Rigid-Flex Circuits

The identifying characteristic of a rigid-flex circuit is the presence of one or more sections of the circuit in the form of rigid construction, while the rest of the circuitry is of the flexible type. Conductors are present on both the rigid and the flex parts. Multi-layer rigid-flex boards will have plated through holes extending between the rigid and flexible sections and electrically connecting multiple conductor layers.

Although more expensive than alternative flex designs, rigid-flex circuits are ideal for applications requiring placing the board in three-dimensional space and components are often mounted on both sides of the rigid section. Defined by IPC 6013 as a Type 4 circuit, the rigid-flex circuit construction is different from a flexible circuit with a rigid stiffener attached. Being partly rigid and partly flexible, rigid-flex circuits combine the best of both types of circuits, leading to several advantages and benefits to the user.

Advantages and Properties of Rigid-Flex

Several small to large industrial/commercial/domestic electronic systems now regularly use rigid-flex circuits, because of specific advantages such as:

• Flexibility to manufacture the board to fit into the device:Most modern electronic devices are compact, lightweight, and often flexible. It is easy to design a rigid-flex circuit to fit into the device, as against modifying the design of the device to fit the specifications of the board.
• Flexibility to design the board to fit into confined spaces:With electronic design tending towards smaller dimensions, space inside the device is always at a premium. As rigid-flex circuits can easily bend and fold, the design can fit perfectly into small spaces, contributing largely towards miniaturization of products.
• Reduction in overall package size:As rigid-flex circuits can be made lightweight and compact by design, this reduces the overall size of the product package.
• Increase in integrity and reliability:By design, rigid-flex circuits can avoid using solder joints, connector, or contact crimps, leading to better integrity and reliability in the product.
• Reduction in circuit failure:As rigid-flex circuits integrate both rigid and flexible circuitry, there are fewer number of interconnects, leading to substantial reduction in failures.
• Ability to withstand temperature extremes:The excellent thermal stability of polyimide used in manufacturing rigid-flex circuits provides the ability to withstand temperature ranges beyond the working range of generic PCB materials.
• Reduction of manufacturing and material procurement costs:Rigid-flex circuits require fewer materials for their assembly. For instance, rigid-flex circuits can replace wire-harnesses consisting of wires, connectors, and contact crimps, therefore reducing the overall cost of the assembly of the PCB.
• Ability to resist radiation and UV exposures, oils, and harsh chemicals:The materials used for manufacturing rigid-flex circuit can withstand very harsh environmental conditions and substances.
• Ability to accommodate SMD’s easily on both sides:By design, only the rigid part of the circuit can have SMDs mounted on both sides. However, it is not advisable to mount components on parts of the circuit that are likely to flex and bend during operation.
• Possibility of designing with varied material options and layouts:Depending on application requirement, designers can select the substrate material for rigid-flex circuits as polyimide or polyester (PET), conductor as rolled copper or electro-deposited and adhesives as polyimide, polyester, acrylic, or epoxies.
• Ability to withstand aggressive industrial conditions such as shock and vibration:With careful design, rigid-flex circuits can have a long working life even under adverse industrial conditions.

Conclusion

To discuss whether utilising a rigid-flex PCB is suitable for your unique design and specifications, please don’t hesitate to contact the team at PCB Global as we have combined experience of more than 30 years in the PCB manufacturing industry and will be able to assist you with any areas of PCB design and fabrication that you may require advice or recommendations. Please email you design file to sales@pcbglobal.com           for a rapid and competitive quote.