Invert your thermal model to good effect

Electronic thermal simulations are most commonly formed by specifying a power dissipation within a package and using numerical solution techniques to derive what the resulting temperatures are within and around the package, PCB etc. If the package temperature is too high you’ve got issues that you’ll need to resolve via various thermal management approaches. You can turn the model definition on its head by specifying a package temperature as an input are getting a solution for power dissipation. From the solvers point of view it’s just two sides of an equation. From your point of view it provides useful information.

In an IC package heat is dissipated on the silicon die. This leads to the die reaching a certain temperature, the value of which depends on how easily heat can exit the die, through the package, into the PCB, the air, a heatsink, through an enclosure etc. This temperature at the heat source is called the junction temperature. It’s this value that is related to a specified maximum junction temperature and thus thermal compliance can be quantified.

Instead of a package power dissipation value (which is difficult to obtain accurately) you can set in your electronics thermal tool of choice (that will likely or of course be FloTHERM, FloTHERM.PCB or FloEFD) the silicon to be at the maximum junction temperature that the package is rated at. This value should be much easier to obtain. It should be, you were going to use it to judge thermal compliance anyway! Perform another thermal simulation and you can observe what power dissipation comes out of this fixed temperature silicon.

Such a power dissipation is the maximum power dissipation that could be dissipated by the package whilst the junction temperature does not go above its maximum value. Useful information in and of itself.

Some things to be aware of though… that predicted maximum power dissipation will be valid only for that package in that layout for that PCB in that environment. Any change to layout, environment etc. and you’d have to do a recalc.

Try it, turn your simulation on its head, see what comes out.

21st July Nottingham

Post Author

Posted July 21st, 2009, by

Post Tags

, , ,

Post Comments

1 Comment

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

One comment on this post | ↓ Add Your Own

[…] I’d follow the previous post up with a slightly more detailed description of exactly how to set-up a model with a fixed temp die […]

Add Your Comment

Archives

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!