Structural design requirements of rigid-flex pcb

The rigid-flex board is a printed circuit board with the characteristics of the FPC soft board and the rigid board of the PCB by combining with the rigid circuit board after pressing and other processes, according to the relevant process requirements. Therefore, it can be used in some products with special requirements. It has both a certain flexible area and a certain rigid area, which is of great help to save the internal space of the product, reduce the volume of the finished product, and improve the performance of the product. So, do you know what are the structural requirements for designing a rigid-flex board?

1. The flexible layer is designed to be on the same single sheet as much as possible on the inner layer and in the middle as much as possible.
For example: 8-layer board, top/bottom each made a single chip, 2/3, 4/5, 6/7, each single chip, flexible layer selection priority 4/5>2/3=6/ 7
10-layer board: T, 2/3, 4/5, 6/7, 8/9, B, the flexible layer selection priority is 4/5=6/7>2/3=8/9

2. Due to the limitation of space or bending angle, the design can adopt the design of soft area extending into the board to meet the bending radius and space requirements. At this time, the soft and hard gap must be at least 1mm. The distance between the soft and hard boards is recommended to be between the soft boards. Greater than 0.8mm, between the soft board and the hard board, and the distance between the hard board and the hard board is greater than 2mm

3. The length requirement of the soft zone is related to the bending angle and radius.
4. Consider the 3D structure of the board after bending to avoid mutual interference with device installation (height limitation).
5. The length of the soft zone is recommended to be greater than 5mm, and the limit value is 4mm, otherwise it may not be processed by some board factories.
6. When the device is placed in the hard area, the distance between the edge of the device and the soft and hard bonding area is greater than 1mm, and the soft area should not be punched as far as possible. The hard area is recommended to be drilled at a distance greater than 2mm from the soft and hard bonding area.
7. Choose circular arc transition as far as possible for the soft and hard joints. The radius depends on the actual situation. It is recommended to be 6.35mm but generally does not reach this value. It is recommended to be at least 0.5mm.

8. The wiring of adjacent layers in the soft zone adopts staggered wiring, avoid overlapping wiring as much as possible, so that the softness of the soft zone can be uniform and the bending life can be increased.

9. The wiring in the soft zone should be straight in and out as much as possible. If the structure is restricted to the soft and hard joints, try to use circular arc transitions, and also make circular arcs at the corners of the soft zone.

10. If the signal across the soft zone does not need to be controlled impedance, and copper should be laid on the soft zone (power ground signal), it is recommended to lay copper grids.
11. If the signal across the soft zone needs to control the impedance, it should be noted that the signal line still needs a reference plane in the soft zone, and the impedance line width needs to be calculated separately, and the line width may change suddenly.
12. Try not to put the device in the soft area. If you install the device, you need to set the pad on the corresponding soft layer instead of top/bottom when building the library.

The above are the design requirements of rigid-flex PCB,If you have any questions, please feel free to contact our online customer service.POE provides OEM production services, including PCB, PCBA, prototype pcb assembly from design, procurement, proofing to mass production, etc. to provide a series of complete services to ensure the smooth progress of the project in the production stage! Help solution providers solve the problem of bulk component procurement and improve the efficiency of R&D and production.