The slide show below represents the artwork levels of an 8 layer rigid flex. Four layers are rigid layers and four are flexible. It is highly recommended to do a balanced construction. For example, in the circuit below, you will see 2 rigid copper layers on the top and bottom outside, and 4 flex copper internal layers.
The application is for a defibrillator (medical device). You can see that there are connectors required on two different sides of the circuit. This circuit is carrying signals and power.
Top Silkscreen - The images below will be printed onto the top of the finished circuit with indelible ink. This assists with component placement.
Top Soldermask - Soldermask is used for the rigid areas as an insulator to protect the copper. This is the artwork to place the soldermask on the top rigid area layer.
Top Layer of Copper - This is artwork for layer one of the rigid area.
Layer Two Copper - Since layer one and two are rigid, we use a material called pre-preg to insulate the layers. A pre-preg (from pre-impregnated) is fiberglass impregnated with resin.
Layer Three Copper - This is the first layer of flex copper. Again pre-preg will be used to insulate the copper layers to the rigid. The bottom side of layer 3 will have a flexible insulator made of polyimide.
Layer Four Copper - This is the second flex copper layer. The bottom side of layer 4 will have a flexible insulator made of polyimide.
Layer Five Copper - This is the third layer of flex copper. Again, this will have a polyimide insulator.
Layer Six Copper - This is the last flex copper layer.
Layer Seven Copper - As we get to the bottom of the circuit, we are back to a rigid circuit construction.
Layer Eight Copper - Layer 8 is the last layer of copper in the circuit.
Bottom Soldermask - Soldermask is used to cover the exposed copper to the outside world.
Bottom Silkscreen - Silkscreen that identifies component placement and any other data the customer wants to place on the flex to identify the circuit.
Drill File - The drill file identifies the drill holes required in the circuit. The holes are plated to make electrical connections between the layers of copper.
Outline - The outline file is to create tools to cut the circuit out of the panel.
Voila' An 8 layer rigid flex! If you are interested in more details about rigid flex construction, please request a design manual or call PFC!