The Rigid-flex printed circuits are combined from flexible and rigid prinetd circuits, which connect to each other by plated thruog holes and plated vias.
Rigid-Flex design need to follow the design parameters of multilayer printed circuits. For the production we need the Gerber data in RS274-X format and drilling files (Excellon, Sieb & Meyer 1000 és 3000 format) but also we need a mechanical layer where we can see the rigid-flexible transitions. Furthermore we need the correct stack-up, which contains the order of the layers, the type and thickness of used materials and the total thickness.
We are able to produce this product with maximum 4 layers, can be 2 layers flexible and 2 layers rigid stack-up Rigid-Flex circuits. See this figure for an option:
The opposite of the type illustreted on the figure is also possible to produce; where the flexible part is oon the top and the rigid layer is on the bottom. During pressing cycle the insulation between the flexible and rigid part is made by the 50µm thick epoxy adhesive layer.
Base materials of rigid printed circuit: FR4, thicknesses: 0.36mm, 0.51mm, 0.71mm, 1.0mm, 1.2mm, 1.5mm, 2.0mm, 2.4mm
Base material of flexible circuits: 25µm or 50µm thickness polyimide
Copper thickness (base): 18µm or 35µm
The base material of the carrier:
Rigid: FR4 wide range of types https://www.isola-group.com/wp-content/uploads/data-sheets/is400.pdf
Flexible: Polyimide (Kapton) GTS Flexible Materials Ltd company GTS 7800 material http://www.gts-flexible.com/products-table/gtsppage/5/
Blind vias: it is possible on rigid-flex PCBs as well. The blind via makes the connection between two copper layers of the rigid and/or flexible circuit. Buried via, which connects two inner layers in case of rigid-flex PCB there is no possible to make buried via.
Coverlay: 25µm thick polyimid with 25µm thick adhesion layer, it can be used instead of solder mask painting in some cases, for example on the flexible circuit where it is necessary to cover copper areas on inner layer.
Solder mask: on the outer layer of the rigid printed circuit is screen printed by different colours such as green, red, blue, black, white colours, the outer layer of the flexible circuit is screen printed by green flexible solder mask.
Legend print: it is possible on the rigid and flexible printed circuit outer layer, colours we can apply are white, black and yellow.
Surface finish: ENIG immersion gold and immersion silver. The Rigid-Flex printed circuits can have surface finish applied by chemical treatment so the hot air levelling (tin or tin-lead) is impossible in this case.
Mechanical finish: routing in single units or panel format with technical frame and breaking tabs preferred by assembling compenies.
Further possibilities: flexible connector with stiffener (not reflow resistant), galvanic, hard gold plating on connectors.