What is Fiducial Mark on PCB Board?
The fiducial mark on a PCB (Printed Circuit Board) is a reference point used during the assembly process, particularly in Surface Mount Technology (SMT). These marks are critical for ensuring that the automated machines, such as pick-and-place robots or optical inspection systems, correctly align components on the PCB. Fiducial marks provide a clear reference for machines to calibrate the board’s orientation and ensure that the components are placed accurately, especially for fine-pitch or densely packed components.
What the Characteristics of Fiducial Marks?
1, Appearance: Fiducials are typically circular, copper-plated pads on the surface of the PCB, free of solder mask or any other material. They are often surrounded by a clear area to make them easily distinguishable.
2, Global vs. Local Fiducials:
- Global Fiducials: These are placed on the edges of the PCB to provide a reference for the entire board.
- Local Fiducials: These are placed near fine-pitch components, such as ICs or connectors, to assist with accurate placement of individual parts.
3, Size and Placement: The size and position of fiducial marks are carefully chosen to be easily detected by vision systems. Generally, a 1mm to 2mm diameter is typical, with a clearance of 2-3 times the diameter around it, free from traces or components.
What the Purpose of Fiducial Marks?
- Alignment and Orientation: Fiducial marks help in aligning the PCB precisely under the machine’s vision system, ensuring that all components are placed in the correct positions and orientation.
- Error Minimization: Fiducials are especially important in high-precision applications, where slight misalignments can result in functional issues.
- Automated Optical Inspection (AOI): Fiducials are also used by AOI systems to verify the board’s position during the inspection process after component placement.
Without fiducial marks, machines would struggle to locate the exact position of the PCB, leading to incorrect component placement, which could result in product defects, especially in densely populated or complex boards.
In summary, fiducial marks are essential in modern PCB manufacturing processes for ensuring accuracy, precision, and quality during automated assembly and inspection
