Tag Archives: manufacturing

Industry Developments: Extrusion Profile Heat Sinks

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

Extruded metal heat sinks are among the lowest cost, widest used heat spreaders in electronics thermal management. Besides their affordability, extruded heat sinks are lightweight, readily cut to size and shape, and capable of high levels of cooling.

Metal Choices

Most extruded heat sinks are made from aluminum alloys, mainly from the 6000 alloy series, where aluminum dominates. Trace amounts of other elements are added, including magnesium and silicon. These alloys are easy to extrude and machine, are weldable, and can be hardened.

Common alloys for extruded heat sinks are the 6063 metals. These can be extruded as complex shapes, with very smooth surfaces. 6061 aluminum is also used for extrusions. Its tensile strength (up to 240 MPa) is superior to 6063 alloys (up to 186 MPa). In addition to heat sinks, these aluminum alloys are popular for architectural applications such as window and door frames. [1]

Extrusion Profile Heat Sinks
Figure 1. An extruded aluminum heat sink with a black anodized finish. [2]

The surfaces of these metals can be anodized to replace their naturally occurring surface layer of aluminum oxide. Anodizing provides more heat transfer, corrosion resistance and better adhesion for paint primers. It is an electrochemical process that increases surface emissivity, corrosion and wear resistance, and electrical isolation.

The Extruding Process

Aluminum alloys are popular for extruding as heat sinks because they provide both malleability and formability. They can be easily machined and are as little as one-third the density of steel. This results in extrusions that are both strong and stable, at a reduced cost relative to other materials.

Figure 2. Heated aluminum alloy billets are pushed through a die to produce extruded length heat sinks and other parts. [3]

The aluminum extrusion process starts with designing and creating the die that will shape the heat sink profile. Once this has been done, a cylindrical billet of aluminum is heated up in a forge to high temperatures, generally between 800-925°F (427-496°C). Next, a lubricant is added to the aluminum to prevent it from sticking to any of the machinery. It is then placed on a loader and pressure is applied with a ram to push heated aluminum through the die.

During this process, nitrogen is added in order to prevent oxidation. The extruded part will pass completely through the die and out the other side. It has now been elongated in the shape of the die opening. The finished extrusion is then cooled, and if necessary, a process of straightening and hardening creates the finished product.

They can be cut to the desired lengths, drilled and machined, and undergo a final aging process before being ready for market. [4]

Finished heat sinks typically come with anodized surfaces, which can enhance their thermal performance. Alternatively, a chromate finish provides some corrosion protection, or can be used as a primer before a final paint or powder coating is applied. [5]

Shapes of Extruded Heat Sinks

Extruded heat sink profiles range from simple flat back fin structures to complex geometries for optimized cooling. They can be used for natural (passive) or forced convection (active) with an added fan or blower. Extruded profiles can also include special geometries and groove patterns for use with clip or push pin attachment systems. [6]

Figure 3. Extruded heat sinks are available in many shapes and lengths. [6]

Extrusions are also available in bulk lengths, e.g. 8 feet, which can be cut to different lengths per customer needs.

Optimizing Thermal Performance

6063 aluminum alloy has a thermal conductivity of 201-218 W/(mK). Higher tensile strength 6061 aluminum’s thermal conductivity ranges from 151-202 W/(mK).

Besides choosing the aluminum alloy, selecting an optimal extruded heat sink should factor in its overall dimensions and weight, the specified thermal resistance, and the extrusion shape (flat-back, flat-back with gap, hollow, double-sided, etc.). [7]

Extruded heat sinks can be designed with very thin, and thus more, fins than other sink types. They can be extruded with aspect ratios of around 8:1, which can greatly optimize heat sink performance. A heat sink’s aspect ratio is basically the comparison of its fin height to the distance between its fins.

In typical heat sinks the aspect ratio is between 3:1 and 5:1. A high aspect ratio heat sink has taller fins with a smaller distance between them for a ratio that can be 8:1 to 16:1 or greater.

Figure 4. Different thin fin extruded heat sinks mounted on a PCB. [8]

Thus, a high aspect ratio heat sink provides greater density of fins in a given footprint than with a more common size sink. The great benefit is the increased amount of heat dissipating surface area it provides due to its additional fins. Further, these heat sinks do not occupy any more length or width. The result is a more efficient heat sink with higher performance per gram in the same footprint. [9]

Applications

An extruded heat sink is used mainly to increase the surface area available for heat transfer from high-power semiconductor devices, thus reducing a given semiconductor’s external case temperature, as well as its internal junction temperature.

