PCB 拼板指南 — SMT 用钢网就绪面板

Three reasons. First, SMT assembly machines need a minimum panel size (typically 50×50mm) for fixturing — small boards must be panelized to be assembled efficiently. Second, panel ordering is cheaper per unit than single-piece ordering at most fabs because the fab's processing cost is per-panel, not per-board. JLCPCB charges $2 for 5 single 100×100mm boards but $5 for 25 panelized 50×50mm boards (5× the count for 2.5× the price). Third, panels survive shipping better — the rigid panel resists bending that would crack solder joints on individual boards.

V-cut: best for rectangular boards with straight edges; the fab cuts a V-groove that lets you snap the panel apart by hand. No edge irregularities, but limits panel layout to grid arrangements. Mouse bites: small drilled holes along a routed slot let you snap panels apart; works for any board shape including curves. Leaves small bumps on the edge — sandable but visible. Tab routing: full router cuts with bridge tabs at strategic points; cleanest result but most complex panel design. For rectangular hobby boards, v-cut is fastest. For odd-shaped or production boards needing clean edges, mouse bites or tab routing.

KiCad doesn't have native panelization, but the kikit plugin (free, open source) handles it. Install via Plugin and Content Manager. Then use Tools > External Plugins > KiKit Panelize. KiKit supports v-cut, mouse bites, tab routing, and frame rails. Output is a separate .kicad_pcb file with the panel that you submit to fab. Alternative tools: PCBNew Panel script, GerberPanelizer (Therac), PcbPanelize (online). For Altium and EasyEDA, panelization is built-in via the Embedded Board feature. For Eagle, use the panel.ulp script.

Required for SMT assembly. Fiducials: three small round copper-on-soldermask-removed marks (1mm diameter) at three corners of the panel, used by the SMT machine's vision system to align the panel. Place at panel corners, not on individual boards (one set per panel suffices). Tooling holes: 3-4mm diameter NPTH (non-plated through hole) at panel corners, used by the assembly fixture to register the panel. Most fabs require both for SMT panelization. JLCPCB will skip both if you don't include them and instead use board-edge alignment, which is less accurate.

Rails are extra strips of FR4 along the panel edge that don't contain any boards. They're required if the assembly machine clamps the panel by the edge (most do). Standard rail width: 5-10mm on each long edge. Some fabs require rails on all four sides; others only on the two long edges. JLCPCB's panelization service handles rails automatically when you select the panel option during ordering — they add 5mm rails on the appropriate edges. For self-panelized DIY panels submitted as Gerber, include 5mm rails on at least the top and bottom of the panel orientation that will go into the SMT machine.