Abstract:
A printed circuit board includes: an insulating substrate, and a patterned conductive layer having a signal line and fixed on the insulating substrate, where signal lines on different planes of the patterned conductive layer are electrically connected to a via hole through a pad. An inner wall of the via hole is formed of a conductive bar and an insulating bar that penetrate the via hole; the pad is at an edge of the via hole and is connected to the conductive bar; the pad has an unclosed structure. In the printed circuit board according to the present invention, the size of the pad is significantly reduced by arranging the pad at partial edge of the via hole, thereby effectively improving a layout density of the patterned conductive layer, hence reducing the size of the printed circuit board, and satisfying the market demand for smaller electronic products.

Description:
BACKGROUND OF THE PRESENT INVENTION 
     1. Field of Invention The present invention relates to a printed circuit board. 
     2. Description of Related Arts 
     The printed circuit board employs an insulating board as a base material, and is cut into a certain size. At least one patterned conductive layer is attached onto the board and holes are arranged thereon (for example, component holes, fastening holes, and plated-through holes). The board is used for replacing the base on which electronic devices are mounted, and for connecting the electronic elements. This type of board is made by means of electronic lithography, and is therefore referred to as a printed circuit board. The printed circuit board is an important electronic component, and supports electronic devices. 
     Electronic products are becoming smaller in size and have more functions, and the size of the printed circuit board is also becoming smaller. However, the number of via holes and the interference between signal lines have constantly restricted the size reduction of the printed circuit board; hence, it is difficult to make a breakthrough in substantial size reduction of the printed circuit board. For example, if the pad at the edge of the via hole is too close to the signal line arranged near the pad, interference will occur. So, a certain distance should be maintained between the via hole and the signal line. For another example, the via hole of the printed circuit board is closely related to the circuit connections of the electronic devices arranged on the printed circuit board and/or the circuit connections among multiple layers of printed circuit boards. Therefore, each circuit connection requires a via hole; as a result, the size and the number of via holes further restrict the size reduction of the printed circuit board. 
     Therefore, to improve the via hole so as to effectively reduce the size of the printed circuit board is a problem that needs to be solved by persons skilled in the art. 
     SUMMARY OF THE PRESENT INVENTION 
     Accordingly, an object of the present invention is to provide a printed circuit board. The printed circuit board comprises an insulating substrate, and a patterned conductive layer having a signal line and fixed on the insulating substrate, where signal lines on different planes of the patterned conductive layer are electrically connected to a via hole through a pad; an inner wall of the via hole is formed of a conductive bar and an insulating bar that penetrate the via hole; the pad is at an edge of the via hole and is connected to the conductive bar; the pad has an unclosed structure. It can be considered as partial plated through hole/via. 
     Preferably, the via hole has one or more conductive bars therein, and one or more pads are disposed at the edge of the via hole; two adjacent conductive bars are spaced by the insulating bar; and two adjacent pads are insulated from each other. 
     Preferably, the number of the conductive bars in the via hole is two, and the two conductive bars are symmetrically disposed with a central axis of the via hole as a symmetry axis. 
     Preferably, one conductive bar in the via hole is connected to one signal line of a differential signal line pair through the pad connected thereto; another conductive bar in the via hole is connected to another signal line of the differential signal line pair through the pad connected thereto. 
     Preferably, one conductive bar in the via hole is connected to the signal line through the pad connected thereto; another conductive bar in the via hole is connected to a ground signal line through the pad connected thereto. 
     Preferably, a distance between the pad at the edge of the via hole and the signal line arranged near the via hole is greater than a distance between a part of the edge of the via hole without pad and the signal line arranged near the via hole. 
     Preferably, one differential signal line in a differential signal line pair is connected to the conductive bar in one via hole through the pad, and another differential signal line is connected to the conductive bar in another via hole through the pad; one differential signal line and the conductive bar connected thereto are symmetrical to the other differential signal line and the conductive bar connected thereto; each of the two via holes further has another conductive bar connected to a ground signal line. 
     Preferably, the conductive bar occupies an area from 20° to 160° of the inner wall of the via hole. 
     Preferably, the pad occupies an area from 20° to 160° of the edge of the via hole. 
