Developments in Advanced Thermal Materials · developments in thermal materials difficult. • Thermal resistance within the semiconductor package and at every level of electronic

© Copyright 2015 DS&A LLC

David L. Saums, Principal DS&A LLC

Amesbury MA USA www.dsa-thermal.com

Keynote Presentation

IMAPS France 10th Anniversary Workshop on Thermal Management and Micropackaging

La Rochelle, France 4-5 February 2015

Developments in Advanced Thermal Materials

Outline

• Purpose: An overview of recent advancements with thermal materials

• Needs for Advanced Thermal Materials

• Developments in Thermal Interface Materials:

The Ideal TIM? TIM Selection TIM Development Factors Graphite TIMs are Not All the Same! Metallic TIMs

• Advanced Heat Spreader Developments:

Graphite: TIMs or Heat Spreaders? Active Heat Spreader Developments: Flexible and Rigid Thermal Ground Planes

• Developments in CTE-Matched Composite Materials

Developments in Advanced Thermal Materials February 4-5, 2015

IMAPS France 10th Anniversary Workshop on Thermal Management and Micropackaging, La Rochelle


Overview

• The electronics industry is very heavily fragmented into various sectors. Examples:

Major semiconductor sectors:

Power semiconductors (including power, RF, LED, mixed)

Integrated circuits (including processors, memory, ASICs, mixed)

Major market segments: Vehicle powertrains, onboard systems Computing systems, telecommunications, networking Medical systems and sensors Aerospace, military, and harsh environments Lighting Imaging and data storage Wearables, sensors, MEMs, and IoT

• Fragmentation sometimes creates barriers, making identification of new developments in thermal materials difficult.

• Thermal resistance within the semiconductor package and at every level of electronic systems remains a major focus for reliability improvement.

• This presentation is intended as a brief overview of recent advances in thermal materials and heat spreader concepts.




Developments in Thermal Interface Materials




Is an “Ideal TIM” Possible to Develop?

• Is an “ideal” TIM material specification possible to develop?

• Can one TIM be a universal solution?

• Caveats:

Required functions of different types of TIM materials determine product specifications for an “ideal” TIM by material type.

A major distinction must be made between TIM material types which require mechanical fastening and those that do not – such as adhesives.




Is an “Ideal TIM” Possible to Develop?

• Is an “ideal” TIM material specification possible to develop?

Silicone-based thermal compounds and phase-change compounds are the closest to a universal solution and are available in:

• Dispensable paste form

• Dry-to-the-touch compound applied to a carrier (Al foil, Cu foil; Kapton MT, other dielectric materials)

• Ingot or bulk format for dispensing systems

Gap-fillers – less-challenging application requirements

Thermally-conductive adhesives (TCA) and electrically-conductive adhesives (ECA) do not require mechanical fastening – an important and basic difference in functionality.

• Multiple requirements for a single type of TIM result in compromises, as no single application specification can be viewed in isolation.

• No single TIM material type can serve as a universal solution for all applications.




How is a TIM Selected?

• What is the primary function desired for the TIM? Direct metal-to-metal contact

Electrical isolation

Critical high heat flux device – premium thermal performance required

Adhesive attachment only – no mechanical fasteners

No metal-to-metal contact: large gap to be filled with a compliant material

Others

• Is there a secondary function desired? Shock absorbency

EMI shielding

Reworkability

Others




Pri

mary

Fu

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on

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TIM Material Function – How are TIM Materials Used in Practice?

Minimum thermal resistance (Rth)

Structural fastening

Reduced Rth (versus air) over large gaps

Electrical insulation

Critical minimum thermal resistance (Rth) for high heat flux

What is to be achieved as the primary TIM function?





What is to be achieved as the primary TIM function?

