Patent Publication Number: US-2022232696-A1

Title: Circuit board for transmitting high-frequency signal and method for manufacturing the same

Description:
FIELD 
     The subject matter relates to circuit boards, and more particularly, to a circuit board for transmitting high-frequency signal and a method for manufacturing the circuit board. 
     BACKGROUND 
     Transmission lines are linear structures for transmitting electromagnetic signals, which are widely used in various electronic devices and electronic equipments. In mobile phones, considering the integrity of signal transmission and the mutual interference between a power line, a signal line, and a control line, the transmission line is designed to have the structure of a stripline. However, such design leads to a large width of transmission line, which fails to meet actual needs. 
     SUMMARY 
     Therefore, a circuit board for transmitting high-frequency signal is needed, which can reduce the wide of the transmission line. 
     An embodiment of the present disclosure provides a method for manufacturing a circuit board for transmitting high-frequency signal, including providing a first circuit board, the first circuit board including a first conductive wiring layer, a first base layer, and a second conductive wiring layer stacked in that order; providing a second circuit board, the second circuit board including a second base layer and a third conductive wiring layer stacked together, the third conductive wiring layer including at least one power line, at least one signal line, at least one control line, at least two first ground lines, and at least one second ground line, the signal line and the control line disposed at opposite sides of the power line, the first ground lines disposed at opposite sides of the signal line, the second ground line disposed at a side of the control line away from the power line, the second circuit board divided into a first region containing the signal line and a second region besides the first region, the second region the power line and the control line disposed in the second region; providing at least one third circuit board, each third circuit board including a third base layer and a fourth conductive wiring layer stack together; providing a fourth circuit board, the fourth circuit board including a fourth base layer and a fifth conductive wiring layer stacked together, the fifth conductive wiring layer including at least one power line or at least one control line; providing a fifth circuit board, the fifth circuit board including a fifth base layer and a sixth conductive wiring layer stacked together, and the sixth conductive wiring layer including at least one power line or at least one control line; providing a sixth circuit board, the sixth circuit board including a sixth base layer and a seventh conductive wiring layer stacked together, the seventh conductive wiring layer being a ground shielding layer; stacking the first circuit board, the second circuit board, and the third circuit board, and stacking the fourth circuit board, the sixth circuit board, and the fifth circuit board on the third circuit board, causing the sixth circuit board to be between the fourth circuit board and the fifth circuit board, and pressing them to cause each of the fourth circuit board, the sixth circuit board, and the fifth circuit board to correspond to the first region, thereby obtaining the circuit board for transmitting high-frequency signal. 
     Furthermore, the method can further include cutting the circuit board for transmitting high-frequency signal to form two terminal areas and a transmission line area between the terminal areas, each terminal area including a portion of the circuit board for transmitting high-frequency signal corresponding to the first region and another portion of circuit board corresponding to the second region, the transmission line area including another portion of the circuit board for transmitting high-frequency signal corresponding to the first region. 
     Another embodiment of the present disclosure also provides a circuit board for transmitting high-frequency signal, including: a first circuit board including a first conductive wiring layer, a first base layer, and a second conductive wiring layer stacked in that order; a second circuit board including a second base layer and a third conductive wiring layer stacked together, the third layer including at least one power line, at least one signal line, at least two first ground lines, at least one second ground lines, the signal line and the control line disposed at opposite sides of the power line, the first ground lines disposed at opposite sides of the signal line, the second ground line disposed at a side of the control line away from the power line, the second circuit board divided into a first region containing the signal line and a second region besides the first region, the second region the power line and the control line disposed in the second region; at least one third circuit board each including a third base layer and a fourth conductive wiring layer stacked together; a fourth circuit board including a fourth base layer and a fifth conductive wiring layer stacked together, the fifth conductive wiring layer including at least one power line or at least one control line; a sixth circuit board including a sixth base layer and a seventh conductive wiring layer stacked together; a fifth circuit board including a fifth base layer and a sixth conductive wiring layer stacked together, and the sixth conductive wiring layer including at least one power line or at least one control line; wherein the first circuit board, the second circuit board, the third circuit boards are stacked in that order, the fourth circuit board, the sixth circuit board, and the fifth circuit board are disposed on the third circuit board and correspond to the first region, the sixth circuit board is disposed between the fourth circuit board and the fifth circuit board. 
