What Are The Advantages Of Rigid Flex PCB

March 25, 2020 Cadence PCB Solutions

Rigid flexibility shown in a printed circuit board

 

It’s shocking to think that I could smoothly perform a full split in my heyday but now struggle to pick up a dropped pen from the floor. Age, or rather the lack of exercise, can rob you out of any signs of flexibility you had in your youth. It makes me wonder how electronics managed to be made so securely while being as rigid as they had always been. I think of the absolute tanks of television sets from the ‘90s, and how, half the time, hitting them actually helped get their signal back on track. 

The sight of me huffing and puffing over a pen is embarrassing, and I’ll give anything to reclaim some of the flexibility that I once possessed. Since turning back the time is impossible, I’m left to devote my attention to bringing the best out of a rigid flex PCB. You’ll want to know what can be done with any rigid flex PCB should you choose to utilize them in your hardware. Here we discuss the potential use-cases for rigid flex PCBs, and where they excel in any electronics designs.

What Is A Rigid-Flex PCB

As the name implies, a rigid flex PCB is a combination of both rigid and flexible substrates. One or more flexible circuits are used to connect subcircuits on rigid PCBs. Rigid flex PCBs are usually produced with flexible polyimide material on copper cladding substrate and connects to the rigid FR4 board

The flexible part of the rigid flex PCB usually features a multilayer built with padded through holes securing the interconnectivity between layers. Rigid flex PCB has grown from merely using the flexible substrate as a replacement for wire harnesses, to having actual subcircuits built on the flexible area itself. 

Advantages Of Rigid-Flex PCB

Designing a rigid flex PCB is considerably more challenging than conventional rigid PCB. However, there are good reasons why rigid flex is used in some designs, particularly one that involves fitting the board in tight spaces. 

Increase Reliability

Connectors serve their purpose when there’s a need to remove the wire harness from the PCB routinely. For a design that involves multiple interlinking subcircuits in an enclosure, adding connectors to the PCB only increases the risk of failure.

Implementing a rigid flex design removes the need for board-fto-board connectors. This also leads to lesser solder joints, which are sometimes prone to failure. 

 

Printing and assembling a printed circuit board

Point-to-point testing is easier with a rigid flex PCB.

 

Space Saving

Often, the designs that call for a rigid flex PCB is one where space is a luxury. For example, handheld thermal scanners can benefit from a rigid flex PCB design as there isn’t much space to fit in wire harnesses and high profile connectors. Instead, with the interconnecting circuit built-in on the flexible substrate, you’ll have more space to route the traces around. 

Reduce Cost

Rigid flex PCBs are generally cheaper than their rigid counterparts, as the former is harder to produce. However, using rigid flex PCBs may reduce the overall cost of the product. As wired interconnects are replaced by the conductive layers of flexible material, you’ll save on the cost of assembly, which in some cases, involves manual labor. 

As a rigid flex PCB is a complete circuit on its own, there isn’t a need for installing a wire harness in the enclosure it is mounted on. Such a wiring job takes up precious time and is an additional cost for each unit of the product.

Ease Of Testing

It is also easy to automate testing of a rigid flex PCB as all the subcircuits are already interconnected when the PCB is manufactured. The ability to eliminate connectivity issues before the components are assembled, further, prevent unnecessary wastage and expenses. 

Challenges Of Rigid-Flex PCB Design

There is a pressing demand for PCB designers skilled in rigid flex design, as products are undergoing a phase of miniaturization. Before you take on the challenge, it’s important to realize that designing a rigid flex PCB requires different skillsets.

Instead of taking a pure electrical approach, you’ll need to start envisioning the design in a 3-dimensional environment. A rigid flex design is usually fitted into an enclosure, and the mechanical elements must be considered. 

Example of a rigid flex PCB

Designing a rigid flex PCB needs a 3-dimensional approach.

 

The flexible part of the PCB is sometimes bent to a certain degree, which means you’ll need to weigh in the mechanical stress on the material. The bend line, or bend area, needs to be carefully dealt with to prevent premature failure.

Avoid vias and pads in the bend areas as the mechanical stress may weaken the paddings. Traces should also be routed perpendicularly to the bending line for structural stability. You can add dummy traces to strengthen the bend area along with the existing traces. 

Instead of solid copper planes, the flex area should have a hatched-polygon for the ground plane. This can be done easily if you’re using OrCAD PCB Designer that’s optimized for rigid flex design. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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