Abstract:
The invention provides a shield structure that allows an easy installment of a shield case on a circuit board with more strength and firmness even if the shield case is warped or distorted. The proposed shield case includes a frame member consisting of four sidewalls and a cover member covering a farther end of the frame member from the circuit board. The frame member comprises a supporting member for sustaining the frame member on the circuit board and end faces confronting the circuit board. The supporting member comprises three projections protruding from the end face toward the circuit board.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a shield structure for electronic circuit parts for shielding electronic circuit parts disposed on a circuit board. 
     2. Background Art 
     Electronic circuit parts, such as those used in cellular phones, are disposed or packaged on a circuit board. Specific electronic parts among the mentioned electronic circuit parts, for example electronic parts for handling high frequency wave, are covered with a shield case made of a conductive body, and are shielded electrically and magnetically. 
     FIG. 6 shows a conventional shield structure for electronic circuit parts. Referring to FIG. 6, a plurality of electronic circuit parts are disposed or packaged on a circuit board  1 , and a shield case  2  is installed on the circuit board  1  to cover specific electronic circuit parts. The shield case  2  is of a rectangular solid box shape with an open end, and is fixed by soldering on the circuit board  1  with the open end facing the circuit board, so as to enclose specific circuit parts. This shield case  2  of rectangular solid box shape is placed so that each end face of the four sidewalls contact the circuit board  1 , i.e., so that the shield case  2  contacts the circuit board  1  at four end faces thereof, and each end face and the circuit board  1  are soldered with a solder  3 . Additionally, reference numeral  3   a  indicates a faulty soldered part. 
     FIG. 7 is a shield structure for electronic circuit parts disclosed in the Japanese Laid-open Patent Application No. 27691/1997. The open-end faces of the shield case  2  are provided with four fixing hooks  4  projecting in L-shape. The circuit board  1  is provided with rectangular holes  5  corresponding to the four fixing hooks  4 , and metallic pads  6  each adjacent to each of the rectangular holes  5 . Each of the four fixing hooks  4  of the shield case  2  is inserted through each rectangular hole  5 , and folded so as to be in contact with the metallic pad  6 , and then fixed to the circuit board  1  by soldering. In this structure, the shield case  2  is installed on the circuit board  1  sustained at four points. 
     As described above, the shield cases has been conventionally installed on the circuit board either by soldering the four faces as shown in FIG. 6, or by soldering the four sustaining points as shown in FIG.  7 . However, the sidewalls of a shield case of rectangular solid box shape may be warped or distorted because the shield cases are generally molded by bending or pressing process. If any of the sidewalls of the shield case is warped or distorted in case of the four-face contact as shown in FIG.  6  and the contact faces do not constitute a plane surface, the four faces will not fully contact the circuit board, and consequently sufficient attaching strength cannot be secured by soldering, which may eventually result in an accident that the shield case gets out of and falls from the circuit board. 
     Moreover, in the four-point sustention structure as shown in FIG. 7, if the shield case is warped or distorted, it may be impossible to insert the four fixing hooks  4  through the corresponding four rectangular holes  5 , or to fold any of the fixing hooks  4  though the insertion is barely achieved. Consequently, the shield case cannot be installed on the circuit board. 
     It is certain that such disadvantage caused by warp or distortion of a shield case can be solved by reworking each contact face of the shield case to improve the flatness precision of the four contact faces in case of four-face contact as in FIG. 6, or by eliminating the warp or distortion through a heat treatment of the shield case in case of four-point sustention structure as in FIG.  7 . But, the aforementioned reworking or heat treatment requires extra operations, which will result in a disadvantage of cost increase. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing disadvantages incidental to the prior arts, and object of the present invention is to propose an improved shield structure for electronic circuit parts, which allows an easy installation of a shield case on a circuit board with more strength and firmness, even if the shield case is warped or distorted. 
     To accomplish the foregoing object, a shield structure for electronic circuit parts according to the present invention comprises a circuit board on which a plurality of electronic circuit parts are disposed and a shield case which is installed on said circuit board to enclose and shield specific electronic circuit parts among said plurality of electronic circuit parts; wherein said shield case comprises a frame member including four sidewalls and a cover member covering the farther end of the frame member from said circuit board; said frame member includes a supporting member for sustaining said frame member on said circuit board and an end face confronting the mentioned circuit board; and said supporting member is composed of three projections protruding from the said end face toward the mentioned circuit board. 
     As a result of such an arrangement, the shield case can be securely joined to the circuit board by three-point sustention, and fixed securely and firmly at the joints, without any additional subsequent treatment such as reworking or heat treatment. 
