1. Copper plate itself caused by thermal expansion and contraction;

2. When the graph is transferred, the material of black film and red film is celluloid, which expands and shrinks under the influence of humidity and temperature; The hole positions between the exposed graphic film and PCB after expansion and contraction do not match, and the hole positions do not match. Finally, after the delivery of the product, there is a tolerance with the component jack and product shell, so when making printed circuit board, the film should not be too large, and the temperature and humidity should be strictly controlled.

3. The expansion and contraction of the screen, the consequences caused by the expansion and contraction are the same as 2.

How to improve PCB shrinkage

In a strict sense, the internal stress of each roll of materials is different, and the process control of each batch of production plates will not be exactly the same. Therefore, the grasp of the expansion and contraction coefficient of materials is based on a large number of experiments, and the process control and data statistical analysis is particularly important. In practical operation, the expansion and contraction of flexible plate is divided into stages:

First of all, from the open to the baking plate, this stage is mainly caused by temperature:

To ensure the stability of the expansion and contraction caused by the baking plate, first of all, the consistency of the process control, under the premise of uniform material, each baking plate heating and cooling operation must be consistent, not because of the pursuit of efficiency, and the finished baking plate in the air for heat dissipation. Only in this way, in order to maximize the elimination of material internal stress caused by the expansion and contraction.

The second stage occurs in the process of graph transfer. The expansion and contraction of this stage is mainly caused by the change of stress orientation in the material.

To ensure the circuit increases and stability of the transfer process, all can’t baked good board for grinding plate operation, directly through the chemical cleaning line surface pre-treatment, after pressure membrane surface must level off, board face let stand before and after the exposure time must be sufficient, after the finish line transfer, due to the change of the stress orientation, flexible plate will present a different degree of crimp and contraction, Therefore, the control of the line film compensation is related to the control of the rigid-flexible joint precision, and the determination of the range of the expansion and contraction value of the flexible plate is the data basis for the production of its supporting rigid plate.

The expansion and contraction of the third stage occurs during the pressing process of rigid flexible plate, which is determined by the main pressing parameters and material properties.

The factors affecting the expansion and contraction in this stage include the heating rate of the pressing, the setting of the pressure parameters and the copper residual rate and thickness of the core plate. In general, the smaller the residual copper ratio is, the larger the expansion and contraction value is. The thinner the core board, the greater the expansion and contraction value. However, from large to small, is a gradual process of change, therefore, film compensation is particularly important. In addition, due to the different material nature of flexible plate and rigid plate, its compensation is an additional factor to be considered.