Author Archives: Norm Quesnel

National Thermal Engineer Day at ATS

July 24th is the hottest day of the year, so naturally that is the perfect day to celebrate the contributions thermal engineers make to everyday life. You don’t know what thermal engineers do? Sadly enough, you are not alone. Thermal engineers are often overshadowed in society by electrical and software engineers when in reality, the thermal engineers are enabling electronics to function.

Thermal engineers work with heat energy and its transfer between different mediums and also into other usable forms of energy. Without thermal engineering, the electronics we use every day would not function.

ATS decided it was time for thermal engineers to gain recognition, thus, National Thermal Engineer Day was started. It is now recognized every year on July 24th. We celebrated the second annual National Thermal Engineer Day here at ATS on Friday, July 22nd, 2016. It was a success celebrating the work done by thermal engineers.

 

President, CEO, and founder of ATS, Kaveh Azar, shared his input on the importance of thermal engineers, “We make things happen in the electronics industry. We have a very tough job but as a result of the position, we never get recognized. We are doing the bulk of the work. We are making these things happen. We are making the electronics function.”

 

ATS employees spent the afternoon enjoying a barbecue and playing games, taking in the warmth of the sun on one of the hottest days of the year.

 

Cassandra Moore of our Sales Order Management team took a break from working with customer’s to enjoy the awesome food.

 

Sharon Koss, ATS’s Vice-President for Operations and Business Development, Dahra, Engineering Intern and Diane Chalmers, of our Sales Order Management Team, found the grilled steak and chicken to be great dishes for ATS’s National Thermal Engineer Day outing.

 

ATS’s Chief Technology Officer, Dr. Bahman Tavassoli, enjoying some rare time out of the lab.

 

Arlain Cherry from our Engineering team was happy to break away from his current project just long enough to enjoy some sunshine, food and good laughs.

 

Pete Clonda, Sr. Director of Operations Logistics, and Brent Bennett, Manufacturing Team, enjoying a friendly (but competitive!) game of bean bag toss.  Peter Konstatilakis chases after a frisbee.

 

Many of you reading this have likely seen one of Greg Wong’s many “how to” videos including “how to make a thermocouple” and “how to apply thermal interface material: thermal tape”.  He took a break from Engineering to celebrate National Thermal Engineer Day.

 

Marketing Specialist Becca Leonard took a break from graphics and web design to Celebrate National Thermal Engineer Day by taking the amazing photographs in this blog post!

 

What celebration would be complete without a cake?  Our National Thermal Engineer Day Cake was a delicious hit, courtesy of Whole Foods Markets.

 

Celebrate with us next year and every year after that! July 24th is National Thermal Engineer Day.  Learn more and sign up for a pin at this link:  National Thermal Engineer Day.

 

See you all next year at National Thermal Engineer Day, July 24th, 2017!

Thermal Solutions for Servers Part 2

This is part 2 of our 2 part series on server cooling.  To read part 1 click to this link:  Thermal Solutions for Servers Part 1

Part Two – Racks, Cards and Components

When the components inside a server get too hot, onboard logic may turn them off to avoid damage to the server. But not all components are protected like this. Along with the effects of an unscheduled server shutdown, if and when a hot server does not power down, its output could be compromised and its lifespan could be shorter than expected.

While much infrastructure and wide area cooling is employed in server installations, there is often a need for additional cooling of individual cards or select components on some cards. There are different ways to provide this localized cooling. Some are proven and traditional, and other ways are less conventional but have shown to be effective.

The following are some current examples of cooling solutions at the rack, card and individual component level.

Liquid Cooling for Racks

Internal

Direct Contact Liquid Cooling (DCLC) is a cooling solution from CoolIT Systems that uses the thermal conductivity of liquid to provide concentrated cooling to select surface areas, such as server racks and their components. DCLC systems can replace or minimize the need for system air conditioners and fans, and instead allow higher rack densities. Any server in any rack can be liquid cooled by DCLC.

