Tag Archives: maxiFLOW

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

We Own 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.

How Did Thermal Performance of Aluminum Heat Sink Compare to Copper?

Advanced Thermal Solutions, Inc. (ATS) was recently tasked with creating a more cost-effective and lighter solution for a customer that was looking to replace a relatively large heat sink, which was dissipating the heat from four components on a printed circuit board (PCB). The customer did not want a skived heat sink, so ATS engineers created a custom aluminum heat sink embedded with copper heat pipes to draw the heat away from the components.

Aluminum Heat Sinks

ATS engineers worked on a comparison of a copper heat sink with an aluminum heat sink that had embedded heat pipes running above the components. Analysis showed that the aluminum heat sink nearly matched the thermal performance of the copper and was within the margin required by the client. (Advanced Thermal Solutions, Inc.)

ATS engineers used analytical modeling and CFD simulations to examine the thermal performance of two aluminum heat sink designs: one with heat pipes that stopped at the edge of the components and the other with heat pipes that ran above the components. Analysis demonstrated that the design with heat pipes running above the components kept junction temperatures within 2°C of the original copper heat sink and an average difference of less than 1°C.

Peter Konstatilakis, a Field Application Engineer at ATS who worked with the client on this analysis, sat down with Marketing Communications Specialist Josh Perry to discuss the technical details behind the thermal analysis and the results that were presented to the customer.

JP: Thanks for taking the time to talk about this project Peter. What was it that they approached you with? What was the problem or the challenge?
PK: There was a long lead time with sourcing this copper; it’s a relatively large and heavy part.  This size bar of copper isn’t typically stocked. So, we were having sourcing issues with this non-standard copper stock and they were having weight and cost issues. They had to cut this heat sink in half for testing because they were overweight on the board. Through shock and vibe testing, if the heat sink is too heavy then it can actually rip out of the board.

An alternative was to make the heat sink through a manufacturing process called skiving. Skived heat sinks have a fin count tolerance, so you may have more fins than are specified or you might have less fins, and some of the fins may be curved, which poses cosmetic issues with skived heat sinks; the fins aren’t perfectly straight. It’s not really an issue thermally, especially if companies don’t see the heat sinks too often, but this client’s customers see the boards, see the heat sinks, and they wanted them to look perfect.

Instead of having to get this copper, we thought, why don’t we make an aluminum heat sink with heat pipes? That’s sort of where this came from.

JP: So the problem with skiving a heat sink was mostly an issue with aesthetics?
PK: Yeah, exactly. The tolerance on the fin spacing was +/- three fins, due to the high number of fins. I did a quick analytical analysis with our heat sink calculation tool and the difference in thermal resistance was maybe 1%. That was because the heat sink has such a large surface area and losing a fin or two only changes the performance by a percent or less. On a smaller heat sink, you will see a greater difference. I told the customer but they said that they still didn’t want to go with skived for aesthetic reasons. Instead, we extruded aluminum and then we put heat pipes in the base.

JP: Why was it necessary to add heat pipes to the heat sink?
PK: The big thing, in this case, is the spreading. You can see the locations of the components and then how large the heat sink is. There’s definitely a lot of spreading resistance in the base because there’s so much distance between the heat sink and all the components, so that’s the main issue that we were trying to take care of with the heat pipes. An aluminum heat sink with heat pipes is definitely a lot lighter than a copper heat sink, about three times lighter. Overall it’s much easier to source and also much cheaper. I think it’s again about three times as much for copper.

JP: When this challenge came across your desk, what was the first thing that you looked at? How did you approach the challenge?
PK: What I did was look at our analytical tool again and I modeled this heat sink in all copper. Since there are four components it’s a little complicated, but I modeled them as one component in the middle of the heat sink with gap pad and everything and got the performance of that heat sink. Once I did that, I ran CFD simulations on the copper heat sink with the components placed as they are in the application and the performance values were within 15%. So, doing that, we knew that we had a good CFD model.

After running the baseline simulations on the copper, I moved onto the aluminum heat sink knowing that we had a good CFD model and that we could trust the results. I used the aluminum heat sink and put heat pipes in the base. I started with heat pipes out in front of the components and then the next simulation was with heat pipes above the components. Obviously, if the heat pipes are above the component then you’ll get a little better spreading resistance and the heat will flow better.

