The main purpose of PI (Polyimide) reinforcement in Flexible Printed Circuit (FPC) is to enhance the mechanical strength and stability of FPC. Here are some reasons:

1. Improve mechanical strength: FPC is usually relatively soft and susceptible to external forces such as bending and stretching. PI reinforcement can increase the thickness and hardness of FPC, improve its mechanical strength, enable it to better withstand these external forces, and reduce deformation and damage during use.

2. Enhanced reliability: PI materials have good heat resistance, chemical resistance, and insulation performance. By using PI reinforcement, the reliability of FPC can be improved, allowing it to operate normally under harsh environmental conditions such as high temperature, humidity, corrosive media, etc.

3. Improving circuit board performance: PI reinforcement can reduce signal attenuation and distortion in FPC, and improve the quality and stability of signal transmission.

4. Easy to assemble and process: PI reinforcement can provide better support and fixation for FPC, making it easier to operate during the assembly process. At the same time, it can also improve the stability of FPC during processing, such as in processes such as etching and drilling.

5. Increase the lifespan of circuit boards: PI reinforcement can extend the service life of FPCs, reduce the frequency of maintenance and replacement, and lower costs.

It should be noted that the specific application and effectiveness of PI reinforcement will be influenced by various factors, such as the design of FPC, usage environment, performance requirements, etc. In practical applications, it is necessary to uate and select according to specific situations to ensure that FPC can meet relevant technical requirements and usage needs.