News:

The root of expansion and contraction is determined by the characteristics of materials. To solve the problem of expansion and contraction of soft and hard bonded plates, Polyimide, the material of flexible plates, must be introduced first:

(1) Polyimide has excellent heat dissipation performance and can bear the thermal shock when lead-free soldering is treated at high temperature;
(2) For small devices requiring greater emphasis on signal integrity, most equipment manufacturers tend to use flexible circuits;
(3) Polyimide has the characteristics of high glass transfer temperature and high melting point, so it should be processed above 350 ℃ in general;
(4) In organic dissolution, polyimide is insoluble in general organic solvents.

The expansion and contraction of flexible plate material is mainly related to the matrix material PI and adhesive, that is, it has a great relationship with the imidization of PI. The higher the imidization degree, the stronger the controllability of expansion and contraction.

According to the normal production law, after cutting, the flexible board will have different degrees of expansion and contraction in the process of graphic line formation and soft and hard combination pressing. After graphic line etching, the density and trend of lines will lead to the stress reorientation of the whole board surface, which will eventually lead to the general regular expansion and contraction changes of the board surface; In the process of soft-hard bonding, because the expansion and contraction coefficients of the surface covering film and the matrix material PI are inconsistent, there will be a certain degree of expansion and contraction in a certain range.

In essence, the expansion and contraction of any material is caused by the influence of temperature. In the lengthy manufacturing process of PCB, after many hot and wet processes, the expansion and contraction values of materials will change slightly to varying degrees, but from the long-term actual production experience, the changes are regular.