So, you want to predict component temperatures do you? Part I

Prediction of component temperatures is central to electronics cooling simulation, the management of their temperatures  is central to electronics cooling design. Either way, heat is dissipated inside a component, component gets hot, if component gets too hot, component stops working. When creating an electronics cooling simulation model the question of how to thermally represent the components is key.

The vast majority of electronics cooling simulations performed today use a technology called CFD, computational fluid dynamics. A 3D CAD type definition of the components, PCBs, heatsinks, chassis, fans etc. are input. The equations that predict temperatures and air flow distribution are solved by clever number crunching executables. Finally the predicted temperatures and air flow can be examined in both graphical (CFD: color for directors) or tabular formats.

temp2

Why is there any question about how to model components, surely you would just define them as they exist in reality? It all comes down to data availability. Components (packaged silicon normally) are quite complex, incorporating many different parts, with different materials, from bond wires to lead frame, from a spreader to the die itself. Having to manually create all that for EACH component would be madness.

So, why not get such a description from the component manufacturer? Well, they tend to be quite secretive about the internals of their packages. There’s a lot of IP bound up in there, last thing they want to do is to provide a full 3D physical description of it to all and sundry.

Where does this leave the poor thermal engineer? With little data and pressing needs, a number of different component modelling methodologies have emerged over the last 20 or so years.

For this first part of this blog series we’ll cover the most common, a lumped block representation. A 3d homogeneous block with a single material.

pqfp_block

In terms of data, the one thing that is available is the package footprint size, this is required for routing and manufacturing design (as is often the case with the more unique disciplines, thermal eats the crumbs that fall from the giants table). If you’ve got a footprint shape then the only other thing you’ll need to make a 3D model is the height.  The component height can itself be quite rare,  maybe less nowadays as component libraries become more refined and the need for mechanical interference checks becomes much more common place.

In reality a component will have a range of temperatures throughout it. The die being the hottest, the peripheral corners being the coldest. Components will be specified to work up to a maximum junction (die) or case (usually middle+top) temperature. How on earth can we get a range of temperatures out of a component model that is just one lump? Well, you can’t. Why not at least dissipate the heat in that block where the die actually is? Well, don’t bother, even if you did know how big the die was there is still no advantage in accuracy as you’re not modelling all the other heat flow paths in any detail. You can’t be half accurate when trying to be accurate. You’re just going to have to lump it, literally, and spread all the heat throughout your block representation.

library2Last thing required is a material definition. A 3D thermal simulation requires that all solids have a thermal conductivity defined (to enable a steady state thermal prediction) and density and specific heat (to obtain the thermal capacitance) in addition if a transient thermal simulation is required. Well fear not young thermal engineer. We, your preferred vendor, have created a library of ‘typical lumped packages’ materials with values that will result in typical case temperature predictions when modelling your components as lumped blocks. If you buy the best you get the best, even when it helps you create a more accurate block.

Next time you see some nice piccies of an electronics cooling model, check out how the components are modelled. More than likely they’ll be blocks. Not the best approach by far, in fact it is the least accurate but easiest to define. How inaccurate? Hard to say as it varies a lot. On average I’d say between 10-30% error on case temperature rise with no indication of junction temperature at all. Not bad considering what you’re not representing.

9th October 2009, Ross-on-Wye

Post Author

Posted October 9th, 2009, by

Post Tags

, , ,

Post Comments

11 Comments

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. Robin Bornoff's blog

Comments

11 comments on this post | ↓ Add Your Own

Commented on October 12, 2009 at 3:19 am
By Chris Hill

“So, why not get such a description from the component manufacturer? Well, they tend to be quite secretive about the internals of their packages…”

Ahem. If it’s NXP MOSFETs you’re after, then for several years we’ve made detailed models available for most of our devices. Used to be downloadable from smartparts3d, and now available direct from the NXP website.