     As described above, the printed circuit board having a via hole according to the present invention has the following beneficial effects: the signal line and the conductive bar on the inner wall of the via hole are connected by the pad arranged at a part of the edge of the via hole, so the space occupied by the pad and the conductive bar is effectively reduced, thereby reducing the size of the printed circuit board. In addition, multiple conductive bars arranged on the inner wall of the via hole can share one via hole to transmit various signals; therefore, the problem in the prior art that one via hole can only transmit one signal is solved; the number of via holes is effectively decreased, and the size of the printed circuit board is further reduced. Furthermore, in the present invention, a distance between the pad at the edge of the via hole and the signal line arranged near the via hole is greater than a distance between a part of the edge of the via hole without pad and the signal line arranged near the via hole, so the distance between signal lines that transmit different signals in the patterned conductive layer is significantly improved. The distance between the signal lines is increased through the width of the via hole, so that the crosstalk between different signals is reduced, and the signal transmission quality is improved. In addition, in the present invention, when one differential signal line pair needs to transmit signals with the patterned conductive layer of other planes through a via hole, the signal line pair is respectively connected to two conductive bars on the inner wall of a via hole, thereby effectively reducing the parallel variation between the signal lines and improving the transmission quality of differential signals. Further, in the present invention, the signal line and a ground signal line on the circuit thereof are respectively connected two conductive bars on the inner wall of a via hole, so the signal is close to a ground return path as much as possible, and the signal loss is reduced; meanwhile, the impedance continuity of high speed signals is ensured, and when the high speed signal reaches a layer transition position of the via hole, signal reflection at an impedance discontinuity point is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a patterned conductive layer of a printed circuit board in the prior art. 
         FIG. 2  is another view of a patterned conductive layer of a printed circuit board in the prior art. 
         FIG. 3  is still another view of a patterned conductive layer of a printed circuit board in the prior art. 
         FIG. 4  is a schematic structural view of a printed circuit board consistent with the present invention. 
         FIG. 5  is a schematic structural view of an embodiment of an inner wall of a via hole of a printed circuit board consistent with the present invention. 
         FIG. 6  is a schematic structural view of another embodiment of a printed circuit board consistent with the present invention. 
         FIG. 7  is a schematic structural view of still another embodiment of a printed circuit board consistent with the present invention. 
         FIG. 8  is a schematic structural view of still another embodiment of a printed circuit board consistent with the present invention. 
         FIG. 9  is a schematic structural view of still another embodiment of a printed circuit board consistent with the present invention. 
     
    
    
     LIST OF THE NUMERALS 
     
         
           1 . printed circuit board 
           11 . insulating substrate 
           12 ,  12 F,  12 A,  12 B,  12 C,  12 D,  12 E. via hole 
           13 ,  13 F 1 ,  13 F 2 ,  13 F 3 ,  13 A 1 ,  13 A 2 ,  13 B 1 ,  13 B 2 ,  13 C,  13 D 1 ,  13 D 2 ,  13 E 1 ,  13 E 2 . conductive bar 
           14 ,  14 F 1 ,  14 F 2 ,  14 F 3 . insulating bar 
           15 . patterned conductive layer 
           16 ,  16 A 1 ,  16 A 2 ,  16 B 1 ,  16 C 1 ,  16 C 2 ,  16 D 1 ,  16 D 2 ,  16 E 1 ,  16 E 2 . signal line 
           17 ,  17 A 1 ,  17 A 2 ,  17 B 1 ,  17 B 2 ,  17 C 1 ,  17 C 2 ,  17 D 1 ,  17 D 2 ,  17 E 1 ,  17 E 2 . pad 
       
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The implementation manners of the present invention are described in detail through specific embodiments. Persons skilled in the art could easily understand other advantages and efficacies of the present invention according to the content disclosed in the specification. The present invention may also be implemented or applied in other specific implementation manners. Modifications or variations can be made on details of the specification based on different points of views and without departing from the spirit of the present invention. 
     Referring to  FIG. 4  to  FIG. 9 , it should be noted that the drawings provided in the embodiment are merely schematic representations of basic ideas of the present invention. The drawings only show components related to the present invention, and are not drawn according to the number, shapes, and sizes of components in practical implementations. The patterns, number, and ratio of the components in practical implementation may vary randomly, and the component layout pattern may be more complex. 
     As shown in  FIG. 4 , a printed circuit board  1  comprises a patterned conductive layer  15  and an insulating substrate  11 . 
     The insulating substrate  11  has a via hole  12 . The insulating substrate  11  is any substrate made of an insulating material and applicable to the printed circuit board  1 , which comprises but is not limited to a rigid insulating substrate  11 , a flexible insulating substrate  11 , and the like. The via hole  12  is used for forming a blind hole, a buried hole, or a through hole, etc. The via hole  12  may be in any shape, which comprises but is not limited to a round shape, a square shape, or a T shape. 
