Category Archives: thermal management

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]

Leave a comment

Posted in heat sink, thermal management

Tagged ,

Webinar on Thermal Management of Defense Electronics to be Held 10/14/10 @2PM EST

Posted on October 7, 2010 by | Leave a comment

We’re holding another thermal management webinar on Thursday, October 14 at 2PM EST. The topic is, “Thermal Management of Military Electronics.”

Electronics warfare systems, cyber-warfare, surveillance, guidance systems, UAV, Direct Energy Weapons and more are all part of our defense infrastructure. As in any electronics, thermal management is critical to these systems to insure long MTBF and proper operation through its life cycle. Attendees will understand the tradeoffs of cost vs. thermal management in order to choose a strategy best suited for their military electronics project.

The webinar is being underwritten by ATS so there’s no charge to attendees! You can register at this link, “Thermal Management of Defense Electronics”

If you want to get a jump on this topic before the webinar, check out Courtney Howard’s article in Military and Aerospace Electronics entitled, “Electronics thermal management gives rise to industry innovation to keep aerospace and defense systems cool“

Leave a comment

Posted in Military, Thermal Design, thermal management

Tagged ,

Six questions to ask to guide your engineering investigation to the right heat sink

Posted on October 4, 2010 by | Leave a comment

Here’s a series of questions our engineers walk through when faced with a new thermal management 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.

ATS can also help with this process either by doing the engineering investigation for you or providing a heat sink solution to your findings. You can learn about us and our heat sink offering by clicking out our web site, qats.com.

Leave a comment

Posted in Thermal Analysis, thermal management

Tagged

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

Leave a comment

Posted in Case Studies, heat sink, LED, thermal management

Tagged , , ,

What is Jet Impingement Cooling and How is it applied for Thermal Management of Electronics (Part 2 of 2)

Posted on September 14, 2010 by | 1 comment

Jet Shape and its effect on cooling

Jets are deployed in different shapes that impact the eventual heat transfer from the impinged jet surfaces. These shapes include round and square. There can be a single jet or multiple smaller jets where the data has shown to have better performance than a single jet. Figure 2 shows the temperature gradient in a jet impingement application. [3] The jet was seeded with liquid crystal to show the thermal transport, its interaction, and the temperature gradient.

Figure 2: Temperature Gradient in a Jet

Figure 2: Temperature Gradient in a Jet

The heat transfer coefficient is maximized at the center, and the distribution is shown in Figure 3. [4]

Figure 3 – Heat transfer coefficient distribution

Figure 3: Heat Transfer Coefficient Distribution

Figure 4 shows the local heat transfer coefficient for air jet impingement as a function of dimensionless distance for a jet diameter of 1 mm, Re = 10,000 at different H/d. It is seen that at H/d = 1, H is higher than the other two values. In this experiment, an H = 2,500 W/m2K was achieved.

Figure 4 - Heat transfer coefficient for an air jet at d = 1 mm, Re = 10,000

Figure 4: Heat Transfer Coefficient for an Air Jet at d = 1 mm, Re = 10,000

Figure 5 shows the heat transfer coefficient for a water jet, as reported by Garimella [2] that has attained a value of 60,000 for confined submerged jets. The x axis is the ratio of jet to target spacing to nozzle diameter. The top curve was for 4.6 m/sec (10 gram/sec), the middle curve was for 6.9 m/sec, and the bottom was for 9.2 m/sec.

Figure 5 - Heat transfer coefficient for single submerged confined water jet

Figure 5: Heat transfer coefficient for single submerged confined water jet

Recently, Motakef, et al, described the achievement of a heat transfer coefficient of 500,000 with a water microjet, and 20,000 with an air microjet. [5] In their design, they manufactured a 3-D structure with hundreds of microjets that were 300 microns size. The jets are kept at a distance of a few hundred microns from the surface. The special manifold design allows the returned flow to exhaust without interfering with the main jets. This design significantly increases the heat transfer coefficient. Without the manifolding the heat transfer coefficient degrades to that of a macro-jet. Figure 6 shows a sample of this honeycomb structure.

Figure 6 - A 10 x 20 x 1.7 mm MJCA micro jet structure

Figure 6 – A 10 x 20 x 1.7 mm MJCA micro jet structure

Even though a very high heat transfer coefficient can be achieved using jet impingement, the packaging of such a system is very challenging. The following must be carefully considered and studied:

  1. What type of fluid should be used? Is it air or liquid? If it is air, what is the noise implication? If it is liquid, how will the liquid be drawn out of the system without damaging the electronics parts if there is any leakage?
  2. What type of compressor is needed to generate the high speed jet? Is its size practical for commercial use? What is its life span?
  3. What type of filter should be used to prevent the nozzle from clogging? What is the effect of the filter on the fluid line pressure drop? What would be the impact of semi-clogged nozzles on the pressure drop?
  4. What is the cost of such a system, and does it justify its application for that specific application?

To reach part 1 of this series click to: What is Jet Impingement Cooling and How is it applied for Thermal Management of Electronics (Part 1 of 2)

Need help on apply Jet Impingement Cooling in your thermal designs? ATS offers Jet Impingement technology and consulting for ATCA, Telecomm and 1U compute Chassis. You can learn more at our post, Jet Impingement for thermal management: a practical approach to using it in 1U Server Chassis or calling us at 781-769-2800 or email us at [email protected]

 

References:

  1. Womac, D., Ramadhyani, S., Incropera, F., Correlating equations for impingment cooling of small heat sources with single circular jets, Transactions of the ASME, Vol. 115, PP 106-115, 1993.
  2. Fitzgerald, J., Garimella, S., Flow field effects on heat transfer in confined jet impingement, Transactions of the ASME, Vol. 119, pp. 630-632, 1997.
  3. Ashforth-Frost, S., Ridel, U., Thermal and hydrodynamic visualization of a water jet impinging on a flat surface using microencapsulated liquid crystals, International Journal of Fluid Dynamics, Vol 7, Article, 1-7, 2002.
  4. Glynn, C., ODonovan, T. and Murray, D., Jet impingement cooling, Department of Mechanical and Manufacturing Engineering, Trinity College, Dublin.
  5. Motakef, S., Overholt, M., Micro-fabricated solutions to management of high heat flux systems, CapeSym, Inc., Natick, Massachusetts.

1 Comment

Posted in thermal management

Tagged , , ,