Patent Abstract:
In a lamination type semiconductor device, in the case where a power source plane is wrapped by a closed area to prevent the needless radiation from being leaked to the outside of the semiconductor package, a planar conductor for shield having an area intersecting with the respective layers is required. However, in a device for manufacturing the lamination type semiconductor device, a process for manufacturing the above-mentioned conductor cannot be realized ordinarily. In order to make the process possible, it is required to modify or replace a manufacturing apparatus of the semiconductor device, and accordingly a manufacturing cost will be considerably increased. In the present invention, a guard ring is arranged in an surrounding area of a power source plane. The guard ring is connected to a GND plane of another layer through a via. Consequently, the RF radiation occurs between the power source plane and the guard ring.

Full Description:
INCORPORATION BY REFERENCE 
       [0001]    This patent application is based on Japanese Patent Application No. 2010-055682. The disclosure of the Japanese Patent Application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device using a multilayer board. 
         [0004]    2. Description of Related Art 
         [0005]    In a multilayer board of a semiconductor device using a BGA (Ball Grid Array) package, a power source plane and a GND (Ground) plane are generally provided in an inner layer. The general power source plane and the GND plane are each a sheet of conductor that spreads to be an area being as large as possible in the layer, basically. 
         [0006]    Generally, the general power source plane and the GND plane are opposed to each other in a same area. This causes a generation of needless RF (radio frequency) radiation due to the electromagnetic coupling between these two planes. In this case, since radiated to the outside of a package of the semiconductor device, there is a possibility that the RF radiation badly affects external circuits or device. 
         [0007]    As a method for preventing the RF radiation from being leaked to the outside of the semiconductor device, a technique for wrapping the power source plane with another conductor, for example, is known. 
         [0008]    Regarding the above description, Patent Document 1 (Japanese Patent Application Publication JP2003-218541A) discloses a description according to an EMI reducing structure board. The EMI reducing structure board includes a sheet conductor for power source, a dielectric substance, two sheets of sheet conductors for ground, and a sheet conductor for connection. Here, the dielectric substance entirely wraps the surface of the sheet conductor for power source. Moreover, two sheets of the sheet conductors for ground and the sheet conductor for connection configure one conductor of closed area, and the closed area conductor further wraps the sheet conductor for power source wrapped by the dielectric substance. That is, two sheets of the sheet conductor for ground sandwich the sheet conductor for power source wrapped by the dielectric substance from the surface and the reverse surface. The sheet conductor for connection is connected to two sheets of the sheet conductor for ground, and entirely surrounds side surfaces of the sheet conductor for power source wrapped by the dielectric substance. 
         [0009]    In addition, Patent Document 2 (Japanese Patent Application Publication JP2004-363347A) discloses a description regarding a multilayer printed circuit board. The multilayer printed circuit board includes signal layers, two sheets of power source layers, insulation layers, two sheets of ground layers, and a shield. Here, two sheets of the power source layers are arranged to be parallel with and to be separated from each other. The signal layers are arranged between two sheets of the power source layers to be parallel with and to be separated from each other. The insulator of the insulation layers entirely wraps the surfaces of the power source layers and signal layers. Two sheets of the ground layers and the shield are connected and configure one conductor of closed area, and the closed area conductor further wraps the power source layers and signal layers each wrapped by the insulator. That is, two sheets of the ground layers sandwich the insulator wrapping these power source layers and signal layers from the surface and reverse surface thereof. The shield is connected to two sheets of the ground layers, and entirely surrounds side surfaces of the power source layers and signal layers wrapped by the insulator. 
       SUMMARY 
       [0010]    In a lamination type semiconductor device, in the case where a power source plane is wrapped by a closed area to prevent the needless radiation from being leaked to the outside of the semiconductor package, a planar conductor for shield having an area intersecting with the respective layers is required. However, in a device for manufacturing the lamination type semiconductor device, a process for manufacturing the above-mentioned conductor cannot be realized ordinarily. In order to make the process possible, it is required to modify or replace a manufacturing apparatus of the semiconductor device, and accordingly a manufacturing cost will be considerably increased. 
