Embedded-cHow-ToBeginner · 4 min read

How to Add Fiducial Marks on PCB: Step-by-Step Guide

To add fiducial marks on a PCB, place small, round copper pads isolated from other traces at strategic locations, usually near component areas. Use your PCB design software's fiducial tool or manually create these marks on the top and bottom layers to help machines align the board during assembly.

📐

Syntax

Fiducial marks are typically created as small circular copper pads with no solder mask covering. They are placed on the top and bottom layers of the PCB. The key parts include:

Diameter: Usually 1-3 mm for visibility.
Clearance: No other copper or solder mask within a small radius.
Position: Near component clusters or board corners for easy machine recognition.

plaintext

FiducialMark {
  diameter: 1.5mm;
  copper_pad: circular;
  solder_mask: none;
  position: (x, y) coordinates near components;
  layer: top and bottom;
}

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Example

This example shows how to add fiducial marks in a PCB design tool by creating circular pads with no solder mask on the top layer at specified coordinates.

plaintext

AddPad(
  shape = 'circle',
  diameter = 1.5,  
  position = (10, 5),
  layer = 'top',
  solder_mask = 'none'
)

AddPad(
  shape = 'circle',
  diameter = 1.5,  
  position = (90, 5),
  layer = 'top',
  solder_mask = 'none'
)

Output

Two circular fiducial marks appear on the top layer at (10mm, 5mm) and (90mm, 5mm) with no solder mask.

⚠️

Common Pitfalls

Common mistakes when adding fiducial marks include:

Placing fiducials too close to other copper features, causing recognition errors.
Using incorrect sizes that are too small or too large for machine vision.
Not placing fiducials on both top and bottom layers if double-sided assembly is needed.
Covering fiducials with solder mask, which hides them from cameras.

plaintext

Wrong:
AddPad(shape='circle', diameter=0.5, position=(5,5), layer='top', solder_mask='covered')

Right:
AddPad(shape='circle', diameter=1.5, position=(5,5), layer='top', solder_mask='none')

📊

Quick Reference

Aspect	Recommendation
Diameter	1-3 mm
Shape	Circular copper pad
Solder Mask	None (exposed copper)
Placement	Near components or board corners
Layers	Top and bottom for double-sided PCBs
Clearance	No copper or mask within 1 mm radius

✅

Key Takeaways

Place fiducial marks as small circular copper pads without solder mask.

Ensure fiducials are spaced away from other copper features for clear machine vision.

Add fiducials on both top and bottom layers if the PCB is double-sided.

Use standard sizes (1-3 mm diameter) for reliable recognition.

Position fiducials near component clusters or board edges for best alignment.