Flexible Circuit Board
When conductive traces are bonded on a flexible substrate, the outline achieved due to this is defined as a flexible printed circuit board. Such kind of PCB offers an unmatched flexibility of packaging geometry without missing on the accuracy and repeatability that is typical of a printed circuit. A typical flexible PCB prototype results from the hybridization of normal circuit boards and round wire designed in a way to complement each other and produce a functional unit. It is an ideal substitute for wire and wire harness assemblies having added advantage of cost-effectiveness and better performance. Also, they are anytime more space-efficient and occupy the smaller footprint in the environments where these are installed. Thus, the flexible printed circuit board is ideal for space restricted environments.
Different types of Flexible Circuit Board Structures
The fundamental make-up of a flexible circuit board remains the same in all its types. The only difference lies in the conditions which the flexible PCB manufacturers apply while producing these. Here is a comparative description of various types of commonly used flexible printed circuit boards.
Photo by japaneseclass
Single-sided FPC Boards
Flexible circuits of single-sided type comprise of a single conducting layer made of a metal or a metal-bonded polymer stuck on a dielectric film which is flexible in nature. Components can be placed only on the one side of this board. Holes are created either by drilling or by using laser on the base film. The component leads are made to interconnect with the help of soldering, through the holes on the side where these are created. These types of flex PCB boards can be fabricated without applying any cover film, still in commercial use, the application of a protective covering one the circuits is highly recommended and is in common practice too. This board is made by using network printing. In this procedure, the resistive film is printed on bare copper, followed by etching and the solder mask is applied before punching the board to create holes for finished parts.
The common example of implementation of single-sided FPC board is found in automotive lighting fixtures that employ LED glass. The LED glass is made of LED films, that is an outcome of using surface mounted devices on the conductive films that are sputtered.
Double-Sided FPC Boards
By double-sided FPC boards, one means that the circuit board is composed of two conducting layers. The circuit of this type can be fabricated with or without plating through holes. But, for practical reasons, plated through hole style of board is more in demand and is common among FPC manufacturers. Those FPC boards that are constructed without plating through holes and related components are accessible from one side only and are popularly known as ‘Type 5’ FPC boards. This term is more common in military conditions where double-sided FPC Boards form an important component of various devices.
Speaking of certain cases specifically, the ends of electronic apparatus are left on both sides of the board, allowing the user to place apparatus on any side of his choice. However, this is not a generalized procedure and the maker may employ other ways of terminating the components on circuit boards.
Considering the design requirements, the maker can apply protective covering on one or both sides of the circuit board; he may also choose to leave the board exposed. In general practice, the protective covering, however, is applied on both sides of the flexible circuit board before putting it on sale. The double-sided FPC board is in high demand because its substrate provides flexible ground for preparing intersecting connections with added ease. Due to the availability of either of cross connections, the double-sided FPC can be used as substrate for building many single-sided circuits.
The flexible circuit boards comprising of three and additional layers of conducting material such as copper etc. are known as multi-layer flexible circuits or multi-layer flex circuits. While in other types, the interconnections are enabled by plating through holes, in multi-layer flexible circuits, openings are supplied to give access to features at lower levels. Some manufacturers may laminate the whole of the circuit, while others may leave the areas exposed for facilitating plating through-holes. Irregular lamination is done to add more flexibility and is preferred when added flexibility is sought after. The irregular lamination is achieved by leaving those areas unbounded where bending or flexing is to be done.
Common applications of Flexible Printed Circuit Boards
Flexible Printed Circuit Boards are commonly utilized in these devices and systems:
- Exercise monitors
- Personal entertainment devices
- Medical devices
- Cellular phones
- Flexible solar cells and others.
Since flexible PCBs offer ease of lodging them in space-restricted environments, most of the compact devices run electronically make use of these boards.
In addition to above, the FPCs are lodged on the moving print head of printers so that the signals can be coordinated to make arms move. These also help in moving the read/write heads of disk drives. This is one of the most common examples of usage of FPC one can find around.
Flexible printed circuit boards can be single layered, double-layered or multi-layered depending upon the level of complexity required to be achieved. These can be laminated or may be left exposed depending upon the design requirements. Most of the compact electronic devices of present times make use of FPC boards as these are of great use in space-restricted environments. Since compactness is a likable feature, flex PCBs are here to stay.