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Tips on Layout for Routing
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Paul Spark 2 years ago
I have looked on the tutorial on this website and Youtube but I cannot seem to find a good guide on how to layout components in such a way that auto routing will be successful. I have tried both cloud and local router methods for autorouting but figured they probably use the same algorithms.. so I installed FreeRouting. FreeRouting is now onto its 53rd pass and it is still struggling to route my design. I don't know whether it will be successful after 24 hours or not. I have tried to place components on my board so that the header connectors work for me but I am wondering if there is something fundamentally wrong with my component placement? Can somebody please recommend a good resource or set of tips for placing ICs on a board? I have made slightly simpler boards with DipTrace in the past - that always did the autorouting for me without any troubles. I tried using EasyEDA this time as I thought it would be the best choice if I want to have my boards assembled with JLCPCB.
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Paul Spark 2 years ago
Pass #211 now.. Time to give up? Is there something seriously wrong with my placement? ![image](https://i.imgur.com/BVeM1E9.png)
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andyfierman 2 years ago
A screenshot of your PCB layout is helpful but access to your project (schematic  plus pcb) would be more so.
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andyfierman 2 years ago
Your screenshot does not show it: are you allowing routing on both top and bottom layers? Are you just using two layers?
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Paul Spark 2 years ago
I believe I am using 2 layers. I tried to experiment with manually routing a couple of rat lines and I was able to go between top and bottom layers. Is there a way in which I can share my project with you without publicly sharing it?
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Paul Spark 2 years ago
@andyfierman I have added you as a project member. I hope that helps :-)
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UserSupport 2 years ago
HI you can try autorouting tool Electra
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Paul Spark 2 years ago
@usersupport I will see if I can find Electra and give it a go.. FreeRouting isn't succeeding. Its been running all day and gotten up to over 600 passes. ![image](https://i.imgur.com/RRYEIbq.png)
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UserSupport 2 years ago
you need to try to modify your components layout, to let the auto router finish
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Paul Spark 2 years ago
@usersupport Yeah, I was hoping to get some guidelines on that. I'm not sure what is "good practice" vs "bad practice". Do I just need to move components around so there is less "cross over" of connections? I planned my board so it would work for me from an external connectivity perspective (it is a daughter board designed to connect to a QMTech Cyclone V FPGA development board).
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Paul Spark 2 years ago
@usersupport I guess it's too complicated for Electra too: ![image](https://i.imgur.com/x6ld2aw.png) One of the things I read in the EasyEDA Tutorial page was that you can't use "/" characters? It wasn't very clear on this page: [https://docs.easyeda.com/en/PCB/Route/index.html#Routing-Conflict](https://docs.easyeda.com/en/PCB/Route/index.html#Routing-Conflict) ![image](https://i.imgur.com/wbTQxn5.png) Does this mean that I cannot label NetPorts with names such as "/CE" ? Should I be changing those to "CE#" ?
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UserSupport 2 years ago
No,you need to re-layout the component position, it is not the net name issue, it's the position issue, An irrational layout will not make the autoroute finish
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Paul Spark 2 years ago
@usersupport It would be really helpful to know what an irrational layout is (or what a rational layout is). I have tried moving components around but I still can't get past 82% completion. Maybe @andyfierman will come up with some ideas. I don't understand why this layout is deemed so complex.
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andyfierman 2 years ago
There is no magic spell to get good results with an Autorouter. An Autorouter is just a faster way of making a bigger mess of your PCB. It takes hard work and practice. Most of that comes from a thorough understanding of good layout which only really comes from learning to do good manual routing first. The real key to getting good results with an Autorouter is to get a placement that allows the minimum of crossovers to get from one pad to another. Another way of saying this is that the route should follow as direct a path as possible. Which is often incompatible with a pre-conceived board layout (which may well have been planned without thinking of the routing issue for the board or something that may have to plug into it). If there are fast edged (and that does not necessarily mean high clock frequency) signals such as logic and switching power supply nets then you need to route them carefully anyway. The silly thing is that once you have a layout that meets the above criterion, you are quite close to the point where you can manually route it as fast as the autorouter and almost certainly better. Rule 1: If the layout and the routing matter: do it manually! That said I had a 4000 series (slow edged logic signals) board that was quite complex so played with the layout to get the most direct ratline paths I could and then ran the auto router a few times with minor placement changes to see how it got on and then connected the supply and ground using copper floods with a few layer changing tracks. Overall it was faster than manually routing the whole board but not by much and then only because I had a clear idea of what Iwas trying to achieve and a lot of leeway in terms of very few tight signal and power integrity (SI and PI) constraints. There are some notes in (2.2) in (2) in: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a)<br> <br> ![image.png](//image.easyeda.com/pullimage/H4Nwco3KL1AkanukvWikJHlGU68UUlbTmb6qd9Yh.png)
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Paul Spark 2 years ago
@andyfierman I seem to have problems using the links you provide. They always seem to take me to the same page. If I use the above link and search for "PCB design notes", Firefox finds nothing. If I search for "2.2", I find nothing. So what I am hearing is that I need to go away and manually route my entire board. There are some better placement choices I can make which will require me to revisit my schematic and re-place all the components onto the board again. I guess I just need to suck it up and accept that it is going to take time. It's shame the auto router couldn't do selections. Some parts are obvious 1:1 parallel mappings.
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andyfierman 2 years ago
It's no use just going to the page and then searching it. Read it carefully and _then follow the links from that page to all the nested links in the pages that they link to._
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Paul Spark 2 years ago
So..  I finally got there. Getting rid of the double headers helped a lot, reducing trace cross-over. EasyEDA itself wouldn't autoroute but FreeRouting did. I had about 10 DRC errors to sort out. Luckily rotating my SRAM TSOPs did the trick. I now have boards in production at JLCPCB.. so fingers crossed they don't have mistakes on them! Certainly been a challenge this time around. At least next time I shouldn't have the need for as many "debug" headers.
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andyfierman 2 years ago
And next time you'll have that bit more experience to help with the initial placement so the routing (however you do it) will be easier.
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