Abstract:
The present invention relates to a shielding element for electric and/or electronic components of an electric and/or electronic circuit, comprising an annular side wall ( 11 ) for surrounding those elements ( 25 ) of a circuit that have to be shielded against electromagnetic radiation, said side wall ( 11 ) defining a bottom and a ceiling opening ( 15 ), and a cover ( 12, 12 ′) for closing the ceiling opening ( 15 ). To provide a shielding element that facilitates a sampling of an electric and/or electronic circuit arrangement said cover ( 12, 12 ′) is either detachable attached to said side wall ( 11 ) by joint means that comprises a predetermined breaking ( 26 ) line or defined together with said side wall ( 11 ) as parts of an integral cap ( 32 ) by a predetermined breaking line ( 26 ). In both cases said predetermined breaking line ( 26 ) has to be destroyed for detaching said cover ( 12, 12 ′) from said side wall ( 11 ).

Description:
[0001]     The present invention relates to a shielding element for electric and/or electronic components of an electric and/or electronic circuit, in particular to a shielding element that is used to shield such components mounted on a printed circuit board.  
       BACKGROUND OF THE INVENTION  
       [0002]     Shielding elements are used in electric and/or electronic circuits to screen specific components of the circuit against an electromagnetic radiation, in particular against spurious emission or irradiation. In particular, screening or shielding elements are used to comply with the requirements of EMC (electro magnetic compatibility) standards.  
         [0003]     Usually such shielding elements comprises an annular side wall that can be mounted on a printed circuit board in a usual way, e.g. by soldering, and that surrounds the components to be shielded. After mounting the annular side wall and the components to be shielded onto the printed circuit board, a cover is used to close a ceiling opening that is defined by the upper edge of the annular side wall. A bottom opening that is defined by the lower edge of the side wall is closed by the printed circuit board. The terms “upper” and “lower” are used in this description to define the location of parts of the shielding element relative to the printed circuit board irrespective of the orientation of the printed circuit board itself. Hence, the upper edge of the side wall is that edge that is in a remote position whereas the lower edge is that edge that is in contact with the printed circuit board after mounting.  
         [0004]     As described above, mounting of a conventional shielding element onto a printed circuit board needs two mounting steps: First, mounting the side wall to the printed circuit bar and second, fixing the cover to the side wall.  
       SUMMARY OF THE INVENTION  
       [0005]     It is an object of the present invention to provide a shielding element for electric and/or electronic components of an electric and/or electronic circuit that facilitates assembling of the circuit.  
         [0006]     This object is achieved by a shielding element that comprises an annular side wall for surrounding those elements of a circuit that have to be shielded against electromagnetic radiation, the side wall defining a bottom and a ceiling opening, and a cover for closing the ceiling opening, wherein the cover is detachable attached to the side wall by joint means that comprises a predetermined breaking line and has to be destroyed for detaching the cover from the side wall.  
         [0007]     According to the present invention the shielding element can be mounted onto a printed circuit board or there like as one piece in one step but allows to open the ceiling opening of the shielding element by detaching the cover from the side wall by destroying a predetermined breaking line. Thus, the components screened by the shielding element are accessible for repair and maintenance without removing the complete shielding element but only the cover thereof. Since the cover of the inventive shielding element according to the invention is a lost part. After removing it the ceiling opening has to be closed by a usual cover element that can be mounted on the remaining annular side wall of the shielding element in a conventional manner, e.g. by snapping on or clamping.  
         [0008]     Another advantage of the inventive shielding element is that the predetermined breaking line can act as a seal that proves that no unauthorized person has opened the cover. Otherwise in case that the predetermined breaking line has been destroyed this means that access to the components screened by the shielding element was possible.  
         [0009]     According to an advantageous development of the present invention the cover comprises a strip-like peripheral portion overlapping a corresponding strip-like portion of the annular side wall and the predetermined breaking line is formed in an overlapping area of the cover and the side wall. In particular, it is possible that the cover is provided with a peripheral flange extending substantially perpendicular to its main surface and forming the portion for overlapping the annular side wall. Alternatively, the annular side wall is provided with an annular flange extending into the ceiling opening and forming the portion to be overlapped by the cover.  
