Abstract:
A wiring board including a plated through hole provided on the wiring board, and an indicator provided around the plated through hole. The indicator indicating a processing state related to the plated through hole.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to and claims priority to Japanese Patent Application No. JP2007-057826 filed on Jul. 3, 2007 in the Japan Patent Office, and incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The embodiment relates to a wiring board. The embodiment is favorably adapted to a wiring board having a plated through hole connected to a conductive layer including a signal wiring. 
         [0004]    2. Description of the Related Art 
         [0005]    A multi-layer wiring board is employed as a wiring board so as to form a high-frequency circuit and a high-speed digital circuit and the like. The multi-layer wiring board includes a plated through hole so as to pull out the conductive layer including the signal wiring formed in the multi-layer wiring board to the surface of the board. 
         [0006]    In  FIG. 1 , a wiring board  1  is a multi-layer wiring board. A signal wiring  2  is formed with a conductive layer formed in the multi-layer wiring board. A plated thorough hole  3  is formed so as to be electrically connected to the signal wiring  2  in the wiring board  1 . The plated through hole  3  is formed by plating a conductive material such as copper onto the inner wall of a non-plated through hole. 
         [0007]    The signal wiring  2  is electrically connected to the plated through hole  3  by connecting to the plated through hole  3  near the center of the plated through hole  3 . The plated through hole  3  is formed in the wiring board  1  so as to pull out the signal wiring  2  to the surface of the wiring board  1 . An electronic signal is provided from the surface of the plated through hole  3 , and is transmitted to the signal wiring  2  near the center of the plated through hole  3 . The part where the signal wiring  2  is connected becomes a branch point of signal paths because the plated through hole  3  is extended below the part where the signal wiring  2  is connected. 
         [0008]    Signals transmitted through the plated through hole  3  are transmitted to the signal wiring  2  from the branch point, and some of the signals are also transmitted down below the plated through hole  3 . The downside of the branch point in the plated through hole  3  is a path in which signals are transmitted because the downside of the branch point is a conductive part, even though the downside of the branch point is not a signal path. As described above, in case a signal path is branched into two, the part which is not an original signal path is referred to as “stub”. 
         [0009]    A signal transmitted to a stub from the branch point is reflected at the bottom of the plated through hole  3 , and is then returned to the branch point. At that time, the signal transmitting from the branch point hits the reflected signal in the plated through hole. This may adversely affect a transmission characteristic of the signals. For example, signals such as high-frequency signals and high-speed digital signals are affected significantly. 
         [0010]    For example, Japanese Laid-open Patent Publication No. 2005-116945 is known as a method for removing a stub. Japanese Laid-open Patent Publication No. 2005-116945 discloses a technology for removing a plated through hole and a board nearby by drilling. Such technology may be referred to as “back-drilled method” or “stub countersunk method”. 
         [0011]    In the back-drilled method shown in  FIGS. 2A-2C , the part where the plated through hole  3  is formed is removed with a drill  4  whose diameter is slightly bigger than the diameter of the plated through hole  3 . As a result, the part corresponding to a stub in the plated through hole  3  is removed. The hole formed with the drill  4  is referred to as “back-drilled hole”.  FIG. 2A  shows that the plated through hole  3  is formed.  FIG. 2B  shows the process of drilling the plated through hole  3  with the drill  4 .  FIG. 2C  shows that a back-drilled hole  5  is formed by drilling the plated through hole  3 . 
         [0012]    However, if the central axis of the drill is positioned out of the central axis of the plated through hole, there is possibility that the part corresponding to a stub in the plated through hole remains even after the back-drilled processing. By checking the back-drilled hole visually, it is possible to determine whether or not the part corresponding to a stub in the plated through hole is completely removed. However, the determination is not made easily if the diameter of the plated through hole is small. 
       SUMMARY 
       [0013]    It is an object of the embodiment to at least partially solve the problem in the conventional technology. 
         [0014]    According to an aspect of an embodiment, a wiring board, comprising: a plated through hole provided on the wiring board; and an indicator provided around the plated through hole, indicating a processing state related to the plated through hole. 
         [0015]    According to another aspect of the embodiment, a method of manufacturing a wiring board, the method comprising: forming a plated through hole in the board; forming an indicator around the plated through hole on a surface of the board, the indicator can be checked visually; and removing a part of the plated through hole in the indicator together with the board nearby, for forming a processing hole. 
         [0016]    The above and other object, features, advantages and technical and industrial significance of this embodiment will be better understood by reading the following detailed description of presently preferred embodiments, when considered in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a cross-section diagram of a wiring board in which a plated through hole is formed. 