         [0011]    According to an aspect of the present invention, a semiconductor device includes: a first conductive plane on which a first voltage is applied; a second conductive plane on which a second voltage is applied; an insulator arranged between the first conductive plane and the second conductive plane; a guard ring arranged in a same conductor layer to the second conductive plane and in a surrounding area of the second conductive plane with a clearance therebetween; and a via connecting the first conductive plane and the guard ring through the insulator. The gap is smaller than a thickness of the insulator between the first conductive plane and the second conductive plane. 
         [0012]    According to the present invention, a guard ring is arranged in an surrounding area of a power source plane. The guard ring is connected to a GND plane of another layer through a via. As a result, the RF radiation occurs between the power source plane and the guard ring so that it is possible to suppress the irradiation of needless radiation to the outside of the package. 
         [0013]    A semiconductor device according to the present invention is able to suppress emission of needless radiation to the outside of a package without considerably increasing a manufacturing cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
           [0015]      FIG. 1  is a cross sectional view schematically showing an example of overall configuration of a semiconductor device according to an embodiment of the present invention; 
           [0016]      FIG. 2  is a bird&#39;s-eye view illustrating by picking out an insulator, a power source plane, and a guard ring of the semiconductor device according to the embodiment of the present invention; 
           [0017]      FIG. 3  is a cross section schematically showing an RF radiation irradiated from the semiconductor device according to the embodiment of the present invention; 
           [0018]      FIG. 4  is a cross sectional view schematically showing a configuration of a semiconductor device according to Patent Document 1; 
           [0019]      FIG. 5  is a bird&#39;s-eye view schematically showing a configuration of a power source plane and a GND plane in a semiconductor device according to a comparative example; and 
           [0020]      FIG. 6  is a cross sectional view schematically showing RF radiation irradiated from the semiconductor device according to the comparative example. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring to attached drawings, embodiments for carrying out a semiconductor device according to the present invention will be explained below. 
         [0022]      FIG. 1  is a cross sectional view schematically showing an example of overall configuration of the semiconductor device according to an embodiment of the present invention. The semiconductor device of  FIG. 1  includes: BGA balls  16 ; a first layer  10 , a second layer  20 , and a third layer  30  of a multilayer board; a semiconductor chip  38 ; and bonding wires  44 . 
         [0023]    The first layer  10  includes first wirings  12 , a first insulator  11 , and a GND plane  13 . The second layer  20  includes a second insulator  21 , vias  26 , a power source plane  25 , and a guard ring  23 . The third layer  30  includes a third insulator  31  and second wirings  32 . 
         [0024]    The balls  16 , the first wirings  12 , the first insulator  11 , the GND plane  13 , the second insulator  21 , the power source plane  25 , the third insulator  31 , the second wiring  32 , and the semiconductor chip  38  are stacked in layers in this order from the bottom. The guard ring  23  is arranged in the same wiring layer as that of the power source plane  25 . In addition, each of the vias  26  is arranged in the same layer as that of the insulator  21 . Each of the vias  26  is composed of conductor formed to be a ring-shape along a side wall of an opening part provided to the insulator  21 , and the inside is filled with a via filler  28 . The via filler  28  may be a conductive material and may be an insulating material. In the case where the via filler  28  is insulating material, the insulator  11  or the insulator  31  may be filled. Moreover, the vias  26  and the guard ring  23  may be formed in the same process. 
         [0025]    The ball  16  is connected to the first wiring  12 . The first wiring  12  may be partially covered with a solder resist that is not shown in the drawing. The power source plane  25  is connected to any of the balls  16  through a via that is not shown in the drawing. The GND plane  13  is connected to any of the balls  16  through the via that is not shown in the drawing. The GND plane  13  is connected to the guard ring  23  through the vias  26 . An electronic circuit of the semiconductor chip  38 , the circuit being not shown in the drawing, is electrically connected to the second wirings  32  via the bonding wires  44 . 
