There is a bright future ahead for flexible electronics. If you've not yet heard of this, the other term for this technology is flex circuits. It's not a new technology but it is an innovation that has recently been modernized and there is a multitude of applications for its use. To familiarize you with flexible electronics, here is everything that you need to know about it and why we believe that the outlook is good.
What is flexible electronics?
Flexible electronics, aka flex circuits, is an innovation in electronics technology that involves the use of flexible plastic substrates as a base structure to assemble electronic circuits through the mounting of electronic devices on the plastic substrates. A special type of conductive polyester film is most commonly used in this process. This is one method and another is to screen print silver circuits on polyester material to create flex circuits. There is a manufacturing process that implements the use of circuit board forms to form the basic shape of the flexible boards involving etching techniques to achieve the thinnest possible substrate to make them flexible with a good bending radius. Flexible silicon is one medium that is used by some manufacturers.
Materials used in flex circuits
The rigid-flex boards we referred to may range between two to several more layers in their construction. Polymer thick film flex circuits ate those which have the conductors printed directly into a base of a polymer film. These type generally consist of single conductor layered structures, however, those which consist of multiple layers are made with layers of insulation between those which are printed with conductors. Some are printed on one side and others are printed on both sides. PTF circuits are a lower cost alternative for several different applications requiring low power at higher voltages, such as keyboards and other similar applications.
The elements of a flex circuit include the base material, bonding adhesive, and metal foil. When discussing the base material, this refers to the foundation for the laminate which is usually a flexible polymer film. This material offers the ideal characteristics for use in flexible electronics while offering a broad spectrum of possible thicknesses to accommodate a range of electronics applications. The types of film which are used as a base material include PET, which is polyester, PI or polyimide, PEN or polyethylene naphthalate, PEI or polyetherimide, a variety of FEPs or fluoropolymers or copolymers. Each manufacturer has their own preferences when it comes to the blending of materials to achieve the desired outcome for the finished product, but all possess advantageous thermal, chemical, mechanical and electrical properties.
The bonding adhesive is the medium which is used to produce the laminate for the flex circuit layers. Specific adhesives are used for this step in the process, which work optimally with the base material to ensure a good bond which provides durability over time. There are a variety of thicknesses bonding adhesive, as in the base materials and the thickness depends upon the function of the application and the other types of materials used. It does get a bit technical, but this is an overview of the process.
The third important material used in the creation of flexible circuits is a metal foil. This is an important element as it is the conductive material that is essential for the proper functioning of the Flex circuit. It is the metal foil material that is used to create the circuit path through the etching process. There are several different types of metal foils used, depending on the type of flex circuit to be created. The most popular choice is copper because of its cost efficiency and its ability to perform the necessary function. Again, there are eight types of copper foil which are used in the creation of flex circuits.
The history of flexible electronics
Flexible electronics have been around for a long time. The earliest known use of this technology occurred in 1903 when Albert Hansen used a paraffin coated paper combined with flat metal conductors to create a more primitive form of the technology. Roger W. Curtis and Cledo Brunetti published a work called "Printed Circuit Techniques" in 1947, which was printed in the November 1947 issue of the National Bureau of Standards Circular 468. This kicked off an interest in flex circuit technology. During this era, there were writings from the lab of Thomas Edison with similar notations using graphite powder, linen paper, and cellulose gum to create flexible circuits, but these ideas were not fully realized in a form that was used on any known scale, still, the idea was there. It was Royden Sanders who made progress in the more modern form which involved the printing and etching of flat conductors on flexible materials which would replace the archaic wire harnesses with this new innovation and he managed to secure a patent for his innovation. Since this time printed wiring became the preferred method for wiring electronics and it's becoming more commonplace with the advancement of time.
Academic studies focused on flexible electronics technology
According to authors K. Jain ; M. Klosner ; M. Zemel ; S. Raghunandan, there are a number of benefits associated with the use of flexible electronics. This is a technology that is becoming used more frequently because of the vast number of applications which are enhanced by its use. The benefits of flex circuits are that they are light in weight and they maintain a low profile. There are also disadvantages associated with their use, such as the challenges that are created through the use of lithographic pattering on some of the flexible substrates which are currently in use.
