Rigid printed circuits boards (PCBs) are manufactured by bonding many layers of materials and creating copper layers for connectivity. The layers are rigid in nature.
Most applications use rigid PCBs and assemble components and connectors to this structure.
FLEXIBLE CIRCUIT BOARDS
Flexible circuits are available from 1 to many layers. With stiffeners added to certain areas to increase the rigidity. This is particularly important for strain relief, components or where connected to mechanical devices, such as connectors.
Flex circuits are used in consumer devices, automotive applications and others, where space and flexibility are important.
Other advantages include:
- Cost – specifically in high volume use
- Increased heat dissipation
- Faster assembly
Disadvantages to flex circuits include:
- Increased cost in initial design – not for low volume, specialised production
- Very difficult to repair a damaged circuit
- Prone to damage by inexperienced operators
RIGID-FLEX CIRCUIT BOARDS
Rigid flex circuits are created by combining a number of flex layers with a number of rigid boards internally or externally. Typical nomenclature is 2F6R – 2 layers of flex and 6 layers of rigid boards.
Rigid flex is used in aerospace, medical, military and many other applications. The reasons for choosing rigid flex can include:
- Reduced space needs
- Costs in larger volumes by eliminating expensive connectors
- Device weight loss due to connectors and less rigid layers
- Reduced connectors reduces the solder joints and can increase reliability
- Savings in assembly pricing.
- Simplified test conditions
This EDN article by David Read https://www.edn.com/design/pc-board/4429893/The-case-for-rigid-flex-PCB-technology explains in detail the cost advantages to Rigid Flex.
But there is a downside; many PCB design packages do not enable easy design of rigid flex. They don’t have the ability to enable the flexing and fitting aspects of the boards. Often, it is sensible to simulate the design in 3D and working with a mechanical designer. The design packages that support 3D can prove more useful in this case.
A few things to note:
- The flexible polymide shrinks once the bonded copper foil is etched away. This will need to be addressed at the design process.
- During assembly, the flex circuit will experience some stress due to bending, and this may cause fractures.