Category Archives: CFD

CFD With Analytical Modeling Gives ATS Edge

Posted on April 25, 2018 by | 3 comments

In January, Advanced Thermal Solutions, Inc. (ATS) and engineering simulation software leader Future Facilities announced that ATS had purchased multiple seats of 6SigmaET, an electronics thermal simulation software, adding to its CFD (computational fluid dynamics) capabilities.

CFD

ATS engineers are now using 6SigmaET to perform CFD on electronics cooling applications to find optimized thermal solutions for customers. (Advanced Thermal Solutions, Inc.)

In a joint press release from the two companies, ATS founder and CEO Dr. Kaveh Azar said, “We have decades of experience with a broad base of commercially available CFD tools. For the electronics thermal management analyses, 6SigmaET showed excellent agreement with our empirical and analytical modelling.

He added, “We were equally impressed with its ease of use and a short learning curve. Our engineering team was able to apply the tool to different levels of simulation extending from component to system level modelling. The speed of convergence and ease of use of 6SigmaET, have made it the first CFD software to use.”

6SigmaET becomes the lead thermal simulation software for ATS engineers dealing with standard electronics cooling challenges. ATS engineers will be able to quickly and efficiently simulate junction and ambient temperatures across boards and components or define airflow to find fan operating points or get a better understanding of pressure drop in a system.

Dr. Azar continued, “We always want to be working with the best breed of tools to deliver the innovative, high-quality and cost-effective thermal management and packaging solutions our customers expect. As a result, this addition is good news for our customers. The rich features of the 6SigmaET thermal simulation package not only enable us to do more when it comes to simulation, but also allows us to further deliver the solution to our clients in a shorter time interval. It is my highest compliment to 6SigmaET development team for putting together such a robust and effective software.”

Adding 6SigmaET to ATS CFD capabilities, which also includes FloTHERM from Mentor and Autodesk CFD (formerly CFdesign), enables engineers to save customers time in the design phase and makes it easier for ATS engineers to devise optimal thermal solutions.

ATS engineer Anatoly Pikovsky said, “Visual is definitely a great thing to have. If you look at this temperature map, for instance, you can look at the defined map and say right away, okay I have a very high temperature right in the middle.”

Pikovsky, who was working on Autodesk CFD to design a customized cold plate for a customer, demonstrated how the software allows for him to analyze the pattern of fluid flow through complex geometries that were imported from SolidWorks drawings. He used the software to show hot spots and fluid velocity and how small changes, such as the number of fins within the cold plate, could alter the results.

Field Application Engineer Vineet Barot explained that he used 6SigmaET on a board in which there was pressure drop coming from vents at the end of the board. In simulations, he was able to add fins to the heat sink without altering the fan operating point and quickly provide a thermal solution that was presented to a customer. He said, “If you had a standard 1-U chassis you can build it from scratch and run it in half an hour.”

While CFD continues to evolve to handle more complex problems, while also becoming easier to use for engineers, simulations are only part of the solution.

ATS engineers also perform analytical modeling, literally putting pen to paper with basic thermodynamic equations, to define the problem and provide a reference point for simulations. Coupling analytical and computer modeling is what sets ATS apart from its competitors because it ensures that thermal solutions provided by CFD are correct.

“CFD will give you a solution, whether it’s right or wrong, it will give you a solution,” Pikovsky said. “That’s the way it’s designed. Analytical coupled with CFD gives you a good reference point to know whether you’re in the ballpark.”

Analytical modeling also speeds up the process of finding an optimized solution. Rather than spending days or weeks plugging in different fin numbers and heights or trying numerous heat sink geometries, ATS engineers can define a small range of iterations, limiting the variables for CFD, to avoid countless simulations, each of which could take hours to run.

Pikovsky said, “Maybe you’ve designed a heat sink for certain airflow and you want to determine the number of fins. You can do it with CFD, but you start varying fins and it’s going to take you days. Analytical is great because you can determine the optimal number of fins and start CFD with that.”

CFD is a critical component of ATS thermal consulting and design services. 6SigmaET has quickly been adopted by ATS engineers as the lead software and been used in the design of thermal solutions for a number of customers in the past few months.

But, it is the combination of CFD with ATS engineers’ emphasis on analytical modeling that has made ATS a leader in the thermal management of electronics.

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.

