Patent Publication Number: US-2011069470-A1

Title: Electromagnetic interference noise reduction board using electromagnetic bandgap structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2009-0089666, filed with the Korean Intellectual Property Office on Sep. 22, 2009, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a board, more specifically to a noise reduction board that can reduce an EMI noise by use of an electromagnetic bandgap structure. 
     2. Description of the Related Art 
     As the operating frequencies of electric products become higher, electromagnetic interference (EMI) has been perceived as a chronic noise problem. Particularly, the operating frequencies of electronic products have reached a few ten megahertzs (MHz), or even a few gigahertzs (GHz), making the EMI problems more serious. Subsequently, finding a solution to the problems is desperately needed. Among the EMI problems occurring at a board, a solution for the noise problems particularly occurred at the edge of the board has not been little studied, making it difficult to completely shield the noise at the board. 
     EMI noise refers to a noise that creates a noise problem caused by interference when an electromagnetic (EM) wave generated in one electrical circuit, component or part is transferred to another electrical circuit, component or part. The EMI noise can be broadly categorized into two types, namely, a radiation noise (reference numerals  10  and  30  in  FIG. 1 ) and a conduction noise (reference numeral  20  in  FIG. 1 ). 
     The radiation noise  10 , which is radiated towards an upper side of the board (that is, the mounting surface of an electronic part), may be commonly shielded by covering an upper portion of the board by use of an electromagnetic shielding cap, for example, a metal cap. However, few studies have tried to find an effective solution for the radiation noise  30  (hereinafter, referred to as an “edge noise”), which is radiated towards the outside of the board when a conduction noise  20  inside the board is conducted to the edge of the board. 
     If a technology is developed to reduce the edge noise at the edge of the board through a simple modification of the board structure, it is expected to significantly reduce the development time and costs, compared to the conventional method, which has tried to solve the problem through the use of a metal cap or a circuit. Additionally, such technology can have more merits in terms of space utilization and power consumption, and can easily remove a noise in a frequency band of a few gigahertzs (GHz), making it effective in solving the EMI noise problem at the edge of the board. 
     SUMMARY 
     The present invention provides an electromagnetic interference (EMI) noise reduction board that can shield the radiation noise radiated from the edge of the board, by inserting an electromagnetic bandgap structure capable of shielding a noise ranging a certain frequency band into a portion of the board corresponding to the edge of the board. 
     The present invention also provides an EMI noise reduction board that can be advantages in space utilization, production cost and power consumption, by simply modifying the structure of the board so as to easily shield the radiation noise radiated from the edge of the board. 
     Other problems that the present invention solves will become more apparent through the following embodiments described below. 
     An aspect of the present invention features an electromagnetic interference (EMI) noise reduction board having an electromagnetic bandgap structure for shielding a noise, including: a first area having a ground layer and a power layer; a second area placed in a side portion of the first area having an electromagnetic bandgap structure therein. The electromagnetic bandgap structure can include a plurality of first conductive plates placed along the side portion of the first area, a plurality of second conductive plates placed on a planar surface that is different from the first conductive plates so as to overlap with the first conductive plates, and a via configured to connect the first conductive plate and the second conductive plate. 
     The first area and the second area can be a multi-layer having 4 or more layers, and the via can be a penetration via that penetrates the second area vertically. Also, the via can be a blind via. 
     In addition, one of the first conductive plate and the second conductive plate can have a bump or an indentaion shape corresponding to an outline shape of the first area, and at least any one pair of adjacent conductive plates among the plurality of first conductive plates can be electrically connected to each other by a connection line. 
     The first conductive plate can be electrically connected to the ground layer by a connection line, and the second area can be selectively arranged in a certain portion of the side portion of the first area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing for describing an electromagnetic interference (EMI) noise problem; 
         FIG. 2  is a sectional view of an EMI noise reduction board according to an embodiment of the present invention; 
         FIG. 3  is a side view of an EMI noise reduction board according to an embodiment of the present invention; 
         FIG. 4  is a front view of an EMI noise reduction board according to an embodiment of the present invention; 
         FIG. 5  is a perspective view of an EMI noise reduction board according to an embodiment of the present invention; 
         FIGS. 6 to 15  are front views of EMI noise reduction boards according to various embodiments of the present invention; and 
         FIGS. 16 to 18  are plan views of EMI noise reduction boards according to various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to particular modes of practice, and it is to be appreciated that all changes, equivalents, and substitutes that do not depart from the spirit and technical scope of the present invention are encompassed in the present invention. 