Figure 5. Extruded heat sinks mounted on processors by clips (left) and push pins (right). [10]

This allows the semiconductor devices to perform at their highest level, with maximum reliability. Such semiconductor devices include (but are not limited to) RF power transistors, RF power amplifiers, Power MOSFETs, IGBTs, inverter power modules, and thyristor modules.

Figure 5. Extruded heat sinks screwed onto a brick DC-DC converter. [11]

In some power conversion circuit applications, large diodes, rectifiers, diode modules and even high-power resistors (thick film, etc.) can also require thermal contact with an extruded heat sink. For cooling DC-DC power converters and power modules, extruded heat sinks are available for full, half, quarter and one-eighth brick sizes

References

  1. https://en.wikipedia.org/wiki/6063_aluminium_alloy
  2. http://www.aluminumextrusionsprofiles.com/sale-7552970-black-anodized-aluminium-heat-sink-profiles-extruded-aluminum-heatsink-radiators.html
  3. https://www.aec.org/page/basics_basics
  4. https://www.clintonaluminum.com/6061-aluminum-vs-6063-in-extrusion-applications
  5. http://www.wakefield-vette.com/products/natural-convection/thermal-extrusions-overview/CategoryID/15/Default.aspx
  6. https://www.boydcorp.com/thermal/heat-sinks/extruded.html
  7. http://www.richardsonrfpd.com/Pages/Product-End-Category.aspx?productCategory=10188
  8. http://www.getecna.com/products/heat-sinks/
  9. https://www.qats.com/cms/2013/04/11/increased-performance-from-high-aspect-ratio-heat-sinks/
  10. https://www.qats.com/Heat-Sink/Attachments
  11. https://www.powerelectronics.com/thermal-management/heat-sinks-cool-brick-dc-dc-converters

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 
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Are More Efficient Heat Sinks Really Costlier?

The question arises, why pay more for a higher-efficient heat sink that is also smaller and lighter in weight, especially in cases whereby a simple, larger but heavier cast or extruded heat sink can also do the job? In most cases, the single piece part price is the main driver as to why engineers and purchasers stay with lesser effective solutions. This is generally because they believe that they are saving money for the company in the long-run.

But, is this really true?

It is very easy to compare the price of two single heat sinks, a highly efficient one versus a standard extruded type with the same thermal performance. But such a simplistic comparison does not take into account the flow performance, effect on neighboring and downstream components, weight, volume usage, etc.

More Efficient Heat Sinks

(Advanced Thermal Solutions, Inc.)

What makes a heat sink an efficient heat sink you may wonder? Such a heat sink is optimized for both flow and heat transfer and, hence, makes much better use of the volume available for cooling and the existing cooling air. The geometry of the heat sink is optimized by using thin fins and a special design to lower the air resistance, resulting in the highest possible velocity in the fin field, while minimizing the effect of bypass flow. Because of this, it also has a lesser intrusive effect to the flow, which has a positive effect on the neighboring and downstream flows. This produces lower pressure drops over the board and through the system. The result of a comparison test, presented by Lasance C.J.M. and Eggink H.J., demonstrates this. [1]

The shape and the number of fins create the available surface area. The more surface area in contact with cooling air, the more energy can be dumped into the air and, therefore, the lower the heat sink temperature. Most important, the component temperature will also be lower. Of course, this is only valid if the temperature of cooling air going through the fin field is still lower than the fin temperature; otherwise, no net heat transfer from the heat sink to the air will occur. As has been shown in the literature, there exists an optimum correspondence between the number of fins and the overall cooling effect of these fins.