         [0010]     According to a refinement of the present invention the breaking line is formed by spot welding, soldering or gluing the cover to the annular side wall in the overlapping area.  
         [0011]     In case that gluing is used to form the predetermined breaking line it is preferred that a tear of wire or strap is integrated into the predetermined breaking line to cut off the gluing line to facilitate removing the cover from the side wall.  
         [0012]     Another possibility to facilitate the opening of the shielding element is to provide the cover thereof with tear open means for removing it from the side wall wherein these tear open means are preferably formed by a tongue for engaging a tear open tool.  
         [0013]     Thus, the shielding element can be opened like a can used for beverages or food with the only difference that the tool for opening is not fixed to the shielding element but has to be available by a person who will open the shielding element. Please note, that it is also possible to fix an opening tool to the shielding element. However, to avoid unauthorized access to the shielded components it is preferred to refrain from fixing an opening tool to the shielding element.  
         [0014]     According to another aspect of the present invention a shielding element comprises an annular side wall for surrounding those elements of a circuit that have to be shielded against electromagnetic radiation, the side wall defining a bottom and a ceiling opening, and a cover for closing the ceiling opening, wherein the annular side wall and the cover are defined as parts of an integral cap by a predetermined breaking line.  
         [0015]     This kind of shielding element according to the present invention has the additional advantage that it can be formed from sheet metal by means of a punching and bending press.  
         [0016]     If the shielding element is not only necessary for screening the components against spurious emission or irradiation but also to protect the components against dust, water and the like it is preferred the predetermined breaking line is formed by a half cut or by at least one notch.  
         [0017]     On the other hand, if it&#39;s necessary, that the area shielded by the shielding element needs to be ventilated, e.g. for heat discharge, it is preferred that the predetermined breaking line is formed by at least one perforation.  
         [0018]     According to a preferred refinement of the present invention two parallel predetermined breaking lines are formed by notches and/or perforations to define a tear open strap.  
         [0019]     In case that notches are used to define a determined braking line, in particular a tear open strap, it is possible to provide one notch in the outer surface of the shielding element and the other in the inner surface thereof. However, it is preferred that the two parallel notches are both formed in one surface of the cap.  
         [0020]     According to another development of the present invention the cover is provided with an engaging element for being engaged by a tear open tool, wherein the engaging element is preferably formed by a hole for inserting an engaging pin of a tear open tool. The hole is either defined by a half cut or a notch or is already punched through in dependence on the kind of forming the predetermined breaking line.  
         [0021]     Instead of a hole one or more tongues can be provided as engaging element(s). In this case the tongue or tongues is/are defined by predetermined breaking lines, too.  
         [0022]     The breaking lines can be provided either in a side wall portion adjacent to an upper edge thereof or in a cover portion adjacent to its peripheral edge. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The present invention will be explained in more detail hereinafter with reference to accompanying drawings showing preferred embodiments of the present invention.  
         [0024]      FIG. 1  shows a cross sectional view of a shielding element according to the present invention;  
         [0025]      FIG. 2  shows a cross sectional view of a part of a shielding element according to the present invention to illustrate another type of predetermined breaking line;  
         [0026]      FIG. 3  shows a cross sectional view of a part of a shielding element of the present invention to illustrate an additional kind of predetermined breaking line;  
         [0027]      FIG. 4  shows a cross sectional view of a shielding element according to another embodiment of the present invention,  
         [0028]      FIG. 5  shows a top view of the shielding element according to  FIG. 4 ;  
         [0029]      FIG. 6  shows a cross sectional view substantially along line VI-VI in  FIG. 5 ;  
         [0030]      FIGS. 7   a  to  7   f  show cross sectional views of a part of a shielding element substantially along line VII-VII in  FIG. 5  for illustrating different kinds of breaking lines used with a shielding element according to a second aspect of the present invention;  
         [0031]      FIGS. 8   a  and  8   b  show cross sectional views of a shielding element according to the present invention closed by a cover after destroying the predetermined breaking line for repair;  
         [0032]      FIG. 9  shows a top view of a part of a shielding element according to the present invention to illustrate the arrangement of predetermined breaking lines for forming a tear open strap; and  
         [0033]      FIG. 10  shows a top view of a part of a shielding element according to the present invention to illustrate the arrangement of breaking lines for forming tongues as engaging elements for a tear open tool. 
