Thermally Functionalized Structural Materials for Consumer Devices Aaron Vodnick

Transcription

1 Thermally Functionalized Structural Materials for Consumer Devices Aaron Vodnick IMAPS NE May 2015

2 Overview Our focus is a material to more effectively dissipate heat TIMs Chip Substrate Heat Sink Heat Spreader Driving Forces: Consumer Devices with increasing power density Need to Maximize Convective & Radiant Heat Transfer Internal Space at Premium Growing interest in advanced heat spreading materials 2

3 Secondary Heat Spreaders iphone 6 Macbook Galaxy S5 Secondary heat spreaders are found in nearly every high performance consumer electronics device. 3

4 Heat Spreader Materials Thermal Conductivity of Common Materials X-Y Thermal Conductivity (W/m*K) Graphite Metals Oriented Graphite has impressive thermal conductivity. Thermal Transport Limited by Thickness Graphite typically consumes ~50+ m of Z-Height 300 m Steel 25 m Graphite 25 m Adhesive/Organic 4

5 Bulk Conductivity Advantage Thermal Conductivity x Thickness (W/K) " " In-Plane Thermal Conductance Graphite Thickness 0.3mm Thick Structural Member Considering bulk performance, replacing a steel + graphite structural component with a conductive metal can improve thermal properties micron Graphite 25 micron Graphite Copper Aluminum Titanium Stainless Steel There is a need for a cost effective, highly conductive, Structural Material out of conventional metals that is capable of high volume stamping & forming. 5

6 Structural Materials Structural Materials Have Two Primary Functions. (1) Stiffness (2) Strength In devices, this is predominantly in Bending. We can learn from the Construction Industry. (1) Start with Stiff Structural Material (2) Remove Under-Utilized Core (3) Substitute Thermally Functional material Steel & Aluminum are a cost-effective material combination. 6

7 Component Manufacturability Metal Structural components are most often stamped and formed in reel-to-reel process Input materials are large coils of metal, often thousands of pounds. 7

8 SS-Al Composite Optimization At Ratio: 3-Layer Composite Optimal Material has Large Stiffness & High Thermal Conductivity: 80% The Stiffness of Stainless Steel Flexural Modulus (GPa) Modulus x Conductivity (Normalized) ~15% Thermal Conductivity (W/m*K) 10x Steel s X-Y Thermal Conductivity (160 W/m*K) % SteelSkin Thickness 53% the Density (4.3 g/cm 3 ) Costs ~2-4x Stainless per component 8

9 Clad Stainless-Aluminum What does this mean for Electronics Design? Replace Steel + Graphite systems with a Single Low-Cost Material. Replace Aluminum Alloy Components with smaller structural materials. 9 The Bulk Conductivity of Clad Stainless-Aluminum provides substantially more in-plane conductance than thin Graphite Films. Price: 2-4x The cost of Stainless Steel. Thermal Conductivity x Thickness (W/K) In-Plane Thermal Conductance Accounting for Thickness " " 1700 W/m K 1500 W/m K 17 m Graphite 25 m Graphite 0.3mm Clad SS/Al

10 Comparison to Other Solutions Need to consider Super-system when considering heat transfer. Non Steady-State Transfer Governed by Thermal Diffusivity: Graphite cannot spread heat without first warming the thick steel component. Average X Y Thermal Diffusivity (mm 2 /sec) Thermal Diffusivity vs. Bending Modulus Magnesium Aluminum mm Steel w/ 25 m Graphite 0.5mm Steel w/ 25 m Graphite Titanium Clad Stainless/Aluminum 316 Stainless Effective Bending Modulus* (MPa) *Modulus of Steel + Graphite assumes no contribution from Carbon Film or Adhesive layer. 10 Superior Diffusivity + Higher Modulus = Thinner Components

11 Experimental Setup Heat applied through Copper 60 C Thermal Imaging Camera Sample Insulation Hot Plate *Constant Temperature Hot Plate Convection allowed from Top & Bottom of Horizontal Sample. Thermal heat spreading was tracked over the surface of 0.55mm thick samples as a function of time. 104mm Stainless Steel 57mm 11

12 Comparative Heat Spreading Results 12

13 Composite vs. Steel + Graphite Direct substitution of Steel/Aluminum Composite for Steel + Graphite System. Reduced SOC Height by 50 m. 35 C Ambient Steel + 50 m Graphite SS/Al Composite 0.36mm Stainless m Graphite + 25 m adhesive. 0.36mm Composite 0.41mm Total Thickness 13

14 Midplane Temperature Distribution Graphite outline in RED. Steel + Aluminum Composite Provides: More uniform temperature distribution. Reduced temperatures near SOC. Higher temperatures at far end of midplane. Steel + Aluminum Composite 14

15 Display Glass Temperature Distribution Steel + Graphite Steel + Aluminum: 1.3 C Reduction in max temperature 25% Reduction in temperature gradient. Promotes improved heat dissipation from surfaces. Enables more power consumption & less throttling. Lower Cost Steel + Aluminum Composite 15

16 Summary A Clad Stainless-Aluminum composite was developed as a Heat Spreader & Structural Material in One. Bulk Thermal Transport provides superior heat dissipation vs. common graphite Solutions Composite Stiffness and Thermal Diffusivity Advantages promise z-height and cost savings over current solutions. The low cost material is Fully Formable for high volume production. 16