Hi,
I am a newbie trying to clone Uno R3, working on PCB routing in Eagle one wire by one wire.
Here is my question:
It is pretty weird for me that, in the official .brd file, there are a lot of vias there without any routes connected. And a lot of routes go around some "useless" vias, making a detour, instead of directly connect two points.
Could anyone tell me why should the design be like that?
Thank you!
These are probably making connections to GND but, we need to know the examples you are referring.
.
LarryD:
These are probably making connections to GND but, we need to know the examples you are referring..
Here is a screenshot I made from the .brd of Uno R3, inside which there is a big detour and 3 useless vias.
LarryD:
These are probably making connections to GND but, we need to know the examples you are referring.
.
Here is the second screenshot, with 4 useless vias and one detour around a useless via.
I call them "useless" because there was no route to connect the via.
The most useless area is around power polygon, U1 (NCP1117ST50T3G), where there are 7 useless vias.
Please help me check it.
Thank you!
Those vias are used to connect the ground plane on one side to the other.
The detour keeps away from the crystal.
Most likely to connect to ground planes.
http://dangerousprototypes.com/2012/07/18/eagle-polygons/
Leo..
Take the same same screen shots with Rats Nest selected, that will enable the Ground planes to be seen, and the connections to pins that are not visible now.
LarryD:
Those vias are used to connect the ground plane on one side to the other.
The detour keeps away from the crystal.
The most useless area is around power polygon, U1 (NCP1117ST50T3G), where there are 7 useless vias.
Please have a check. In the same polygon, I am pretty sure that we do not need so many vias to connect between grounds.
Thank you!
The 1117 regulator?
Probably heatsinking.
Two ground plane heatsinks on opposite sides connected together is a cooler chip.
Leo..
CrossRoads:
Take the same same screen shots with Rats Nest selected, that will enable the Ground planes to be seen, and the connections to pins that are not visible now.
Yes, that make my doubt even more clear.
Here is another screeshot with redundant vias, please have a check.
Thank you!
Adds thermo mass for the regulator.
.
The vias under and next to the regulator are definately for heatsinking.
And supply/smoothing caps need good grounding.
What is the problem with more vias.
Leo..
So, what you mean when you refer to "useless" or "redundant" vias, is that you have basically no expertise in electronic engineering.
Fair enough. The "take-home" message here is that designing electronic circuits or PCBs involves more - much more - than connecting point A to point B. You have to know electronics. 
Thank you guys. I will remember a good grounding for power and smoothing caps.
Here is another screeshot with more vias than I could understand. Could you guys help me learn the knowledge of how should we design them?
Thank you!
liziyuanhaha:
Also, there is a small Circle on the right top corner of ICSP1, which is even hard to recognize; what does that do?Thank you!
It indicates pin #1.
"Fiducial" is a mark on the final PCB that the assembly machine can see (with a camera) so that it can align the board while placing the components. It has no electrical purpose.
liziyuanhaha:
Here is another screeshot with more vias than I could understand. Could you guys help me learn the knowledge of how should we design them?And there is a star with indicating one of the three "FD"s(FIDUCIALMOUNT), is that important?
Any via on a board that isn't obviously associated with a trace will almost definitely fall into one of the two categories that have been explained above i.e. they're either for connecting the ground planes on the top and bottom of the board (this is called stitching) or else they're to provide an conduit for heat from a component to give a greater surface area (the bottom of the board) to dissipate heat.
Fiducials are markers on the board to allow a pick and place machine with a vision system to detect the position of the board and correct any alignment issues. See Fiducial tips edit - hadn't seen MorganS' post above beating me to that explaination
Thank you!
I just finished my Uno Clone, and understand most of the grounding vias now.
liziyuanhaha:
Thank you guys. I will remember a good grounding for power and smoothing caps.Here is another screeshot with more vias than I could understand. Could you guys help me learn the knowledge of how should we design them?
Definitely linking groundplanes so there's no parts of it flapping around at logic frequencies and
causing EMI. Any two layer board has to make compromises with its ground plane, since it will
have to swap sides a lot. 4 and 6 layer boards have at least one dedicated ground layer.
