The softness and hardness of flexible printed boards (FPBs) are critical design parameters that can significantly impact their performance, functionality, and compatibility with different applications. Adjusting the softness and hardness of FPBs allows designers to tailor these boards to meet the specific requirements of various electronic devices.

　　The softness or hardness of an FPB is mainly determined by the materials used in its construction. The base substrate, which provides the mechanical support for the circuit traces, plays a crucial role. Common substrate materials include polyimide, polyethylene terephthalate (PET), and liquid crystal polymers (LCP). Polyimide is widely used due to its excellent mechanical, thermal, and electrical properties. By adjusting the thickness and composition of the polyimide layer, the softness and hardness of the FPB can be modified. Thinner polyimide layers generally result in more flexible boards, while thicker layers or the addition of reinforcing fillers can increase the hardness.

　　In addition to the substrate, the adhesive layers used to bond different components and layers of the FPB also affect its softness and hardness. Adhesives with different formulations can have varying degrees of flexibility and rigidity. For example, some adhesives are designed to be more elastic, allowing the FPB to bend and flex easily, while others are more rigid, providing better mechanical support and stability. The choice of adhesive depends on the specific application requirements. In applications where the FPB needs to be highly flexible, such as in wearable electronics, more elastic adhesives are preferred.

　　The design of the circuit traces and the components mounted on the FPB can also influence its softness and hardness. Thicker and wider circuit traces can add rigidity to the board, while the use of surface - mount components with smaller footprints can reduce the overall stiffness. Additionally, the arrangement and density of the components on the FPB can affect its flexibility. A more evenly distributed component layout can help maintain a consistent level of softness or hardness across the board.

　　In some cases, special techniques are used to achieve specific softness and hardness characteristics. For example, embossing or texturing the surface of the FPB can change its mechanical properties. These techniques can be used to create areas of the board with different levels of flexibility, allowing for better integration with other components or to meet specific ergonomic requirements. By carefully considering the materials, adhesives, circuit design, and manufacturing techniques, designers can precisely adjust the softness and hardness of flexible printed boards to optimize their performance in a wide range of applications.