PCB design

[r4r]

Hi, everyone!

Here is my first PCB design, I've spent many time. Should I fix something?

Heard about GND loops that is bad, but what about power loop?
And I doubt about copper pour. How do you think, in this particular situation this is good or not?

[RobBarter]

Nice.   Also a novice like you, however I think your thru holes are too close to the pads of the components near the top?

[mariush]

any reason you can't place u4 on top , let's say near u2 or between connectors?
would help with all those traces cutting the copper fill on bottom
can you replace c2 with ceramic capacitor (or several in parallel) or a surface mount capacitor?
This and battery are the only through hole parts.

if possible consider movng the battery holder below chip, near connectors.
Would allow you to shift the main chip up and shorten and reduce all those traces going to left i/o pins leaving you loads of room to move at least the capacitors for oscillator on top.
move RESET button on left side above the io pins ?
move 3.3v and ground on left as well so you don't need that long trace on bottom going to both sides of board.
Maybe if possible, have the whole row of pins a few mm to the right, leaving more room for that 3.3v trace to go between edge of board and pins.

are those r5,r6,r8 same value? maybe you can replace with single part with multiple resistors in parallel to reduce space used.

Here's a very crude mockup i made in ms paint, shifting some components a bit



and loads of room on back side for ceramic capacitors and resistors under where u3 used to be and under the battery holder... your only issue is gonna be where the 3v from battery lands right in the center of the board, but you can route that trace to where it's needed easily

you could also get those 4 traces on the bottom going down to the connector closer together so they don't break that ground fill so much

[r4r]

Also a novice like you, however I think your thru holes are too close to the pads of the components near the top?

About 2.5mm from edge to edge. Arduino nano has roughly the same distance between chip pads and IO holes. But you're right, I think I'll put capacitors horizontally.

mariush, thanks! Will try to modify PCB like you suggested.

[akowalczyk]

Looks great for a first PCB 

As a recommendation, I'd avoid going with 45 degree components unless the datasheet specifically calls it out. If those are the caps for the crystal, I'd suggest rotating them around so that the grounds are closer together, it may get you a bit less noise on the clock line if you're lucky

For your through-hole mounts, make sure you have a decent amount of distance between the copper surrounding the hole and the hole itself. 20 thou (roughly 0.5mm) should do. The rest of your electrical rules look good.

Is there any reason C2 is electrolytic here? What value is it? You may be able to downsize to either a few larger SMDs or a tantalum, but either way it'll be shorter than what you have there and easier to build a case around. If it's going to a SD card holder (which it looks like it is) I don't think you need all that much capacitance

Overall this is a great start, I'd agree with everyone else to see if you can get more parts on the top, but I see nothing that would prevent the board from working

[r4r]

Thank you, akowalczyk!

Is there any reason C2 is electrolytic here? What value is it?

I use its through-hole to pass power rail between layers, instead of a via. You absolutely right about SD card, this cap is 220uF to help while writing. Maybe it's too much capacitance, I don't know...

According to all advices, as much as I could, ended up with this design:

[kizmit99]

I would suggest taking a closer look at the footprint/layout requirements for your uSD cardslot.  The ones I've looked at using all had a "Pattern Prohibition Area" covering most (if not all) of the area "under" the component itself.  I'm not certain whether this means Gnd-only, or no traces at all?  But I suspect the tracks you have under the part are (technically) a no-no.

It's also looks like you plan to break off the top section as a separate project - If you're planning to have this built by one of the cheap PCB places you may run into an upcharge for doing that.  Perhaps you could connect the gnd planes on the bottom at a few spots to try to "hide" this???

[Tek Tech]

It looks lovely. What software did you use?

BTW, on the other side of SD connector you have a large "island" connected to ground on the other side via a single tiny thru-hole. Is there a reason you didn't connect it to the ground in multiple points?

[r4r]

I would suggest taking a closer look at the footprint/layout requirements for your uSD cardslot.

There is no mentions about restricted areas beneath card slot. But it looks reasonable enough, I've removed any conductive from.

It's also looks like you plan to break off the top section as a separate project - If you're planning to have this built by one of the cheap PCB places you may run into an upcharge for doing that.

Yes, exactly. No extra charge if I split it by myself. PCB manufacturer (JLCPCB) even allow to put "cut lines" on the silk layer for free. But any "row of holes" i.e. perforations, slots (and V-cuts of course) are treated the same way - like different PCBs with all the consequences.

It looks lovely. What software did you use?

BTW, on the other side of SD connector you have a large "island" connected to ground on the other side via a single tiny thru-hole. Is there a reason you didn't connect it to the ground in multiple points?

DipTrace 3.1. It has some limitations due to the license type I have, but in my projects that's more than enough. Also I was told about KiCad as totally free alternative with similar capabilities.

Sorry, I don't get it. You mean island near SCK pin? To pass GND from bottom layer to the top. Prevent "floating" piece of copper between capacitor and SCK.

[kizmit99]

There is no mentions about restricted areas beneath card slot.

Just out of curiosity - do you have a part number for the uSD card slot you're planning to use?

[r4r]

kizmit99,

In fact, I don't know part number, gonna use uSD slot from ebay:
https://www.ebay.com/itm/2X-CONNETTORE-SLOT-SCHEDA-MICRO-SD-14X15mm-PCB-SMD-TransFlash-TF-memory-card-cs/262993476886?hash=item3d3ba1fd16:g:VxcAAOSwZ4dZHukX

More over, I couldn't find layout for this item, so had to draw it from blueprints provided by seller. Pretty tedious work have to say... 

[kizmit99]

The data sheet for that part (which I think this is a better link to: http://images.100y.com.tw/pdf_file/10-TFP09-2-12B.pdf) does show an area surrounded by a dashed line in the recommended layout.  That area isn't described in the datasheet, but from others I've looked at (and from looking at the bottom of the part) I suspect that area is meant to be free of (at least) unmasked copper.  Whether it should be free from copper altogether, I'm not sure.  I think the concern is the little metal fingers and the exposed spring making contact with the board in that area...
If it were me, I would route no traces through that area, and not even flood it with the GND plane.

Best of luck with your project! 

[r4r]

Thank you, kizmit99!

If it were me, I would route no traces through that area, and not even flood it with the GND plane.

Good advice, this is make sense therefore I already done like you said. 

[mariush]

How would you feel about sharing the DipTrace project with us, or at least send it to me and other interested persons through private messages?

I'd like to play around with the layout a bit and maybe give more suggestions and I'm just too lazy to re-create the footprints and everything in DipTrace from scratch. I'm thinking of some things, moving some parts around, but I'd rather not suggest it only to see it's not actually possible due to part sizes.

It's easy to recreate but still takes time, and your circuit is not complex enough to make it difficult to clone it from the pictures, if that would be a worry.

[Ice-Tea]

Normally, caps and resistors pertaining to the oscillator are kept on the same side of the PCB, as close to the xtal as possible.

[r4r]

It's easy to recreate but still takes time, and your circuit is not complex enough to make it difficult to clone it from the pictures, if that would be a worry.

Sure, this is not secret at all. =) Couple of ICs and some resistors...