What are fiducial markers?
A Fiducial marker is a rounded shape of copper and it will act as a reference point for pick and place machines during assembly process.
These Fiducial PCB markers commonly will help machines to recognize the PCB Orientation and Orientation of surface mount components having packages with tiny pitch like BGA, QFN, QFP…,
What are Types of fiducial markers?
Fiducial markers are two types, they are
- Global Fiducials
- Local Fiducials
- Global Fiducials are a copper reference pads placed on the edge of Printed Circuit Boards
- it will allow the machine to know or to determine the orientation of board with respect to X and Y axis
- The markers which are placed at outside of the corner of packages having tiny pitch surface mount component are known as local fiducials.
- This fiducial helps assembly machines to precisely locate the footprint of component and to reduce errors in placement of components.
What is Standard size of fiducial markers?
- The standard size of fiducial markers should be between 1 and 3 mm
- A clearance area similar to diameter of the marker should be maintained
- Some manufactures preferred mask clearance 3 times greater than marker diameter, for example we have 1 mm copper area then clearance should be 3 mm
- See below image to understand about fiducial marker creation.
General Fiducial placement Guidelines:
- For Global Fiducials, we need at least 2 and preferably 3markers for precision accuracy in component placement. Incase insufficient space in the board we need at least 1 global fiducial marker.
- The markers should be positioned at opposite ends from one another and separated as far as possible on the board.
- When using 3 Fiducial markers, place them in a triangular shape.
- These Fiducial markers should have a distance of 0.3 inches to the edge of the board, without including the mask area of fiducial.
- For local fiducials place at least two fiducial markers diagonally on the outside edge around the fine pitch surface mounted component