Robin Bornoff's blogRobin Bornoff's blog RSS
Two different package styles, two very different thermal responses when a extruded plate fin heatsink is placed on each. At the very least a FloTHERM simulation can be used to observe the thermal behaviour of a product concept, beyond that it can be used to understand *why* the thermal behaviour is what it is.
A common enough question. Heatsinks are often perceived to be the magic answer to all electronics cooling challenges. They should be called ‘area extenders’ as heat does not just disappear into them. Heat spreads throughout a heatsink passing to the air over a much larger area than it would otherwise do. Air can then do its magic, whisking the heat away thus keeping the electronics that generated that heat nice and cool. So why not just shove a heatsink on top of any thermally critical component?
In the royal family of thermal IC package modelling types, a detailed model is King. All critical 3D geometry is modelled explicitly, no abstraction into a thermal resistor equivalent model, no hiding all the proprietary design information inside either. Pros and cons of detailed models I covered a few years ago in this blog. Packaged ICs are complex, constructed of many parts, with many different material properties. If you’re going to take a detailed modelling approach (rather if you’re lucky enough as an end user to obtain a detailed a model) you’ll be wanting to ensure the model is as accurate as possible. How can you do that without destructively testing a physical equivalent and spending loads on material testing machines and SEM time? Use a T3Ster based experimental testing approach instead!
By way of an apology for the more verbose blogs I’ve been issuing recently I’d like to present you with a blog that serves no other purpose than to show a pretty picture. CFD as an acronym has quite a few different interpretations. Contracts for Difference if you’re into your financials. Colour For Directors if you’re in marketing. Cheats, Frauds and Deceivers if you’re feeling very cynical. Computational Fluid Dynamics if you’re an engineer. Whilst most real engineering work involves simulation of one or two key numeric parameters, there is fun to be had in the creation of pictures. To either brighten your day or to encourage others to take your simulation based proposed design modifications seriously.
Arrgghhh, like a monologuing evil movie villain I’ve been waffling on too much. Here’s a picture of a surface mounted TO263, showing heat flux ribbons going from the die, through the package and PCB and into an oncoming air stream. The plane plot is a clipped distribution of the hotter temperatures. All simulated with FloTHERM.
Click on the picture to get a high rez image. Good for desktop backgrounds or even recreation rooms like the one just installed in the Mentor Graphics Hampton Court (UK) office:
5th April 2013 Ross-on-Wye
Electronics cooling simulation was born out of the world of CFD, rather fully conjugate heat transfer simulation where convective, radiative and conductive affects are considered concurrently. Back in the day much talk was had about turbulence modelling, convective discretisation schemes and linear equation solvers, all typical CFD subjects but somewhat out of place in the context of what became the real issue for thermal design engineers performing electronics cooling simulation; thermal data availability.
The JESD51-14 standard was published in November 2010, prepared by the JEDEC JC-15 Committee on Thermal Characterization. It outlines a new process to measure what is the most common IC package thermal metric, Theta_jc. This is the thermal resistance between the die and the package case face. More specifically the face of the package that is to be cooled by an external heatsinking method. Theta_jc wasn’t a new metric that required a new method to be proposed to measure it so what was the motivation for this standard? You can learn more about something when considering -why- that thing was done beyond -what- the thing actually is.
The temperature rise that electronic components attain in operation is due to 3 things. The power that they dissipate, the ambient temperature surrounding the product and the various thermal bottlenecks that the heat passes through on its journey from the source to the ambient. An accurate simulation requires all 3 aspects to be modelled correctly. In terms of the bottlenecks, conductive resistance is critical, especially close to the heat source where the heat flux values (W/m2) are high, due often to the small areas through which the heat flows. A (1D) conductive resistance is commonly characterised by the thickness of the solid object divided by its thermal conductivity times its area. Getting the conductivity correct is a must in any electronics thermal simulation.
