Author Archives: Josh Perry

Thermal Management of High-Powered Servers

While power demands have increased, engineers are tasked with placing more components into smaller spaces. This has led to increased importance for optimizing the thermal management of servers and other high-powered devices to ensure proper performance and achieve the expected lifespan.

Servers
This article brings together content that ATS has posted over the years about cooling high-powered servers from the device- to the environment-level. (Wikimedia Commons)

With server cooling taking on increased priority, there are several ways of approaching the problem of thermal management, including device-level solutions, system-level solutions, and even environment-level solutions.

Over the years, Advanced Thermal Solutions, Inc. (ATS) has posted many articles related to this topic. Click the links below to read more about how the industry is managing the heat for servers:

  • Industry Developments: Cabinet Cooling Solutions – Although their applications vary, a common issue within these enclosures is excess heat, and the danger it poses to their electronics. This heat can be generated by internal sources and intensified by heat from outside environments.
  • Effective cooling of high-powered CPUs on dense server boards – Optimizing PCB for thermal management has been shown to ensure reliability, speed time to market and reduce overall costs. With proper design, all semiconductor devices on a PCB will be maintained at or below their maximum rated temperature. 

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

Webinar on Limits of Air Cooling in March

Advanced Thermal Solutions, Inc. (ATS) is hosting a series of monthly, online webinars covering different aspects of the thermal management of electronics. This month’s webinar will be held on Thursday, March 28 from 2-3 p.m. ET and will cover the limits of air cooling and the role of liquid cooling in . Learn more and register at https://qats.com/Training/Webinars.

Webinar: EV Battery Thermal Management

Maintaining the proper operating temperature for electric vehicle (EV) batteries is a critical component of the spread of EV across the world. If batteries are too hot, then the batteries will degrade faster, and safety becomes a concern. At lower temperatures, battery capacity and performance suffer.

EV Battery Thermal Management
The webinar below will cover techniques for maintaining proper battery temperatures in electric vehicles. (Wikimedia Commons)

Thermal management of batteries is important for EV to live up to the potential that manufacturers promise and that consumers desire. But, how can the temperature be maintained at the proper operating levels during use and how can manufacturers cope with the varied environments that the vehicles will operate in?

As an earlier post on EV battery thermal management explained, the main concerns for engineers are:

  1. At temperatures below 0°C (32°F), batteries lose charge due to slower chemical reactions taking place in the battery cells. The result is a significant loss in power, acceleration and driving range, and higher potential for battery damage during charging.
  2. At temperatures above 30°C (86°F) the battery performance degrades, posing a real issue if a vehicle’s air conditioner is needed for passengers. The result is an impact on power density and reduced acceleration response.
  3. Temperatures above 40°C (104°F) can lead to serious and irreversible damage in the battery. At even higher temperatures, e.g. 70-100°C, thermal runaway can occur. This is triggered when the runaway temperature is reached. The result is a self-heating chain reaction in a battery cell that causes its destruction while propagating to adjacent cells.

This hour-long webinar from thermal management expert Dr. Kaveh Azar, founder and CEO of Advanced Thermal Solutions, Inc. (ATS), presents some of the techniques that design engineers have employed to keep EV batteries within the proper temperature range both during operation and charging.


For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

Tubed and Submerged-Fin Cold Plates in Electronics Thermal Management

By Norman Quesnel
Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)

Many of today’s electronic devices need the performance of liquid cooling to meet the thermal demands of certain hot components. Liquid cold plates are common cooling systems in high power lasers, fuel cells, battery coolers, motor drives, medical equipment, avionics and other high-power, high-heat flux applications.

Cold Plates
Figure 1. A Custom liquid cold plate design by D6 Industries. [1]

Cold plates provide localized cooling by transferring heat from a device to a liquid that flows to a remote heat exchanger and dissipates into either the ambient or to another liquid in a secondary cooling system. Component heat flows by conduction through a thermal interface material and the metal plate to the metal tubing. Then it flows by convection from the internal surface of the fluid path material into the flowing coolant.

