Category Archives: heat sink

6 questions to guide your engineering investigation in choosing the right heat sink for your application

Posted on October 8, 2010 by | Leave a comment

Here’s a series of questions our engineers walk through when faced with a new thermal mangement project that requires choosing the right heat sink.

Component or Device Details: This includes asking questions to determine the components power level (generally expressed in watts), maximum temperature (Case or Junction C), package size, package type (BGA, flip chip, etc.), package material, and package configuration (exposed die or heat spreader, etc.)

System Airflow: Is there a fan or blower? Is it ducted or unducted? Is it pushing air onto the area needing thermal management or pulling air over the component needing thermal management? Or is it convection cooled?

Space Constraints: What is the allowable height off the PCB? What is the maximum heat sink height allowed? Is heat sink overhang over the component allowed? If heat sink over hang isn’t allowed, would it be allowed if a heat sink were cut out in place to allow closely positioned heat sinks to not be effected (yet overhang would happen in other places).

System Operating Conditions: What is the known to be maximum ambient temperature outside the system? What is the allowed maximum ambient inside the system? Is there a maximum altitude in which the system may eventually operate? Are there shock and vibration specifications to be considered (such as in MIL, NEBS, or ETST)?

Attachment Method Allowed: What attachment method is allowed for the heat sink? Are there pre-drilled, “industry accepted” holes already so that a push-pin heat sink is allowed or is it preferred that there are no holes in the PCB? Can a clip be used? Is a clip needed for compression of thermal interface material or simply to attach a heat sink loosely? If a clip is okay, how much keep out area around the components is available.

Thermal Interface Material In this section we ask questions to determine the best thermal interface material to use. Choosing and applying the right thermal interface material can reduce case temperature by as much as 50% We’ll want to know if the component has any surface irregularities or all out roughness, and we’ll need to know the surface area of the contact area.

We’ll take answers from all the questions and use them to help us get a complete picture of the thermal requirements for a given project. Stepping through questions such as these can be a logical road map to doing some basic thermal analysis that can lead to the right heat sink for your application.

If you need a team to hep you through the engineering investigation phase or if you’ve been through that phase already and just need a heat sink that meets your specifications, contact ATS! You can learn more about us at our website http://qats.com or you can email us with your request sending mail to [email protected]

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Copper Heat Sinks? Aluminum Heat Sinks? Does it matter what you make a heat sink from?

Posted on October 4, 2010 by | 1 comment

True or False?  Heat sink materials make a difference in how efficient a heat sink will be?

Well, like a lot of things in thermal management, it depends on the constraints of your application. Neither copper heat sinks nor aluminum heat sinks are always the default choice.

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

 

Recently, ATS performed a study to provide some clarity to users on how different “standard” materials act as heat sinks. Our study included copper heat sinks, aluminum heat sinks and graphite foam heat sinks. We published our article in ECN under the title, “Comparing the Impact of Different Heat Sink Materials on Cooling Performance“.

The results of our study were quite interesting.  As you can see from the following graph, graphite was a good material but not the best. Copper and Aluminum performed better and similarly.

Comparison of copper, aluminum and graphite foam heat sinks

Our conclusions were:

  • Copper and Aluminum are very close in thermal performance. If weight is an issue or cost, then Aluminum is the way to go. The size of your heat sink or the thermal interface material can often make the difference too.
  • Pure copper has about 2x the conductivity of aluminum but that inherent advantage is only helpful when
  1. Air Flow speeds are 800LFM
  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 400LFM 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 heatsink is often up to 3x the equivalent sized aluminum heatsink
  • Graphite foam-derived heat sinks show promise in specific applications, but exhibit several drawbacks in mainstream electronics cooling.

You can read the full study at ECN by clicking to “Comparing the Impact of Different Heat Sink Materials on Cooling Performance“. You can also check out our earlier conversations on this topic by clicking to our posts, “Is CPU Cooling best done with a Copper Heatsink or Aluminum Heatsink?” and “Intel’s nano-technology breakthrough for heat sinks has R&D promise but real-world applications are in the future; An ATS thermal management technology analysis”

Also, if you are a member of Linked-In, there is a Thermal Management group that is worth joining, plus, there is a sub-group off of that focusing on next generation materials for heat sinks. Well worth joining!

