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Today we will Talk about Fiducials Markers and its Importance.

What is a Fiducial Mark/Marker?

Basically Fiducials are nothing but SMD Pad (Copper Pad) with Its double dimension Solder Mask Opening area.

Its a round solder mask opening with round SMD Pad (Bare copper) in the centre, uses as a marker for a circuit pattern recognition.

The SMD Pad (Bare Copper) has a smaller diameter than the solder mask opening.

Fiducial Mark on the PCB

*Size of fiducial markers

The minimum recommended size for fiducials is 1.0 mm.

It is good practice to keep all fiducial marks the same size as some assembly equipment is less flexible in its ability to recognise different size marks on the same printed circuit board.

The Size of Fiducial Marker depends on assembly machines

(SMT Pick & Place Machines).

-- Dimensions of 1 mm (40 mil) diameter of SMD Pad

(bare copper) with 2 mm (80 mil) solder mask opening diameter (the most Common used Fiducials.)

-- And 1.6 mm (63 mil) diameter of SMD Pad

(bare copper) 3.2 mm (125 mil) solder mask opening diameter are excellent for almost all Assembly machines.

-- All assembly Machines accepts 40/80 and 63/125 (Mil) sized fiducials.

We can easily understand by this Picture.

-- in simple way, we can understand the concept to Design Fiducial Markers....

The Solder Mask Opening will be always just Double of Bare Copper or SMD Pad.

*******Types of Fiducials********

There are Two Types of Fiducial Markers:

1. Local Fiducial.

2. Global Fiducial.

*********Local Fiducial***********

A Local fiducials Mark used for Fine Pitch Components or Footprints (QFPs and BGAs) to locate the positions on PCB Boards, which require precise placement.

A Local fiducial mark (or marks) used to locate the position of an individual land pattern or Footprint or component that may require more precise location, such as a 0.5mm pitch Components.

One or more local fiducial marks shall be used, when it is necessary to correct for transnational (X- and Y-position).

Single Local Fiducial for Fine Pitch Components.

Dual Local Fiducial for a Fine Pitch Component.

*******Global Fiducial***********

A Global fiducial Mark used for WHOLE PCB to locate the positions Boards for SMT Pick Place Machine.

Global fiducials are used to locate the position of all features on an individual PCB, and they’re a must for a pick-and-place machine to situate a board to the CAD data programmed into the SMT machine.

Minimum Three or Maximum Four Global fiducial marks shall be used, when it is necessary to correct for transnational (X- and Y-position) for PC Boards.