KEMI Docs · PCB practice
PCB Panelization — V-cut vs Tabs vs Mouse Bites and SMT Specs
Last updated: 2026-09-16
A small board ordered as a single piece cannot run through an SMT line and costs more per unit. Panelization arrays several boards on one panel to be separated later, and the separation method you choose decides edge precision, cost and component placement limits. This article covers how to choose between the three methods and the panel specs assembly houses require.
1
Three separation methods
| Method | Suits | Edge | Limits |
|---|---|---|---|
| V-cut (V-score) | rectangular, straight edges | smooth, slightly rough | no parts within 1 mm of the groove, not below 0.6 mm thickness |
| Tabs + mouse bites | curved or irregular outlines | nubs remain (sanding) | no parts or traces at tab positions |
| Tabs (routed only) | irregular, edge quality irrelevant | large tab marks | cheapest and strongest, needs cutters to separate |
The rule is simple: all-straight outline → V-cut; any curve or inside corner → tabs. Mixing both on one panel (V-cut on straight sides, tabs on curved) is possible and most fabs accept it.
2
V-cut specifications
- 30° groove, remaining web 0.3-0.4 mm on a 1.6 mm board. Thinner breaks in transit; thicker cannot be snapped by hand.
- V-cut lines must run straight across the entire panel — there is no such thing as a V-cut that stops midway.
- Keep parts, traces and vias 1.0 mm from the groove centreline on both sides (blade width plus exposed-copper risk).
- Array boards with 0 mm gap — V-cut needs no spacing, giving the best panel utilisation.
3
Tab and mouse-bite specifications
- Routing gap between boards 2.0 mm (end-mill diameter), tab width 5-8 mm, at least two tabs per side plus one per 100 mm on long sides.
- Mouse bites: 0.5 mm drill, 0.75-0.8 mm centre spacing, five in a row. Centres on the board outline leave a small nub; move them 0.1-0.2 mm inward to leave none.
- No components within 3 mm of a tab — bending stress during separation cracks MLCCs (the most common field failure cause).
- No connectors on tab positions. On boards with many edge connectors, fix the tab positions first, then place connectors.
4
Panel specs SMT houses require
| Item | Value | Why |
|---|---|---|
| Rails (breakaway) | 5 mm+ on both long sides (8 mm recommended) | conveyor clamp zone, component keep-out |
| Fiducials | 3 per panel (asymmetric diagonal), 2 per board | vision alignment — 1 mm copper dot, 3 mm mask opening |
| Tooling holes | 2-4 non-plated 2.0-3.0 mm in rail corners | test and assembly jig location |
| Panel size | 50×50 mm minimum, typically under 250×350 mm | line limits — check each house's maximum |
| Orientation mark | arrow in rail silkscreen | prevents loading the wrong way |
KEMI defaults
Straight outline, 1.6 mm → V-cut, 0 gap, 8 mm rails. Irregular → 5 mm tabs with 0.5/0.8 mouse bites, 2 mm gap. Boards per panel in even counts (2×2, 2×4) for SMT convenience; for small prototypes (10 or fewer) individual boards are actually cheaper.
⚠ Don't draw the panel in your design files
Most fabs take single-board Gerbers and panelize themselves. A home-drawn panel that misses their specs causes rework. Draw the panel only when fab and SMT happen at one house, to that house's spec sheet.
FAQ
Can V-cut boards be snapped by hand?
Yes, but bending a long board stresses parts near the score line (MLCCs especially); use a depanelizer above about 20 cm.
How are mouse-bite nubs finished?
Sandpaper or a file. If the nubs would foul an enclosure, allow 0.3 mm on the outline.
How much does panelization save?
Bare PCB cost is area-based and barely changes; the saving is in SMT setup and placement time, noticeable from a few dozen assembled boards up.
See also
This article summarises the working rules KEMI uses in real design and fabrication work. For production, part datasheets and fab specifications take precedence.