PCB News - Three main characteristics of FPC flexible circuit board

Three main characteristics of FPC flexible circuit board

1. FPC flexible circuit board flexibility and reliability
At present, there are four types of FPC: single-sided, double-sided, multilayer flexible board and rigid-flex circuit board.
1. Single-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 patterns, 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 ester and polyvinyl chloride.
2. Double-sided flexible board is a conductive mode by etching both sides of a layer of insulating base film. The metalized hole-type connection on both sides of the insulating material forms a conductive path, which meets the flexibility of design and use functions. The cover film can protect single-sided and double-sided wires, and can indicate the location of components.
3. Traditional rigid and flexible boards are selectively laminated together by rigid and flexible substrates. The structure is compact, and the metallization is formed for conductive connection. If a printed board has components on the front and back, then a rigid board is a good choice. But if all the components are one aspect, it is more economical to choose a double-sided flexible board with a layer of FR4 reinforced material laminated on its back.
4. Multi-layer flexible board single-sided or double-sided flexible circuits are laminated together, using 3 or more layers and metalized holes to form drill collars and electroplating. Conductive paths are formed between different layers. This eliminates the need for a complicated welding process. Multilayer circuits provide higher reliability and better heat transfer. There are huge functional differences in electrical conductivity and easier assembly performance. When designing the layout, you should consider the size of the components, the number of layers, and flexible interactions.

5. The flexible circuit of mixed structure is a multilayer printed board, and the conductive layer is made of different metals. The 8-layer board uses FR-4 as the inner layer of the medium and polyimide as the outer layer of the 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 hybrid structure is mainly used for the relationship between electrical signal conversion and thermal conversion and the comparison of electrical performance. This is the only feasible solution under extreme low temperature conditions.
It can be evaluated by the convenience and total cost of interconnection design to achieve the best cost performance.
2. The economy of FPC flexible circuit board
If the circuit design is relatively simple, the total volume is not large, and the space is suitable, the traditional interconnection method is often much cheaper. If the straight line is complex, handles many signals, or has special electrical or mechanical performance requirements, flexible circuits are a good design choice. When the application ruler exceeds the capacity of rigid circuits in size and performance, flexible assembly is the most economical. Can 12 shots be taken with a 5 million hole film? Flexible circuit with mil pad and 3mil line and spacing. Therefore, it is more reliable to mount the chip directly on the film. Because it may not be a flame retardant for ion drilling pollution source. These films may have protective and curing effects at higher temperatures, resulting in higher glass transition temperatures. The reason why this flexible material is more cost-effective than rigid materials is that the connector has been 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 raw material cost is 1.5 times that of rigid circuits; high-performance polyimide flexible circuits are up to 4 times higher. The flexibility of materials makes it difficult to automate handling in the manufacturing process, resulting in a decrease in output; defects in the final assembly process, such as falling off flexible accessories and broken wires. This situation is more likely to occur when the design is not suitable for the application. Under high stresses caused by bending or forming, it is often necessary to select reinforcing materials or reinforcing materials. Although the cost of raw materials is high and manufacturing is troublesome, the foldable, bendable and multi-layer puzzle function will reduce the size of the overall assembly, reduce the use of materials, and reduce the overall assembly cost. The flexible circuit industry is undergoing a small but rapid development. The polymer thick film method is an efficient and low-cost production process. The ship entered the port with a selective silk screen conductive polymer ink on an inexpensive flexible substrate. A typical flexible substrate is PET. The polymer thick film conductor package includes wire mesh metal filler or toner filler. The polymer thick film method itself is very clean, uses lead-free SMT adhesives, and does not require etching. Because of its use and low cost of substrates, the price of polymer thick film circuits is 1/10 of that of polyimide copper film circuits; this is 1/2-1/3 of the price of rigid circuit boards. The polymer thick film method is particularly suitable for the control panel of the device. Polymer film is used in 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 circuits. Save costs and reduce energy consumption.
Generally speaking, flexible circuits are indeed more expensive than rigid circuits. In the manufacture of flexible boards, this problem must be faced in many cases. In fact, many parameters are out of tolerance. The difficulty in making flexible circuits lies in the flexibility of the materials.
FPC flexible circuit board cost
Despite the aforementioned cost factors, the price of flexible assembly is declining, getting closer and closer to traditional rigid circuits. The main principle is that due to the introduction of new materials, the production process and structural changes have been improved. The current structure makes the product more thermally stable, with few major mismatches. Because the copper layer is thinner, some new materials can make more precise lines, making the components lighter and more suitable for small-sized spaces. In the past, copper foil was combined with a glued medium through a rolling process. Now, it is possible to directly adhere to the medium without the need for an adhesive to produce copper foil. These techniques can get a copper layer of several microns, 3 meters. Even narrower precision lines. Remove some stickiness through the flexible circuit of the agent is flame retardant. This can speed up the uL certification process and further reduce costs. The use of solder masks for flexible circuit boards and other surface coatings further reduce the cost of flexible assembly.
In the next few years, smaller, more complex, and more expensive FPC flexible circuit boards will require updated assembly methods and more hybrid and flexible circuits. The challenge for the flexible circuit industry is to use its technology to keep in touch with the needs of computers, telecommunications, and consumers, and to keep the active market in sync. In addition, flexible circuits will play an important role in lead-free operation.