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The figure below shows a single FR-4 PCB that has narrow "bridges" (marked with arrows). How narrow can these bridges be so the PCB is still structurally sound?

I imagine that the width will depend on the PCB thickness, but none of the PCB manufacturers that I know has this information available online.

Is there a rule of thumb for this dimension, or is it up to each manufacturer?

PCB example

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  • \$\begingroup\$ Ask your PCB fab. \$\endgroup\$
    – Hearth
    Commented Oct 14, 2023 at 2:45
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    \$\begingroup\$ "structurally sound" conveys no useful information. No one can answer a question that has no information. If you know the torsion, tensile, and/or shear forces being applied to the board, and, of course, the dimensions, the substrate supplier should be able to help. \$\endgroup\$
    – AnalogKid
    Commented Oct 14, 2023 at 3:15
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    \$\begingroup\$ Hmm, there was a relevant mikeselectricstuff video, but I can't find it at the moment; it was many years ago. He went into some detail of something he did with snap-together PCBs, with narrow segments milled as snaps or friction tabs. If nothing else, his YT videos are worth binging for manufacturing and teardown topics. \$\endgroup\$ Commented Oct 14, 2023 at 4:16

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You need to call the PCB manufacturer and find out what they can do.

As a wild guess I would imagine 0.10 inches (2.5 mm) would be possible with FR-4. The 90° inside corners should be a radius so the board can be milled out, provide durability, and reduce cost. A 0.03125 inch (0.8 mm) radius is common.

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