How do I remove necks and dead copper on internal planes? - Page 1
Forum section: electronics / general

author: dmg
author_rank: Regular Contributor
timestamp: January 11, 2017, 04:43:21 pm
content: Hi,I always have a very annoying problem when doing multilayer boards in Altium that I don't know how to get rid of apart from manually patching it with fills.It happens when I have a multilayer board with internal planes (negative planes moslty used for power and ground), and some unconnected via pattern makes altium generate the mess you see in the attached pic.It sometimes generates narrow necks too, which aren't detected by the DRC. I'm not sure if I'm doing something wrong or what, but I can't find an automatic solution for the problem, like you have for polygons and such. Any help with this?Thanks

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 11, 2017, 05:43:37 pm
content: You don't...Add shapes to the layer manually, to cover the bits. Make sure to update them if you move things around later.Better to delete the layer from the stackup, add a Signal Layer in the same position, and use a Polygon to pour it.Plane layers are also really basic with how they connect (spokes and clearance). They don't handle oval pads or slot holes.Tim

author: dmg
author_rank: Regular Contributor
timestamp: January 11, 2017, 10:45:01 pm
content: Quote from: T3sl4co1l on January 11, 2017, 05:43:37 pmDamn. Up to this day I used the internal planes and patched the messy areas with fills and stuff, it was a also a reason to check the whole board for potentally starved planes and such. I recently got updated to Altium 17 and got asked to make a minor variant modification for a design to get a new batch of it made. PCB didn't change, but when outputting documentation it said 4 DRC clearance errors. Turns out it was some of the patching fills that for some reason now were considering as stupid violations.Won't use internal polygons again.

author: ajawamnet
author_rank: Regular Contributor
timestamp: January 15, 2017, 07:03:42 pm
content: I've never read anything concerning the removal of neg planes in AD. In fact from what I've seen in AD17 they've added some features for managing planes.I do a lot of designs with Altium - been an owner since 1995. I do about 130 design a year.Currently working on a design that has 12 layers with 10 being planes with splits. There's over 82 split planes. If I were to do that with internal polys it'd be a nightmare.In fact, AD17 has some issues with nested split planes causing hangs in being able to save. Check the Altium forum posts.As to top/bot pours again I stay away from that. A lot of designers love to add outer layer pours with the idea that it'll somehow aid in EMI emissions and susceptibility. In fact, at the local test lab, we've found it can actually exacerbate radiation due to things like return paths, coupling, etc..We did a design for a medical device for a leading medical device supplier where one of the engineers wanted us to do outer layer pours. So we did (even stitched it with vias) and the result was just hideous - "... congratulations, that's the highest EMI we've ever seen in the lab" was the comment from testers. When we removed the outer layer copper it passed.It also creates uncontrolled coplanar wave guides, that for most designs are not an issue but as you get into higher speed signals can have a detrimental effect on impedance. Also on multilayer designs you now have to deal with asymmetric striplines.There are good reasons to do pours ( as in CPW) and the like, but you really need to know what the topology requires and design to that. Even high-end field solvers/post layout simulators can fail to find issues that can be caused by randomly pouring copper.

author: gawachter
author_rank: Newbie
timestamp: January 08, 2018, 11:45:37 pm
content: Place a polygon pour cutout over the dead copper.

author: julianhigginson
author_rank: Frequent Contributor
timestamp: January 09, 2018, 02:09:33 am
content: I really like plane layers compared to poly pours on normal layers.. YES they need a bit of attention, and altium could easily just make them work 100% with a bit of work around the via clearance and plane connect stuff (which I have long given up on them ever doing) but I think the feature is definitely usable for real designs, if you keep in mind there's always a couple of things to manually check, and I don't see it going anywhere.I have tried an experiment recently by doing a few of my recent 4 layer (outer tracks, inner planes) designs with poly pours on internal layers instead of plane layers. due to recommendations on this forum. Basically, I found it fiddly and annoying, and I needed to spend more time routing because of it.For me, the whole magic of plane layers is they are inverted - so they can visually exist in the design and be properly visible without blocking everything else out wherever they go. This means if you have a split plane with a few different power domains on it, you can see EXACTLY where the edges of the plane is for the power domain you need, both when placing and moving a component, and when routing component pins down to the plane.With poly pours on a normal layer, the plane becomes very hard to see through, and so having it at all visible means you can't see other things you need to see, like potential blocking objects on the other side of the board when you're trying to route something.. the alternative seems to be polygons in draft mode (which for me is not visible enough, may as well not be there) or just shelving all polygons (which means the polygons aren't even there to electrically interact with and you can't see them when you need to route to one...) or turning off the view of the layers you have planes on... again, working blind... I literally have no idea how you'd effectively do an 8 layer or more board with poly pours on normal layers. it would be a nightmare. you wouldn't be able to see anything and you wouldn't be able to target the net regions you needed to. And an added bonus is - if you want to work with online DRC, as soon as you drop a via while routing, with your power and ground planes enabled, BOOM, the whole screen turns bright green and you can't see anything!! the only alternative here seems to be turning the online DRC off.Also, for plane layers, adjusting split plane relative placement becomes a matter of moving a line. with poly pour on normal layers it's all grabbing polygon edges and corners and trying to mash things into shape then extend other things to match while visually maintaining clearance. so fiddly!In short, I think the only way I could effectively do a 12 layer board that needed for some reason to have poly pours instead of plane layers would be to do it with plane layers, finish it to the point I could release it that way, THEN add in normal layers with poly pours to match each of the original plane layers... then delete the plane layers.