Drilling is a flexible circuit an important processing operation, as the flexible circuits material was soft and easy to deformation, It’s different from the rigid printed circuit boards when drilling. The process is as following:

lamination → fixed → drilling → demolition board

lamination: it is going to pile up the copper substrate material or the protective film material together at a certain layers, and at the bottom and top layer with  plate and covered tightly with a single-sided adhesive tape together.

CMD Circuits offer you more information about the flexible circuits here blog.