Thermal Trends in Harsh Environment Electronics Ross Wilcoxon Rockwell Collins Advanced Technology Center

Trends in Avionics (and related systems) Systems used in a wider variety of environments: UAVs, ground vehicles, hand-held, etc….. “pervasiveness”: everyone can talk to everyone (and everything) else Reduce weight for fuel savings and transportability Need for re-use: end-users want to be able to use the same system in different platforms Functional capability (leading to power dissipation) increasing, while the platform space and cooling approach stays the same Ever increasing use of COTS (Commercial Off The Shelf) – components, assemblies, standards…

Systems used in a wider variety of environments: UAVs, ground vehicles, hand-held, etc….. “pervasiveness”: everyone can talk to everyone (and everything) else

Reduce weight for fuel savings and transportability

Need for re-use: end-users want to be able to use the same system in different platforms

Functional capability (leading to power dissipation) increasing, while the platform space and cooling approach stays the same

Ever increasing use of COTS (Commercial Off The Shelf) – components, assemblies, standards…

Impacts of these Trends on Thermal Management High end thermal solutions generally weigh quite a bit; weight/size reduction and improved thermal management are often at odds (as any laptop designer would tell you) Loss of cooling requirements longer than 1 hour and the system needs to be designed to survive indefinitely with no cooling less than 1 hour and you can get some transient benefit that scales directly with the weight of the system (unless you do something special, such as add phase change material) Reuse of functionality by different entities (ground troops, UAV’s, weapons, tactical aircraft, etc.) leads to widely varying boundary conditions unmanned equipment can have especially interesting boundary conditions… Primary thermal choke points are generally at the two ends of the path: getting heat out of the component and out of the system

High end thermal solutions generally weigh quite a bit; weight/size reduction and improved thermal management are often at odds (as any laptop designer would tell you)

Loss of cooling requirements

longer than 1 hour and the system needs to be designed to survive indefinitely with no cooling

less than 1 hour and you can get some transient benefit that scales directly with the weight of the system (unless you do something special, such as add phase change material)

Reuse of functionality by different entities (ground troops, UAV’s, weapons, tactical aircraft, etc.)

leads to widely varying boundary conditions

unmanned equipment can have especially interesting boundary conditions…

Primary thermal choke points are generally at the two ends of the path: getting heat out of the component and out of the system

Thermal Management Impact to Cost Spray Cooled COTS Boards COTS Boards with spreaders stunned silence cries uncontrollably requires CPR cost (units: Program Manager Reaction) power (W/board) temporary serenity 10 100 1000 Spray Cooling Liquid Flow Thru Modules Board/Thermal Spreader Assemblies High Copper Boards life cycle cost may be reduced if technology enables higher level COTS usage Fan Cooling Liquid Cooled Chassis

Emerging Thermal Technologies Wilcoxon’s Rule of Electronics Cooling: ‘The first and last mm in the thermal path can be limited by physics; everything in between is generally limited by budget.’ First mm (at/near the die) Next generation die attach, thermal interface materials, etc. that use Carbon NanoTubes and other nanotechnology materials (DARPA Nano Thermal Interfaces (NTI) program, DARPA THREAD, etc.) Die level microchannel cooling for high heat flux Advanced expansion matched thermal materials using diamond, graphite, etc. for spreading heat from the die (DARPA Thermal Ground Plane (TGP) program, etc.) Last mm (from the system) Higher performance air cooling (lighter, higher cooling capacity, etc.) (DARPA Microtechnologies for Air-Cooled Exchangers (MACE) program, etc.) Advanced fans (piezo fans, synthetic jets, etc.) Cost effective/high reliability liquid cooling

Wilcoxon’s Rule of Electronics Cooling: ‘The first and last mm in the thermal path can be limited by physics; everything in between is generally limited by budget.’

First mm (at/near the die)

Next generation die attach, thermal interface materials, etc. that use Carbon NanoTubes and other nanotechnology materials (DARPA Nano Thermal Interfaces (NTI) program, DARPA THREAD, etc.)

Die level microchannel cooling for high heat flux

Advanced expansion matched thermal materials using diamond, graphite, etc. for spreading heat from the die (DARPA Thermal Ground Plane (TGP) program, etc.)

Last mm (from the system)

Higher performance air cooling (lighter, higher cooling capacity, etc.) (DARPA Microtechnologies for Air-Cooled Exchangers (MACE) program, etc.)

Advanced fans (piezo fans, synthetic jets, etc.)

