Are you new to PCB manufacturing or designing and wonder what Fiducial PCB are and if they are indispensable in modern manufacturing techniques? Well, in that case, you are in the right place. This post will offer a concise but comprehensive into the matter.
What are Fiducial Markers?
Fiducial PCBs are basically printed circuit boards with fiducial markers. So assuming that you already know about PCBs, let us understand what fiducial markers are.
A Fiducial marker is a round-shaped copper that identifies a reference point for assembly machines to pick and place. They can help machines understand the orientation of your PCB as well as surface mount components on it.
The packages on these components have tiny pitches, such as Ball Grid Arrays (BGAs), Quad Flat Package (QFP), and Quad Flat-No-Lead (QFN)
Types of Fiducial Markers
Fiducial markers come in two categories when it comes to printed circuit board designing.
· Global Fiducial Marker – refers to copper reference point found at the edge of your printed circuit board. This fiducial marker allows the assembling machine to understand the orientation of your board in terms of X and Y Axis. You can also use the global fiducial marker to compensate for skews in case the PCB clamps.
· Local Fiducial Marker – refers to copper markers placed at the external corner of your quad-packaged surface mounting component. Your assembly machines use a local fiducial marker to identify the footprint of your components precisely. This reduces the errors in fiducial placements, especially when you have large quad-packaged and fine-pitched components in your PCB designs.
Are Fiducial Markers Still Necessary
According to some, removing fiducial markers on smaller printed circuit boards can allow you to maximize the space for any signal traces. As the PCB designing and manufacturing technology advances, you can omit local fiducial markers under certain circumstances.
For example, on smaller PCBs, your modern-day assembly machines can easily place SMT components via identifiers set in place by global fiducial points. Moreover, if your printed circuit board has components with a larger diameter, it may be acceptable to omit the fiducial markers as modern-day machines can accurately place components without an identifier. These include any surface mount components that have a pitch of 1.0mm or larger.
If you are a PCB manufacturer with the latest in-house designing and manufacturing machinery, you can take out the fiducial markers. However, if you are going to outsource your designs and manufacturing, then you must consider the manufacturer’s machine’s capabilities.
If their assembly machines need fiducial markers to read the layout of your PCB and where to place the component, you will have to mention them.
Speaking about the global fiducial markers, no matter how advanced your PCB manufacturing machines are, you should never omit them from your PCB design,
Best Practices for Fiducial PCBs
Fiducial markers on your printed circuit boards will help you get the best out of your assembling machines. However, here are some essential tips for your consideration.
· You always make a fiducial marker in circular shape via a non-drilled copper layer.
· The Fiducial marker on your PCB must not have any solder mask.
· Speaking about the optimization of the fiducial marker’s size, always keep it from 1 to 3 mm.
· You must also maintain a clearance area exactly equal to the diameter of your marker.
· For the local fiducial marker, you must place a minimum of 2 markers diagonally at your surface mount component’s external edge.
· For global fiducial markers, you must place 3 markers at your board’s edge to achieve the best accuracy. In case you do not have enough space, then use at least 1 marker.
· Your PCB’s fiducial markers must maintain a minimum distance of 0.3 inches from the edge of the PCB.
In the end, you must always check if your soldering mask opening and fiducial PCB sizes are correct. Some manufacturers may modify your Fiducial PCBs size in case you forget to size them correctly. Therefore, discuss with the assemblers before your board goes for mass manufacturing.