Category Archives: Heat Sink Attach

Edge Computing and Thermal Management

By Rebecca O’Day and Norman Quesnel
Senior Members of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)

Expanding the Internet of Things (IOT) into time-critical applications such as with autonomous vehicles, means finding ways to reduce data transfer latency. One such way, edge computing, places some computing as close to connected devices as possible. Edge computing pushes intelligence, processing power and communication capabilities from a network core to the network edge, and from an edge gateway or appliance directly into devices. The benefits include improved response times and better user experiences.

While cloud computing relies on data centers and communication bandwidth to process and analyze data, edge computing provides a means to lay some work off from centralized cloud computing by taking less compute intensive tasks to other components of the architecture, near where data is first collected. Edge computing works with IoT data collected from remote sensors, smartphones, tablets, and machines. This data must be analyzed and reported on in real time to be immediately actionable. [1]

Edge Computing Architecture Scheme with Both the Computing Power and Latency Decreasing Downwards.
FIgure 1: Edge Computing Architecture Scheme with Both the Computing Power and Latency Decreasing Downwards [2]

In the above edge computing scheme, developed by Inovex, the layers are described as follows:

Cloud: On this layer compute power and storage are virtually limitless. But, latencies and the cost of data transport to this layer can be very high. In an edge computing application, the cloud can provide long-term storage and manage the immediate lower levels.

Edge Node: These nodes are located before the last mile of the network, also known as downstream. Edge nodes are devices capable of routing network traffic and usually possess high compute power. The devices range from base stations, routers and switches to small-scale data centers.

Edge Gateway: Edge gateways are like edge nodes but are less powerful. They can speak most common protocols and manage computations that do not require specialized hardware, such as GPUs. Devices on this layer are often used to translate for devices on lower layers. Or, they can provide a platform for lower-level devices such as mobile phones, cars, and various sensing systems, including cameras and motion detectors.

Edge Devices: This layer is home to small devices with very limited resources. Examples include single sensors and embedded systems. These devices are usually purpose-built for a single type of computation and often limited in their communication capabilities. Devices on this layer can include smart watches, traffic lights and environmental sensors. [2]

Today, edge computing is becoming essential where time-to-result must be minimized, such as in smart cars. Bandwidth costs and latency make crunching data near its source more efficient, especially in complex systems like smart and autonomous vehicles that generate terabytes of telemetry data. [3]

Edge Computing and Thermal Management - Leap Mind's Small Edge Computing Device
Figure 2: A Small Scale Edge Computing Device from LeapMind [4]

Besides vehicles, edge computing examples serving the IoT include smart factories and homes, smartphones, tablets, sensor-generated input, robotics, automated machines on manufacturing floors, and distributed analytics servers used for localized computing and analytics.

Major technologies served by edge computing include wireless sensor networks, cooperative distributed peer-to-peer ad-hoc networking and processing, also classifiable as local cloud/fog computing, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented reality and virtual reality. [5]

Autonomous Vehicles and Smart Cars

New so-called autonomous vehicles have enough computing hardware they could be considered mobile data centers. They generate terabytes of data every day. A single vehicle running for 14 to 16 hours a day creates 1-5TB of raw data an hour and can produce up to 50TB a day. [6]

A moving self-driving car, sending a live stream continuously to servers, could meet disaster while waiting for central cloud servers to process the data and respond back to it. Edge computing allows basic processing, like when to slow down or stop, to be done in the car itself. Edge computing eliminates the dangerous data latency.

Edge Computing Reduces Data Latency to Optimize Systems in Smart and Autonomous Vehicles
Figure 3: Edge Computing Reduces Data Latency to Optimize Systems in Smart and Autonomous Vehicles [7]

Once an autonomous car is parked, nearby edge computing systems can provide added data for future trips. Processing this close to the source reduces the costs and delays associated with uploading to the cloud. Here, the processing does not occur in the vehicle itself.

Other Edge Computing Applications

Edge computing enables industrial and healthcare providers to bring visibility, control, and analytic insights to many parts of an infrastructure and its operations—from factory shop floors to hospital operating rooms, from offshore oil platforms to electricity production.

Machine learning (ML) benefits greatly from edge computing. All the heavy-duty training of ML algorithms can be done on the cloud and the trained model can be deployed on the edge for near real-time or true real-time predictions.

For manufacturing uses, edge computing devices can translate data from proprietary systems to the cloud. The capability of edge technology to perform analytics and optimization locally, provides faster responses for more dynamic applications, such as adjusting line speeds and product accumulation to balance the line. [8]

Figure 4: EdgeBoard by Baidu is a Computing Solution for Edge-Specific Applications [9]

Edge Computing Hardware

Processing power at the edge needs to be matched to the application and the available power to drive an edge system operation. If machine vision, machine learning and other AI technologies are deployed, significant processing power is necessary. If an application is more modest, such as with digital signage, the processing power may be somewhat less.