Regards…

Commented on October 12, 2009 at 3:50 am
By Robin Bornoff

Always the exception that proves the rule! I’m going to be getting on to ‘detailed models’ at the end of this blog series. But yes, NXP is a rare exception in that they do supply (detailed) models of their packages. It would be interesting to know what it is about NXP’s view of their MOSFETs that results in them supplying them, i.e. why no IP, why is it that there is nothing to hide? Is it the relative simplicity of the packaging style? What I’m getting at is why does NXP supply such packages and hardly anyone else does!!!

Commented on November 6, 2009 at 2:09 am
By Robin Bornoff

About 20-15 years ago the most experience people had was to use 10 W/mK for a lumped rep of a component. Over the years, with an increase of application of CFD to electronics cooling and the subsequent experience, the approach has been refined. Even today there is a ‘hierarchy of accuracy’, from block models all the up through compact thermal models to detailed models. In terms of recommendation I recommend detailed models (do you use FloTHERM.PACK http://www.flopack.com ?), but that was not your question! If you can not find any more info and so have to model the component as a block I would advise the ‘Typical lumped packages’ materials library. This is a refinement on the 5-15 W/mK range, based on some detailed vs. lumped characterisation work we conducted. The values of k have been calibrated to provide block predictions of case temperature and better reflect the types of lower conductivity packages found today compared to the types that were around 20 years ago. For a bit more info please check out: http://www.mentor.com/products/mechanical/multimedia/pcb-thermal-simulation-the-state-art_reg.cfm?int=1&id=3d15bc1d-fe24-457c-88e8-9859681f8bbd

Commented on November 13, 2009 at 5:07 am
By Mind Your Head(room) Again « John Parry’s Blog

[…] to make creating package thermal models easy. I’d recommend you read Robin Bornoff’s blog ‘So, you want to predict component temperatures do you?’ for an on-going discussion of package thermal […]

Commented on November 16, 2009 at 6:07 am
By A trip to MPH and Top Gear Live « Robin Bornoff’s blog

[…] current blog series titled “So, you want to predict component temperatures do you?” is a big chunky theme that will require quite a few more parts until completion. As a break I […]

Commented on December 14, 2009 at 6:23 am
By long mi

Can you mail the “PCB Thermal Simulation – The State of the Art” to me? formelong@gmail.com Thank you!

Commented on December 14, 2009 at 8:24 am
By long mi

Some value of “Typical lumped packages” are so low such as ChipArray=0.1,TSOP=0.1…most of that are 0.x.But as we know the Flotherm commended that plastic package=5,ceramic package=15.Both the value are bigger than most of package in “Typical lumped packages”.so why and what method is better?

Commented on December 17, 2009 at 8:04 am
By Robin Bornoff

In the sliding scale of model accuracy and representation any block method is going to be less accurate than other better methods of representation (e.g. thermal resistor network or detailed). The ‘Typical lumped package’ materials are preferable to the typical ceramic or plastic materials that are a throw back to earlier times. Best advise: use FloTHERM.PACK or hassle your component supplier for good quality characteristic thermal data.

Commented on December 18, 2009 at 8:16 am
By Robin Bornoff

[…] a range of methods available to thermally represent IC packages that I covered in this previous blog series. The derivation of such representations is the thermal characterisation obligation of the suppliers […]

[…] a range of methods available to thermally represent IC packages that I covered in this previous blog series. The derivation of such representations is the thermal characterisation obligation of the suppliers […]

