Flexible electronics , also known as flex flexuits, is a technology for assembling electronic circuits by installing electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester films. In addition, the flex circuit can screen silver circuits printed on polyester. Flexible electronic assemblies can be manufactured using identical components used for rigid printed circuit boards, allowing the board to adapt to the desired shape, or flexing during its use. An alternative approach to flexible electronics suggests various etching techniques to attenuate the traditional silicon substrate to several tens of micrometers for reasonable flexibility, referred to as flexible silicon (5 mm bending radius).
Video Flexible electronics
Manufacturing
Flexible printed circuits (FPC) are made with photolithographic technology. An alternative way to make flexible foil circuits or flexible flat cables (FFCs) is to laminate very thin copper strips (0.07 mm) between two PET layers. This PET layer, usually 0.05 mm thick, is coated with a thermosetting adhesive, and will be activated during the lamination process. FPC and FFC have several advantages in many applications:
- A tightly assembled electronic package, where electrical connections are required in 3 axes, such as cameras (static applications).
- Electrical connections where assembly should be flexed during normal use, such as folding phones (dynamic applications).
- The electrical connections between sub-assemblies to replace wire harnesses, which are heavier and larger, such as in cars, rockets, and satellites.
- Electrical connections where board thickness or space constraints are the driving factors.
Advantages of FPC
- The potential to replace some rigid boards or connectors
- One-sided circuits are ideal for high dynamic or flexible applications
- FPC Stacked in various configurations
Disadvantages of FPC
- Increased cost through rigid PCB
- Increased risk of damage when handling or using
- The more difficult assembly process
- Repair and rework is difficult or impossible
- Generally a worse use of a panel results in increased cost
Maps Flexible electronics
Apps
Flex circuits are often used as connectors in a variety of applications where flexibility, space savings, or production constraints limit the ease of service of rigid circuit boards or hand wires. The general application of flex circuits is on the computer keyboard; most keyboards use flex circuits for matrix switches.
In LCD fabrication, glass is used as a substrate. If a thin flexible plastic or metal foil is used as a substrate instead, the entire system can be flexible, as the film deposited on a substrate is usually very thin, on the order of several micrometers.
Organic light-emitting diodes (OLEDs) are typically used in place of backlights for flexible display, making the display of organic light-emitting diodes flexible.
Most flexible circuits are passive cable structures used to connect electronic components such as integrated circuits, resistors, capacitors and the like, but some are only used to make interconnections between other electronic assemblies either directly or through connectors.
In the automotive field, flexible circuits are used in instrument panels, controls under the hood, circuits to be hidden in the main parts of the cabin, and in ABS systems. In flexible circuits the computer peripherals are used on the moving print head printers, and to connect signals to the moving arm that carry the read/write heads of the disk drive. Consumer electronics devices make use of flexible circuits in cameras, personal entertainment devices, calculators, or sports monitors.
Flexible circuits are found in industrial and medical devices where many interconnects are required in a compact package. Mobile phones are another widespread example of flexible circuits.
Flexible solar cells have been developed to turn on the satellites. These cells are lightweight, rollable to launch, and easily propagated, making them suitable for applications. They can also be stitched into backpacks or outerwear.
History
Patents issued at the turn of the 20th century show that early researchers envisioned ways of making flat conductors flanked by layers of insulating materials to electrical circuit layouts to serve in early telephone switching applications. One of the earliest descriptions of what can be called the flex circuit excavated by Dr. Ken Gilleo and disclosed in the British patent by Albert Hansen in 1903 in which Hansen describes a construction consisting of a flat metal conductor on a paraffin coated paper. The laboratory books of Thomas Edison of the same period also show that he thought to coat the patterns of cellulose sap applied to linen paper with graphite powder to create what is clearly a flexible circuit, although there is no evidence that he was reduced to practice.
In the 1947 publication, "Printed Circuit Techniques" by Cledo Brunetti and Roger W. Curtis, a brief discussion of the manufacture of circuits on flexible insulation materials (eg paper) suggests that the idea already existed and in the 1950s inventors of Sanders Associates. (Nashua, NH) Victor Dahlgren and founder Royden Sanders made significant steps to develop and patent processes for printing and etching flat conductors on flexible base materials to replace wire harness. An advertisement from 1950 placed by Photocircuits Corporation in New York shows their active interest in flexible circuits as well.