     Furthermore, the circuit board for transmitting high-frequency signal can include two terminal areas and a transmission line area between the terminal areas, each terminal area include a portion of the circuit board for transmitting high-frequency signal corresponding to the first region and another portion of the circuit board corresponding to the second region, the transmission line area includes another portion of the circuit board for transmitting high-frequency signal corresponding to the first region. 
     In the present disclosure, the power line and the control line in the transmission line area of the circuit board for transmitting high-frequency signal  100  are vertically disposed above the signal line, thereby preventing the power line, the control line, and the signal line from being on a same horizontal position. Thus, the width of the transmission line area can be reduced. In addition, the power line and the control line are separated arranged, that is, the power line and the control line are isolated from each other by the seventh conductive wiring layer, thereby avoiding the mutual interference between the power line and the control line, thus improve the signal transmission quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of an embodiment of a first copper-clad laminate according to the present disclosure. 
         FIG. 2  is a diagrammatic view showing a first blind hole being defined in the first copper-clad laminate of  FIG. 1 . 
         FIG. 3  is a diagrammatic view showing electroplating in the first blind hole of  FIG. 2 . 
         FIG. 4  is a diagrammatic view showing a first copper foil layer and a second copper foil layer of  FIG. 3  being etched. 
         FIG. 5  is a diagrammatic view of an embodiment of a second copper-clad laminate according to the present disclosure. 
         FIG. 6  is a diagrammatic view of a third copper foil layer of  FIG. 5  being etched. 
         FIG. 7  is a diagrammatic view showing a second blind hole being defined in the second copper-clad laminate of  FIG. 6 , and a conductive material being filled in the second blind hole. 
         FIG. 8  is a diagrammatic view of an embodiment of a third circuit board according to the present disclosure. 
         FIG. 9  is a diagrammatic view showing the first circuit board of  FIG. 4 , the second circuit board of  FIG. 7 , a third circuit board of  FIG. 8 , a fourth circuit board, a sixth circuit board, and a fifth circuit board being stacked together. 
         FIG. 10  is a diagrammatic view showing the first circuit board, the second circuit board, the third circuit board, the fourth circuit board, the sixth circuit board, and the fifth circuit board of  FIG. 9  being pressed together. 
         FIG. 11  is a diagrammatic view showing a solder mask layer being formed on the intermediate body of  FIG. 10  to obtain a circuit board for transmitting high-frequency signal. 
     
    
    
     NUMERIC DESCRIPTION FOR MAIN ELEMENTS 
     
         
         Circuit board for transmitting high-frequency signal  100   
         First copper-clad laminate  10   
         First copper foil layer  101   
         First base layer  102   
         Second copper foil layer  103   
         First conductive wiring layer  104   
         Second conductive wiring layer  105   
         First blind hole  11   
         First conductive portion  12   
         First circuit board  20   
         Second copper-clad laminate  30   
         Second base layer  301   
         Third copper foil layer  302   
         Third conductive wiring layer  31   
         Power line  311   
         Signal line  312   
         Control line  313   
         Second conductive portion  32   
         Second circuit board  40   
         First region  41   
         Second region  42   
         Third circuit board  50   
         Third base layer  501   
         Fourth conductive wiring layer  502   
         Third conductive portion  51   
         Fourth circuit board  60   
         Fourth base layer  601   
         Fifth conductive wiring layer  602   
         Fifth circuit board  61   
         Fifth base layer  611   
         Sixth conductive wiring layer  612   
         Sixth circuit board  62   
         Sixth base layer  621   
         Seventh conductive wiring layer  622   
         Intermediate body  70   
         Stepped portion  71   
         Solder mask layer  80   
         Adhesive layer  81   
       
    
     Implementations of the present disclosure will now be described, by way of embodiments, with reference to the attached figures. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Implementations of the disclosure will now be described, by way of embodiments only, with reference to the drawings. The disclosure is illustrative only, and changes may be made in the detail within the principles of the present disclosure. It will, therefore, be appreciated that the embodiments may be modified within the scope of the claims. 
     Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The technical terms used herein are not to be considered as limiting the scope of the embodiments. 
     Implementations of the disclosure will now be described, by way of embodiments only, with reference to the drawings. It should be noted that non-conflicting details and features in the embodiments of the present disclosure may be combined with each other. 
     The present disclosure provides a method for manufacturing a circuit board for transmitting high-frequency signal, which includes following steps. 
     Step S 1 , referring to  FIG. 1 , a first copper-clad laminate  10  is provided. 
     The first copper-clad laminate  10  includes a first copper foil layer  101 , a first base layer  102 , and a second copper foil layer  103  stacked in that order. In an embodiment, the first base layer  102  is a flexible copper-clad laminate (FCCL). 
     The first base layer  102  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the first base layer  102  is made of polyimide. 
     Step S 2 , referring to  FIG. 2 , at least one first blind hole  11  is defined in the first copper-clad laminate  10 , which passes through the first copper foil layer  101  and the first base layer  102 . 
     The first blind hole  11  does not penetrate the second copper foil layer  103 , that is, a bottom of the first blind hole  11  is closed by the second copper foil layer  103 . The first blind hole  11  can be formed by laser drilling. The position and the number of the first blind hole(s)  11  can be changed according to actual needs. 
     Step S 3 , referring to  FIG. 3 , a first conductive portion  12  is formed in each first blind hole  11  by electroplating. 
     The first conductive portion  12  is electrically connected to the second copper foil layer  103 , and an end of the first conductive portion  12  away from the second copper foil layer  103  can be substantially flush with the first copper foil layer  101 . 
     In an embodiment, copper is used for electroplating. In other embodiments, a conductive material may be filled in each first blind hole  11  to form the first conductive portion  12 . The conductive material can be a conductive paste (such as solder paste), a metal (such as copper), etc. 
     Step S 4 , referring to  FIG. 4 , the first copper foil layer  101  and the second copper foil layer  103  are etched to form a first conductive wiring layer  104  and a second conductive wiring layer  105 , respectively. Then, a first circuit board  20  is obtained. 
     The first conductive wiring layer  104  and the second conductive wiring layer  105  are formed by an exposure and development process. 
     Step S 5 , referring to  FIG. 5 , at least one second copper-clad laminate  30  is provided. 
     Each second copper-clad laminate  30  includes a second base layer  301  and a third copper foil layer  302  stacked together. In an embodiment, the second base layer  301  is a flexible copper-clad laminate (FCCL). 
     The second base layer  301  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the second base layer  301  is made of polyimide. 
     Step S 6 , referring to  FIG. 6 , the third copper foil layer  302  is etched to form a third conductive wiring layer  31 . 
     The third conductive wiring layer  31  includes at least one power line  311 , at least one signal line  312 , at least one control line  313 , at least two first ground lines (not label in the figures), and at least one second ground line (not label in the figures). The signal line  312  and the control line  313  are disposed on opposite sides of the power line  311 . The first ground lines are disposed on opposite sides of the signal line  312 , and the second ground line is disposed on a side of the control line  313  away from the power line  311 . The control line  313  can transmit a control signal. The third conductive wiring layer  31  can be formed by an exposure and development process. 
     Step S 7 , referring to  FIG. 7 , at least one second blind hole (not labeled) is defined in each second copper-clad laminate  30 , which passes through the second base layer  301 . 
