermal Grease for
Networking Applications
Susheela Narasimhan
Juniper Networks, Inc.
&
Hyo Xi and Chris Lee
Honeywell Electronics Materials

2. 2
Discussion
• Device Thermal Trends
• Thermal Requirements & Test Criteria
• Results & Material Selection
• Reliability and Phase Change Materials

3. 3
Power Increases More Than Seven Times After 2000
Merchant Silicon Power in Networking Applications

4. 4
Power Cycling Trends in Networking Applications

5. 5
Temperature Variations as a Result of Power Cycling

6. 6
#
Customer
Need
Descrip1on
Requirement
Tests
1
Longevity
Long
warranty
periods;
long
term
thermal
reliability
Constant
thermal
impedance
through
cycling
and
at
least
8-­‐10
years
Temperature
and
power
cycling
2
Opera1ng
Condi1ons
Performance
under
harsh
opera@ng
condi@ons;
external
factors
including
temperature,
humidity,
shock,
etc.
Ambient
up
to
40°C
at
customer
site
and
55-­‐61°C
in
NEBS
tes@ng
-­‐5°C
to
61°C
with
chip
/
heat
sink
interface
at
100
-­‐105°C
3
Thermal
Performance
Thermal
dissipa@on
of
extreme
heat
generated
by
high
power
and
high
density
devices
Lowest
thermal
Impedance
Required
Impedance
of
about
0.01
–
0.02°C
in^2
/W
4
Bond
Line
Thickness
Bond
line
thickness
~7-­‐8
mil
thickness
in
order
to
meet
lid
and
heat
sink
flatness
requirements
7-­‐8
mils
Thermal Needs, Requirements & Test Criteria

7. 7
Issues with Greases in Power Cycling Applications
• Greases are subject to thermal expansion of the heat
sink and ASIC lid during power cycling which can cause
pump out and result in dry-out scenarios of the interface
between the heat sink and the chip
Name of Sensor
Grease
Application
Phase Change
Application
Chip 1
91.0
92.0
Chip 2
92.0
91.2
Chip 3
98.0
97.5
Chip 4
100.0
99.0
PCM Can Provide Equal Thermal Performance as Grease w/o Issue

8. 8
Illustration of Pump Out
Grease pump out and
creation of voids
Phase change application forming
a continuous interface between heat
sink and ASIC lid

9. 9
Key Factors for Thermal Dissipation
• Thermal Impedance
- The lower impedance, the faster heat dissipation
- Interface contact resistance + TIM resistance
• Bulk Conductivity
- The higher conductivity, the faster heat dissipation
• Bond Line Thickness
- The thinner BLT, the faster heat dissipation
• Pre-load Pressure
- Different material has different pressure reflection
• Interface Condition Impact
- Better interface surface condition, faster heat dissipation due to
less void trapped

10. 10
Viscosity
Melt temp
Solid Liquid/gel state
• Optimal Surface wetting
• Low Contact Resistance
• Low Thermal Impedance
Increasing Temperature !
45 °C
Theoretical Curve: PCM Viscosity vs. Temperature

11. 11
PCM Polymer
• Higher Molecular Weight
- Structural integrity
• Long Chain Polymer Structure
vs.
PCM
• Short Chain
• Good Flow-ability, wetting
but…
• Potential for Migration, Dry-
Out and Pump-Out Issues
• Long Chain
• Stable and Consistent Filler
• Minimizes Filler Migration /
Separation Over Accelerated
Life Test (HTB, Temp Cycle)
Grease
PCM Polymer Structure Enables Reliable, Long-Term Performance

12. 12
Honeywell
PCM
Initial 1000 cycles
Silicone
Grease
Thermal Cycling Test Condition:
• -55°Cx10min + 125°Cx10 min, for 500 to 1000 cycles
• Sandwich PCM & grease between aluminum and glass plates set at 200µm gap
• TI Test : ASTM D5470
Thermal Cycle (-55 °C to 125 °C)
vs. Grease
HEM PCM vs. Silicone Grease
Grease breaks down Grease TI degrades
Silicone Grease
Honeywell PCM
Honeywell Provides Stable Polymer Structure with No Pump-Out Issue

13. 13
Honeywell
PCM
Initial 400 hr
Silicone
Grease
High Temperature Baking (HTB) Test Condition:
• HTB = 150°C
• PCM & thermal grease dispensed on smoked glass plates
• TI Test : ASTM D5470
High Temp Bake at 150 °C
vs. Grease
Oil bleeding from grease Grease TI degrades
0.09 0.110.12
1.78
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
Initial Baking 400 Hr
Honeywell PCM
Competitor grease
HEM PCM vs. Silicone Grease
Silicone Grease
Honeywell PCM
Honeywell PCM Does Not Suffer From Silicone Oil Bleed

14. 14
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 200 400 600 800 1000
ThermalImpedance(°C-cm2/W)
Hours
High Temperature Bake at 150 °C
TI vs. Hours of Exposure
PTM3180
Grease A
Grease B
Test Condition: 150°C continuous baking
Test Method: Laser Flash, ASTM E1461
PTM5000
Significantly Better Reliability Than Silicone Grease
Thermal Reliability: PCM vs. Silicone Greases

15. 15
Honeywell PCM Technology
• Fundamentally three primary
components in PCM
• Each are vital to robust
polymer matrix integrity and
filler optimization
• Filler
- Thermal
• Wax/Polymer
- Structural integrity
• Additives
- Cross linking, ATO, etc
TIM
Performance
and
Reliability
Thermal
Filler
Wax/
Polymer
Additives
PCM Formulation is Critical to Performance

16. 16
Extended Reliability: PTM6000
ASTM E1461
• Thermal Stability >3000 hrs @ 150°C
• HAST > 192hrs@ 130°C/85%RH
• Superior Reliability
High Temperature Baking TI vs. Time
Polymer Chemistry Enables Improved Reliability
HAST TI vs. Time

17. 17
Improved Thermal Impedance: PTM7000
• Lower Thermal Impedance: <0.06 oCcm2/W @ Thinnest BLT
• Wider Process Window for Pre-Load Pressure Range
• Test Data demonstrated on Thermal Test Vehicle
Test Method: Cut bar, ASTM D5470
PTM7000 Demonstrates Lower Thermal Impedance

18. 18
TTV Results
TTV (thermal test vehicle) study
Design of TTV
CPU/GPU chip height delta 50um
PTM5000PTM7000 Grease

19. 19
Summary
• Increased power densities of network devices
challenge the performance and reliability of Thermal
Interface Materials
• Accelerated life tests are critical to TIM selection
criteria
• Robust polymer chemistry of Phase Change Materials
enables low thermal impedance with proven long
term thermal stability and reliability

20. Thank You