Intel’s Xeon D-2100 processor is made to support edge computing. It is a lower power, system on chip version of a Xeon cloud/data server processor. The D-2100 has a thermal design point (TDP) of 60-110W.  It can run the same instruction set as traditional Intel server chips, but takes that instruction set to the edge of the network. Typical edge applications for the Xeon D-2100 include multi-access edge computing (MEC), virtual reality/augmented reality, autonomous driving and wireless base stations. [10]

Figure 5: The D-2100 Processor Dissipates Between 60 -110W. Thermal Management Depends on the Type of Device and Where it is Used [11]

Thermal management of the D-2100 edge focused processor is largely determined by the overall mechanical package the edge application takes. For example, if the application is a traditional 1U server, with sufficient air flow into the package, a commercial off the shelf, copper or aluminum heat sink should provide sufficient cooling.  [11]

Edge Computing Server from ATOS Featuring the Intel Xeon D-2187 Edge CPU Processor
Figure 6: An Edge Computing Server from ATOS Featuring the Xeon D-2187 from Intel’s D-2100 Family of Processors [12]

An example of a more traditional package for edge computing is the ATOS system shown in Figure 6. But, for less common packages, where airflow may be less, more elaborate approaches may be needed. For example, heat pipes may be needed to transport excess processor heat to another part of the system for dissipation.

One design uses a vapor chamber integrated with a heat sink. Vapor chambers are effectively flat heat pipes with very high thermal conductance and are especially useful for heat spreading. In edge hardware applications where there is a small hot spot on a processor, a vapor chamber attached to a heat sink can be an effective solution to conduct the heat off the chip.

Coca Cola's Freestyle Fountain An Edge Computing Example
Figure 7: Coca-Cola’s Freestyle Fountain, a Non-Traditional Edge Computing System, Features an Intel I7 CPU, DRAM, Touchscreen, WiFi and HiDef Display [13]

The Nvidia Jetson AGX Xavier is designed for edge computing applications such as logistics robots, factory systems, large industrial UAVs, and other autonomous machines that need high performance processing in an efficient package.

Nvidia Jetson AGX Xavier Edge Computing and AI Processor
Figure 8: Nvidia’s Jetson AGX Xavier Produces Little Heat But Could Have Thermal Issues in Edge Computing Applications [14]

Nvidia has modularized the package, proving the needed supporting semiconductors and input/output ports. While it looks like if could generate a lot of heat, the module only produces 30W and has an embedded thermal transfer plate. However, any edge computing deployment of this module, where it is embedded into an application, can face excess heat issues. A lack of system air, solar loading, impact of heat from nearby devices can negatively impact a module in an edge computing application.

Nvidia Jetson AGX Xavier Processor Development Kit
Figure 9: Nvidia’s Development Kit for the Jetson AGX Xavier Includes Heat Sink and Heat Pipes [15]

Nvidia considers this in their development kit for this module. It has an integrated thermal management solution featuring a heat sink and heat pipes. Heat is transferred from the module’s embedded thermal transfer plate to the heat pipes then to the heat sink that is part of the solution.

For a given edge computing application, a thermal solution might use heat pipes attached to a metal chassis to dissipate heat. Or it could combine a heat sink with an integrated vapor chamber. Studies by Glover, et al from Cisco have noted that for vapor chamber heat sinks, the thermal resistance value varies from 0.19°C/W to 0.23°C/W for 30W of power. [16]

A prominent use case for edge computing is in the smart factory empowered by the Industrial Internet of things (IIoT). As discussed, cloud computing has drawbacks due to latency, reliability through the communication connections, time for data to travel to the cloud, get processed and return. Putting intelligence at the edge can solve many if not all these potential issues. The Texas Instruments (TI) Sitara family of processors was purpose built for these edge computing machine learning applications.

TI Stara ARM Processors for Edge Computing and IIOT
Figure 10: TI’s Sitara Processors are Design for Edge Computing Machine Learning Applications [17]

Smart factories apply machine learning in different ways. One of these is training, where machine learning algorithms use computation methods to learn information directly from a set of data. Another is deployment. Once the algorithm learns, it applies that knowledge to finding patterns or inferring results from other data sets. The results can be better decisions about how a process in a factory is running.  TI’s Sitara family can execute a trained algorithm and make inferences from data sets at the network edge.

The TI Sitara AM57x devices were built to perform machine learning in edge computing applications including industrial robots, computer vision and optical inspection, predictive maintenance (PdM), sound classification and recognition of sound patterns, and tracking, identifying, and counting people and objects. [18,19]

This level of machine learning processing may seem like it would require sophisticated thermal management, but the level of thermal management required is really dictated by the use case. In development of its hardware, TI provides guidance with the implementation of a straight fin heat sink with thermal adhesive tape on its TMDSIDK574 AM574x Industrial Development Kit board.

TI AM574x Industrial Development Kit
Figure 11: TI TMDSIDK574 AM574x Industrial Development Kit [20]

While not likely an economical production product, it provides a solid platform for the development of many of the edge computing applications that are found in smart factories powered by IIoT. The straight fin heat sink with thermal tape is a reasonable recommendation for this kind of application.

Most edge computing applications will not include a lab bench or controlled prototype environment. They might involve hardware for machine vision (an application of computer vision).  An example of a core board that might be used for this kind of application is the Phytec phyCORE-AM57x. [21]

Phytec phyCORE-AM57x for Machine Vision Applications
Figure 12: The Phytec phyCORE-AM57x Can Be used in Edge Computing Machine Vision Applications [22]

Machine vision being used in a harsh, extreme temperature industrial environment might require not just solid thermal management but physical protection as well.  Such a use case could call for thermal management with a chassis. An example is the Arrow SAM Car chassis developed to both cool and protect electronics used for controlling a car.

Chassis for Automotive Application that Protects Components and Provides Thermal Management
Figure 13: Chassis for Automotive Application that Protects Components and Provides Thermal Management [23]

Another packaging example from the SAM Car is the chassis shown below, which is used in a harsh IoT environment. This aluminum enclosure has cut outs and pockets connecting to the chips on the internal PCB.  The chassis acts as the heat sink and provides significant protection in harsh industrial environments.

