If you have ever worked on a production line, you know how important it is to align products correctly. Even small deviations can lead to big disasters, including excessive material waste, unusable products, and equipment damage. The same rings true when it comes to building circuit boards. This intricate process includes panelization (where the location is determined for the boards that comprise them) and PCB layout (which includes designing the placement of components on boards). For today’s automated manufacturing, PCB fiducials are the markings that ensure these alignments.
What Are PCB Fiducials?
Building circuit boards consists of two distinct stages—fabrication and assembly—plus a well-defined series of steps. For most of these steps, specialized equipment performs the activities. Assembly, for example, has pick and place machines select and place components on their corresponding footprints on bare boards. Accomplishing this essential and extremely accurate task requires markings which guide the machine. These markings are referred to as PCB fiducials.
As shown in the figure below, there are three types of PCB fiducials.
Types of PCB Fiducials
These fiducial markings, located in the outermost four corners above, ensure proper alignment of the panel which
is likely to be one of several standard sizes.
Similar to panel PCB fiducials, global markings define the exterior of the circuit board
and board edge clearance perimeter.
Local PCB fiducials are markings that provide orientation for placing components on the board during assembly.
PCB fiducial marks are most often circular, but may be square and diamond-shaped. Irrespective of their shape or size, these markings are essential for today’s PCBA manufacturing. Automation, which is utilized to varying degrees by CMs that build electronic circuit boards, would not be possible without PCB fiducials.
Fiducial markers are critical for manufacturing and the automated assembly of PCBs. PCB layout in particular requires precise placement of SMT components and spacing between surface elements. Proper orientation is needed for machinery to accurately preserve this dimensionality during the fabrication and assembly processes. For boards, fiducials indicate the space for component placement as well as the boundaries for spacing. Similarly, for panels, these marks indicate the location of the boards within them.
3 PCB Manufacturing Trends You Need to Know
Guidelines for the Best Usage of PCB Fiducials
PCB fiducials are critical for most designs that include SMT components; however, maximizing their use requires that you follow certain guidelines.
How to Optimize PCB Fiducials Usage
- Select the PCB fiducial type
Although panel, global, and local PCB fiducials have similar purposes, they will likely vary in location, shape, and number. Therefore, type selection should be your first priority.
- Select where to place the fiducial
For panel and global fiduciaries, opt for corner locations of the panel or board to ensure proper edge clearance. Also, place a fiducial next to each SMT component.
- Select the best size and shape for the marking
A common size for PCB fiducials is a 2mm solder mask opening diameter with a 1mm diameter copper marking center. However, it is best to consult IPC-751 for guidance on size, shape, and clearance for fiducials.
- Select how many PCB fiducials to use
No absolute number of required fiducials exists; however, a good rule of thumb is to use a minimum of three for panel markings, two for global markings, and one for local markings.
- Consult with your PCB Assembly CM
PCB fiducials aid in the assembly process and should involve consultation with your CM to ensure your selections align optimally with the assembly equipment and process.
|Tempo's Custom PCB Manufacturing Service
At Tempo Automation, the industry leader for fast, high-quality PCBA prototyping and on-demand production, we employ a software-based digital thread manufacturing process that maximizes automation to build your boards. We will work with you to optimize fiducial marking utilization and ensure the accuracy of your SMT component placements.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.