Minimum thermal resistance (Rth): Primarily achieved with minimum thickness and with clamping force applied

Thin TIM Materials:

Metallic and liquid metals

Polymer-solder hybrids

Phase-change

Thermal greases

Thermally-conductive adhesives:

Curable or two-part dispensed

Structural fastening and reduced thermal resistance

Reduced Rth (versus air) over large gaps (i.e., > 0.254mm/0.010”)

Gap-fillers (i.e., > 0.254mm/0.010”)

Electrical insulation and minimized thermal resistance

Dielectric Materials (Electrically-isolating)

Critical minimum thermal resistance (Rth) for high heat flux, with reworkability highly desirable

Metallic materials (predominant):

Metallic and liquid metals

CNT arrays,

Reflowed solders





Primary Function Material Category Causation

Minimum thermal resistance (Rth): Primarily achieved with minimum thickness and with clamping force applied

Thin TIM Materials: Thermal greases Phase-change Polymer-solder hybrids Metallic and liquid metals

Surface roughness, flatness

Structural fastening Reduced thermal resistance Shock dampening

Thermally-conductive adhesives: Pressure sensitive preforms Curable or two-part dispensed

Thermal-mechanical

Minimum Rth, heat spreading, and CTE control TIM1 Materials: Solders, Gels, PCM, greases

Die-Attach Adhesives, CNT

Thermal-mechanical, CTE (die to organic, ceramic, or metal surfaces)

Reduced Rth (versus air) over large gaps (i.e., > 0.254mm/0.010”)

Gap-fillers Physical gaps, multiple surfaces

Large-area heat dissipation, temperature control, temperature modulation

Graphite, Elastomeric Sheets

Multiple heat sources, often in restricted spaces (typ., telcom, notebook and handheld, LED arrays)

Electrical insulation w/minimized thermal resistance

Electrically-Isolating Electrical insulation requirement

Min thermal resistance w/high-volume multiple contact w/non-flat surfaces – without residue

Burn-in/Test Powered device functional testing

Critical min. Rth for high heat flux; reworkability highly desirable

Metallic, CNT, Solders Critical heat flux, CTE mismatch solutions; high value components © 2015 DS&A LLC




Developing a Logical TIM Selection Process

• A TIM selection process based on application and process requirements:

Thermal Interface Material Classification Selection and Evaluation

© 2003-2015 DS&A LLC

Important Requirements for TIM Material Type Selection Prioritized TIM Material

Requirements Property Typical Value

Alternative or Opposing Value

1. Electrical Dielectric Properties Electrically Conductive Electrically Non-Conductive

2. Mechanical

Fastening Mechanical Fasteners

Adhesive Mechanical Fasteners

Adhesive

Thickness Minimum Maximum Minimum Maximum

Surface Roughness, Flatness Minimum Maximum Minimum Maximum

3. Application Process Dispensing/Placement Automated Manual Semi-

Automated Preform Only

4. Thermal

Thermal Resistance Minimum Maximum Minimum Maximum

Operating Temperature Range Minimum Maximum Minimum Maximum

UL Flammability Rating UL V-0 UL V-0 -- --

5. Cost Material only/application process

only/total cost Material only

Application process only

-- --

6. Environmental/Health/Safety Constituent analysis: silicones, toxicity, environmental, H&HS

(safety)

Government, industry, company regulations




Test and Evaluation of TIM Material Properties for Selection

Property Category Property Parameter Method/Value

Thermal Resistance (Impedance) Through-plane (primary) bulk + contact ASTM D 5470-12 (°C-mm2/W) JEDEC 51-14 (Transient)

Thermal Conductivity Homogeneous, bulk (isotropic) ASTM D5470-12 (Steady-state) JEDEC 51-14 (Transient) Laser flash

Non-homogeneous, bulk (through-plane) ASTM D5470-12 (Steady-state) JEDEC 51-14 (Transient)

Non-homogeneous, bulk (in-plane) Scanning pulsed laser

Testing Conditions for Thermal Impedance Data Collection

Test methodology

ASTM D5470-12 (Steady-state) JEDEC 51-14 (Transient) Laser flash

TTV (in-situ)