Today, flexible circuits which are also well known in various parts of the world as flexible printing cable, flex print, flexi circuit, are widely used. The big credit is due to the efforts of Japanese electronic packaging engineers who have found countless new ways to use flexible circuit technology. Over the last decade, flexible circuits remain one of the fastest growing segments of the interconnect product market. The newer variations in flexible circuit technology are the so-called "flexible electronics" that generally involve the integration of active and passive functions in processing.
Flexible circuit structure
There are some basic construction flexible circuits but there are significant variations between different types in terms of their construction. The following is a review of the most common types of flexible circuit circuits
One-sided flexible circuit
Single-sided flexible circuits have a single conductor layer made of metal or conductive (metal-filled) polymers on flexible dielectric films. The component termination feature can only be accessed from one side. Holes can be formed in the base film to allow the passing lead component to interconnect, usually by soldering. Single-sided flexible circuits can be made with or without a protective layer such as a cover or cover, but the use of a protective film over the circuit is the most common practice. The development of surface-mounted devices in intermittent conductive films has enabled the production of transparent LED films, used in LED Glass but also in flexible automotive lighting compositions.
Double access or back flex circuit
Flex double access, also known as flex barbelakang, is a flexible circuit that has a single conductor layer but is processed thus allowing access to the selected feature of the conductor pattern from both sides. While this type of suite has certain benefits, special processing requirements for accessing features limit their use.
Fluid flexible circuit
The sculptured flexible circuit is a new part of the normal flexible circuit structure. The manufacturing process involves a special flexible multi-step flexible binding method that produces flexible circuits that have a finished copper conductor in which the thickness of the conductor differs in various places along its length. (Ie, thin conductors in flexible and thick areas at the point of interconnection.).
Two-sided flexible circuits
The two-sided flexible circuit is a flexible circuit that has two layers of conductors. These flexible circuits can be fabricated with or without plated through holes, although the variation of the plated holes through is much more common. When constructed without a hole through the hole and the connection feature is accessed from one side only, the circuit is defined as "Type V (5)" according to military specifications. This is not a common practice but it is an option. Because of the coated hole, the termination for electronic components is provided for both sides of the circuit, allowing the components to be placed on both sides. Depending on the design requirements, the flex circuit back and forth can be made with a protective cover on either one, second or none side of the complete circuit but most often produced with a protective coating on both sides. One of the main advantages of this type of substrate is that it allows crossover connections to be made very easy. Many single-sided circuits are built on a two-sided substrate just because they have one of two crossover connections. An example of this use is the circuit that connects the mousepad to the laptop's motherboard. All connections on the circuit lie only on one side of the substrate, except for very small crossover connections that use the second side of the substrate.
Multilayer flex circuits
The Flex circuit has three or more layers of conductors known as multilayer flex circuits. Generally these layers are interconnected by hollowing through the holes, although this is not a definition requirement because it is possible to provide openings to access lower circuit level features. The layers of multilayer bending circuit may or may not be continuously coated along the construction with clear exception of areas occupied by gilded holes. The practice of disconnected laminate is common in cases where maximum flexibility is required. This is done by leaving an unbound area where flexing or bending will occur.
Rigid-flex circuit
The rigid-rigid circuit is a hybrid construction flex circuit that consists of a rigid and flexible substrate that is laminated together into a single structure. Rigid circuits should not be confused with a rigid bending construction, which is simply a flexible circuit in which the stiffener is mounted to support the weight of the electronic components locally. Rigid or rigid flex circuits can have one or more layers of conductors. So while the two terms may sound similar, they represent a very different product.
Rigid bending layers are also electrically interconnected in a perforated way through a hole. Over the years, the rigid-flex circuit has enjoyed tremendous popularity among military product designers, but this technology has found increased use in commercial products. Although often considered a special product for low volume applications due to the challenge, an impressive effort to use this technology was made by Compaq computers in the production of boards for laptop computers in the 1990s. While PCBA's main stiff-flex PC flex does not flex while in use, the next design by Compaq uses a rigid-rigid circuit for a hinged display cable, passing 10s of 1000 indentations during testing. In 2013, the use of rigid-rigid circuits in consumer laptop computers is now common.
Rigid-flexible boards are usually multilayer structures; However, two metal coating construction is sometimes used.
Thick band of polymer film
Flexible polymer film circuitry (PTF) is a true printed circuit in a conductor that is actually printed on a polymer base film. They are usually single layer conductor structures, but two or more metal layers can be printed sequentially with an insulating layer printed between the printed conductor layers, or on both sides. While the conductivity is lower conductor and thus unsuitable for all applications, the PTF circuit has successfully served in a variety of low power applications at slightly higher voltages. Keyboards are a common application; however, there are a variety of potential applications for a cost-effective approach to the manufacture of flex circuits.