           [0018]      FIG. 2A ,  FIG. 2B  and  FIG. 2C  are diagrams showing a back-drilled method. 
           [0019]      FIG. 3  is a cross-section perspective view of a wiring board. 
           [0020]      FIG. 4  is a wiring board which is given a marking according to a first embodiment. 
           [0021]      FIG. 5A  and  FIG. 5B  are diagrams showing a position of a back-drilled hole according to a first embodiment. 
           [0022]      FIG. 6A ,  FIG. 6B  and  FIG. 6C  are diagrams showing a process of marking formation. 
           [0023]      FIG. 7  is a diagram showing that a land is entirely covered with a marking. 
           [0024]      FIG. 8  is a wiring board which is given marking according to a second embodiment. 
           [0025]      FIG. 9A  and  FIG. 9B  are diagrams showing a position of a back-drilled hole according to a second embodiment. 
           [0026]      FIG. 10A  and  FIG. 10B  are diagrams showing deformation examples of marking. 
           [0027]      FIG. 11  is a wiring board in which a land is formed according to a third embodiment. 
           [0028]      FIG. 12A  and  FIG. 12B  are diagrams showing a position of a back-drilled hole according to a third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    A wiring board of the present embodiment is explained using  FIG. 3 .  FIG. 3  discloses that an electronic component  12  is loaded on a mounting surface of a wiring board  10 . The wiring board  10  is comprised of a multi-layer wiring board  10   a  formed by laminating plastic such as glass epoxy and polyimide. A terminal  12   a  of the electronic component  12  is inserted into a plated through hole  14  formed in the multi-layer wiring board  10   a,  and is connected to the plated through hole  14  with an electrically conductive adhesive such as a solder. In the multi-layer wiring board  10   a,  a signal wiring  10   b  is formed and connected to the plated through hole  14 . 
         [0030]    The plated through hole  14  is formed by plating a conductive material, such as copper, onto the inner wall of a non-plated through hole formed in the multi-layer wiring board  10   a.    
         [0031]    A land  16  whose diameter is slightly bigger than the diameter of the plated through hole  14  is formed at both ends of the plated through hole  14 . The land  16  is formed both on the mounting surface and the back surface of the wiring board  10 , and the plating processing of the plated through hole  14  is performed at the same time. 
         [0032]    A solder resist  18  is applied to the back surface of the multi-layer wiring board  10   a,  leaving the part where the land  16  is exposed. A back-drilled hole  20  is formed so as to remove the part corresponding to a stub in the plated through hole  14  to which the high-frequency signal is transmitted. 
         [0033]    Next, a first embodiment is explained. According to the first embodiment, a marking is printed in the area where a back-drilled hole should be formed. The marking is surrounded by a solder resist  18  and has an annulus ring shape with a highlighted color. 
         [0034]      FIG. 4  discloses that a marking  30  having an annulus ring shape is printed in the area where the back-drilled hole  20  should be formed. The marking  30  operating as an indicator is provided to check visually the position of the back-drilled hole  20  after the back-drilled hole  20  is formed. In  FIG. 4 , the inside of the dotted line circle is the area where the back-drilled hole  20  should be formed. This area is referred to as “countersunk area”. The dotted line circle showing the countersunk area is presented to explain the present embodiment for convenience sake. Thus, the dotted line circle is actually not drawn on top of the wiring board  10 A. The dotted line circle showing the countersunk area has almost the same shape as the external diameter of the back-drilled hole  20 . However, the presented dotted line circle is slightly bigger than the external diameter of the back-drilled hole  20  for convenience sake of drawing. 
         [0035]    The marking  30  is a printed part having an annulus ring shape whose external diameter is slightly smaller than the countersunk area and whose inner diameter is bigger than the inner diameter of the plated through hole  14 . The marking  30  is an indicator in which coloring materials such as color ink and colored resin are printed into an annulus ring shaped pattern included in the countersunk area. 
         [0036]    The solder resist  18  is applied to the surrounding area of the marking  30 . The solder resist  18  is generally dark green. It is preferable that the marking  30  is white or deep light blue so as to be visually distinguishable from the color of the solder resist  18 . 
         [0037]    The marking  30 , for example, can be formed by printing white ink or deep light blue ink into a pattern of an annulus ring shape using a silk-screen printmaking process. For example, the marking  30  can also be formed by ink-jet producing a jet ink which is broken into droplets of coloring materials. 
