Abstract:
A printed circuit board and a forming method for forming the printed circuit board are disclosed. The printed circuit board includes a substrate and a conductive layer. The substrate includes a through hole, wherein one side of the through hole of the substrate corresponds to a first diameter, and the other side of the through hole of the substrate corresponds to a second diameter. The second diameter is greater than the first diameter. The conductive layer is placed on the inner surface of the through hole for electrically connecting the two sides of the substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a printed circuit board, and more specifically, to a printed circuit board having a via and a forming method thereof.  
         [0003]     2. Description of the Prior Art  
         [0004]     Printed circuit boards are necessary components in the electronics industry, which can be applied to electronic products&#39; motherboards for mounting other electronic components and providing wires to be utilized by other electronic components. Alternatively, a printed circuit board can be an adapter of a semi-product and mount the semi-product on a motherboard. Processing steps of a printed circuit board according to a related art include drilling, electroplating, wire etching, pressing, anti-soldering, tin-emitting etc. When a printed circuit board is utilized as an adapter, an application method of it is to drill and electroplate the adapter to form a via which is electrically connected between circuits on the front of the adapter and circuits on the back of the adapter. The front of the adapter is utilized for installing an application circuit, and the back of the adaptor adsorbs solder by using the via, in order for the application circuit to be mounted on the motherboard. In this way, the application circuit on the front of the adapter can be connected to circuit(s) on the motherboard using the via.  
         [0005]     Sometimes, for protecting the application circuit from being oxidized or being destroyed by external factors, a method well known in the art is to packet and mold the application circuit. In order to prevent the compound(s) utilized during the molding process from flowing through the via to the back of the printed circuit board, it is necessary to manually seal a terminal of the via on the front of the printed circuit board with insulating stickers. Furthermore, when mounting the adapter on the motherboard, an insulating sticker can prevent the solder from flowing from the back of the printed circuit board to the front of the printed circuit board, so the application circuit will not short circuit. However, when the size of the via becomes very small, it is difficult to perform the above-mentioned operations manually. A method according to another related art is to fill a terminal of the via on the front of the printed circuit board with a blocking material, such as a solder mask, and at the same time, keep a terminal of the via on the back of the printed circuit board not filled, to adsorb the solder. However, the present method still has some limitations; for example, when the diameter of the via is too small, the terminal of the via on the back of the printed circuit board may not adsorb sufficient solder; when the diameter of the via is too large, the blocking material may sink causing the front of the printed circuit board to not be smooth, and furthermore, the filled blocking material may not bear the force from the molding process, causing the via to break and the compound to flow.  
       SUMMARY OF THE INVENTION  
       [0006]     One of the objectives of the claimed invention is therefore to provide a printed circuit board and a forming method in order to resolve the above-mentioned problems.  
         [0007]     According to the claimed invention, a printed circuit board (PCB) is disclosed. The printed circuit board comprises a substrate and a conductive layer. The substrate comprises a through hole. One side of the through hole of the substrate corresponds to a first diameter, and the other side of the through hole of the substrate corresponds to a second diameter, wherein the second diameter is greater than the first diameter. The conductive layer is placed on the surface of the through hole for electrically connecting the two sides of the substrate.  
         [0008]     According to the claimed invention, a printed circuit board is disclosed. The printed circuit board comprises a substrate and a conductive layer. The substrate comprises a first surface, a second surface and a through hole. The through hole comprises a first part corresponding to a first diameter, wherein a first terminal of the first part is connected to the first surface; a second part corresponding to a second diameter, wherein a second terminal of the first part is connected to a first terminal of the second part, and a second terminal of the second part is connected to the second surface. The second diameter is greater than the first diameter. The conductive layer is placed on the inner surface of the through hole for connecting the first and the second surfaces.  
         [0009]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a cross-section diagram of a printed circuit board according to an embodiment of the present invention.  
         [0011]      FIG. 2  is an enlarged diagram of a through hole shown in  FIG. 1 .  
         [0012]      FIG. 3  is a front view of the printed circuit board shown in  FIG. 1 .  
         [0013]      FIG. 4  is a back view diagram of the printed circuit board shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0014]     Please refer to  FIG. 1 .  FIG. 1  is a cross-section diagram of a printed circuit board  10 , according to an embodiment of the present invention. In the present embodiment, the printed circuit board  10  comprises a substrate  12  and a conductive layer. The substrate  12  comprises surfaces S 1 , S 2  and a plurality of through holes  22 ,  24 ,  26 ,  28  and  32 . The through holes  22 ,  24 ,  26 ,  28  and  32  can be divided into two parts, upper parts  22   a ,  24   a ,  26   a ,  28   a , and  32   a  respectively, and lower parts  22   b ,  24   b ,  26   b ,  28   b , and  32   b  respectively, according to diameters of the through holes  22 ,  24 ,  26 ,  28  and  32 . Also, in the present embodiment, the upper parts  22   a ,  24   a ,  26   a ,  28   a ,  32   a  of the through holes  22 ,  24 ,  26 ,  28 ,  32  have the same diameters R 1  and the same depths D 1 , and the lower parts  22   b ,  24   b ,  26   b ,  28   b ,  32   b  of the through holes  22 ,  24 ,  26 ,  28 ,  32  have the same diameters R 2  and the same depths D 2 , wherein the diameter R 2  is greater than the diameter R 1 . The detailed description of the functions and forms of the conductive layer is included in the following paragraph.  
