Strictly speaking, the internal stress of each roll of FPCB soft hard bonding board is different, and the process control of each batch of production boards will not be exactly the same. Therefore, the grasp of material expansion and contraction coefficients is based on a large number of experiments, and process control and data statistical analysis are particularly important. In practical operation, the expansion and contraction of flexible boards are phased:

Firstly, from cutting to baking, the thermal expansion and contraction during this stage are mainly caused by temperature. To ensure the stability of the baking board caused by fluctuations, the consistency of process control must be ensured. Under the premise of material uniformity, the heating and cooling operations of each baking board must be consistent, and the baking board cannot be placed in the air for heat dissipation just because of the pursuit of efficiency. Only in this way can the expansion and contraction caused by internal stress in the material be maximally eliminated.

The second stage occurs during the pattern transfer process, where the expansion and contraction are mainly caused by changes in the orientation of internal stresses in the material. To ensure the stability of the assembly line process, all baked plates cannot undergo grinding operations and are directly subjected to surface pretreatment through a chemical cleaning line. After film application, the surface must be flat, and the plate must be left to stand for sufficient time before and after exposure. After the circuit transfer is completed, due to changes in stress direction, the flexible board may curl and shrink to varying degrees. Therefore, the control of circuit film compensation is related to the control and effort of the bonding accuracy of the flexible board,

The expansion and contraction in the third stage occur during the compression process of the rigid soft bonding plate, which is mainly determined by the compression parameters and material properties. The influencing factors of expansion and contraction in this stage include the heating rate of compression, the setting of pressure parameters, and the residual copper rate and thickness of the core plate. Generally speaking, the smaller the residual copper rate, the greater the fluctuation value; The thinner the core board, the greater the expansion and contraction values. However, from big to small is a gradual process, so film compensation is particularly important. Furthermore, due to the different properties of flexible and rigid board materials,