I'm working with KiCAD and I want to make a rigid-flex board, but I'm unsure of the board stack-up. The board will have 4 layers and I believe PCBWay uses the 2 internal layers for the flex part of the board, but KiCAD does not allow components to be placed on internal layers. What physical stack configuration should I use, and how do I design the PCB in KiCAD? Hoping others have done this with KiCAD and can help!