To arrive at a better comparison, let us look to other related effects which will result in a system price increase due to the chosen cooling solution:

  1. Effect on the flow
  2. Heat sink weight
  3. Heat sink attachment
  4. Mechanical adjustments required to handle the weight on both a board and system level, and to fulfill mechanical requirements for shock and vibration
  5. Raw material usage to manufacture the cooling solution
  6. Required fan performance
  7. Product reliability
  8. Transportation cost
  9. End of life cost

Figure 1 shows a picture of a flow visualization test through a pin fin and the DUT. Compare the amount of flow entering the pin fin and the DUT, which in this case is a maxiFLOW™ heat sink. Most of the water “hitting” the pin fin is bypassing it because of the high air resistance of the fin field. Look at the flow that is left over downstream of the pin fin, which is lower than the upstream flow. Imagine what will happen if we put multiple pin fins in a row downstream of each other because we have to cool multiple devices in a row.

Fig. 1- Flow Test on Both a Pin-Fin (Left) and DUT (Right) in a Water Tunnel. The flow is from top to bottom. (Advanced Thermal Solutions, Inc.)

The first pin fin will have sufficient cooling but, the further we go downstream, the less effective the heat sink becomes. Limited air will be available for cooling, because most of the air is bypassing the heat sinks. What is the first reaction without knowing anything about the flow structure? We need a larger heat sink downstream to get the same cooling effect; or maybe we need to consider a more powerful fan system to drive more air through the system. However, if we would have started from a system level point of view instead of concentrating on a single heat sink, we would have studied the flow field and the interaction between the heat sink and the flow more closely, and we could have arrived at a better solution.

For example, in many cases the total number of heat sinks can be reduced, because other components are better cooled and probably do not require additional cooling.

Standard extruded heat sink profiles and cast heat sinks normally have a thick base and thick fins and are made of lesser thermally conductive aluminum alloys. The lower conductivity is a result of the additives that are included, to make the manufacturing of the product easier. The base and the fins tend to be thicker, because it is more difficult to manufacture thin and tall fins. Especially for natural convection, the optimum heat sink from a thermal point of view can easily be a factor of ten thinner than what is offered. The main design driver for these types of heat sink is the ease of manufacturing and not the overall thermal performance. The end result is a more voluminous and heavier heat sink that makes bad use of the available volume and has a negative effect on the flow.

To have a stable mechanical design, a stronger mechanical attachment to the component/board is required to handle the weight of standard heat sinks, as compared to high performance ones. An efficient light weight heat sink can still be attached by taping, glue, and other attachment methods, which use the component itself as an anchor.

Counting the weight of a standard heat sink and its attachment mechanism together, the overall product weight will be quite higher than for a design based on more efficient cooling solutions.

The same is valid for those LED designs that use the housing as a heat sink. The housing often is made by extrusion or casting processes, which limit the freedom of design. They are generally made of zinc aluminum (Zamac) with a thermal conductivity around 115 W/mK; whereas aluminum used for molding is between 100-150 W/mK; brass annealed is around 60 W/mK; aluminum alloy AL 6063 has a thermal conductivity of 201 W/mK and aluminum alloy AL 1050A reaches 229 W/mK.

Heat spreading is an important factor in most LED applications, and drives the thermal design of LED cooling. If analysis shows heat spreading is important, the consequence is that for lower conductivity materials, the only option is to either increase the base thickness or embed heat pipes or vapor chambers, adding to cost and weight.

LED Thermal Solution

Ephesus LED lighting solutions, with ATS thermal management design, was used in the recent Super Bowl at U.S. Bank Field in Minneapolis.

Forged heat sinks are made of high conductivity aluminum, but the manufacturing method itself is very limited in design freedom. So, in general, to get a better performance, a larger heat sink is required. For natural convection, the use of thermally conductive plastic could be of interest because of its lower weight and greater design freedom. Plastics enhanced with carbon fibers could also be used but require special attention because of their non-orthogonal conduction behavior. Other options are designs that are a combination of highly efficient heat sinks and heat pipes, to either improve heat spreading when the heat sink is much larger than the source, or to transport the heat from the source to a remote heat sink.

Apart from the attachment of the heat sink to one or more component, the overall weight of the board, including the cooling solutions, affects the overall mechanical design. Additional mechanical features are needed to make the product mechanically stable and these features will add cost and weight and further limit the design freedom.

As discussed before, a more voluminous heat sink solution requires more raw material. The initial manufacturing process of aluminum, however, is energy intensive, something we would like to decrease in a world where reduction of energy consumption is key. Fortunately, it can be recycled without the loss of its properties and the recycling process uses only a fraction of the energy in the initial manufacturing process. Finally, there are manufacturing techniques such as bonding, folding and skiving, that do not suffer from these sustainability issues.

