Flexible electronics
These PET layers, typically 0.05 mm thick, are coated with an adhesive which is thermosetting, and will be activated during the lamination process.
The growing markets related with flexible and/or portable electronics, such as for self-powered IoT systems, have driven the development of bendable thin-film photovoltaics (PV) in view of enhancing the energetic autonomy of such off-grid devices.
[3] It has been shown that this class of PV technologies is already capable of reaching high solar-to-electricity efficiencies, at the level of rigid wafer-based solar cells, particularly when integrated with effective light-trapping structures.
Such photonic schemes allow high broadband absorption in the thin PV absorber materials, despite their reduced thickness required for mechanical bendability.
[6] Printed electronics are in use or under consideration include wireless sensors in packaging, skin patches that communicate with the internet, and buildings that detect leaks to enable preventative maintenance.
[7] There is a particularly growing interest for flexible smart electronic systems, including photovoltaic, sensing and processing devices, driven by the desire to extend and integrate the latest advances in (opto-)electronic technologies into a broad range of low-cost (even disposable) consumer products of our everyday life, and as tools to bring together the digital and physical worlds.
[9][10][11][12] Another company, Rotimpres based in Spain, has successfully introduced applications on different markets as for instance; heaters for smart furniture or to prevent mist and capacitive switch for keyboards on white goods and industrial machines.
[13][14] Patents issued at the turn of the 20th century show interest in flat electrical conductors sandwiched between layers of insulating material.
One of the earliest descriptions of what could be called a flex circuit was unearthed by Dr Ken Gilleo[15] and disclosed in a 1903 English patent by Albert Hansen that described a construction consisting of flat metal conductors on paraffin coated paper.
Thomas Edison’s lab books from the period indicate that he was thinking to coat cellulose gum applied to linen paper with graphite powder to create what would have clearly been flexible circuits, though no evidence indicates that it was reduced to practice.
In the 1950s Dahlgren and Sanders made significant strides developing and patenting processes for printing and etching flat conductors on flexible base materials to replace wire harnesses.
Credit is due to the efforts of Japanese electronics packaging engineers who have found ways to employ flexible circuit technology.
Holes may be formed in the base film to allow component leads to pass through for interconnection, normally by soldering.
When constructed without plated through holes, connection features are accessed from one side only, and the circuit is defined as a "Type V (5)" according to military specifications.
Commonly the layers are interconnected by means of plated through holes, though this is not required because it is possible to provide openings to access lower circuit level features.
Rigid-flex circuits are a hybrid combining rigid and flexible substrates laminated into a single structure.
Each element of the flex circuit construction must be able to consistently meet the demands placed upon it for the life of the product.
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.
Polyimide films are most prevalent owing to their blend of advantageous electrical, mechanical, chemical and thermal properties.
When it comes to temperature resistance, the adhesive is typically the performance limiting element of a laminate especially when polyimide is the base material.
The IPC identifies eight different types of copper foil for printed circuits divided into two much broader categories, electrodeposited and wrought, each having four sub-types.)
[citation needed] Specifications are developed to provide a common ground of understanding of what a product should look like and how it should perform.