     In the description of the present invention, certain detailed descriptions of related art are omitted when it is deemed that they may unnecessarily obscure the essence of the invention. 
     While such terms as “first” and “second,” etc., may be used to describe various components, such components must not be limited to the above terms. The above terms are used only to distinguish one component from another. For example, a first component may be referred to as a second component without departing from the scope of rights of the present invention, and likewise a second component may be referred to as a first component. 
     The object of an EMI noise reduction board according to an embodiment of the present invention is not to shield a conductive noise inside the board but to prevent the conductive noise that is conducted to the edge of the board from being radiated to the outside of the board. For this, as shown in  FIGS. 2 and 3 , a printed circuit board according to an embodiment of the present invention includes: the first area  100  having a ground layer  110  and a power layer  120 ; and the second area  200  placed in a side portion of the first area  100  having an electromagnetic bandgap structure (hereinafter “EBG structure”) therein. The EBG structure includes a plurality of first conductive plates  210  placed along the side portion of the first area  100 , a plurality of second conductive plates  220  placed on a planar surface that is different from the first conductive plate  210  so as to overlap with the first conductive plate  210 ; and vias  250 ,  250   a  configured to connect the first conductive plate  210  and the second conductive plate. 
     As mentioned above, the conductive plates  210 ,  220  and a dielectric  105 , which is interposed between the conductive plates  210 ,  220 , constitue a capacitance component, and the vias  250 ,  250   a  constitute an inductance component. The EBG structure for shielding a noise, namely, an L-C filter is constituted by combination of the capacitance component and the inductance component. 
     As shown in  FIG. 3 , the printed circuit board according to an embodiment of the present invention has a structure of shielding an EMI noise radiated from the side portion of the board by forming the conductive plates  210 ,  220 ,  230 ,  240  on the edge portion of the board, overlapping the plates, and connecting the plates by the vias  250 ,  250   a . Since a capacitance value between an upper layer and a lower layer can be increased due to the conductive plates  210 ,  220 ,  230 ,  240  that are overlapped to one another, the effect of shielding the EMI noise, which is conducted to the edge of the board, from being radiated to the outside of the board can be increased. 
     A plurality of metal layers  110 ,  120 ,  130 ,  140 , such as the ground layer  110  and the power layer  120 , are provided on the first area  100 .  FIGS. 3 and 5  show a structure in which the ground layer  110  is provided on a top layer and the power layer  120  is provided below the ground layer  110 . Two metal layers  130 ,  140  provided below the power layer  120  may have a structure of being connected to the ground layer  110  by the via  150 , as shown in  FIG. 5 . A clearance hole can be formed on the power layer  120 , for electrical separation from the via  150 . 
     However, the configuration of the first area  100  as described above is just an example, and thus changes on the configuration and arrangement of the first area  100  can be made in various ways. 
     The plurality of conductive plates  210 ,  220 ,  230 ,  240  are arranged to be overlapped to one another in the second area  200  placed on the side portion of the first area  100 , in which the ground layer  110  and the power layer  120  are provided, as shown in  FIGS. 4 and 5 . In detail, the plurality of first conductive plates  210  are arranged on a same planar surface along the side portion of the first area  100 , and the second conductive plates  220  are arranged on a planar surface that is different from the first conductive plates  210  along the side portion of the first area  100 . Here, the second conductive plates  220  are arranged to be overlapped with the corresponding first conductive plates  210 . These overlapped first conductive plates  210  and second conductive plates  220  are connected to one another by the vias  250 . 
     Here, the first conductive plate and the second conductive plate are not used to indicate a conductive plate configured to perform a specific function, but to distinguish conductive plates  210 ,  220 ,  230 ,  240  that are arranged on different planar surfaces. Moreover, each of the conductive plates  210 ,  220 ,  230 ,  240  can have the same size and shape, but it is also possible to have a different size or shape, as required by design, if necessary. 
