A product that has 100s, if not 1000s of parts offers certain, shall we say, ‘challenges’ when it comes to creating a 3D virtual prototype in a CAE simulation software. Whereas the mainstay of classic CFD simulations involve predicting the air flow over a handful of parts, applying CFD successfully to electronic thermal simulation requires a technology that can handle 100s of parts and 10s of 1000s of solid/solid and solid/fluid interfaces. Something FloTHERM has excelled at for over 22 years now.

Not all CAE Applications are Equal

With so much cluttered complexity and complex heat flow paths in an electronic product the use of simulation is highly valuable, especially as a tool to enable a designer to become a thermal design expert. I gave up trying to double guess the thermal performance of a system before a simulation was conducted ages ago. I would have thought that for this DVD application, when simulating the effects of a breakdown in the effectiveness of the TIM connecting the TO with the heat spreader I would have seen a nice large thermal bottleneck in the TIM. Some thermal expert I’m not…

I modelled the failed TIM by simply reducing its thermal conductivity. A more quantified approach (that likely would be done as part of a paid consultancy, not this vocational blog) might have employed T3Ster to measure the TIM thermal resistance itself, to be used as an input to this simulation. The FloTHERM simulation indicates that the junction temperature rise of the TO220 increases by 20% to over 100 degC. The next question should be why? and what can we do (could we have done) about it?

The bottleneck number, invented by us and implemented now in FloTHERM, is a method of indicating not where something is hot, but why. It pin points regions that are responsible for the increase in the temperature of the electronics. It’s simply constructed as well, just the dot product of heat flux (how much heat is flowing) and temperature gradient (how difficult heat finds it to flow) vector properties at any and all points in the simulation. The result is a thermal bottleneck ‘map’. Red is high bottleneck, blue is low.

When the TIM fails the heat, as it rushes through the path of (relatively) least resistance, ends up necking down through the screw that holds the tab of the TO to the heat spreader. Despite the screw being made of nice highly conducting metal (aren’t they all?) there is so much heat, also bending in and out of the screw shaft, that it ends up being the biggest bottleneck in the system.

Should really point out the other bottlenecks in and around the package. The lead that’s fused to the die flag carries some heat through a small cross section. The rest of the bottlenecks can be seen in the die attach and sure, some in the TIM itself.

So what could have been done to mitigate the increase in temperature when the TIM failed. Chose a better (read: more expensive) TIM is the obvious one. Chose a better package is another. Maybe design things so that two TOs were used maybe? Failing those lets look further afield to see where other bottlenecks exist.

‘Iso surfaces’ are useful post processing objects to visualise the distribution of a variable outputted as part of a simulation. They are surfaces at a constant value. Choosing a high bottleneck number and plotting the resulting bottleneck iso-surface we can see more than just what was on the center section plane plots used so far.

The bottlenecks where the spreader pins connect to the bottom plane of the PCB offer an opportunity to affect the thermal performance through a change in the design. Even when the TIM fails a lot of the heat still makes its way to the spreader. As pointed out in the previous blog, the spreader is no way big enough to transfer all the heat to the air, a lot of it ends up going through its pins into the PCB.

Beyond looking like a lopsided moustache or a pair of pony tails the heat flux lines show the bunching of the heat flow, coloured by bottleneck number, they indicate that surely doing something in that area will have an effect upstream back to the die. Exactly how much affect we’ll see next time.

30th January 2012, Ross-on-Wye

In a recent article entitled “Who is Managing Your Brand Image?” my colleague, Graham Kilshaw, explained how customer behavior has effected a significant shift in marketing, from direct response advertising to brand advertising.

As customers gather on social sites where they share opinions and, in turn, are influenced by the preferences of others, marketers are growing increasing aware that their brand images are being created and shaped, with or without their involvement.

In the past, marketers were concerned primarily with “closing the deal”; whereas now customers prefer to build relationships with brands that they can trust.  If our prime focus as marketers continues to emphasize “making the sale,” we may just lose the sale, along with our brand image.

Few would argue that the explosion in social media can be attributed to changes in customer behavior and demand.  Customers are growing less interested in sales pitches, turning their attention to high-quality, relevant information that solves a problem or answers a question.

For this reason, there has been an unprecedented growth in content marketing as a means of responding to the customer’s needs.  According to marketing company, HiveFire, 82% of B2B marketers have adopted the practice of content marketing.

Content marketing takes a holistic, multi-touch approach, whereby a company provides ongoing information to educate customers, thus building long-term relationships and, consequently, managing their brand image.  It employs all types of media channels—print and digital, including magazines, newsletters, and social media platforms.

