Data card perimeter shield

Abstract: A data card is provided which has an electrically conductive rail extending along its opposite sides and part of its rear, and connected to a ground plane of a circuit board of the card, to provide EMI (electromagnetic interference) shielding along the perimeter of the card. The rail has top and bottom edge portions that are each bent into a U shape to extend around top and bottom ridges at the side of the card body to lock the rail in place. One edge portion includes a projecting tab which is bent to extend inwardly and engage the ground plane of the circuit board. The moulded card body has a through hole in its side portion, and the tab can extend into that hole before extending inwardly to the circuit board ground plane.

Description: This invention relates to data cards. Data cards are commonly constructed with a moulded plastic body of moderate width and length, such as 5.3cm by 8.5cm, but small thickness, such as 5mm. A circuit board assembly that is installed on the body, includes one or more integrated circuits that usually store data but may include only processing circuitry. Metallic top and bottom covers complete the card. Such data cards are especially useful in electronic equipment or devices of small thickness, such as lap top computers that may have a thickness of much less than 2.54cms. Standard JEIDA cards have a thickness of five millimetres, which enables them to be inserted into thin slots of the electronic device. One such construction is described in European Patent Specification EP-A0417648 and comprises a synthetic resin frame into which a circuit board can be mounted in a recess. Top and bottom sheet metal cover plates are employed which are interconnected via narrow mutually hook portions which extend across the sides of the frames. Such a construction is susceptible of interference through the perimeter of the card. British Patent Number GB-A2248973 describes an IC card having a frame for receiving a circuit board and conductive top and bottom covers. The top and bottom covers are each grounded by means of a lead extending from a ground terminal of an end connector. This provides for elimination of build up of static electricity between the top and bottom covers and wiring on the card. Such a construction would also provide EMI shielding by way of the covers but is again susceptible of interference through the perimeter of the card. While the top and bottom metallic covers provide good EMI (electromagnetic interference) shielding, there still can be considerable leakage through the perimeter of the card. A perimeter EMI shielding which adds a minimal amount to the size of the card, and which is readily installable so it securely holds to the moulded body and is connected to the ground plane of the circuit board, and which preferably also helps to ground the covers, would be of value. According to the present invention there is provided a data card which includes a housing having a moulded plastic frame with a top and a bottom, opposite side portions, and forward and rearward ends, the housing also having Electromagnetic interference shielding comprising sheet metal top and bottom covers lying respectively on the top and bottom of the frame, the card also including a circuit board assembly which lies in the housing and which includes a board having a ground conductor and at least one circuit component mounted on the board, characterised in that the Electromagnetic interference shielding includes sheet metal rail portions extending along the outer side of the side portions of the frame, the rail portions extending along more than half the height and along more than half the length of the frame side portions to cover most of the area of the side portions, and the rail portions being electrically connected to the covers and to the board ground conductor. The data card may have frame sides characterised in that the Frame sides have a pair of ridges including a ridge at their top and a ridge at their bottom, and the rail portions each have top and bottom edge portions that are each bent in a U shape to extend around a different one of the ridges. The data card may include a shielding characterised in that the shielding includes an integral laterally extending tab lying adjacent to one of the side portions the tab having a free end engaging the ground conductor. The invention will be best understood from the following description of one exemplary embodiment of the invention when read in conjunction with the accompanying drawings in which: Figure 1 is an isometric view of a data card of the present invention, showing it in conjunction with an electronic device which can receive it; Figure 2 is an exploded isometric view of the data card of Figure 1; Figure 3 is an isometric view of the body of the card of Figure 2, with the shielding rails attached, but without the circuit board assembly or covers in place; Figure 4 is an isometric view of one of the rails of the card of Figure 3, in its fully deformed position except for the tabs thereof; Figure 5 is a partial sectional view taken on the line 5 - 5 of Figure 3, but with the circuit board assembly and covers in place; Figure 6 is a sectional view taken on the line 6 - 6 of Figure 3 with the circuit board assembly and covers in place; Figure 7 is a sectional view of the rail of Figure 4, prior to its installation on the card body; and, Figure 8 is a sectional view of the rail of Figure 7, taken through a tab thereof, showing it in its fully formed position. Figure 1 illustrates a data card 10 of the present invention, which is adapted to be inserted into a slot 12 of an electronic device 14. The particular device shown being a thin lap top computer. As shown in Figure 2, the data card includes a housing 20 comprising a moulded plastic frame 22 and top and bottom covers 24, 26. The frame 22 has a top and bottom 32, 30, first and second opposite sides 34,36, and forward and rearward ends 40,42. A circuit board assembly 44 is mounted on the frame 22, the assembly including a circuit board 46 and a plurality of electronic components including an integrated circuit component 48 mounted on the circuit board. A connector 50 mounted on the forward end of the frame is connected to multiple tracks on the board, of which at least some extend to the electronic components mounted on the board. When the data card 10 is moved in a forward direction F into an electronic device, contacts of the connector 50 engage corresponding contacts on the electronic device. In many cases, the integrated circuit components, such as 48, store data. The particular data card shown includes a rear connector 52 which can receive a miniature plug (not shown) to enable transmission of data between the card and an outside source (e.g. a modem), the connector having multiple contacts 54 engaged with multiple tracks on the circuit board. It is highly desirable to provide EMI (electromagnetic interference) shielding for the data card, to suppress the passage of signals into the card that might be picked up by circuitry in the card, and to suppress the radiation of signals by the card. When the card lies deep within an electronic device such as a lap top computer, it