Abstract:
An electro magnetic (EM) wave shielding device includes at least one metal plate and an EM wave absorbing material configured on a lateral side of the metal plate. The lateral side of the metal plate configured with the EM wave absorbing material covers a test point region of a circuit board, thereby absorbing and shielding EM waves generated by the test point region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 098208539 filed in Taiwan, R.O.C. on May 15, 2009 the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a shielding device, and more particularly to an electro magnetic (EM) wave shielding device, which covers a test point region of a circuit board. 
         [0004]    2. Related Art 
         [0005]    With the rapid progress of the electronic science, functions and applications of various electronic products become increasingly diversified, and accordingly, the design and development of the printed circuit boards (PCBs) disposed in the electronic products face greater challenge. During the manufacturing of the circuit boards, in order to exclude non-researching and non-designing faults, for example, short circuit or disconnecting problems resulted from a poor manufacturing process of the circuit boards, or problems (for example, mis-insertion of parts) resulted from carelessness during the assembling process on the production line, in-circuit test (ICT) including short circuit or disconnecting test must be performed before a large shipment of circuit boards, so as to ensure the shipment quality of the circuit boards. 
         [0006]    Currently, as for a method for confirming the quality of the circuit board, specific wires for testing electrical functions are usually configured among a plurality of wires printed on a surface of the circuit board. Meanwhile, test points electrically connected to the wires are disposed on the circuit board. Then, testing jigs for testing the test points are provided, so as to perform the ICT testing operation on the quality of the circuit board. However, once the quality test of the circuit board is finished, the test points disposed on the circuit board do not have any other function, but become one of the sources for producing EM interferences (EMIs) of the PCB. 
         [0007]    The EMI has become one of the severe problems in the current electronic industry, which causes interferences to other electronic elements disposed on the circuit board, and influences the normal running operations thereof, such that the EMI must be reduced as much as possible. Recently, considering the method for lowering the EMI, in addition to disposing a ground layer on the circuit board, a ground copper foil is usually laid on a test point region, so as to increase a grounding area, thereby lowering the EMI by reducing the impedance of certain grounding loops. Alternatively, a metal shield mask is disposed on the test point region, thereby lowering the EMI. However, the EM wave shielding capability of the copper foil is rather limited, and thus, no desirable EMI shielding effects can be provided. Although the EM wave shielding capability of the metal shield mask is better than that of the copper foil, the metal shield mask occupies a certain volume in usage, and a space on the circuit board for disposing the metal shield mask is quite limited, such that the usage of the metal shield mask is restricted to a large extent. 
         [0008]    Therefore, as for the EMI problem of the test point region on the circuit board, people in the industry are still searching for an EMI shielding method capable of overcoming the usage restrictions due to the limited space of the circuit board and improving the shielding capability. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the above problems, the present invention is an EM wave shielding device, which is capable of modifying problems of the conventional methods for preventing or lowering EMIs that an EMI shielding effect is rather limited, and is restricted by a using space of a circuit board. 
         [0010]    The present invention provides an EM wave shielding device, covering a test point region of a circuit board, in which the circuit board is disposed in a case, and the test point region of the circuit board generates EM waves. The EM wave shielding device comprises at least one metal plate, and at least one EM wave absorbing material configured on a lateral side of the metal plate. The lateral side of the metal plate configured with the EM wave absorbing material covers the test point region, thereby absorbing and shielding the EM waves emitted from the test point region. 
         [0011]    In the EM wave shielding device according to the present invention, an EM wave absorbing material is adhered to the lateral side of the metal plate, and the EM wave absorbing material covers the test point region of the circuit board, thereby absorbing the EM waves generated by the test point region. Meanwhile, the metal plate is further used to block the EM waves penetrating the EM wave absorbing material, so that the EM waves are effectively absorbed and isolated at the test point region of the circuit board, without being delivered to the electronic parts on the other regions of the circuit board. In addition, the EM wave shielding device according to the present invention covers the test point region in a shape of a thin plate structure, which is not restricted by the available space of the circuit board. 
         [0012]    The above descriptions of the disclosure of the present invention and the following descriptions of the embodiments are merely intended to exemplify and explain the spirits and principles of the present invention, and offer further explanations on the claims of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus is not limitative of the present invention, and wherein: 
           [0014]      FIG. 1  is a schematic three-dimensional exploded view of a first embodiment of the present invention; 
           [0015]      FIG. 2  is a schematic cross-sectional view of the first embodiment of the present invention; 
           [0016]      FIG. 3  is a schematic three-dimensional exploded view of the first embodiment of the present invention, in which a metal plate is fixed on a circuit board by positioning posts; 
           [0017]      FIG. 4  is a schematic cross-sectional view of the first embodiment of the present invention, in which the metal plate is fixed on a circuit board by the positioning posts; 
           [0018]      FIG. 5  is a schematic three-dimensional exploded view of the first embodiment of the present invention, in which an EM wave shielding device is disposed on two opposite lateral sides of a test point region; 
           [0019]      FIG. 6  is a schematic cross-sectional view of the first embodiment of the present invention, in which the EM wave shielding device is disposed on the two opposite lateral sides of the test point region; 
           [0020]      FIG. 7  is a schematic three-dimensional exploded view of a second embodiment of the present invention; 
           [0021]      FIG. 8  is a schematic cross-sectional view of the second embodiment of the present invention; 
           [0022]      FIG. 9  is a schematic three-dimensional exploded view of a third embodiment of the present invention; and 
           [0023]      FIG. 10  is a schematic cross-sectional view of the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    An EM wave shielding device according to the present invention is used to cover a test point region of a circuit board, for example, a test point region of a single-sided, double-sided, or multi-layer PCB, a logic board, or an etched circuit board, thereby absorbing and shielding EM waves generated by the test point region. 
         [0025]    Referring to  FIGS. 1 and 2 , a circuit board  10  is disposed in a case  20  of an electronic device, and is fastened on the case  20  through screws  210 . A plurality of electronic elements  110 , for example, chipsets, heat sink, interface card slots, capacitors, and power outlet, a test point region  120 , and a plurality of fixing holes  130  are disposed on the circuit board  10 . The plurality of fixing holes  130  is opened on positions of the circuit board  10  adjacent to the test point region  120 . A plurality of test points  121  is distributed on the test point region  120 , and generates EM waves. An EM wave shielding device  30  according to a first embodiment of the present invention comprises a metal plate  310  and an EM wave absorbing material  320 . A thickness of the metal plate  310  is approximately 0.75 mm to 1.5 mm, and a thickness of the EM wave absorbing material  320  is approximately 0.4 mm to 0.6 mm. The EM wave absorbing material  320  is disposed on a lateral side of the metal plate  310 . However, the thickness of the metal plate  310  and the thickness of the EM wave absorbing material  320  may be varied correspondingly according to the practical using demands without being limited to the thickness mentioned in this embodiment. 
         [0026]    When the EM wave shielding device  30  according to the present invention is installed on the circuit board  10 , the lateral side of the metal plate  310  configured with the EM wave absorbing material  320  covers the test point region  120 , and then the EM wave shielding device  30  is fixed on the circuit board  10  by using an adhesive (not shown). Alternatively, referring to  FIG. 1 , a plurality of via holes  311  is opened on surrounding peripheries of the metal plate  310 , a plurality of notches  321  is disposed on the EM wave absorbing material  320 , and the plurality of via holes  311  and the plurality of notches  321  both correspond to the fixing holes  130  around the test point region  120 . Then, fixing parts  40 , for example, screw bolts, plugs, or screws, sequentially pass through the via holes  311  of the metal plate  310 , the notches  321  of the EM wave absorbing material  320 , and the fixing holes  130  of the circuit board  10 , such that the EM wave shielding device  30  is fixed on the test point region  120 . 
         [0027]    If the fixing parts  40  are in a form of screws, the screws have a plurality of screw teeth, and inner edges of the via holes of the metal plate and the fixing holes of the circuit board have a plurality of screw threads matching with the screw teeth of the screws, such that the screw teeth of the screws are fitted with the screw threads on the inner edges of the via holes of the metal plate and the fixing holes of the circuit board, and then the screws are fastened in the via holes and the fixing holes, so that the metal plate and the EM wave absorbing material are stably disposed on the circuit board. When the fixing parts  40  are in a form of screw bolts, each of the screw bolts has a head portion and a locking portion on two ends respectively, in which a diameter of the head portion is greater than that of the locking portion, the locking portion has a plurality of screw teeth, and a diameter of the locking portion matches with an inner diameter of the via holes of the metal plate and an inner diameter of the fixing holes of the circuit board. In usage, the locking portion of each screw bolt sequentially passes through the via hole of the metal plate, the notch of the EM wave absorbing material, and the fixing hole of the circuit board, and is protruded from a lateral side of the circuit board facing the case. Then, a screw nut is screwed on the screw teeth of the locking portion of the screw bolt. In this way, the metal plate, the EM wave absorbing material, and the circuit board are clamped between the head portions of the screw bolts and the screw nuts, thereby increasing a holding strength of the EM wave shielding device on the circuit board. When the fixing parts  40  are in a form of plugs, each plug usually has a head portion and an elastic flange capable of shrinking inwards on two ends respectively, and after passing through the fixing hole of the circuit board, the plug is clipped on the circuit board by using the elastic flange, such that the metal plate, the EM wave absorbing material, and the circuit board are clamped and fixed between the head portions and the elastic flanges of the plugs, thereby fixing the EM wave shielding device on the circuit board. 
