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I've done rigid-flex PCB designs a number of times in the past but it was long enough ago that I cannot remember how I solved this issue. My design has three sections - the main board, the flex, and a daughter board. The flex obviously connects the two rigid boards. The problem is that I cannot seem to place tracks across where the split lines are defined, meaning using the interactive routing tool I can't run traces from the main board over the flex to the daughter board. When I place a trace and move it so that it crosses the line, the error I see is this:

enter image description here

Altium clearly thinks that just because I go from a rigid section to a flex section, that I am going outside the board outline (which is not true). I have no idea what the poly region is, and I do not see anything on the "Multilayer" layer indicating a poly region.

My board stackup is shown below:

enter image description here

I have tried running tracks on all of the four layers and all of them behave the same way.

How does one draw tracks across different sections of a rigid-flex design? My guess is the problem has something to do with the stackup but I can't place my finger on it.

I am using Altium Designer 18.1.7.

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  • \$\begingroup\$ I have a gut feeling, though no certainty (not at Altium PC right now), that this is due to the fact that your non-conductive layers change material between sections in the bottom view. If that is the case, that may be fixable without changing that "discontinuity", though I'd have to try a few things to figure it out myself, but first experiment, force them continuous and see what happens. Clarity: I think it sees no way of attaching your daughterboard to the whole, due to the stackup incompatibility and just gives up. \$\endgroup\$ – Asmyldof Jun 27 '18 at 18:11
  • \$\begingroup\$ I'll be talking to my manufacturer about this. I was able to get around the error simply by turning off the "board outline" constraints in the rules. A "split line" is defined as a "board outline" and prevents me from routing straight through. That being said, the stackup is still something that needs exploration and I'll need to communicate with our vendor for that. \$\endgroup\$ – DerStrom8 Jun 27 '18 at 18:30
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It looks like your layers are not continuous between your stackups. The copper layers in a rigid flex are usually sandwiched on the inner layers, like this:

enter image description here

But maybe your manufacturer uses a different stackup.

I would make your stakup look like this ( the inner layers are continuous) and make sure you put the flex overlays on the flex section and see what happens.

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  • \$\begingroup\$ The problem with that is that I don't want a 59 mil core through the middle of my flex. I did check another tutorial and they used two of the upper layers instead of the two center layers \$\endgroup\$ – DerStrom8 Jun 26 '18 at 19:57
  • \$\begingroup\$ Actually, it's one of the examples that came with Altium: youtube.com/watch?v=aeRd1b6oGto \$\endgroup\$ – DerStrom8 Jun 26 '18 at 20:09

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