Patent Publication Number: US-2022225511-A1

Title: Rigid-flexible circuit board with easy and simple manufacture and method for manufacturing the same

Description:
FIELD 
     The present disclosure relates to a circuit board and a manufacturing method thereof, in particular to a rigid-flexible circuit board and a method for manufacturing the rigid-flexible circuit board. 
     BACKGROUND 
     A rigid-flexible circuit board comprises at least one rigid region and at least one flexible region, allowing durability and flexibility in the circuit board. The rigid-flexible circuit board is suitable for use even with precision electronic products, such as portable electronic products, medical electronic products, and military equipment. 
     A manufacturing method of the rigid-flexible circuit board can include steps of first, manufacturing a soft wiring substrate; next, laminating a hard wiring substrate on the soft wiring substrate; finally, forming an opening in a predetermined area of the hard wiring substrate, so that part of the soft wiring substrate is exposed from the opening to form a flexible area, while the rest of the soft wiring substrate forms a rigid area together with the hard wiring substrate. The above method is complex and costly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view showing a wiring substrate according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic cross-sectional view showing a flexible single-sided metal clad laminate according to an embodiment of the present disclosure. 
         FIG. 3  is a schematic cross-sectional view showing an intermediate structure formed by laminating the wiring substrate of  FIG. 1  on the flexible single-sided metal clad laminate of  FIG. 2 . 
         FIG. 4  is a schematic cross-sectional view showing a conductive hole and an outer conductive layer formed on the intermediate structure of  FIG. 3 . 
         FIG. 5  is a schematic cross-sectional view showing a solder mask layer formed on the outer conductive layer of  FIG. 4 . 
         FIG. 6  is a schematic cross-sectional view showing a double-sided copper clad laminate according to an embodiment of the present disclosure. 
         FIG. 7  is a schematic cross-sectional view showing a first through hole formed on the double-sided copper clad laminate of  FIG. 6 . 
         FIG. 8  is a schematic cross-sectional view showing a conductive hole and a conductive layer formed on the double-sided copper clad laminate of  FIG. 7 . 
         FIG. 9  is a schematic cross-sectional view showing a wiring substrate according to an embodiment of the present disclosure. 
         FIG. 10  is a schematic cross-sectional view showing a rigid-flexible circuit board according to an embodiment of the present disclosure. 
         FIG. 11  is a schematic cross-sectional view showing a rigid-flexible circuit board according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The technical solutions in the embodiments of the present disclosure are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present disclosure. The described embodiments are only some of the embodiments of the present disclosure, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative efforts are within the scope of the present disclosure. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those understood by the common worker in the art. The terminology used in the description of the present disclosure is for the purpose of describing particular embodiments and is not intended to limit the disclosure. 
     Some embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. The features of the embodiments and examples described below can be combined with each other without conflict. 
     Referring to  FIG. 1  to  FIG. 4 , a method for manufacturing a rigid-flexible circuit board  100  according to an embodiment of the present disclosure includes the following steps: 
     Step S 1 , referring to  FIG. 1 , a wiring substrate  10  is provided, and at least one opening  101  is defined on the wiring substrate  10  to divide the wiring substrate  10 , the opening  101  penetrates and completely separates the wiring substrate  10  into two parts. 
     In the present embodiment, the opening  101  may be formed by, but is not limited to, mechanical drilling, laser drilling, or etching. 
     In the present embodiment, referring to  FIG. 1 , the wiring substrate  10  is a double-sided wiring substrate and includes an insulating layer  11  and two inner conductive wiring layers  13  on opposite surfaces of the insulating layer  11 . The opening  101  penetrates the insulating layer  11  and the two inner conductive wiring layers  13 . 
     A material of the insulating layer  11  may be one selected from a group consisting of polyimide, teflon, polysulfide, polymethylmethacrylate, polycarbonate, polyethylene terephthalate, polyimide polyethylene terephthalate copolymer, and a combination thereof. The insulating layer  11  may also protrude from an inner wall of the opening  101  relative to the two inner conductive wiring layers  13 , so that a step exists between the insulating layer  11  and each of the two inner conductive wiring layers  13  at the opening  101 . 
     Step S 2 , referring to  FIG. 2 , two flexible single-sided metal clad laminates  30  are provided. Each of the two flexible single-sided metal clad laminates  30  includes an insulating base layer  31 , a first metal layer  33 , and an adhesive layer  35 . The first metal layer  33  and the adhesive layer  35  are disposed on opposite surfaces of the insulating base layer  31 . 
