First, let's consider the ordinary rigid printed circuit boards, whose base materials are usually fiberglass and epoxy resins. In fact, these materials are a kind of fiber, although we call it "rigidity", you can still feel its elasticity if you take a single layer out. Because of the curing epoxy resin, can make the plate layer more rigid. Because it is not flexible enough, it cannot be applied to certain products. But for a lot of simple assembly, the Board will not continue to move the electronic products are appropriate.
In more applications, we need more flexible plastic film than epoxy resin. Our most commonly used material is polyimide (PI), which is very soft and firm, and we cannot easily tear or extend it. It also has incredible thermal stability and can easily withstand the temperature changes in the process of reflow, and in the process of temperature fluctuations, we can hardly find its telescopic deformation.