     It is preferable that, in the shield structure for electronic circuit parts according to the invention, said circuit board is provided with a circuit pattern formed thereon and a solder bed formed on said circuit pattern, and each of said projections is soldered to said circuit pattern penetrating through the solder bed, and gap is formed at least one part between said end face and the circuit pattern, and said gap is not larger than 0.1 millimeter. 
     As a result, the above described shield structure can secure a sufficient shielding effect, while absorbing the warp or distortion of a shield case as a variation in the gap. 
     It is also preferable that, in the shield structure for electronic circuit parts according to the present invention, said circuit board is provided with a circuit pattern formed thereon and a solder bed formed on said circuit pattern, and each said projections is soldered to said circuit pattern penetrating through the solder bed, and gap is formed at least one part between said end face and the circuit pattern, and a solder is inserted in at least one part of said gap. 
     As a result, the above described shield structure can secure a more firm shielding effect, while absorbing the warp or distortion of a shield case as a variation in the gap dimension. 
     It is also preferable that, in the shield structure for electronic circuit parts according to the invention, the first sidewall of said four sidewalls is provided with the first and the second projections of said three projections, and the second sidewall of said four sidewalls confronting said first sidewall is provided with the third projection of said three projections. 
     As a result, the three-point sustention structure can be stabilized all the more. 
     It is also preferable that, in the shield structure for electronic circuit parts according to the invention, said first, second and third projections are placed so as to fall on each vertex of an isosceles triangle. 
     As a result, the three-point sustention structure can be stabilized all the more. 
     It is also preferable that, in the shield structure for electronic circuit parts according to the invention, said first sidewall is provided with an extension extending across the mentioned circuit board in the direction of thickness thereof, and said first and second projections are placed on both sides of said extension. 
     As a result, the positioning and close joint of the first sidewall and the circuit board can be achieved by means of the mentioned extension. 
     It is also preferable that, in the shield structure for electronic circuit parts according to the invention, said second sidewall is provided with two extensions extending across said circuit board in the direction of thickness thereof, and said third projection is placed between each of these extensions. 
     As a result, the positioning and close joint of the second sidewall and the circuit board can be achieved by means of the mentioned extensions. 
     Further, a shield structure for electronic circuit parts according to the invention comprises a circuit board on which a plurality of electronic circuit parts are disposed, and a shield case which is installed on said circuit board to enclose and shield specific electronic circuit parts among said plurality of electronic circuit parts; wherein said shield case is provided with a frame member including first and second sidewalls confronting each other, third and fourth sidewalls confronting each other and a cover member covering the farther end of the frame member from said circuit board; said first sidewall is provided with an extension extending across said circuit board in the direction of thickness thereof and two projections placed on both sides of the extension; said second sidewall is provided with two extensions extending across said circuit board in the direction of thickness thereof and a projection placed between said two extensions; and said third and fourth sidewalls are provided with end faces confronting said circuit board, each of said projections protruding to said circuit board for supporting said shield case. 
     As a result of such arrangement, the positioning and close joint of the first and the second sidewalls and the circuit board can be achieved by means of the mentioned extensions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing Embodiment 1 of a shield structure for electronic circuit parts according to the present invention. 
     FIG. 2 is a sectional view taken along the line II—II of FIG.  1 . 
     FIG. 3 is a sectional view taken along the line III—III of FIG.  1 . 
     FIG. 4 is a sectional view taken along the line IV—IV of FIG.  1 . 
     FIG. 5 is a perspective view showing Embodiment 2 of a shield structure for electronic circuit parts according to the invention. 
     FIG. 6 is a perspective view showing a conventional structure. 
     FIG. 7 is a perspective view showing another conventional structure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     FIG. 1 is a perspective view showing Embodiment 1 of a shield structure for electronic circuit parts according to the present invention. The shield structure according to the embodiment 1, which is incorporated for example in cellular phones, comprises a circuit board  10  disposing or packaging a large number of electronic circuit parts (not shown) and a shield case  20  shielding specific electronic circuit parts among the large number of electronic circuit parts. In cellular phones, a large number of electronic circuit parts such as transmitting and receiving circuits, driving circuit for liquid crystal display and control circuits thereof are employed, and those electronic circuit parts are disposed or packaged on the circuit board  10 . Such electronic circuit parts include a plurality of electronic circuit parts for treating high frequency wave, which are distinguished as specific electronic circuit parts and are shielded electrically and magnetically by the shield case  20 . 
     The circuit board  10  is formed with a copper layer on the main surface of upper or lower, or both faces of an insulating substrate  11  made of insulating material, and a circuit pattern  12  formed by patterning the copper layer according to a prescribed pattern. A large number of electronic circuit parts such as semiconductor integrated circuit elements, resistive elements, capacitative elements, inductive elements are disposed or packaged and soldered to the circuit pattern at predetermined positions on the circuit pattern  12 . FIG. 1 only shows the pattern  12  for connecting the shield case  20  to a reference potential point, i.e., earth potential, but practically a large number of other circuit patterns  12  are placed. The circuit pattern  12  on the circuit board  10  is provided with a solder bed  13  for soldering electronic circuit parts on predetermined positions, and this solder bed  13  is used for soldering. 