SAM Car Electronics and Computing Chassis
Figure 14: Aluminum Chassis with Cut Outs and Pocketts to the Enclosed PCB with Semiconductors [23]

Edge computing cabinetry is small in scale (e.g. less than 10 racks), but powerful in information. It can be placed in nearly any environment and location to provide power, efficiency and reliability without the need for the support structure of a larger white space data center. 

The Jetson TX2 Edge Computing Platform from NVIDIA
Figure 15: The Jetson TX2 Edge Computing Platform from Nvidia [24]

Still, racks used in edge cabinets can use high levels of processing power. The enclosure and/or certain components need a built-in, high-performance cooling system.

Hardware OEMs like Rittal build redundancy into edge systems. This lets other IT assets remain fully functional and operational, even if one device fails. Eliminating downtime of the line, preserving key data and rapid response all contribute to a healthier bottom line.

Although edge computing involves fewer racks, the data needs vital cooling protection. For edge computers located in remote locations, the availability of cooling resources may vary. Rittal provides both water and refrigerant-based options. Refrigerant cooling provides flexible installation, water based cooling brings the advantage of ambient air assist, for free cooling. [25]

Immersion Liquid Cooling from LiquidCool
Figure 16: LiquidCool Immersion Cooling Technology Eliminates the Need for Air Cooling

LiquidCool’s technology collects server waste heat inside a fluid system and transports it to an inexpensive remote outside heat exchanger. Or, the waste heat can be re-purposed. In one IT closet-based edge system, fluid-transported waste heat is used for heating an adjacent room. [26]

Green Revolution Cooling provides ICEtank turnkey data centers built inside ISO shipping containers for edge installations nearly anywhere. The ICEtank containers feature immersion cooling systems. Their ElectroSafe coolant protects against corrosion, and the system removes any need for chillers, CRACs (computer room ACs) and other powered cooling systems. [27]

A Summary Chart of Suggested Cooling for Edge Computing

The following chart summarizes air cooling options for Edge Computing applications:

Figure 17: Edge Computing Air Cooling Options Summary Chart
Figure 17: Edge Computing Air Cooling Options Summary Chart [click for larger version]

The Leading Edge

The edge computing marketplace is currently experiencing a period of unprecedented growth. Edge market revenues are predicted to expand to $6.72 billion by 2022 as it supports a global IoT market expected to top $724 billion by 2023. The accumulation of IoT data, and the need to process it at local collection points, will continue to drive the deployment of edge computing. [28,29]

As more businesses and industries shift from enterprise to edge computing, they are bringing the IT network closer to speed up data communications. There are several benefits, including reduced data latency, increased real-time analysis, and resulting efficiencies in operations and data management. Much critical data also stays local, reducing security risks.

References

  1. https://www.networkworld.com/article/3224893/what-is-edge-computing-and-how-it-s-changing-the-network.html
  2. https://www.inovex.de/blog/edge-computing-introduction/ https://www.datacenterknowledge.com/edge-computing/searching-car-network-s-natural-edge
  3. https://www.bloomberg.com/news/articles/2019-06-17/ai-needs-edge-computing-to-make-everyday-devices-smarter
  4. https://www.networkcomputing.com/networking/how-edge-computing-compares-cloud-computing
  5. https://medium.com/velotio-perspectives/a-beginners-guide-to-edge-computing-6cfea853aa11
  6. https://www.datacenterknowledge.com/edge-computing/searching-car-network-s-natural-edge
  7. https://www.wespeakiot.com/will-edge-computing-devour-cloud/
  8. https://www.designnews.com/automation-motion-control/edge-computing-emerges-megatrend-automation/27888481159634
  9. https://www.design-reuse.com/news/45423/xilinx-baidu-brain-edge-ai-edgeboard.html
  10. https://www.intel.com/content/www/us/en/products/docs/processors/xeon/d-2100-brief.html
  11. https://software.intel.com/en-us/articles/intel-xeon-processor-d-2100-product-family-technical-overview
  12. https://atos.net/en/2019/press-release/general-press-releases_2019_05_16/atos-launches-the-worlds-highest-performing-edge-computing-server
  13. https://venturebeat.com/2012/09/11/this-coke-machine-has-an-intel-core-i7-processor-and-it-can-take-your-picture/
  14. https://www.custompcreview.com/news/nvidia-announces-jetson-x2-edge-computing-platform/
  15. https://developer.nvidia.com/embedded/jetson-agx-xavier-developer-kit#resources
  16. “Glover, G., Chen, Y., Luo, A., and Chu, H., “Thin Vapor Chamber Heat Sink and Embedded Heat Pipe Heat Sink Performance Evaluations”, 25th IEEE Symposium, San Jose, CA USA 2009.
  17. http://www.ti.com/tool/SITARA-MACHINE-LEARNING#descriptionArea
  18. https://www.mathworks.com/discovery/machine-learning.html
  19. http://www.ti.com/tool/SITARA-MACHINE-LEARNING#descriptionArea
  20. http://www.ti.com/tool/TMDSIDK574
  21. https://www.phytec.com/phytec-announces-a-new-system-on-module-som-based-on-the-new-sitara-am57x-processor-family-from-texas-instruments/
  22. http://processors.wiki.ti.com/index.php/File:PhyCORE-AM57x_SOM.jpg
  23. https://www.qats.com/cms/2017/10/09/ats-collaborates-sam-car-featured-cnbc-program-jay-lenos-garage/
  24. https://www.custompcreview.com/news/nvidia-announces-jetson-x2-edge-computing-platform/
  25. https://www.rittal.us/contents/edge-computing-and-uncontrolled-environments/
  26. https://www.liquidcoolsolutions.com/edge-server/#single/null
  27. https://www.grcooling.com/edge-computing/
  28. https://blog.apc.com/2019/05/15/four-reasons-configure-to-order-rack-pdus-edge-computing-environments/
  29. https://www.techrepublic.com/article/edge-computing-the-smart-persons-guide/

