PCB Design Optimization: What it Means and New Methods
Presented at PCB West 2021 (Oct 6, 2021)
PCB designers often speak of “design optimization,” and causal PCB design optimization has found a stronger mathematical footing in the engineering literature over the last 10 years. In particular, transmission line design requires satisfying multiple design objectives and constraints that may be in conflict, and engineers need tools and methods to help them balance design objectives while staying within their design constraints. For ultra-high-speed boards, designers need to optimize transmission line designs within the relevant signal bandwidth, which can extend to hundreds of GHz. Newer signaling specifications and standards (e.g., USB4, DDR5, and IEEE 802.3 standards) require this level of optimization throughout the signal bandwidth to demonstrate compliance, and design teams need a set of tools that help expedite this type of optimization. Current PCB design optimization methods are typically measurement-based or field-solver-based, but CAD packages lack support for these tasks or for accepted analytical methods in PCB design optimization.
This presentation outlines the current state of PCB design optimization techniques used to produce useful designs, while balancing multiple design goals. An alternative method for design optimization from analytical equations describing transmission lines will be presented. Some practical examples for striplines, microstrips, and mode-selective waveguides will be presented. These models are fully causal and account for dispersion, dielectric losses, skin effect losses, and copper roughness in a real PCB. The presented method is applicable to any transmission line with a known analytical or numerical model, and the method uses standard evolutionary computation techniques to optimize the design. Similar techniques can be implemented in advanced field-solver tools, but designers with basic coding skills can use some simple open-source packages to build their own design optimization routines for transmission lines. Furthermore, the transmission line design optimization method presented here can be used to balance multiple design objectives, which is not currently possible in PCB CAD packages.
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