Category Archives: How To

Announcing our ATS Electronics Cooling Webinars for Third Quarter of 2012

ATS, Advanced Thermal Solutions, Inc. will present technical webinars on electronic cooling topics in July, August and September 2012. Each of these free events will provide engineering-level training in a key area of modern thermal management.

Here are the different webinar topics and presentation times:

Using Thermal Interface Materials to Improve Heat Sink Thermal Performance

July 26, 2012 at 2:00 p.m. ET

To cool hotter components, engineers are using larger fans and heat sinks, and increasing surface areas. These hardware enhancements can add significantly to design costs. In many cases, cooling performance can be improved by using a higher performance interface material between the case and the heat sink. Participants will learn the importance of lowering thermal resistance using thermal interface materials, or TIMs, and the different kinds of TIMs available from the market.

Air Jet Impingement Cooling

August 23, 2012 at 2:00 p.m. ET

Ongoing increases in power in devices such as processors and IGBTs mean that higher capacity cooling methods are needed to remove excess heat. One such method is the jet impingement of a liquid or gas onto a surface on a continuous basis. Lab experiments at ATS have shown up to a 40% improvement in cooling achieved using this method. This webinar will explore jet impingement cooling theory, implementation and best practices.

LED Thermal Management in Commercial and Consumer Lighting Applications

September 27, 2012 at 2:00 p.m. ET

Excess heat directly affects both short-term and long-term LED performance. The short-term effects are color shift and reduced light output, while the long-term effect is accelerated lumen depreciation and thus shortened useful life. Participants will learn how to diagnose and solve thermal issues in consumer and commercial LED applications.

Each of these one-hour online tutorials will include detailed visuals, real world examples, instructions, definitions and references. Audience questions will be answered by the presenters during and after the presentation. One or more ATS PhD-level thermal engineers will be presenting live.

There is no cost to attend these ATS webinars, but virtual seating is limited. Registration is available online at http://www.qats.com, or by calling 1-781-949-2522.

http://qats.com/Training/Webinars/7.aspx

 

The Importance of Heat Flux Sensors

Heat flux sensors are practical measurement tools which are useful for determining the amount of thermal energy passed through a specific area per unit of time. Measuring heat flux can be useful, for example, in determining the amount of heat passed through a wall or through a human body, or the amount of transferred solar or laser radiant energy to a given area.

Affixing a thin heat flux sensor to the top of a component will yield two separate values which are useful in determining the convection heat transfer coefficient. If the heat flux can be measured from the top of the component to the ambient airstream and if the temperature at the top of the component and of the ambient airstream is measured, then the convection coefficient can be calculated.

Where:

q = Heat flux, or transferred heat per unit area

h = Convection coefficient

TS = Temperature at the surface of the solid/fluid boundary

TA= Ambient airstream temperature

Using a heat flux sensor can be useful for lower powered systems under natural convection scenarios. Under forced convection, the heat lost to convection off the top of a component can often be significantly higher than the heat lost to the board, particularly if the board is densely populated and the temperature of the board reaches close to the temperature of the device. Under natural convection situations, often the balance of heat lost to convection and heat lost through the board becomes more even and it therefore is of even greater interest to the designer to understand the quantity of heat dispersed through convection.

Experiments done at Bell Labs alluded to the effect of board density on the heat transfer coefficient. In these experiments, thin film heat flux sensors are affixed to DIP devices which populate a board. The total heat generation of the board is kept constant, so the removal of components from a densely populated board only increases the heat generation per component. The results of this particular experiment highlight an increase in the ratio of heat lost through convection from the surface of the component as board density increases and individual device power decreases.

 Surface Heat Flow vs. Board Density

Qs/Qt = the ratio of total heat flow through device surface to total heat generation

σ = the ratio of total device surface area to total board area

If a board was to be sparsely populated, a greater percentage of heat can be transferred to the board due to larger thermal gradients; however since the overall surface area of the sum of devices decreases, to some extent the heat transfer coefficient must increase to reflect a balance. As the number of components decreases, the power generation increases per component, and the larger resulting temperature gradients in the region around the component yield more convective flow and thus an increase in the heat transfer coefficient. On the other hand, if the board becomes more densely populated, the proportion of heat transferred through the surface, as compared to through the board increases, and the overall increase in heat transferred through the surface yields increased flow and heat transfer at an individual component surface.

The use of a heat flux gauge is an important tool for the electronics designer. In particular, by using a heat flux gauge, it is possible to experimentally determine the heat transfer coefficient at a certain location on the electronics board where it would have had to be simply predicted or estimated previously. Due to the complexity of many electrical systems as well as the irregular nature of many boards, often analytical or CFD methods are not accurate and the best approach is empirical techniques. The use of the heat flux sensor can give results which would be difficult to calculate using analytical or numerical simulations. However, like most other instruments, it is important to use the sensor correctly and carefully to decrease the errors within a system and increase the reliability.

The Principal Methods for Measuring Thermal Conductivity in Electronics Cooling Studies

A paper by Advanced Thermal Solutions, Inc., ATS, compiles the major methods used by engineers for measuring thermal conductivity. In all, the paper describes and compares 17 proven methods for measuring thermal conductivity in electronics.

In one section of the paper, these methods are grouped according to the time dependence of the heat applied to the sample. Each method is classified under steady-state, periodic or pulsed. Another section compares the performance of each thermal conductivity measurement method, and provides an idea of sample size and preparation, and the operator skill required. There is also a list of the equipment typically needed to conduct each of these thermal tests.

According to the ATS article, the wide choice of methods may first appear to be a disadvantage. However, once understood for their application-specific benefits the advantages become evident. Materials to be tested, part geometry and part test temperatures will usually be the primary criteria.

As always, the relative cost and expected level of accuracy will also be important factors. Avoiding complicated boundary conditions, irregular part geometry, difficult heater placement/construction and encouraging the difficult task of one-dimensional heat flow will greatly simplify the measurement process. Multiple benefits will result from reducing the cost and assembly difficulty of the experimental set-up while avoiding those errors often introduced when attempting to construct complicated analytical/mathematical models.

How to Apply Thermal Interface Material: Thermal Grease

In another video from our lab, Greg, an ATS thermal engineer, demonstrates the sometimes tricky application of thermal grease.  Thermal grease is among the best TIM conductors, but, it’s messy! Check Greg’s careful application for how to do it:

How to Apply Thermal Interface Material: Thermal Tape

In our latest short “how to” video, ATS engineer Greg demonstrates the correct way to apply thermal tape to your heat sink. It’s one minute, 30 seconds in length and will help you get it right if you’ve never applied tape before: