Flexible circuit boards have developed over time. They are now used in various applications in the medical industry, including drug delivery systems and watches that closely monitor circulatory and respiratory data and send it to the wearer's cardiologist. In various medical applications, flexible circuit boards have mechanical advantages over rigid PCBs.

Therefore, the entire terminal product (medical equipment) can be placed on the human body (such as hearing aids).

2. Flexible circuit boards can form complex 3D shapes and branch into multiple connectors, while rigid PCBs cannot.

3. Flexible circuit boards can interface with rigid PCB boards, while flat cables do not require relatively high and bulky connectors, or in the case of rigid flexible structures. They can be integrated with circuit boards without the need for external connectors.

All these unique characteristics of flexible circuit boards and composite boards make them ideal choices for wearable devices and medical applications.