A cold plate in electronics cooling is often an aluminum block with an embedded, coolant-filled metal tube. Another common cold plate type is made with metal shells that are brazed or friction-welded together and filled with a liquid coolant.  On the inside, the metal shells have integral cooling fins that are submerged in the coolant.

Tubed Cold Plates

Embedded tube designs are the simplest version of cold plate cooling devices. They feature a continuous tube set into grooves in a metal plate, and are often bonded in place with thermal epoxy. The flowing coolant moves heat from the component away from the cold plate to a heat exchanger, where it is cooled before being pumped back into the plate. 

A common example of a tubed cold plate features an aluminum plate with an exposed copper tube. The tubes can be routed in different pathways to optimize the thermal performance.

The tubing can be continuous or constructed from straight tubes connected by soldered joints, though joints may increase the potential for leakage.

Figure 2. A Tubed cold plate consists of copper or stainless-steel tubing pressed into a metal plate. [2]

This design can provide a cost-effective thermal solution for component cooling where the heat load is low-to-moderate. Tubed cold plates ensure minimum thermal resistance between the power device and the cold plate by placing the coolant tube in direct contact with the power device’s base. Direct contact reduces the number of thermal interfaces between device and fluid, thus increasing performance for the application.

A variant of this design features a thermal epoxy completely applied over the pressed in tubing and flush with the metal plate surface. These are sometimes called buried tube liquid cold plates. This provides a gap-free thermal interface between the tube and the plate. The epoxy layer protects from any leakage from the metal tube. Another key feature is that that fully buried tube is not exposed to the outside environment.

Figure 3. A buried tube cold plate’s metal tube is covered with a conductive epoxy layer. [3]

The choice of liquid coolant affects thermal performance as well. Choosing the right coolant depends to a great extent on the tube material. Copper tubes are compatible with water and most other common coolants, while stainless steel tubes can be used with deionized water or corrosive fluids.

One cold plate OEM offers a proprietary technology with a tube locking system and pressing techniques that ensure the tube is flush with the plate surface, providing good thermal contact with the component being cooled. This manufacturing method eliminates the need for thermal epoxy between the tube and plate which improves thermal performance. [4]

Submerged Fin Cold Plates

Another type of cold plate is an all-metal construction with brazed or friction welded internal fin field.

Figure 4. Standard, liquid coolant-containing metal cold plate [5]

The integral, internal fins increase the surface area that contacts the fluid and enhances heat transfer. Fin shape and fin density affect the performance of heat exchangers and cold plates. By their geometry, the fins also create turbulence, which minimizes the fluid boundary layer and further reduces thermal resistance.

One high-performance version features tightly packed aluminum pin fins that create turbulence with low flow rate values, resulting in high thermal performance with low pressure drop. In this design, the high density of the internal fins increases the heat transfer area without adding bulk to the cold plate assembly. [6]

Figure 5. Close-spaced pin fins with complex geometry create turbulence with low flow rate values inside submerged fin cold plates. [6]

In most high-performance applications, fins are made of copper or aluminum. Aluminum fins are preferred in aircraft electronic liquid cooling applications due to their lighter weight. Copper fins are mostly used in applications where weight is not an important factor, but compatibility with other cooling loop materials is.

For submerged-fin cold plates, many different fin geometries can be tested to find the best improvement in performance. Some of the most commonly used are louvered, lanced offset, straight, and wavy fins.

Figure 6. Fin designs for submerged-fin cold plates. Clockwise from top: louvered, lanced offset, wavy, and straight fins. [7]

With cooling requirements increasing in many areas of electronics, engineers are turning to liquid cooling to replace air cooling. Lower cost, safer liquid cooling systems have also spurred the trend to liquid cooling.

The prime example is the cold plate – relatively simple in design, affordable, available in alternative versions, and extremely customizable. Cold plates should be considered wherever thermal performance above air cooling is needed.

References:

  1. https://d6industries.com/portfolio/custom-designs-liquid-cold-plate-hydroblock/
  2. https://www.lytron.com/Cold-Plates
  3. http://www.wakefield-vette.com/products/liquid-cooling/liquid-cold-plates/standard-liquid-cold-plates.aspx
  4. https://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Assessing-the-Quality-of-a-Tubed-Cold-Plate
  5. https://www.qats.com/Products/Liquid-Cooling/Cold-Plates
  6. http://www.cooltech.it/products/liquid-cold-plates/
  7. https://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Fins-for-Cooling-Success

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com. To register for Qpedia and to get access to its archives, visit https://www.qats.com/Qpedia-Thermal-eMagazine.


