Basic Board design inquaries regarding via's, polygon, FIDUCIALS, MOUNTING HOLES etc.

[Tasrif]

Hello,
I have few confusions I would like to be clear about. Thank you in advance for answering the questions.

1. Why do we use Multiple Via on Ground plate and Power tracks? Is it just because of the increasing current flow? If so is there any rule for using the number of via's or position of via's on the tracks based on the ampere(A)?
2. Why do we use polygon in the top layer? We can just simply use the tracks and not use a polygon pour? Electrically the connections will be correct, So what's the purpose of a polygon?
3. For multiple-layer, we need to match 50-ohm impedance. My question is how to do it? Is there any guideline for this?
4. Where is the correct position for FIDUCIALS? Also, What is the major reason for FIDUCIALS?
5. Why 3 of the MOUNTING HOLES are connected to ground in the Arduino design (28Pin's project) and one MOUNTING HOLE is not connected? Can't we just connect all four of those or not connected any of those to GND?
6. There is a License layer which contains all the licence information of the project. Where can I find this licence information? Is it just from the Arduino website? Do we need to include License information for open-source hardware?
7. Lastly, What information do we need to put on the Manufacturing Notes layers? Do you have a list or formate suggestion form this?

[Lakshmi]

1. On the Power trace it depends on the current consumption of the IC. You can calculate these using the Saturn PCB Tool.
For more info have a look at this video:
https://www.youtube.com/watch?v=56Fv...ature=youtu.be

https://www.youtube.com/watch?v=icRzEZF3eZo

2. polygons are also used in places where you need to carry high currents or wide trace can be used.

3. From the Manufacturer/PCB tool could calculate.
When you ask the Manufacturer about the stack-up details, you need to mention controlled impedance values and accordingly,
they'll suggest the trace width for a given reference plane.
(Not sure you're particularly asking about RF tuning.)

4. You can place the fiducials on the corner or near to BGA/high pin count IC.

https://www.youtube.com/watch?v=5M7K_SaZ6Rw

https://designhelp.fedevel.com/forum...3890-fiducials

5.Usually Mounting Hole will be connected to GND or sometimes can be left unconnected. Regarding Arduino design, you might have to ask
on their forum.

6. I'm not sure about this maybe others might answer.

7. https://designhelp.fedevel.com/forum...brication-note.

PS: most of these questions been already answered, so its better if you could spend time and search here before posting which could save you time.

[robertferanec]

Thank you very much Lakshmi

5) I didn't use plated GND hole, because that hole is almost in collision with one of the pins (there was no space). But you can connect it if you like.

6) License: You can just copy it. I think I used the same license as Arduino. You can always have a look here: https://creativecommons.org/share-your-work/