         [0015]     Please refer to  FIG. 2 .  FIG. 2  is an enlarged diagram of the through hole  22  shown in  FIG. 1 . A conductive layer  42  is placed on the inner surface of the through hole  22  and parts of the through hole  22  connected to the surfaces S 1 , S 2 , to electrically connect the surfaces S 1  and S 2 . The material of the conductive layer  42  can be copper or gold. Therefore, a via with electric properties is formed by the through hole  22  and the conductive layer  42 . In the present embodiment, the conductive layer  42  is generated by electroplating. The upper part  22   a  of the through hole  22  is utilized for being filled with a blocking material  44 , and the lower part  22   b  of the through hole  22  is not filled in order to allow adsorption of a metal conductor in a liquid state therein. After the metal conductor in the liquid state cools, the metal conductor is attached onto the conductive layer  42  in order to mount the printed circuit board  10  on an electronic device. In the present embodiment, the blocking material  44  is a solder mask utilized for separating the surface S 1  from the surface S 2  and thus preventing any fluid materials from flowing from the surface S 1  to the surface S 2  or flowing from the surface S 2  to the surface S 1 . In the present embodiment, the diameter R 1  of the upper part  22   a  is 0.25 cm (centimeter), and the depth D 1  of the upper part  22   a  is 0.1 cm. The diameter R 2  of the lower part  22   b  is 0.5 cm, and the depth D 2  of the lower part  22   b  is 0.7 cm. It should be noted that if the diameter R 1  of the upper part  22   a  is too large, the blocking material  44  may sink and therefore the blocking effect may be affected. If the diameter R 2  of the lower part  22   b  is too small or the depth D 2  is not deep enough, the effect of the lower part  22   b  adsorbing the above-mentioned metal conductor may be affected. In addition, a terminal of the through hole  22  on the surface S 1  is further covered by an anti-soldering material  46  to prevent the through hole  22  and a circuit (not shown) installed on the surface S 1  from short circuiting. Please note that the anti-soldering material  46  utilized in the present embodiment is also the above-mentioned solder mask utilized to simplify the producing process; however, the anti-soldering material  46  and the blocking material  44  in the present invention can be implemented with different materials and are not limited to the materials utilized in the present embodiment. Moreover, a plurality of vias can be formed by using the through holes  24 ,  26 ,  28 ,  32  in conjunction with other conductive layers, and since the structures of the through holes  24 ,  26 ,  28 ,  32  are similar to the through hole  22 , a description of the structures thereof is omitted here for the sake of brevity.  
         [0016]     Please refer to  FIG. 3 .  FIG. 3  is a front view of the printed circuit board  10  shown in  FIG. 1 . The metal loops  92 ,  94 ,  96 ,  98 ,  102  shown in  FIG. 3  are parts of the conductive layer  42  on the surface S 1  shown in  FIG. 2  and are utilized for connecting the surrounding circuits. The front of the printed circuit board  10  (the surface S 1  shown in  FIG. 1 ) is utilized for having an application circuit placed on it. For this purpose, the surface S 1  comprises a plurality of metal pads  62 ,  64  and a plurality of printed conducting wires  66 ,  68 ,  72 ,  74 ,  76 ,  78 ,  82 ,  84 ,  86  and  88 . The metal pads  62 ,  64  are utilized for mounting electronic components of the above-mentioned application circuit, and the printed conducting wires  66 ,  68 ,  72 ,  74 ,  76 ,  78 ,  82 ,  84 ,  86 ,  88  are utilized for electrically connecting the above-mentioned electronic components and the metal loops  92 ,  94 ,  96 ,  98 ,  102  (vias corresponding to the through holes  22 ,  24 ,  26 ,  28 ,  32  respectively) to form the application circuit. In the present embodiment, after installing the application circuit, the printed circuit board  10  has to perform a molding process well known in the art. The upper parts  22   a ,  24   a ,  26   a ,  28   a ,  32   a  of the through holes  22 ,  24 ,  26 ,  28 ,  32  are filled with the blocking material, and therefore, although the compound utilized during the molding process is a fluid, the compound will not flow to the back of the printed circuit board  10  (the surface S 2  shown in  FIG. 1 ) through the through holes  22 ,  24 ,  26 ,  28 ,  32 , keeping the printed circuit board  10  clean.  
         [0017]     Please refer to  FIG. 4 .  FIG. 4  is a back view diagram of the printed circuit board  10  shown in  FIG. 1 . The metal loops  112 ,  114 ,  116 ,  118  and  122  shown in  FIG. 4  are parts of the conductive layer  42  on the surface S 2  shown in  FIG. 2 . In the present embodiment, the back of the printed circuit board  10  is utilized for being connected to a motherboard or other printed circuit boards of an electronic device. Therefore, the lower parts  22   b ,  24   b ,  26   b ,  28   b ,  32   b  of the through holes  22 ,  24 ,  26 ,  28 ,  32  have to remain open in order to adsorb a metal conductor in a liquid state (not shown). Since the upper parts  22   a ,  24   a ,  26   a ,  28   a ,  32   a  of the through holes  22 ,  24 ,  26 ,  28 ,  32  are filled with the blocking material, the solder will not flow to the front of the printed circuit board  10  through the through holes  22 ,  24 ,  26 ,  28 ,  32 , preventing the application circuit on the front of the printed circuit board  10  from short circuiting. It should be noted that the diameters of the upper parts and the lower parts of the through holes may change according to characteristics of the blocking material or the metal conductor and are not limited to those in the above-mentioned embodiment. The through hole utilized in the present invention can even be a cone through hole. Any through hole with different diameters is covered in the present invention.  
         [0018]     In contrast to the related art, the present invention installs a through hole with different diameters on the printed circuit board. Hence, the diameters of the through hole can be designed according to manufacturing or processing requirements of different layers of the printed circuit board.  
         [0019]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.