The following two main characteristics of flexible circuit board:
2. The Economics of Flexible Circuits
If the circuit design is relatively simple, the total volume is not large, and the space is suitable, most of the traditional interconnection methods are much cheaper. If the circuit is complex, handles many signals or has special electrical or mechanical performance requirements, a flexible circuit is a better design choice. Flexible assembly is most economical when the size and performance of the application exceed the capabilities of rigid circuits. 12mil pads with 5mil through-holes and 3mil lines and spaces can be fabricated on a single film. Therefore, it is more reliable to mount the chip directly on the film. Because it does not contain flame retardants that may be a source of ionic contamination. These films may be protective and cure at higher temperatures, resulting in higher glass transition temperatures. The reason for the cost savings of flexible materials over rigid materials is the elimination of connectors.
The high cost of raw materials is the main reason for the high price of flexible circuits. The price of raw materials varies greatly, and the cost of raw materials used in the lowest cost polyester flexible circuit is 1.5 times that of the raw material used in rigid circuits. High-performance polyimide flexible circuits are as high as 4 times or more. At the same time, the flexibility of the material makes it difficult to automate processing during the manufacturing process, resulting in lower yields. Defects in the final assembly process, including peeling off flexible attachments, line breakage. This type of situation is more likely to happen 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. Although its raw material cost is high and it is troublesome to manufacture, the foldable, bendable and multi-layer paneling function will reduce the size of the overall assembly, and the material used will be reduced, so that the total assembly cost will be reduced.
The flexible circuit industry is in a small but rapid development. The polymer thick film method is an efficient and low-cost production process. The process selectively screen prints conductive polymer inks on inexpensive flexible substrates. Its representative flexible substrate is PET. Polymer thick film conductors include screen-printed metal fillers or carbon powder fillers. The polymer thick film method is inherently clean, uses lead-free SMT adhesives, and does not require etching. Because of its use of additive process and low cost of substrates, polymer thick film circuits are 1/10 of the price of copper polyimide film circuits; 1/2 to 1/3 of the price of rigid circuit boards. The polymer thick film method is especially suitable for the control panel of the device. On mobile phones and other portable products, the polymer thick film 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 and costly than rigid circuits. In the manufacture of flexible boards, many cases have to face the fact that many parameters are out of tolerance. The difficulty in making flexible circuits is the flexibility of the material.
3. Cost of Flexible Circuits
Despite the above-mentioned cost factors, the price of flexible assembly is falling, becoming similar to traditional rigid circuits. The main reasons for this are the introduction of newer materials, improved production processes and changes to the structure. The current structure makes the product more thermally stable, with very few material mismatches. Some newer materials allow for more precise lines due to thinner copper layers, making components lighter and more suitable for fitting into small spaces. In the past, copper foil was attached to adhesive-coated media using a rolling process. Today, copper foil can be produced directly on the media without the use of adhesive. These techniques can get several microns thick copper layer, get 3m. 1 precision lines with even narrower widths. The flexible circuit has flame retardant properties after some adhesives have been removed. This both speeds up the uL certification process and further reduces costs. Flexible circuit board solder masks and other surface coatings further reduce the cost of flexible assembly.
In the coming years, smaller, more complex and more expensive flex circuits will require newer methods of assembly and the addition of hybrid flex circuits. The challenge for the flexible circuit industry is to take advantage of its technology to keep pace with computing, telecommunication, consumer demand and dynamic markets. In addition, flexible circuits will play an important role in the lead-free movement.
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