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I am planning to design a bookbinder with airgap rigid flex PCB using Altium.

Based on guidelines from Altium, and various other sources, it is important to have "staggered lengths", to prevent the PCB from buckling when it is bent.

However, I can not see any documentation on how to stagger the lengths. I have contacted a PCB manufacturer and they have suggested that you might need different gerber files. Is the best option to essentially produce a separate PCB for each flex layer? I have included my WIP stackup. Note there is an air gap in between flex layers, but this is not shown by Altium.

https://www.altium.com/documentation/altium-designer/designing-rigid-flex-pcb

Bookbinder example picture

Example stackup

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    \$\begingroup\$ altium doesn't make the PCB - the manufacturing company (that you choose) does. Can the manufacturing company make this? If they can, you could ask them how you should note this on your design so they'll do it. \$\endgroup\$
    – user253751
    May 16 at 8:46
  • \$\begingroup\$ I have no idea how they manufacture a PCB that's partly solid and partly flex. \$\endgroup\$
    – user253751
    May 16 at 10:39
  • \$\begingroup\$ About the air gap, Altium doesn't know you want an air gap. And I don't know how to tell it you do. This is definitely one too discuss with your manufacturing partner. \$\endgroup\$
    – The Photon
    May 16 at 14:47
  • \$\begingroup\$ Or ask on the Altium forums. \$\endgroup\$
    – The Photon
    May 16 at 14:48
  • \$\begingroup\$ @user253751 It’s called rigid-flex and is quite common. \$\endgroup\$
    – winny
    May 16 at 16:37

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The PCB manufacturer routes the layers separately before stacking them up, so that the inner "flex" layers are contiguous and exposed in the desired areas, called "substacks" which are assigned to board regions in Altium.

When you create multiple substacks, you can use them for each of the flex sections that span across a bend. Altium shows an example of this in the guide "Designing a Rigid-Flex PCB in Altium Designer." (See section "Material Usage" under "Adding and Editing a New Substack.")

Here is the relevant image from that guide:

Bookbinder style flex substacks example in Altium

What isn't covered in any great detail, is the Intrusion Right and Intrusion Left properties shown at left in the image. The text of the guide only has this to say about intrusion:

Place the required number of Regions. Regions can be drawn so they are overlapped, note that this does not define the extent that a flex region overlaps into a rigid region, that is defined by the Intrusion values in the Stackup definition.

I would definitely recommend consulting with the PCB fabricator what the intrusion amounts should be so that the bend doesn't put too much strain on any single layer.

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    \$\begingroup\$ +1 and to add, highly recommend to identify the mfg , and get their design requirements, before starting the design. \$\endgroup\$
    – crasic
    May 16 at 16:13
  • \$\begingroup\$ Thank you for the response! I have contacted a manufacturer and have been working with their recommended stackup. My understanding is that the intrusion property describes how much the Flex is embedded into the PCB? It does not appear to support having variable length Flexes to create "staggered lengths" for a bookbinder design \$\endgroup\$
    – JAS
    May 17 at 0:59
  • \$\begingroup\$ @JAS My initial thought was that you would specify a different intrusion amount for each substack, having, for example the lowest layer "intrude" more than layers above it. Additional text under Design Considerations says: "Staggered lengths - to avoid layer buckling when flexed (bookbinding), stagger the layer lengths by approx 1.5 times the layer's thickness." This doesn't sound like intrusion amounts, so there may be another property. I recommend asking on Altium's forum. \$\endgroup\$
    – JYelton
    May 17 at 15:19
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    \$\begingroup\$ Thanks @JYelton I have created a post on Altium forums, and will update here if/when there is a clear answer \$\endgroup\$
    – JAS
    May 18 at 23:46

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