The cause of the expansion and contraction is determined by the characteristics of the materials. To solve the problem of the expansion and contraction of FPCB soft and hard bonding plates, we must first introduce the flexible plate material polyimide:
Soft and hard combination plate
(1) Polyimide has excellent heat dissipation performance and can withstand the thermal shock of lead-free welding high temperature treatment;
(2) For small devices that need more 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. Generally, it should be processed above 350 ℃;
(4) In terms of organic dissolution, polyimide is insoluble in general organic solvents.
The rise and fall of flexible plate materials are mainly related to the matrix materials PI and glue, that is, to the imidization of PI. The higher the degree of imidization, the more controllable the rise and fall.
According to the normal production rules, flexible boards will have varying degrees of expansion and contraction during the formation of graphic lines and the combination and pressing of soft and hard FPCB after blanking. After the etching of graphic lines, the density and trend of lines will lead to the reorientation of the stress on the whole board surface, which will eventually lead to the general regular expansion and contraction changes on the board surface; In the process of soft and hard bonding and pressing, due to the inconsistent expansion and contraction coefficients of the surface coating film and the base material PI, a certain degree of expansion and contraction will also occur within a certain range.
In essence, the expansion and contraction of any material are caused by the influence of temperature. During the lengthy manufacturing process of FPCB, after many hot and wet processes, the expansion and contraction value of the material will change slightly to varying degrees, but from the perspective of long-term actual production experience, the change is still regular.