Why should I route traces by hand when I have my autorouter? - Page 1
Forum section: electronics / beginners

author: iamericmin
author_rank: Contributor
timestamp: November 20, 2019, 12:17:18 am
content: Hi everyone,I'm a teenager and as my hobby I design PCBs. I always autoroute them since I'm already so busy with learning about new chips, programming, peripherals, etc. I mean, why painstakingly hand-route when my computer can do it for me?However, as I quickly found out that many hobbyists and experts hand-route most, if not all the traces on their boards. This got me worried since I want to be an EE major in college(I'm a senior) and I still don't know how to hand-route. I also still don't get why I would route everything by hand when the autorouter does everything perfectly for me.So, why should I learn hand routing and when should I get started? How do I learn it? To me it just seems like a really hard math puzzle that I will never be able to learn. It looks scary and complicated.Thanks!

author: wraper
author_rank: Unknown
timestamp: November 20, 2019, 12:22:10 am
content: Because simply trowing task on autorouter generally will result in very shitty PCB. Getting decent result out of it is not trivial.QuoteProbably you just don't realize how shitty it is.

author: iamericmin
author_rank: Contributor
timestamp: November 20, 2019, 12:30:36 am
content: Hi wraper, thanks for the quick reply.Can you please explain on the "shitty" aspect? Like, how does the autorouter screw up my board? I thought this only mattered for high-signal or high-power circuits.

author: ataradov
author_rank: Super Contributor
timestamp: November 20, 2019, 12:38:48 am
content: It also matters for analog performance. And if you look close enough, everything is analog.It also depends on complexity, If you have something like Arduino board, I bet even auto-router will not screw it up bad enough.But you still need to do placement by hand. And once you do this, routing is not all that hard.You learn by doing and also looking at other people's routing.

author: wraper
author_rank: Unknown
timestamp: November 20, 2019, 12:40:26 am
content: Quote from: iamericmin on November 20, 2019, 12:30:36 amPost example of your board to discuss what's screwed up there.

author: pmercier
author_rank: Contributor
timestamp: November 20, 2019, 12:44:21 am
content: Exemples of cases you need to route manually :- prevent crosstalk between some traces- artwork- you want a specific layout or trace path around some component- traces with controlled impedance- signal synchronisation (some pro autorouter must be able to do that)- HF circuitsYou'll know when it's time to route your traces by hand. For low speed circuitry, low power why bother doing it by hand if the autorouter give you satisfaction for your use case ?

author: ataradov
author_rank: Super Contributor
timestamp: November 20, 2019, 12:45:00 am
content: Also, here is the example of an excellent review of a very complex board (Server Motherboard):Chances are you will never need 90% of the things mentioned there. But it is still a worthwhile watch if you have any interest in the industry. Even if you won't use it, it will help you understand how to read other people's work. It is a very entertaining and enjoyable series.

author: tautech
author_rank: Super Contributor
timestamp: November 20, 2019, 12:47:28 am
content: Good placement is key to getting a board nicely routed.

author: ataradov
author_rank: Super Contributor
timestamp: November 20, 2019, 12:47:34 am
content: Quote from: pmercier on November 20, 2019, 12:44:21 amBecause you will never learn to actually do it when the design becomes more complex. Of course if you never expect to run into complex designs, then it is fine.

author: pmercier
author_rank: Contributor
timestamp: November 20, 2019, 12:49:15 am
content: One month ago i did a breakot board for an oscillo expension port.I was lazy and asked the router to do it for me. It worked fine when using 4 layers, but i wanted 2 and it couldn't find a way to do it. But it was obvious how to do it by hand, so falled back to hand routing.

author: konzill
author_rank: Newbie
timestamp: November 20, 2019, 12:49:32 am
content: Dave has a video about this:Basically routing is in the class of complex problems that computers are still not that good at. Its just too open ended. Specifying all of the things that a human will consider when routing a board is somewhere between very hard and impossible.It falls into the same class of problems as thehttps://en.wikipedia.org/wiki/Travelling_salesman_problem, except in this case you are trying to plan routes for many travelling salesman and the routes are not allowed to intersect.

author: pmercier
author_rank: Contributor
timestamp: November 20, 2019, 12:52:34 am
content: Quote from: ataradov on November 20, 2019, 12:47:34 amI agree on this one, but everything come in time. No need to rush every competences on a teenager

author: iamericmin
author_rank: Contributor
timestamp: November 20, 2019, 12:59:31 am
content: Thanks. Attached below is a PCB of a wristwatch I made. It contains two 7-segment LEDs, a Nordic nRF52832, 5 more LEDs, a coin cell, and some passives. It is my most complex project to date. The PCB files are in a zip folder in the Autodesk Eagle .brd and .sch format. I also have screenshots of the schematic and PCB(without silkscreen).I always place all my components by hand, being conscious of the autorouter and silkscreen artwork. If the autorouter struggles to find a way, I reorient some of my components to make life easier for the computer. But I never route any of the traces myself.Here is a link to my PCB page from the fabhouse's website:http://dirtypcbs.com/store/designer/details/harambe/6335/time-machine-mk-ivThanks!

author: ataradov
author_rank: Super Contributor
timestamp: November 20, 2019, 01:11:39 am
content: The layout here is not pretty. But here is the thing. You are using a radio, even if it is just a module. And for radios "works" is different from getting the actual performance. It may or may not matter in your case, or course.In this case you see traces and a via near the antenna region. Usually this is not great for performance. Typically module manufactures will specify to either keep the area clear of any traces or flood fill it with the ground plane.Yes, section 2.3. "RF Layout Suggestion (aka Keep-Out Area)" of the module datasheet suggests a proper layout for this module. The requirements are completely disregarded here. Again, it will work, but the range is likely to be compromised.

author: pmercier
author_rank: Contributor
timestamp: November 20, 2019, 01:17:51 am
content: Seem to be a pretty complex layout. Perhaps choosing the pin assignation on the nrf module differently can simplify it.