     The second blind hole does not pass through the third conductive wiring layer  31 , that is, a bottom of the second blind hole is closed by the third conductive wiring layer  31 . The second blind hole can be formed by laser drilling. The position and number of the second blind hole(s) can be changed according to actual needs. 
     Step S 8 , a conductive material is filled in each second blind hole to form a second conductive portion  32 . Then, a second circuit board  40  is obtained. 
     The second conductive portion  32  is electrically connected to the third conductive wiring layer  31 , and an end of the second conductive portion  32  away from the third conductive wiring layer  31  can be substantially flush with the second base layer  301 . 
     The second circuit board  40  is divided into a first region  41  containing the signal line  312  and a second region  42  besides the first region  41 . The power line  311  and the control line  313  are disposed in the second region  42 . 
     The conductive material can be a conductive paste (such as solder paste), metal (such as copper), etc. In an embodiment, the conductive material is conductive paste. 
     Step S 9 , referring to  FIG. 8 , at least one third circuit board  50  is provided, which includes a third base layer  501  and a fourth conductive wiring layer  502  stacked together. At least one third conductive portion  51  is disposed in the third base layer  501 , which is electrically connected to the fourth conductive wiring layer  502 . The method for manufacturing the third circuit board  50  can be substantially the same as that for manufacturing the second circuit board  40 . That is, the fourth conductive wiring layer  502  can be obtained by etching a copper foil layer through the exposure and development process, and the third conductive portion  51  can also be obtained by defining a blind hole in the third base layer  501  and filling a conductive material therein. 
     In detail, a third copper-clad laminate (not shown) is provided, which includes the third base layer  501  and a fourth copper foil layer (not shown) stacked together. The fourth copper foil layer is etched to form the fourth conductive wiring layer  502 . At least one third blind hole (not shown) is defined in the third copper-clad laminate, which passes through the third base layer  501 ; And the third circuit board  50  is obtained by filling each third blind hole with conductive material to form the third conductive portion  51  electrically connected to the fourth conductive wiring layer  502 . 
     Step S 10 , referring to  FIG. 9 , provides a fourth circuit board  60 . 
     The fourth circuit board  60  includes a fourth base layer  601  and a fifth conductive wiring layer  602 . The difference between the fifth conductive wiring layer  602  and the third conductive wiring layer  31  is that the fifth conductive wiring layer  602  includes at least one power line  311 , but does not include the signal line  312 , the control line  313 , the first ground lines, and the second ground line. 
     Step S 11 , a fifth circuit board  61  is provided. 
     The fifth circuit board  61  includes a fifth base layer  611  and a sixth conductive wiring layer  612 . The difference between the sixth conductive wiring layer  612  and the third conductive wiring layer  31  is that the sixth conductive wiring layer  612  includes at least one control line  313 , but does not include the signal line  312 , the power line  311 , the first ground lines, and the second ground line. 
     Step S 12 , a sixth circuit board  62  is provided. 
     The sixth circuit board  62  includes a sixth base layer  621  and a seventh conductive wiring layer  622 . In an embodiment, the seventh conductive wiring layer  622  is a ground shielding layer. 
     Step S 13 , referring to  FIG. 10 , the first circuit board  20 , the second circuit board  40 , two third circuit boards  50 , the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  are stacked in that order and pressed, so that the second conductive portion  32  corresponds to the second conductive wiring layer  105 , the third conductive portion  51  corresponds to the third conductive wiring layer  31 , and each of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  corresponds to the first region  41 . Then, an intermediate body  70  is obtained. 
     The first conductive wiring layer  104  and the fourth conductive wiring layer  502  are disposed at the outermost of the intermediate body  70 . The fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  are disposed on the fourth conductive wiring layer  502 . 
