Must - Know for Rigid - Flexible PCB Production! Tips for Avoiding Warping and Other Issues

Rigid - flexible PCBs are circuit boards that combine the characteristics of flexible circuit boards (FPC) and rigid circuit boards through processes such as lamination according to relevant process requirements. Rigid - flexible PCBs are widely used in LCD PCBs, automotive PCBs, industrial PCBs, medical PCBs, communication PCBs, air - conditioning PCBs, and lighting PCBs.

I. Advantages of Rigid - Flexible PCBs

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

2. High - precision applications where reliability is more important than cost considerations.

3. High - density applications. Some components lack the necessary connector and cable surface area, and this problem can be solved with rigid - flexible PCBs.

4. Applications that require multiple rigid PCB boards.

 II. What Problems Should Be Noticed in the Production of Rigid - Flexible PCBs?

1. Whether it's substrate lamination or pure prepreg lamination, attention should be paid to the fact that the warp and weft directions of the glass cloth should be the same, and the thermal stress should be eliminated during the lamination process to reduce warping.

2. The rigid PCB should have a certain thickness. Because the flexible part is very thin and without glass cloth, after being affected by environmental and thermal shocks, its changes are different from those of the rigid PCB parts. If the rigid PCB parts are not well - defined and the difference in thickness or hardness is obvious, severe warping will occur, thus affecting soldering and use.

3. For the processing of the flexible PCB window, there are usually methods of pre - milling and post - milling. If it's pre - milling, the accuracy of milling should be ensured, and soldering and deflection should not be affected too much. If it's post - milling, you can wait until all pre - treatments are completed and the 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.

Rules for Rigid-Flex PCB Design

1. The FPC layers of the rigid-flex PCB are designed to be as deep as possible on the same panel and preferably in the middle.
For example, for an 8-layer rigid-flex PCB, make one layer at the top/bottom, and for layers 2/3, 4/5, and 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 the bending radius and space.

3. The length of the flexible PCB is related to the bending angle and radius.

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

5. It is recommended that the length of the flexible part be greater than 5mm, with a minimum value of 4mm.

6. When components are placed in the rigid PCB area, the distance between the edge of the component and the rigid-flex area should be greater than 1mm.

7. The flexible PCB should avoid drilling holes as much as possible.

8. Arc transitions should be used as much as possible for rigid-flex connections.

9. For the wiring of adjacent layers in the flexible 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 signal of the flexible PCB does not require impedance control and copper is needed in the flexible PCB part, it is recommended to use grid copper.

12. If a device construction library is installed for the flexible PCB components, set the pads on the corresponding soft layer instead of the top/bottom.

PCB MASTER 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 www.pcbmaster.com for inquiries. We will quickly reply with quotations for rigid-flex PCBs according to your needs and also provide one-stop services for rigid-flex PCB assembly.

Appreciation of Rigid-Flex PCB Products

Model: 8-layer Rigid-Flex PCB (R-FPCB)
Materials: FR4 + PI
Structure: FR4 4L + FLEX 4L
Finished Thickness: 0.2mm + 0.8mm
Copper Thickness: 10Z
Color: Green/White
Surface Finish: Immersion Gold
Minimum Trace/Space: 5mil/5mil
Minimum Hole: Mechanical Hole 0.2mm
Application: Equipment Switching PCB