Tag Archives: thermal interface material

How to Select a Heat Sink: Why Thermal Management is a Challenge

Today we are kicking off a series of articles on how to select a heat sink for an OEM project. The principles are the same for overclockers building their own systems with one difference. In OEM projects, mechanical engineers usually (but not always) have a chance to simulate the design before hand and suggest changes to chassis and layout to help with airflow.

So, let’s get started with some basics. First, why is thermal management a challenge? There’s a few reasons and many of these are only getting worse if you consider them from the world of thermal engineering.

First on our list is higher frequency circuits. The International Technology Roadmap for Semiconductors notes that, “projected power density and junction-to-ambient thermal resistance for high-performance chips at the 14 nm generation are >100 W/cm2 and <0.2°C/W, respectively.” In other words, semiconductors are simply getting hotter as their clock speeds are increased.

Second, generally, semiconductors are being assembled into smaller packages. The packages are smaller, the circuits are denser and this combination means that they are warmer.

Third on our list of why thermal management is a (growing) challenge is low acoustic noise requirements. End users don’t want to be deaf just for using electronics. The result is many specifications that set a reasonable acoustic range for their equipment, often in the 100LFM to 400LFM range. This relatively low airflow is great for end users but creates a real challenge for mechanical engineers and systems integrators trying to create a solid system that meets end users needs and still operates at its optimal levels.

Fourth, circuit designers determine component placement. On the surface of this, this is how it should be. Electrical engineers have alot of pressure on them to reduce board latency and design for performance. While they often consider the thermal needs of the systems and circuits, it’s not their primary design point. For mechanical engineers that is what we do and so our challenge is the balancing act of working with EE’s to insure great placement, but also great airflow.

Fifth and finally, thermal management is a challenge because EMI shielding. Higher frequency components require better shielding and that shielding can restrict airflow.

When we pick this topic up next, we’ll cover why temperature is so important to manage. If you have any questions in the mean time about heat sinks or thermal management, contact us and lets see how can make your next project a success! Email us at ATS thermal engineersats-hq@qats.com , call us at 781-769-2800 or visit our heat sink catalog at qats.com


How to choose a heat sink attachment method to secure your heat sink and for optimal heat transfer (part 1 of 2)

Heat sink attachment posts are a little like watching paint dry: it’s boring but a necessary evil. What’s to worry about right? You slap your heat sink down and go. It should require as much analysis as choosing the New England Patriots to win the Superbowl this year!

But this kind of approach can actually limit a key part of your thermal management solution. The attachment matters and in some cases may improve your heat sink’s performance 20% or more. That translates into the very important topics of:  better system reliability, lower cost of the thermal management solution, and optimal system performance since it can operate at the right speed. This will be part one of a two part series. In this part we’ll cover thermal tape, epoxy and wire form”z-clips”. In part two we’ll cover clips, push pins and stand offs and have a special offer for our readers to get all this information in a handy download. So, let’s get into this.

108K different push pin heat sink assembly configurations featuring 3 different pitch heat sink types, 3 different fin geometries, brass and plastic push pins


There are six main methods you can use:

  1. Thermal Tape
  2. Epoxy
  3. Wire Form “Z-Clips”
  4. Clips
  5. Threaded Stand-offs (PEMS) and Compression Springs
  6. Push-Pins and Compression Springs

Let’s talk about the pros and cons of each of these, and provide some photos so, if your unfamiliar with these, you can see what they look like and how they work.

