With the continuous increase in the yield ratio of flexible PCBs and the application and promotion of rigid-flex PCBs, it is now more common to add soft, rigid or rigid-flex when talking about PCBs, and say that it is a few-layer FPC. Generally, an FPC made of a soft insulating substrate is called a soft FPC or a flexible FPC, and a rigid-flex composite PCB is called a rigid-flex PCB. It meets the needs of today's electronic products for high density, high reliability, small scale, and lightweight progress. It also satisfies the strict economic requirements and the needs of market and technology competition.