     
    
       [0034]     In the different figures of the drawings similar elements are provided with the same reference signs.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     As shown in  FIG. 1 a  shielding element for screening electric and/or electronic components of an electric and/or electronic circuit comprises an annular side wall  11  and a cover  12 . The side wall  11  is mounted onto a printed circuit board  13  in conventional manner, e.g. by soldering or the like. The annular side wall  11  comprises an annular flange  14  that extents into an inside direction and defines a ceiling opening  15  that is closed by the cover  12 . The cover  12  comprises a tongue  16  that can be used as an engaging element for engagement with a tear of tool for tearing off the cover  12  from the annular side wall  11 .  
         [0036]     The cover  12  is detachable attached to the side wall  11  in the overlapping area between the flange  14  and a peripheral margin of the cover  12 .  
         [0037]     The predetermined breaking line can form by soldering, spot welding or by gluing. In the letter case it is preferred to use a conductive adhesive. The cover  12  can be made of sheet metal or a metallic foil.  
         [0038]     For opening the ceiling opening  15  of the shielding element shown in  FIG. 1  the tongue  16  is bent away from the side wall  11  so that a tear open tool can be brought into engagement with the tongue to tear off the cover  12  from the annular side wall  11 . For example, it is possible to use a tear open tool having a wind up bar with a slit into which the tongue  16  can be inserted so that the cover is wrapped around the wind up bar during removing the cover from the annular side wall.  
         [0039]     To obtain a flat upper surface of the inventive shielding element the flange  14  is provided with a supporting portion  14 ′ that is depressed in such a way that a cover  12  supported by the supporting portion has its surface in alignment with the upper surface of the remaining flange  14 . In this case the cover  12  is glued to the side wall  11 . i.e. to the supporting portion  14 ′ by means of an adhesive, preferably by means of a conductive adhesive  17 .  
         [0040]     A tear of wire  18  or tear of strap can be integrated into the glued region to cut the adhesive  17  for removing the cover  12  from the side wall  11 .  
         [0041]     According to  FIG. 3  the cover  12 ′ is provided with a pheripheral flange  19  extending substantially perpendicular to a main surface of the cover  12 ′ so that the cover  12 ′ is substantially cap shaped. The peripheral flange is attached to the side wall  11 ′ in a fixing area  20  by means of spot-welding, soldering or gluing. First and second notches  21  provided in the peripheral flange  19  defining a predetermined breaking line, in particular a breaking line formed by a tear open strap  22  that can be removed for separating the cover  12 ′ from the fixing area  20  and for removing the cover  12 ′ from the side wall  11 ′ to open the ceiling opening.  
         [0042]     According to  FIG. 4 a  shielding element according to another embodiment of the present invention is formed as an integral cap  23  made from sheet metal. The integral cap comprises an annular side wall  11  and a ceiling portion  24 . The cap  23  is mounted on a printed circuit board  13  to screen electric and/or electronic components  25  against environmental influences, in particular against electro magnetic radiation or emission.  
         [0043]     As can be seen in  FIG. 5  the ceiling portion  24  is divided into a peripheral flange  14  and a cover  12  by a predetermined breaking line  26  that can be formed, e.g. by a perforation  29 . To remove the cover  12  from the cap  23  by breaking the predetermined breaking line  26 , holes  27  are provided in the cover  12 . The holes  27  can be punched through so that an engagement pin of a tear open tool can be inserted therein. However, as shown in  FIG. 6  the holes  27  in the cover  12  can be formed by a half cut, i.e. they are not punched through but remains closed by a plug  28  formed by displacing material during half cutting the hole  27 . In this case the hole  27  have to be punched through first by a corresponding engagement pin to remove the plug  28  completely prior to completely inserting an engagement pin of a tear open tool.  
