Guide On Flexible Circuit Boards Design

Flexible Circuit

A flexible printed circuit can be defined as an outline of conductive traces bonded on a flexible substrate. Flexible circuit board provides an unlimited freedom of packaging geometry while retaining the accuracy density and repeatability of printed circuits. A characteristic flex circuit board comprises a hybrid of ordinary printed circuit boards and round wire, complementing each other. They are a kind of high dependability substitute for wire and wire harness assemblies that help save costs and at the equal time maintain the excellence of performance. We detail below the unique characteristics of our flex circuits (our Single and Double Sided Flex PCBs). The most convincing difference between flexible circuits is flexibility. Flexible circuits are regularly much thinner and are able to conform to the spacing limitations and environments into which they are installed.

What is a Flexible Circuit?

Flexible Circuit board is also known as a flex circuit, it is a knowledge of assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as a Polyimide. Flexible electronic assemblies might be manufactured using matching components used for rigid printed circuit boards, allowing the board to conform to a preferred shape, or to flex throughout its use. These flexible printed circuits (FPC) are ready with a Photolithographic technology.

Flexible Circuit Board Design

Appropriate to the flexible PCB technology, confident design and assembly considerations must be accounted for. Opportunely, the design rules for flex circuits are much related to the design rules for traditional PCBs. That is, the designer must pay concentration to certain design aspects

• Maintain minimum hole size
• The smallest trace widths
• Lowest space between traces and pads
• Least distances to design edges
• Flex circuit/board sketch tolerances
• Distance of copper geometries from flex circuit/board edges
• Copper and on the whole design thicknesses

Traditional PCBs and flex circuits split some, but not all, of the manufacturing procedure steps. For case, the flexible circuit board material (typically copper clad Polyimide) is chosen, drilled, plated, photo-imaged, implement and imprinted just like the conservative PCB process. The next step, also correlated for both PCBs and flex circuits, involves the panels being baked to remove any moisture from the wet processes. It is after this step where the conventional PCB and flex circuit processes starting to differ. Instead of going to the fuse mask station, as would occur with traditional PCBs, flex circuits go to the cover lay station.

A flex circuit board cover lay, also known as a cover film, is a lamination process used to summarize and protect any peripheral circuitry of the flex circuit. The cover lay serves the similar function as the solder mask does for conventional PCBs with the dissimilarity being the added component of flexibility. Naturally, the thickness of the cover lay is prepared of 1 mil thick Polyimide with a 1mil thick, attach adhesive, but other thicknesses are accessible to meet precise design necessities. The Polyimide and adhesive cover lay is laminated using force and heat. The heat allows for simple flow of the adhesive which is needed because it must fill-in any and all gaps among the traces and pads to stop the trapping of air between layers. To a flex circuit designer this means the cover lay openings for a characteristic 1 oz. The copper plan must be outsized by 10 mils, which is appreciably bigger than the typical huge of 2-3 mils used on conventional PCB solder masks.

There are two reasons for this bigger oversize. The first being the acceptance of the drill size(s) and locations; flex circuits characteristically need a looser acceptance than conventional PCBs because their materials have less dimensional stability. The second cause for bigger oversize is to account for the adhesive which squeezes out into the openings. The goal is to contain a design such that the adhesive flows out to the pad but never on top of the pad, which affects the range of the annular ring. Once the lamination procedure is finished any element and/or characteristic openings are made using a drilling, routing, or laser cutting. Etching cannot be used.

Flex area, an area of design to consider when designing a flex circuit, consists of both the place for where and how often the flexing occurs on the flex circuit. Flex circuits are frequently designed for two typical flex applications. The first is referred to as static, or flex-to-fit, which basically means the flex circuit is flexed to fit into the congregation and will flex less than 100 times in its lifetime. The second application, termed dynamic flex, involves the design to not only be flex-to-fit in the assembly but also flexing during normal operation of the application. A dynamic flex design must be more robust since flexing will occur on a regular basis. It needs to withstand tens of thousands, or millions, of flexes depending on the application. Either of these two flex applications need some forethought regarding the trace routing and pad placement in the flex area. For example, it is significant not to have any apparatus and/or a solder pads in the flex area besides of the design flex type (static or dynamic).

The solder joint will be the weakest part of the circuit and it will fail quickly because solder, whether it’s leaded or lead-free, is rigid and is not intended to bend, flex or twist. It is best to keep all solder points at least an 100 miles away from flex areas, though more is better if real estate allows for it. Regarding routing, traces should be routed through the flex areas perpendicularly. This approach takes advantage of the flexibility of the copper—rolled annealed copper has grain and, if run horizontally in the flex area, may split or break. Although copper is the most general material for traces, field metals are also obtainable for detailed applications such as corrosion resistance, spring properties, or where radio density is preferred. It’s best to path traces at a 90-degree position through the flex area followed by any needed direction changes to contain the final design.

You might develop CAD tools for both the design and the output of Gerber’s files as you would for any traditional PCB, and both the fabrication and congregation sketch certification is the same between the two design types. However, keep in intelligence that angles in flex designs are not chosen. Be convinced your software design tool is set consequently such that the corners are surrounding instead of angular throughout the layout stage of your flex circuit

Flexible Circuit Structures

There are a few fundamental constructions of flexible circuit boards, but there is an important variation between the different types of conditions in their production. Following is an evaluation of the most general types of flexible circuit board constructions.