A photo of heat sink attachment using thermal tape Thermal Tape:  This is a pressure sensitive adhesive tape, generally acrylic.  The benefits are mainly that it’s generally easy to attach and it’s inexpensive. It’s also the lowest cost approach for aluminum heat sink attachment. But there are drawbacks.  For heavier heat sinks, thermal tape generally doesn’t secure a heat sink strongly. That same drawback can effect you if you are going through NEBS testing, tape generally has a problem securing a heat sink well in those environments.  Also, you have to ensure the surface of the heat sink and the chip are very clean so that the tape bonds well and can fulfill its dual role of affixing a heat sink securely to your chip AND acting as thermal interface material. Speaking of thermal interface, tape is generally considered a moderate to low thermal conductor.

attaching a heat sink to a semiconductor using thermal epoxy Thermal Epoxy: This is a material that is either single or dual-part mixed adhesive with thermally conductive fillers like silver. It has outstanding mechanical adhesion: even copper heat sinks will not move off the semiconductors they are attached to (or any other surface for that matter if you place your epoxy laden heat sink down on your bench for some reason). It’s also fairly inexpensive costing a bit more than tape.  There are drawbacks. First, it has to be refrigerated. Second, it takes skill to apply it so that you don’t put on too much or too little, after all, you are using this material BOTH to secure your heat sink AND to act as thermal interface material to conduct the heat from your semiconductors to your heat sink.  Second, all surfaces must be squeaky clean, like with thermal tape.  And finally, hope you never have to rework your board because epoxy is hard to remove and often times will destroy your boards. That’s right. Its glue! One way to loosen that glue up is by heating it using a heat gun or thermal welder, (Kamweld, our sister company, has some nice ones).

wire form z-clips attach heat sinks to PCB boardsWire-Form “Z-Clips”: Basically this a cheap mechanical attach method that often works well.  A stainless steel wire formed clip is used to both compress the heat sink onto the chip and to hold it down. Key? You need to use thermal interface material (TIM) on that bottom of that sink in order to have the right heat transfer from the chip to the heat sink. Why would you use a Z-Clip?  For one, it provides a strong and secure mechanical attach. For shock and vibration environments such a strong mechanical attach is a must.  Second, this kind of attachment is easy to apply and easy to remove PLUS it’s non destructive to the semiconductors as opposed to epoxy and occasionally tape. Finally, it applies a preload onto the TIM and that preload actually improves thermal performance. All this being said there are few downsides. First, it requires engineering to develop and use, and that can add development cost to your programs development budget. Second, it can take a few steps in assembly, marginally increasing the assembly time.

An advancement in this space can been seen at our colleagues at Alpha Novatech with their “Quick Set” series. In a nutshell, Quick Set requires a small mounting pins be placed onto a PCB. Mounting pins only require 1.8mm[.071″] diameter holes in the PCB.  Then a heat sink can be clipped on creating a secure attachment that uses minimum space.  It also appears it can handle oversize heat sinks too, a real boon with large footprint semiconductors.

So that’s part 1!  In part two we’ll cover “standard” clips, push pins and stand offs and have a special offer for our readers to get all this information in a handy download. To reach part 2 please click here, “How to Choose a Heat Sink Attachment Method to Secure Your Heat Sink and for Optimal Heat Transfer (part 2 of 2)

If you’re looking for a solution on heat sink attachment and need to bounce this off us, feel free to! ATS sells various heat sinks attachment options, of course, and we’ll talk about that next time, but we’re  happy just to discuss your options in your application, so call us at 781-769-2800, email us at sales.hq@qats.com or visit our website at http://qats.com

Fujipoly releases new, high performance additions to its Sarcon line of Thermal Interface Material

Fujipoly, a firm we featured in the ATS Thermal Interface Material Resource Roundup, have released a duo of additions to their fine line of Sarcon specially formulated thermal interface materials. Applicable to an aluminum heat sink, copper heatsink or other applications requiring low thermal resistance gap filler pad compounds, Sarcon 100GR-HL and SARCON XR-Um-Al are both available now from Fujipoly.

SARCON XR-Um-Al is a uniquely formulated gap filler compound that has a putty-like consistency. This physical property contributes to the material’s extremely low contact and thermal resistance while maintaining a thermal conductivity of 17 watt/m-k. The gap filler pad is manufactured with a thin aluminum carrier film for customer-friendly application. The low adhesion aluminum barrier enables users to remove the carrier film after installation with no pull-out effect. This thermal interface material is available in sheets up to 50mm x 50mm with thicknesses ranging from 0.2mm to 0.5mm.