Doug Dixon, Marketing Communications Director at Henkel Electronic Materials, recently commented to us:

“Henkel’s vision is to be the global leader in brands and technology and converting on this vision means delivering high performance products and meaningful technology.  From a marketing point of view, we realize that customers have many different touch points and information delivery preferences.  To that end, we have engaged in a multi-pronged, content-driven marketing strategy that provides useful information for specialists in the markets we serve.”

At Electronics Cooling, our aim is to provide you with these necessary channels to reach your target customers.  One excellent tool is Electronics Cooling Resources, a newsletter that showcases any type of content to your target customer.  With Electronics Cooling Resources, you can establish yourself as a thought leader through a varieties of content, including:

• podcasts
• photos
• “how to” videos
• written testimonials
• testimonial videos
• case studies
• white papers
• webcasts
• webinars
• infographics

Instead of leaving it up to your customers to define your brand image, you can start responding to their questions and needs through valuable content that engages them right where they are.

No marketer wants their brand to be hijacked; but if it has, you can not only reclaim your brand image but also shape your reputation and improve custom loyalty.  If you would like to discuss the possibilities of content marketing with Electronics Cooling, contact me, Paul Salotto at psalotto@item-media.net.

There are a few options when it comes to modelling components, most of which I covered in this blog series. Some more accurate than others, others less desirable for a vendor to supply than some.

And speaking of component vendors… NXP Semiconductors, formerly Philips Semiconductors, started back in 2006. Today they focus on ‘no-big-chip-in-the-middle’ products, a delightfully honest phrase to describe a high performance mixed signal strategy. The pioneering use of FloTHERM at both NXP and Philips goes back many years. Today NXP provide detailed FloTHERM models of their power MOSFETs packaged in TO220, DPAK, D²PAK, LFPAK and various other styles. (see http://www.nxp.com/models/thermal.html).

The 3D thermal package models are downloaded and placed into an existing FloTHERM model, i.e. the application environment the packages are to be deployed in. Their operating power dissipation is defined, a thermal prediction made by FloTHERM and the following typical outputs produced…

FloTHERM model of 4x PSMN9R0-30YL LFPAKs mounted with copper pads under the tabs

LFPAK surface temperatures

Heatflux distribution from one of the dies

Inherent in the application of such power electronics parts is the transient nature of their operation, transient from a thermal perspective where the power cycles are such that the resulting temperatures are forever changing. So called Zth curves provide a measure of the thermal resistance response of a package to either a single or a series of power pulses, from on times in the order of 1e-6 seconds and upwards.

Zth Curve for BUK652R0-30C N-channel TrenchMOS intermediate level FET

Knowing the periodic power profile one can make initial estimates as to the thermal response of the package using the Zth curve. More detailed 3D predictions can then be made in FloTHERM (using the available detailed models) where, for example, assumptions about the thermal environment of the package do not have to be guessed.

A pulse power profile leads to the well recognised saw tooth thermal response in time. Taking a pulse of power on for 50ms every 100ms the resulting saw tooth profile can be simulated by FloTHERM.

Taking a vertical slice through the 3D FloTHERM model of the package one can visualise the thermal soaking effects the package experiences during these 1st 15 cycles.

The FloTHERM model downloads from the NXP web site run at over 1000 per month. The availability of these, in conjunction with various compact electrical models, thermal design guides etc. typifies the value added approach that tier 1 vendors such as NXP take. An approach that is certainly appreciated by those engineers using and simulating NXP products. As a simulation software vendor we definitely applaud any effort to make the life of our own software userbase easier. The point being that together we allow our customers to make their design mistakes in software first, minimising the risk of their 1st physical prototype failing, getting their products to market more cost effectively and to the ultimate satisfaction of the end user!

4th January 2012, Ross-on-Wye

Scorchio

I’m sure a wide variety of things have been photocopied, especially during company Christmas parties, but maybe never a PCB. It turned out to be the best way to capture the underside of the power board, both to capture the said scorching, also to get a map of the copper distribution that I’d need later when building the thermal model.

From a thermal perspective the TO220 amplifier was evidently the most critical component, the scorching was on the underside of the board directly beneath it. It was screwed to a vertical aluminium heat spreader with thermal paste used to achieve a good contact between the package case face and the spreader. Back in the day it took me a while to get my head round the idea that thermal contact between two objects can be enhanced by adding something else between them. The point being that you can never squeeze all the air out from between two solid contacting faces. Unlike moving air that is a great transporter (convector) of heat, stagnant air isn’t. Coming in at a tiny 0.026 W/mK (thermal conductivity) air is actually a great thermal insulator. Even the smallest amount of trapped air will cause a large thermal bottleneck. Getting goosebumps on your skin when cold is a Darwinistic throwback to that fact.