Test coupon area mm2/in2

Surface flatness mm/mm (“/”)

Surface roughness Ra, Rs (µ-in)

Clamping force applied Bar/PSI

Input power applied W

Ambient (chamber) temperature °C

Thickness mm (”) © 2015 DS&A LLC




Factors for TIM Development and Testing

• TIM vendors do not control individual application requirements:

Type of device and specifics of device packaging

Mating surface (heat sink or cold plate) conditions

Clamping force or retention device pressure applied

Maximum/minimum case temperatures

Metallization, surface finish, unusual physical requirements

Electrical properties

Contaminants, banned constituents, environmental and toxicity requirements

Reliability requirements (thixotropicity, outgassing, HAST, pot life, and similar)

Rework requirements and implications for TIM2:

1. Factory rework requirements and importance

2. Field rework requirements and importance

Relative cost requirements: bulk material costs versus application process cost

Shipping, storage, and handling requirements




Factors for TIM Development and Testing (Continued)

Life and reliability requirements

• Challenges of power and thermal cycling

• Testing to end-of-life – by type of device and application

• Measurement of Rth at end-of-life vs. Time-0

Packaging requirements for dispensing

• One or several of the above factors can influence success or failure for development of a new TIM material or an existing TIM used for a new application.

• TIM development therefore must conform to either:

Set of target specifications developed as an amalgam by the TIM vendor

Single target specification developed by an OEM or semiconductor manufacturer, working with one or more TIM vendors, to formulate a highly-specific set of requirements for a critical application.




Attributes Which Apply to all TIM Materials




Standard Requirements for All TIM Materials

Material Attribute Value or Type

Automated Placement/Dispensing Formats

Vacuum Roll format

Liquid dispensed

Flammability Rating UL 94 V0

Working Life X Hours @ X°C

High Temperature Storage (Completed Final Assembly) Y Hours @ Y°C

High Temperature Storage (as supplied) Z Hours @ Z°C

Transit Temperature Maximum

Low Temperature Transit/Storage Minimum

Material Stability

% loss of tack permissible;

Dimensionally stable;

No moisture sensitivity during processing

Outgassing % Permissible © 2015 DS&A LLC




Example, Development Target Specifications, Ideal Attributes for a Single Category of TIM Material




Idealized TIM Attributes: Thin Dispensable Zero-Force IC TIM1 – Part 1 of 3

Material Category

Primary Function Assumptions Product Attribute

Thin Dispensable Zero-Force TIM1

Dispensable TIM1 for application to die backside for flip chip IC applications with minimum thermal impedance value at near-zero clamping force applied on asymmetric surfaces.

Primary applications: Integrated circuit surface-mount organic bare-die packages (BGA/LGA/CGA/FCPGA), having limited surface area and near-zero clamping force applied at asymmetric contact surface. Heat source: 200-484mm2, Q = 100 - 300W (typ.)*

Thermal Impedance

Thermal Conductivity

Bond Line Thickness Post-Assembly

Typical Clamping Force Applied

Typical Contact Surface Area

Wettability

Contaminants

Particulates

Silicone Stability

Material Stability © 2015 DS&A LLC





Material Category





Operating Temperature

Cure Schedule

Pot Life

Thermal Cycling

Power Cycling

Humidity and Bake

HAST

Shock/Vibration

Reliability

Reworkability © 2015 DS&A LLC





Material Category





Dielectric Strength Volume Resistivity (ASTM D257)

Dielectric Constant

Thixotropicity

Modulus of Elasticity

Corrosivity

Reusability

Automated Dispense Format

Cost © 2015 DS&A LLC




Oriented Fiber Graphite TIM




Developments in Oriented Fiber Graphite TIM

• Not all oriented-graphite TIM materials perform the same.

Testing is required to determine thermal performance of any oriented-graphite TIM.

Wide variation from manufacturer to manufacturer.

Many different grades.

