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Flexible PCB is a kind of high reliability, which is made of polyimide or polyester film as base material, excellent flexible printed circuit board, with high density, light weight, thin thickness characteristics, mainly used in mobile phones, laptops, PDAs, digital cameras, LCM and many other products. Flexible circuits are usually the only solution for miniaturization and mobility requirements on the current connector (cutting-edge) electronic device assembly board. Flex PCB The total weight and volume of flexible assembly is 70% less than that of traditional round wire wiring harness.
Flex and reliability of flexible PCB
Currently prevailing four kinds of flexible PCB: single-sided, double-sided, multi-layer and rigid-flexible combination. Friedman said: The cost of single-sided flexible plate is lowest. When the electrical performance requirements are not high, and can be single side wiring, you should choose single-sided Flexible plate. "This most common form has been commercially used, Flex PCB such as printer inkjet cartridges and computer memory." One-sided flexible plate has a layer of chemical etching of conductive graphics, on the flexible insulating substrate surface of the conductive graphic layer for the rolling copper foil. Insulating substrates used as flexible assemblies can be polyimide (Kapton), polyethylene terephthalate (PET), aromatic polyamide fiber paper (Nomex) and polyvinyl chloride (PVC).
The two-sided flexible plate is a conductive pattern etched on two surfaces of the base film. The metal hole connects the graphics on both sides of the insulating material to form a conductive pathway to meet the flex design and use function. And the cover film can protect the single, Flex PCB double-sided wire and indicate the location of the components.
Multilayer flexible plate is three or more layers of single-sided flexible circuit boards or double-sided flexible PCB laminated, through the drilling, electroplating to form a metal hole, Flex PCB in different layers formed a conductive pathway. In this way, no complicated welding process is required. Although the number of conductive layers designed into this kind of flexible type can be infinite, in order to ensure the assembly convenience, the interaction of assembly size, Flex PCB layer number and flexibility should be taken into account in the design of the layout.
The traditional rigid-flexible plate is composed of a stiff and flexible substrate with a selective formation. The structure is close, and the conductive connection is formed by the metallization hole. Flex PCB In view of the reliability and price factors, the factory should try to keep as few layers as possible.
Flexible PCB industry is in a small but rapid development. The polymer thick film method (PTF) is an efficient and low-cost technology for PCB production. The process is on the cheap flexible substrate, selectively screen-printed conductive polymer inks. Its representative flexible base material is pet. Flex PCB The PTF conductor includes a silk-screen metal filler or a toner filler. PTF itself is very clean and uses lead-free SMT adhesives without etching.
There is also a hybrid structure of flexible circuit boards, it is also a multilayer board, but the multilayer plate conductive layer by different metal composition. This hybrid structure is mostly used in the relationship between the conversion of electrical signals and the heat transfer and the severe low temperature of electrical properties. In this case, Flex PCB the flexible hybrid circuit is the only feasible solution.
Whether the composition of these flexible circuit boards is cost-saving and optimally utilized, it can be evaluated by the convenience and total cost of the internal-connected design. "The overall way of the company is different, the cell phone is a block layout, the portable computer is the X-y orientation of the layout; Flex PCB These products are made from different materials with varying prices to reduce the cost of connecting leads in each root. Each design is evaluated by typology to achieve optimal performance-price ratios.
II. Economic nature of flexible PCB
If the design of the circuit is relatively simple, the total volume is small, and the space is suitable, the traditional method of interconnection is much more cost-effective. Flex PCB Flexible PCB is a good design choice if the circuit is complex, processing many signals, or having special electrical or mechanical properties. Flexible materials have a potential cost-saving reasons compared to rigid materials, which are exempt from plug-connectors.
High-cost raw materials are the main reason for the high price of flexible PCB. Although the raw material is more expensive and troublesome, the Dipalermo still believes that folding, bending and multilayer tile function will reduce the overall assembly size and reduce the total assembly cost.
Third, the cost of flexible PCB is further reduced
Despite the above-mentioned cost factors, the price of flexible assemblies is falling and is becoming close to the traditional PCB. This is mainly due to the introduction of updated materials, improved production processes, and the reasons for changing the structure. For example, the use of acrylic adhesives was canceled on a rigid-flex-plate assembly with many layers.
Now some newer materials can produce finer lines because the copper layer is thinner. Thinner copper layers make components more lightweight, while lighter, thinner assemblies make flexible components more suitable for smaller spaces. In the past, we used roll-pressing technology to glue copper foil to adhesive-coated media. Today, you can generate copper foil directly on the media without using a sticky agent. These technologies can get a few microns of the copper layer, making the industry get 3 mil or even narrower lines of fine width. "After removing the binder from the flexible PCB, the flexible PCB has a flame retardant performance."
This can accelerate the UL certification process and further reduce costs. When the flexible circuit board continues to develop rapidly from the initial military industrial applications to civilian and consumer applications, it is more important to obtain UL certification. Flexible plate solder mask and other surface coatings make the cost of flexible assembly further reduced. In the past decade, Flex PCB some of these new materials and processes have greatly reduced costs. At the same time, it is precisely because the products are widely recognized and demand, the cost of flexible materials is also declining.
In the next few years, more filial and more complex and more expensive flexible PCB assembly will require more innovative assembly, and need to increase the hybrid flexible circuit board. Flex PCB The challenge for the flexible PCB industry is to strengthen its technical advantages and keep pace with the computer, long-distance communication, consumer demand and active market. In addition, flexible PCB will play an important role in the lead-free action.