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ATS Thermal Management Case Studies show real world thermal problems and solutions

Posted on September 22, 2010 by | Leave a comment

We’ve written a number of case studies on thermal analysis and thermal design for LED Lights, thermally optimizing a PCB, and even liquid cooling. We thought we’d put them in one place up to now to make them easier to find. You can do this yourself as well by clicking on the drop down box “blog article categories” in the right hand column of our blog and choosing the category “case study”.

LED Lights:

Telecommunciations

Homeland Security

PCB:

Semiconductor Automatic Test Equipment

System Level Optimization

Computer High Power Boards

Liquid Cooling

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

Posted on September 20, 2010 by | Leave a comment

In part 1 of our 2 part series, we laid the ground work for our two part series by noting that there are six main methods you can use to secure a heat sink to a semiconductor

  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

In part one we covered 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.

Commercial heat sink clip and ATS maxiGRIP heat sink clip Heat Sink Clips: Heat sink clips are Plastic or plastic/wire clips that grip the components. They are a step above z-clips in ease of use and application. Where a Z-Clip requires a PCB anchor, standard heat sink clips do not. In fact, as long as you have keep out area available around a chip and height available, a clip is a great option. There are many options in using a clip. There are very basic clips, such as those from Malico, which quickly and easily hold a heat sink onto a semiconductor and more advanced clips such as what we at ATS offer in our maxiGRIP and superGRIP clips. The main benefits of a clip are, first, they apply a pre-load to the TIM (thermal interface material) improving thermal performance. Second, they require no holes or anchors in the PCB. This is a very big benefit since clips do not reduce the trace space available for board layout. Third, clips make rework easy by allowing heat sinks to be easily removed and reapplied without damaging the PCB board. Finally, some clips, like maxiGRIP and superGRIP provide a strong enough mechanical attach to pass NEBS, ETSI and MIL shock and vibration. There are some downsides that need to be noted though. First, designers need to insure they design in some keep out area around the semiconductors so that a clip can be used. That also assumes that the design team has considered a thermal management strategy during the architect phase of the product too. Secondly, clips do add extra assembly time since they have to be manually applied.

heat sink being attached to a board using a PEMThreaded Standoffs (PEMS): These are threaded mechanical assemblies that offer the highest level of retention and stability. This approaches benefits include, first, that they are a strong mechanically. They will pass shock and vibe for NEBS, ETSI and MIL.  Second, they provide the highest TIM preload, insuring excellent performance from whatever thermal interface material you choose. Third, they are ideal for heavy copper heat sinks. Finally, they make installation and rework easy since a simple unscrewing of the attach allows the non-destructive removal of the heat sink.  But, as with all heat sink attach methods, there are a few drawbacks to consider. First, they require holes in the PCB removing valuable space for trace. Second they tend to be expensive, especially given that holes need to be drilled into a PCB board to use them.

push pin attach for heat sinks Push-Pins: These are generally plastic or brass push-pin that offer quick and easy mechanical attachment. They are generally equally strong to a threaded standoff (PEMs) approach to heat sink attach. Push pins offer a very strong TIM preload as well as being ideal for large, heavy copper heat sinks. Some of the drawbacks include requiring holes in the PCB board which reduces the trace length space available, a generally complicated assembly process, and finally a fairly high price relative to other solutions.

That wraps up our two part series on heat sink attachment options.

Special offer for our readers to get all this information in a handy download
There’s a lot of material in our two part series on heat sink attachment. To make referencing our series quicker, we’ve assembled this material into a two page “Resource Guide” completed with images as a handy reminder during your next thermal management project.To get a copy, simply drop some email to us at [email protected] with the words, “HEAT SINK ATTACH OFFER” in the subject line and we’ll send a copy to you.

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 [email protected] or visit our website at http://qats.com

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

Posted on September 17, 2010 by | 3 comments

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 [email protected] or visit our website at http://qats.com

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