A board can be perfectly manufacturable and still be painful to assemble. These layout rules reduce assembly risk before the stencil is cut.
Assembly layout rules
| Feature | Recommendation |
|---|---|
| Component-to-edge | 3 mm minimum; 5 mm preferred |
| Component-to-component | 0.3 mm minimum for 0201; 0.5 mm for standard SMT |
| Fiducials | 3 global, 1 mm dot with 2 mm clear area; 2 local per fine-pitch device |
| Tooling holes | 2 x 2.0 mm non-plated in the rail, diagonally placed |
| Test points | 1.0 mm minimum diameter, 2.5 mm pitch, accessible from one side |
| Orientation | All polarized parts in a consistent direction where possible |
| Keep-out | No tall components inside the reflow shadow of a large connector |
| Panel rails | 5-10 mm rails with mouse-bites or V-score as agreed |
Fine-pitch and BGA
- Via-in-padFill and planarize; unfilled vias wick paste and cause voids.
- Solder mask between padsUse a mask-defined or copper-defined pad strategy consistently.
- Thermal reliefProvide adequate copper for reflow, but avoid asymmetric thermal mass.
- CourtyardKeep other parts outside the package courtyard to allow rework.
- X-ray accessAvoid stacking BGAs directly over each other on opposite sides.
Test access
If you plan ICT or flying probe, bring every net to a test pad or via on a 2.5 mm grid where possible. Label test points on the assembly drawing and tell us which nets are critical. Functional test fixtures also need mounting holes and connector access — define these before the layout is frozen.
Send the assembly drawing with the Gerber. A board that has been reviewed for assembly takes less time to quote and much less time to debug on the line.
Frequently asked questions
Do I need fiducials on every board?
For automated assembly, yes. Three global fiducials are standard; fine-pitch devices benefit from local fiducials.
Can you assemble without tooling holes?
Often yes, but panel handling and fixture location become harder. Tooling holes are strongly recommended for production.
What is the minimum component spacing?
0.3 mm for 0201 and 0.5 mm for standard SMT, assuming the placement equipment and rework access are considered.