Phase Change Materials- Networking Applications
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The document discusses the advantages of phase change materials (PCM) over thermal grease in networking applications, emphasizing their long-term thermal reliability and performance under high power densities. It highlights various testing criteria and results demonstrating that PCM offers lower thermal impedance and stability compared to traditional greases, which suffer from issues like pump-out during power cycling. Additionally, the document outlines the critical components of PCM technology that contribute to its reliability when subjected to harsh operational conditions.
Phase Change Materials- Networking Applications
- 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