     In the present embodiment, first, a single-sided copper clad laminate  30   a  may be provided, the single-sided copper clad laminate  30   a  includes the insulating base layer  31  and a copper layer as the first metal layer  33  laminated on the insulating base layer  31 . Then, the adhesive layer  35  is pasted onto a surface of the insulating base layer  31  away from the copper layer. A material of the adhesive layer  35  may be thermoplastic adhesive, which may be, but is not limited to, one selected from a group consisting of thermoplastic polyimide (TPI), polyetheretherketone, and a combination thereof. 
     In other embodiments, the adhesive layer  35  may be formed on the surface of the insulating base layer  31  away from the copper layer by coating, spraying, or printing. 
     Step S 3 , referring to  FIG. 3 , one of the two flexible single-sided metal clad laminates  30 , the wiring substrate  10 , and another of the two flexible single-sided metal clad laminates  30  are stacked and pressed in that order to form an intermediate structure  40 . Each of the two flexible single-sided metal clad laminates  30  is combined with the wiring substrate  10  through the adhesive layer  35 . After the pressing, the adhesive layers  35  of the two flexible single-sided metal clad laminates  30  infill the opening  101  and are bonded with each other. 
     Specifically, an area of each of the two flexible single-sided metal clad laminates  30  corresponding to the opening  101  may be concave towards the opening  101  and closely combined with the inner wall of the opening  101 . 
     In the present embodiment, before the pressing, the two flexible single-sided metal clad laminates  30  are pasted on the two inner conductive wiring layers  13  through the adhesive layers  35 . 
     When pressing, the adhesive layers  35  are heated to decrease viscosity, so that the adhesive layers  35  flow into and infill a gap between the wiring substrate  10  and the insulating base layer  31  and the opening  101 , and the two flexible single-sided metal clad laminates  30  are thereby closely combined with the wiring substrate  10 . Since the insulating layer  11  protrudes from the inner wall of the opening  101  relative to the two inner conductive wiring layers  13 , adhesion between the adhesive layers  35  and the opening  101  is improved. 
     Step S 4 , referring to  FIG. 4 , at least one first conductive hole  41  is formed on the intermediate structure  40  to electrically connect the first metal layers  33  of the two flexible single-sided metal clad laminates  30  with the wiring substrate  10 , and two outer conductive wiring layers  330  are formed from the first metal layers  33 . 
     The manufacturing method of the rigid-flexible circuit board  100  is simple and easy to operate. The area corresponding to the opening  101  of the rigid-flexible circuit board  100  will become the flexible area of the rigid-flexible circuit board  100 . The usual commencing step of forming the flexible area is omitted in this manufacturing method, which simplifies the manufacturing process and avoids damage or pollution to the circuit board in the commencing step. 
     In some embodiments, after the step S 4 , the method may also include step S 5 . Referring to  FIG. 5 , two solder mask layers  50  are formed on surfaces of the two outer conductive wiring layers  330  away from the wiring substrate  10 , the two solder mask layers  50  infill gaps in the two outer conductive wiring layers  330  and the first conductive hole  41 . 
     In the present embodiment, the wiring substrate  10  is manufactured as follows: 
     Step one, referring to  FIG. 6 , a double-sided copper clad laminate  10   a  is provided. The double-sided copper clad laminate  10   a  includes the insulating layer  11  and two base copper layers  13   a  on opposite surfaces of the insulating layer  11 . 
     Step two, referring to  FIG. 7 , two first through holes  130  are formed on the two base copper layers  13   a  of the double-sided copper clad laminate  10   a  to expose part of the insulating layer  11 . The two first through holes  130  on the two base copper layers  13   a  are opposite to each other. 
     In the present embodiment, the first through holes  130  are formed by mechanical drilling. 
     Step three, referring to  FIG. 8 , two second conductive holes  15  adjacent to opposite sides of the first through hole  130  are formed to electrically connect the two base copper layers  13   a,  and a conductive layer  13   b  is deposited on each of the two base copper layers  13   a.  A second metal layer  13   c  is constituted by one base copper layer  13   a  and one conductive layer  13   b  stacked on the one base copper layer  13   a.    
