Flexible circuits provide unlimited configuration opportunities that often results in very odd shapes and sizes. Circuit boards often are rectangular or may have some notches or curved outlines routered. Because of this nuance, steel rule dies and hard tool dies are probably used more often for flexible PCBs than for boards, at least for ultra-high-volume applications. Laser definition of the circuit outline is also a common flex circuit process.
Normally, flex PCBs are designed using polyamide as base material. PCB design process for double sided PCB is usually same but we have to take care for cross talks reduction, signal interference, copper thickness, and impedance requirements (for specific like RF design). Similar is the case with multi-layer PCB designs as they have challenges of cross-over, impedance matching, lamination problem, etc. Normally vias are manufactured as plated holes.
You can see Flex circuit applications in gaming systems, battery packs, cellphones, fuel pumps, calculators automobile and aviations and the list of applications are endless.
One of the more challenging parts of managing today’s electronic product development process is integrating the various players in a project. PCB designers often find themselves sandwiched in the middle between Industrial or Mechanical designers and Electrical designers. Each side presents different and conflicting requirements, and it often falls to the PCB designer to resolve these differences. The purpose of this article is to detail how to describe board mechanical information in a way that is easy and straightforward for a PCB designer to use, eliminates common sources of error, and facilitates checking.
Applications
Flexible PCBs constitute about 10–15% of all PCBs produce globally, so there are far more applications that use hardboards than flex. The biggest advantage for flex is that it can reduce the size, weight and amount of hardware used for many electronic packages. It is best described as an “electronic interconnect packaging solution.
In his disclosure, much described a multilayer circuit with rigid and flexible dielectrics and PTH interconnections. What’s most significant in this concept is that the conductor runs in the PCB area (rigid, component mounting) extend into the flex part, obliterating the interface between PCB and flex circuitry. The copper foil layers are “coextensive” throughout. Consequently, rigid flex circuitry eliminates almost half of the PTH barrels as well as the pins that are used to join flex circuitry to PCB, the associated solder joints and the PCB area that’s needed for the interface.
Flex Circuit Design & Manufacturing Materials
1. Liquid Photoimageable Solder Mask –
2. Double Coated Acrylic Foam Tapes & Transfer Tapes
3. Adhesive Transfer Tapes with
4. DuPont All-Polyimide Flexible Laminate
5. DuPont Pyralux
6. DuPont Pyralux
7. Cirlex Polyimides
8. Nippon Steel Chemical Co Flexible Copper Cladd Polyimide Laminate
9. Nippon Steel Chemical Co SPB Series Polyimide bonding adhesives
10. Nippon Steel Chemical Co SPC Series Polyimide Coverlay films
11. Kepro Circuit Systems Immersion Tin Plating Solutions
12. Rogers LPI
13. Kyocera Industrial ceramics
14. Panasonic FELIOS Adhesiveness’ Flexible Laminates
Rigid Flex
The first question to ask is whether the rigid-flex circuit board must bend and fold in daily use. If the answer is “yes,” select materials that provide the best product reliability and longevity. This type of board is called a “dynamic flex.” Of course, high-speed signal integrity cannot be ignored when designing a dynamic flex board, but PCB reliability should come first in this type of application.
The tradeoff here is that to control the impedance of a signal path and maintain good signal integrity, most designers route high-speed signals over solid copper ground planes. Solid, unbroken copper ground planes are not very flexible, however, and can impact the reliability of the PCB.