         [0038]    The back-drilled hole  20  is formed after the marking  30  is formed as an indicator. Thus, the part of the plated through hole  14 , that is, the part corresponding to a stub, is removed. The external diameter of the marking  30  is set to the same as that of the back-drilled hole  20  or is set to be slightly smaller than that of the back-drilled hole  20 . Therefore, when forming the back-drilled hole  20 , if the drill is correctly positioned at the countersunk area, that is, if the drill is positioned with accuracy and the position of the back-drilled hole  20  is not out of the countersunk area, the marking  30  is entirely removed with the drill. Therefore, the marking  30  is removed and cannot be seen after the back-drilled hole  20  is formed. This state is shown in  FIG. 5A . The dotted line circle in  FIG. 5A  shows the countersunk area. The dotted line circle in  FIG. 5B  also shows the countersunk area. 
         [0039]    On the other hand, when the drill is positioned with less accuracy and the position of the back-drilled hole  20  is considerably out of the countersunk area, a part of the marking  30  remains unremoved as shown in  FIG. 5B . In  FIG. 5B , a part of the plated through hole  14  seen at the bottom of the back-drilled hole  20  is out of the back-drilled hole  20 . The part outside of the plated through hole  14  remains unremoved. This state shows that the stub is not removed completely, and is referred to as “bad back-drill”. It is possible to determine that a bad back-drill occurs whereat if the marking  30  remains after the back-drilled hole  20  is formed. It is possible to check easily and visually whether or not the marking  30  remains, or how much of the marking  30  remains because the marking  30  is formed in a color having a high level of visibility. 
         [0040]    It is preferable to decide on an external diameter of the marking  30  in consideration of the external diameter of the plated through hole  14 . That is, it is preferable to decide on an external diameter of the marking  30  so as to check visually the remaining part of the marking  30  when the back-drilled hole  20  is out of the desired position, and the external diameter of the back-drilled hole  20  does not exceed the external diameter of the plated through hole  14 . If the external diameter of the marking  30  is too small, the visibility of the marking  30  is low even if the part of the plated through hole  14  remains. On the contrary, if the external diameter of the marking  30  is too big, the remaining part of the marking  30  is big and the visibility of the marking  30  is too high if the back-drilled hole  20  is slightly out of the desired position. Thus, the misalignment of the plated through hole  20  may be considered a bad back-drill by mistake, even though the misalignment of the plated through hole  20  is within the accepted range. 
         [0041]    Next, a method of forming the marking  30  is explained using  FIG. 6 .  FIG. 6A  discloses that the plated through hole  14  is formed in the multi-layer wiring board  10   a.  In this case, the land  16  and the plated through hole  14  are formed at the same time. In  FIG. 6A , the top surface of the multi-layer wiring board  10   a  corresponds to the back surface of the wiring board  10 A, and the upside of the signal wiring  10   b  in the plated through hole  14  is targeted to be removed as a stub. 
         [0042]      FIG. 6B  discloses that the solder resist  18  is applied to the back surface of the multi-layer wiring board  10   a  after the plated through hole  14  is formed in the multi-layer wiring board  10   a.  The solder resist  18  is applied to slightly cover outside of the circumference of the land  16 , so that the land  16  surrounding the plated through hole  14  is exposed. The solder resist is also applied to the mounting surface, i.e., the top surface, of the multi-layer wiring board  10   a.    
         [0043]      FIG. 6C  discloses that the marking  30  is printed by a silk-screen printmaking process. According to the present embodiment, the marking  30  is formed to nearly cover the center of the land  16  having an annulus ring shape in the radial direction. As shown in  FIG. 7 , it is preferable to nearly cover the center of the land  16  when the marking  30  covers the land  16  entirely. This is because the plated through hole  14  may be adversely affected if a material of the marking  30  comes inside the plated through hole  14 . The marking  30  can be formed by ink-jet other than the silk-screen printmaking process. 
         [0044]    After the marking  30  is formed, the back-drilled hole  20  is formed in the position of the plated through hole  14  having a stub to remove. The back-drilled hole  20  is formed by the process shown in  FIG. 2 . A stub in the plated through hole  14 , e.g., a signal path of high-frequency signals or high-speed signals, which may be adversely affected by the existence of a stub, should be removed. 
         [0045]    The above-described formation process of the marking  30  and formation process of the back-drilled hole  20  are performed within a manufacture process of the wiring board  10 A. 
         [0046]    After the back-drilled hole  20  is formed, a test is performed to determine whether or not a bad back-drill occurs. This test can easily determine whether or not a bad back-drill occurs. That is, the test can determine the removing state of the plated through hole  14  by visually checking how much of the marking  30  remains on the wiring board. 
