PCB News - PCB layer deviation definition and FPC flexible circuit board

General definition of PCB layer deviation

Layer deviation refers to the difference in concentricity between the layers of the PCB that originally requires alignment. The scope of its requirements is controlled according to the design requirements of different PCB board types. The smaller the distance between the hole and the copper, the stricter the control is to ensure its conduction and overcurrent capability.

Commonly used methods to detect layer deviation in the production process:

At present, the method often used in the industry is to add a group of concentric circles at the four corners of the production board, set the distance between the concentric circles according to the requirements of the production board layer deviation, and pass the X-Ray inspection machine or X-drill during the production process. The drone checks the deviation of the concentricity to confirm its layer deviation.

Analysis of the causes of PCB layer deviation:

1. The reasons for the inner layer deviation

The inner layer is mainly the process of transferring the graphics from the film to the inner core board, so the layer deviation will only be generated during the graphics transfer production process. The main reasons for the layer deviation are: inconsistent expansion and contraction of the inner film, exposure machine Factors such as misalignment, improper operation during the alignment of personnel and exposure.

Second, the reason for the PCB board pressing layer deviation

The main reasons for the bias of the laminated layer are: the inconsistency of the expansion and contraction of the core plates of each layer, poor punching and positioning holes, fusion dislocation, riveting dislocation, and sliding plates during the pressing process.

FPC flexible circuit board protection method

Common methods are:

1. The minimum radius of the inner corner on the flexible profile is 1.6 mm. The larger the radius, the higher the reliability and the stronger the tear resistance. At the corners of the shape, you can add a line near the edge of the board to prevent the FPC from being torn.

2. The cracks or grooves on the FPC must end with a round hole with a diameter of not less than 1.5 mm, which is also necessary when two adjacent parts of the FPC need to be moved separately.

3. In order to obtain better flexibility, it is necessary to select the bending area in a uniform width area, and as far as possible the FPC width change and the uneven trace density in the bending area.

4. Stiffener, also known as stiffener, is mainly used to obtain external support. The materials used include PI, polyester, glass fiber, polymer materials, aluminum, steel, etc. Reasonable design of the position, area and material of the reinforcement board has a great effect on avoiding FPC tearing.

5. In the multi-layer FPC design, the air gap layered design needs to be carried out in the area that is often bent during the use of the product. Try to use thin PI material to increase the softness of the FPC and prevent the FPC from cracking during repeated bending.

6. When space permits, a double-sided tape fixing area should be designed at the joint between the golden finger and the connector to prevent the golden finger and the connector from falling off during the bending process.

7. The FPC positioning screen should be designed at the connection between the FPC and the connector to prevent the FPC from skewing during the assembly process.

The above is an introduction to the definition of PCB layer deviation and FPC flexible circuit board. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology