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Explained the three characteristics of FPC flexible circuit board

September 5, 2022

1. Flexibility and reliability of FPC flexible circuit board
At present, there are four types of FPC: single-sided, double-sided, multi-layer flexible board and rigid-flex circuit board.
①Single-sided flexible board is the lowest cost printed board with low electrical performance requirements. For single-sided wiring, a single-sided flexible board should be used. It has a layer of chemically etched conductive pattern, and the conductive pattern layer on the surface of the flexible insulating substrate is a roll of copper foil. It can be polyimide, polyethylene terephthalate, aramid and polyvinyl chloride.

② Double-sided flexible board is a conductive mode made by etching a layer of insulating base film on both sides. The metallized hole-type connection on both sides of the insulating green material forms a conductive path, which satisfies the flexibility of design and use functions. The cover film protects single- and double-sided wires and indicates component location.

③ Traditional rigid and flexible boards are selectively laminated together by rigid and flexible substrates. Compact structure, metallized forming conductive connection. If a printed board has components on both the front and the back, a rigid board is a good choice. But if all the components are on one side, it is more economical to choose a double-sided flexible board with a layer of FR4 reinforcement on the back.

④Multilayer flexible board single-sided or double-sided flexible circuits are laminated together using 3 or more layers and drill collars L and electroplating formed by metallized holes. Conductive paths are formed between the different layers. This eliminates the need for a complicated soldering process. Multilayer circuits offer higher reliability and better heat transfer There is a huge functional difference in electrical conductivity and easier assembly performance. When designing your layout, you should consider the size of components, the number of layers, and flexible interactions.

⑤ The flexible circuit of the hybrid structure is a multi-layer printed board and the conductive layers are made of different metals. The 8-layer board uses FR-4 as the inner layer of the dielectric and polyimide as the outer layer of the dielectric, and the leads extend from three different directions of the main board, and each lead is made of a different metal. Constantan, copper and gold were used as individual leads. This hybrid structure is mainly used to compare the relationship between electrical signal conversion and thermal conversion and electrical performance, which is the only feasible solution under extreme low temperature conditions.

It can be evaluated by the convenience and total cost of interconnect design to achieve the best price/performance ratio.

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2. The economy of FPC flexible circuit board
If the circuit design is relatively simple, the overall volume is not large, and the space is suitable, traditional interconnection methods tend to be much cheaper. If the straight lines are complex, handle many signals, or have special electrical or mechanical performance requirements, flex circuits are a good design choice. Flexible assembly is most economical when application rulers exceed the capabilities of rigid circuits in size and performance. Can you get 12 shots with 5 million holes of film? Flex circuit with mil pads and 3mil lines and spacing. Therefore, it is more reliable to mount the chip directly on the film. Because it may not be a flame retardant for ionic drilling pollution sources. These films may protect and cure at higher temperatures, resulting in higher glass transition temperatures. The reason this flexible material is more cost effective than rigid materials is that connectors are eliminated.
The high cost of raw materials is the main reason for the high price of flexible circuits. Polyester flexible circuits have a large price difference and low cost. The cost of raw materials is 1.5 times that of rigid circuits; high-performance polyimide flexible circuits are up to 4 times more. The flexibility with the material makes it difficult to automate the manufacturing process, resulting in a drop in yield; defects such as loose flexible attachments and broken wires during final assembly. This is more likely when the design doesn't fit the application. Under high stress caused by bending or forming, the choice of reinforcement or reinforcement is often required. Despite the high cost of raw materials and cumbersome manufacturing, the foldable, bendable, and multi-layer puzzle capabilities will reduce the size of the overall assembly, reduce material usage, and reduce overall assembly costs. The flexible circuit industry is undergoing a small but rapid development. The polymer thick film method is an efficient and low-cost production process. Ships inbound with selective silkscreen conductive polymer inks on inexpensive flexible substrates. A typical flexible substrate is PET. Polymer thick film conductor packages include wire mesh metal fillers or toner fillers. The polymer thick film method itself is very clean, uses lead-free SMT adhesives, and does not require etching. Because of its use-adding process and low substrate cost, the price of polymer thick film circuit is 1/10 of that of polyimide copper film circuit; this is 1/2-1/3 of the price of rigid circuit board. The polymer thick film method is particularly suitable for the control panel of the device. Polymer film for portable products such as mobile phones This method is suitable for converting components, switches and lighting devices on printed circuit boards into polymer thick film method circuits. Save costs and reduce energy consumption.
Generally speaking, flex circuits are indeed more expensive than rigid circuits. In the manufacture of flexible boards, this problem is faced in many cases, in fact, many parameters are out of tolerance. The difficulty in making flexible circuits is the flexibility of the material.

3.FPC flexible circuit board cost
Despite the aforementioned cost factors, the price of flexible assemblies is falling, moving closer and closer to traditional rigid circuits. Main principles Due to the introduction of new materials, improved production processes and structural changes. The current structure makes the product more thermally stable and there are few major mismatches. Thanks to thinner copper layers, some new materials allow for more precise lines, making components lighter and better suited for smaller spaces. In the past, copper foil was combined with a glue-coated medium through a rolling process. Now, copper foil can be produced by directly adhering the dielectric without the need for adhesives. These techniques can get copper layers of several microns, 3 meters. Even narrower precision lines. After removing some stickiness the flex circuit is flame retardant. This can speed up the uL certification process and further reduce costs. Solder masks and other surface coatings for flexible circuit boards further reduce the cost of flexible assembly.
In the coming years, smaller, more complex, and more expensive FPC flexible circuit boards will require newer assembly methods and more hybrid flexible circuits. The challenge for the flexible circuit industry is to use its technology to stay relevant to computing, telecommunications, consumer demands, and keep pace with active markets. In addition, flex circuits will play an important role in lead-free operation.