     The shield case  20  is molded into a rectangular solid box shape by bending sheet metal made of conductive material such as copper or copper pyrites. The shield case  20  has a rectangular-shaped frame member  30  and a cover member  45 , and the mentioned frame member  30  and cover member  45  are molded integrally in one body. The frame member  30  comprises four sidewalls  31 ,  32 ,  33  and  34 , among which the first sidewall  31  and the second sidewall  32 , also the third sidewall  33  and the fourth sidewall  34  are respectively confronting each other in parallel. The frame member  30  is sustained and mounted on the circuit board  10  in such a manner that each of the sidewalls  31 ,  32 ,  33  and  34  makes perpendicular to the main surface of the circuit board  10 . 
     The end on one side of the frame member  30 , i.e., the farther end from the circuit board  10  is covered with the cover member  45 , while the other end of the frame member  30 , i.e., the end closer to the circuit board  10  is an open end. Since the end of the frame member  30  closer to the circuit board  10  is open, specific electronic circuit parts among a large number of electronic circuit parts can enter into the shield case  20  through the mentioned open end, and can be enclosed or surrounded and shielded by the shield case  20 . 
     At the end of the frame member closer to the circuit board  10 , the end faces  31   a ,  32   a ,  33   a  and  34   a  of the sidewalls  31 ,  32 ,  33  and  34  are respectively confronting the main surface of the circuit board  10 . These end faces  31   a ,  32   a ,  33   a  and  34   a  are approximately parallel to the main surface of the circuit board  10 , and confronting the circuit pattern  12  on the main surface of the circuit board  10  with a minimal gap g in between. 
     The end faces  31   a  of the first sidewall  31  and  32   a  of the second sidewall  32  are respectively provided with a supporting member  35  for sustaining the shield case  20  on the circuit board  10 . This supporting member  35  is composed of three projections  36 ,  37  and  38 , by which the supporting member  35  sustains the shield case  20  at three points on the circuit board  10 . Two projections  36  and  37 , and the remaining projection  38  of the three projections are respectively protruding from the end face  31   a  of the first sidewall  31  and from the end face  32   a  of the second sidewall  32 , by a prescribed height p (see FIGS. 3 and 4) upon the end face  31   a  and the end face  32   a.    
     The three projections  36 ,  37  and  38  are located at three vertexes of a triangle. The projection  38  is located at the middle of the projections  36  and  37  when viewed to the direction confronting the sidewalls  31  and  32 , therefore the mentioned triangle is an isosceles triangle with the side between the projections  36  and  37  as base and with the projection  38  as peak. This isosceles triangle stabilizes the three-point sustention structure of the supporting member  35  all the more. 
     FIGS. 2,  3  and  4  specifically show more clearly the structure of the supporting member  35  in the shield structure shown in FIG.  1 . FIG. 2 is a sectional view taken along the line II—II of FIG.  1  and viewed to the arrow direction, FIG. 3 is a sectional view taken along the line III—III of FIG. 1 which vertically cuts the sidewall  31 , and FIG. 4 is a sectional view taken along the line IV—IV of FIG. 1 which vertically cuts the sidewall  32 . 
     Referring to FIGS. 2,  3  and  4 , the end faces  31   a ,  32   a ,  33   a  and  34   a  of the respective sidewalls  31 ,  32 ,  33  and  34  are parallel to the main surface of the circuit board  10 , and confronting the upper face of the circuit pattern  12  with a prescribed gap g in between. The projections  36 ,  37  and  38  are protruding substantially forming a triangle shape from the end faces  31   a  and  32   a , and each of the protruding vertexes  36   a ,  37   a  and  38   a  is joined to the upper face of the circuit pattern  12  penetrating through the solder bed  13 . The solder bed  13  solidifies after once melting by heat treatment, to solder each electronic circuit part and each of the projections  36 ,  37  and  38  on the circuit pattern  12 . Each of the projections  36 ,  37  and  38  is soldered close to the protruding vertex  36   a ,  37   a  and  38   a  joined to the circuit pattern  12 . Number  39  in FIG. 1 shows soldered sections of each of the projections  36 ,  37  and  38 . 
     More specifically, in actual product, thickness of the solder bed  13  is for instance 0.1 millimeter (mm), gap g is 0.1 to 0.2 mm, and the protruding height p of the projections  36 ,  37  and  38  is 0.1 to 0.2 mm. Thickness of each sidewall  31 ,  32 ,  33  and  34  is 0.1 to 0.3 mm. 