     Furthermore, the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  have the same width. The first circuit board  20 , the second circuit board  40 , and the third circuit boards  50  have the same width. Since each of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  corresponds to  41  described in the first region  41 , the width of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  is less than the width of the first circuit board  20 , the second circuit board  40 , and the third circuit boards  50 . 
     In other embodiments, the order for stacking the fourth circuit board  60  and the fifth circuit board  61  may be interchanged. 
     After pressing, the first circuit board  20 , the second circuit board  40 , the third circuit boards  50 , the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  are connected to each other. 
     Since the width of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  is less than the width of the third circuit boards  50 , a stepped portion  71  is formed on the third circuit boards  50  with respect to the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61 . 
     Step S 14 , referring to  FIG. 11 , a solder mask layer  80  is formed on the intermediate body  70  to obtain the circuit board for transmitting high-frequency signal  100 . 
     The solder mask layer  80  covers the first circuit board  20  and the fifth circuit board  61 . The solder mask layer  80  also covers the stepped portion  71  (that is, the solder mask layer  80  covers the sidewalls of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61 , and an outer surface of the third circuit board  50  not covered by the fifth circuit board  61 ). In an embodiment, an adhesive layer  81  is formed on the intermediate body  70  before forming the solder mask layer  80 . Then, the solder mask  80  is formed on the adhesive layer  81 . The solder mask layer  80  can protect the first circuit board  20 , the third circuit boards  50 , and the fifth circuit board  61 . 
     The solder mask layer  80  can be made of a solder mask ink such as green oil. The adhesive layer  81  can be mad of polyethylene. 
     Each of the fourth circuit board  60 , the fifth circuit board  61 , and the sixth circuit board  62  also has a conductive portion (not shown), so that the fourth circuit board  60 , the fifth circuit board  61 , the sixth circuit board  62 , the third circuit boards  50 , the second circuit board  40 , and the first circuit board  20  can be electrically connected to each other. 
     Step S 15 , the circuit board for transmitting high-frequency signal  100  is cut to form two terminal areas (not labeled) and a transmission line area (not labeled). 
     The transmission line area is disposed between the terminal areas. Each terminal area includes a portion of the circuit board for transmitting high-frequency signal  100  corresponding to the first region  41  and another portion of the circuit board  100  corresponding to the second region  42 . The transmission line area includes another portion of the circuit board for transmitting high-frequency signal  100  corresponding to the first region  41 . Each terminal areas can be connected to another electronic device (not shown). 
     In an embodiment, the first conductive portion  12 , the second conductive portion  32 , and the third conductive portion  51  are coaxial, which cooperatively form a conductive channel (not labeled). Each signal line  312  is disposed between two adjacent conductive channels. When at least two signal lines  312  are included, two adjacent signal lines  312  are separated by the conductive channel. In other embodiments, the first conductive portion  12 , the second conductive portion  32 , and the third conductive portion  51  may also be misaligned to each other to increase the flatness of the circuit board for transmitting high-frequency signal  100 . 
     Referring to  FIG. 11 , the present disclosure further provides a circuit board for transmitting high-frequency signal  100 , which includes a first circuit board  20 , a second circuit board  40 , a third circuit board  50 , a fourth circuit board  60 , a sixth circuit board  62 , a fifth circuit board  61 , and a solder mask layer  80 . 
     The first circuit board  20  includes a first conductive wiring layer  104 , a first base layer  102 , and a second conductive wiring layer  105  stack in that order. In an embodiment, the first base layer  102  is a flexible copper-clad laminate (FCCL). 
     The first base layer  102  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the first base layer  102  is made of polyimide. 
     At least one first conductive portion  12  is disposed in the first base layer  102 , which is electrically connected to the first conductive wiring layer  104  and the second conductive wiring layer  105 . The first conductive portion  12  can be made of a conductive paste (such as solder paste), metal (such as copper), etc. In an embodiment, the first conductive portion  12  is made of copper. The position and the number of the first conductive portion(s)  12  can be changed according to actual needs. 
