Multilayer flexible printed circuit board

Abstract

A flexible printed circuit board with multiple layers includes an inner wiring substrate and at least one outer wiring plate. Each outer wiring plate is connected to one surface of the inner wiring substrate, and defines at least one through hole which passes through the outer wiring plate to expose the inner wiring substrate. Each outer wiring plate further includes an adhesive plate connected to the inner wiring substrate. The adhesive plate includes a stepped portion extending towards a center of the through hole.

What is claimed is: 
     
         1 . A multilayer flexible printed circuit board comprising:
 an inner wiring substrate; and   at least one outer wiring plate, each outer wiring plate connected to one surface of the inner wiring substrate;   wherein each outer wiring plate defines at least one through hole passing through the outer wiring plate to expose the inner wiring substrate, each outer wiring plate comprises an adhesive plate connected to the inner wiring substrate, the adhesive plate comprises a stepped portion extending towards a center of the through hole.   
     
     
         2 . The multilayer flexible printed circuit board of  claim 1 , wherein the inner wiring substrate comprises a first isolated plate, and a first inner conductive wiring layer and a second inner conductive wiring layer connected to two opposite surfaces of the first isolated plate, wherein the adhesive plate of one of the at least one outer wiring plate is connected to a surface of the first inner conductive wiring layer facing away from the first isolated plate, and the adhesive plate of another of the at least one outer wiring plate is connected to a surface of the second inner conductive wiring layer facing away from the first isolated plate, and wherein at least one electrically conductive hole is defined in the inner wiring substrate which electrically connects the first inner conductive wiring layer to the second inner conductive wiring layer. 
     
     
         3 . The multilayer flexible printed circuit board of  claim 2 , wherein the first isolated plate is made of a polymer selected from a group consisting of polyimide, polytetrafluoroethylene, poly thiamine, poly (methyl methacrylate), polycarbonate, polyethylene terephthalate, and polyimide-polyethyleneterephthalate, or any combination thereof. 
     
     
         4 . The multilayer flexible printed circuit board of  claim 2 , wherein each electrically conductive hole comprises a connecting hole which passes through the first isolated plate, the first inner conductive wiring layer, and a copper layer formed on an inner wall of the connecting hole. 
     
     
         5 . The multilayer flexible printed circuit board of  claim 2 , wherein each outer wiring plate further comprises a second isolated plate and an outer conductive wiring layer connected to the second isolated plate, and wherein each adhesive plate is connected to a surface of the second isolated plate facing away from the corresponding outer conductive wiring layer. 
     
     
         6 . The multilayer flexible printed circuit board of  claim 5 , wherein the second isolated plate is made of a polymer selected from a group consisting of polyimide, polytetrafluoroethylene, poly thiamine, poly (methyl methacrylate), polycarbonate, polyethylene terephthalate, and polyimide-polyethyleneterephthalate, or any combination thereof 
     
     
         7 . The multilayer flexible printed circuit board of  claim 6 , wherein the second isolated plate has a thickness of about 3 micrometers to about 10 micrometers. 
     
     
         8 . The multilayer flexible printed circuit board of  claim 1 , wherein the adhesive plate has a thickness of about 10 micrometers to about 25 micrometers. 
     
     
         9 . The multilayer flexible printed circuit board of  claim 1 , wherein the stepped portion extends towards the center of the through hole by a distance of about 2 millimeters to about 5 millimeters. 
     
     
         10 . The multilayer flexible printed circuit board of  claim 1 , wherein the dry film has a thickness of about 15 micrometers.