On the rc5 sense board at its real 0.2 mm clearance, ten pins of the
0.5 mm pitch STM32 could only reach a pocket of seven or eight cells
inside their own pads: the grid columns miss the narrow legal band past
the pad tip, so twelve connections could not route even on an empty
board. For a crowded pin (a neighbouring pad of another net closer than a
trace can pass) whose nearby cells are such a pocket against pads and
keepouts, offer straight stubs along each axis to the first open cell,
accepted only if the stub clears every other net's pad by the full
margin, measured exactly. All twelve then route alone; on the full board
unrouted connections drop from 61 to 59, the rest being congestion.
rsp2k
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