Cause analysis and improvement of Rigid PCB's shrink
The source of the Rigid PCB rise and shrink is determined by the characteristics of the material, to solve the problem of shrinking the rigid-flex plate, we must first introduce the material polyimide of the flexible plate:
(1) polyimide has excellent heat dissipation performance and can withstand the thermal shock of lead-free soldering at high temperature;
(2) For small devices requiring greater emphasis on signal integrity, most equipment manufacturers tend to use flexible circuits;
(3) Polyimide has a high glass transfer temperature and high melting point characteristics, in general, in the case of 350 ℃ above processing;
(4) in organic dissolution, polyimide does not dissolve in the general organic solvent.
The shrinkage of flexible plate material is mainly related to the matrix material Pi and gum, that is, the sub amination of Pi is very important, the higher the degree of amination, the stronger the controllability of the shrinkage. In accordance with the normal production rules, the flexible plate after the opening of the material, in the formation of graphics lines, as well as the process of rigid-flexible combination of compression will have a different degree of contraction, after the graphics line etching, the density of the line and direction, will lead to the entire plate stress reorientation, resulting in the surface of the general regularity of the rise and shrink changes In the process of rigid-flexible combined compression, due to the inconsistency of the shrinkage coefficient between the surface covering film and the Matrix material Pi, a certain degree of shrinkage will be produced in a certain range.
In essence, the shrinkage of any material is caused by the influence of the temperature, in the Rigid PCB lengthy production process, the material after a lot of hot and humid processes, the value will have varying degrees of small changes, but on the long-term actual production experience, the change is still a regular.