     Specifically, two communication holes  15   a  which penetrate each second metal layer  13   c  and also the insulating layer  11  are formed on the double-sided copper clad laminate  10   a  by laser, residue of resin in the communication holes  15   a  is removed, the two communication holes  15   a  are electroplated to form the two second conductive holes  15 , and two conductive layers  13   b  are deposited on the two base copper layers  13   a  respectively by electroplating. 
     Step four, referring to  FIG. 9 , each of the two inner conductive wiring layers  13  is formed from one second metal layer  13   c,  and a second through hole  110  is formed on the insulating layer  11  at a position corresponding to the two first through holes  130 . The second through hole  110  communicates with the two first through holes  130 . The second through hole  110  and the two first through holes  130  constitute the opening  101 . 
     In the present embodiment, a size of the second through hole  110  is smaller than a size of each of the two first through holes  130 , so that the insulating layer  11  protrudes out of the two inner conductive wiring layers  13  towards a central axis of the opening  101 . This avoids damage of the two inner conductive wiring layers  13  when the second through hole  110  is formed. 
     Specifically, in some embodiments, the two second metal layers  13   c  may also be thinned before the two inner conductive wiring layers  13  are formed. 
     In other embodiments, the wiring substrate  10  may be manufactured by other methods. In other embodiments, the wiring substrate  10  may be a multi-layer wiring substrate, which is formed by a build-up method on above double-layer wiring substrate. 
     Referring to  FIG. 10 , an embodiment of the rigid-flexible circuit board  100  is provided. The rigid-flexible circuit board  100  includes the wiring substrate  10 , the two adhesive layers  35 , and the two outer conductive wiring layers  330 . The wiring substrate  10  defines at least one opening  101  penetrating the wiring substrate  10  to divide the wiring substrate  10  and separate the same in two. The two outer conductive wiring layers  330  are stacked on opposite surfaces of the wiring substrate  10 , each of the two adhesive layers  35  is bonded between one of the two outer conductive wiring layers  330  and the wiring substrate  10 , and the adhesive layers  35  infill the opening  101 . An area of the rigid-flexible circuit board  100  corresponding to the opening  101  becomes a flexible region, while other areas of the rigid-flexible circuit board  100  remain as rigid regions. 
     Specifically, referring to  FIG. 11 , an area of each of the two outer conductive wiring layers  330  corresponding to the opening  101  is concave towards the opening  101 , to be closely combined with the inner wall of the opening  101 . 
     The wiring substrate  10  may be a double-sided wiring substrate or a multi-layer wiring substrate. In the present embodiment, the wiring substrate  10  is a double-sided wiring substrate and includes the insulating layer  11  and two inner conductive wiring layers  13  bonded to opposite surfaces of the insulating layer  11 . The opening  101  splits the insulating layer  11  and the two inner conductive wiring layers  13 . In the present embodiment, the insulating layer  11  may also protrude from the inner wall of the opening  101  relative to the two inner conductive wiring layers  13 . 
     The material of the insulating layer  11  may be one selected from a group consisting of polyimide, teflon, polysulfide, polymethylmethacrylate, polycarbonate, polyethylene terephthalate, polyimide polyethylene terephthalate copolymer, and a combination thereof. 
     The material of the adhesive layer  35  may be thermoplastic adhesive, which may be, but is not limited to, one selected from a group consisting of thermoplastic polyimide (TPI), polyetheretherketone, and a combination thereof. 
     The rigid-flexible circuit board  100  also includes the first conductive hole  41  electrically connecting the wiring substrate  10  with the two outer conductive wiring layers  330 . 
     The rigid-flexible circuit board  100  also includes two insulating base layers  31 . Each of the two insulating base layers  31  is located between one of the two adhesive layers  35  and one of the two outer conductive wiring layers  330 . 
     The rigid-flexible circuit board  100  also includes the two solder mask layers  50  disposed on surfaces of the two outer conductive wiring layers  330  away from the wiring substrate  10 . The two solder mask layers  50  may also infill the first conductive hole  41 . 
     The above is only a preferred embodiment of the present disclosure, and is not intended to limit the scope of the present disclosure. Although embodiments of the present disclosure are described above, it is not intended to limit the present disclosure. The present disclosure may be modified or modified to equivalent variations without departing from the technical scope of the present disclosure by any person skilled in the art. Any simple modifications, equivalent changes and modifications made to the above embodiments remain within the scope of the technical solutions of the present disclosure.