Picking the Right Heat Sink Attachment to Avoid Costly PCB Damage

The design of a printed circuit board (PCB) is a complicated process that requires engineers to consider a number of different issues before the board is ready to move beyond prototype and into production. Engineers must think about the physical constraints of a board on component size and placement, the electrical interaction between components, the signal loss through wires and traces, and the thermal management of each component and the system as a whole. [1]

Heat Sink Attachment

ATS maxiFLOW heat sink with superGRIP attachment on a PCB. (Advanced Thermal Solutions, Inc.)

With all of that to consider, it is no wonder that many designs go through several iterations before moving into the production stage. Since the process is already complex and there is a certain amount of trial-and-error in designing a PCB, engineers will look for ways to avoid unnecessary rework that will add significant cost to the project in terms of both time and money.

As noted in a previous article, the type of heat sink attachment technology that an engineer chooses will impact the ease with which a design can be reworked and the amount of damage to the board that will be caused if a change needs to be made.

Push pins, threaded standoffs and z-clips require holes or anchors be drilled into a board, which leaves permanent damage if a component needs to be moved to a new location and could also impact signal routing. There is even the possibility of a short in installation, which also would damage the board. [2]

Non-mechanical attachments such as thermally conductive tape and epoxy are not guaranteed to provide the optimal thermal management because there is “risk of die damage and poor thermal performance due to uneven heat sink placement,” according to a case study from the Altera Corporation. [3]

The case study also said that thermal tape and epoxy have “high risk of damaging the device or PCB” when compared to mechanical attachment technology coupled with thermal interface material (TIM) or phase change material (PCM). In fact, to remove a heat sink attached with epoxy requires an even temperature of 115-120°C.

As the video below shows, removing thermal tape from a heat sink (even one that is not attached to a board) requires a lot of work and tools. If the heat sink is attached to a component, the process to remove it could damage the board or other devices in the vicinity:

A recent chart from NEMI (National Electronics Manufacturing Initiative) indicated that the cost of assembly can be very high per I/O (input/output) on the PCB – considering some of the new BGAs have hundreds of I/O and there are dozens of BGAs on the board, the cost can be prohibitively expensive to put together a board irrespective of the product sector. [4] Obviously, full reworks necessitated by the use of damaging heat sink attachments raise those costs exponentially.

Heat Sink Attachment

Board assembly roadmap from NEMI showing the conversion costs by product sector. [4]

Advanced Thermal Solutions, Inc. (ATS) has created a mechanical attachment technology that makes rework easy and allows engineers to make changes to the design without damaging the PCB or the components. superGRIP™ is a two-part attachment system with a plastic frame clip that fastens around the edge of the component and a metal spring clip that fits between the fins of the heat sink and quickly and easily attaches to the frame.

As the video below demonstrates, superGRIP™ can be installed and removed with common household tools and will provide a steady, firm pressure to ensure optimal thermal performance of the heat sink and the reliability of the device:

The advantage of superGRIP™ is not limited to its ease of use and the time and money that will be saved in reworking a PCB design. The pressure strength and security of the superGRIP™ attachment system allows the use of high-performance phase change materials that can improve heat transfer by as much as 20 times over standard thermal tapes. [4]

superGRIP™ comes with Chomerics Thermflow T-766, a foil PCM with a thickness of 0.0035 millimeters that has an operating range of -55°C to 125°C. According to Chomerics, the T-766 and other traditional non-silicone thermal interface pads “completely fill interfacial air gaps and voids. They also displace entrapped air between power dissipating electronic components. Phase-change materials are designed to maximize heat sink performance and improve component reliability.” [5]

Chomerics added, “Upon reaching the required melt temperature, the pad will fully change phase and attain minimum bond-line thickness (MBLT) – less than 0.001 inch or 0.0254 mm, and maximum surface wetting. This results in practically no thermal contact resistance due to a very small thermal resistance path.”

The combination of frame and spring clip provides uniform force over the heat sink and ensures no movement to optimize the impact of the PCM, while not damaging the solder holding the BGA component in place on the board. ATS engineers designed the attachment technology so that the in-plane and normal forces of both the frame and the spring clip hold the heat sink without stressing the solder even through NEBS (Network Equipment Building Systems) shock and vibration testing. [6]

Save time, save money, and avoid unnecessary headaches during the design phase by using ATS superGRIP™ technology.

References
[1] http://www.electronicdesign.com/boards/11-myths-about-pcb-layout
[2] “How the maxiGRIP™ attachment system impacts component mechanical behavior,” Qpedia Thermal eMagazine], May 2008.
[3] https://www.altera.com/content/dam/altera-www/global/en_US/pdfs/literature/an/an657.pdf
[4] http://thor.inemi.org/webdownload/newsroom/Articles/CA0599.pdf
[5] https://www.qats.com/cpanel/UploadedPdf/ATS_superGRIP_Launch_Release_
FINAL_with_Photo_0427092.pdf

[6] http://vendor.parker.com/852568C80043FA7A/468ea5de5ac341d385257d39005641c7/
9A63F6EE5B922F278525787600620419/$FILE/Phase_Change_Excerpt-5-08.pdf

[7] “How the maxiGRIP™ attachment system impacts component mechanical behavior,” Qpedia Thermal eMagazine, May 2008.