Figure 1. A Liquid-to-Liquid heat exchanger module for cooling board components in cabinets. [CoolIT Systems]

An example of the DCLC technology is CoolIT’s CHx40 Liquid-to-Liquid heat exchanger for single cabinets. The 2U CHx40 module distributes clean, treated coolant, and can manage 40kW of processor load per rack, or 50 servers per rack.

The benefits from this system are increased density availability for CPUs and GPUs. CoolIT Systems server modules can cool any combination of CPU, GPU and memory components, with customization available for VR, ASIC, FPGA and other devices. Servers with these modules remain hot-swappable and simple to service.

The Fujitsu Liquid Loop Cooling technology uses a hybrid cooling model.  To remove heat, there are six pumps for each processor, which circulate coolant over hot spots and back to an air-cooled radiator. The cooling system is sealed and maintenance-free.

Figure 2. Liquid Loop Cooling Allows Heat Sinks to be Smaller and Located Away from Hot Spots. [Fujitsu]

In order to cool hot spots with air, heat sinks and fans must be located at the hot spots. However this can result in components like memory or IO being further away from the processors. The space between a CPU and memory chips largely affects memory access time, degrading overall performance. In liquid cooling, heat sinks can be located away from hot spots because heat is moved via cool liquid tubes to heat sinks. This allows processors and other components like memory and IO to be close enough to reduce access time.

By not only eliminating server design restrictions, but also integrated memory controllers to the processor, memory access time is reduced to one-fifth of the previous SPARC server. The Liquid Loop Cooling system has reduced heat sink sizes. Further, this efficient cooling helps reduce the noise which may be created by lower fan rotation.

External

A not as new, but quickly developing method for thermally managing racks of server cards is by submersion cooling. Typically, a series of boards and all their components are immersed in a non-conductive liquid. The liquid absorbs the component heat and transfers it away from the card.

Figure 3. ElectroSafe coolant flowing over servers in a CarnoJet System also protects components from environmental contaminants. [Green Revolution Cooling]

An example is the CarnoJet System from Green Revolution Cooling which has been proven to provide an overall increase in a server’s performance. The system features inert ElectroSafe coolant, which keeps server components an average of 20°C lower than obtainable by an air-cooled environment. This improved cooling allows for faster processor clock speeds and higher density racks. Servers immersed in the coolant are protected from dust, moisture, and oxidation, which are major sources of equipment failure. The coolant is constantly filtered and in motion. This provides a rinsing effect that prevents any kind of particulate accumulation.

Other benefits of submersion cooling include cost savings on large scale air conditioning systems and their maintenance, and on power requirements. But despite many advantages, liquid cooling still faces obstacles to becoming more widely used. The concept itself can cause apprehension with some engineers. But at high densities of server hardware, liquid cooling may be a smart solution.

Fan Cooling

There are many active server rack accessories to help improve cooling. Among them are enclosure blowers, rack air conditioners, and cooling fans. Here we’ll look at some fans.

Fans can be used to cool rack set ups where larger AC units may not be practical. Internal fans typically take up as little as 1U of rack space and can install directly into a rack or enclosure.

Figure 4. A rack mounted fan unit that provides 90 cubic feet of air per minute to cool hotspots in a server cabinet. [Data Comms Direct]

For lower density racks, fans can be a viable solution when increased cooling is needed. Fans facilitate the movement of ambient air through the rack. They can be mounted on a cabinet’s ceiling, sides, and doors, or incorporated directly in the rack as slide out fan trays. To improve the effectiveness of any fans, proper airflow management is needed. This may need the use of blanking panels, gaskets or sealing tape.

Figure 5. An integral fan helps cool hot components on a PCIe card. [Pentek]

Many server processors require active heat sinks – where flowing air or liquid enhances the sink’s cooling performance. A common example is incorporating a small fan within a sink’s cooling fins. As an example, a PCIe carrier card, found in some server schemes, has a cutout opening directly under the warmest components. This allows the use of a fan-equipped heat sink that removes heat effectively from those components on the inside surface of an attached XMC module. The embedded fan forces air across the fins for active cooling.