Furthermore, a lesser efficient heat sink such as a pin fin or standard extruded type of heat sink, will lead to higher air resistance and lesser optimized flow over the components/ board and through the system. To overcome the higher air resistance and allow for more flow to compensate for the reduced airflow, a more powerful fan or more fans are required. A more powerful fan can mean either a larger fan type or permitting the current fan to run at a higher rotational speed. However, doubling the fan speed means increasing the input power to the fan by a factor of 8. As a result, more heat is dissipated in the system, the power supply has a higher current usage and more power is dissipated in the fan itself. This will lead to a higher fan temperature, thus reducing its lifetime. On top of this, a higher fan speed and more flow will result in higher noise levels.

Optimizing your thermal design by optimizing around the heat sink could in some cases avoid the use of a fan at all, making up for the extra costs of a more sophisticated heat sink. The use of more efficient cooling solutions will lead to a more optimized overall thermal design of the system, influencing directly the thermally and thermo-mechanically related reliability issues of the overall system. The transportation cost of the cooling solution to the manufacturer of the system also has a price. This price is based on shipped volume and weight. Efficient cooling solutions are lower in volume and lower in weight, so will yield a reduction in transportation costs. The weight factor is also applicable for the final product, as a product equipped with lesser weight cooling solutions will be cheaper to transport.

Apart from transport issues, a human effect is applicable: take, for instance, an LED-based streetlamp. Lifting a 30 kg lamp and installing it on a pole, versus lifting a 20 kg lamp, speaks for itself. Additionally, the pole needs to be designed in such a way that it can handle the weight of the lamp, potentially reducing the costs of a lesser weight lamp. Every product has a certain economic and technical lifetime and will be recycled afterwards. The cooling solution need to be recycled too. The heat sink, lamp enclosure – in most cases made of aluminium – can be recycled in a cost and energy effective way; but the lesser mass we recycle, the better.

In summary, the conclusion must be that it pays off to focus on the costs of the total system, and not only on the costs of the individual parts. In times long gone by, it was standard practice that project leaders got bonuses for buying parts as cheap as possible. Needless to say, such an attitude cannot survive in a world where end-users buy total systems, not a collection of parts. However, in the case of heat sinks, we still notice a sub-optimal purchasing policy, often based on lack of knowledge and outdated protocols.

References
1- Lasance, C.J.M., Eggink, H.J., “A Method to Rank Heat Sinks in Practice: The Heat Sink Performance Tester,” Proc. 21st SEMITHERM, pp. 141-145, San Jose, CA.

The New Qpedia Thermal eMagazine is Out

Qpedia Thermal eMagazine, Volume 7, Issue 4, has just been released and can be downloaded at: http://www.qats.com/Qpedia-Thermal-eMagazine/Back-Issues.

Featured articles in this issue include:

Dropwise Condensation in Vapor Chambers
Considerable attention has been devoted in the past to the evaporation process taking place in a vapor chamber. However, increased heat fluxes at the condensation end have prompted efforts to improve the condensation performance of the vapor chambers. This article presents a review of a novel method for improving the thermal performance of a vapor chamber condensing section by using special surfaces promoting dropwise condensation.

 

Heat Sink Manufacturing Using Metal Injection Molding

Using Metal Injection Molding It is only in the last few years that metal injection molding (MIM) has gained a foothold in the thermal community and its salient advantages have become more evident. The MIM process allows intricate features to be added into the heat sink design to boost thermal performance and its production process is very scalable compared with machining. Injection molding enables complex parts to be formed as easily as simple geometries, thereby allowing increased design freedom.  This article explore the merits of copper material in the MIM process.

 

Industry Developments: Thermoelectric Modules and Coolers

Thermoelectric modules (TEMs) are rugged, reliable and quiet devices that serve as heat pumps. The real heat-moving components inside TEMs are thermoelectric coolers or TECs. These are solid-state heat pumps and are designed for applications where temperature stabilization, temperature cycling, or cooling below ambient, are required. Today, TEMs are used in electro-optics applications, such as the cooling and stabilizing of laser diodes, IR detectors, cameras (charge coupled device), microprocessors, blood analyzers and optical switches. This article explores some of the latest developments in these devices.

