Flex and reliability of flexible PCB
At present, flexible PCB has: single-sided, double-sided, multilayer flexible plate and flexo plate four kinds.
① single-sided Flexible plate is the lowest cost when the electrical performance requirements of the printed circuit board. Single-sided flexible plate should be used when wiring. It has a layer of chemically etched conductive graphics, on the flexible insulating substrate surface of the conductive graphic layer for the rolling copper foil. Insulating substrates can be polyimide, polyethylene terephthalate, Flex PCB aryl amide fiber ester and polyvinyl chloride.
② double-sided Flexible plate is on the two sides of the insulating base film each has a layer of etched conductive graphics. The metal hole will form a conductive pathway to the two sides of the insulating material to meet the design and use function of the flex. Flex PCB And the cover film can protect the single, double-sided wire and indicate the position of the component.
③ Multilayer Flexible plate is 3 or more layers of single-sided or double-sided flexible PCB laminated together, through the drilling postman L, electroplating to form a metal hole, the formation of conductive pathways between different layers. In this way, no complicated welding process is required. Multilayer circuits have great functional differences in higher reliability, better thermal conductivity and more convenient assembly performance. Flex PCB In the design of the layout, should take into account the size of the assembly, the number of layers and the impact of flexibility.
④ traditional rigid flexible plate?? is composed of rigid and flexible substrates with selective strata pressure. The structure is tight, and the conductive connection is formed by metallization postman L. If a printed destroyer, the opposite side have components, rigid flexible plate is a good choice. Flex PCB But if all the components are on one side, use a double-sided flex plate and laminate on the back with a layer of FR4 reinforcing material that will be more economical.
⑤ hybrid structure of flexible PCB is a multilayer board, conductive layer by different metal composition. A 8-layer board uses FR-4 as the inner layer of media, using polyimide as the outer media, extending the lead from three different directions of the motherboard, each lead made of different metals. Kang Cu alloy, copper and gold respectively as separate lead. This hybrid structure is the only feasible solution to the relationship between the conversion of electrical signals and the heat transfer and the severe low temperature of electrical properties.
It can be evaluated by the convenience degree and the total cost of the internal-connected design to achieve the best performance price ratio.
Economy of flexible PCB
If the circuit design is relatively simple, the total volume is small, and the space is suitable, the traditional interconnect way is much cheaper. Flexible PCB is a good design choice if the circuit is complex, processing many signals or having special electrical or mechanical properties. Flex PCB The flexible assembly method is the most economical when the applied size and performance exceed the capacity of the rigid circuit. On a thin film can be made into the inner with 5mil through hole 12mil pad and 3mil line and spacing flexible circuit board. Therefore, it is more reliable to directly mount the chip on the film. Because it does not contain the potential to be the source of ion-drilling flame retardants. These films may be protective and cured at higher temperatures, resulting in higher glass temperatures. Flexible materials are less costly than rigid materials because they are exempt from plug-ins.
High-cost raw materials are the main reason for the high price of flexible PCB. Raw Material price difference is big, the lowest cost of polyester flexible circuit board used raw materials cost is rigid circuit of raw materials used 1. 5 times times; High Performance Polyimide flexible PCB is up to 4 times times or higher. Flex PCB At the same time, the flexibility of the material makes it difficult to automate processing in the manufacturing process, resulting in a decline in production; defects are easily found in the final assembly process, including the stripping of flexible attachments and line breaks. Such situations are more likely to occur when the design is unsuitable for application. Under the high stress caused by bending or forming, it is often necessary to select reinforcement material or reinforcing material. Despite the high cost of raw materials, trouble-making, but folding, bending and multi-layer board function, will reduce the overall size of the assembly, the material used to reduce the total cost of assembly.
Flexible PCB industry is in a small but rapid development. Polymer thick film is an efficient and low-cost production process. The process is on the cheap flexible substrate, selectively screen printing conductive polymer inks. Its representative flexible base material is pet. The polymer thick film method conductor includes a silk-screen metal filler or a toner filler. The polymer thick film method itself is very clean, Flex PCB uses the lead-free SMT adhesive, does not have to etch. Because of its use of additive process and low cost of substrate, the polymer thick film method circuit is 1/10 of the price of the copper polyimide film circuit and the price of the rigid circuit board is 1/2~1/3. The polymer thick film method is especially suitable for the control panel of the equipment. In mobile phones and other portable products, the polymer thick film method is suitable to convert the components, switches and lighting devices on the printed circuit board into a polymer thick film method circuit. Both cost savings and energy consumption.
Generally speaking, flexible PCB is indeed more expensive and expensive than rigid circuit. Flexible plates in manufacturing, in many cases have to face the fact that many of the parameters beyond the tolerance range. The difficulty in making flexible PCB is the flexibility of the material.