is especially important to suppress the transmission of signals from the card that might be picked up by circuitry in the electronic device. The top and bottom covers 24, 26 are formed of electrically conductive material, such as stainless steel, to provide good EMI shielding. However, prior data cards have not provided good shielding along the perimeter of the card, that is, the outside of the card between the top and bottom covers. The moulded frame 22 is generally of moulded material of low electrical conductivity (at least about two orders of magnitude less than that of copper, and generally at least four orders of magnitude less). In accordance with the present invention, EMI shielding is provided around much of the perimeter of the data card, by perimeter shield rails 70, 72. As shown in Figures 3 and 4, each rail such 70 is formed from sheet metal, as by forming it of 0.01016 cms thick copper alloy which is gold plated. Each rail has a side portion 74 that extends along a corresponding side 34 of the frame 22, and an end portion 76 which extends 90° from the side portion to extend along part of the rearward end 42 of the frame. It would be feasible to use a single rail which extends around both the opposite sides 34,36 and the rear end 42. However, the middle of the rear end is occupied by pin-receiving holes of the rear connector 52 which must receive pins of a mating connector, which makes it more difficult to use a single rail. The connector 52 can be formed with an EMI barrier structure, but the rails 70,72 do not extend behind the connector. In a similar manner, the front connector (50 in Figure 2) is not shielded by the rails, and the forward portions of each side are not shielded because of the need for polarising keys 80,82 at the front end. However, each rail, such as 70, has a height slightly more than the height of the frame 22 and a length more than half the length of the frame (between its ends 40, 42) so each side rail covers most of the peripheral area at each side 34,36 of the data card. In fact, each rail covers about 80% of the area of each side. The end portions 76 of the two rails cover about one third of the rear peripheral portion of the card. The data card has an imaginary vertical axis 84 that is equally spaced from its opposite sides and from its opposite ends, and has an imaginary longitudinal centerplane 86 lying halfway between the opposite sides 34,36. As shown in Figure 5, each frame side such as 34 has top and bottom ridges 90,92. The rail 70 has top and bottom edge portions 94,96 that are each bent in a U shape to extend around each ridge, and thereby securely hold the rail to the frame side. The frame has a support wall 100 that forms a support surface 102 that supports the circuit board 46. There is substantial space between the top face 104 of the circuit board and the top cover 24, and between the bottom face 106 of the circuit aboard and the bottom cover 26. Electronic components on the circuit board can lie on and project from the top face and/or bottom face of the circuit board, and the space accommodates such projecting components. The frame also forms a sideward locating wall 108 which closely surrounds the circuit board 46. As shown in Figures 3 and 6, the rail 70 has a pair of tabs 110,112 which are designed to project down through a pair of through holes 114,116 in the frame side or side portion 34. Each tab is bent into a narrow U curve at 120, to leave a tab free end 122 extending along the bottom of the support wall 100. The free end 122 extends inwardly (toward the longitudinal centerplane 86 and at least partially toward the axis 84). The support wall has a recess 124 for accommodating the free ends of each tab, to enable the circuit board to lie securely against the support surface 102 and still allow the free end 122 of the tab to pass to a position to engage the circuit board 46. The ground conductor 60 of the circuit board includes a peripheral portion 130 that extends on the top and bottom faces 104,106 at the peripheral portion 134 of the board 136 of the circuit board. As a result, the free end 122 of the tab engages the peripheral portion 130 of the ground conductor of the circuit board, to thereby connect the circuit board ground conductor to the rail 70. It may be noted that the tab free end 122 will be soldered to the ground conductor as indicated at 138. Also, the circuit board can be securely held to the frame as by adhesive. The locating wall 108 at the frame side has a slot 140 at the location of each tab. The slot facilitates forming of the tab 110 after it is projected downwardly through the hole 114 in the frame. After such downward projection, the tab is deformed, as shown. The U curve 120 in the tab is useful to receive a projection 142 formed along the edge of the top cover 24. This serves to ground the top cover 24 as well as helping to hold the cover in place. It may be noted that the cover also can be held to the Frame by adhesive, and also can be grounded by a grounding contact comparable to contact 54A shown in Figure 2. The other rail 72 is attached to the frame in a similar manner, except that its tabs, such as 150, are differently bent as shown in Figure 6. The tab 150 engages the peripheral portion 130 of the circuit board ground conductor and receives a bottom cover projection 152. The tabs can serve not only to ground the rail and the cover, but also to prevent shifting of the rail. Where the top and bottom covers are readily removable, the U loops of the tabs provide a means to help ground the tabs and help hold them in position. Thus, the invention provides means for providing EMI (electromagnetic interference) protection along the periphery of a data card, in a low cost construction that adds minimally to the width and length of the card. This can be accomplished by providing electrically conductive rail portions formed of sheet metal that extends along at least one side of the frame and which cover more than half the height and length to thereby cover most of the area of the frame sides. The rail portions are electrically connected to the ground conductor of the circuit board mounted in the frame. Where a rear connector is provided on the data card, two rails are used, each of which has a side portion covering most of the area at a corresponding side of the card frame and has a 90° bent end portion covering a portion of the rear end of the frame. The frame can be moulded with top and bottom vertically extending ridges, and the rail can be formed with top and bottom edge portions that extend in substantially a U bend around each ridge. The rail can be provided with at least one tab extending from one of the edge portions, with the tab extending through a through hole formed in the frame immediately inside the ridges. After the tab is projected downwardly through a hole, it is bent so a free end of the tab lies against a support wall that supports the circuit board assembly, and preferably lies in a recess in the support wall. It should be noted that terms such as "top", "bottom", "vertical", etc. have been used herein only to aid in the description of the invention, and that the data card can be used in any orientation with respect to gravity.