Add Your Comment

Archives

November 2014
  • If You’re Going to Lose it, You Might as Well Use it!
  • October 2014
  • Thermal Bottlenecks. This is Hot, This is Why.
  • Blue LEDs. Since When is Improvement Invention?
  • Leg Hair? What a Drag
  • The Electronics Cooling Metaphorical Drinking Game
  • September 2014
  • Xilinx Patent for Critical Tj Prediction
  • Dell Precision – Spot on Thermal Design
  • Top 10 FloTHERM V10 Features – #11: Odds and Sods
  • Top 10 FloTHERM V10 Features – #10: Improved Solar Calculator
  • Top 10 FloTHERM V10 Features – #9: Data Center Simulation
  • August 2014
  • Top 10 FloTHERM V10 Features – #8: Thermostatic Control with Hysteresis
  • July 2014
  • Top 10 FloTHERM V10 Features – #7: Super-fast Parallel CFD Solver
  • June 2014
  • Top 10 FloTHERM V10 Features – #6: Integrated Summary Columns
  • Top 10 FloTHERM V10 Features – #5: FloSCRIPT
  • Top 10 FloTHERM V10 Features – #4: Updated CAD
  • Top 10 FloTHERM V10 Features – #3: FEA Interfacing
  • February 2014
  • Top 10 FloTHERM V10 Features – #2: Advanced Find
  • Top 10 FloTHERM V10 Features – #1: New GUI
  • January 2014
  • Come and Learn about the Latest Release of FloTHERM, V10
  • Heat Your Home Office for 8p a Day. Part 5 – Putting it All Together
  • December 2013
  • Heat Your Home Office for 8p a Day. Part 4 – Comfort Temperature
  • Heat Your Home Office for 8p a Day. Part 3a – Was Dave Right?
  • November 2013
  • Heat Your Home Office for 8p a Day. Part 3 – It Takes Time
  • Heat Your Home Office for 8p a Day. Part 2 – Thermal Interception
  • Heat Your Home Office for 8p a Day. Part 1 – Really?
  • Happy 25th Birthday FloTHERM !
  • July 2013
  • Why Not Just Shove a Heatsink on Top of it? Part 3: Pads, Vias and Undersinking
  • May 2013
  • 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
  • April 2013
  • Experiment vs. Simulation, Part 5: Detailed IC Package Model Calibration Methodology
  • CFD – Colourful Friday Distractions
  • Experiment vs. Simulation, Part 4: Compact Thermal Models
  • February 2013
  • Experiment vs. Simulation, Part 3: JESD51-14
  • January 2013
  • Experiment vs. Simulation, Part 2: TIM Thermal Conductivity
  • Experiment vs. Simulation, Part 1: Them and Us.
  • September 2012
  • “Why Cartesian Grids Are Good”
  • August 2012
  • Where’s the Best Place to Put a Radiator in a Room? Part 5: Get a Job
  • Where’s the Best Place to Put a Radiator in a Room? Part 4: Premature Simulation
  • July 2012
  • Where’s the Best Place to Put a Radiator in a Room? Part 3: 13% Better
  • Where’s the Best Place to Put a Radiator in a Room? Part 2: PMV and other TLAs
  • Where’s the Best Place to Put a Radiator in a Room. Part 1: Such Things are Important
  • May 2012
  • Agile software development practices in the Mechanical Analysis Division
  • A Little Goes A Long Way (But A Lot Doesn’t Go Much Further)
  • April 2012
  • More Than Two Decades and Still Going Strong; FloTHERM and FloVENT V9.3 Now Released
  • Simulation Software So Simple Even Teenagers Can Use It
  • February 2012
  • Bottlenecks and Interface Materials; Part 3 – Relieving Thermal Bottlenecks Reduce Temperatures
  • January 2012
  • Bottlenecks and Interface Materials; Part 2 – When TIMs Go Bad
  • Bridging the Simulation Supply Chain; NXP Semiconductors, a Case in Point
  • Bottlenecks and Interface Materials; Part 1 – Great Thermal Bedfellows
  • Emails, more Emails and Jeff Bridges
  • LEDs; The future’s bright and hot.
  • December 2011
  • From Megawatts to Milliwatts; sub-micron scale thermal modelling with FloTHERM
  • November 2011
  • What! All that just for that? The bonkers world of CPU cooling.
  • October 2011
  • Ho, Ho, Ho! Facebook moves to Lapland
  • All Detailed Thermal IC Package Models are Wrong… Probably
  • Underfloor Electric Heating. Part III – Penny wise, pound foolish.
  • August 2011
  • Underfloor Electric Heating. Part II – Infrared Thermography
  • Underfloor Electric Heating. Part I: In by Christmas
  • June 2011