Aluminum Heat Sinks

The first of two aluminum heat sink designs had heat pipes that stopped at the components. This design was not as effective as when the heat pipes ran above the components. (Advanced Thermal Solutions, Inc.)

JP: How significant of a difference was it?
PK: From the base line of the copper heat sink, it was around a 1-2°C difference, on average.

After looking at these two simulations, I met with Dr. Kaveh Azar (founder, CEO and President of ATS) to discuss the results. With the heat pipes above the components, we were seeing an average difference of less than 1%. It performs worse by less than 1% and I’m currently doing a couple of other simulations to see if we can improve that by adding more heat pipes, making the heat pipes wider, or even running less conservative heat pipes since the conductivity I’m running with is 2000 W/m-K axially and 400 W/m-K through the cross section. Really, the axial conductivity should be around 20,000-50,000 W/m-K, and the copper wall and wick effective conductivity is around 100-200 W/m-K due to the low conductivity of the porous copper sintered wick. The conservative values I used were to get the simulation up and running, while I’ll end up analytically determining the respective heat pipe conductivity.

I’m also doing an all-aluminum simulation just so we can see what that looks like and so we can see how much better the copper heat sink is in general.

This turned into just looking at the heat sink and trying to put heat pipes in them to seeing if we could also vary the length and see if we could get better performance. Your pressure drop increases as the length increases, so the higher the pressure drop then the lower the air flow is going to be in the system, the lower the airflow then the lower the performance. There is sweet spot for the length. I’m looking at that with our analytical calculator. And then the base thickness as well, we’re looking at that too.

Aluminum Heat Sinks

The results of the CFD analysis showed that the average temperature difference between the copper and the second aluminum heat sink design was less than one degree. (Advanced Thermal Solutions, Inc.)

JP: With the aluminum heat sink within 1% of the copper, did that make switching from copper worth it for the customer?
PK: It definitely did. If you’re within 1% and the customer has a little margin already, then it’s worth it because it’s three times lower cost, lower weight, and it will look better because it’s extruded rather than skived.

JP: Just to clarify, what is the difference between skiving and extruding?
PK: Extruding, basically, is pushing a hot piece of metal through a die that is in the shape of a heat sink, so it’s like putting play-doh through a die. You get a heat sink with the fin pitch and everything, where skiving uses a copper block and they come in with a blade and peel the fin out. The blade comes in and pushes a layer up. You can skive aluminum as well and they’re about the same cost, but you can’t extrude copper for a heat sink.

This showed our thermal capability to the customer. It showed that we can design custom heat sinks. We can make them more cost-effective, better performing, whatever they need.

JP: When you’re working through these types of challenges, how much of it becomes a foundation of knowledge that you can then take to another customer’s project?
PK: The more experience that you have, the better. Like any field, the more experience you have then you can look at something and know right off the bat if it’s going to work or not. It also helps in terms of understanding how to model certain applications and where to start with the design.

JP: Did we run these simulations here or did we have (ATS engineer) Sridevi Iyengar run the simulations in India?
PK: We did it here. Sri does a lot, but she uses FloTHERM and I’m quicker with Autodesk CFDesign. FloTHERM can be used for bigger systems because it takes less of a mesh. Generally, FloTHERM only works in rectangular coordinates, where CFDesign works with tetrahedrons, allowing the simulation of angled objects. Since it works with tetrahedrons though, it takes longer to mesh and run than FloTHERM. You can’t really have anything angled in FloTHERM and obtain accurate results. We ended up having to angle the heat pipes in order to contact the components, which are in a different plane than the rest of the heat sink.

JP: I know it is a priority at ATS, but why was it important to have an analytical component, not just CFD, in finding a solution?
PK: Analytical modeling is used to ensure that the CFD results make sense. When you see the graphs from CFD, it looks appealing to the eye and you get drawn to it. It’s science and engineering that is made visible, whereas heat transfer and fluid dynamics (for air) are invisible to the naked eye. Another method of ‘seeing’ heat transfer is using an infrared thermal camera or liquid crystal thermography, while a water tunnel or inducing smoke into the flow can be used to see fluid flow. The analytical also gives us a good first judgement and solid design direction.

