What are fiducial markers (marks)?
Fiducial marks or markers are circuit pattern recognition markers. Basically it is a round solder mask opening with round bare copper in the center. Bare copper has a smaller diameter than the solder mask opening. See picture 1.
Picture 1. Fiducial Mark
What is the purpose of fiducial marks?
Pick and place machines use Fiducial marks as referent points on the PCB to position the Surface Mount Components (Packages) on the PCB during assembly of the Printed Circuit Board.
What is the size of fiducial marks?
It depends on assembly machines. Dimensions of 3.2mm solder mask opening diameter and 1.6mm diameter of bare copper or 2mm solder mask opening diameter and 1mm diameter of bare copper are excellent for almost all Assembly machines. Picture 2. shows dimensions of the fiducial marks.
Picture 2. Dimensions of the fiducial marks
Do I need fiducial markers on both sides of the PCB?
Only if you have SMD components on both sides of the PCB.
How many fiducial marks on my PCB should I have and where should I position them?
There aren’t strict rules for the number of fiducial marks. It is good if you position two fiducial marks on opposite corners of the PCB near corner edges. If you have BGA, QFN, QFP packages with small pitch on the PCB, it is very useful to position one fiducial mark near every one of those packages/footprints. Picture 3. shows positions of the fiducial marks on the board.
Picture 3. Positions of the fiducial marks on the PCB
Do I need fiducial marks on PCB panel edge?
It is also helpful to place four fiducial markers near panel corners. It also depends on assembly machine. Picture 4. shows positions of the fiducial marks on the panel edge.
Picture 4. Positions of the fiducial marks on the panel edge