         [0047]    As described above, in the present embodiment, the marking  30  in a color having a high level of visibility is provided in the position where the back-drill hole  20  is formed. Due to this, a part of the marking  30  remains on top of the wiring board  10 A if the formation position of the back-drilled hole  20  is out of the desired position. Thus, it is possible to check easily and visually the misalignment of the back-drilled hole  20 . Therefore, the present embodiment can easily determine that the part corresponding to a stub in the plated through hole  14  remains, and can properly respond such as restarting a back-drill immediately. 
         [0048]    Next, a second embodiment is explained using  FIG. 8 .  FIG. 8  discloses that a marking  32  having an annulus ring shape is printed outside of the area where the back-drilled hole  20  should be formed. After the back-drilled hole  20  is formed, the marking  32  is formed as an indicator to check visually the position of the back-drilled hole  20 . In  FIG. 8 , the inside of the dotted line circle is shown as the area where the back-drilled hole  20 , i.e., a countersunk area, should be formed. The dotted line circle showing the countersunk area is presented to explain for convenience sake of drawing, but is actually not drawn on top of the wiring board  10 B. The dotted line circle has almost the same shape as the external diameter of the back-drilled hole  20 . However, the dotted line circle is presented as a circle whose diameter is slightly bigger than the external diameter of the back-drilled hole  20  for convenience sake of drawing. 
         [0049]    The marking  32  is a printed part having an annulus ring shape whose internal diameter is slightly bigger than the countersunk area, and is formed on top of the solder resist  18 . The solder resist  18  is generally dark green. Thus, it is preferable that the marking  32  has a color such as white or deep light blue to be visually distinguishable from the color of the solder resist  18 . 
         [0050]    The marking  32  can be formed by printing a color ink such as white ink or deep light blue ink using a silk-screen printmaking process. The marking  32  also can be formed by various processes such as ink-jet. 
         [0051]    The back-drilled hole  20  is formed after the marking  32  is formed. Due to this, a part of the plated through hole  14  is removed. The internal diameter of the marking  32  is set to the same as the external diameter of the back-drilled hole  20 , or is set to be slightly bigger than the external diameter of the back-drilled hole  20 . Therefore, if the drill is correctly positioned at the position of the drill when the back-drilled hole  20  is formed, that is, if the drill is positioned with accuracy and the position of the back-drilled hole  20  is not out of the countersunk area, the whole marking  32  remains on top of the wiring board  10 B, even after the back-drilled hole  20  is formed. This state is shown in  FIG. 9A . The dotted line circle in  FIG. 9A  shows the countersunk area. The dotted line circle in  FIG. 9B  also shows the countersunk area. 
         [0052]    On the other hand, when the drill is positioned with less accuracy and the position of the back-drilled hole  20  is considerably out of the countersunk area, a part of the marking  32  is removed as shown in  FIG. 9B . In this case, a part of the plated through hole  14  remains unremoved because the position of the back-drilled hole  20  is considerably out of the plated through hole  14 .  FIG. 9B  shows that a part of the plated through hole  14  is out of the back-drilled hole  20 .  FIG. 9B  shows that a part of the plated through hole  14  seen at the bottom of the back-drilled hole  20  is out of the back-drilled hole  20 . The part outside of the plated through hole  14  remains unremoved. This state shows that the stub is not completely removed and a bad back-drill occurs. Therefore, it is possible to determine that a bad back-drilled occurs when the remaining part of the marking  32  can be seen visually and easily after the back-drilled hole  20  is formed. Since the marking  32  is formed in a color having a high level of visibility, it is possible to determine visually whether or not the part of the marking  32  is removed, or how much of the marking  32  remains. That is, the present embodiment can determine easily and visually whether or not a bad back-drill occurs by forming the marking  32 . 
         [0053]    It is preferable to decide on an external diameter of the marking  32  in consideration of the external diameter of the plated through hole  14 . It is preferable to decide on an external diameter of the marking  32  so as to check easily and visually that the entire circumference of the marking  32  remains when the back-drilled hole  20  is out of the desired position, and the external diameter of the back-drilled hole  20  does not exceed the external diameter of the plated through hole  14 . If the external diameter of the marking  32  is too small, the back-drilled hole  20  exceeds the external diameter of the marking  32  when the back-drilled hole  20  is slightly out of position. This may be considered a bad back-drill by mistake even though the misalignment of the plated through hole  20  is within the accepted range. On the contrary, if the external diameter is too big, the entire circumference of the marking  32  remains even if the part of the plated through hole  14  remains. Thus, it may not be able to determine whether or not a bad-back drill occurs even though a bad back-drill actually occurs. 
         [0054]    The formation process of the marking  32  is the same as that of marking  30  according to the first embodiment. Thus, the explanation of the formation process of the marking  32  is omitted. 
