Altium Net Tie on Internal Plane

[cjurczak]

Is it possible to place a net tie on an internal layer? 

I'm trying to tie an analog ground, to my digital ground at a single point on one of my internal plane layers.  This directive is per the datasheet, but I'm having trouble figure out how to make Altium do what I want.  I need to tie a small analog ground (only on one layer), to digital ground plane(s).  This means I change them all to the same net name, because they would be connected to subsequent ground planes in the stackup. 

In the screen shot you can see the outline of my AGND plane, with a small opening on the right.  I want to tie the AGND plane to the remaining DGND plan at one point, whether it is a via, or a small portion of copper on a internal plane. 

If you have any input it would be appreciated. 

[Bud]

Place a net tie on the schematic, this  will keep the net names.

[cjurczak]

I have a net tie on my schematic, the problem is when I place the footprint on the internal plane it becomes a void, and not a connection point. 

[ajb]

If you need a single-point connection between areas of a plane layer you probably need to draw lines to make the required cuts.  Plane layers are negative layers, so they work a lot differently from signal layers.  You could also switch to a signal layer and then use polygons/tracks--plane layers perform better for complex boards, but for simple boards signal layers with planes work fine and can give you a bit more flexibility.  I'm not sure that you would be able to do a net tie on an internal signal layer though, since net ties are treated as components.  Can you define internal layer features in a component footprint?  I've never thought to try.

Side note, regardless of what the datasheet says, it's pretty rare that slicing up your ground planes is really the best solution, as it comes with other potential pitfalls and can be very hard to get right in a design that's more than just that one mixed-signal IC. 

[cjurczak]

Yeah, last friday I came to a similar conclusion that I will likely just have to switch it from a plane to a signal layer, and created a couple of polygons.  We have a track record with this switching supply, 0.85V core voltage supply, and a split in the plane meets our needs, and this board has ~5 ground planes, so the effects of the split on one ground plane isn't so bad.  I have checked, and you can assign a net tie component to an inner layer, plane layer or signal layer.  But it will not function as intended on a internal plane layer.