PCB Technical - How to design and reinforce the Rigid Flex PCB

Rigid Flex PCB is a kind of PCB circuit board that combines soft board and hard board. In terms of design, it is very different from soft board design and hard board design.

1. Design requirements for flexible zone line:

1) Tear shape shall be adopted between thick line and thin line to prevent sudden expansion or contraction of the line;

2) Use smooth corners to avoid sharp corners.

2. Under the condition that the electrical requirements are met, the pad shall be the maximum value. The transition line at the connection between the bonding pad and the conductor shall avoid right angle, and shall be smooth. The independent bonding pad shall be provided with a pad toe to strengthen the supporting effect.

3. Dimensional stability: add copper design as much as possible, and design as many solid copper berths as possible in the waste area.

4. Design of covering film window:

1) Add manual alignment holes to improve alignment accuracy;

2) The window design shall consider the range of glue flow. Generally, the window opening is larger than the original design, and the specific size shall be provided by ME with design standards;

3) Small and dense window opening can adopt special mold design: rotary punch, skip punch, etc.

5. Design of rigid deflection transition zone:

1) Smooth transition of the line, and the direction of the line shall be perpendicular to the bending direction;

2) The conductor shall be evenly distributed in the whole bending area;

3) The wire width shall be maximized in the whole bending area, and PTH design, Coverlay and No flow PP design shall not be used in the transition area.

6. Design of flexible area with air gap requirements:

1) No through hole is allowed in the part to be bent;

2) Protective copper wire shall be added at the most two sides of the line. In case of insufficient space, protective copper wire can be added at the inner R corner of the bending part;

3) The connecting part of the line shall be designed as an arc;

4) The larger the bending area is, the better without affecting the assembly.

7. Other

Do not share the tool holes of the soft board, such as punch holes, ET, SMT positioning holes, etc.

FPC is widely used in electronic products, but due to its low mechanical strength and easy cracking, it needs to be bonded with reinforcing materials to strengthen the strength of FPC. So, do you know what types of FPC reinforcement are?

1) PI reinforcement: the tolerance can be controlled within+/- 0.03mm, with high precision and high temperature resistance (130 ℃ - 280 ℃). PI reinforcement thickness: 0.075mm, 0.1mm, 0.125mm, 0.15mm, 0.175mm, 0.2mm, 0.225mm, 0.25mm.

2) Steel sheet reinforcement: it requires manual assembly, which is more complex and costly. Steel sheet reinforcement thickness: 0.1mm, 0.2mm.

3) FR4 reinforcement: if the thickness is less than 0.1mm, the tolerance can be controlled within ± 0.05mm. If the thickness is ＞ 1.0mm, the tolerance is ± 0.1mm. FR4 reinforcement thickness: 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 1.6mm.

The advantages and disadvantages of FPC Flexible PCB reinforcement are that PI tolerance is small but not very hard, FR4's thicker thinking choice tolerance is larger, and the steel sheet is hard and stable, and it is not easy to rework after manual assembly.