Optimization for the length of the heat sink and the base thickness, I did with our analytical tool. CFD simulations take a lot of time, so I can narrow down the number of designs and determine what we want to simulate. Rather than doing 10 different simulations, when each takes on average three or four hours, I can get instant results and say, okay, a 5 mm base is the sweet spot, so let me try in CFD 4 mm thickness, 5 mm, and 6 mm; narrowing it down to three simulations.

Analytical modeling gives us quick what-if scenarios, which we say a lot, and it definitely helps give you an understanding of what to expect. If the numbers are way off then I know something is wrong in the CFD model and I check to see if my mesh and other parameters are correct. It humbles you almost and it helps you understand the application and what you’re simulating. The last thing you want to do is give a customer incorrect data.

It gives you two independent solutions. We say analytically this solution is validated, so we have faith in the model. Now, here is the model and it shows better what we want to do.

To learn more about Advanced Thermal Solutions, Inc., visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.

Power Brick: #GoldStandard Heat Sinks for DC/DC Converters

Power Brick

ATS Power Brick heat sinks are the #GoldStandard for cooling eighth, quarter, half, and full brick DC/DC power converters. (Advanced Thermal Solutions, Inc.)


Advanced Thermal Solutions, Inc. (ATS) has a line of Power Brick heat sinks (available through Digi-Key Electronics and Arrow) that are specially designed to cool eighth-, quarter-, half-, and full-sized DC to DC power converters and power modules. Power Brick heat sinks feature ATS’ patented maxiFLOW™ design, which reduces the air pressure drop and provides greater surface area for more effective convection cooling.

Power Brick heat sinks are a critical component for the optimal thermal management of electronic devices because DC/DC power converters are used in many applications and across a number of industries, including communications, health care, computing, and more.

DC/DC converters are electronic circuits that convert direct current (DC) from one voltage to another. Converters protect electronic devices from power sources that are too strong or step up the level of the system input power to ensure it runs properly. The process works by way of a switching element that turns the initial DC signal into a square wave, which is alternating current (AC), and then passes it through a second filter that converts it back to DC at the necessary voltage.

As explained in an article on MaximIntegrated.com, “Switching power supplies offer higher efficiency than traditional linear power supplies. They can step-up, step-down, and invert. Some designs can isolate output voltage from the input.”

When converting electrical input to the proper voltage, DC/DC converters operate at a specified efficiency level, with some energy lost to heat. ATS Power Brick heat sinks provide the necessary step of dissipating that heat away from the converter to lower the junction temperature. This will optimize the performance of the component and ensure the longevity of the converter.

Anodization boosts Power Brick heat transfer capability

The pleasing gold color that has made Power Brick one of the most popular lines of heat sinks for DC/DC converters stems from the anodization process that ATS uses for its heat sinks. Anodization, as noted in an earlier blog post on this site, “changes the microscopic texture of a metal, making the surface durable, corrosion- and weather-resistant.”

Surface anodization works by turning the metal into the anode (positive electrode) of an electrolytic circuit. By passing an electric current through an acidic electrolytic solution, hydrogen is released at the cathode (negative electrode) and oxygen is released at the anode. The oxygen on the surface of the metal anode forms a deposit of metal oxide of varying thickness – anywhere from 1.8-25 microns.

The previous article explained, “The advantages of surface anodizing are the dielectric isolation of the cooling components from their electronics environment, and the significant increase in their surface emissivity.”

The emissivity coefficient of an anodized surface is typically 0.83-0.86, which is a significant boost from the standard coefficient of aluminum (0.04-0.06). By increasing the emissivity of the metal, there is also a significant enhancement of the metal’s radiant heat transfer coefficient.

The eye-catching gold color of ATS Power Brick heat sinks is added during the anodization process.

maxiFLOW™ design gives Power Brick an edge

Anodization of heat sinks is a standard practice to ensure that the metal components can withstand the rigors of dissipating heat from high-powered components. The feature that gives an ATS Power Brick heat sink the significant edge on its competitors is its patented maxiFLOW™ fin geometry, which has higher thermal performance for the physical volume it occupies compared to other heat sink designs.

maxiFLOW™ design is a low-profile, spread-fin array, which offers greater surface area for convection cooling. While it offers more surface area, it does not require additional space within the electronics package. This is an important feature in today’s electronics devices, which have an ever-increasing component density and in which space is always at a premium. This is an especially important feature for designers that want to cool DC/DC converters but are limited in the amount of available room.

