Strictly speaking, the internal stress of each roll of FPCB soft and hard combined board is different, and the process control of each batch of production board is not exactly the same. Therefore, the grasp of the coefficient of material expansion and contraction is based on a large number of experiments, process control and data statistical analysis is particularly important. Specific to the actual operation, flexible plate expansion is phased:
First of all, from cutting to baking board, the thermal expansion and cold contraction at this stage is mainly caused by temperature: to ensure the stability of baking board caused by fluctuations, the first is the consistency of process control, unity under the premise of material, each baking board heating and cooling operation must be consistent, not because of the pursuit of efficiency, and put the baking board in the air for heat dissipation.
The second stage occurs in the process of pattern transfer. The expansion and contraction of this stage are mainly caused by the change of the orientation of the internal stress of the material. In order to ensure the stability of the pipeline process, all the baking plates cannot be grinded, and the surface pretreatment is carried out directly through the chemical cleaning line. The surface must be smooth after laminating, and the layout standing time before and after exposure must be sufficient. After the line transfer is completed, the flexible plates will curl and shrink in different degrees due to the change of the stress direction. Therefore, the control of line film compensation is related to the control and effort of the soft plate combined precision.
The expansion and contraction of the third stage occurs in the pressing process of rigid and soft bonded plate. The expansion and contraction of this stage is mainly determined by the pressing parameters and material characteristics. The factors affecting expansion and contraction at this stage include the temperature rise rate of pressing, 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 larger the shrinkage value; the thinner the core plate, the larger the expansion and contraction value. However, it is a gradual process from large to small, so film compensation is particularly important.