         [0044]     As shown in  FIG. 7   a  the predetermined breaking line  26  can be formed by a single notch  21 . According to  FIG. 7   b  the breaking line  26  can be also formed by two notches  21  one of which is provided in the upper surface of the ceiling  24  whereas the other notch  21  is formed in a parallel manner in the inner or lower surface of the ceiling  24 .  
         [0045]     As shown in  FIG. 7   c  both notches  21  for forming the predetermined breaking line  26  are provided in the outer surface of the cap  23 .  
         [0046]      FIG. 7   d  is an enlarged view of a part of the shielding element according to  FIGS. 4 and 5  showing the openings  29  of the perforation in more detail. Instead of small holes it is also possible to use slits or the like for the perforation  29  defining the predetermined breaking line  26 .  
         [0047]      FIG. 7   e  shows a predetermined breaking line formed by a half cut.  
         [0048]     A half cut can be provided by means of a bending and punching press that is used for producing an annular side wall portion for a conventional shielding element since instead of punching through or cutting out the ceiling opening of the annular side wall the ceiling opening is only half cut by reducing the cutting depth of the punching tool to less than the thickness of the ceiling of the cap. Therefore, the cap for an inventive shielding element can be produced without essential modifications of the machinery used for producing conventional shielding elements.  
         [0049]     After removing the cover  12  from the cap  23  and after repairing the components within the annular side wall  11  a replacement cover  32  is put onto the annular side wall in a conventional way. The replacement cover  32  can be clamped or snapped on the side wall in a conventional way.  
         [0050]     According to  FIG. 7   f  the predetermined breaking line is provided in the side wall  11  of the cap  23  so that the cover  12 ′ is formed by the ceiling  24  and an upper portion of the annular side wall  11 . Although it is possible to provide one or more notches, or a perforation to form the predetermined breaking line  26 , it is indicated as a notch  21 . For mounting a replacement cover  32  two or more supporting tongues  30  are provide at the side wall  11 . The tongues are arrange in a spaced relationship along the annular side wall  11  and are formed for example by cutting out and bending parts of the annular side wall.  
         [0051]     As shown in  FIG. 8   b  a peripheral flange of a replacement cover  32  is inserted between the tongue  30  and the annular side wall  11  preferably to being clamped thereby.  
         [0052]     In case that a pair of notches or perforations is used to define the predetermined breaking line  26 , it is possible to arrange the notches  21  or perforations in the manner shown in  FIG. 9  to define a tear open strap  31 . The tear open strap  31  is provided with a strap portion  33  having a hole  27  partly or completely cut out as an engaging means for engaging a pin of a tear open tool.  
         [0053]     To open the shielding element having a breaking line as explained in connection with  FIG. 9  an engagement tool, in particular an pin thereof is inserted into the hole  27  of the flap portion  33 . Then the flap portion is broken out of the ceiling  24  so that it can be gripped for tearing off the tear open strap  31  along the breaking line  26 .  
         [0054]     According to  FIG. 10  tongues  34  of the cover  12  are defined by additional breaking lines  26 ′. As shown in  FIG. 10  aperture regions  35  are defined by the additional breaking lines  26 ′ and the main breaking line  26 .  
         [0055]     To open a shielding element formed by a cap  23  provided with a breaking line pattern  26 ,  26 ′ as shown in  FIG. 10  the aperture regions  35  are punched through first to open the aperture and then a suitable tear open tool can be used to bent the tongues  34  into an up ward position in which a suitable tear open tool, e.g. an wind up bar with corresponding slits for accommodating the tongues  34  can be brought into engagement with the tongues for removing the cover by winding it up.  
         [0056]     According to the present invention a shielding element is provided that simplifies the production of a electronic or electronic circuit since only one part has to be handled during the production process. Since a destroyable predetermined breaking line is used as a joint between a cover and a side wall of the shielding element, the shielding element protects the circuit elements covered thereby against unauthorized access. Furthermore, connection problems are solved and microfony can be reduced.