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

Choosing the Right Heat Sink Attachment for Densely Populated PCB

In 1965, Fairchild Semiconductor Director of R&D and soon to be Intel co-founder Gordon Moore wrote “The Future of Integrated Electronics,” which was intended as an internal paper to define the most cost-effective number of components per integrated circuit. As he looked ahead to the next decade, Moore argued that the number of components per chip would double every year.

The paper was edited and published by Electronics in 1965 as “Cramming More Components onto Integrated Circuits”. Ten years later, Moore, then with Intel, spoke at the IEEE International Electron Devices Meeting and showed that his initial prediction was correct and estimated that the rate of increase would slow to “a doubling every two years, rather than one.”

Heat Sink Attachment

superGRIP heat sink attachment technology offer minimal addition to component footprint on densely packed PCB. (Advanced Thermal Solutions, Inc.)

This prediction has now become widely known as Moore’s law. It has become a tenet of the electronics community and continues to propel the industry forward at a time when the number of transistors on a chip (which was around 65,000 in 1975) now exceeds one billion. [1]

These high-powered components are common on printed circuit boards (PCB) in every day electronics from mobile devices to computers to automobiles. Recently, the Defense Advanced Research Program Agency (DARPA) announced that it will spend $200 million on the Electronics Resurgence Initiative to seek new materials and manufacturing techniques in expectation that Moore’s law will come to a natural end. [2]

Not only are the components themselves getting higher-powered, but increased demand for functionality in ever-smaller packages has meant that these components are increasingly being squeezed into tighter areas. A 2012 article on Tech Design Forums, based on information from Mentor Graphics’ Technology Leadership Awards, indicated that while PCB size had been “relatively constant,” the “average number of components has quadrupled in 15 years.” [3]

As the forum noted, “Despite attempts by IC (integrated circuit) suppliers to cut power dissipation, as IC speeds and densities increase so does the heat they dissipate. And putting these ICs into smaller and smaller form factors compounds the problem. This causes significant thermal management challenges that must be met at the IC package, PCB and system levels.”

OCM Manufacturing, a low- to mid-volume manufacturer of electronics products, offered a chart that detailed standard spacing of components on a PCB, but also added, “With that said, there are no hard and fast rules for component spacing. Tightly packed components may have very good yield and problems may arise only during rework.” [4]

Heat Sink Attachment

Match each component in the rows with whatever it’s adjacent to in the columns to see the preferred and minimum spacing between those two components, in millimeters. [4] (OCM Manufacturing)

Of course, all of that power will inevitably lead to increased heat across the system. Coupled with the decrease in space between components, which puts constraints on the amount of airflow across a component and leads to heat from one chip being passed on to the next, thermal management is a critical aspect of PCB design to an even greater extent than before. [5]

Heat sinks remain the most cost-effective method for cooling chips. The benefits of heat sinks, the thermal impact of different materials, and the development of new fin geometries are all discussed in depth elsewhere on this blog, but this article asks, “What is the best way to attach heat sinks, especially in a component-dense environment?”

As Dr. Kaveh Azar, founder and CEO of Advanced Thermal Solutions, Inc. (ATS), wrote in ECN Magazine, “An engineer starting the process of thermal management must first determine the cooling needed and then consider the mechanical aspects of attaching the heat sink.” [6]

He added, “The thermal consideration is foremost on our decision tree. Once we have resolved the cooling issue, including the heat sink size and the type of thermal interface material (TIM) needed, we need to ask the question of how this heat sink will be attached to the device or the PCB.”

There are several options for design engineers to consider, but each comes with its own set of challenges. Thermal tape and thermal epoxies [7] would obviously add nothing to the existing component footprint, but tape has proven better for low-powered chips and epoxies require time to cure and are essentially permanent, making potential rework more time-consuming and costly.

Push pins, threaded standoffs and z-clips are mechanical attachment technologies that are common in the electronics industry but all require expanded footprints as well as holes or anchors in the PCB, which may not be available on high-density boards. Holes and anchors also make signal routing more difficult in the design phase and there is a possibility of a standoff or solder anchor causing a short during installation that could result in damage to the board. [8]

To meet this need, ATS developed superGRIP™. The two-part attachment system features a plastic frame clip that fastens securely around the perimeter of the component and a metal spring clip that slips through the fins of a heat sink and locks to the frame clip on both ends. [9]

The system is designed to need minimal space around the component. [10] The frame clip is made of a plastic resin that allows it to be very thin but also very strong, which was demonstrated during shock and vibration testing. The interior frame profile locks securely around the bottom edge and sides of the component package. The horseshoe tabs secure the clip to ensure the proper pressure on the heat sink.

The following chart shows the superGRIP™ clearance guidelines, although custom options are available and may be needed depending on the design:

superGRIP

The required board keep-out region for ATS superGRIP heat sink attachment technology. (Advanced Thermal Solutions, Inc.)

superGRIP™ was also designed and tested to ensure maximum airflow through the heat sink. In a tightly-packed system where airflow is at a premium, superGRIP™ provides the necessary attachment security with only minimal impact on the flow. In addition, the plastic used in the frame clip stays cool in high-heat environments, rather than adding fuel to a potentially combustible situation.

superGRIP

CFD simulations with ATS superGRIP attachment demonstrating its minimal impact on airflow across a system. (Advanced Thermal Solutions, Inc.)

