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What are PCB Fiducials, and how important are they?

If you have ever been in the manufacturing industry, you must know how essential it is for products to align correctly. Even slight changes can bring huge disasters like unusable products, damaged equipment, and material wastage. This is the exact scenario with the manufacturing process of printed circuit boards. It is a complex process that requires a PCB design and penalization of the components. PCB facials have been in the market for quite some time, which ensures the automated manufacturing process of the PCB and ensures its alignment.

What Are PCB Fiducials?

The manufacturing process of printed circuit boards is divided into two main stages. Manufacturing and Assembly follow a series of well-defined steps. In these steps, the most advanced equipment conducts the process. For instance, in the assembly, there is a robot that picks and places the components on the circuit board. This process requires precision which is done through marking led by a machine. These markings are known as PCB fiducials.

Types Of PCB Fiducials

PCB fiducial

There are basically three distinct kinds of PCB fiducials.

· Panel:

The panel markings are located on the above four external corners, providing adequate standard-size alignment of the panel. 

· Global:

The global PCB fiducial is the same as the panel markings; it depicts the perimeters of board edge clearance and the exterior surface of the printed board.

· Local:

Local PCB marking provides direction and exposure for placing the electronic components on the printed circuit board during the assembly.

The PCB fiducials marking are mostly in circular shape and sometimes diamond or square shape too. Regardless of their size and shape, these fiducials are crucial for the manufacturing process of PCB. Without PCB fiducials, the process of automation wouldn’t be viable in the manufacturing process of PCB.

Fiducial marking is essential in the automated assembly and fabrication of PCBs. The design of PCB especially requires accurate placement of the solder-mounted components and tracing between elements. Proper and detailed orientation is required for machinery to operate accurately during the assembly and fabrication process. In printed circuit boards, PCB fiducials identify the area to place the component and the boundaries for the area. In the panels, PCB markings identify the area of the circuit board in them.

Guide For The Best Use Of PCB Fiducials

PCB fiducials are a complex process, especially for designs that contain surface-mounted components. However, in order to use them properly, here are some guidelines that help you to get through this.

Optimizing PCB Fiducials Use


· PCB Fiducial Type

Although local, global, and panel markings have the same goal yet they differ in size, shape, location, and number. That is why considering the type is one of the first priorities.

· Place For Fiducial

For global and panel marking, choose corner places of the board, so that edge clearance goes well. Also, put a fiducial mark right next to every solder-mounted component.

· Adequate Shape & Size

A common and widely used size of the PCB marking or fiducial is about 2mm solder opening diameter along with a marking the center of copper with 1mm diameter. Therefore, it is recommended to consult with experienced technicians for the right shape, size, and clearance for PCB fiducial.

· The Number Of Fiducials

There is not a specific number of fiducials that exist. But an adequate number of panel fiducials is three, the global fiducial is two, and local fiducials is one. 

· Consult With PCB Assembly like RAYPCB

PCB fiducial is a complex process and helps in the automated process of assembly; therefore, it is necessary to consult with the CM to make sure that the alignment you make is optimal for the assembly. 

Size of PCB Fiducials

The general size of PCB fiducial is about 1mm to 3mm. However, the exact size of the fiducial depends upon the usage and the assembly machines it uses. Some manufacturers advised adding three markings right at the intersection of the circuit board. This provides two angular placement measurements and also allows the robot pick-and-place to figure out the right orientation. While some manufacturers also depict specific sizes but it still depends upon the assembly equipment they use.

Generally, the solder opening diameter is double the copper fiducial’s diameter. However, some manufacturers also like the diameter of the solder triple. Moreover, ensure that the diameters or size of each fiducial, no matter the type, must be consistent throughout the board, and they might vary by just 25 micrometers.

If you are manufacturing a double-layer PCB, then the fiducials of each board must sit right over one another. This is quite amusing that most manufacturers never tell you that the layout of PCB fiducials must be the same. Not only the layout but the size of the PCB fiducial of both the top and button layers, even the solder opening, must be of the same size.

The local fiducial prefers to be as small as it can be. Usually, the size of local marking is 1mm with a solder opening of 2mm. The size of the local fiducial must not be bigger than 1mm, so that trace routing flows evenly without leaving space for other electronic components. For smaller electronic components like a mini resistor or BGA do not require local fiducial for placing if the assembly equipment is precise enough, then it knows where to place the components. 

It is recommended to always check the size of the PCB fiducial and the diameters of the solder opening before sending the PCB layout to the manufacturer. Fiducials are termed as a mechanical thing in the circuit board which is not connected with anything else. Therefore, it is easy to change the trace of the custom fiducial and change it with the new one if needed. Some manufacturers also help in modifying the fiducial size if they need size precision.

The Altium designer is one the online software that helps in designing and placing the PCB fiducials markers, polygons, pads, and copper features to design an outclass PCB. Its integrated capability of providing a single platform for designing both PCB and circuit design helps a lot. Moreover, it also allows you to share your project once you are done designing with other manufacturers. 

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