Several classifications of flexible printed circuit boards

  At present, there are mainly four types of flexible circuits: single-sided, double-sided, multilayer and rigid flexible circuit boards.

 1. Single-sided flexible board is the lowest cost printed board that does not require high electrical performance. In single-sided wiring, a single-sided flexible board should be used. It has a layer of chemically etched conductive patterns, and the conductive pattern layer on the surface of the flexible insulating substrate is a rolled copper foil. The insulating substrate can be polyimide, polyethylene terephthalate, aramid cellulose ester and polyvinyl chloride.

  2. The double-sided flexible board is a conductive pattern made by etching on both sides of the insulating base film. The metallized hole connects the patterns on both sides of the insulating material to form a conductive path to meet the design and use function of flexibility. The cover film can protect single and double-sided wires and indicate where the components are placed.

  3. Multilayer flexible board is to laminate 3 or more layers of single-sided or double-sided flexible circuits together, and form metallized holes by drilling and electroplating to form  conductive paths between different layers. In this way, there is no need to use a complicated welding process. Multilayer circuits have huge functional differences in terms of higher reliability, better thermal conductivity and more convenient assembly performance. When designing the layout, the mutual influence of assembly size, number of layers and flexibility should be considered.

  4. The traditional rigid-flex board is composed of rigid and flexible substrates selectively laminated together. The structure is compact, and the metallized hole L forms a conductive connection. If there are components on the front and back of a printed board, a rigid-flex board is a good choice. But if all the components are on one side, it will be more economical to choose a double-sided flexible board and laminate a layer of FR4 reinforced material on its back.

  The flexible circuit of hybrid structure is a kind of multilayer board, and the conductive layer is made of different metals. An 8-layer board uses FR-4 as the inner layer medium and polyimide as the outer layer medium. Leads extend from three different directions of the main board, and each lead is made of a different metal. Constantan alloy, copper and gold are used as independent leads. This kind of hybrid structure is mostly used in the low temperature conditions where the relationship between electrical signal conversion and heat conversion and the electrical performance are relatively harsh, and it is the only feasible solution.

  Can be evaluated by the convenience of the interconnection design and the total cost to achieve the best performance-price ratio.