Technology Review: Thermal Interface Materials

(This article was featured in an issue of Qpedia Thermal e-Magazine, an online publication dedicated to the thermal management of electronics. To get the current issue or to look through the archives, visit http://www.qats.com/Qpedia-Thermal-eMagazine.)

Qpedia continues its review of technologies developed for electronics cooling applications. We are presenting selected patents that were awarded to developers around the world to address cooling challenges. After reading the series, you will be more aware of both the historic developments and the latest breakthroughs in both product design and applications.

Thermal Interface Materials
This Technology Review will focus on recent developments in Thermal Interface Materials. (Wiklmedia Commons)

We are specifically focusing on patented technologies to show the breadth of development in thermal management product sectors. Please note that there are many patents within these areas. Limited by article space, we are presenting a small number to offer a representation of the entire field. You are encouraged to do your own patent investigation.

Further, if you have been awarded a patent and would like to have it included in these reviews, please send us your patent number or patent application.

In this issue our spotlight is on thermal interface materials.

There are many U.S. patents in this area of technology, and those presented here are some recent. These patents show some of the salient features that are the focus of different inventors.

Thermal Interface Material with Carbon Nanotubes
US 7253442 B2 – Hua Huang, Chang-Hong Liu and Shou-Shan Fan


A thermal interface material includes a macromolecular material, and a plurality of carbon nanotubes embedded in the macromolecular material uniformly. The thermal interface material includes a first surface and an opposite second surface. Each carbon nanotube is open at both ends thereof, and extends from the first surface to the second surface of the thermal interface material. A method for manufacturing the thermal interface material includes the steps of: (a) forming an array of carbon nanotubes on a substrate; (b) submerging the carbon nanotubes in a liquid macromolecular material; (c) solidifying the liquid macromolecular material; and (d) cutting the solidified liquid macromolecular material to obtain the thermal interface material with the carbon nanotubes secured therein.

An object of the present invention is to provide a thermal interface material having a reduced thickness, small thermal interface resistance, good flexibility and excellent heat conduction. To achieve the above-mentioned object, the present invention provides a thermal interface material comprising macromolecular material and a plurality of carbon nanotubes embedded in the macromolecular material uniformly. The thermal interface material also comprises a first surface and an opposite second surface. Each carbon nanotube is open at two ends thereof, and extends from the first surface to the second surface of the thermal interface material.

Unlike in a conventional thermal interface material, the carbon nanotubes of the thermal interface material of the present invention are disposed in the macromolecular material uniformly and directionally. Thus, each carbon nanotube of the thermal interface material can provide a heat conduction path in a direction perpendicular to a main heat absorbing surface of the thermal interface material. This ensures that the thermal interface material has a high heat conduction coefficient. Furthermore, the thickness of the thermal interface material of the present invention can be controlled by cutting the macromolecular material. This further enhances the heat conducting efficiency of the thermal interface material and reduces the volume and weight of the thermal interface material.

Moreover, each carbon nanotube is open at two ends thereof, and extends from the first surface to the second surface of the thermal interface material. This ensures the carbon nanotubes can contact an electronic device and a heat sink directly. Thus, the thermal interface resistance between the carbon nanotubes and the electronic device is reduced, and the thermal interface resistance between the carbon nanotubes and the heat sink is reduced. Therefore, the heat conducting efficiency of the thermal interface material is further enhanced.

Transferrable Compliant Fibrous Thermal Interface
US 6676796 – Michael Pinter, Nancy Dean, William Willet, Amy Gettings and Charles Smith

In one aspect of the invention there is provided a fibrous interface material sandwiched between two layers of a removable paper or release liner. The interface comprises flocked, e.g. electroflocked, mechanically flocked, pneumatically flocked, etc., thermally conductive fibers embedded in an adhesive or tacky substance in substantially vertical orientation with portions of the fibers extending out of the adhesive. An encapsulant is disposed to fill spaces between portions of the fibers that extend out of the adhesive, leaving a free fiber structure at the fiber tips.