Many “Graphite TIM materials” are actually heat spreaders and not TIM materials at all.




Developments in Oriented Fiber Graphite TIM

• Example of how significantly different thermal performance may be for graphite “TIM” materials – which are in fact heat spreaders, not TIM:




Data source: Indium Corporation

Graphite No. 1: 0.457mm/0.018” Graphite heat spreader w/Plastic laminate and PSA adhesive coating Graphite No. 2: 0.064mm/0.0025” Graphite heat spreader w/Plastic laminate and PSA adhesive coating Graphite No. 3: 0.508mm/0.020” Graphite heat spreader No plastic laminate, no PSA adhesive coating Graphite No. 4: 0.347mm/0.005”GrafTech eGraf Grafoil® No plastic laminate, no PSA adhesive coating

Developments in Oriented Fiber Graphite Thermal Interface Materials

Material Type

Vendor Product Designation Thickness

(µm)

Bulk Thermal Conductivity

X-Y axis W/mK

Z-axis W/mK

TIM

Dexerials EX20200XX Gap-filler 100-200 N/A 15-20

Graftech Grafoil® GTA-005, GTA-030 130-760 140 5.5-7.0

Hitachi TC-001 150-500 40-901




Note: 1. Not otherwise defined.

Developments in Oriented Fiber Graphite Heat Spreaders

Material Type

Vendor Product Designation Thickness

(µm)

Bulk Thermal Conductivity

X-Y axis W/mK

Z-axis W/mK

Graphite Sheet Heat

Spreader

DSN DSN5017 17 1600-1900 15-20

TTCL TGS-17 17 1700 15

Panasonic PGS EYG-S-25 25 1600 N/A

Graftech eGraf® SpreaderShield Flexible Graphite SS1500

17 1500 3.4

Panasonic PGS EYG-S-100 100 700 N/A

Graftech eGraf® SpreaderShield Flexible Graphite SS600

127 600 3.5

Graftech eGraf® HiTHERM™ 700 127 240 6




Developments in Metallic TIM





• Indium shims and flat foils have been utilized for decades as thermal interface materials, primarily for:

Flange-mount RF power semiconductors

Specialized applications for modules in military, aerospace, and diode laser systems

• Development of patterned indium foils by Indium Corporation as the Heat-Spring® family of TIM materials:

Indium and indium alloys

Indium and aluminum

Sn+








Bulk Thermal Resistance

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0 20 40 60 80 100 120 140 160 180 200

Pressure (psi)

Th

erm

al R

esis

tan

ce (

cm

2-o

C/W

)

Thermal Grease #1 (2 mil)

Thermal Grease #2 (2 mil)

3 mil Indium Foil

3 mil HEAT-SPRING

Improvement at clamping force >45PSI (~3 bar)

Data source: Indium Corporation


• An example of aerospace OEM testing to determine the improvement in thermal resistance for a flange-mount RF semiconductor package follows:

Two GaN RF devices (26W, 36W dissipation) mounted in identical flange-mount packages

Two different clamping forces tested

Indium “Heat-Spring” TIM versus traditional silicone-based thermal grease

On average, “Heat-Spring” reduced thermal resistance by 28% relative to grease

Average impact of different torque values was reduced from >6% to <2% w/”Heat-Spring”








W W

Tested at two different power levels (26W, 36W) and two different clamping pressures

Developments in Heat Spreader Materials: Aluminum-Stainless Steel Clad Heat Spreaders







Aluminum-Stainless Steel Clad Composite Heat Spreaders

Apple iPhone 3G

Note: No use of graphite sheet or other thermal materials in older, lower power handsets such as i3G.


• Mobile and handheld device markets have generated very rapid developments in graphite sheet heat spreading materials Referred as thermal interface materials -- incorrectly.

Graphite sheet heat spreaders -- manufactured with an 18µm adhesive layer and attached to a stainless steel sheet.