Flexible circuit materials
Every element of the flex circuit construction must be able to consistently meet the demands placed on it for the life of the product. In addition, the material must work reliably along with other elements of flexible circuit construction to ensure ease of manufacture and reliability. The following is a brief description of the basic elements of flex circuit construction and function.
Basic material
The base material is a flexible polymer film that provides the foundation for lamination. Under normal circumstances, the base material flex circuit provides most of the physical and electrical properties of the primary of the flexible circuit. In the case of circuitless construction of circuits, the base material provides all the characteristic properties. While very wide thickness is possible, most flexible films are provided in a narrow range with relatively thin dimensions from 12 Âμm to 125 Âμm (1/2 mile to 5 mils) but thinner and thicker materials are possible. Thinner materials are of course more flexible and for most materials, the stiffness increases in proportion to the thickness cubes. So for example, means that if the thickness is doubled, the material becomes eight times stiffer and will only deflect 1/8 as much under the same load. There are a number of different materials used as base films including: polyester (PET), polyimide (PI), polyethylene naphthalate (PEN), polyetherimide (PEI), along with various fluropolymers (FEP) and copolymers. Polymide films are the most prevalent because of their combination of favorable electrical, mechanical, chemical, and thermal properties.
Bonding adhesives
Adhesives are used as a binder to make laminates. When it comes to temperature resistance, adhesives are usually a laminate performance limiting element especially when the polymide is the base material. Due to previous difficulties associated with polymide adhesives, many current polymide flex circuits use adhesive systems from different polymer families. But some newer thermoplastic polymide adhesives make important roads. Like the base film, the adhesive has a different thickness. The selection of thickness is usually a function of the application. For example, different adhesive thicknesses are commonly used in the manufacture of cover layers to meet the different filling requirements of copper foil thickness that may be encountered.
Metal foil
Metal sheets are most often used as flexible conductive laminate elements. Metal foil is the material of a circuitry that is usually engraved. A wide variety of metal foils with various thicknesses are available from which to select and make flex circuits, but copper foils, serving most of all flexible circuit applications. The price balance and excellent electrical and electrical performance attributes of Copper make it an excellent choice. There are actually many types of copper foils. IPC identifies eight types of copper foils for printed circuits divided into two broader categories, electrodeposition and forgings, each having four sub-types.) Consequently, there are a number of copper foil types available for flex circuit applications to serve the end product range different. With most copper foils, a thin surface treatment is usually applied to one side of the foil to increase its adherence to the base film. Copper foil has two basic types: wrought (rolled) and electrodeposition and their properties are very different. Rolled and annealed foils are the most common choice, but the gilded thin films are becoming increasingly popular.
In some non-standard cases, circuit manufacturers may be invited to make special laminates using certain alternative metal foils, such as special copper alloys or other metal foils under construction. This is done by coating the foil onto the base film with or without the adhesive depending on the nature and nature of the base film.
Flexible system industry standards and specifications
Specifications are developed to provide a common understanding of how a product should look and how it should perform. Standards are developed directly by manufacturers associations such as Association Connecting Electronics Industries (IPC) and by users of flexible circuits.
See also
References
Further reading
-
Wong, William S.; Salleo, Alberto (2009). "Flexible electronics (Materials and Applications)". Electronic Materials: Science . 11 . doi: 10.1007/978-0-387-74363-9. ISSN 1386-3290. - Coombs, Clyde (2007). Printed Circuits Handbook (6th ed.). New York: McGraw-Hill Professional. ISBN: 9780071467346.
- Fjelstad, Joseph (2007). Flexible Circuit Technology, Third Edition (PDF) (3rd ed.). Seaside, OR: BR Publishing, Inc. ISBNÃ, 978-0-9796189-0-1.
- Gilleo, Ken (1998). Flexible Circuit Handbook (ed 1992). New York: Springer. ISBN: 9780442001681.
- Stearns, Thomas (1995). Flexible Printed Circuitry (1st ed.). New York: McGraw-Hill Professional. ISBN: 9780070610323.
- Gurley, Steve (1984). Flexible Circuit . New York: CRC Press. ISBN: 9780824772154.
External links
- Flexible OLED
Source of the article : Wikipedia
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