Manufacturing-ready PCB layout — clearances, vias and fiducials.

Why a manufacturing-ready layout matters

A manufacturing-friendly layout is one of the biggest levers for a successful prototype and series project. It lowers cost, shortens throughput times and raises quality — all before the first board is even populated. The guidelines below are deliberately framed as recommendations: not every rule applies rigidly to every design, but every deviation should be a conscious decision.

The single most effective step is a design review before the first order. Having your layout checked before manufacturing catches critical points on screen — not at the solder joint. In the prototype they are cheap to fix; in the series the same findings cost many times more.

SMT components

For surface-mount (SMT) components, clearance and distribution rules apply above all:

• At least 3 mm clearance to the scoring notch or breakaway web. This leaves enough room for the machine transport area and for later depanelisation without mechanically stressing components.
• Even distribution on double-sided builds: if both sides are populated, spread the components as evenly as possible across top and bottom. This keeps the thermal load in reflow symmetric and reduces warping.
• Large components and connectors on one side where possible: heavy and bulky parts belong together — ideally on the same side. This simplifies handling and stabilises the assembly process.

THT components

For through-hole (THT) components, soldering aspects add to the clearance rules:

• 3 mm clearance to the separation: as with SMT, keep a minimum distance to the panel separation.
• Cover vias at the THT annular ring: open vias right at the annular ring pose a short-circuit risk and must be covered.
• Arrange THT on one side where possible: this reduces manual work and makes automated soldering economical in the first place.
• Grid pitch for selective soldering: at least 2.00 mm, ideally 2.54 mm. Grids that are too tight cannot be soldered selectively without issues.
• Layout thermal reliefs where required: on large copper areas, thermal reliefs are mandatory — otherwise the area wicks away the solder heat and the joint runs cold.
• Distance THT annular ring to SMT pad: at least 3 mm — depending on the soldering process. For wave soldering it is at least 7 mm, so the wave does not reach the SMT pads.

General layout rules

Beyond SMT and THT there are principles that apply to every assembly:

• Closed vias only: open vias are to be avoided — in the pad they are especially critical because they can wick solder away.
• Assembly print (silkscreen): no assembly print is needed for SMT components; for THT components it is an advantage, as it eases orientation and placement.
• Symmetric layer build-up: aim for a symmetric stack-up. An asymmetric build leads to board warping.
• Group heavy components on double-sided builds: with two-sided assembly, keep heavy components grouped on one side.

Placing fiducials correctly

Fiducials are the reference marks the placement machine uses to align the board precisely. Without them, reproducible fine positioning is impossible. The proven arrangement:

• 3 fiducials in an "L" in the corners, preferably along the short side.
• 1 additional fiducial in the fourth corner, offset from the diagonal — as a poka yoke against inserting the board the wrong way round.
• Distance to the edge: 4 mm on the short side, at least 6 mm on the long side (transport rail).
• Never under components — the camera must see the mark freely.
• Gold-plated fiducials preferred, as they offer a consistent, well-detectable contrast over time.

// Fiducial dimensions per SMTEC Design Guidelines