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30 I-CONNECT007 MAGAZINE I APRIL 2026 limited information was available, and all I had to work with was a somewhat redacted cell phone picture of the two software instances side by side in an Excel sheet (Figure 1). These scenarios usually lead to a degree of detective work to isolate the root cause of the discrepancy. So, I set about manually entering the data and checking on my own version of the field solver. The scenario involved modelling and using crosshatched (mesh) ground planes. I thought it would be good to revisit the rationale for using mesh planes and the dimensional (and other) con- siderations when deploying them. Crosshatch Planes Revisited From a signal integrity purist's point of view, crosshatched planes are non-ideal: A full copper plane provides a consistent return path. However, PCB engineering often involves a compromise between the mechanical and electrical worlds, especially with flex circuits. Meshing/crosshatching is extremely useful on flex as it keeps the flex, well, flexible. It's no use having perfect signal integrity if the flex becomes brittle and fails owing to forc- ing solid copper plains in a stripline to act as an "I" beam, making the flex "inflexible." Here, the use of crosshatch is vital if the flex circuit is to survive its design lifetime of flexing. This is clearly more important in flex, such as with hinged and moving applications, rather than flex-to-fit, which may only be flexed a few times during assembly and repair. Crosshatch is also useful on thinner stackups, flexible or not, to achieve a given impedance whilst keeping the line width manufacturable. A meshed return plane will require a wider trace for a given impedance. This can be helpful when a fabricator is bouncing on the lower limits of pro- cess capability. Considerations It's important to keep the mesh as small as pos- sible. You can make large apertures in the mesh, but this will lead to EMI problems and, in extreme cases, cause impedance to vary along the line. Think of fiber weave effects on steroids. But if kept small in relation to the wavelength, the crosshatch is a viable and practical way to keep things flexible. Single-ended and differential?: Interestingly, crosshatch has a greater effect on single-ended transmission lines than differential because in dif- ferential pairs (depending on the coupling per- centage), much of the return current flows in the complementary side of the pair, so the closer the coupling, the less the effect of the hatch. Alignment: Often, you will see that guidance is to align over the hatch at 45 degrees and over the center of the crosses. However, this is not always possible. Often, the hatch is specified to the fabri- cator and added at the CAM stage rather than in CAD. It's best to know that much of the crosshatch- ing in flex is added at the fabrication stage—that might be changing, and if you think otherwise, let me know. At Polar, we get requests to add cross- hatch to flex impedance coupons in the CGen T H E P U LS E Figure 1: Two software instances side by side in an Excel sheet (from a cellphone picture).