Unlike other attachment technologies, superGRIP™ also requires no separate tooling and can be installed or released with a common tool such as a screwdriver. [11] This makes any potential rework easier. It is important to note the direction of the airflow when placing a heat sink, so it must also be considered when placing the frame clip as well.

References
[1] http://www.computerhistory.org/siliconengine/moores-law-predicts-the-future-of-integrated-circuits/
[2] http://www.eetimes.com/document.asp?doc_id=1331974 and https://www.darpa.mil/news-events/2017-06-01
[3] http://www.techdesignforums.com/practice/technique/overcoming-increasing-pcb-complexity-with-automation/
[4] http://ocmmanufacturing.com/resources/resource/dfm-tip-spacing-components-on-a-pcb/
[5] http://www.electronicdesign.com/embedded/engineer-s-guide-high-quality-pcb-design
[6] https://www.ecnmag.com/article/2011/09/know-your-choices-mounting-heat-sinks-hot-components
[7] https://www.masterbond.com/industries/heat-sink-attachment
[8] “How the maxiGRIP™ attachment system impacts component mechanical behavior,” Qpedia Thermal eMagazine, May 2008.
[9] https://www.qats.com/cpanel/UploadedPdf/ATS_superGRIP_Launch_Release_FINAL_with_Photo_0427092.pdf
[10] https://www.qats.com/cms/wp-content/uploads/2013/12/superGRIP-Clearance-Guidelines1.pdf
[11] https://www.qats.com/cms/wp-content/uploads/2013/12/superGRIP-Installation-Guidelines.pdf

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

#WeCoverTheBoard: ATS Has Thermal Solutions to Cover the Whole Board

We Cover The Board

Advanced Thermal Solutions, Inc. (ATS) has an extensive line of heat sinks and board level thermal solutions that allow ATS engineers to work with industry-leading components and solve the industry’s toughest thermal challenges. (Advanced Thermal Solutions, Inc.)

Advanced Thermal Solutions, Inc. (ATS) has an extensive product line of innovative, off-the-shelf and custom heat sinks and attachments that provides the broadest range of designs to meet the demanding thermal challenges presented by today’s high-powered electronics. Led by its patented maxiFLOW™, which provides the highest thermal performance for physical volume it occupies compared to other heat sinks on the market, ATS has a solution to meet any thermal problem.

In addition, ATS engineers have world-renowned expertise in thermal management and are capable of designing liquid and air cooling solutions using heat sinks, heat pipes, heat exchangers, fans, and cold plates. ATS has more than two decades of solving the industry’s toughest thermal challenges and have a proven record of success in handling the industry’s leading components.

From the latest generation of Intel processors to Altera’s high-powered Stratix FPGA to Qualcomm’s ARM processors to Texas Instruments, Nvidia, NXP, Cavium, and many more, ATS has the experience, the analytical capability, and the products to provide you with the necessary thermal management.

Board Level Solutions

maxiFLOW™ – maxiFLOW™ heat sink design provides the highest thermal performance for the physical volume that it occupies as compared to other heat sink designs. maxiFLOW™ heat sinks are ideally suited to meet the thermal requirements of a broad range of electronics packages, including: BGA, QFP, LCC, LGA, CLCC, TSOP, DIPs and LQFP.

Straight Fin – ATS offers a large variety of high performance Straight fin heat sinks that can be used in many applications where the direction of the airflow is clearly defined. The straight fin heat sink can be utilized in areas where the maxiFLOW™ flair-fanned cannot be used, providing an excellent alternative for cooling thermally sensitive devices.

Cross-Cut – Electronics packages are numerous and range from BGA, QFP, LCC, LGA, CLCC, TSOP, DIPs, LQFP and many others. ATS offers a large variety of cross cut heat sinks that can be used in a variety of applications where the direction of the airflow is ambiguous. The cross cut allow for the heat sink to receive air from any direction.

Pin Fin – Electronics packages are numerous and range from BGA, QFP, LCC, LGA, CLCC, TSOP, DIPs, LQFP and many others. ATS offers a large variety of cross cut heat sinks that can be used in a variety of applications where the direction of the airflow is ambiguous. The cross cut tape on allow for the heat sink to receive air from any direction and can be easily attached to the device by a thermally conductive tape.

fanSINK™ – In many electronic systems, such as telecomm and datacom chassis, or 1U, 2U servers and blades, the system air flow rate is not adequate for cooling of high power devices. Therefore, additional air flow introduced at the device level is required. ATS offers a large family of fanSINK™ products for applications where FPGA or ASICs in BGA packages are deployed. ThefanSINK™ can be either clipped on to the device by maxiGRIP™ or superGRIP™ heat sink attachment technologies or taped on.