Figure 6. A Candlestick sensor measures air temperature and velocity at different locations on server cards. [Advanced Thermal Solutions, Inc.]

Sensors can be helpful for finding dead spots in cooling airflow. They can help determine if moving a fan or using a different fan with a higher CFM rating improves cooling results. Since air flow is hard to visualize, the best solution is often found by trial and error.

Component Level Cooling

A new active heat sink solution for server CPUs, including the Intel Xeon (Haswell and Skylake), AMD Opteron series and Cavium ThunderX ARM CPUs.  The thermal solution integrates a heat sink, heat pipes or vapor chamber, and blower. The DualFLOW heat sink is designed in low profile for 1U and 2U rack servers. It has rows of embedded heat pipes in its base to help transfer large volumes of component heat into a dense fin field. The blower on top draws air inward, across the many fin surfaces, then pushes this warmed air out and away.

Figure 7. A DualFLOW heat sink with heat pipes embedded in its base and a PWM-enabled blower on top. [Advanced Thermal Solutions, Inc.]

The DualFLOW heat sink can be mounted onto PCBs using PEMs or screws inside springs. Both kinds of hardware allow adjusting so the heat sink is mounted for optimum performance. Its initial mounting force is 9.2 PSI. A thermal grease interface assures excellent thermal transfer from component to the heat sink’s base. For added cooling performance, a PWM controllable fan can be mounted above the heat sink fin field.

References:
1. https://journal.uptimeinstitute.com/a-look-at-data-center-cooling-technologies/
2. http://www.coolitsystems.com/index.php
3. http://www.fujitsu.com/global/products/computing/servers/unix/sparc/technology/ecology/llc.html
4. https://www.blackbox.com/
5. http://www.datacenterjournal.com/whats-stopping-liquid-cooling/
6. http://www.pentek.com/pipeline/22_2/cooling.cfm
7. http://www.dcdi.co.uk/product/25/19-racks/136/fans-rack-cooling/617/3u-19-rack-mounted-3-fan-unit
8. http://www.qats.com/Products/Instruments/Temperature-and-Velocity-Measurement/Sensors/Candlestick-Sensor
9. http://www.cableorganizer.com/computer-cabinets/rack-fans.htm
10. http://www.electronicsprotectionmagazine.com/main/articles/increase-rack-cooling-efficiency-and-solve-heat-related-problems/

Thermal Solutions for Servers Part 1

In this two part blog series, ATS gives an overview of the challenges and solutions in cooling servers that are used for cloud computing.

Part One – Aisles and Cabinets

A major issue with servers is the heat they generate and the heat that surrounds them. This heat has to be managed to ensure proper server performance. Even server installations with integral cooling systems may have to contend with higher power electronics or higher volumes of hot processors than they were originally designed for.

Server rooms, enclosures, racks and PCBs are all typically crowded, which poses challenges to cooling solutions at every level. And, in most cases, multiple solutions are needed. The good news is that for each of these applications, a range of cooling methods is usually available.

At the macro level these methods include cabinet positioning, ventilation fans, blanking panels to maximize cold air flow, portable air conditioning units, and skirts and barriers to direct cold air. At the micro level, liquid cooling integrated with heat sinks and spreaders provide effective chip level cooling.

Figure 1. Hot aisle/cold aisle room layouts are widely regarded as the starting point for heat management and energy efficiency in server rooms. [42U Data Center Solutions]

For server rooms, laying out hot aisles in between cold aisles has helped solve many heat issues and remains in common use. Typically, air from the hot aisles is captured by CRAC (computer room air conditioning) units, cooled, and then distributed to the cold rows via perforated flooring systems.

Portable air conditioners, such as the ClimateCab AC units by Black Box, attach directly to racks or enclosures to directly cool components. Many sizes of combined cabinet/AC units are available, including Black Box’s range of NEMA 12 server cabinets with M6 or tapped rails and various cooling capacities.

