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  • Analysis and Improvement of the Rise and Decline of rigid and flexible PCB
     
    Date :2017-8-19

     

    The source of the ups and downs is determined by the characteristics of the material. To solve the problem of the rise and fall of rigid and flexible PCB, we must first introduce the polyimide of the flexible plate material:

    (1) polyimide has excellent heat dissipation performance, can withstand lead-free soldering heat treatment when the high temperature;
    (2) For most small devices that require greater emphasis on signal integrity, most equipment manufacturers tend to use flexible circuits;
    (3) polyimide has a high glass transition temperature and high melting point characteristics, under normal circumstances to be more than 350 ℃ processing;
    (4) in the organic solution, the polyimide does not dissolve in the general organic solvent.

     

    The rise and fall of the flexible plate material mainly with the matrix material PI and glue has a relationship, that is, with the imine of PI has a great relationship, the higher the degree of imidization, the stronger the controllability of the stronger. According to the normal production rules, the flexible plate in the open after the formation of graphics lines, as well as the combination of soft and hard bonding will produce different degrees of shrinkage in the graphics circuit after etching, the line of intensity and direction, Will lead to the whole board stress re-orientation, and ultimately lead to the general emergence of the plate regularly rise and fall changes in the soft and hard bonding process, due to surface coating and matrix material PI expansion coefficient is inconsistent, Range to produce a certain degree of ups and downs.

     

    From the essential reasons, the rise and fall of any material are affected by the temperature caused by the length of the PCB in the production process, the material after a lot of hot and humid process, the value of the expansion will have varying degrees of subtle changes, but on Long-term actual production experience, change or regular.

     

    How to control and improve?

     

    In the strict sense, the internal stresses of each roll of material are different, and the process control of each batch is not exactly the same. Therefore, the grasp of the material shrinkage factor is based on a large number of experimental basis On the process control and statistical analysis of data is particularly important. Specific to the actual operation, the expansion and contraction of the flexible plate is a phased:

    First from the open material to the baking board, this stage is mainly affected by the temperature caused by the rise and fall:

    To ensure that the baking plate caused by the ups and downs stabilized, first of all process control consistency, in the premise of uniform materials, each baking board temperature and cooling operation must be consistent, not because of blind pursuit of efficiency, and will The baked board is placed in the air for heat dissipation. Only in this way can the maximum extent possible to eliminate the material caused by internal stress rise and fall.

    The second stage occurs in the process of pattern transfer, this stage of the rise and fall is mainly due to changes in the internal stress caused by the material.

     

    To ensure that the process of line transfer up and down the stability of all baked good plate can not be grinding plate operation, directly through the chemical cleaning line for surface pretreatment, the surface after the lamination to be flat, before and after the exposure plate surface time to be sufficient, After the completion of the line transfer, due to the change of the stress orientation, the flexible plate will show different degree of curl and shrinkage, so the control of the line film compensation is related to the control of the hardness of the soft and hard combination, while the flexibility plate range To determine the production of its rigid plate is based on the data.

     

    The third stage of the ups and downs occurred in the process of soft and hard board, this stage of the main expansion and compression parameters and material properties of the decision.

     

    The factors of this stage include the heating rate of pressure, the pressure parameter setting and the residual copper ratio and thickness of the core. In general, the smaller the residual copper, the greater the value of the expansion; the thinner the core, the greater the value of the expansion. However, from large to small, is a gradual process of change, therefore, film compensation is particularly important. In addition, due to the nature of the flexible plate and the rigid plate material, the compensation is a factor that requires additional consideration.

     

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