Power Brick – DC/DC power converters are an essential part of PCB design and their performance requires a stable temperature for optimum performance. ATS has produced a broad array of high performance power brick heat sinks, based off of the patented maxiFLOW™ design, to effectively cool DC/DC power converters and power modules deployed in a host of electronics applications. ATS’ power brick heat sinks are available in full, half, quarter and eighth packaging.

pushPIN™ – With over 108K different push pin heat sink assembly configurations, ATS offers the largest push pin heat sink offering in the market. Select from fine and ultra-fine pitch heat sinks designed for high velocity air flows and coarse pitch heat sinks for low velocity air flow conditions. Offered in straight fin, cross-cut and the ultra performance maxiFLOW™ fin geometries, ATS pushPIN™ heat sink line is suited to meet a wide variety of applications for components ranging in size from 25mm-70mm. Push pins are offered in brass and plastic and are packaged with different compression springs to achieve precise force required for secure attachment.

blueICE™ (Ultra Low Profile) – In many electronics systems, such as Telecomm, Datacomm, Biomedical equipment and others, card-to-card spacing is small, yet stringent thermal requirements remain the same. Electronics packages such as BGA, QFP, LCC, LGA, CLCC, TSOP, DIP, LQFP are commonly used with stringent thermal requirements in a tight space with limited airflow. Ultra low profile heat sinks offered by ATS range from 2 to 7mm in height and are ideally suited for tight-space application electronics since they offer the best thermal performance. Their thermal resistance is as low as 1.23° C/W within an air velocity of 600 ft/min.

Standard Board Level – ATS’ high quality, low cost, aluminum stamped heat sinks are ideal for low power thermal management solutions. The simple design and manufacturing of these heat sinks allows high volume manufacturing and reducing assembly costs. Stamped heat sinks are ideally used for TO packages and other power devices.

Extrusions – Aluminum extrusions are the most cost-effective solutions for the majority of electronic cooling applications. ATS offers a wide variety of aluminum profiles used for heat sink fabrication and other aluminum applications. Whether you are seeking a standard extrusion profile or the expertise from our design team to create a new and innovative profile, ATS has the capabilities and expertise to meet your requirements.

Heat Sink Attachments

superGRIP™ – superGRIP™ is a two component attachment system which quickly and securely mounts heat sinks to a wide range of components, without needing to drill holes in the PCB. superGRIP™ provides a strong, even attachment force with minimal space required around the components perimeter, making it ideal for densely populated PCBs. superGRIP™ is available with ATS maxiFLOW™ heat sink and straight fin heat sinks.

maxiGRIP™ – maxiGRIP™ is a unique, two component attachment system which quickly and securely mounts heat sinks to a wide range of components, without needing to drill holes in the PCB. The steady, even attachment force provided by maxiGRIP™ allows the heat sink and thermal interface material to achieve maximum thermal performance. maxiGRIP™ is available with ATS maxiFLOW™, straight fin, fanSINK™ and device specific heat sinks.

Thermal Tape
– The interface material plays a pivotal role in transporting the heat from the component to the heat sink. The tape is applied to the base of the heat sink and then the heat sink is attached to the component. For tape to work well, proper cleaning of the component surface and the base of heat sink is required. Also, it is usually necessary to apply the tape with a certain amount of pressure.

Attaching Heat Sinks with Push Pins

Heat Sink with push pin attachment and maxiFLOW fins

In certain conditions, lightweight heat sinks can be mounted to hot components with thermally conductive adhesive tape.

But, many heat sinks need a mechanical attachment system for optimum thermal performance and security. These systems typically feature metal and/or plastic hardware, along with a high performance TIM (thermal interface material).

Several attachment systems are available, and one way to categorize them is by whether or not the circuit board becomes part of the solution. For example, will holes be drilled into the board for mounting pins or anchors to help clamp down the heat sink?

If such holes can be safely added around a component, the most versatile heat sink attachment method is push pins. These are now used with many commonly available heat sinks. The sinks have integral holes that align with standard PCB locations. Each pin has a pointed barb end that attaches permanently through the drilled hole. A wire spring on the pin adds a continuous compressive force.

Push pin type heat sinks provide many options for a wide variety of conditions under which electronics are deployed.  They come in a range of material and lengths, as well as choices of springs.

Common push pin material options include:

  • Plastic push pin
  • Brass push pin
  • Stainless Steel PEM

Plastic Push Pins are useful for applications where the push pin heat sink attachment should not conduct heat or electricity. They are a good choice when weight is a critical design factor.  Plastic is also a good option when water or high humidity conditions can occur. Corrosion and chemical resistance are two key advantages of plastics. As with any plastic fastener, the plastic itself has to be particularly robust in order to handle the strain of fastener insertion and subsequent high stress around the pin.

plastic push pins to attach a heat sink to a PCB

Thought should be given to the material type of the pin and the plating used in the PCB through hole that will sheath the fastener when you attach the heat sink to the PCB.  Depending on what material is used, that material will have a CTE (co-efficient of thermal expansion) that needs to be matched to the attachment being specified.

Brass push pins are useful for applications that are corrosive, high heat, and require a strong, durable, material for attachment.  Brass can also be used in situations where it is important that sparks not be struck, as in fittings and tools around explosive gases. Brass attachment should not be used in environments that include ammonia or that release ammonia as this compound can cause stress corrosion cracking in brass.

Brass can often be cheaper than the same attachment in stainless steel since brass costs much less to machine.  Brass is a reasonably good conductor of heat as well (109 W/(m KM)), increasing the overall thermal management of an application where it used to secure a heat sink.

brass push pin attachment for heat sinks being mounted to a PCB

And, push pin fasteners cost less than metal PEMs, which can be similarly used to mount heat sinks via PCB holes.