Another aspect of the invention is a method of making a fibrous interface. In the method, thermally conductive fibers of desired length are provided and, if necessary, cleaned. A release liner is coated with an adhesive or tacky substance, and the fibers are flocked to that release liner so as to embed the fibers into the adhesive or tacky substance with a portion of the fibers extending out of the adhesive.

The adhesive is cured and the space between fibers if filled with a curable encapsulant. A second piece of release liner is placed over the fiber ends. Then the fibers in the adhesive with the release liner over the fibers in the adhesive with the encapsulant in the spaces between the fibers is compressed to a height less than the normal fibers’ length and clamped at the compressed height.

Thereafter the encapsulant is cured while under compression to yield a free fiber tip structure with the fiber tips extending out of the encapsulant.

Liquid Metal Thermal Interface for an Integrated Circuit Device
US 7348665 B2 – Ioan Sauciuc and Gregory Chrysler


One possible solution to meet the heat dissipation needs of microprocessors and other processing devices is to employ an active cooling system—e.g., a liquid based cooling system that relies, at least in part, on convective heat transfer initiated by the movement of a working fluid—rather than (or in combination with) heat sinks and other passive heat removal components. Disclosed herein are embodiments of a cooling system for an integrated circuit (IC) device—as well as embodiments of a method of cooling an IC device—wherein the cooling system includes a liquid metal thermal interface that is disposed between a die and a heat transfer element, such as a heat spreader or a heat sink. Embodiments of a method of making a liquid metal thermal interface are also disclosed.

This patent is for a liquid metal thermal interface for an integrated circuit die. The liquid metal thermal interface may be disposed between the die and another heat transfer element, such as a heat spreader or heat sink. The liquid metal thermal interface includes a liquid metal in fluid communication with a surface of the die, and liquid metal moving over the die surface transfers heat from the die to the heat transfer element. A surface of the heat transfer element may also be in fluid communication with the liquid metal.

Per Figure 2, the cooling system 200 is coupled with an IC die 10. During operation of the IC die 10, the die may generate heat, and the cooling system 200 is capable of dissipating at least some of this heat, such as may be accomplished by transferring heat away from the IC die 10 and to the ambient environment. The IC die 10 may comprise any type of integrated circuit device, such as a microprocessor, network processor, application specific integrated circuit (ASIC), or other processing device.

Heterogeneous Thermal Interface for Cooling
US 7219713 B2 – Jeffrey Gelorme, Supratik Guha, Nancy LaBianca, Yves Martin and Theodore Van Kessel

The present invention is a thermal interface for coupling a heat source to a heat sink. One embodiment of the invention comprises a mesh and a liquid, e.g., a thermally conductive liquid, disposed in the mesh. The mesh and the thermally conductive liquid are adapted to contact both the heat source and the heat sink when disposed there between. In one embodiment, the mesh may comprise a metal or organic material compatible with the liquid. In one embodiment, the liquid may comprise liquid metal. For example, the liquid may comprise a gallium indium tin alloy. A gasket may optionally be used to seal the mesh and the liquid between the heat source and the heat sink. In one embodiment, the heat source is an integrated circuit chip.

In another aspect of the invention, a method for cooling a heat source with a heat sink is provided. In one embodiment, the method includes providing a thermal interface having a mesh and a liquid disposed in the mesh. The thermal interface is interposed between the heat source and the heat sink, such that the mesh and the liquid are in contact with the heat source on a first side of the thermal interface and in contact with the heat sink on a second side of the thermal interface.

In another aspect of the invention, a method of fabricating a thermal interface for assisting the thermal transfer of heat from a heat source to a heat sink is provided. In one embodiment, the method includes providing a mesh. A liquid is disposed in the mesh in sufficient quantity to substantially fill the mesh. The liquid comprises liquid metal. Optionally, the liquid metal may subsequently be frozen in place.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com. To register for Qpedia and to get access to its archives, visit https://www.qats.com/Qpedia-Thermal-eMagazine.