         [0028]    In the first embodiment of the present invention, the fixing parts  40  in the form of screws are taken as an example for description, but the present invention is not limited here. 
         [0029]    Accordingly, after the EM wave shielding device  30  is fixed on the circuit board  10  through the fixing parts  40 , the EM wave absorbing material  320  and the metal plate  310  are sequentially formed on the test point region  120  of the circuit board  10 , such that the EM waves emitted from the test point region  120  are firstly absorbed by the EM wave absorbing material  320 , thereby lowering a strength of the EM waves, and then the EM waves are blocked by the metal plate  310  disposed on an external part, thereby being restricted in the test point region  120 , so that the EM waves generated by the test point region  120  cannot be delivered to the other electronic elements  110 , for example, interface card slots and heat sink on the circuit board  10 , thereby effectively lowering an EMI produced by the test point region  120  on the electronic elements  110 . 
         [0030]    In addition to fixing the EM wave shielding device of the present invention to the circuit board by using the fixing parts, referring to  FIGS. 3 and 4 , a plurality of positioning posts  312  is extended from a lateral side of the metal plate  310  facing the circuit board  10 , and the positions where the positioning posts  312  are protruded on the metal plate  310  correspond to the plurality of fixing holes  130  of the circuit board  10 . Therefore, the plurality of positioning posts  312  of the metal plate  310  correspondingly passes through the plurality of fixing holes  130  of the circuit board  10 , such that the EM wave shielding device  30  is fixed on the test point region  120  of the circuit board  10 , which is merely a different operation manner for fixing the EM wave shielding device  30  on the circuit board  10 , and the present invention is not limited here. 
         [0031]    In addition, the EM wave shielding device  30  according to the present invention may be disposed on two opposite lateral sides of the circuit board  10 , thereby enhancing the EM wave shielding performance. Referring to  FIGS. 5 and 6 , the EM wave shielding device  30  according to the present invention is respectively disposed on two opposite lateral sides of the circuit board  10 , and corresponds to the test point region  120  of the circuit board  10 . The lateral side of each metal plate  310  configured with the EM wave absorbing material  320  respectively covers the test point region  120 , such that the test point region  120  is sandwiched between two metal plates  310 . Therefore, due to being absorbed by the EM wave absorbing materials  320  and isolated by the metal plates  310 , the EM waves generated by the test point region  120  has a lower strength, so as to prevent the EM waves that are not absorbed by the EM wave absorbing materials  320  from overflowing from the other lateral side of the circuit board  10  opposite to the test point region  120 , and prevent other electronic elements  110  on the circuit board  10  from being interfered by the EM waves to affect the operation performance thereof. 
         [0032]    Referring to  FIGS. 7 and 8 , a circuit board  10  is disposed in a case  20  of an electronic device, and is fastened on the case  20  through screws  210 . A plurality of electronic elements  110 , a test point region  120 , and a plurality of fixing holes  130  are disposed on the circuit board  10 . The plurality of fixing holes  130  is opened on positions of the circuit board  10  adjacent to the test point region  120 . A plurality of test points  121  is distributed on the test point region  120 , and generates EM waves. An EM wave shielding device  30  according to a second embodiment of the present invention comprises a metal plate  310 , an EM wave absorbing material  320 , and a mylar  330 . A thickness of the metal plate  310  is approximately 0.75 mm to 1.5 mm. A plurality of via holes  311  is opened on the metal plate  310 , and the positions of the via holes  311  correspond to the fixing holes  130  of the circuit board  10 . The EM wave absorbing material  320  is disposed between the metal plate  310  and the mylar  330 . A thickness of the EM wave absorbing material  320  is approximately 0.4 mm to 0.6 mm, and the EM wave absorbing material  320  is configured with notches  321  corresponding to the via holes of the metal plate  310 . A thickness of the mylar  330  is approximately 0.2 mm to 0.3 mm, and the mylar  330  is further opened with through holes  331  corresponding to the via holes  311  of the metal plate  310 . However, the thickness of the metal plate  310 , the thickness of the EM wave absorbing material  320 , and the thickness of the mylar  330  may be correspondingly varied according to the practical using demands, which are not limited to the thickness mentioned in this embodiment. 