Graphite sheet heat spreaders have excellent bulk thermal conductivity in one plane:

Heat spreader examples from current Apple iPhone, Samsung handhelds:

Samsung Galaxy S5 Apple iPhone6

Stainless steel with Graphite heat spreader




0

500

1000

1500

17 micronGraphite

25 micronGraphite

Copper PureAluminum

Titanium StainlessSteel

X-Y

Th

erm

al C

on

du

ctiv

ity

(W/m

*K)





• A new clad stainless steel over aluminum core processing capability has been developed, to yield a new type of “functionalized” heat spreader: 80% of the stiffness of stainless steel

Thermal conductivity approximately 10X that of steel

53% of the density

This high volume capable cladding technology is targeted towards:

1. Replacing combinations of steel heat spreaders plus applied graphite sheet “TIMs”

2. Replacing aluminum components with smaller, lighter weight clad functionalized spreaders.

• Prototype testing of “eStainless™” clad SST+Al core heat spreaders:





10% Stainless Steel + Aluminum Composite

19% Stainless Steel + Aluminum Composite

Thickness (mm) 0.20 0.25

Thermal Conductivity 179 143

Density (g/cm3) 3.79 4.71

Bending Modulus (GPa) 145 166

Source: A. Vodnick, Materion Technical Materials, “Thermally Functionalized Structural Material for Consumer Devices”, IMAPS Advanced Technology Workshop on Thermal Management 2015, Los Gatos CA USA, October 28-30, 2014.

Developments in Active Heat Spreaders and Thermal Ground Planes




Developments in CTE-Matched Active Heat Spreaders

Organization Concept Fluid Reported Apparent

Thermal Conductivity Reported

Power Density

University of Twente/Thales Nederland (Netherlands, 2007)

Embedded two-phase heat pipe within organic PCB

Deionized Water 1000-2800W/mK N/A

IBM (US, Canada, 2005)

Silicon microchannel liquid cooling attached to server server processor package or die

Water N/A 300-400W/cm2

ACT/CPS/Honeywell (US, 2010)

AlSiC plate with embedded heat pipes

Water 400-490W/mK N/A

ABB (Switzerland, 2013)

Embedded Open Loop Pulsating Heat Pipe (OLPHP) within organic PCB

3M Novec® 649 Ethanol

3M Novec 7200 N/A 2.5W/cm2

Rockwell Collins Inc. (US, 2014)

Embedded pumped liquid metal within organic PCB

Galinstan™ >1,000W/mK N/A

CT

E-M

atc

hed S

ubstr

ate

s




ABB OLPHP, Open Loop Pulsating Heat Pipe (Kearney, 2013)

ACT AlSiC Plate with Embedded Heat Pipe (ACT, CPS, Honeywell)





Sources: J. Weyant, S. Garner, M. Johnson, M. Occhionero, Advanced Cooling Technologies Inc., “Heat Pipe Embedded AlSiC Plates for High Conductivity – Low CTE Heat Spreaders”, IEEE Semitherm 26thConference, Santa Clara CA USA, February 21-25, 2010. D. Kearney, J. Griffin, ABB, “An Integrated Passive Cooling Solution for PCB Substrates”, IMAPS France 8th Workshop on Thermal Management and Micropackaging, La Rochelle, France, February 6-7, 2013.

• Development of flow channels for a liquid metal pumped loop heat spreader manufactured with standard organic PCB processing and materials

• Galinstan liquid metal as fluid enables: Use of solid-state magnetic pump

Good effective thermal conductivity of Galinstan (~15W/mK)

• Pump: Electrodes and low power (~100mW)

to create Z-direction magnetic field

Capable of being manufactured in very small sizes (>1.6cm3)

• Goals: High effective thermal conductivity

Low liquid volume (~20g)

Low power consumption


Organic substrate

Pump

Embedded Flow Channels

Copper inserts for heat

input/output

Source: R. Wilcoxon, N. Lower, D. Dlouhy, Rockwell Collins Inc., “A Compliant Thermal Spreader with internal Liquid Metal Cooling Channels”, IEEE Semitherm 2010, San Jose CA USA, March 2010.