Before you sell it, or commission it, you want to be sure that it works. Monies have been spent on getting things this far, some of it on you via your overhead and your expansive salary (yeh, ok, I hear you). Expectation is that your organisation will make more money back. Last thing you want is to have your product fail, have to be tweaked, fixed, respun, redesigned or canned. What you’d like is for the first prototype to just work, meet its design constraints, pass all the QA checks and be shipped. Once out there in the market you certainly don’t want to start seeing field returns. Today we see simulation and experimental measurement used in conjunction to keep the product design wheels of the technology industry moving. It wasn’t always the case.
I put the title in quotes as it’s the title of a blog post by John Chawner at Pointwise who keeps a pleasantly vendor neutral(ish) blog about all things CFD called ‘Another Fine Mesh’, including the excellent weekly ‘This Week in CFD’ that is becoming a bit of a mecca for the CFD community. John’s blog focusses on a white paper Mentor issued recently about How to Choose an Effective Grid System for CFD Meshing. I thought it would be a good opportunity to talk about the motivation and strategy that has resulted in such meshes being central to the technologies of FloTHERM, FloVENT and FloEFD, our flagship CFD tools.
Effective use of a Computational Fluid Dynamics (CFD) simulation tool requires at least a working knowledge of fluid dynamics itself. Tools alone don’t make for a good engineer. When interviewing for jobs within the Mechanical Analysis Division (and way back into Flomerics days too) a common question posed to tease out such an understanding is to describe the air flow patterns in and around a radiator placed under a cold window. The range of answers we’ve heard over the years has been quite outstanding.
About Robin Bornoff's blog
Views and insights into the concepts behind electronics cooling with a specific focus on the application of FloTHERM to the thermal simulation of electronic systems. Investigations into the application of FloVENT to HVAC simulation. Plus the odd foray into CFD, non-linear dynamic systems and cider making.
- Why Not Just Shove a Heatsink on Top of it? Part 2: Heat Flow Budgets
- Why Not Just Shove a Heatsink on Top of it? Part 1
- Experiment vs. Simulation, Part 5: Detailed IC Package Model Calibration Methodology
- CFD – Colourful Friday Distractions
- Experiment vs. Simulation, Part 4: Compact Thermal Models
- Experiment vs. Simulation, Part 3: JESD51-14
- May 2013 (2)
- April 2013 (3)
- February 2013 (1)
- January 2013 (2)
- September 2012 (1)
- August 2012 (2)
- July 2012 (3)
- May 2012 (2)
- April 2012 (2)
- February 2012 (1)
- January 2012 (5)
- December 2011 (1)
- November 2011 (1)
- October 2011 (3)
- August 2011 (2)
- June 2011 (3)
- May 2011 (1)
- April 2011 (4)
- March 2011 (1)
- February 2011 (1)
- January 2011 (4)
- December 2010 (1)
- November 2010 (3)
- October 2010 (2)
- August 2010 (2)
- July 2010 (4)
- June 2010 (2)
- May 2010 (4)
- April 2010 (2)
- March 2010 (3)
- February 2010 (3)
- January 2010 (8)
- How much do ‘U-Value’ good thermal insulation? Part I
- Keeping the caveman warm – HVAC blog
- FloVIZ, the free FloTHERM/FloVENT CFD results viewer, try it, it’s free
- ‘Heat Trees’ – taking a leaf out of natures book
- The Most Extreme CFD Model Ever Ever – Explained
- FloTHERM and its new XML neutral file format
- The Most Extreme CFD Model Ever Ever
- So, you want to predict component temperatures do you? Part VII
- December 2009 (2)
- November 2009 (3)
- October 2009 (3)
- September 2009 (3)
- August 2009 (3)
- July 2009 (9)
- At the Speed of Heat
- A Load of HVAC TLAs
- How-to: Invert your thermal model to good effect
- Clogged cooling fins, a cautionary tale
- Invert your thermal model to good effect
- “I work with computers”
- Fractals: Gods Artwork, Part II
- Fractals: Gods Artwork, Part I
- “All models are wrong, but some are useful” Part V
- June 2009 (5)
- May 2009 (3)