     The second circuit board  40  is disposed on the second conductive wiring layer  105 . The second circuit board  40  includes a second base layer  301  and a third conductive wiring layer  31  stacked together. In an embodiment, the second base layer  301  is a flexible copper-clad laminate (FCCL). 
     The second base layer  301  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the second base layer  301  is made of polyimide. 
     At least one second conductive portion  32  is disposed in the second base layer  301 , which is electrically connected to the third conductive wiring layer  31 . The second conductive portion  32  corresponds to the second conductive wiring layer  105 . The second conductive portion  32  can be made of a conductive paste (such as solder paste), metal (such as copper), etc. In an embodiment, the second conductive portion  32  is made of conductive paste. The position and the number of the second conductive portion(s)  32  can be changed according to actual needs. 
     The third conductive wiring layer  31  includes at least one power line  311 , at least one signal line  312 , at least one control line  313 , at least two first ground lines (not label in the figures), and at least one second ground line (not label in the figures). The signal line  312  and the control line  313  are disposed on opposite sides of the power line  311 . The first ground lines are disposed on opposite sides of the signal line  312 . The second ground line is disposed on a side of the control line  313  away from the power line  311 . The control line  313  can transmit a control signal. 
     The second circuit board  40  is divided into a first region  41  containing the signal line  312  and a second region  42  besides the first region  41 . The power line  311  and the control line  313  are disposed in the second region  42 . 
     The third circuit board  50  is disposed on the third conductive wiring layer  31 . The third circuit board  50  includes a third base layer  501  and a fourth conductive wiring layer  502  stacked together. In an embodiment, the third base layer  501  is a flexible copper-clad laminate (FCCL). 
     The materials of the third base layer  501  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the third base layer  501  is made of polyimide. 
     At least one third conductive portion  51  is disposed in the third base layer  501 , which is electrically connected to the fourth conductive wiring layer  502 . The third conductive portion  51  corresponds to the third conductive wiring layer  31 . The third conductive portion  51  can be made of conductive paste (such as tin paste), metal (such as copper), etc. In an embodiment, the third conductive portion  51  is made of conductive paste. The position and the number of the third conductive portion(s)  51  can be changed according to actual needs. 
     The fourth circuit board  60  is disposed on the fourth conductive wiring layer  502  and corresponds to the first region  41 . The fourth circuit board  60  includes a fourth base layer  601  and a fifth conducting line layer  602 . The fifth conducting line layer  602  includes at least one power line  311  or at least one control line  313 . In an embodiment, the fourth base layer  601  is a flexible copper-clad laminate (FCCL). 
     The fourth base layer  601  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the fourth base layer  601  is made of polyimide. 
     The sixth circuit board  62  is disposed on the fifth conductive wiring layer  602  and corresponds to the first region  41 . The sixth circuit board  62  includes a sixth base layer  621  and a seventh conductive wiring layer  622 . In an embodiment, the seventh conductive wiring layer  622  is a ground shielding layer. In an embodiment, the sixth base layer  621  is a flexible copper-clad laminate (FCCL). 
     The sixth base layer  621  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the sixth base layer  621  is made of polyimide. 
     The fifth circuit board  61  is disposed on the seventh conductive wiring layer  622  and corresponds to the first region  41 . The fifth circuit board  61  includes a fifth base layer  611  and a sixth conductive wiring layer  612 . The sixth conductive wiring layer  612  includes at least one power line  311  or at least one control line  313 . In an embodiment, the fifth base layer  611  is a flexible copper-clad laminate (FCCL). 
     The fifth base layer  611  can be made of a resin selected from a group consisting of liquid crystal polymer (LCP), polyphenylene sulfide (PPS), poly tetra fluoroethylene (PTFE), epoxy resin, polypropylene (PP), BT resin, polyphenylene oxide (PPO), polypropylene (PP), polyimide (PI), perfluoroalkoxy, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN). In an embodiment, the fifth base layer  611  is made of polyimide. 
