Strictly speaking, the internal stress of each roll of FPCB soft and hard bonding plates is different, and the process control of each batch of production plates will not be the same. Therefore, the grasp of the material expansion and contraction coefficient is based on a large number of experiments, and the process control and data statistical analysis are particularly important. In actual operation, the expansion and contraction of the flexible board are staged:
FPCB soft and hard combination plate
First of all, the expansion and contraction of the baking board are mainly caused by the temperature: to ensure the stability of the expansion and contraction caused by the baking board, the consistency of process control is the first step. On the premise of uniform materials, the temperature rise and drop operations of each baking board must be consistent, and the baking board cannot be put in the air for heat dissipation because of the pursuit of efficiency. Only in this way can the expansion and contraction caused by the internal stress of the material be eliminated to the greatest extent.
The second stage occurs in the process of pattern transfer, and the expansion and contraction in this stage are mainly caused by the change of stress orientation in the material. To ensure the stability of expansion and contraction in the process of line transfer, all baked boards cannot be ground, and the surface shall be pretreated directly through the chemical cleaning line. The surface must be flat after the film is pressed, and the board surface must have sufficient standing time before and after exposure. After the line transfer is completed, the flexible board will show varying degrees of curl and contraction due to the change of stress orientation, Therefore, the control of line film compensation is related to the control of the accuracy of the combination of hardware and software. At the same time, the determination of the expansion and contraction range of the flexible board is the data basis for the production of its supporting rigid board.
The third stage of the expansion and contraction occurs in the process of pressing the soft and hard bonding plates, and the expansion and contraction in this stage are mainly determined by the pressing parameters and material properties. The factors affecting the expansion and contraction at this stage include the heating rate of pressing, the setting of pressure parameters, and the copper residue rate and thickness of the core plate. In general, the smaller the copper residue rate, the larger the rise and fall value; The thinner the core plate is, the larger the shrinkage value is. However, from big to small is a gradual change process, so film compensation is particularly important. In addition, due to the different nature of flexible plate and rigid plate materials, its compensation is an additional factor to be considered.