Single-sided Flexible Circuits

Single-sided flexible circuits contain a single conductor layer prepared of either a metal or conductive (metal filled) polymer on a flexible dielectric film. Component execution features are available only from one side. Holes may be created (drilled or laser) in the base film to allow component leads to pass during for interconnection, usually by soldering. Single sided flex circuits are able to be fabricated with or without such protective coatings as cover layers or cover coat, nevertheless the use of a protective coating above circuits is the most common practice.

Single Sided Flex Circuit

The implement of surface mounted devices on sputtered conductive films have enabled the manufacture of apparent LED Films, which is used in LED Glass but moreover in flexible automotive lighting composites.

Double- Sided Flexible Circuits

Double-sided flex circuit boards are a flex circuits have two conductor layers. Thesis flex circuits can be fabricated with or without plated through holes, though the plated through hole variation is much more general. When construct without plated through the holes and association features are access from one side simply, the circuit is a defined as a “Type-5” according to the military condition.

Double Access Flexible Circuit Board

It is not a general practice, but it is an option, terminations for electronic apparatus are provided for on both sides of the circuit, thus allow the apparatus to be placed on each side. Depending up on design necessities, double-sided flex circuits can be fabricated with protecting cover layers in one, both or neither side of the finished circuit, but are mainly frequently formed with the protective layer on both sides. One major benefit of this type of substrate is that it allows intersect connections to be prepared very easily. Many single sided circuits are built on a double sided substrate immediately since they have one of two intersect connections.

Sculptured Flexible Circuits

Sculptured flex circuits are a novel separation of typical flexible circuit structures. The developed procedure involves a particular flex circuit multi-step etching method which yields a flexible circuit have finished copper conductors wherein the thickness of the conductor differs in several places along their length. (i.e. the conductors are thin in flexible areas and thick at interconnection points).

Sculptured Flexible Circuits

Multilayer Flexible Circuits

Flex circuits have three or additional layers of conductors are known as multilayer flex circuits. Normally the layers are interconnected by means of plated through holes, though this is not a condition of the definition for it is probable to supply openings to access lower circuit level features. The layers of the multilayer flex circuit may or may not be incessantly laminated mutually throughout the building with the noticeable exemption of the areas engaged by plating through-holes. The practice of irregular lamination is familiar with cases where utmost flexibility is compulsory. This is accomplished by leaving unbounded the areas wherever flexing or bending is to happen.

Multilayer Flexible Circuits

Rigid-Flex Circuits

Rigid-flex circuits are a hybrid manufacture flex circuit consisting of rigid and flexible substrates which are laminated mutually into a single structure. Rigid-flex circuits must not be confused with rigidized flex constructions are just flex circuits to which a stiffener is attached to maintain the weight of the electronic apparatus locally. A rigidized or stiffened flex circuit can contain one or extra conductor layers. Thus, while the two terms might sound comparable, they signify products that are reasonably dissimilar. The layers of a rigid flex are also usually electrically interconnected by means of plated through holes. Over the years, rigid-flex circuits include wonderful popularity amongst military product designer; though the technology has found improved use in commercial products.

Rigid-Flex Circuit Board

While frequently careful a specialty product for low volume applications as of the challenges, an extraordinary effort to use the technology was prepared by Compaq computer in the construction of the boards for a laptop computer in the 1990s.While the computer’s major rigid-flex PCBA did not flex through uses, succeeding designs by Compaq utilized rigid-flex circuits for the hinged exhibit cable, passing 10s of 1000s of flexures during testing. By 2013, the use of rigid-flex circuits in customer laptop computers are now familiar. Rigid-flex boards are in general multilayer structures; however, two metal layer constructions are occasionally used.

Applications of Flexible Circuits

Flexible Circuits are frequently used as connectors in different applications where flexibility, space savings, or construction constraints limit the service capability of rigid circuit boards or hand wiring. In LCD fabrication, glass is used as a substrate. If thin, flexible plastic or metal foil is used as the substrate instead, the whole system can be flexible, as the film deposit on top of the substrate is frequently very thin, on the order of a few micrometers. Organic light-emitting diodes (OLEDs) are usually used instead of a backlight for flexible displays, making a flexible organic light-emitting diode display.

The majority flexible circuits are passive wiring structures that are used to interconnect electronic components such as  resistor, capacitors, integrated circuits, and the like, though some are used simply for making interconnections between other electronic assemblies also directly or by means of connectors. In the automotive field, flexible circuits are used in apparatus panels, under-hood controls, circuits to be covered within the headliner of the cabin, and in ABS systems.

In computer peripherals flexible circuits are used on the moving print head of printers to connect the signals to move arms, moving the read/write heads of disk drives. Customer electronics devices build with a flexible circuits in cameras, individual entertainment devices, calculators, or exercise monitors. Flexible circuits are established in manufacturing and medical devices where various interconnections are necessary in a compacted package. Cellular telephones are another extensive example of flexible circuits. Flexible solar cells are used for powering satellites. These cells are lightweight, can be rolled up for launching and are simply deployable, create them a good competition for the application. They can also be a sewn into backpacks or outerwear.

Thus, this is all about flexible circuit boards, circuit board design, flexible structures. We hope that you have got a better understanding of this concept.Furthermore, any doubts regarding this concept or to implement any electrical and electronics projects, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what is the application of flexible board circuit?

Photo Credits:

• Single-sided Flexible Circuit powerdesignservices
• Double- Sided Flexible Circuit flexiblecircuit
• Sculptured flexible circuit saturnflex
• Multilayer flexible circuit sclpcbgroup
• Rigid-flex circuit bestfpc