     An inner wall of the via hole  12  is formed of a conductive bar  13  and an insulating bar  14  that penetrate the via hole  12 . The material of the conductive bar  13  comprises but is not limited to copper foil. The insulating bar  14  is preferably an inner side wall of the insulating substrate  11 . More preferably, the conductive bar  13  occupies an area from 20° to 160° of the inner wall of the via hole  12 . Preferably, the via hole  12  has one or more conductive bars  13  therein, and two adjacent conductive bars  13  are spaced by the insulating bar  14 . For example, as shown in  FIG. 5 , three conductive bars  13 F 1 ,  13 F 2 , and  13 F 3  are arranged on the inner wall of the via hole  12 F, where the conductive bar  13 F 1  and the conductive bar  13 F 2  are spaced by an insulating bar  14 F 1 ; the conductive bar  13 F 2  and the conductive bar  13 F 3  are spaced by an insulating bar  14 F 2 ; the conductive bar  13 F 3  and the conductive bar  13 F 1  are spaced by an insulating bar  14 F 3 . 
     Preferably, the via hole  12  has two conductive bars  13  therein, and the two conductive bars  13  are symmetrically disposed with the central axis of the via hole  12  as a symmetry axis. 
     Manners that the inner wall of the via hole  12  is formed of the conductive bar  13  and the insulating bar  14  which penetrate the via hole  12  comprise but are not limited to: 1) plating copper foil onto the inner wall of the via hole  12  by using an electroplating tool, and then removing partial conductive material through chemical etching, so as to obtain the structure in which the conductive bar  13  and the insulating bar  14  penetrate the via hole  12 ; and 2) electroplating a conductive material at a designated position on the inner wall of the via hole  12  by using a mould, so as to obtain the structure in which the conductive bar  13  and the insulating bar  14  penetrate the via hole  12 . 
     The patterned conductive layer  15  has signal lines  16  and pads  17 , and is fixed on the insulating substrate  11 . The patterned conductive layer  15  comprises any conductive layer that is made of a metal material based on a preset circuit layout pattern, and is capable of providing electric power or signals for devices arranged on the printed circuit board  1 , where the material of the patterned conductive layer  15  comprises but is not limited to copper foil. 
     The signal line  16  is used for transmitting high speed signals, differential signals, ground signals, and the like, where the high speed signal refers to a signal whose transmission delay is less than ⅙ of rise time thereof, and the high speed signal comprises but is not limited to a double data rate (DDR) signal and a universal serial bus (USB) signal. 
     The pad  17  is located at the edge of the via hole  12  and is connected to the conductive bar  13 . The pad  17  has an unclosed structure. The shape of the pad  17  comprises but is not limited to: a C shape, a U shape, an L shape, and an arc shape. Preferably, the pad  17  occupies an area from 20° to 160° of the edge of the via hole  12 . The width of the pad  17  and the conductive bar  16  may be the same or different. The number of the pads  17  depends on the number of the conductive bars  13 . When the number of the pads  17  is more than one, two adjacent pads  17  are insulated from each other. 
     It should be noted that, persons skilled in the art should understand that the patterned conductive layer  15  may be fixed on one side of the insulating substrate  11 , and may also be fixed on both sides of the insulating substrate  11 . Different planes of the patterned conductive layer  15  are insulated from each other by the insulating substrate  11 . 
     It should be also noted that, persons skilled in the art should understand that the manner for fixing the patterned conductive layer  15  on the insulating substrate  11  is not elaborated herein. For example, a metal material is plated on the insulating substrate  11  through electroplating and based on a preset circuit layout pattern, to obtain the patterned conductive layer  15 . For another example, a metal material is first plated all over the insulating substrate  11 , and then partial metal material is removed through chemical etching and based on a preset circuit layout pattern until the insulating substrate  11  is exposed, to obtain a conductive layer consistent with the preset pattern. 
     The printed circuit board  1  is described in detail below with reference to the examples shown in  FIG. 6  to  FIG. 9 . 
     As a preferable solution, two conductive bars in the via hole  12  are respectively connected to a differential signal line pair through two pads. 
     As shown in  FIG. 6 , the via hole  12 A has a conductive bar  13 A 1  and a conductive bar  13 A 2  therein; a signal line  16 A 1  and a signal line  16 A 2  form a differential signal line pair. The pad  17 A 1  and the pad  17 A 2  are connected to the conductive bar  13 A 1  and the conductive bar  13 A 2 , wherein the signal line  16 A 1  is connected to the pad  17 A 1 , and the signal line  16 A 2  is connected to the pad  17 A 2 . The signal line  16 A 1  and the conductive bar  13 A 1  are symmetrical to the signal line  16 A 2  and the conductive bar  13 A 2  about the central axis of the via hole  12 A. 
     It should be noted that persons skilled in the art should understand that the positions of the conductive bar  13 A 1  and the conductive bar  13 A 2  are merely an example but are not intended to limit the present invention. 
     As another preferable solution, one conductive bar in the via hole is connected to a signal line through the pad connected thereto; another conductive bar in the via hole is connected to a ground signal line through the pad connected thereto. 