         [0026]      FIG. 2  is a bird&#39;s-eye view illustrating by picking out the insulator  21 , the power source plane  25 , and the guard ring  23  of the semiconductor device according to this embodiment of the present invention.  FIG. 2  only shows the insulator  21 , the power source plane  25 , and the guard ring  23 , and other components are not represented. 
         [0027]    The guard ring  23  is arranged in the surrounding area of the power source plane  25 . A sufficient clearance is provided between the guard ring  23  and the power source plane  25 , and thus the insulation is ensured. In a part of the guard ring  23 , a part of the via fillers  28  is exposed. 
         [0028]    In  FIG. 2 , a state of propagation of an electromagnetic wave due to an RF noise caused by the power source plane  25  is schematically shown by arrows. The electromagnetic wave is terminated at the guard ring  23  due to the potential difference between the guard ring  23  and the power source plane  25 . Since the power source plane  25  and the guard ring  23  are closely arranged with each other, it can be suppressed that the electromagnetic wave wraps around other region than the power source plane  25  and the guard ring  23 . 
         [0029]    An example of sizes of the respective components will be shown below. In the semiconductor device according to this embodiment of the present invention, the following values can be adopted; for example, an external dimension of the laminated board is substantially 35 mm×35 mm, the thicknesses of the insulators  11 ,  21 , and  31  are substantially 150 μm, the dielectric constants of the insulators  11 ,  21 , and  31  are substantially 4, the thicknesses of the wiring  12 , the power source plane  25 , the GND plane  13 , and the wiring  32  are substantially 35 μm, the width of the guard ring  23  is substantially 500 μm, the clearance between the guard ring  23  and the power source plane  25  is substantially 100 μm. In particular, in order to prevent the generation of the RF radiation between the GND plane  13  and the power source plane  25 , it is important that the clearance separating the guard ring  23  from the power source plane  25  is narrower than the thickness of the insulator  21  that separates the GND plane  13  from the guard rings  23 . The potential difference between the power source plane  25  and the GND plane  13  can be set to substantially 3.3V or less. 
         [0030]      FIG. 3  is a cross section schematically showing the RF radiation  42  irradiated from the semiconductor device according to this embodiment of the present invention.  FIG. 3  only shows the GND plane  13 , the insulator  21 , the guard ring  23 , the power source plane  25 , the via fillers  28 , and the vias  26 , and other components are not represented. 
         [0031]    As shown in  FIG. 3 , in the semiconductor device according to this embodiment of the present invention, the RF radiation  42  is generated between the power source plane  25  and the guard ring  23 . For this reason, in the semiconductor device according to this embodiment of the present invention, the RF radiation  42  is hard to be leaked to the outside, which is different from the RF radiation  41  of a comparative example shown in  FIG. 6  explained later. 
         [0032]    In order to strengthen this effect, the dielectric constant of the second insulator  21 , for example, may be set to a larger value than those of the first insulator  11  and third insulator  31 . 
         [0033]    It is desired that the plurality of vias  26  are provided in order to prevent the voltage in the guard ring  23  from being floated and that the distance between the vias  26  is so closed that the purpose can be achieved. However, the distance between the vias  26  is not required, for example, to be a half wavelength or less of a frequency of RF radiation. 
         [0034]    The above-mentioned via  26  can be easily provided by a common device for manufacturing the lamination type semiconductor device. 
         [0035]      FIG. 4  is a cross sectional view schematically showing the configuration of the semiconductor device according to Patent Document 1. The semiconductor device of  FIG. 4  includes a power source plane  125 , a first GND plane  113 , a second GND plane  133 , a shielding conductor  129 , and an insulator  121 . In  FIG. 4 , other components are not represented. 
         [0036]    In the semiconductor device of  FIG. 4 , the power source plane  125  is entirely wrapped by a conductor of closed area including the first and second GND planes  113  and  133  and the shielding conductor  129 . The insulator  121  is arranged between the power source plane  125  and the conductor of closed area. 