SARCON 100GR-HL is a thermal gap filler pad manufactured with a hardened top surface. The unique, one-sided treatment is less tacky than the opposing surface allowing the thermal pad to consistently adhere to either the target electrical component or opposing heat sink. The hard surface allows for effortless removal without tearing or damaging the material during assembly and rework operations. Sarcon® 100GR-HL transfers heat with a thermal conductivity of 2.8 W/m°K and a thermal resistance of .44°Cin2/W at 72.5 PSI. This 1.0mm thick, flame retardant TIM is available in sheets up to 300mm x 200mm.

Thermal interface material is an important part of a thermal management system. So important in fact we’d like to point our readers to a couple of resources we’ve put together here at ATS. The first is our white paper, “When to use thermal interface material with your heatsink and why?” The second is an on-demand webinar we have made available to the thermal engineering community entitled, “Heat Sink Selection Made Easy“, in which we cover a bit about thermal interface material relative to heatsink selection. These materials are free of charge of course. If you’ve got questions or need a bit of help with your thermal engineering, give us a try, companies like Lucent, and Motorola already have. Call us at 781-949-2521 or email us at sales.hq@qats.com

Is CPU Cooling best done with a Copper Heatsink or Aluminum Heatsink?

The topic of whether a CPU heat sink should be a copper heat sink or aluminum heat sink comes up in every thermal management design. And the short answer as to which material to use is:

“It depends.”

There are many variables in designing the right heat sink, some of which include:

  • Thermal management cost budget relative to BOM cost
  • Orientation of boards (vertical or horizontal)
  • How much weight or stress can be applied to the target chip
  • How much keep out around a chip exists
  • Air flow to the chip
  • Air flow in and through the system (maybe you don’t need a heat sink at all as noted in an earlier ATS White Paper)
  • Component dimensions
  • Component height
  • Target junction temperature
  • Target case temperature

Let’s just focus on the material question though, copper heatsink vs. aluminum heatsink. Chris Soule, Engineering Director at Thermshield, has done a nice one page write up on the topic. Some of his key points include:

  • Pure copper has about two times the conductivity of aluminum but that inherent advantage is only helpful when
  1. Air Flow speeds are 800 LFM
  2. The hot spot on the CPU or other semiconductor is small in comparison to the size of the chip itself.
  • When air flow is 400 LFM or lower or the hot spot on the CPU or semiconductor is spread throughout the chip, then Aluminum is a better choice.
  • The cost of a copper heat sink is often up to three times the equivalent sized aluminum heat sink

In our labs here at ATS, we’ve found that if an aluminum heatsink by itself does not have the necessary thermal condutivity, then using phase change thermal interface material (such as those listed in our Thermal Interface Roundup Post) with the proper pressure applied can make the difference in cooling.

So which do you use? Copper or Aluminum? It depends on the variables noted including your budget. One thing is for sure, there is no clear, one sized fits all answer and the thermal engineer should carefully decide. Hopefully before the electrical design is complete!

maxiFLOW Heat Sink with superGRIP Heat Sink attach improves chip level Thermal Management

A headline like “maxiFLOW Heat Sink with superGRIP Heat Sink attach improves chip level Thermal Management” is a pretty bold statement but it’s one we stand behind at ATS. The reason has to do with the complicated vectors around making a heat sink work properly in a chip level application including how the fins are designed for proper airflow direction over the surface of the heat sink.

We developed maxiFLOW to actually channel the air properly down onto the heat sink and through it. The result of proper air flow management is better cooling, as depicted in these CFD outputs:

To get more information or to purchase maxiFLOW Heat Sinks with superGRIP attachment, click to our maxiFLOW web page at this link: ATS maxiFLOW/superGRIP Heat Sinks.