  • Come, meet FloTHERM/VENT/EFD users, learn and enjoy!
  • PC Overclocking and Aftermarket Modding. Part III – Power vs. Frequency?
  • PC Overclocking and Aftermarket Modding. Part II – Liquid Nitrogen Overclocking, How Cool is That?
  • May 2011
  • PC Overclocking and Aftermarket Modding. Part 1 – When Colour Matters.
  • April 2011
  • Desktop PC with Integrated Toaster – As if!
  • Thermal Design Perfection Starts with the use of FloTHERM PACK
  • We Love FloTHERM V9.2
  • Desktop PC with Integrated Toaster – the Future is Now
  • March 2011
  • Do you know the way to San Jose?
  • February 2011
  • Beer Fridge – A Case Study in Thermal Design. Part 6 – Baffles and Bottlenecks
  • January 2011
  • FloEFD HVAC Module – Taking Built Environment CFD Simulation to the Next Level
  • Beer Fridge – A Case Study in Thermal Design. Part 5 – Time for a FloBEER
  • Beer Fridge – A Case Study in Thermal Design. Part 4 – FloBEER
  • Beer Fridge – A Case Study in Thermal Design. Part 3 – Side Up or Upside Down?
  • December 2010
  • Beer Fridge – A Case Study in Thermal Design. Part 2 – TEC Effect
  • November 2010
  • Beer Fridge – A Case Study in Thermal Design. Part 1 – A Gift
  • What Can You Learn When You Turn It On?
  • We Love FloTHERM – 8 Reasons to Upgrade to V9.1
  • October 2010
  • On the Vilification of Smokers
  • Identifying Thermal Bottlenecks and Shortcut Opportunities – Taking Simulation to the Next Level
  • August 2010
  • How many frogs does a horse have?
  • It’s a wireless world! No it isn’t.
  • July 2010
  • Are you using ‘Smart’ in a way I am not familiar with?
  • An Interview With… Clemens Lasance
  • I was led to believe we’d have flying cars by now
  • Red Hot Electronic Thermal Analysis?
  • June 2010
  • The art of modelling using CFD. Part VI – Peripheral Boundary Conditions
  • The art of modelling using CFD. Part V – Grid
  • May 2010
  • The art of modelling using CFD. Part IV – Fans
  • The art of modelling using CFD. Part III – TIGs
  • The art of modelling using CFD. Part II – Grilles
  • The art of modelling using CFD. Part I – What happens if you cross art with science?
  • April 2010
  • How much do ‘U-Value’ good thermal insulation? Part VII – “Ooo, shut that door”
  • “A Faster Horse” – Mentor ‘IDEAS for Mechanical’ driving product development
  • March 2010
  • How much do ‘U-Value’ good thermal insulation? Part VI – revenge of the radiative heat flux
  • IC package representation is central to Electronics Cooling
  • How much do ‘U-Value’ good thermal insulation? Part V
  • February 2010
  • How much do ‘U-Value’ good thermal insulation? Part IV
  • How much do ‘U-Value’ good thermal insulation? Part III
  • How much do ‘U-Value’ good thermal insulation? Part II
  • January 2010
  • 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
  • So, you want to predict component temperatures do you? Part VI
  • So, you want to predict component temperatures do you? Part V
  • November 2009
  • A trip to MPH and Top Gear Live
  • So, you want to predict component temperatures do you? Part IV
  • So, you want to predict component temperatures do you? Part III
  • October 2009
  • So, you want to predict component temperatures do you? Part II
  • So, you want to predict component temperatures do you? Part I
  • Underfloor Thermal Insulation; Why? Part III
  • September 2009
  • Underfloor Thermal Insulation; Why? Part II
  • Underfloor Thermal Insulation; Why? Part I
  • Is all Software Rubbish?
  • August 2009
  • Thermatronic Stagnation (nothing to do with male deers)
  • Fractals: Gods Artwork, Part III
  • Thermatrons Must Leave
  • July 2009
  • 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
  • 3D Electronics Cooling CFD, with FloTHERM, in Pictures
  • Spend some time with FlyGuy
  • “All models are wrong, but some are useful” Part IV
  • Flying
  • “All models are wrong, but some are useful” Part III
  • May 2009
  • “All models are wrong, but some are useful” Part II
  • “All models are wrong, but some are useful” Part I
  • Welcome along!