         [0055]    In the present embodiment, the marking  32  in a color having a high level of visibility is formed as an indicator outside of the position where the back-drilled hole  20  is formed. Due to this, a part of marking  32  is removed if the formation position of the back-drilled hole  20  is out of the desired position. Thus, the misalignment of the back-drilled hole  20  can be checked easily and visually. Therefore, it is possible to easily determine that a part of the plated through hole  14  remains due to the misalignment of the back-drilled hole  20 , and properly respond such as restarting a back-drill immediately. 
         [0056]      FIG. 10A  discloses an example of a plurality of markings  34 , instead of the marking  30 , which are allocated continuously at even intervals in the annulus ring shaped area.  FIG. 10B  discloses an example of a plurality of markings  36 , instead of the marking  32 , which are allocated continuously at even intervals in the annulus ring shaped area. As with the first embodiment and the second embodiment, these deformation examples can visually determine the misalignment of the back-drilled hole  20 , by allocating a plurality of the markings at even intervals in the annulus ring shaped area. 
         [0057]    A third embodiment is explained using  FIG. 11 . In the present embodiment, a land  16 A which is bigger than a normal land is formed as an indicator instead of the marking  30  according to the first embodiment. In  FIG. 11 , the land  16 A as an indicator is formed into almost the same size as the countersunk area shown with a dotted line circle. The land  16 A should be removed with the back-drill. Also, the land  16 A may be bigger than a normal land because the land  16 A does not have to operate as a normal land. 
         [0058]    The external diameter of the land  16 A is set to the same as the external diameter of the back-drilled hole  20 , or is set to be slightly smaller than the external diameter of the back-drilled hole  20 . Therefore, when forming the back-drilled hole  20 , if the drill is correctly positioned at the countersunk area, that is, if the drill is positioned with accuracy and the position of the back-drilled hole  20  is not out of the countersunk area, the land  16 A is entirely removed with the drill. Accordingly, the land  16 A is removed and cannot be seen after the back-drilled hole  20  is formed. This state is shown in  FIG. 12A . The dotted line circle in  FIG. 12A  shows the countersunk area. The dotted line circle in  FIG. 12B  also shows the countersunk area. 
         [0059]    On the other hand, when the drill is positioned with less accuracy and the position of the back-drilled hole  20  is considerably out of the countersunk area, a part of the land  16 A remains unremoved, as shown in  FIG. 12B . This case shows that a part of the land  16 A remains because the position of the back-drilled hole  20  is considerably out of the plated through hole  14 . In  FIG. 12B , the part of the plated through hole  14  seen at the bottom of the plated through hole  14  is out of the back-drilled hole  20 . The misalignment of the plated through hole  14  remains unremoved. This state shows that the stub is not completely removed and a bad-back drill occurs. Therefore, it is possible to determine that a bad aback-drill occurs when the remaining part of the land  16 A can be seen after the back-drilled hole  20  is formed. The land  16 A is formed from metal such as copper, thereby having a high level of visibility. Accordingly, it is possible to check easily and visually whether or not the land  16 A remains. It is possible to determine easily and visually whether or not a bad back-drill occurs by forming the land  16 A. 
         [0060]    It is preferable to decide on an external diameter of the land  16 A in consideration of the external diameter of the plated through hole  14 . That is, it is preferable to decide on an external diameter of the land  16 A so as to check easily and visually the remaining part of the land  16 A when the external diameter of the back-drilled hole  20  does not exceed the external diameter of the plated through hole  14 . If the external diameter of the land  16 A is too small, the visibility of the land  16 A is low even if the part of the plated through hole  14  remains. On the contrary, if the external diameter of the land  16 A is too big, the remaining part of the land  16 A is big and the visibility of the land  16 A is too high when the back-drilled hole  20  is slightly out of the desired position. Thus, this may be considered a bad back-drill by mistake, even though the misalignment of the plated through hole  20  is within the accepted range. 
         [0061]    The present embodiment does not need to add a special process so as to form the land  16 A before the back-drilled hole is formed because the land  16 A is formed by a process such as plating within the formation process of the plated through hole  14 . 
         [0062]    In the present embodiment, the land  16 A having a high level of visibility is provided as an indicator over almost the entire area where the back-drilled hole  20  is formed. Due to this, it is possible to easily check the misalignment of the back-drilled hole  20  even if the formation position of the back-drilled hole  20  is out of the desired position because the part of the land  16 A remains on top of the wiring board  10 A. Accordingly, the present embodiment can easily determine that the part of the plated through hole  14  remains due to the misalignment of the back-drilled hole  20 , and can also properly respond such as restarting a back-drill immediately.