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Posted in CFD, Consulting, Modeling, Simulation

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Heat Sink Design: ATS Engineers Bring Ideas to Life

Posted on June 29, 2017 by | 1 comment

Marketing Communications Specialist Josh Perry sat down with Product Engineering Manager Greg Wong to discuss the process that Advanced Thermal Solutions, Inc. (ATS) engineers go through to create a heat sink and find a thermal solution for customers.

Watch the full conversation in the video below and scroll down to read the transcript of the interview.

JP: Greg, thanks again for joining us here in marketing to explain what it is that goes into designing a heat sink for a customer. So, how does that process begin?
GW: We usually start with a few basic parameters; we call them boundary conditions. So, we start with a few boundary conditions, basics like how much airflow we have, how much space constraint we have around a heat sink, and how much power we’re dissipating, as well as the ambient temperature of the air coming into the heat sink.

So, those are the real basic parts that we need to start out with and sometimes the customer has that information and they give it to us, and usually we double-check too, and then other times the customer has parts of the information, like they know what fan they want to use and they know what kind of chassis they’re putting it in and we take that information and we come up with some rough calculations so we can arrive at those things like air flow and stuff like that.

JP: When you get the data from the customer, how do you determine what the problem is, so that way you can move forward?
GW: We usually start out with an analytical analysis. So, we put pen to paper and we start out with basic principles of heat transfer and thermal resistance and stuff like that so we can understand if what we’re trying to achieve is even feasible and we can come up with some basic parameters just using that analytical analysis.

Like we can calculate what kind of heat sink thermal resistance we need or we can calculate how much air flow we need or, if we have several components in a row, we can calculate what the rough air temperature rise is going to be along that chain of parts. So, there’s a lot we can do when we get the basic information from the customer just on pen and paper.

JP: What’s the next step beyond analytical?
GW: Well, we can do some lab testing or a lot of times we also use CFD simulations and, if our customer has a model they can supply us, we can plug that into the CFD simulations and we can come up with an initial heat sink design and we can put that into the simulations as well and then we set those up and run them.

The great thing, having done these analytical analyses beforehand, we know what to expect from CFD simulations. So that way, if the simulations don’t run quite right, we already have an understanding of the problem, we know what to expect, because CFD is not 100 percent reliable.

I mean, you can go and plug all this stuff in there but you really have to understand the problem to know if the CFD is giving you a good result. So, oftentimes that’s the next stage of the process and from there we can actually produce low-volume prototypes right here in Norwood (Mass.), in our factory. We have CNC machines and manual milling machines, lathes, all that kind of stuff, and we can produce the prototypes and test them out here in our labs.

JP: How much of a benefit is it to be able to create a prototype and to be able to turn one around quickly like that?
GW: Oh, it’s great. I mean, if we had to wait to get parts from China it will take weeks to get. We can turn them around here in a few days and the great thing about that is we can test them in our labs and, you know, when it comes to getting results nothing beats the testing.

I mean, you can do analytical analysis, you can do CFD simulations, but when you actually test the part in a situation that is similar to what the actual thing is going to be that’s where the real meat comes down.

Heat Sink Design

ATS engineers take customer data and using analytical modeling and CFD simulations can design the right cooling solution to meet the customer’s specific thermal needs. (Advanced Thermal Solutions, Inc.)

JP: So, we test the prototypes before sending them out to the customer? We do the testing here or do we send it to them first?
GW: It all depends on what the customer requires. Sometimes the customer has a chassis that we really can’t simulate in our labs, so we might send the prototype heat sinks to the customer and the customer will actually put them into their system to test them out.

Other times, a customer might have a concept and they don’t actually have a product yet, so we’ll mock something up in our labs and we’ll test it and it all just depends what the customer needs and also how complex the problem is.

If it’s a simple heat sink and pretty simple airflow, we might not need to test that because we understand that pretty well, but the more complex the chassis is and how the airflow bends and stuff like that, the greater benefits we get out of lab testing.

JP: Well, I appreciate it Greg. Thank you for taking us through the process of making a heat sink and solving thermal problems for our customers.
GW: Sure Josh. We love seeing new thermal challenges and coming up with ways of keeping stuff cool.

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.

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Posted in CFD, Chassis, Consulting, Engineering, heat sink, heat sink design, Heat Sinks, PCB, Thermal Design

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

Posted on February 2, 2017 by | 4 comments

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.