Independent testing at Northeastern University of various heat sink designs demonstrated that maxiFLOW™ had the lowest thermal resistance for natural and forced convection, particularly when air flow velocity was below two meters per second. For heat sinks with the same base dimensions and fin height, maxiFLOW™ performed the best.

Testing has demonstrated that maxiFLOW™ can produce 20 percent lower junction temperatures and 40 percent lower thermal resistance than other heat sink designs. Utilizing maxiFLOW™ allows ATS Power Brick heat sinks to meet the industry standard base plate temperature of 100°C.
For more information about maxiFLOW™, watch the video below:

Power Brick meets industry standards

In the DC/DC market, there are a number of standard footprints that manufacturers use to offer flexibility for designers in choosing a vendor and in laying out a PCB. ATS has addressed the industry standard footprints with its Power Brick heat sinks. This will facilitate the use of the heat sinks for thermal management.

By optimizing the thermal management and meeting industry standards, Power Brick heat sinks can provide cost savings and reduce MTBF. Rather than having to over-design a system or a layout, engineers can turn to Power Brick as a thermal solution.

It is not only the industry standard footprints that Power Brick heat sinks have matched but also the standard hole patterns, which meet the standards set by the Distributed-power Open Systems Alliance (DOSA) to make assembly easy. The three millimeter holes (and soon 3.5 mm) match up to sizes commonly used in power brick manufacturing to ensure the proper connection for the heat sink (to avoid increasing the thermal resistance) and also to avoid using additional space in the tight confines of a PCB.

For the above reasons, Power Brick heat sinks are the “gold standard” for cooling DC/DC converters. Learn more in the video below:

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

References

i http://uk.rs-online.com/web/generalDisplay.html?file=automation/dc-converters-overview&id=infozone
ii https://www.maximintegrated.com/en/app-notes/index.mvp/id/2031
iii https://www.qats.com/cms/2010/11/09/how-heat-sink-anondization-improves-thermal-performance-part-1-of-2/
iv https://www.qats.com/cms/wp-content/uploads/2013/09/Qpedia_Oct08_How-Air-Velocity-Affects-HS-Performance.pdf

Case Study: PCB Cooling for Telecom Application

PCB Cooling for Telecom

The layout of the PCB with the smaller but most power-dissipating component on the left and the larger, but less power-dissipating component on the right. Originally both components were covered by straight-fin heat sinks embedded with heat pipes. (Advanced Thermal Solutions, Inc.)


Engineers at Advanced Thermal Solutions, Inc. (ATS) were brought into a project to assist a client with cooling a PCB that was going to be installed in telecommunications data center. The board currently had heat sinks embedded with heat pipes covering the two hottest components but the client wanted a more reliable and cost-effective solution.

ATS engineers used the company’s patented maxiFLOW™ heat sinks to replace the heat pipes and through analytical and CFD modeling determined that by switching to maxiFLOW™ the junction temperature and case temperature would be below the maximum allowed.

Challenge: The client had a new PCB over which air could flow from either direction and two of the highest power dissipating components were on opposite sides.

Chips/Components: WinPath 3 and Vector Processor

Analysis: Analytical modeling and CFD simulations determined the junction temperature with air going from left-to-right and right-to-left and ensured it would be lower than the maximum allowable (100°C for one component and 105°C for the other).

Test Data: With air flowing from left-to-right, CFD simulation determined that the junction temperatures would be 89.3°C and 101.4°C – below the maximum temperatures of 100°C and 105°C. With air flowing from right-to-left, the junction temperature of the most power-dissipating component was 100°C, which was right at the maximum, and the second was at 87°C, which was below it.

Solution: The original heat sinks embedded with heat pipes were switched for maxiFLOW™ heat sinks, with their placement offset slightly to create a linear airflow, and the same levels of thermal performance were achieved.

PCB Cooling for Telecom

ATS engineers changed the embedded heat sinks for maxiFLOW™ heat sinks and received the same thermal performance with a more reliable and cost-effective solution. (Advanced Thermal Solutions, Inc.)