Thermal interface material – white sticky stuff

So, adding a paste/gel/putty/tape between the two objects will add some additional solid resistance but totally remove that pesky air resulting in an overall reduction in contact thermal resistance. That’s the theory anyway, unless you invest in a particularly cheap thermal interface material that can dry out, crack and lose its surface adhesion advantage. Why is it that cheap electronics always break? Go figure.

Building the FloTHERM model of the board was straight forward. The FloEDA application window allows for the import of populated PCB data to be imported directly from Expedition, Boardstation etc. Alternatively it can be used to quickly sketch out 3D PCB representations, including the layer stackup with the neat ability to import an image that represents the distribution of copper on each layer. For this board I imported the photocopier scanned image of the bottom layer then used FloEDA’s unique image processing capabilities to convert that into a thermal conductivity map of the distribution of FR4/Cu on the bottom layer.

The To220 detailed model was created using FloTHERM PACK. This involved a parametric definition of its construction and then pressing the ‘download detailed model’ button! The screw connecting it through the spreader plate and the spreader plate itself was manually defined in FloTHERM. The thermal interface itself was modelled as a 300 micron thick block with appropriate thermal conductivity.

With an assumed dissipation of 2.0W the predicted junction temperature comes out at a respectable 88 degC. This model remember represents the ‘working’ design where everything behaves as it was designed to do.

Examination of the heat flux vectors give further insight as to where the heat is flowing so as to produce the resulting temperature field. From the die, 85% of the heat passes through the thermal interface and on into the heat spreader. The other 15% passes down the leads, through the board to be spread throughout the bottom plane of the PCB where it is convected and radiated away to the rest of the DVD chassis.

Taking 2D slices through a 3D model often doesn’t take into account the more complex heat flow paths the heat weaves through on its way from its source (die) to the ambient. Looking at lines of heat flux in a semi-transparent view of the geometry highlights an interesting heat flow feature…

If the aluminium spreader was big enough so as to do its job properly all the heat would pass through it and from its vertical faces on into the surrounding air. As can be seen from the heat flux lines, a certain percentage actually passes through its pins back down into the PCB. Further examination of the predicted heat flux values indicates that, out of the 1.7W that passes into the spreader, 0.46W (27%) necks down through the pins. A thermal resistance in itself.

Never liking to see a bad thermal design, it’s at this stage I tend to get all indignant and demand to know why FloTHERM wasn’t applied in the design of this product. And this is the intended design, we haven’t even got onto the thermal interface failure yet!! Ach, enough of the moaning already. In Part 2 we’ll get on to what happens when the thermal interface fails, using the display of the BN (bottleneck) number to help understand why and where the thermal design is deficient, allowing us to propose and simulate some targeted remedial thermal design modifications.

18th January 2012, Nottingham.

Learn more from Mersen.

Learn more from Jaro.

Learn more from Fujipoly.

Learn more from Ironwood.

In addition to energy efficiency and product safety for lighting fixtures and lamps, the laboratory will provide services for consumer electronics, information technology equipment, televisions, power supplies, audio/video, battery chargers, displays, imaging equipment, and set top boxes. The new facility features several type C goniophotometers for testing lamps and luminaries and a type A goniophotometer for testing automotive and airport lighting as well as retroreflective material. A group of very spacious environmentally controlled life testing rooms were also designed into the building for ENERGY STAR testing.

Learn more from TÜV SÜD.

Learn more from Omega.

SWITCH bulbs use 80 percent less electricity than incandescent bulbs and last for about 25,000 hours no matter often you switch them on or off.

Learn more from SWITCH.

Learn more from Cree.

The Microsoft team forged ahead with the project, building and testing a system with tiny directional antennas at the top of each rack to send and receive data. A central controller monitors traffic patterns, finds network bottlenecks, configures the antennas and turns on the wireless links when more bandwidth is required. Signals go out on a horizontal plane and are steered right or left. The design sped up traffic by at least 45 percent in 95 percent of the cases tested.

Learn more from the NY Times.

The experimental graphene made by U.S. and Chinese researchers has also proven 60 percent more effective at transferring heat than typical graphene — a carbon sheet just one atom thick.

Efficient heat removal would also allow for smaller and more-powerful electronic devices that not only put computing power in everyone’s hands, but also allow for smarter gadgets connected to sensors and the Internet.

The secret to graphene’s success comes from its makeup. Natural carbon is found in concentrations of about 99 percent “carbon 12″ and 1 percent “carbon 13,” based on differences in its atomic mass. Researchers removed just one percent of carbon 13 to make it an “isotopically pure” carbon — about 99.99 percent carbon 12.

The specially engineered graphene was heated with a laser beam to test its heat transfer abilities at the University of Texas at Austin.

Learn more from MSNBC.

Learn more from European Commission Cordis.