Hi, I want to ask really noob question but I couldn't find it. I think it won't be a problem but I want to ask you, what happen if I use for example 10 capacitors and resistors 0603 ,10 capacitors and resistors 0402 , 10 capacitors and resistors 0805 etc. Is this cause something ?
What if I use 7805 TO 220 and the other components on 0201 size, will this cause something ? Thank you.
How would you use them is what matters...
They don't have the same specs for example a 0805 resistor might have a power rating of 0.25W when a 0402 resistor would be at 0.1W. You would have as well differences for Max Working Voltage or Max Overload Voltage.
➜ choose the components that are suited for the job
Okay thank you. I choice different footprints thats why I want to ask. I put 8 10uF 1210 caps and I put 20 0.1 uF caps, I put 6 5uF 0603. I understood your comment , it is not matter. It will work if their value is correct.
It’s not just their value it’s what you do with them and requirements
The above comments are correct but generally any of the above will work for me. I usually use a size that will allow me to easily lay out a board in the size and configuration I want. My general usage is 1206. I also use 0805 devices, smaller parts are hard to see. I stay to one size as much as possible on a board to keep assembly simpler. If you go to fast or high frequency signals layout and size can and do become problematic.
Okay, thank you. I am using two IC . One IC's components 0402 one IC's components 0603 but they are in the same board. For example W5500 used 0603 on their board so I did. RP2040 used 0402 and I did it but I will use them together in the one board. That's why I asked different footprints.
If you go to fast or high frequency signals layout and size can and do become problematic.
I think that's not a problem on my circuit. (I hope)
Again, thank you.
In general, you want to minimize the number of separate components that your board uses, and probably minimize the number of different footprints. Manufacturing costs will depend (perhaps) on the number of different components, and having a bunch of different size may result in confusion/errors during assembly (loading up the wrong reel into the pick-and-place machine, for example.)
A large through-hold component like that will probably need a separate assembly step for the small-pitch SMT stuff. Increases assembly costs and time. (This is one reason you can frequently find "kits" with the SMT components already soldered on, or all-SMT boards where you're expected to solder on the pin headers yourself. In addition to it making it easier for beginning hobbyists to solder (only the BIG components), the SMT soldering is automated and quite cheap compared to TH components.
Thank you.
Why a 7805? That is so old technology- a 7805 on an SMD board just seems out of place.
So much depends on if you are going to populate the board your self, or are going to hire someone else to do it. You also need to add the cost of a solder stencil or programming a computerized solder paste machine.
Paul
It is really cheap and easy connections. I used in breadboard, 7805 is working good with my projects.
Okay, thank you. I am gonna populate it myself so It is okay I guess.
Better power dissipation.
The SMT linear regulators used on (semi)modern Arduinos don't need to dissipate any less power than a full-sized 7805 (for the same input voltage), but they have less thermal conductivity to cooling air/etc, and are more likely to heat up and fail for overheating reasons.
A lot of the tiny Arduino designs (Arduino Nano and clones) have really questionable thermal design, and aren't good at supplying anywhere near the current that their datasheet, or the regulator data sheet, implies they can. 
This is one reason why the NKC "Freeduino" board I designed (helped design) way back when ended up with a full-sized 7805...
(even newer boards, like the Nano Every, have a switching regulator module that should eliminate this problem. But they're a lot more expensive.)
Hi,
100mA..
Tom...
The OP specifically said TO-220.
And the UNO, don't forget, is hardly any better.
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