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.

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Posted in Analysis, CFD, Consulting, heat sink design, Thermal Analysis

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Discussion of Thermal Solution for Stratix 10 FPGA

Posted on October 28, 2016 by | Leave a comment

An Advanced Thermal Solutions, Inc. (ATS) client was planning on upgrading an existing board by adding Altera’s high-powered Stratix 10 FPGAs, with estimates of as many as 90 watts of power being dissipated by two of the components and 40 watts from a third. The client was using ATS heat sinks on the original iteration of the board and wanted ATS to test whether or not the same heat sinks would work with higher power demands.

In the end, the original heat sinks proved to be effective and lowered the case temperature below the required maximum. Through a combination of analytical modeling and CFD simulations, ATS was able to demonstrate that the heat sinks would be able to cool the new, more powerful components.

ATS Field Application Engineer Vineet Barot recently spoke with Marketing Director John O’Day and Marketing Communications Specialist Josh Perry about the process he undertook to meet the requirements of the client and to test the heat sinks under these new conditions.

JP: Thanks again for sitting down with us to talk about the project Vineet. What was the challenge that this client presented to us?
VB: They had a previous-generation PCB on which they were using ATS heat sinks, ATS 1634-C2-R1, and they wanted to know if they switched to the next-gen design with three Altera Stratix 10 FPGAs, two of them being relatively high-powered, could they still use the same heat sinks?

Stratix 10 FPGA

The board that was given to ATS engineers to determine whether the original ATS heat sinks would be effective with new, high-powered Stratix 10 FPGA from Altera. (Advanced Thermal Solutions, Inc.)

They don’t even know what the power of the FPGAs is exactly, but they gave us these parameters: 40°C ambient with the junction temperatures to be no more than 100°C. Even though the initial package is capable of going higher, they wanted this limit. That translates to a 90°C case temperature. You have the silicon chip, the actual component with the gates and everything, and you have a package that puts all that together and there’s typically a thermal path that it follows to the lid that has either metal or plastic. So, there’s some amount of temperature lost from the junction to the case.

The resistance is constant so you know for any given power what the max will be. The power that they wanted for FPGAs 1 and 2, which are down at the bottom, was 90 watts, again this is an estimate, and the third one was 40 watts.

JP: How did you get started working towards a solution?
VB: Immediately we tried to identify the worst-case scenario. Overall the board lay-out is pretty well done because you have nice, linear flow. The fans are relatively powerful, lots of good flow going through there. It’s a well-designed board and they wanted to know what we could do with it.

I said, let’s start with the heat sinks that you’re already using, which are the 1634s, and then go from there. Here are the fan specs. They wanted to use the most powerful fan here in this top curve here. This is flow rate versus pressure. The more pressure you have in front of a fan, the slower it can pump out the air and this is the curve that determines that.

Stratix 10 FPGA

Fan operating points on the board, determined by CFD simulations. (Advanced Thermal Solutions, Inc.)

This little area here is sometime called the knee of the fan curve. Let’s say we’re in this area, the flow rate and pressure is relatively linear, so if I increase my pressure, if I put my hand in front of the fan, the flow rate goes down. If I have no pressure, I have my maximum flow rate. If I increase my pressure then the flow rate goes down. What happens in this part, the same thing. In the knee, a slight increase in pressure, so from .59 to .63, reduces the flow rate quite a bit.

Stratix 10 FPGA

CFD simulations showed that the fans were operating in the “knee” where it is hard to judge the impact of pressure changes on flow rate and vice versa. (Advanced Thermal Solutions, Inc.)

So, for a 0.1 difference in flow rate (in cubic meters per second) it took 0.4 inches of water pressure difference, whereas here for a 0.1 difference in flow rate it only took a .04 increase in pressure. That’s why there’s a circle there. It’s a danger area because if you’re in that range it gets harder to predict what the flow will be because any pressure-change, any dust build-up, any change in estimated open area might change your flow rate.

The 1634 is what they were using previously. It’s a copper heat pipe, straight-fin, mounted with a hardware kit and a backing plate that they have. It’s a custom heat sink that we made for them and actually the next –gen, C2-R1, we also made for them for the previous-gen of their board, they originally wanted us to add heat pipes to this copper heat sink, but I took the latest version and said, let’s see what this one will do. For the third heat sink, I went and did some analytical modeling to see what kind of requirement would be needed and I chose one of our off-the-shelf pushPIN™ heat sinks to work because it was 40 watts.

