Connecting to a ground pour in a multi-layer pcb in eagle

[Anonymous]

I need help to understand how to connect Vias properly on multi-layer PCBs.
I created a 4 layer PCB (Top - GND - V3.3 - Bottom)

Then I created a cutout area in the copper on all 4 layers around the crystal. Then created a copper fill area for a local ground on Layer 2 (GND plane). Now I want to connect on layer 1 to the local ground plane below the crystal with a via.

The copper pour on layer 2 is named GND:

But I don't get it done properly. I tried:
1) Adding a via on top layer, and naming it GND, but then it connects to the ground pour on the top layer.
2) Adding a via on the second layer, and tried to route a wire to that via, but also this does not work as the via is then circumvented.

The grey outline is the polygon I created as a local copper fill, for the ground plane below the crystal on Layer 2. As there is no connection made yet, it does not fill.

How do I connect from the load capacitor C17 to the local ground plan on Layer 2?

I also tried starting with a trace, adding via and switching trace to layer 2 (GND) but it still does not fill the pour when hitting the ratsnest button.

[one-of-the-robs]

I suspect what's happening is that the cutout you placed on layer 2 is preventing the polygon inside it from filling, as it's all cut out. The fix is probably to change the rank of that polygon to be "more important" than the cutout. I'm not in a position to check at the moment but I think the rank works downward, so 1 is the most important, in which case you probably need to set both the overall polygon and the cutout to rank 5 and work down from there.

P.S. you want to swap C16 and C17!

[Anonymous]

Good point about swaping the caps!

Hm. still not sure how that would work. So yes, I have defined a cutout area on each layer. But then i created a separated polygon within this cutout, and named it "GND". My idea was placing a via with "via 'GND'' in the command line and then switch the trace to layer 2 (GND PLANE) to then connect to this polygon. But the ratsnest still does not fill the polygon. So that didnt work.

Maybe I am skipping something important here? 

Not sure about the layer-prios how that would work, as they all are call GND. 

[one-of-the-robs]

No, it's not "layer priorities", it's the POLYGON RANK - look up the help or manual. It's all about when polygons (of the same name or otherwise) overlap on the same layer, and it defines how Eagle treats the stack, i.e. which polygon gets filled into that overlap. My suspicion (although I've not tested it) is that a polygon within a cutout polygon needs to be higher ranking (lower number, I think) than the cutout in order to take priority and actually get filled, instead of removed by the cutout.

[Anonymous]

I have checked for the Polygon Rank, but the Cutouts don't have that option to edit in their properties, whereas the solid polygon pours have the rank fiel. The polygon Pour that is the full layer 2 has a rank of 1. the smaller one I created around (below) the crystal has rank 2, but the cutout has no rank to adjust.

[one-of-the-robs]

OK, so perhaps you need to re-think your cutout completely, but you should first try swapping those ranks as I think they're the wrong way round.

(If there's no rank associated with a cutout polygon then the only behaviour I can see that makes sense is that it blocks any and all polygons of that name. It's just possible it only blocks polygons that enclose it, in which case your smaller polygon is still being blocked by the superior rank of the big one)

[Anonymous]

I also tried the following:

I defined a new GND2 connection in the schematic for the crystal:

My thinking is, that then it should be clearly separated from other GND connections.

I also set the rank of the polygon pour to 1 but still nothing is connecting.

When I place a via by using the command "via 'GND2'" i would expect it would make a connection and fill the pour but it remains shaded only.

Is there any other way to create a GND Pour on a 4 layer board for a crystal?

[Anonymous]

Apologies for being a bit slow right now. But which rank should I change? As the cutout does not have a rank, but only the larger Pour on Layer 2 and the Crystal GND pour i created, i tried to set different ranks for the crystal GND pour with no effect though

[one-of-the-robs · Accepted solution]

You have to set the ranks the right way round.

If there is a small polygon within a big polygon, the small one must have a "more important" (numerically lower) rank than the big one, otherwise it just gets covered over. So set your big (whole board) polygons all to rank 5. However, I misspoke earlier and this trick only works for polygons on different nets.

The cutout polygon is an absolute exclusion - it prevents ALL polygons from filling within it, regardless of name or rank. It is thus probably not the tool you want here, although it would be possible to draw it as a "C" shape so that the inner polygon is not "within" it. In fact the inner polygon may not even be required, as you can use the inside edge of the C to define it.

Alternatively, rename your crystal ground as you tried but then remove the cutout entirely on that layer. The inner polygon is now on a different net to the outer, so by giving it a numerically lower rank and setting the desired clearance in the "isolate" property you can achieve what you're after. You will need to pull a trick to make a connection between the two nets at one point - I use a bridging device whose symbol is just two pins end to end and whose footprint is two SMD pads both at the same place. It creates some DRC errors but they can be approved.

[Anonymous]

That worked. Excellent solution! I did not read anywhere so far that the cutout is an absolute exclusion! I removed the cutout, set the outer GND to Rank 5 and the inner pour GND2 to Rank 1, then increased the isolation around it. Now the via connects to GND2 and the pour fills in properly. I love it... thank you! You really saved my day AND my board in one go!

[Anonymous]

Just a quick one on that bridging device:

I created one like this:

Where do I position it on the board then? As when I create the trace between GND2 and GND, it also adds isolation around that track but it is not really a device I wanna place:

As you can see below the lower left via there is the imaginary device placed, butwhen i route it, it makes it look a bit awkward looking.

[Anonymous]

Actually I just changed the process a bit, but still a bit confused. I got a library for such "short" devices. Inserted it into the schematic as follows:

Now it wants me to place it on my Top Layer (Layer 1). Here is my challenge: The actual GND layers I want to connect are GND and GND1 on LAYER 2.

So does this mean I have to go with via's through layer 1 to connect to the respective GND layers on Layer 2?

In the lower left you see SH1. But I don't want actual pads created there. A bit confusing still.

[one-of-the-robs]

Ah, yes, I'd overlooked that. It proves rather hard to connect two different nets on an inner layer. You could just draw some copper in but that's not a nice solution because it doesn't show on the schematic and won't warn you if you break it. Perhaps somebody else may have a suggestion?

[Anonymous]

So just for making life "easier" which it totally doesn't... Lets assume i call both polygon pours "GND" in the inner layer.

How do I generate then the separation between pours? Even if I change the rank, it does not separate it or cut it out. 

I spent now 3 days on this single problem and I am close to switching to KICAD................ (where it is done in 3 steps.)

Maybe I just don't get it, but a lot of things don't make sense right now. This must be a common problem?

[one-of-the-robs · Accepted solution]

I think you need to adopt my other suggestion, which doesn't involve different nets but needs a cutout polygon that only covers the bit you want excluded. As it's a little hard to describe I've attached a screen recording. I did this on layer 1 because I'm on the free version of V9 at the moment but the principle applies to all layers.

[Anonymous]

That literally solved it. Seeing that video totally helped: 

Layer 2 has now a separated Ground plane (same net) that is only connected via one point. and a cutout on the top layer. This only took 4 days! 🙂

Thank you for all your patience and commitment to help me out on this!!! 

[victor.vanderelst]

This video was exactly what I needed thank you!