1. Technical Field
The present disclosure relates to printed circuit boards, particularly to a method for manufacturing a rigid-flexible printed circuit board.
2. Description of Related Art
Rigid-flexible printed circuit boards (R-F PCBs) are widely used in electronic devices. The R-F PCB has a rigid portion and a flexible portion. The rigid portion is configured for assembling electronic components and maintaining electrical connections among the electronic components. The flexible portion is connected to the rigid portion and can be bent relative to the rigid portion. Thus, a large number of electronic components can be assembled on the rigid portion of the rigid flexible printed circuit board without occupying a large amount of space.
A typical method for manufacturing an R-F PCB is described as follows. First, a flexible printed circuit board (FPCB) is manufactured. Second, a rigid printed circuit board (R-PCB) is laminated on the FPCB, and copper conductive tracks are formed on the R-PCB. Third, an opening is formed in a region of the R-PCB for exposing part of the FPCB, thereby forming a flexible portion. Other parts of the FPCB and the corresponding R-PCB form a rigid portion. Thus, an R-F PCB having a flexible portion and a rigid portion is obtained. Before forming the R-PCB, a coating layer and a peelable binder layer is sequentially laminated on the FPCB in the flexible portion. Sometimes, an electro-magnetic shielding layer and another coating layer are formed between the coating layer and the peelable binder layer in the flexible portion. When the R-PCB is laminated on the FPCB, these additional layers in the flexible portion will cause the thickness of the flexible portion to be much greater than that of the rigid portion. In a following a step, solder-resistant materials are printed on the R-PCB, and then the solder-resistant materials are exposed and developed to form a solder-resistant layer for protecting an electrical trace layer on the R-PCB. The differences between the flexible portion and the rigid portion may cause a photo mask used in the exposure step to not entirely contact the surface of the rigid printed circuit board in the rigid portion. This will reduce the quality of the R-F PCB.
What is needed, therefore, is a method for manufacturing a rigid-flexible printed circuit board, to overcome the above mentioned limitations.