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The Shaughnessy Report: With Field Solvers, GIGO Hurts

The “left shift” concept has been underway for at least five years, as EDA tool providers offer more powerful functionality earlier in the stages of PCB design and layout. This month, we focus on one tool that’s been shifting leftward for some time now: the field solver.

Once the domain of the experienced SI engineer, these computational tools—or at least some of their functions—are now available in PCB design software tools. With improved user interfaces, field solvers are being used by PCB designers and design engineers, many of whom have not mastered electromagnetics theory.

Electromagnetic theory all starts with James Clark Maxwell, whose four differential equations form the framework for understanding e-mag theory. Field solvers are complicated programs that solve a subset of Maxwell’s equations. Field solvers come in 2D, 2.5D, and 3D formats, and use several methods, such as the finite element method (FEM), finite difference (FD), and boundary element method (BEM) to extract parasitic circuit models.

When we first started planning this issue on field solvers, one thing became clear right away: Field solvers can be fairly difficult tools to use, even for veteran SI specialists, and it’s even tougher to make sure that you’re using the correct data so that you get the results that you need. Signal integrity experts we spoke with said that even experienced engineers could wind up with “garbage in, garbage out” (GIGO) if they aren’t careful.

There are hundreds of ways to go wrong with a field solver. As we see in this issue, some cases of GIGO derive from plugging in the wrong data, such as using IPC spec sheet info about board thickness instead of the “as pressed” number from your fabricator. Other designs have gone awry when field solver users didn’t account for Dk changing with temperature. We heard a chorus of engineers saying, “Don’t trust datasheets.”

This particular left-shift is happening for a reason: There just aren’t enough full-time signal integrity experts with advanced degrees and decades of experience in the industry. And if you can find them, they (rightly) charge a lot of money for their services. There are far more PCB designers than there are SI experts, so left-shifting computational horsepower into the hands of the PCB designer is a great way to mitigate this shortage of SI gurus.
But for a non-degreed PCB designer, using a field solver might feel like drinking from a firehose.

Design tool companies would love to develop a field solver with “PhD” (Push here, dummy) functionality. But we’re not there yet. You still must know something about Maxwell’s equations, or you’re going to have problems.

So, for the July 2022 issue of Design007 Magazine, we asked our expert contributors to share their thoughts on field solvers, and what new users need to know to get up to speed. Todd Westerhoff and Bill Hargin discuss the evolution of field solvers and offer some handy tips and techniques for new users. Zach Peterson focuses on the divide between typical field solvers and layout software, and the need for the two to converge into one environment. Columnist Martyn Gaudion details a bit of “field solver finesse” for the modeling of transmission lines. Brad Griffin and Nolan Johnson explore Cadence’s Clarity field solver functions, and columnist Barry Olney digs deep into cutting-edge techniques for the 2D field solver. Heidi Barnes takes a look at “the practical side” of field solvers and offers tips for avoiding GIGO.

We also bring you columns from Stephen Chavez, Tim Haag, and brand-new Electrolube columnist Saskia Hogan. We have an article by Cody Stetzel on flex guidelines, and another installment in Anaya Vardya’s continuing DFM101 series.

It’s summertime, but it doesn’t look like this industry is taking much of a vacation! See you next month.

Download your PDF copy of this issue for future reference.