         [0033]    When the EM wave shielding device  30  according to the second embodiment of present invention is installed on the circuit board  10 , a lateral side of the mylar  330  covers the test point region  120  of the circuit board  10 , and then the mylar  330 , the EM wave absorbing material  320 , and the metal plate  310  are sequentially formed on the test point region  120 , and finally, fixing parts  40  sequentially pass through the via holes  311  of the metal plate  310 , the notches  321  of the EM wave absorbing material  320 , the through holes  331  of the mylar  330 , and the fixing holes  130  of the circuit board  10 , so as to fix the EM wave shielding device  30  on the test point region  120  of the circuit board  10 . The mylar  330  is used to isolate and protect a circuit layout (not shown) in the test point region  120 , and provides an excellent electrical isolation effect. Then, the EM wave absorbing material  320  absorbs the EM waves generated by the test point region  120 , and the EM waves are further blocked by the metal plate  310 , thereby lowering an EMI of the EM waves generated by the test point region  120  on the electronic elements  110  on other regions of the circuit board  10 . 
         [0034]      FIGS. 9 and 10  are respectively a schematic three-dimensional exploded view and a schematic cross-sectional view of a third embodiment of the present invention. Referring to  FIGS. 9 and 10 , an EM wave shielding device according to the third embodiment of the present invention is used to cover a test point region of a circuit board, so as to isolate and lower the strength of EM waves emitted from the test point region. The circuit board is disposed in a case  20  of the electronic device, and is fastened on the case  20  through screws  210 . A plurality of electronic elements  110 , a test point region  120 , and a plurality of fixing holes  130  are disposed on the circuit board  10 . The plurality of fixing holes  130  is opened on positions of the circuit board  10  adjacent to the test point region  120 . A plurality of test points  121  is distributed on the test point region  120 , and generates EM waves. 
         [0035]    The EM wave shielding device  30  comprises two metal plates  310 , two EM wave absorbing materials  320 , two mylars  330 , and an EMI gasket  340 . Firstly, the two EM wave absorbing materials  320  are respectively disposed on a lateral side of each of the two metal plates  310 , and then, the two mylars  330  are respectively disposed on the two EM wave absorbing materials  320 , so as to form two stacking structures of the mylar  330 , the EM wave absorbing material  320 , and the metal plate  310  respectively. Then, a lateral side of each stacking structure having the mylar  330  covers two opposite lateral sides of the circuit board  10  respectively, and corresponds to a position of the test point region  120  on the circuit board  10  respectively. Then, the two stacking structures are fixed on the circuit board  10  through fixing parts  40  (shown in  FIG. 10 ), so as to prevent the EM waves that are not absorbed by the EM wave absorbing materials  320  from overflowing from the other lateral side of the circuit board  10  opposite to the test point region  120 . Finally, the EMI gasket  340  is disposed between the case  20  and the metal plate  310 , and the EMI gasket  340  respectively contacts the case  20  and the metal plate  310 , and thus, the configuration of the EM wave shielding device  30  is completed. 
         [0036]    Therefore, the mylars  330  isolate and protect a circuit layout (not shown) in the test point region  120  of the circuit board  10 , and provide an insulating protection effect. The EM wave absorbing materials  320  absorb the EM waves generated by the test point region  120 . The metal plates  310  isolate and block the EM waves, such that the EM waves cannot be delivered to the other regions outside the test point region  120  of the circuit board  10 . Meanwhile, by using the EMI gasket  340 , the EM waves are guided and drained to the case  20 , such that the harm of the EMI generated by the test point region on the electronic elements  110  of the circuit board  10  is reduced to the lowest degree, thereby satisfying the level specified in the legal safety code of the EMI in each country. 
         [0037]    The EM wave shielding device according to the present invention comprises the metal plate and the EM wave absorbing material. The EM wave absorbing material covers the test point region of the circuit board, such that the EM waves generated by the test point region are firstly absorbed by the EM wave absorbing material. After the strength of the EM waves is reduced, the metal plate further blocks the EM waves in the test point region, such that the EM waves generated by the test point region cannot be delivered to the other regions of the circuit board, thereby effectively lowering the EMI produced by the test point region on the electronic elements on the circuit board. Furthermore, the EM wave shielding device according to the present invention is disposed in a form of a thin plate, and when being installed on the circuit board, the EM wave shielding device is adhered to the circuit board, which does not influence other electronic elements already disposed on the circuit board and is not restricted by the limited available space either. 
         [0038]    In addition, as for the usage of the EM wave absorbing material, the EM wave absorbing material generally has a high cost, and if a large number of EM wave absorbing materials are used to prevent the EMI of the circuit board, a manufacturing cost of the circuit board is greatly increased. If merely the metal plate is used as the material for lowering the EMI, a metal shield mask is generally formed to lower the EMI. In this case, it is still doubted that the usage of the metal material also results in an increased manufacturing cost. Therefore, the EM wave absorbing material according to the present invention not only achieves an excellent EMI shielding efficiency, but also reduces the amount of the required EM wave absorbing materials and metal plates, so as to lower the manufacturing cost.