Net Result: The client received the required level of cooling in the PCB, regardless of the direction of air flow, and with a more reliable and cost-effective solution than had been previously been in use.

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

Technical Discussion of ATS Telecom PCB solution

Last year, Advanced Thermal Solutions, Inc. (ATS) was brought in to assist a customer with finding a thermal solution for a PCB that was included in a data center rack being used in the telecommunications industry. The engineers needed to keep in consideration that the board’s two power-dissipating components were on opposite ends and the airflow across the board could be from either side.

Telecom PCB

The PCB layout that ATS engineer Vineet Barot was asked to design a thermal solution for included two components on opposite ends and airflow that could be coming from either direction. (Advanced Thermal Solutions, Inc.)

The original solution had been to use heat sinks embedded with heat pipes, but the client was looking for a more cost-effective and a more reliable solution. The client approached ATS and Field Application Engineer Vineet Barot examined the problem to find the best answer. Using analytical and CFD modeling, he was able to determine that ATS’ patented maxiFLOW™ heat sinks would provide the solution.

Vineet sat down with Marketing Director John O’Day and Marketing Communications Specialist Josh Perry to discuss the challenges that he faced in this project and the importance of using analytical modeling to back up the results of the CFD (computational fluid dynamics).

JP: Thanks for sitting down with us Vineet. How was the project presented to you by the client?
VB: They had a board that was unique – where it would be inserted into a rack, but it could be inserted in either direction. So, we faced a unique challenge because airflow could be from either side of the board. There were two components on either side of the board, so if airflow was coming from one side then component ‘A’ would get hot and from the other side then component ‘B’ would get hot. The other thing was that the customer, who is a very smart thermal engineer, had already set up everything and he was planning on using these heat sinks that had heat pipes embedded in them. The goal was to try and come up with a heat sink that would do the same thing, hopefully without requiring the heat pipes.

JO: Can we talk for a second about the application? You mentioned that airflow was from either side, the board was going to be used in a data center or a telecom node?
VB: It was for a telecom company.

JP: Was there a reason he didn’t want to use a heat pipe?
VB: I think probably cost and reliability. We use heat pipes embedded in the heat sinks too, so it’s not a something we never want to use, but the client wanted to throw that at us and see if we had alternatives.

JP: Can you take us through the board and the challenges that you saw?
VB: As you can see from this slide, there are four main components and two of the hottest ones are on the edge. Airflow can be from right to left or left to right, so which one would be the worst-case scenario?

Telecom PCB

JO: From right to left, I think?
VB: Correct. This one is a straightforward one to figure out because not only is the component smaller but the power is also higher. Even though [air] can go both ways, there’s a worst-case scenario.

This was the customer’s idea – a straight-fin heat sink with a heat pipe and he put one block of heat pipe in there instead of two or three heat pipes that would normally be embedded in there. You can clearly see what the goal was. You have a small component in here, you want to put a large heat sink over the top and you want to spread the heat throughout the base of the heat sink. All the other components are also occupied by straight-fin heat sinks.

JO: Okay, at this point in the analysis, this is the rough estimate of the problem that you face?
VB: This is a straightforward project in terms of problem definition, which can be a big issue sometimes. This time problem definition was clear because the customer had defined the exact heat sink that they wanted to use. It’s not a bad heat sink they just wanted an improvement, cost-wise, reliability-wise.

This is the G600, which is the air going from left to right. The two main components are represented here and we want to make sure that the junction temperatures that the CFD calculated is lower than the maximum junction temperatures allowed, which they were. These heat sinks work. As we always like to do at ATS, we like to have two, independent solutions to verify any problem. That was the CFD result but we also did the analytical modeling to see what these heat sinks are capable of and the percent difference from CFD was less than 10 percent. Twenty percent is the goal typically. If it’s less than 20 percent then you know you’re in the ballpark.

(Advanced Thermal Solutions, Inc.)

(Advanced Thermal Solutions, Inc.)