Screwed in PEM fasteners are perfect for applications where there is only a plain, round hole. They provide high push-out and torque-out resistance. The holes for these fasteners do not need to be specially prepared by deburring or chamfering.  PEMs are also good for meeting DFMA requirements because there are few parts to handle and few assembly steps. Because many of the PEMs used in heat sink applications are made from stainless steel, they have good corrosion resistance, strength and fabrication characteristics.  Like brass, stainless steel is excellent for use in corrosive environments.  But stainless steel’s low thermal conductivity (16 W/(m KM) means that in applications where the heat conduction of the heat sink attachment must be as low as possible, while still providing corrosion resistance and strength, stainless steel can be a reasonable choice.

push pin attachment schematic showing length

brass and plastic push pins side by side comparison

The right length for a push pin is determined by the combined thickness of the heat sink base, the hot component, thermal interface material (TIM) and the thickness of the board.

The other variable is the choice of compression springs, an essential feature on push pin fasteners. Springs add the force needed to hold the assembly together. They’re sized for the length of the pin. Here, length refers to the space between the bottom of the heat sink and the top of the PCB. Overall height refers to the length of the pin, from is barbed tip to the top of its flat head. For ATS brass push pins, overall heights for brass push pin sizes range from 9 to 20mm. Plastic push pins are a standard 7.3 mm in length.

stainless steel springs for push pin heat sink attachment

Spring Choices

Wire compression springs come in choices of size (diameter and length) and material type. The pin length dictates the free length of the spring, but its solid length – when fully compressed, varies by the spring’s diameter and its material. The basic material choices are music wire, a commonly used carbon steel alloy, and stainless steel 302 wire. The music wire has a standard zinc plated finish, and the stainless steel wire has a passivated finish per ASTM A967.

The compressive force for achieving the solid length is determined by the combination of the spring’s free length, wire diameter and its inside and outside coil diameters. For ATS push pin springs, compression requirements range from 0.211 up to 3.543 lbs/mm. The final spring choice should provide a force that meets the performance needs of the TIM, and does not cause undo upward force on the component or on the PCB itself. Too great an insertion force can result in the die cracking and consequent component failure.

Installing Push Pins

All push pins feature flexible barbs that lock securely into PCB holes. The location of the holes in the heat sink will determine where holes must be drilled into the board. Industry standards for these locations are readily available for board designers or from ATS. The required hole diameter for all ATS push pins is 3.175 mm

Each push pin has a flexible barb at its install end that engages with the bottom of the hole in the PCB; once installed, the barb securely retains the pin. The compression spring holds the assembly together and maintains contact between the heat sink and component.

Pre-Load Advantages

Push pin springs add a pre-load pressure on the TIM in the completed assembly. Pre-load is the force holding the sink/TIM/component assembly together before the component is operating. Once the component heats up, a phase-change TIM will turn liquid (from a waxy solid) to increase thermal transfer. The push pins’ permanent pre-load pressure helps optimize the TIM’s thermal transfer performance with every power up and resulting TIM phase change.

Attachment Using PEMs

Push pin fasteners cost less than metal PEMs, which can be similarly used to mount heat sinks via PCB holes. However, PEMs have some advantages.

PEMS for mounting heat sinks to a PCB Board

Screwed in PEM fasteners are perfect for applications where there is only a plain, round hole. They provide high push-out and torque-out resistance. The holes for these fasteners do not need to be specially prepared by deburring or chamfering.  PEMs are also good for meeting DFMA requirements because there are few parts to handle and few assembly steps. Because many of the PEMs used in heat sink applications are made from stainless steel, they have good corrosion resistance, strength and fabrication characteristics.  Like brass, stainless steel is excellent for use in corrosive environments.  But stainless steel’s low thermal conductivity (16 W/(m KM) means that in applications where the heat conduction of the heat sink attachment must be as low as possible, while still providing corrosion resistance and strength, stainless steel can be a reasonable choice.

References for this post:

  1. Canadian Centre for Occupational Health and Safety, “Non-Sparking Tools”, http://www.ccohs.ca/oshanswers/safety_haz/hand_tools/nonsparking.html
  2. Thermal conductivity of material, Engineering Toolbox  http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
  3. Machine Design, “Comparing Brass and Stainless Steel Inserts”, http://machinedesign.com/materials/comparing-brass-versus-stainless-steel-threaded-inserts
  4. ECN Magazine, “The Art of Using Plastic Instead of Metal”, https://www.ecnmag.com/article/2005/04/art-using-plastic-instead-metal
  5. Mechanical Design, “Joining Plastic”, http://machinedesign.com/fasteners/joining-plastic
  6. PEM, The Self Clinching Fastner Handbook, http://www.pemnet.com/fastening_products/pdf/Handbook.pdf
  7. Angelica Spring, “Stainless Steel Music Wire”, http://angelicaspringcompany.com/index.php?Stainless%20Steel%20Music%20Wire – See more at: http://www.coolingzone.com/index.php?read=539&onmag=true&type=press#sthash.DtkLI2ig.dpuf
  8. Design Guidelines for the Selction and and Use of Stainless Steel  https://www.nickelinstitute.org/~/Media/Files/TechnicalLiterature/DesignGuidelinesfortheSelectionandUseofStainlessSteels_9014_.pdf

Brass, Plastic, and PEM Push Pin Heat Sink Attachments Offer the Right Solution for Almost Any Environment and Application http://www.coolingzone.com/index.php?read=539&onmag=true&type=press

Temperature Cycling Fatigue Electronics  (plated through hole fatigue)
http://www.dfrsolutions.com/white-papers/temperature-cycling-fatigue-electronics/

Optimizing thermal and mechanical performance in PCBs: http://www.smtnet.com/library/files/upload/712mangroli