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Posted on 24/04/2015

One very important aspect of recent technological innovations involves the introduction of Rigid Flex Printed Circuit Boards in various high technology applications. Rigid Flex PCB’s are Printed Circuit Boards that are composed of various rigid areas along with various flexible areas. The rigid areas provide durability of the board while the flexible areas provide adaptability to the application of the board. Because of the PCB’s semi-flexible nature, it is commonly used in various military and medical electrical equipment.

Rigid flex PCB’s are made out of a combination of different materials, compared to standard non-flex PCB’s. The rigid areas are comprised of FR4 material, while the flexible areas are made from PI or PET. The connection joining the rigid to the flex is made up of epoxy or resin that allows for flexible and adaptable movements. Advantages of rigid flex PCB’s go beyond its adaptable shape, it is also highly resistant to temperature, resistant to static interference and is chemically stable.

The flexible boards are known as passive wiring structures, which are used to interconnect electronic components like integrated circuits, resistors and capacitors. In the consumer electronics industry, flexible circuits are used in cameras, personal entertainment devices, calculators and exercise monitors.

There are a large number of types of flexible circuits used in many various electronic devices. Some of which include; single-sided flex circuits, double access or back bared flex circuits, sculptured flex circuits, double sided flex circuits, multilayer flex circuits, polymer thick film flex circuits and not to forget, the most versatile to use, rigid flex circuits. Rigid flex boards allow integrated interconnection between several rigid structures. This technology allows the reduction in the required number of soldered joints as well as plug in connections along with the number of cables and wires required which reduces complication and increases quality and reliability.

The rigid flex printed circuit boards have many advantages over rigid PCB’s, but the main advantage is the maintenance of strong interconnections that are physically connected, rather then two separate entities that increase the strength of the connection whilst minimizing the space taken up by the board. The costs associated with producing the rigid flex boards are high as the processes in between each step of production, such as soldering and testing, are lengthy and must be done with great care.

There are two kinds of rigid flex PCB’s; one is a Semi-flex board and the other is a Multi-flex board. The semi-flex board is a lower cost option where the flexible areas consist of thin FR4 material, highly suited to a board created with a small number of bends. On the other hand, the multi-flex board consists of a polyimide film coating the entire surface of the board, flexible areas and rigid areas alike, suitable for applications that only require a small bend.

The multi-flex boards are known as hybrid designs as they are comprised of both rigid and flexible substrates by which the electrical interconnections between each layer are made through metal-plated vias, plated through-holes (which go through both rigid and flex areas) and/or micro-holes. Multi-flex boards allow both the rigid and flexible layers to be electrically connected by plated through holes. 

Multi-flex boards have a range of stack-up possibilities that provides the designer/engineer with a greater freedom when designing and selecting materials. There are two basic designs, which are commonly utilised in multi-flex boards; asymmetrical and symmetrical. The asymmetrical layer stack-up is the simplest form of any multi-flex board where the flexible material is placed on one side, and the rigid material is placed on the opposite side of the board; hence the term ‘asymmetrical’ as both sides are presented with different material. The stack-up on asymmetrical multi-flex boards is not limited to only single layers, as it can contain multi-layers. The amount or frequency of copper deposited when plated-through hole will determine the overall flexibility of the finished product. Designers/engineers must take this into consideration when designing a rigid flex board as well as considering the ‘conductivity’ when applying copper to the design. Multi-flex boards with asymmetrical layer stack-ups are relatively easy and cheap to produce.

When the flexible base is located between the two rigid layers, this is called a symmetrical layer stack-up in the multi-flex board. The flexible layer can be pre-fabricated according to the designer’s specifications. The conductive patterns of the middle flexible layers are selectively protected by the coverlays (which is a dry film solder mask) that must match the rigid exterior conductive patterns, forming a good registration of stack-up. Due to the symmetrical building and distribution of materials, the stack-up technique provides a higher mechanical and thermal stability as well as allowing a very high layer-count rigid flex board to be produced.

In respect to component assembly the rigid flex printed circuit boards can be handled and treated with the same production methods as per standard rigid printed circuit boards including being set up as a panelized production panels for assembly through SMT process ensuring efficient productivity.

PCB Global have supplied Rigid Flex Printed Circuit Boards up to 10 layers for many applications in Medical, Communications, Defense and Automotive just to name a few and has supplied customers with these applications all throughout Europe, USA, Australia and India.

For a fast quotation for all your Rigid Flex PCB’s requirements please email your design file to sales@pcbglobal.com, as these PCB’s are currently out of the spectrum of our online capabilities, however, quotations for standard rigid PCB’s up to 20 layers and Aluminum PCB’s up to 4 Layers please visit our web site www.pcbglobal.comfor an instant online quotation.

Our online capabilities include the standard 2 to 20 layer PCB’s, FR4 TG130/140, FR4 High TG=170, Thickness 0.8mm to 3.2 mm, Copper Finish 1oz - 2oz – 3oz & 4oz, Surface Finish - HASL Leaded and ROHS HAL - ENIG Immersion Gold with various solder mask and component legend colours. These qualities, among with our rapid rigid flex quotations, are unique to PCB Global as we have found no other online PCB manufacturer can offer these specifications or services in such a prompt lead time. PCB Global can offer a complete line of products and services from Standard, Fast and Express Quick-Turn Prototype manufacturing, low to medium volume pre-production to high volume mass production services, all at the click of a button!

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