Figure 2. AC Units attached to server enclosures save money by cooling the cabinet and not an entire room. ([Black Box Network Services]

Server-filled data centers are often built as add-ons to existing facilities. The cooling system provided for these custom-added centers can be less reliable than the central HVAC installation, resulting in periodic down-times and longer-term outages. Portable air conditioners are available to provide extra cooling to heat sensitive areas during system outages or when extreme conditions occur. These units can protect equipment – and inhabitants – from overheating when the temperature demands exceed the capacity of a building’s climate system.

One example of these AC units is the Office Pro 63 portable cooler from MovinCool. This is a high end, high performance cooler. It provides 60,000 Btu/h cooling performance which can readily cool large spaces such as server/telecom equipment rooms. The Office Pro 63 has a programmable controller for continuous operation, and an automatic condensate pump.

Figure 3. The Office Pro 63 Portable Cooler Provide 60,000 Btu/h Cooling to Lower Temperatures in Electronic Equipment Rooms. [MovinCool]

MovinCool also produces the CM12, a ceiling-mounted packaged air conditioner. It fits into an existing drop-ceiling to save space in server rooms with limited floor space.

A range of specialty portable coolers can provide spot cooling in troublesome server hot spots. This capability can remove the need and expense of installing a permanent air conditioning system. These devices are economical and efficient, cooling only the area or object which must be cooled. Portable coolers require minimal installation, and are easily moved from one room to another. Cooling air is delivered instantly.

Figure 4. The 5KK30 Air-Cooled Portable Air Conditioner with 29,000 Btu/h Cooling Capacit]. [Koldwave]

For multiple hot spots, the air-cooled portable 5KK30 system from Koldwave delivers cooling air to different locations via three air flexible air outlets. The quiet-running unit is designed for ambient temperature is simple to install and operate. It has a cooling capacity of 29,000 Btu/h.

The engineers at TrippLite recommend the use of blanking panels to fill unused rack spaces. This forces cold air through equipment and prevents hot air from recirculating through open spaces. Snap-in 1U blanking panels install easily and the 1U size fills empty rack spaces evenly. Tripplite suggests installing brush strips, gaskets and grommets to block air leaks around cable channels and other gaps.

Another technological approach is the use of vortex enclosure cooling systems. These work by maintaining a slight pressurization inside a cabinet to keep electrical and electronic components clean and dry. Most vortex systems are thermostatically controlled to maintain enclosure temperatures within a specified temperature range.

The core of this technology is vortex tubes, mechanical devices that separate compressed gas into hot and cold streams. Air emerging from the cold end can reach -50°C, while air emerging from the hot end can reach 200°C. The tubes have no moving parts.

EXAIR Cabinet Cooler systems use vortex tube technology to create a cold air outlet flow which is pumped into an electronic cabinet. As air is pushed into the cabinet the Cabinet Cooler system also provides its own built-in exhaust so there is no need to vent the cabinet. This creates a positive purge on the cabinet which will keep out dirt, dust and debris.

Figure 5. The ETC Dual Cabinet Cooler System Minimizes Compressed Air Use and Produces 20F Air for Cabinet Cooling. [EXAIR]

Every server installation is unique, and from its components to its cabinets to its room environment there are likely to be heat issues. The above discusses some of the more common thermal solutions in use today at the aisle and cabinet level.

Ahead we will discuss cooling solutions for servers at the component and PCB level.  Click here to reach Part 2.

References:

  1. http://www.42u.com/
  2. https://www.blackbox.com/
  3. http://movincool.com/
  4. http://koldwave.com/
  5. http://exair.com
  6. http://www.cableorganizer.com/computer-cabinets/rack-fans.htm
  7. http://www.cableorganizer.com/tripp-lite/smartrack-air-conditioning-unit/
  8. http://www.airpacinc.com/blog/bid/82753/5-Simple-Server-Room-Cooling-Solutions
  9. http://www.chilleddoor.com/discover-chilleddoor
  10. http://www.electronicsprotectionmagazine.com/main/articles/increase-rack-cooling-efficiency-and-solve-heat-related-problems/

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