2 layer PCB Design - preferred tracks to jump to bottom layer?

Working on a custom PCB for using a Nano to program ATtiny chips.

It's a 2 layer board. Going to use bottom layer as ground plane, and routing everything else on top layer.

However, with only about 3 or 4 tracks to go, it seems that I am going to need to do a few jumps from the top layer to the bottom.

So my question is:

Would it be preferable to jump a few of the 5V traces to the bottom, or a few of the signal traces to the bottom (these are ICSP MOSI, MISO, SCK, etc)?

Thanks!

Sure. Assuming you’ve got some thru-hole parts, the ground plane (or “copper pour”) can’t solidly cover the whole back side anyway.

Yes I do have through hole parts.

Sure

But is there a preference to jump the 5v track vs the signal tracks to the bottom layer? Or doesn’t matter?

I doubt it matters, especially at the speeds you will be using. If jumping the 5V will allow you to jump fewer signal lines I would to that.

One suggestion, I would increase the via size from the usual default. IMHO the copper in a hobby via is very thin and creates a weak point. In a typical hobby design it is unlikely increasing the via size to that of a through hole component will make a layout difference but it will result in more copper and thicker copper in the hole(s).

JohnRob:
One suggestion, I would increase the via size from the usual default. IMHO the copper in a hobby via is very thin and creates a weak point. In a typical hobby design it is unlikely increasing the via size to that of a through hole component will make a layout difference but it will result in more copper and thicker copper in the hole(s).

Hobby via? A non-stacked board?

Vias are robust in my experience, for signal or power, over well over 100 pcb 2-layer designs and 3 manufacturers.
For high current you'd be wise to use multiple vias and even fill them with solder (increases thermal
performance too).

Copper is a very good conductor :slight_smile: Vias have pi times their diameter of copper width through the board, this is
usually a lot more than the trace width.

Consider a 0.3mm diameter via plated to 20nm (yes, nanometers), and 1.6mm long

Its resistance would be about 1 ohm, and would handle perhaps 10's of mA thermally.
Standard plating thickness is 35000 nm, and even allowing for thinner plating deep in the via its
clear standard vias aren't flimsy.

steve20016:
Yes I do have through hole parts. But is there a preference to jump the 5v track vs the signal tracks to the bottom layer? Or doesn’t matter?

It usually doesn't matter much, if at all.

I normally don't use power traces, instead using power planes on both sides of the PCB. For convenience GND on top, as then I don't need vias for the MOSFET source pins (using SMD parts where I can). That can get a bit complex for a typical 3-voltage board (12V, 5V, 3.3V) where I also like to keep the ground plane cut in two, connected only at the power supply point of the PCB: one part for the high current switches (usually the 12V bit), one part for the digital bits (keeping the high currents away from the digital parts)

If you have THT parts that'd be the natural candidate for bringing traces to the other side.