Favourite PCB design techniques - Page 1
Forum section: electronics / beginners

author: faust1002
author_rank: Contributor
timestamp: April 04, 2020, 09:38:02 am
content: Hello guys,I am a beginner, who started working on their first hobby project. This meant that I had to design my own PCB. The last time I did it was about 10 years ago. The problem was that PCB design process was extremely painful for me. Therefore I wonder what are your favourite PCB design techniques. Please don't get me wrong. There are countless tutorial available online. But I want to know what is your preferred way of working. For instance- Do you layout your boards "as is" or you work on subblocks first and then, where they are ready, put them on board?- How pedantic you are? For example, do you set an equal distance between all your passives?I know this is not common case, but I have hardly any limitation in terms of PCB size or a number of layers used. I don't work on commercial products and I don't mind spending a couple of quid more to make my PCBs look nice.Kind regards

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: April 04, 2020, 03:20:32 pm
content: It's totally up to you how much time you spend on perfecting things even if it will make no functional difference.Personally I try to make it look as good as I can without overdoing it.So just do what feels right to you

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: April 04, 2020, 03:46:09 pm
content: Depending on what circuit you have designed pcb layout can be unimportant or vital to the functioning of the circuit.I once designed a USB audio mixer. I glibly just mixed in power supply tracks with audio grounds.The result was 1 VAC of hum on output with inputs shorted !Clearly a mess.When I looked into it the charging impulses were modulating the ground line.So I separated audio and power supply tracks and only joined the power to audio at pcb edge connector.This time the audio was excellent.The main thing to watch out for with audio is star grounding high/medium power lines.

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: April 04, 2020, 04:08:10 pm
content: Quote from: nigelwright7557 on April 04, 2020, 03:46:09 pmThat's a pretty decent trap.I'd say layout really matters when high frequencies, currents and precision analog stuff is involved. For simple stuff like a micro with some blinking leds and a display layout wont really matter.

author: faust1002
author_rank: Contributor
timestamp: April 04, 2020, 05:02:07 pm
content: Hello again guys,Thanks for your response. But I am afraid you didn't fully get my point. Therefore let me rephrase my question. I have an a low frequency (up to several hundreds of kHz) analog circuit (a couple of op amps plus a bunch of passives) controlled by 8-bit micro. The design is powered by USB. All SMD, except connectors and buttons. My limitations are- max PCB size => 100mm by 100mm- four layers- single sided loadHow do you start? What do you do first?Kind regards

author: JustMeHere
author_rank: Frequent Contributor
timestamp: April 04, 2020, 09:08:16 pm
content: Quote from: faust1002 on April 04, 2020, 05:02:07 pmTop layer is your component layer/routing layer2nd layer is your ground layer. Be very careful not to break this up. Any though holes must have some copper between the holes. No routing.3rd layer is your power layer. Also a very good idea to not break up this layer.Bottom is your alternate routing layer.Eagle CAD can do this for a small cost.Kicad probably can do this too but I don't use it.You really should have a local power regulator on the board even if your using USB. The length of the cable itself can be a problem when it comes to a sudden demand for power.Step 1: Lay out components.Step 2: Manually route board.Step 3,4,5: Double check your designStep 6: Export your gerber files and send to fabricator

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: April 04, 2020, 09:39:11 pm
content: Quote from: faust1002 on April 04, 2020, 05:02:07 pmI usually start with grouping components that will be used together, then I start placing things on the board, rotate, change pinout if possible (and necessary) to unfuck the ratsnest as much as possible. Once you're happy with the placements you start routing.I start with the "critical" traces first like USB, you don't want to route everything and then do usb last and have to jump between layers, you're better of doing those things as good as possible right away. Once all the sensitive stuff is done I just do the rest. You'll probably endup redoing certain parts as you work your way through.It's probably not as difficult as you think, if you're like me you're probably overthinking it. Just go for it.EDIT: You'll want to place things that really can't move like mounting holes etc first.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: April 05, 2020, 01:18:48 am
content: Quote from: TheHolyHorse on April 04, 2020, 09:39:11 pmI manually place components that come out close together on the schematic the same on the pcb.It not only gives short routing but also sort of makes the pcb look like the schematic so easier to debug it later.My PCBCAD720 software also has a "swap auto-place" function where it goes through all possibilities and if swapping two components places decreases net length it keeps that swap. Not always a massive difference but even a small difference can make the difference between a pcb routing and not routing.

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2020, 01:24:52 am
content: It depends on the board, but typically I group together related components and then start arranging those blocks in the available space. Then I tweak and massage things as I go along, making everything as tidy as possible. Anything involving high speed or high power I spend extra effort on grounding and decoupling.