How some electrical components look
Flexible electronics, also known as flex circuits, is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film. Additionally, flex circuits can be screen printed silver circuits on polyester.
Flexible electronic assemblies may be manufactured using identical components used for rigid printed circuit boards, allowing the board to conform to the desired shape, or to flex during its use.
These flexible printed circuits (FPC) are made with a photolithographic technology. An alternative way of making flexible foil circuits or flexible flat cables (FFCs) is laminating very thin (0.07 mm) copper strips in between two layers of PET.
These PET layers, typically 0.05 mm thick, are coated with an adhesive which is thermosetting and will be activated during the lamination process. FPCs and FFCs have several advantages in many applications:
Tightly assembled electronic packages, where electrical connections are required in 3 axes, such as cameras (static application).
Electrical connections where the assembly is required to flex during its normal use, such as folding cell phones (dynamic application).
Electrical connections between sub-assemblies to replace wire harnesses, which are heavier and bulkier, such as in cars, rockets, and satellites.
Electrical connections where board thickness or space constraints are driving factors.
Advantage of FPCs
Ease for manufacturing or assembly
Single-Sided circuits are ideal for dynamic or high-flex applications
Stacked FPCs in various configurations
Disadvantages of FPCs
Cost increase over rigid PCBs
Increased risk of damage during handling or use
More difficult assembly process
Repair and rework is difficult or impossible
Generally worse panel utilization resulting in increased cost
Flex circuits are often used as connectors in various applications where flexibility, space savings, or production constraints limit the serviceability of rigid circuit boards or hand wiring. A common application of flex circuits is in computer keyboards; most keyboards use flex circuits for the switch matrix.
In LCD fabrication, glass is used as a substrate. If thin flexible plastic or metal foil is used as the substrate instead, the entire system can be flexible, as the film deposited on top of the substrate is usually very thin, on the order of a few micrometers.
Organic light-emitting diodes (OLEDs) are normally used instead of a back-light for flexible displays, making a flexible organic light-emitting diode display.
Most flexible circuits are passive wiring structures that are used to interconnect electronic components such as integrated circuits, resistor, capacitors and the like, however, some are used only for making interconnections between other electronic assemblies either directly or by means of connectors.
In the automotive field, flexible circuits are used in instrument panels, under-hood controls, circuits to be concealed within the headliner of the cabin, and in ABS systems. In computer peripherals flexible circuits are used on the moving print head of printers, and to connect signals to the moving arm carrying the read/write heads of disk drives. Consumer electronics devices make use of flexible circuits in cameras, personal entertainment devices, calculators, or exercise monitors.
Flexible circuits are found in industrial and medical devices where many interconnections are required in a compact package. Cellular telephones are another widespread example of flexible circuits.
Flexible circuits technology has a surprisingly long history. Patents issued at the turn of the 20th century show clear evidence that early researchers were envisioning ways of making flat conductors sandwiched between layers of insulating material to layout electrical circuits to serve in early telephony switching applications.
One of the earliest descriptions of what could be called a flex circuit was unearthed by Dr. Ken Gilleo and disclosed in an English patent by Albert Hansen in 1903 where Hansen described a construction consisting of flat metal conductors on paraffin-coated paper. Thomas Edison lab books from the same period also indicate that he was thinking to coat patterns cellulose gum applied to linen paper with graphite powder to create what would have clearly been flexible circuits, though there is no evidence that it was reduced to practice.