Three Main Characteristics of Flexible Circuit Board (FPC) :
1. Flexibility and reliability of flexible circuits
At present, there are four types of flexible circuits: single-sided, double-sided, multi-layer flexible boards and rigid-flex boards.
①Single-sided flexible board is the lowest cost printed board with low electrical performance requirements. When 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 rolled copper foil. The insulating substrate can be polyimide, polyethylene terephthalate, aramid and polyvinyl chloride.
②The double-sided flexible board is a conductive pattern etched 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 flexible design and use function. The cover film protects single and double-sided conductors and indicates where the components are placed.
③Multi-layer flexible board is to laminate 3 or more layers of single-sided or double-sided flexible circuits together, form metallized holes by drilling and electroplating, and form conductive paths between different layers. In this way, complex welding processes are not required. Multilayer circuits have huge functional differences in higher reliability, better thermal conductivity, and easier assembly performance. When designing the layout, the interaction of assembly size, number of layers and flexibility should be considered.
④The traditional rigid-flex board is composed of rigid and flexible substrates selectively laminated together. The structure is compact, and the conductive connection is formed by metallization. If a printed board has components on the front and back, rigid-flex boards are a good choice. But if all the components are on one side, it is more economical to use a double-sided flexible board with a layer of FR4 reinforcement laminated on the back.
⑤ The flexible circuit of the hybrid structure is a multi-layer board, and the conductive layer is composed of different metals. An 8-layer board uses FR-4 as the inner dielectric and polyimide as the outer dielectric, with leads extending from the main board in three different directions, each made of a different metal. Constantan alloy, copper and gold are used as independent leads. This kind of hybrid structure is mostly used in low-temperature situations where the relationship between electrical signal conversion and heat conversion and electrical performance is relatively harsh, and it is the only feasible solution.
It can be evaluated by the convenience and total cost of the interconnected design to achieve the best performance-price ratio.
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