• Development of prototypes for testing

Galinstan Inlet

Machined Lexan

Epoxy bonded CNC milled glass

Anodic bond/EMS Photoresist Film bond

Diced FZS wafer

Sputtered TiW heater

Sputtered and etched Cu interconnects

Galinstan Outlet






• Prototype development:






• Continuing development experimental work: Experiments with the optimized geometry in Tuckerman and Pease’s paper has been

repeated and we achieved a thermal resistance of 0.0907oC/W at a heat flux of 835W/cm2.

0.120oC/W thermal resistance in Galinstan-based minichannel cooling was achieved, but at 125 kPa rather than 214 kPa.

0.045oC/W target for Galinstan-based minichannel cooling : final step in testing.

Sources: R. Zhang, M. Hodes, Tufts University; R. Wilcoxon, N. Lower, Rockwell Collins Inc., “High Heat Flux, Single-Phase Microchannel Cooling”, IEEE Semitherm 2014, San Jose CA USA, March 9-13, 2014. R. Wilcoxon, N. Lower, D. Dlouhy, Rockwell Collins Inc., “A Compliant Thermal Spreader with internal Liquid Metal Cooling Channels”, IEEE Semitherm 2010, San Jose CA USA, March 2010.





• Continuing development challenges: Microfabrication of test sections compatible with Galinstan, a corrosive liquid metal

CTE mismatches between glass and Lexan sections

Electrical interconnection: 1500W supplied over a 1cm x 1cm heater

Nickel plating for exposed metal parts, plastic wetted pump parts

Oxide formation with Galinstan when exposed to air (requiring vacuum filling).




Sources: R. Zhang, M. Hodes, Tufts University; R. Wilcoxon, N. Lower, Rockwell Collins Inc., “High Heat Flux, Single-Phase Microchannel Cooling”, IEEE Semitherm 2014, San Jose CA USA, March 9-13, 2014. R. Wilcoxon, N. Lower, D. Dlouhy, Rockwell Collins Inc., “A Compliant Thermal Spreader with internal Liquid Metal Cooling Channels”, IEEE Semitherm 2010, San Jose CA USA, March 2010.

Developments in Thermal Ground Planes

Organization Concept Fluid Reported Apparent

Thermal Conductivity

Reported Power

Density

University of Colorado, Boulder (USA)

Flexible ultra-thin, organic PCB thermal ground planes with internal isolation layer

Water 1400W/mK N/A

Pi-MEMS, Inc. (USA)

Ultra-thin titanium thermal ground plane

Water N/A N/A





• Flexible thermal ground plane – Concept: Flexible organic TGP Manufactured using standard organic PCB manufacturing processes

Enable flexible heat spreaders for handheld and mobile devices

• Thicknesses of 0.5mm (potentially, 0.2mm)

• Internal insulator materials

• Very low cost, high volume manufacturing proposed, PCB manufacturing standards

• Future potential to embed within organic PCBs




Source: R. Lewis, S. Xu, Y.C. Lee, R. Yang, L.-A. Liew, University of Colorado, “Flexible Thermal Ground Planes with Thicknesses Below Quarter-mm”, IMAPS Advanced Technology Workshop on Thermal Management 2014, Los Gatos CA USA, October 28-20, 2014..

• Flexible thermal ground plane – Concept: Flexible organic TGP Manufactured using standard organic PCB manufacturing processes

Enable flexible heat spreaders for handheld and mobile devices

• Thicknesses of 0.5mm (potentially, 0.2mm)

• Footprint: 95mm x 50mm (prototypes)

• Effective thermal conductivity: 1400W/mK




Source: R. Lewis, S. Xu, Y.C. Lee, R. Yang, L.-A. Liew, University of Colorado, “Flexible Thermal Ground Planes with Thicknesses Below Quarter-mm”, IMAPS Advanced Technology Workshop on Thermal Management 2014, Los Gatos CA USA, October 28-20, 2014..


