3 ms·

It's probably because most people who come into PCB design assume autorouting is like a compiler: you just need to design the schematic and then the computer do

It's probably because most people who come into PCB design assume autorouting is like a compiler: you just need to design the schematic and then the computer does the rest for you. Even with very good autorouting this is never the case, and if you assume so, especially as a beginner, you will wind up with hilariously bad results. This is why experienced PCB designers will often smack the beginner's hand away from the autorouter. That said, they aren't completely useless (though I've never had a case where I needed it), but they are also a very high effort to improve: it's a thorny optimisation problem to start with, but also what is not appreciated is it's also a really difficult user interface problem, since the designer needs to be able to specify the requirements to the autorouter in high precision enough to get a good result, while also taking less time than just doing the routing themselves (which for experienced PCB designers is not really that long for most cases), especially when placement is just as important for a good result, intermingles with routing to a large degree, and is even harder to specify (placement depends on finding a good compromise between thermal, electrical, and mechanical goals, all of which are difficult to specify precisely). Given they're a big trap to newcomers and also a huge amount of effort for something which has pretty niche applications in practice, I'm not suprised the team behind KiCAD decided it was not worth the effort. If you (or someone else) thinks they can make a more useful one, it's definitely a space where improvements on the current state of tooling can be improved, but don't underestimate the effort involved.

barbegal 4y ago
What specifically are most autorouters bad at? My understanding is that most autorouters are simply using bad algorithms and miss optimizations that a human could spot easily. I was recommended to try this autorouter https://www.eremex.com/products/topor/ https://www.eremex.com/products/topor/ but I haven't got round to trialling it yet. >The designer needs to be able to specify the requirements to the autorouter in high precision enough to get a good result, while also taking less time than just doing the routing themselves Aren't most of those rules the same between projects. Once you have a good setup you're good to go on many projects?
- m-ee 4y ago
  A lot of the routing work is in the placement, setting up components to make the routing as trivial as possible, and the autorouter isn't doing that for you. I don't think it'll do pours either but I haven't used one in years. If it's a simple board with just some power lines and digital signals the auto-router will probably do ok, maybe faster than doing it by hand if you can reuse most of your rules. But if the board is that easy an experienced layout engineer would also make short work of it. Now what if the board is more complex? You have some sensitive analog signals, high speed digital signals, and some RF stuff that. Do you take the time to set up a room in Altium with special rules for the RF stuff? Make some complicated rules so that the high speed digital would mess up either of the other things I mentioned? Could be done, but the trial and error of getting all the design rules right is probably more work than just doing it. The problem is that easy stuff is easy, and doesn't need an autorouter. Hard stuff is still hard with the autorouter and unlikely to save that much time. It's hard to find a use case where you come out ahead. Maybe a board with a massive amount of GPIO and nothing else?
  - formerly_proven 4y ago
    Back when I used Eagle the "oh boy that's so many pins of signals I care so little about" was pretty much the only time I found their autorouter somewhat useful. The remainder of the time I was annoyed because Eagle being essentially just a vector-drawing program doesn't have (or didn't, at the time) push & shove routing which made tweaking layouts so goddarn annoying, in particular because the tools to move stuff around were completely trivial (i.e. they just moved the selected vertices and made no adjustments at all). KiCad is imho way better in almost every way than Eagle (in the versions I am familiar with).
    - Animats 4y ago
      I had that with the autorouter. I was doing a board that had one critical area, a custom switching power supply. The rest was slow signals. The switcher area had to be given a little extra space and some obstacles so the autorouter would do a tight job there. For the rest, whatever the autorouter did was fine. I, too, am amused by how wound up some people get about this. It's a tool.

barbegal 4y ago

What specifically are most autorouters bad at? My understanding is that most autorouters are simply using bad algorithms and miss optimizations that a human could spot easily. I was recommended to try this autorouter https://www.eremex.com/products/topor/ https://www.eremex.com/products/topor/ but I haven't got round to trialling it yet. >The designer needs to be able to specify the requirements to the autorouter in high precision enough to get a good result, while also taking less time than just doing the routing themselves Aren't most of those rules the same between projects. Once you have a good setup you're good to go on many projects?

m-ee 4y ago
A lot of the routing work is in the placement, setting up components to make the routing as trivial as possible, and the autorouter isn't doing that for you. I don't think it'll do pours either but I haven't used one in years. If it's a simple board with just some power lines and digital signals the auto-router will probably do ok, maybe faster than doing it by hand if you can reuse most of your rules. But if the board is that easy an experienced layout engineer would also make short work of it. Now what if the board is more complex? You have some sensitive analog signals, high speed digital signals, and some RF stuff that. Do you take the time to set up a room in Altium with special rules for the RF stuff? Make some complicated rules so that the high speed digital would mess up either of the other things I mentioned? Could be done, but the trial and error of getting all the design rules right is probably more work than just doing it. The problem is that easy stuff is easy, and doesn't need an autorouter. Hard stuff is still hard with the autorouter and unlikely to save that much time. It's hard to find a use case where you come out ahead. Maybe a board with a massive amount of GPIO and nothing else?
- formerly_proven 4y ago
  Back when I used Eagle the "oh boy that's so many pins of signals I care so little about" was pretty much the only time I found their autorouter somewhat useful. The remainder of the time I was annoyed because Eagle being essentially just a vector-drawing program doesn't have (or didn't, at the time) push & shove routing which made tweaking layouts so goddarn annoying, in particular because the tools to move stuff around were completely trivial (i.e. they just moved the selected vertices and made no adjustments at all). KiCad is imho way better in almost every way than Eagle (in the versions I am familiar with).
  - Animats 4y ago
    I had that with the autorouter. I was doing a board that had one critical area, a custom switching power supply. The rest was slow signals. The switcher area had to be given a little extra space and some obstacles so the autorouter would do a tight job there. For the rest, whatever the autorouter did was fine. I, too, am amused by how wound up some people get about this. It's a tool.