JO: Is the push pin heat sink down flow from the 1634, so it’s getting preheated air?
VB: Yes. This is a pull system, so the air is going out towards the fans.

Stratix 10 FPGA

CFD simulations done with FloTherm, which uses a recto-linear grid. (Advanced Thermal Solutions, Inc.)

This is the CFD modeling that ATS thermal engineer Sridevi Iyengar did in FloTherm. This is a big board. There are a lot of different nodes, a lot of different cells and FloTherm uses recto-linear grids to avoid waviness. You can change the shape of the lines depending on where you need to be. Sri’s also really good at modeling. She was able to turn it around in a day.

Stratix 10 FPGA

Flow vectors at the cut plane, as determined by CFD simulations. (Advanced Thermal Solutions, Inc.)

These are the different fans and she pointed out what the different fan operating curves. Within this curve, she’s able to point out where the different fans are and she’s pointing out that fan 5 is operating around the knee. If you look at all the different fans they all operate around this are, which is not the best area to operate around. You want to operate down here so that you have a lot of flow. If you look at the case temperatures, remember the max was 90°C, we’re at 75°C. We’re 15°C below, 15° margin of error. This was a push pin heat sink on this one up here and 1634s on the high-powered FPGAs down here.

Stratix 10 FPGA

JP: Was there more analysis that you did before deciding the original heat sinks were the solution?
VB: I calculated analytical models using the flow and the fan operating curves from CFD because it’s relatively hard to predict what the flow is going to be. Using that flow and doing a thermal analysis using HSM (heat sink modeling tool), we were within five percent. What Sri simulated with FloTherm was if a copper heat sink with the heat pipe was working super well, let’s try copper without the heat pipe and you can see the temperature increased from 74° to 76°C here, still way under the case temperature. Aluminum with the heat pipe was 77°; aluminum without the heat pipe was 81°, so you’re still under.

Basically there were enough margins for error, so you could go to smaller fans because there’s some concern about operating in the knee region, or you can downgrade the heat sink if the customer wanted. We presented this and they were very happy with the results. They weren’t super worried about operating in the knee region because there’s going to be some other things that might shift the curve a little bit and they didn’t want to downgrade the heat sink because of the power being dissipated.

Stratix 10 FPGA

Final case temperatures determined by CFD simulations and backed up by analytical modeling. (Advanced Thermal Solutions, Inc.)

JO: What were some of the challenges in this design work that surprised you?
VB: The biggest challenges were translating their board into a board that’s workable for CFD. It’s tricky to simplify it without really removing all of the details. We had to decide what are the details that are important that we need to simulate. The single board computer and power supply, this relatively complex looking piece here with the heat sink, and we simplified that into one dummy heat sink to sort of see if it’s going to get too hot. It all comes with it, so we didn’t have to work on it.

The power supply is even harder, so I didn’t put it in there because I didn’t know what power it would be, didn’t know how hot it would be. I put a dummy component in there to make sure it doesn’t affect the air flow too much but that it does have some effect so you can see the pressure drop from it but thermally it’s not going to affect anything.

JO: It really shows that we know how to cool Stratix FPGAs from Altera, we have clear solutions for that both custom and off-the-shelf and that we understand how to model them in two different ways. We can model them with CFD and analytical modeling. We have pretty much a full complement of capabilities when dealing with this technology.

JP: Are there times when we want to create a TLB (thermal load board) or prototype and test this in a wind tunnel or in our lab?
VB: For the most part, customers will do that part themselves. They have the capability, they have the rack and if it’s a thing where they have the fans built into the rack then they can just test it. On a single individual heat sink basis, it’s not necessary because CFD and analytical modeling are so established. You want two independent solutions to make sure you’re in the right ballpark but it’s not something you’re too concerned that the result will be too far off of the theoretical. For another client, for example, we had to make load boards, but even then they did all the testing.

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

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Posted in Analysis, CFD, Chassis, Consulting, Heat Sinks, Modeling, PCB, Simulation, Thermal Analysis

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Technical Discussion of ATS Telecom PCB solution

Posted on October 28, 2016 by | 1 comment

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. (ATS) consulting services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

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