The Importance of Fiducial Marks in PCB Assembly
Fiducial Marks in PCB Assembly
In electronic assembly industries that rely on automation, fiducial marks function as alignment markers for indexing systems to orient the board and circuit precisely in direction and skew. They also allow vision systems to precisely insert components on the boards. This is a very important aspect of automated manufacturing, and one misplaced fiducial mark could lead to an automation train wreck!
A fiducial mark is a dimensional benchmark, typically made of metal, that’s etched or imprinted on the pcb printed circuit board assembly during manufacture. It’s a simple way to make the boards easier to identify, and they play an essential role in ensuring that a product is assembled correctly.
Generally, the standard is to place three fiducial marks at the corners of the board. This gives the machine two angular alignment measurements, which when combined with the known position of the panelization rails that hold multiple boards together in fabrication, can determine the correct orientation of a single board. The placement of these fiducials can be defined within your design software, and they are then etched or imprinted on the copper layer of your board as a dotted pattern.
The Importance of Fiducial Marks in PCB Assembly
If you use a PCB designer tool such as Altium’s CircuitStudio, these fiducial markings will be automatically created and positioned on your board for you. They should be sized to be easily detectable by the vision system in your manufacturing plant. For best results, the fiducial marks should be clear of solder masks and silk screens. This is especially important for boards that will be used in high-density applications.
It’s important that the position of the fiducial marks be precise because if they are too far apart, the vision system will be unable to identify them and the board won’t be oriented properly during assembly. For this reason, it’s a good idea to use a grid pattern when creating a PCB schematic to help ensure that the position of these landmarks is accurate and repeatable.
Another benefit of utilizing these reference points is that they can be used to compensate for any shrink or stretch that may occur in the fabrication process. It is possible for a board to shift or change size by tiny amounts as it moves through the oven, and these small changes can have an impact on the alignment of the parts on the board. This is why it’s a good idea to have these fiducial markers on both sides of the board for double-sided SMT boards.
Although it may seem like an insignificant detail, a well-positioned fiducial mark can have a significant effect on the quality of the final product. By following optimal fiducial mark placement strategies, PCB fabricators can improve the performance of their assemblies and boost production rates. This will lead to lower costs for the end user, as well as fewer mistakes that would otherwise necessitate costly recording and redoing of previous work.