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I am designing a board layout in Eagle. Before manual/auto routing, I made a polygon around the corners and named it as GND. Then I used the autorouter for routing. After the routing is complete, there are few yellow wires left and these wires are of GND connections. enter image description here

As you can see in the image, there is a yellow wire attached to the GND of the LED1 and the 3rd pin of the JP2. According to my understanding, this should not happen because I have made the Polygon of GND. What could be the problem. Am I doing something wrong. Please help. Thanks.!

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Well something has to give - either the ground plane has to give up space for the auto routed tracks or all the tracks cannot be autorouted. Personally I would put ground on the bottom layer and use a double sided board - much more robust in terms of EMC.

It also looks like your copper clearance rules are too tight.

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  • \$\begingroup\$ This has to be made on Single Layer. Does providing more space between the components and more clearance will be good enough for it.? \$\endgroup\$ – J.Doe Jul 12 '16 at 9:04
  • \$\begingroup\$ No, adding more space will not result in a PCB where everything gets joined up track wise but it will prevent unwanted shorts due to clearance tolerances in manufacture. Why can't you go for a double layer board. \$\endgroup\$ – Andy aka Jul 12 '16 at 10:59
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The remaining yellow wires are where the autorouter was unable to make the connections. The polygon connecting to the cathode of the LED is not connected to the rest of the ground plane -- it has its own island that is electrically isolated. This is a problem, because there is no return path (hence the yellow airwire). I am not going to take the time to review your board, but I expect you have a similar problem with the other airwire. You'll need to rearrange your components and re-route (by hand would be more reliable -- Machines are very stupid) to make sure you have a solid ground plane and that all connections can be made.

You are severely limited by the single-layer requirement. You need to think very carefully and try multiple times until you get something that works.

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Why limit yourself to single layer? The PCB houses all do double layer as a standad product. I'd doubt you can even find one that will do single layer. Your traces are too fine and closely spaced for home production to be reliably made. Go double layer, with GND plane on both sides, add some vias and Name then GND also, place as needed to connect all the GND areas together.

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You should name "GND" to the polygon and mark as Entire signal. (You should use a polygon not rectangle). If route adouble sided PCB you shoud make another ground plane in the othe side named also GND, then place manually a via named "GND" also and copy it somewhere, specially close to the GND part of the decoupling capacitors

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