Rigid-Flex PCBs Design Guidelines by Hemeixin Electronics Co., Ltd

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Printed circuit boards have become the new standard in electronics. They come in three main categories: rigid PCBs, flex PCBs, and rigid-flex circuit boards. Printed circuit boards are becoming increasingly popular owing to the need for compact, reliable, and durable devices.

Moreover, it’s the more recent type that is slowly increasing in demand. Rigid-flex boards are a hybridized version of rigid and flex PCBs. They incorporate a hardboard as well as a flexible PCB into a single design application.

As a result, this allows for enhanced efficiency in terms of space-saving and creative freedom. Unlike flex PCBs, rigid-flex circuit boards do not require the use of flexible cables and connectors. They integrate a flex layer into a rigid board which can easily be connected to other electrical components. The lack of connecters helps increase device reliability by simplifying the overall circuit design.

Rigid-flex PCBs are lighter, denser in circuitry, and provide better shock absorption than their counterparts. Therefore, they are highly sought after by designers who want to make increasingly reliable and durable consumer electronics, medical appliances, and folding technologies.

Are you interested in designing your own printed circuit boards? Read these rigid-flex PCB design guidelines by one of the leading manufacturers of printed circuit boards in the industry, Hemeixin Electronics.

Rigid-Flex PCB Design Guidelines

Rigid-flex circuit boards are revolutionary, but that does not mean there is a permanent design model for them. Printed circuit boards are custom built to fit the application requirements of different clients. If you're working on building a smartwatch, you might require a different PCB design than the one employed in NASA's satellite systems.

Similarly, every design application requires different levels of flexibility, the board size, and circuit density depending. The mechanical dynamics of PCBs are also different in all devices. So, if you're looking to design a rigid-flex board, consider the following rigid-flex PCB design guidelines to craft the perfect printed circuit board for your application.

Rigid flex pcb Layer Stack Up

You need to figure out the number of layers for your rigid-flex circuit board stack up. Rigid-flex boards can be made of any number of flexible and rigid layers depending on the performance and cost requirements. Refer to this link to figure out the different types of layer stack-ups in rigid-flex PCB design.

Additionally, as a general thumb rule for rigid-flex PCB distance guide, remember the following details:

  • Length of flex area >0 mm
  • Rigid area to flexible area in the PCB >8 mm
  • Distance between holes and flexible area >9 mm

Using an even number of layers is cost-effective for building a rigid-flex circuit board. It is also beneficial to ensure all rigid portions have the same stack up and layers. If different numbers of layers are used, make sure they have a comparable layup and similar thickness.

Coverlay Requirements

You might need to use a coverlay film if you’re rigid-flex circuit board design incorporates one of the following features or materials:

  • FR4 component area rigidizing stiffener
  • EMI or RF shielding film
  • ZIF finger area polyimide stiffener
  • Pressure Sensitive Adhesives

Consider Flex Plane Pattern

It is important to consider the pattern employed on the flex plane. The use of solid copper is not preferred. Although it offers the most effective shielding, copper is also the least flexible material.

Therefore, consider using a cross-hatched ground plane that will not interfere with the flex plane's flexibility. Increased flexibility means the printed circuit board will be less likely to break under stress.

rigid flex pcb Bookbinder Design

The flexible portion of the rigid-flex PCB is very important since it helps in increasing connectivity. To ensure optimal flexibility and reduced wear and tear of the printed circuit board, consider using the bookbinder design of the unbonded flex area. The design uses the progressive length of the flex area and is used in places where a sharp bend is required. The design allows for increased flexibility and helps increase resistance to stress.

Heat Dissipation

Reducing or managing heat dissipation is one of the main requirements of a good rigid-flex PCB design. Depending on the utility of a device, energy requirements, and power consumption, an appliance may or may not generate a lot of heat.

The heat needs to be efficiently dissipated, so the system does not malfunction or get damaged. A good rigid-flex PCB design uses material that provides good insulation and heavy copper weights with a large surface area so heat can dissipate easily.

rigid flex pcb Bending Radius

Rigid-flex PCB design guidelines always emphasize the need to know the minimum bending radius. This is important when deciding the number of layers and the flex PCB design model for a certain application. Visit Hemeixin Electronics for information on calculating the bending radius for single and multi-layered PCB designs.

Additionally, the copper weights must be near the neutral axis. This helps reduce the stress on conductors.

Moreover, when tracing over the bending line, make sure to use straight and perpendicular lines, and distribute them uniformly over the flexible area. For multi-layered designs, incorporating dummy traces, alternate routing between the layers, and reduction in sharp turning traces near the bending region help improve the design's robustness.

The main goal here is to prevent the traces from excessive stretching, which can lead to the formation of cracks. Breakage can also occur in extreme cases. Therefore, it is also important to use 45° or 90° curves when using traces in a dynamic flex application where flex board directional shifts are part of the system's design.

Consult Hemeixin Electronics Co., Ltd

Hemeixin Electronics is one of the leading manufacturers of printed circuit boards. The abovementioned rigid-flex PCB design guidelines are also discussed in more detail on their website. They produce single, double, and multi-layered rigid-flex circuit boards and use the best materials in the market.

Consulting with your manufacturer or design engineer establishes a communication network, so they know your design and application requirements, the nature of the application, and any other considerations you might have.

Furthermore, working with a reliable PCB manufacturer like Hemeixin Electronics will ensure you get the creative freedom you deserve while your rigid-flex circuit board designs will always be in compliance with the official IPC 2223C standards. Contact Hemeixin Electronics today and get in touch with the best design engineers for all your PCB needs!

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