PCB Tech - Rigid-flex board (soft and hard board) knowledge

The essence of the rigid-flex board is to use the FPC as one or two circuit layers of the PCB, and then partially mill the rigidity of the PCB, leaving only the flexible part.

What is a soft and hard board

The birth and development of FPC and PCB gave birth to a new product of soft and hard board. Therefore, the rigid-flex board is the flexible circuit board and the rigid circuit board. After pressing and other processes, they are combined according to the relevant process requirements to form a circuit board with FPC characteristics and PCB characteristics.

Advantages and disadvantages:

Advantages: The rigid-flex board has the characteristics of FPC and PCB at the same time. Therefore, it can be used in some products with special requirements. It has both a certain flexible area and a certain rigid area, which can save the internal space of the product., It is of great help to reduce the volume of the finished product and improve the performance of the product.

Disadvantages: There are many production processes for the rigid-flex board, the production is difficult, the yield rate is low, and the materials and manpower used are more. Therefore, its price is relatively expensive and the production cycle is relatively long.

1. Rigid-flex board is not cheap, why use rigid-flex board?

When designing hardware, cost is often not a key element;

First, reliability: Rigid-flex board can solve the reliability problem of FPC installation.

The FPC is connected through a connector, which brings about installation costs, inconvenient installation, installation reliability problems, and easy short-circuiting, falling off and other problems. After the FPC is installed, repair welding is performed on the FPC and the PCB in the design of a mass-shipped tube machine of Hikvision. Rigid-flex board solves the problem of FPC installation reliability.

Second, the overall cost:

Rigid-flex board, although the price per unit area has increased, but it saves the cost of the connector, and at the same time reduces the installation time, reduces the repair rate, reduces the repair rate, and improves the productivity and reliability. The use of mass-shipped products is often effective in reducing costs.

So the calculated cost:

Rigid-flex board area * Rigid-flex board unit price-processing time cost-FPC loosening and repairing cost * loosening probability-whether the management cost brought by fewer single board types is greater than the original PCB area * PCB unit price + FPC price + connector price

Third, effectively improve signal quality

Since the connection is not made through a connector, the wiring continuity is better and the signal integrity is better.

Traditional IPC uses FPC and connectors to connect the Sensor (video sensor) board and the main control board.

The use of rigid-flex boards can integrate the main control board and the sensor board, which solves many problems and also meets the structural design requirements of the drum machine.

2. Design attention of rigid-flex board:

A. The bending radius of the flexible board needs to be considered. If the bending radius is too small, it will be easily damaged.

B. Effectively reduce the total area, optimize the design and reduce the cost.

C. It is necessary to consider the structure of the three-dimensional space after installation.

D. It is necessary to consider the optimal design of the number of layers of the flexible part of the wiring.