         [0037]    In terms of the manufacturing method of the semiconductor device, the GND planes  113  and  133 , the power source plane  125 , and the insulator  121  can be easily manufactured even in a common manufacturing device. However, since having an area perpendicular to the respective layers of the lamination type semiconductor device, it is hard or impossible for a common semiconductor manufacturing device to manufacture the shielding conductor  129 . Even when the shielding conductor  129  could be manufactured by using a special device, the manufacturing cost will become high. 
         [0038]    The semiconductor device of Patent Document 2 is configured by adding a second power source plane and a signal wiring inside the conductor of closed area of the semiconductor device of  FIG. 4 . Accordingly, in terms of the manufacturing method and the manufacturing cost, the Patent Document 2 is the same as the semiconductor device of Patent Document 1. 
         [0039]    In comparison with the semiconductor device of  FIG. 4 , the semiconductor device of this embodiment has the configuration to suppress the leakage of the RF radiation  42  to the outside, and additionally does not require a conductor corresponding to the shielding conductor. Instead, the semiconductor device of this embodiment is provided with the guard ring  23  and vias  26  as components other than those of the common semiconductor device. The guard ring  23  and the vias  26  can be easily manufactured by a common semiconductor manufacturing device, and accordingly the increase of the manufacturing cost can be avoided. 
         [0040]    In the semiconductor device according to this embodiment of the present invention, if voltages applied to the GND plane  13  and the power source plane  25  are reversed, the effect of this embodiment is not changed. In other words, the semiconductor device of this embodiment may have a configuration where a guard ring connected through the vias to the power source plane is arranged in the surrounding area of the GND plane. 
         [0041]    Moreover, if a conductor layer where the GND plane  13  is arranged and the conductor layer where the power source plane  25  and the guard ring  23  are arranged are exchanged each other, the effect of this embodiment is not changed. In addition, in  FIG. 1 , the GND plane may be added between the wiring  32  and the power source plane  25 , and the GND plane may be further added between the wiring  12  and the GND plane  13 . In this manner, the leakage of the RF radiation  42  to the outside can be further suppressed. 
       Comparative Example 
       [0042]      FIG. 5  is a bird&#39;s-eye view schematically showing a configuration of a power source plane  24  and a GND plane  13  in a semiconductor according to a comparative example. The semiconductor device of  FIG. 5  includes the power source plane  24 , the GND plane  13 , a first insulator  11 , and a second insulator  21 . Other components of the semiconductor device are not represented in  FIG. 5 . 
         [0043]    The first insulator  11  is arranged in a layer lower than the GND plane  13 . The second insulator  21  is arranged between the power source plane  24  and the GND plane  13 . In an actual semiconductor device, the first insulator  11 , the GND plane  13 , the second insulator  21 , and the power source plane  24  are closely stacked in layers in this order from the bottom. In  FIG. 5 , a clearance between the second insulator  21  and the first insulator  11  is shown by being enlarged to show a shape of the GND plane  13 . 
         [0044]      FIG. 6  is a cross sectional view schematically showing an RF (Radio Frequency) radiation  41  radiated from a semiconductor device of the reference technique. The semiconductor device of  FIG. 6  has the same configuration as that of the semiconductor device of  FIG. 5 ; however, the first insulator  11  is not represented in  FIG. 6 . 
         [0045]    Since the power source plane  24  and the GND plane  13  are opposed to each other in a same area, the RF radiation  41  that is needless radiation is generated due to the electromagnetic coupling. On this occasion, since radiated to the outside of a package of the semiconductor device, there is a possibility that the RF radiation  41  badly affects external circuits or devices. 
         [0046]    Meanwhile, according to the present invention, as shown in  FIG. 3 , the RF radiation is hard to be leaked to the outside, which is different from the RF radiation  41 .

Technology Classification (CPC): 7