At present, there are four kinds of FPC: single-sided, double-sided, multilayer flexible plate and rigid flexible plate.
① Deep coupled circuit single-sided flexible board is the printed board with the lowest cost and low requirements for electrical performance. In case of single-sided wiring, single-sided flexible board shall be selected. It has a layer of chemically etched conductive pattern, and the conductive pattern layer on the surface of the flexible insulating substrate is calendered copper foil. The insulating substrate can be polyimide, polyethylene terephthalate, aramid fiber ester and polyvinyl chloride.
② The double-sided flexible plate is a conductive pattern made by etching on both sides of the insulating base film. Metallized holes connect the patterns on both sides of the insulating material to form a conductive path to meet the design and use functions of flexibility. The covering film can protect the single and double-sided wires and indicate the location of the components.
③ Multilayer flexible board laminates three or more layers of single-sided or double-sided flexible circuits together, forms metallized holes through drilling and electroplating, and forms conductive paths between different layers. In this way, complex welding processes are not required. Multilayer circuits have great functional differences in higher reliability, better thermal conductivity and more convenient assembly performance. When designing the layout, the interaction of assembly size, number of layers and flexibility should be considered.
④ The traditional rigid flexible plate is composed of rigid and flexible substrates selectively pressed together. The structure is compact, and the conductive connection is formed by metallized holes. If a printed board has components on both front and back sides, rigid flexible board is a good choice. However, if all components are on one side, it will be more economical to select double-sided flexible plate and laminate a layer of FR4 reinforcement on its back.
⑤ The flexible circuit with hybrid structure is a multilayer board, and the conductive layer is composed of different metals. An 8-layer board uses FR-4 as the inner medium and polyimide as the outer medium. The leads are extended from three different directions of the main board, and each lead is made of different metals. Constantan alloy, copper and gold are used as independent leads respectively. This hybrid structure is mostly used in the relationship between electrical signal conversion and heat conversion and the low temperature with harsh electrical performance, which is the only feasible solution.
It can be evaluated by the convenience and total cost of the internal design to achieve the best performance price ratio.