approaches to laying out a PCB

BobaMosfet

Joined Jul 1, 2009
1,606
@champ1

I strongly recommend using a 2-layer PCB if you can. Ground on bottom, and Vcc on top. Makes layout much easier. A couple of points (and some others here may have mentioned some of these):

  • Consider PCB dimensions- the smaller it is, and the fewer vias, the less it costs (generally). It's going to take so many vias, regardless, so be smart about how you lay them out.
  • Consider inductive and capacitive issues- these don't matter so much for slow stuff, but for signalling (like SPI, etc), this can cause an issue, so route those traces accodingly.
  • Try to organize semiconductors always in the same orientation across the board. In fact, do this for most components- but only insofar as it makes sense to do so. Sometimes, rotating a component can make trace-routing far easier.
  • Take advantage of space underneath through-hole components if you use any- That's a nice open space under a chip, or perhaps under a resistor that can help you route a trace that would otherwise be difficult to get from one point, to another.
  • Be creative- but not crazy. Be aware of trace thickness, and corners, and the ability to use vias to jump from one side of a board to the other to and back gain to get around a choke-point.
  • USE YOUR NETLIST to be sure your PCB connections MATCH your schematic connections after making sure your schematic is correct.
  • Check your schematic and PCB layout 3 times before submitting.
  • When you get a PCB back, do a continuity test on one of them immediately between Vcc & Ground to be sure you haven't accidently connected the two somewhere.

One of the things I _always_ do on PCBs, is I always put an LED on it after the power-circuit. It is the first thing I solder on the border after power-circuitry, because it lets me know a) board is hot, and b) board power is working and planes are divided.

My $0.02-- Good luck and welcome to jumping into this exciting aspect of empowerment :)
 

Irving

Joined Jan 30, 2016
1,264
That way there's no sneak path for the noise around the capacitor.
In a similar vein, if you have other pins on the chip pulled up to Vcc connect them to the Vcc pin and not the Vcc feed, to stop stray noise in or out of the chip. Similarly, don't 'borrow' Vcc from one chip to another.

  • Consider PCB dimensions- the smaller it is, and the fewer vias, the less it costs (generally). It's going to take so many vias, regardless, so be smart about how you lay them out.
Smaller means more boards for your money - if you panel them up yourself. Vias are generally included these days though its wise to check upper limit; the allowance is pretty generous usually.
 

KeithWalker

Joined Jul 10, 2017
1,660
What template did you use (not that I'd use Visio for that)? I have an old version from 1996 (pre-dates Microsoft's acquisition of Visio) that now runs on Win10.
The version I am using is Visio Technical 4.0 that I acquired in 1995. I copied the 3 1/2" floppies over to a CD about 10 years ago. I use it mostly in XP but it will run well in all versions of Windows. Over time I have made my own library of electronic device symbols and footprints that I built using the "Basic" stencils. I still haven't found a more useful technical drawing tool after all these years. I use it to design circuit schematics, PCBs, meter scales, front panels, labels for header strips and just about anything else I need a line drawing or diagram of.
 
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nsaspook

Joined Aug 27, 2009
8,239
With regard to ground planes: have a look at Rick Hartley

He is an absolute Titan in the PCB design field currently. In this video he explains how to design modern high speed boards.
Yes, he's great. The primary point is the signal energy is between the traces, in the plastic. When you think of the PCB as a electromagnetic wave-guide you build the intuition to see problems as the traces and groups of traces are moved.

Don't avoid the auto-router (Topological Router) with modern CAD products or think it can do the whole job. Learn the ways it can help (set up rules for the auto router to handle critical nets) to make better boards. It won't do the whole job but it can let you concentrate on the important details that need hand routing.

Eagle PCB layout example:
 
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Ian0

Joined Aug 7, 2020
1,842
Those tracks are awfully thin, for what is a power board. It might have to take 1Amp.
You need to get yourself a freebie Digikey ruler!* (even the one where they got their own web address wrong) and it tells me that for 35um thick copper (a.k.a. 1oz copper, because it's 1oz per square foot) you need 0.5mm tracks for a 5 degree C temperature rise at 1Amp.
99BF32C5-9C0B-4AA0-AD87-5DC398BCB700.jpeg
But you clearly have room for 2mm tracks, so make them as thick as you can.
Also there's little point in having a ground plane, if you don't connect it to something - 0V would be a suitable place.
Whatever pcb software you're using, when you select "fill" it will probably ask you if you want it connecting to a net, and if so, which one, so select "0V" or "GND" or whatever you called it.
Another thing that I seemed to take ages to learn: when placing your components near the fixing holes, you need to think not just of the size of the nuts that fix it, but the size of the nut runner that you will be using to tighten those nuts.

*I think that when I mentioned the Digikey ruler once before, our friend @crutschow had a pdf of it.
 
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MaxHeadRoom

Joined Jul 18, 2013
22,814
You need to get yourself a freebie Digikey ruler!* (even the one where they got their own web address wrong) and it tells me that for 35um thick copper (a.k.a. 1oz copper, because it's 1oz per square foot) you need 0.5mm tracks for a 5 degree C
They sent me a free one with an order a couple of years back, now I see they charge CAN$7.00 !
Very handy though.
 

click_here

Joined Sep 22, 2020
85
As IanO said, your tracks are too thin, and floating voltage levels on any track are a bad idea, let alone a whole plane!

You may want to put the 7805 up close to the edge to give you the option of screwing it to a heat sink or chassis

And most importantly, you are missing a header on the output

Other than that, it looks good
 
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