     In this Embodiment 1, it is important that the supporting member  35  is composed of three projections  36 ,  37  and  38  for sustaining the shield case  20  at three points. As compared with the conventional four-face contact or four-point sustention, the projections  36 ,  37  and  38  provide a more secure contact and sustention. Each of the projections  36 ,  37  and  38  can be securely joined to the upper face of the circuit pattern  12 , even if the shield case  20  is warped or distorted. This is because the only effect of such warp or distortion is variation in dimension of the gap g as long as the extent of the warp or distortion is within the gap g, and consequently all the three projections  36 ,  37  and  38  are securely and firmly soldered at the respective joints. 
     The three projections  36 ,  37  and  38  placed on the sidewalls  31  and  32  confronting each other make the three-point sustention more stable, and placing these three projections  36 ,  37  and  38  so as to form an isosceles triangle further stabilizes the three-point sustention. 
     As to the minimal gap g formed between the respective end faces  31   a ,  32   a ,  33   a  and  34   a  of the sidewalls  31 ,  32 ,  33  and  34 , and the upper face of the circuit pattern  12 , substantial leakage was not confirmed through an experiment with the mentioned product. Also, soldering each of the end faces  31   a ,  32   a ,  33   a  and  34   a  with the circuit pattern  12  or with the upper face of the substrate  11  so that the solder enters into the gap g is useful to obtain a more assured shielding effect by the shield case  20 . 
     Embodiment 2 
     FIG. 5 is a perspective view showing an embodiment 2 of a shield structure for electronic circuit parts according to the invention. In this Embodiment 2, the first sidewall  31  and the second sidewall  32  of the frame member  30  are respectively provided with extensions  41  and  42 , corresponding to which the ends of the circuit board  10  are respectively provided with a slit  15  and a protruding part  16 . 
     Firstly the extension  41  extends downward from the end of the first sidewall  31  on the circuit board  10  side, across the circuit board  10  and the direction of thickness thereof. On both sides of this extension  41 , the first projection  36  and the second projection  37  are formed in the same manner as in the foregoing Embodiment 1. The extension  41  is crossing with the circuit board  10  at the slit  15  formed on one end of the circuit board  10 , and the inner face of the extension  41  is parallel to the end face at the recess of the slit  15 , and entirely joined to the mentioned end face. As a result of such structure, the positioning of the first sidewall  31  for the circuit board  10 , and a close joint with the circuit board  10  can be achieved. 
     The extension  42  is a continuous section extending from the end of the second sidewall  32  on the circuit board  10  side, the second sidewall  32  confronting the first sidewall  31 . The extension  42  consists of two extension parts  42 A and  42 B, and at the middle of these two extension parts, the third projection  38  is formed in the same manner as in the foregoing Embodiment 1. The extension parts  42 A and  42 B are holding therebetween the bulge  16  formed on the circuit board  10 , and extend downward across the circuit board  10 . The inner faces of the extensions  42 A and  42 B are parallel to the end face of the circuit board  10  on both sides of the bulge  16 , and entirely joined to the mentioned end face. As a result of such structure, the positioning of the second sidewall  32  for the circuit board  10 , and a close joint with the circuit board  10  can be achieved. 
     Though circuit patterns on the circuit board  10  are omitted in FIG. 5, practically a large number of circuit patterns are formed on the circuit board  10   12  in the same manner as in the embodiment 1, and the first, second and third projections  36 ,  37  and  38  are joined to a circuit pattern connected to the reference potential point, i.e., the earth potential. As a result, a secure support by three-point sustention for the shield case  20 , as well as a secure and firm fixation by the solder bed  13  can be achieved, thereby the same advantage as that in the foregoing Embodiment 1 being achieved. 
     In addition, in this embodiment 2, it is also preferred that the three projections  36 ,  37  and  38  be placed so as to fall on each vertex of an isosceles triangle as in the foregoing Embodiment 1. Such a configuration is advantageous to better stabilize the three-point sustention structure as in the foregoing Embodiment 1. 
     Embodiment 3 
     It is also preferable to adopt a further embodiment in combination of the foregoing Embodiments 1 and 2. Firstly, in Embodiment 1, it is possible to modify the arrangement of only the first sidewall  31  to that described in Embodiment 2, and add the extension  41  thereto. In this case, the circuit board  10  should be provided with a slit  15  as shown in FIG.  5 . Secondly, in Embodiment 1, it is also possible to modify the arrangement of only the second sidewall  32  to that described in Embodiment 2, and add two extensions  42 A and  42 B thereto. In this case, the circuit board  10  is provided with the protruding part  16  as shown in FIG.  5 .