• Ultra-thin titanium thermal ground plane – Concept: Ti-TGP

Titanium: high strength to weight ratio yields extremely thin structures

Large prototypes constructed by laser welding Ti/TiO2 wick structure to a machined backplate

Etched surface creates surface roughness striations (1-5µm)




Sources: M. Sigurdson et al., “A Large-Scale Titanium Thermal Ground Plane”, http://dx.doi.org/10.1016/j.ijheatmasstransfer.2013.01.064, International Journal of Heat Mass Transfer (2013). PiMEMS, Inc. ”Ultra Thin and Light Titanium Thermal Ground Plane”, IMAPS Advanced Technology Workshop on Thermal Management 2014, Los Gatos CA USA, October 28-20, 2014.


• Ultra-thin titanium thermal ground plane – Concept: Ti-TGP

Large prototype: 40cm x 7.6cm x 5mm (500g)

Effective thermal conductivity = 5000 – 8000 W/mK

With high-efficiency heat sink, capable of up to 500W (tMAX = 100°C)

Attritbutes:

• High strength, stiffness

• High fracture toughness

• Corrosive resistance in harsh environment

• Compatible with water

• Capable of hermetically welded joining






• Conformal ultra-thin titanium thermal ground plane – Concept Ti-TGP for handheld devices:

90mm (L) x 20mm (W) x 500µm (Thick)

Weight, finished component: 1.0 – 2.1g

Titanium: high strength to weight ratio

Max. device power: 2.0 – 4.5W@80°C TJ (MAX.)






• Conformal ultra-thin titanium thermal ground plane – Concept Ti-TGP for handheld devices

• Titanium vs. copper:

3.2X lighter than copper

5X performance improvement

1.8X improvement in CTE mismatch vs. copper, for silicon die






• Cost comparisons





Developments in CTE-Matched Heat Spreader Composites for GaN RF Semiconductors




Thermal challenges for PCBs with multiple flange-mount and soldered RF devices:

Application of a “button” or “heat sink” as a copper, CuW, Mo, or CuMo slug captured within the RF PCB or under the PCB is a common solution in commercial telcom amplifiers.

“Button” or heat sink or slug material is determined by the system OEM and assembled during final system manufacturing or is incorporated into the RF system PCB by the PCB manufacturer.

Fasteners thru PCB to heat sink

Source, figures: RFMD RFCM2680 applications note, PCB thermal requirements, September 2012.




CTE-Matched Composite Heat Spreaders for GaN RF Semiconductors

Industry goals for phased array radar and other aerospace applications:

Source: R. Borkowski, Raytheon IDS, USA (non-confidential, previously published data.)

Major Goal Solution Target

Increased Power Output

Transition to GaN-on-SiC RF semiconductor technology

Optimize device design

Implement advanced circuit design and modeling

Implement advanced thermal management technologies

Reduced Module Weight

Implement advanced semiconductor technology

Move to higher semiconductor integration levels

Multilayer materials technology

Implement advanced packaging technologies

MMIC/module coatings

Reduced Module Cost

Transition to advanced RF semiconductor technology

Move to higher semiconductor integration levels

Implement automated manufacturing technologies

Implement encapsulation technology





Traditional CTE-matched heat spreader materials for GaN RF package applications:

Parameter or Property

Mo1 Cu-Mo-Cu1 25Cu/50Mo/

25Cu2 20Cu/60 Invar/

20Cu2

CTE (ppm/°C)

5.0 6 7.9 X-Y: 6.0 Z: 7.7

Thermal Conductivity (W/mK)

X: 140 Y: 142

170-182 X-Y: 268 Z: N/A

X-Y: 164 Z: 22

Density (g/cc)

10.2 9.9 - 10.0 9.6 8.5

Young’s Modulus

(GPa) 330 280 220 135

Data Sources: 1. Rockwell Collins Inc., USA; 2. Pecht, M., Agarwal, R., McCluskey, F.P., Dishongh, T.J., Javadpour, S., Mahajan, R., Electronic Packaging Materials and Their Properties, CRC Press, 1998. ISBN 0-8493-9625-5.