       FIG. 7  shows a conductive bar  13 B 1  and a conductive bar  13 B 2  in the via hole  12 B; a signal line  16 B 1  is used for transmitting high speed signals, and a signal line  16 B 2  is a ground signal line (GND) close to the signal line  16 B 1 . The signal line  16 B 1  is connected to the conductive bar  13 B 1  through a pad  17 B 1 , and the signal line  16 B 2  is connected to the conductive bar  13 B 2  through a pad  17 B 2 . Signals are transmitted to signal lines on the patterned conductive layers  15  of different planes. 
     As another preferable solution, a distance between the pad at the edge of the via hole and the signal line arranged near the via hole is greater than a distance between a part of the edge of the via hole without pad and the signal line arranged near the via hole. 
     As shown in  FIG. 8 , a signal line  16 C 1  and a signal line  16 C 2  are arranged near the via hole  12 C. The signal line  16 C 1  is connected to a conductive bar  13 C through a pad  17 C, so as to reduce the crosstalk between the signals transmitted by the signal line  16 C 1  and the signal line  16 C 2 ; a distance between the pad  17 C and the signal line  16 C 2  is greater than a distance between a part of the edge of the via hole  12 C without pad and the signal line  16 C 2 . 
     As another preferable solution, one differential signal line in a differential signal line pair is connected to the conductive bar in one via hole through the pad, and another differential signal line is connected to the conductive bar in another via hole through the pad; wherein one differential signal line and the conductive bar connected thereto are symmetrical to the other differential signal line and the conductive bar connected thereto; each of the two via holes further has another conductive bar connected to a ground signal line. 
     As shown in  FIG. 9 , a via hole  12 D has a conductive bar  13 D 1  and a conductive bar  13 D 2  therein. A via hole  12 E has a conductive bar  13 E 1  and a conductive bar  13 E 2  therein. A signal line  16 D 2  and a signal line  16 E 1  form a differential signal line pair  16 ; a signal line  16 D 1  and a signal line  16 E 2  are respectively ground signal lines (GND) that form the circuits of the signal line  16 D 2  and the signal line  16 E 1 . The signal line  16 D 1  is connected to the conductive bar  13 D 1 , the signal line  16 D 2  is connected to the conductive bar  13 D 2 , the signal line  16 E 1  is connected to the conductive bar  13 E 1 , and the signal line  16 E 2  is connected to the conductive bar  13 E 2 . The signal line  16 D 2  and the conductive bar  13 D 2  are symmetrical to the signal line  16 E 1  and the conductive bar  13 E 1  about the central axis of the via hole  12 D. 
     It should be noted that, persons skilled in the art should understand that the number and positions of the conductive bars on the inner wall of the via hole shown in  FIG. 4  to  FIG. 9  are merely an example, and are not intended to limit the present invention. 
     In conclusion, in the printed circuit board according to the present invention, the space occupied by the pad and the conductive bar is effectively reduced by arranging the pad at partial edge of the via hole to connect the signal line and the conductive bar on the inner wall of the via hole, thereby reducing the size of the printed circuit board. 
     In addition, multiple conductive bars arranged on the inner wall of the via hole can share one via hole to transmit various signals; therefore, the problem in the prior art that one via hole can only transmit one signal is solved; the number of via holes is effectively reduced, and the size of the printed circuit board is further reduced. 
     Furthermore, compared with  FIG. 1 , in the present invention, a distance between the pad at the edge of the via hole and the signal line arranged near the via hole is greater than a distance between a part of the edge of the via hole without pad and the signal line arranged near the via hole, so the distance between signal lines that transmit different signals in the patterned conductive layer is significantly improved. The distance between the signal lines is increased through the width of the via hole, so that the crosstalk between different signals is reduced, and the signal transmission quality is improved. 
     In addition, compared with  FIG. 2  and  FIG. 3 , in the present invention, when one differential signal line pair needs to transmit signals with the patterned conductive layer of another plane through a via hole, the signal line pair is respectively connected to two conductive bars on the inner wall of a via hole, thereby effectively reducing the parallel variation between the signal lines and improving the transmission quality of differential signals. 
     Furthermore, compared with  FIG. 3 , in the present invention, the signal line and a ground signal line on the circuit thereof are respectively connected two conductive bars on the inner wall of a via hole, so the signal is close to a ground return path as much as possible, and the signal loss is decreased; meanwhile, the impedance continuity of high speed signals is ensured, and when the high speed signal reaches a layer transition position of the via hole, signal reflection at an impedance discontinuity point is reduced. 
     Therefore, the present invention overcomes disadvantages in the prior art and thus has a high industrial value. 
     The above embodiments are only to illustrate the principle and efficacies of the present invention, and are not intended to limit the scope of the present invention. All modifications and variations completed by those with ordinary skill in the art without departing from the spirit and scope of the present invention shall fall within the scope of the appended claims of the present invention.