Must-Know for Rigid-Flex PCB Production! Secrets to Avoiding Problems like Warping

Rigid-Flex PCB is a kind of circuit board that combines the characteristics of flexible circuit boards and rigid circuit boards through processes such as lamination according to relevant process requirements. It has both the characteristics of FPC and PCB.  Rigid-Flex PCB is widely used in electrical PCBs such as LCD PCBs, automotive TV PCBs, industrial PCBs, medical PCBs, communication PCBs, automotive PCBs, air-conditioning PCBs, and lighting PCBs.

I. Advantages of Rigid-Flex PCB

1. It has high impact resistance and can be applied in high-stress environments.

2. It is suitable for high-precision applications where reliability is more important than cost considerations.

3. It is applicable for high-density applications. Some components lack the necessary connector and cable surface area, and this problem can be solved by using rigid-flex PCBs.

4. It is applicable for applications that require multiple Rigid-PCB boards.

I. What Problems Should Be Paid Attention to in Rigid-Flex PCB Production?

1. Whether it is substrate lamination or pure prepreg lamination, attention should be paid to ensuring that the warp and weft directions of the PP-core are consistent, and thermal stress should be eliminated during the lamination process to reduce warping.

2. The rigid PCB board should have a certain thickness. Because the flexible part is thin and has no PP-core, after being affected by environmental and thermal impacts, its changes are different from those of the rigid PCB parts. If the rigid PCB parts are not properly determined and there are obvious differences in thickness or hardness, serious warping will occur, which will affect soldering and usage.

3. For the processing of flexible PCB windows, there are usually methods of milling first and milling later. If milling is done first, the accuracy of milling should be ensured, and neither soldering nor deflection should be affected too much. If milling is done later, it is possible to wait until all pre-treatments are completed and final shaping is done, and then use laser cutting to remove the flexible window. At this time, attention must be paid to the depth of FR4 that the laser can cut.

II. What Are the Design Rules for Rigid-Flex PCB?

1. The FPC layers of Rigid-Flex PCB are designed to be as deep as possible on the same piece and as close to the middle as possible. For example, for an 8-layer rigid-flex PCB, make one layer on the top/bottom, and for layers 2/3, 4/5, 6/7, use the priority of 4/5 > 2/3 = 6/7 as the FPC layers.

2. Due to limitations in space or bending angles, the flexible PCB can be inserted into the board to meet the requirements of bending radius and space. 3. The length of the flexible PCB board is related to the bending angle and radius.

4. Consider the three-dimensional structure of the bending backplane to avoid interference (limit height) between device installations.

5. The length of the flexible part is recommended to be greater than 5mm, with a limit value of 4mm.

6. When devices are placed in the rigid PCB area, the distance between the edge of the device and the Rigid and Flex area should be greater than 1mm.

7. Flex-PCB should avoid punching holes as much as possible.

8. Rigid-Flex connections should use arc transitions as much as possible.

9. For the wiring of adjacent layers in the Flex-PCB part, staggered wiring should be adopted and overlapping wiring should be avoided as much as possible.

10. The wiring of the flexible PCB should enter and exit as directly as possible.

11. If the Flex-PCB signal does not require impedance control and the Flex-PCB part requires copper, it is recommended to use grid copper.

12. If device installation libraries are set up for the flexible PCB parts, set the pads on the corresponding soft layers instead of on the top/bottom.

PCB MASTER Company is a supplier of rigid-flex PCBs, committed to providing cost-effective rigid-flex PCBs.  Our goal is to manufacture the best rigid-flex PCB prototypes.  Customers can visit the official website of PCB MASTER (www.pcbmaster.com) for consultation.  We will quickly reply with quotations for rigid-flex PCBs according to your needs and provide one-stop services for rigid-flex PCB assembly.

Rigid-Flex PCB

Model: 8-layer Rigid-Flex PCB (R-FPCB)

Materials: FR4 + PI Structure: FR4 4L + FLEX 4L

Finished Thickness: 0.2mm + 0.8mm

Copper Thickness: 1oz

Color: Green/White

Surface Treatment: Gold Plating

Minimum Trace/Spacing: 5mil/5mil

Minimum Hole: Mechanical Hole 0.2mm

Application: Equipment Switching PCB

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