     Furthermore, the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  have the same width. The first circuit board  20 , the second circuit board  40  and the third circuit board  50  have the same width. Since each of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  corresponds to  41  described in the first region  41 , the width of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61  is less than the width of the first circuit board  20 , the second circuit board  40 , and the third circuit board  50 . 
     In other embodiments, the positions of the fourth circuit board  60  and the fifth circuit board  61  may be interchanged. That is, the fifth circuit board  61  is disposed on the fourth conductive wiring layer  502 , the sixth circuit board  62  is disposed on the sixth conductive wiring layer  612 , and the fourth circuit board  60  is disposed on the seventh conductive wiring layer  622 . 
     Since the width of the fourth circuit board  60 , the sixth circuit board  62  and the fifth circuit board  61  is less than the width of the third circuit board  50 , a stepped portion  71  is formed on the third circuit board  50  with respect to the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61 . 
     The solder mask layer  80  covers the first circuit board  20  and the fifth circuit board  61 . The solder mask layer  80  also covers the stepped portion  71  (that is, the solder mask layer  80  covers the sidewalls of the fourth circuit board  60 , the sixth circuit board  62 , and the fifth circuit board  61 , and an outer surface of the third circuit board  50  not covered by the fifth circuit board  61 ). In an embodiment, an adhesive layer  81  is formed on the intermediate body  70  before forming the solder mask layer  80 . Then, the solder mask  80  is formed on the adhesive layer  81 . The solder mask layer  80  can protect the first circuit board  20 , the third circuit boards  50 , and the fifth circuit board  61 . The solder mask layer  80  can be made of a solder mask ink such as green oil. The adhesive layer  81  can be mad of polyethylene. 
     Each of the fourth circuit board  60 , the fifth circuit board  61 , and the sixth circuit board  62  also has a conductive portion (not shown), so that the fourth circuit board  60 , the fifth circuit board  61 , the sixth circuit board  62 , the third circuit boards  50 , the second circuit board  40 , and the first circuit board  20  can be electrically connected to each other. 
     The circuit board for transmitting high-frequency signal  100  includes two terminal areas (not labeled) and a transmission line area (not labeled) between the terminal areas. Each terminal area includes a portion of the circuit board for transmitting high-frequency signal  100  corresponding to the first region  41  and another portion of the circuit board  100  corresponding to the second region  42 . The transmission line area includes another portion of the circuit board for transmitting high-frequency signal  100  corresponding to the first region  41 . The terminal area can be connected to another electronic device (not shown). 
     In an embodiment, the first conductive portion  12 , the second conductive portion  32 , and the third conductive portion  51  are coaxial, which cooperatively form a conductive channel (not labeled). Each signal line  312  is disposed between two adjacent conductive channels. When at least two signal lines  312  are included, two adjacent signal lines  312  are separated by the conductive channel. In other embodiments, the first conductive portion  12 , the second conductive portion  32 , and the third conductive portion  51  may also be misaligned to each other to increase the flatness of the circuit board for transmitting high-frequency signal  100 . 
     In the present disclosure, the power line  311  and the control line  313  in the transmission line area of the circuit board for transmitting high-frequency signal  100  are vertically disposed above the signal line  312 , thereby preventing the power line  311 , the control line  313 , and the signal line  312  from being on a same horizontal position. Thus, the width of the transmission line area can be reduced. In addition, the power line  311  and the control line  313  are separated arranged, that is, the power line  311  and the control line  313  are isolated from each other by the seventh conductive wiring layer  622 , thereby avoiding the mutual interference between the power line  311  and the control line  313 , thus improve the signal transmission quality. 
     The embodiments shown and described above are only examples. Changes may be made in the detail within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will therefore be appreciated that the embodiments described above may be modified within the scope of the claims.