JO: Do you use a spreadsheet to do these analytical modeling?
VB: HSM, which is our heat sink modeling tool, and then for determining what velocity you have through the fins, the correct way of doing this is to come up with the flow pattern on your own. You go through all the formulas in the book and determine what the flow will be everywhere or figure out what CFD is giving you for the fan curve and check it with analytical modeling. You can look at pressure drop in there, look at the fan curve and see if you’re in the ballpark. You can also check other things in CFD, for example flow balance. Input the flow data into HSM and it will spit out what the thermal performance is for any given heat sink. HSM calculations are based on its internal formulas.

JO: We effectively have a proprietary internal tool. We’ve made a conscious decision to use it.
VB: To actually use it is unique. Not everybody would use it. A lot of people would skip this step and go straight to CFD. We use CFD too but we want to make sure that it’s on the right path.

JP: What do you see as the benefit of doing both analytical and CFD modeling?
VB: CFD, because it’s so easy to use, can be a tool that will lead you astray if you don’t check it because it’s very easy to use and the software can’t tell you if your results are accurate. If you do any calculation, you use a calculator. The calculator is never going to give you a wrong answer but just because you’re using a calculator doesn’t mean that you’re doing the math right. You want to have a secondary answer to verify that what you did is correct.

JP: What was the solution that you came up with for this particular challenge?
VB: We replaced these heat sinks with the heat pipe with maxiFLOW™, no heat pipe needed. One of the little tricks that I used was to off-set the heat sinks a little bit so that these fins are out here and so the airflow here would be kind of unobstructed. And I set this one a little lower so it would have some fins over here, not much, that would be unobstructed. The G600 configurations worked out with the junction temperatures being below what the maximum requirement was without having to use any heat pipes for the main components. There is also a note showing that one of the ancillary components was also below the max. Analytical modeling of that was within 10-11 percent.

The final PCB layout with maxiFLOW heat sinks covering the hottest components on both ends of the board. (Advanced Thermal Solutions, Inc.)

The final PCB layout with maxiFLOW heat sinks covering the hottest components on both ends of the board. (Advanced Thermal Solutions, Inc.)

As you noted, this was the worst-case scenario, going from right to left and you can see because it’s the worst-case scenario this tiny little component here that’s 14 watts that’s having all this pre-heated air going into it, it’s junction temperature was exactly at the maximum allowed. That’s not entirely great. We want to build in a little bit of margin but it was below what was needed.

The conclusion here was that maxiFLOW™ was able to provide enough cooling without needing to use the heat pipes and analytical calculation agreed to less than 20 percent. We would need to explore some alternate designs and strategies if we want to reduce the junction temperature even further because that close to the maximum temperature is uncomfortable. The other idea that we had was to switch the remaining heat sinks, the ones in the middle, which are straight fin, also to maxiFLOW™ to reduce pressure drop and to get more flow through this final component.

(Advanced Thermal Solutions, Inc.)

(Advanced Thermal Solutions, Inc.)

JP: If you have an idea like that, is it something that you broach with the customer?
VB: They really liked the result. If this was a project where the customer said, ‘Yep, we need this,’ then we would have said here’s the initial result and we have an additional strategy. At that point the customer would have said, ‘Yeah this is making us uncomfortable and we need to explore further’ or they would have said, ‘You know what? Fourteen watts is a max and I don’t know if we’ll ever go to 14 watts or the ambient we’re saying is 50°C but we don’t know that it will ever get to 50°C so the fact that you’re at max junction temperature at the worst-case scenario is okay by us.’

JP: Do you always test for the worst-case scenario?
VB: It’s always at the worst-case scenario. It’s always at the max power and maximum ambient temperature.

JP: Was this the first option that we came up with, using maxiFLOW™? Were there other options that we explored?
VB: Pretty much. The way that I approached it was doing the analytical first. You can generate 50 results from analytical modeling in an hour whereas it takes a day and a half for every CFD model – or longer. These numbers here were arrived at with analytical modeling; the height, the width, the top width, were all from analytical modeling, base thickness to measure spreading resistance, all of that was done on HSM and spreadsheets to say this will work.

JP: Do you find that people outside ATS aren’t doing analytical?
VB: No one is doing it, which is really bad because it’s very useful. It gives you a quick idea if it’s acceptable, if this solution is feasible.

To learn more about Advanced Thermal Solutions, Inc. consulting services, visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.