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I am laying out a PCB using EAGLE 7.7.0 for Linux (64 bit).

When I run the Autorouter (high effort) it runs 22 variants of the routing, and all 22 produce 100% complete routing.

Below the dialogue is the standard warning "Percentage may decrease after final processing of polygons". Sure enough, it does: many of the variants, upon selecting them, turn out not to be 100% routed - one or more connections cannot be routed because the polygon ground fills have split into two parts which cannot be connected.

Is there anything I can do to make EAGLE check whether they really are 100% routable, before I permanently select one? At the moment the best method I have is to undo the whole routing, recalculate them all, try the next, and so on.

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  • \$\begingroup\$ Frankly, standard advise is not to use the autorouter. \$\endgroup\$ – Chris Stratton Jan 8 '17 at 18:47
  • \$\begingroup\$ @ChrisStratton Why's that? And what's the alternative? (Do it myself?) \$\endgroup\$ – Mark Smith Jan 8 '17 at 18:48
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    \$\begingroup\$ Indeed, you will get far better results with manual routing - especially on a two layer board where you need to put especially careful attention into the flow of power supply current. \$\endgroup\$ – Chris Stratton Jan 8 '17 at 18:51
  • \$\begingroup\$ @ChrisStratton OK, thank for the tip. I'm happy with the routing is has done on this occasion. Still interested in an answer to the question if anyone has one :-) \$\endgroup\$ – Mark Smith Jan 8 '17 at 18:56
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    \$\begingroup\$ @Chris: That's just the usual whine from people that haven't bothered to properly learn the auto router. It's a great tool, but has to be used carefully and with good understanding of what it can and can't do. It's not just going to do everything for you, but it can be very useful nonetheless. Telling people to just not use it is bad advice. Just because you don't know how to use it properly, doesn't mean it's not a useful tool or that others can't get good results with it. Loose the attitude. \$\endgroup\$ – Olin Lathrop Jan 8 '17 at 20:09
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Is there anything I can do to make EAGLE check whether they really are 100% routable, before I permanently select one?

No.

What you can do is force connectivity between islands. Pick a routing variant you like, identify polygon islands, unroute (a simple undo would do), add a ground trace betwee pads to connect the islands and then reroute.

Using an autorouter is a questionable issue. Many dislike it. I found it to be very useful in my hobby projects. First route manually the critical nets (power/ground, crystal, fast data, etc) and then let the auto router do the rest less critical nets (~60-70% of the nets in my designs).

Another trick is to play with the costs to encourage less and shorter traces on the polygon layer.

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Is there anything I can do to make EAGLE check whether they really are 100% routable, before I permanently select one?

Yes. On the bottom right of the board window you should see an icon that looks like the autorouter command button. Click on this and it will give you the routing variants dialog again, then you can evaluate another variant. Click on 'End Job' when/if you find one you are happy with.

it runs 22 variants of the routing

You can reduce the number of variants by choosing preferred directions (eg. top vertical, bottom horizontal) and unticking 'Variant with TopRouter'.

one or more connections cannot be routed because the polygon ground fills have split into two parts

One way to avoid this problem is don't do polygon fills until after autorouting. There is probably a proper way to do this but I just drag my polygons outside the board area before autorouting, then move them back again afterwards.

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