Mechanical
Board outline, mounting hole pattern, drill schedule and design rules.
The board is laid out on an imperial grid, so the inch figures are the round ones. Millimetres follow in brackets.
Board outline
| Property | |
|---|---|
| Width | 3.000 in (76.20 mm) |
| Height | 3.750 in (95.25 mm) |
| Thickness | 0.063 in (1.6 mm) |
| Layers | 4 |
| Copper weight | 1 oz outer, 1 oz inner |
Mounting holes
Four M4 holes on a rectangular pattern, plated, each ringed with eight stitching vias tying the pad through the stackup.
| Property | |
|---|---|
| Pattern | 2.500 × 3.250 in (63.50 × 82.55 mm) |
| Inset from each edge | 0.250 in (6.35 mm) |
| Hole diameter | 0.169 in (4.3 mm) |
| Pad diameter | 0.339 in (8.6 mm) |
| Stitching via drill | 0.024 in (0.6 mm) |
| Stitching vias per hole | 8 |
The pattern is centred on the board, so each hole sits a quarter inch in from both
nearest edges. H1 is top-left, H2 top-right, H3 bottom-left and H4 bottom-right.
Hole positions from the board’s lower-left corner:
| Ref | X | Y |
|---|---|---|
H1 | 0.250 in (6.35 mm) | 3.500 in (88.90 mm) |
H2 | 2.750 in (69.85 mm) | 3.500 in (88.90 mm) |
H3 | 0.250 in (6.35 mm) | 0.250 in (6.35 mm) |
H4 | 2.750 in (69.85 mm) | 0.250 in (6.35 mm) |
M4 clearance through a 0.169 in hole leaves 0.012 in of play, and the 0.339 in pad is large enough that an M4 washer sits entirely on copper.
Drill schedule
Plated (PTH) — 442 holes
| Diameter | Count | What | |
|---|---|---|---|
| 0.012 in | 0.30 mm | 353 | Signal vias |
| 0.024 in | 0.60 mm | 32 | Mounting hole stitching vias |
| 0.028 in | 0.70 mm | 4 | USB-C P1 shield legs |
| 0.031 in | 0.80 mm | 2 | Solder jumper JP6 |
| 0.037 in | 0.94 mm | 16 | RJ45 J2 |
| 0.039 in | 1.00 mm | 18 | Pin header J1 (6) and PMOD J4 (12) |
| 0.047 in | 1.20 mm | 5 | Pluggable headers J9, J10 |
| 0.051 in | 1.30 mm | 8 | Screw terminals J5–J8 |
| 0.169 in | 4.30 mm | 4 | M4 mounting holes |
Non-plated (NPTH) — 4 holes
| Diameter | Count | What | |
|---|---|---|---|
| 0.023 in | 0.58 mm | 1 | USB-C P1 locating slot, 0.039 × 0.023 in oval |
| 0.026 in | 0.66 mm | 1 | USB-C P1 locating hole |
| 0.130 in | 3.30 mm | 2 | RJ45 J2 mounting posts |
Smallest plated drill is 0.012 in (0.30 mm). The smallest non-plated feature is P1’s
oval slot — note that 0.023 in is its minor axis, not a round hole, and some fabs quote
slots separately.
Design rules
The rules stored in FemtoLCC.kicad_pro are set to JLCPCB’s capability limits:
| Rule | Rule | ||
|---|---|---|---|
| Clearance | 0.004 in (0.10 mm) | Track width | 0.004 in (0.10 mm) |
| Hole to hole | 0.010 in (0.25 mm) | Hole clearance | 0.008 in (0.20 mm) |
| Copper to edge | 0.012 in (0.30 mm) | Via diameter | 0.018 in (0.45 mm) |
| Annular ring | 0.005 in (0.13 mm) | Text / silk width | 0.006 in (0.15 mm) |
Actual minimums on the board are looser than that floor: 0.008 in (0.20 mm) track and 0.004 in (0.10 mm) space.
track_dangling is set to ignore — the one-ended GND stubs in the driver section are
deliberate guard traces, not routing leftovers.
DRC passes with 0 errors and 0 unconnected items, and ERC with 0 violations.