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First post on the forum so please be gentle with me.

I've been tasked with designing a flex / rigid PCB for a military application. The design involves 2 x rigid PCB's interconnected with a flex section. I've done some preliminary work and reckon the layer count of the rigid sections will be 14+ layers.

Questions -

1. Are there any limitations on the number of flex layers i can select?

2. Can i select numerous solid copper planes in the flex section?

 Thanks

1) In a flex/rigid PCB where all plated-thru-holes are confined to the rigid sections, there should be no limit to the number of flex layers as the flex layers are all built on adhesiveless substrates and the cover materials that contain adhesive are cut back at the rigid circuit interface. There is a practical limitation in that as you have more layers in the flexible area, the circuit keeps getting less flexible, to the point that it is essentially a rigid circuit because it is too difficult to bend.

2) Numerous solid copper planes in the flex section are OK, but again consider how flexible this circuit is going to be with many layers of solid copper. I would recommend that you obtain a physical mock-up of your proposed material stack to verify the circuit will fit and bend as expected.

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