New developments, CTE-matched heat spreader materials for GaN RF applications:

Parameter or Property

Cu-Graphite (Cu-MetGraf 7-300)3

Cu1 MoC-Graphite4

(MoGr) CuDia653

CTE (ppm/°C)

7.0 17 1.0-2.75 7

Thermal Conductivity (W/mK)

X-Y: 287 Z: 225

385 600 (@20°C)

800 (@100°C) 950

Density (g/cc)

6.1 8.9 2.45 (@20°C) 3.5 (@100°C)

5.5

Young’s Modulus

(GPa) 76 120-130

48 (@20°C) 64 (@100°C)

300

Data Sources: 3. MMCC LLC, Waltham MA USA 4. CERN, Meyrin, Switzerland (2015) 5. In preferred direction





RF power amplifier packages utilize CTE-matched baseplates (or flange”)manufactured from these types of materials possessing a specific CTE value:

Parameter or Property CTE (ppm/°C) Thermal Conductivity (W/mK) Density (g/cc) Young’s Modulus (GPa)

Ceramic composites, metals, metallic composites:

MoC-Graphite1 1.0 – 2.7 600-800 2.45-3.5 48-64

Molybdenum2 5.0 X: 140; Y: 142 10.2 330

Cu-Mo-Cu2,3 6 170-182 9.9 - 10.0 280

CuMo (85Mo/15Cu) 4 6.6 165 - 184 16.4 360

CuDia655 7 950 5.5 300

CuW (85W/15Cu) 3 7.2 180 - 210 16.4 360

CuMo (80Mo/20Cu) 7.2 X-Y: 210; Z: N/A 9.9 N/A

Cu/Mo70Cu/Cu (“CPC”) 7 7.2 – 9.0 X-Y: 340; Z: 300 9.5 N/A

CuMoCu (25Cu/50Mo/25Cu)6 7.9 X-Y: 268; Z: N/A 9.6 220

Cu/4Cu-Mo/Cu3 8.0 – 10.0 170 10.0 195

Copper 17 385 8.9 120-130

Sources: 1. CERN; 2. Rockwell Collins Inc., USA; 3. Sandvik Osprey 2014; 4. Stratedge, Inc.; 5. MMCC LLC; 6Pecht, M., Agarwal, R., McCluskey, F.P., Dishongh, T.J., Javadpour, S., Mahajan, R., Electronic Packaging Materials and Their Properties, CRC Press, 1998. ISBN 0-8493-9625-5. 7. Quantum Leap Packaging LLC.; Torrey Hills Technologies LLC.





CTE-Matched Thermally-Conductive Heat Spreader Composite Materials

MMCC Cu-Diamond

(2014)




CERN MoC-Gr

(2015)

© 2003-2015 DS&A LLC

Thermal interface materials, heat spreaders, and CTE-matched high thermal conductivity materials are critical to reliability and product life for electronic systems.

This brief summary attempts to outline recent progress made in a number of areas in advanced thermal materials.

There are many development activities worldwide intended to find new ways to reduce thermal resistance within a semiconductor package or electronic system, and improve system reliability.

Please request additional references to technical manuscripts and sources, if interested.

Thank you.




Summary – Advances in Thermal Materials

100 High Street David L. Saums, Principal Amesbury MA 01913 USA E: [email protected] Tel: +1 978 499 4990 Website: www.dsa-thermal.com

Business and product development strategy for electronics thermal management: advanced thermal materials, components, and thermal systems.

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Developments in Advanced Thermal Materials · developments in thermal materials difficult. • Thermal resistance within the semiconductor package and at every level of electronic