Cost effective/high reliability liquid cooling

General Trends in Thermal Management/Thermal Reliability Impacting Harsh Environment Electronics (Systems) Need better system level approaches for thermal management Modular methods that move dissipated power away from the system that adapt to platform requirements Platform designers are increasingly recognizing that they need to address thermal management early on : it appears that both Boeing and Airbus are willing to at least think about putting avionics liquid cooling on their next airplanes What product life do we really need to design to? Will we have flight critical processing on a PowerPC 20 years from now? Prognostics for electronics systems (potential COTS enabler?) Better understanding of how environments, such as temperature, really impact reliability ? (VITA 51.x guidelines on stress screening) More sophisticated power management methods Required by some applications just to reduce the number of batteries System level understanding of availability for real-time processing is essential Designs that better address transient operation and cooling Greater use of phase change materials to carry a system through peak power loads Internal monitoring for thermal shut-down’s (with manual override) Many critical functions in harsh environments with no air cooling More communications hardware (military & commercial) in space : conduction => radiation, highly weight constrained Down hole electronics in oils drilling oil (hot, high pressure, acidic, highly volume constrained, abrasive) New? ways of thinking about reliability 100°C 200°C 300°C 500 atm 1000 atm 1500 atm

Need better system level approaches for thermal management

Modular methods that move dissipated power away from the system that adapt to platform requirements

Platform designers are increasingly recognizing that they need to address thermal management early on : it appears that both Boeing and Airbus are willing to at least think about putting avionics liquid cooling on their next airplanes

What product life do we really need to design to? Will we have flight critical processing on a PowerPC 20 years from now?

Prognostics for electronics systems (potential COTS enabler?)

Better understanding of how environments, such as temperature, really impact reliability ? (VITA 51.x guidelines on stress screening)

More sophisticated power management methods

Required by some applications just to reduce the number of batteries

System level understanding of availability for real-time processing is essential

Designs that better address transient operation and cooling

Greater use of phase change materials to carry a system through peak power loads

Internal monitoring for thermal shut-down’s (with manual override)

Many critical functions in harsh environments with no air cooling

More communications hardware (military & commercial) in space : conduction => radiation, highly weight constrained

Down hole electronics in oils drilling oil (hot, high pressure, acidic, highly volume constrained, abrasive)

New? ways of thinking about reliability

General Trends in Thermal Management/Thermal Reliability Impacting Harsh Environment Electronics (Components) Greater use of wideband gap (WBG) semiconductor materials higher power densities => increase local thermal challenges may be able to operate at higher temperatures => greater need for high temperature packaging materials & methods Continued developments for improved ‘soft’ thermal interfaces that enable greater use of COTS assemblies spray cooling would provide the ultimate soft interface thermal gap fillers get part way there, but a 10x breakthrough would be really handy… As always, Cost is critical – especially in higher volume applications such as automotive, small unmanned vehicles, unattended, handheld, etc. Lead-free electronics : exempt or not for avionics/military equipment, Pb-free parts are what’s available and they will be used require higher processing temperatures have less well understood materials characterization introduce “new” failure mechanisms like tin whiskers

Greater use of wideband gap (WBG) semiconductor materials

higher power densities => increase local thermal challenges

may be able to operate at higher temperatures => greater need for high temperature packaging materials & methods

Continued developments for improved ‘soft’ thermal interfaces that enable greater use of COTS assemblies

spray cooling would provide the ultimate soft interface

thermal gap fillers get part way there, but a 10x breakthrough would be really handy…

As always, Cost is critical – especially in higher volume applications such as automotive, small unmanned vehicles, unattended, handheld, etc.

Lead-free electronics : exempt or not for avionics/military equipment, Pb-free parts are what’s available and they will be used

require higher processing temperatures

have less well understood materials characterization

introduce “new” failure mechanisms like tin whiskers

Summary Effective thermal management 0f future systems, especially those used in harsh environments, requires a broader, system-level perspective than we have done in the (recent) past It’s not just a matter of implementing new technologies; it also requires a better understanding of interactions between design constraints and requirements (again) Are we just repeating history and being forced to relearn lessons that we have forgotten since the 1990’s?? Thanks to everyone who provided inputs to me, including: Nick Chandler (BAE Systems) Dave Hillman (Rockwell Collins) Jonas Johansson (SaabTech AB) Sebastian Jung (Baker Hughes) Bruce Myers (Delphi) Leslie Phinney (Sandia Labs) Jim Robles (Boeing) adapted from: http://www.electronics-cooling.com/html/2005_august_article1.html

Effective thermal management 0f future systems, especially those used in harsh environments, requires a broader, system-level perspective than we have done in the (recent) past

It’s not just a matter of implementing new technologies; it also requires a better understanding of interactions between design constraints and requirements (again)

Are we just repeating history and being forced to relearn lessons that we have forgotten since the 1990’s??

Thanks to everyone who provided inputs to me, including:

Nick Chandler (BAE Systems)

Dave Hillman (Rockwell Collins)

Jonas Johansson (SaabTech AB)

Sebastian Jung (Baker Hughes)

Bruce Myers (Delphi)

Leslie Phinney (Sandia Labs)

Jim Robles (Boeing)