Claims: A data card which includes a housing (20) having a moulded plastic frame (22) with a top (32) and a bottom (30), opposite side portions (34,36), and forward and rearward ends (40,42), the housing also having Electromagnetic interference shielding comprising sheet metal top and bottom covers (24, 26) lying respectively on the top (32) and bottom (30) of the frame (22), the card also including a circuit board assembly (44) which lies in the housing (20) and which includes a board (46) having a ground conductor (60) and at least one circuit component (48) mounted on the board, characterised in that the Electromagnetic interference shielding includes sheet metal rail portions (70, 72) extending along the outer side of the side portions (34, 36) of the frame (22), the rail portions (70, 72) extending along more than half the height and along more than half the length of the frame side portions (34, 36) to cover most of the area of the side portions, and the rail portions (70, 72) being electrically connected to the covers (24, 26) and to the board ground conductor (60). A data card as claimed in claim 1, characterised in that the frame sides (34,36) have a pair of ridges (90, 92) including a ridge (90) at their top and a ridge (92) at their bottom, and the rail portions (70, 72) each have top and bottom edge portions (94, 96) that are each bent in a U shape to extend around a different one of the ridges. A data card as claimed in claim 1 or 2, characterised in that the shielding includes an integral laterally extending tab (110) lying adjacent to one of the side portions (34, 36) the tab having a free end (122) engaging the ground conductor (60). A data card as claimed in claim 1 or claim 2, characterised in that the board (46) has top and bottom opposite faces (104, 106) and has a peripheral portion (134), and the ground conductor (60) has a portion lying on at least one board face at the peripheral portion, in that the frame (22) has a support wall (100) for supporting the top face (104) of the board peripheral portion (134), and the frame has a sideward locating wall (108) extending down from the support wall and surrounding the board and in that the rail portions (70, 72) have top and bottom rail edge portions (94, 96) and one of the rail edge portions (94) includes a projecting tab (110) that extends to a location between the support wall (100) and the board peripheral portion (134) and which engages the ground conductor thereat. A data card as claimed in claim 4, characterised in that the frame locating wall (108) has a slot (140) extending to slightly above the bottom of the support wall (100), and the support wall has a recess (124) aligned with the slot and in that the tab extends through the slot and lies in the recess and engages a ground conductor portion that lies against the support wail. A data card as claimed in claim 5, characterised in that the one of the fame side portions (34) has a through hole (114) extending between its top and bottom with at least part of the hole lying inward of ridges (90, 92) provided one at the top and the other at the bottom in the side portions (34, 36) and in that the rail has upper and lower edge portions (94, 96), the tab (110) extends from the upper edge portion (94) and downwardly into the hole (114), and the tab is bent to extend through the slot (140) into the recess (124). A data card as claimed in any preceding claim, characterised in that the rail portions (70, 72) have a 90° bend forming an end portion (76) that extends along part of one of the ends of the frame. A data card as claimed in claim 1, characterised in that the rail portions (70, 72) extend between the top and bottom covers (24, 26) and extend continuously substantially the entire length of the side portions (34, 36) of the frame (22). A data card as claimed in claims 1 or 8, characterised in that front and rear connectors (50, 52) are located at the forward and rearward ends (40, 42) of the frame (22), with the rear connector (42) being spaced from the side portions (34, 36) of the frame (22) to provide frame end areas, and the electromagnetic interference shielding has end portions (76) extending over the frame end areas.

Inventors: ANHALT JOHN WILLIAM, DOOSE WILLIAM HERMAN, GALARZA WILLIAM, ANHALT, JOHN WILLIAM, DOOSE, WILLIAM HERMAN, GALARZA, WILLIAM
Applicants: ITT MFG ENTERPRISES INC, ITT MANUFACTURING ENTERPRISES, INC.
Application year: 1992
Main classification: G06K19
IPC codes: G06K19