Ongoing research into flex circuits
Although the technology is certainly not new, it is evolving. As with most types of technology, in recent decades huge strides have been made in creating new and better types of flexible electronics for use in the newer applications that are being developed. A variety of publications have recently surfaced delving into new concepts and materials with a broad spectrum of applications and potential applications. In the medical field, research is being conducted on the use of nano green based electrodes for the development of ubiquitous electrocardiogram monitoring. Another area focuses upon multi-functional sensors in electronic skin through the use of Amorphous FeZr metal. Other works concentrate on the use of polymeric foams for the creation of low-pressure capacitive sensors which are highly sensitive yet flexible, the use of transparent nanocellulose paper in the creation of perovskite solar cells, the development of an inorganic layered hybrid film for the creation of transparent electrodes, contact patterning through the use of laser printing to create flex circuits on paper, electromagnetic interference shielding, vapor dealloying with metal nanomesh electrodes and the list goes on.
The biggest disadvantage of flexible electronics is found in the cost of manufacturing. It is believed that this issue will soon be a thing of the past, however. Since the potential is so great within this industry, a lot of research has gone into not only the development of the technology but also into methods that make it more cost effective as well as earth friendly. Another disadvantage is that some of the methods for creating flex circuits are not as effective when it comes to long term performance. The overall goal is to create a medium that will not only maintain extreme flexibility but it will also improve in enhanced performance and durability.
According to the BAO Research website, advances have been made in the field of flexible electronics which contribute to higher performance and a big boost for the manufacturers. We learned that flexible electronics are being made with carbon-based, or organic transistors which produce low-cost sensors in the form of electronic paper. Its always good news for the planet and its inhabitants when a more natural approach is taken and Stanford, as well as UCLA researchers, are discovering methods for manufacturing flexible electronics which are high performance as well as low cost and earth-friendly. They've found a way to use organic single crystals to create larger patterns with some impressive results for the fast carriage of electrical currents. A former drawback to this organic process was the amount of time and expense that was involved in the manufacture because prior to the creation of a stamping process, the crystals had to be laboriously arranged. Through a unique stamping system that utilizes organic crystals and a vapor condensation process, they are able to manufacture them with more speed and efficiency, according to the reports issued, and testing has shown that the products hold up well even under repeated flexing and bending. Although there is a lot more work to be done before this technology has reached the point of being useful in manufacturing, it's a sign that real progress is being made to making the manufacture of flex circuits highly cost-efficient while reducing the carbon footprint.
Advantages of flexible electronics
The benefits of flexible electronics are immense. According to botfactory, this technology has the potential to "transform with the way we make and use electronics". We're all aware that the public is consistent in their demands for goods that are smaller, lighter and more responsive. Electronics manufacturers have been fast to respond to the demands of the public with some fairly impressive advances in their technology by making versions of the PC in smaller laptop and tablet sizes with amazing capabilities. For some industries, their products must become increasingly lighter in weight, faster and more dependable because of the intense competition in the market today. This is an area in which flexible electronics holds the key to giving customers what they want.
Applications for the use of flex circuits
Flexible electronics are being used in a broad range of applications. These ultra-thin circuits can be shaped and molded into patterns that provide exceptional pathways for the electrical currents that power both large and small electronic devices. The technology is widely used in computer devices including personal computers, laptops, tablets, as well as within the mobile telecommunications industry for smartphones and other devices such as gaming consoles of all types. Flex circuits make it possible for manufacturers to do away with the cumbersome and heavy wiring harnesses in many instances, to create a lighter and smaller device, which is in growing demand by a finicky world of consumers. It is also used in medical devices, such as EKG monitors, as well as in wearable technology which is becoming increasingly popular. Flex circuits are found in almost all devices where it is required that the weight is as light as possible.
There is a bright future ahead for flexible electronics. It is a technology that has been in the process of development and evolution for more than a hundred years. Great advances have been made in making the manufacturing process more cost efficient and there are currently ongoing studies researching better methods of production as well as for enhancing the performance and durability of stamped, printed and engraved circuits. New materials are being tested along with improved production methods which are less time and labor intensive. Some researchers are even investigating the use of organic materials, such as those who are currently working on crystal materials in the labs at Stanford University and UCLA. We've already come a long way since the technology was first developed in 1903, but we still have a long ways to go to perfect the process and the finished products which go into vital components that power the electronics we have come to depend on in our daily lives, both at work and at home. The most recent advances have yielded some exciting initial results and we fully expect to hear more about the ongoing research.
Written by Bill Vix
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