 

Technology Review: Reducing Thermal Spreading Resistance in Heat Sinks

In this issue our spotlight is on reducing spreading resistance in heat sinks. There is much discussion about how this phenomenon can be achieved, and these patents show some of the salient features that are the focus of different inventors.

 

Cooling News featuring the latest product releases and buzz from around the electronics cooling industry.

 

Download the issue now.

 

Not a Qpedia subscriber? Subscribe Now for free at: http://www.qats.com/Qpedia-Thermal-eMagazine/Subscribe-to-Qpedia and see why over 18,000 engineers read Qpedia.

New Consulting Project Subscription Plan

ATS has released a Consulting Project Subscription Plan (CPSP) for engineering services. From our corporate headquarters in Norwood, Massachusetts,we offers comprehensive thermal management analysis and design services for the telecommunications, medical, military, defense, aerospace, automotive, and embedded computing industries. The new plan allows ATS engineers to become an extension of your team for a pre-determined amount of hours, providing expert thermal and mechanical engineering consultation, design, simulation, testing and validation.

ATS Design Services

Services include Design, Simulation, Testing, Analysis & Prototyping

The CPSP includes the use of ATS thermal lab facilities and covers all projects approved by an authorized representative of subscribed customers. ATS thermal management analysis and design services encompass both experimental and computational simulations using proprietary tools and computational fluid dynamics software packages such as FLOTHERM and CFdesign.

Thermal Testing & Analysis

Thermal Testing & Analysis

The new subscription plan gives customers priority access to ATS engineering and manufacturing resources for all chip, board, enclosure, and system related projects. ATS studies the full packaging domain, including components, circuit boards (PCBs), shelves, chassis, and system packaging.

Consulting capabilities include:

– heat sink, board and fan characterization

– heat sink design and optimization

– PCB & fan tray design and optimization

– liquid cooling design

– prototyping of heat sinks and complete cooling systems

– wind tunnel testing of components, PCBs, chassis and enclosures

ATS offers rapid prototyping of machined parts and cooling systems from its US facilities. Sheet metal fabrication and cut heat sink prototypes are quickly provided from international partners.

Liquid Crystal Thermography

Liquid Crystal Thermography

ATS believes that customers who wish to remain competitive should consider a design-to-suit opportunity solution first. Contrary to common perception, this proves to be less expensive to the customer in the long run, because of the ensuing gain in product efficiency and compatibility. Working side-by-side with customers worldwide, ATS engineers provide tailored solutions to thermal and mechanical packaging challenges on real projects with real schedules.

To learn more about the consulting project subscription plan, call 781-769-2800, email ats-hq@qats.com, or visit www.qats.com.

ATS Expands Its US-based Manufacturing Facilities

Advanced Thermal Solutions, Inc. has expanded its Massachusetts manufacturing facilities. This was necessary due to an increase in industrial orders and associated production requirements. The needs for metal and plastic parts and finished products have been growing as markets retool and expand, and buyers continually insist on higher quality, faster deliveries and larger volumes.

ATS expanded manufacturing services can provide contract manufacturing services on a fast, highest quality level. The Norwood facility will meet the needs of most global customers, from rapid prototyping and high volume manufacturing.

The enhanced facilities in Norwood, which is also the global headquarter for ATS, are fully equipped, environmentally responsible, and employ highly skilled staffers who work to extremely high professional standards. Multi-point inspections insure the highest quality manufactured products, from one-of-kind to multi-thousand part production orders.

ATS designs and builds for a wide range of industry requirements. Engineers and technicians manufacture for chassis-level integration, e.g. cooling hardware and other functionalities on network communication cabinets. The associates often design and fabricate stands, rack and display cabinets for retail and office environments.

Fabrication capabilities in metal and plastics include:
Metal and Plastic Extruding
Metal Stamping
CNC Machining
Metal Finishing
Sheet Metal Stamping and Plastic Forming
Plastic Welding

Besides its manufacturing facilities in Norwood, ATS operates factories in Futian, China, a thriving region of high tech manufacturing. The Futian facility is designed for making very high volumes of quality parts, as well as inventory and storage, and worldwide distribution services.

To learn more about ATS manufacturing capabilities, please visit: http://www.qats.com/Services/Manufacturing-Services/65.aspx