Concept & Mechanical Designs of Flex & Rigid-Flex PCBs

When considering flex and rigid-flex circuits, there are benefits for both the manufacturer and the OEM to both be involved in the concept development and design of PCBs. Developing an initial understanding of the project details will be crucial in delivery of an effective PCB development project. Communication between the customer’s project management and engineering team should be an early focus in delivery of an effective project.

Oddly Shaped Rigid-Flex PCB

We will seek to confirm whether a flex based solution is appropriate for your proposed application. It is possible that after a review of your requirements, we conclude that using a flexible circuit board may not be appropriate. Through our review process, we hope to be able to ensure the use of appropriate PCB technology. If this means that Rigid-Flex PCBs are not the most appropriate design for your requirements, we will let you know.

When designing Oddly Shaped Rigid-Flex PCBs, there are a number of factors that the manufacturer will need to know. These include:

• Understanding what the designer is trying to achieve in the development of the PCB;
• Identifying the functionality of the flexible PCB;
• The general size and shape requirements of the board;
• Determining whether the design is an active component or a point to point interconnect; and
• Noting whether there are any special signal requirements (such as current carrying or impedance control).

Further detail may also assist in the design, such as knowing whether shielding is required (based on the environmental situation of the board); and whether there a radio frequency design is required. Once these questions have been addressed, we can provide you with a better understanding of how flex and rigid-flex PCBs can deliver solutions for your project.

Part of our process is identifying where additional functionality can be integrated at the design stage. We will also look for opportunities to integrate the separate parts of the design, and look for opportunities to simplify complex designs, which can reduce overall project costs.

Mechanical Design

The second stage of development of a Flex and Rigid-Flex design is ensuring that the mechanical design specifications are in place. We will need to clarify the following factors to ensure there is no risk of trace breakage once the board is inserted into the end product:

• What the minimum bend requirements are for your PCB;
• How the PCB is going to be bent to be positioned in your product; and
• The flex section lengths required to meet the bend requirements.

Flexible PCB with Stiffeners

It is not possible to manufacture all shapes and configurations due to the processes involved in flex and rigid-flex manufacturing. In the same vein, it’s important to be aware that not all sizes are available, as very large parts can affect the dimensional stability and manufacturing tolerances. Therefore, we need to look at the shape and size of the flex part.

We can also add value by identifying options for mechanical design that you may not have considered. Examples include Stiffeners (required to support soldered connects and components, ensuring reliability and PSAs (double sided adhesive tape used to attach the flex). When considering PSA requirements, there are other factors to consider such as the whether the board will be used in high temperatures, whether the PSA needs to be thermally conductive, or to dissipate heat, and whether it needs to be electrically conductive to ground the part to the enclosure.

In some instances there may be requirements for shielding for RF or EMI sensitive applications. If so, consideration needs to be put around the form of shielding to be used (copper, silver ink, or special shielding films).

Finally, in some designs the flex circuit may need epoxy strain reliefs. These are required if there is a bend situated close to a stiffener or to the rigid PCB section.