     Moreover, an insulator ( 105  in  FIG. 3 ) or a dielectric for an interlayer isolation is interposed between the conductive plates  210 ,  220 ,  230 ,  240 . 
     Meanwhile, as shown in  FIGS. 3 to 5 , the first area  100  and the second area  200  can be a multi-layer with 4 or more layers, and the via  250  can be a penetration via that penetrates the second area  200  vertically. When the second area  200  is a multi-layered structure, the conductive plates  210 ,  220 ,  230 ,  240  on each layer are entirely overlapped with the conductive plates on different layers so that it is relatively easy to implement the interlayer connection by using the penetration via  250 . As a result, the manufacturing process can be simplified so that the total manufacturing cost can be reduced. 
     Meanwhile, as shown in  FIGS. 3 and 5 , the first conductive plate  210  can be electrically connected to the first area  100 , i.e., the ground layer  110 , by a connection line  260 . When the first conductive plate  210  is connected to the ground layer  110  in this way, it is possible to secure a relatively large ground so that the noise reduction effect can be further improved. 
       FIGS. 6 to 15  show various alternatives of the EBG structure that is inserted into the second area  200 . 
     Referring to  FIG. 6  first, at least any one pair of adjacent conductive plates among the plurality of first conductive plates  210  can be electrically connected to each other by a connection line  215 . When the connection line  215  is formed between the adjacent first conductive plates  210 , it becomes possible to add the inductance component between the first conductive plates  210  so that a greater freedom in design can be provided for shielding the noise more effectively. Other conductive plates  220 ,  230 ,  240  as well as the first conductive plate  210  can be connected between any pair of adjacent conductive plates by the connection line  215  to add the inductance component. 
     In the EBG structure shown in  FIGS. 6 to 8 , all conductive plates in the second area  200  are electrically connected to one another within the second area  200  by the penetration via  250  and the connection line  215 . 
     Meanwhile, in the EBG structure shown in  FIG. 9 , some conductive plates form an independent path, and each of these conductive plates is connected to the ground layer  110  in first area  100  by at least one connection line  260 . 
     Although the aforementioned embodiments show a structure of using penetration via  250 , which penetrates the second area  200 , to electrically connect each of the conductive plates  210 ,  220 ,  230 ,  240  in the second area  200 , it is also possible for the conductive plates  220 ,  240  to be respectively connected by a blind via  250   a , as shown in  FIGS. 8 and 9 . 
       FIG. 10  shows a structure in which the first conductive plate  210  in the second area  200  is solely connected to the top layer of the first area  100 , namely the ground layer  110 , by the connection line  260 . However, the embodiment of the present invention is not intended to this structure, and as shown in  FIG. 11 , other conductive plates in the second area can be also connected to other layers in the first area by the connection line. Moreover, as shown in  FIG. 12 , the first area can be directly connected to the bottom layer of the second area by the connection line. 
       FIGS. 13 to 15  shows structures corresopndind to those in  FIGS. 10 to 12 , respectively, and in detail, the penetration via  250  in  FIGS. 10 to 12  is replaced by the blind via  250   a.    
     In addition, as shown in  FIG. 16 , when the side portion of the first area  100  has a rectangular shape, the first conductive plate  210  in the second area  200  also has a rectangular shape, but when the first area  100  has a shape other than a retangle, as shown in  FIGS. 17 to 19 , the first conductive plate  210  in the second area  200  also has an outline that can be a bump or an indentaion in various shapes corresponding to the first area  100 . Namely, the first conductive plate  210  can have a bent shape, as shown in  FIG. 17 , a curved shape, as shown in  FIG. 18 , or a triangular shape arranged in a row, as shown  FIG. 19 . 
     Meanwhile, the second area  200  into which the EBG structure is inserted can be arranged on the whole side portion of the first area  100 , but it is also possible to be selectively arranged on a certain portion. By arranging the second area  200  on a certain portion, it is possible to selectively shield the noise from the desired portion, thereby reducing the manufacturing cost. 
     While the spirit of the present invention has been described in detail with reference to particular embodiments, the embodiments are for illustrative purposes only and shall not limit the present invention. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.