Cadence’s Celsius: Don’t End up Holding the Hot Potato!

Estimated reading time: 13 minutes

Dave and I closed our conversation with me asking, “How were we planning on performing thermal analysis on the S4L?” In answer, Dave simply stuck the tip of his index finger in his mouth to wet it and then held it in the air in a traditional “Let’s see which way the wind is blowing” gesture. The sad thing is that I wasn’t surprised.

Celsius Lets Us Turn the Temperature Down
I must be feeling in a literary mood at the moment because I’m reminded of a line in the book Glass Sword by American author Victoria Aveyard which goes, “The thing with heat is, no matter how cold you are, no matter how much you need warmth, it always, eventually, becomes too much.” I cannot but help feel this is apposite to our discussions here.

As I said in my recent article, “As every electronic design engineer on the planet knows (unless they’ve been living under a rock), Cadence has state-of-the-art design and analysis tools for every portion of the design flow—chip design, package design, and board/module design. What is less well known is that, for the past few years, Cadence has been ramping up its capabilities in system-level simulation, analysis, and verification space (where no one can hear you scream)...”

I also noted that, “One underlying problem is that many of today’s software analysis tools were conceived and developed in the era of single-core computing, which means they simply don’t scale well, even if they are run on systems that have multiple cores with multiple threads running on each core. To address this problem, the boffins at Cadence started with a clean slate and created a distributed multiprocessing technology that was designed from the ground up to take full advantage of multiple cores—both central processing units (CPUs) and graphical processing units (GPUs).”

All of which leads us to the Cadence Celsius Thermal Solver, which takes full advantage of Cadence’s distributed multiprocessing technology to deliver virtually unlimited capacity and 10X the speed of legacy 3D finite element analysis (FEA) solvers while maintaining gold-standard accuracy.

In addition to heat sources, it’s also necessary to model the conduction, convention, and radiation of heat throughout the system. In turn, this means it’s necessary to model air flow inside and outside the system while understanding that the dynamics of this flow, and its capacity to remove heat, will be modified by the thermal environments it encounters. Thus, the Celsius Thermal Solver combines its finite element analysis of solid structures with computational fluid dynamics (CFD) analysis for the air flowing around and through the system, thereby providing complete system thermal analysis in a single tool.

Figure 2: The Celsius Thermal Solver combines finite element analysis and computational fluid dynamics algorithms to perform both steady state and dynamic analysis.

The Celsius Thermal Solver is a true 3D solution that can be used to perform both static and transient 3D thermal analysis on ICs, 3D-ICs (that is, chips composed of multiple dice stacked on top of each other), IC packages, system-in-package (SiP) components (which involve multiple IC and/or 3D-IC dice mounted on a common substrate), modules, and PCBs. Furthermore, Celsius can also be used to analyze enclosures, including chassis, racks, and entire systems.

This is quite a feat when you think about it because it involves the ability to work over 10 orders of magnitude, from nanometers (10^-9) to meters (10⁰). There are several factors that make this work, including the fact that Celsius employs an automatic adaptive mesh, which means it adds or removes mesh elements as necessary to provide the required level of accuracy. That is, the automatic adaptive mesh will refine the mesh density in the regions having large temperate gradients so as to obtain more accurate results, while relaxing the mesh density in those regions where the temperature gradients do not vary so dramatically.

There’s also the fact that Celsius scales in an almost linear fashion using an “elastic compute architecture.” What this means is that, if you have only a single core, a simulation will take a certain amount of time. With two cores, the same simulation will take half the time. Where are all these cores coming from? Well, you can use your own on-premises distributed computing solution if you wish. Alternatively, by making their tools cloud-friendly, the folks at Cadence have provided the option for essentially unlimited scaling, which means essentially unlimited capacity.

Something else that must be considered is the classic “chicken or egg” problem (i.e., which came first?). In this case, the electrical and thermal aspects of the system are interrelated and interact with each other; temperature affects electrical resistance, and every element of electrical resistance introduces an additional thermal source. We can’t nail down a good thermal analysis until we’ve locked down the electrical design, and we can’t tie the electrical design down until we've performed our thermal analysis. The solution is to perform electrical-thermal co-simulation; that is, to perform electro-magnetic analysis using Clarity in conjunction with thermal analysis using Celsius.

Celsius and Clarity can both import mechanical structures from all major MCAD tools (thereby facilitating the modeling of enclosures). Also, both tools can easily read design data from all standard chip, IC package, and PCB platforms. Furthermore, Celsius and Clarity both offer unparalleled integration with Cadence’s own tools, such as Virtuoso Layout, SiP Layout, Allegro PCB Designer, and Voltus static and transient power profiling.

In the olden days, a traditional scenario was to work all the way through the development of a system, have the end in sight, discover that something was running too hot, get together with the thermal analysis team, track down the problem, and return to the drawing board with much gnashing of teeth and rending of garb. 

Today, the ability to use tools like the Celsius Thermal Solver in conjunction with the Clarity 3D (FEM) Solver and the Clarity 3D Transient Solver early in the design cycle—alongside the IC, package, PCB, and enclosure tools—means that none of us are going to be left standing alone holding the hot potato. Instead, we can break out the party hats and perform our happy dance. 

References
1. Max’s Cool Beans blog, What the FAQ are Celsius and Fahrenheit?
2. Max’s Cool Beans blog, What the FAQ are Kelvin, Rankine et al?

Clive “Max” Maxfield is the founder of Maxfield High-Tech Consulting and the author of a variety of books, including “Bebop to the Boolean Boogie.” He has been at the forefront of EDA for over 30 years. 

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