Memory card grounding apparatus

Abstract: An IC memory card (10) is provided which when inserted into a slot (12) of an electronic device (14), discharges any static electric charge on the card prior to mating of card and device contacts (32,34). The card has a frame with opposite sides that have metal clips (70,72) while the electronic device has grounding terminals (74,76) which engage the clips (70,72) as the card is inserted.

Description: The present invention relates to memory cards and relates more specifically to such memory cards having grounding arrangements. Memory cards are commonly constructed with a moulded plastic body having opposite sides and ends, a combination circuit board and connector that is installed in the body, and top and bottom metallic covers installed at the top and bottom of the body. Such memory cards are especially useful in electronic equipment or devices of very small thickness, such as laptop computers that may have a width and length of 21.25cm by 27.5cm (8½ inches by 11 inches), and a thickness of much less than 2.5cm (one inch). Standard JEIDA cards have a thickness of five millimetres, which enables them to be inserted into thin slots of the electronic device. The cards often hold a considerable static electric charge, which should be dissipated prior to mating of signal contacts of the card and device. Memory cards are currently provided with grounding contacts at the front of the card that project slightly forward of the rest of the contacts so the card is grounded before the signal contacts are mated. However, a static electric voltage of a few thousand volts can jump a large fraction of 2.5cm (an inch), so there is danger that a static discharge can occur between signal contacts, which can harm the system. Consequently, a static discharge system which provided early discharge of static electricity on a memory card, would be of considerable value. An electronic apparatus is described in EP-A-0328077 in which an IC card is provided with terminals that are shielded by a shutter arrangement which slidingly contacts a metal panel provided on one side of the card. The metal panel is electrically coupled with an oppositely disposed metal panel by a coil spring so that there is electrical continuity between the shutter and the metal panels. The shutter has projections which serve to engage contact members provided in a housing in to which the card is to be inserted so that the shutter is withdrawn and the metal panels are connected to ground. This arrangement is complex in the provision of projections on a shutter for making the grounding contact and does not provide for grounding of a ground plane on the circuit board. The present invention seeks to provide a simple construction which enables grounding of a ground plane of an IC card so that static electricity can be discharged. In accordance with the present invention there is provided an IC card which includes a frame comprising a moulded body having opposite sides and forward and rearward ends and a circuit board assembly which lies in the frame and which includes a board having a ground plane and a plurality of circuit components mounted on the board, the card being constructed to be inserted into a slot of an electronic device until card contacts at the front end of the card mate with device contacts in the device, characterised in that a sheet metal clip of material which has a higher bulk conductivity than the body, is mounted at a stationary position by securement around a side of the body and is exposed at the outside of the card, with the clip being in contact with the ground plane, thereby to enable early static discharge of the ground plane in cooperation with a grounding contact in the electronic device. In an optional refinement of the invention it may be provided that the body has a pair of side beams that each form one of the sides, in that the sheet metal slip extends at least partially around a first of the side beams and in that the circuit board has opposite faces and edges, with a first of the circuit board edges lying adjacent to a first of the body edges and the ground plane of the circuit board including a portion lying on one of the board faces and against a portion of the clip which clip lies again the body side beam. The IC card may be constructed such that the body has a pair of side beams, with a first of the side beams having upper and lower projections and having a slot and in that the sheet metal clip has upper and lower parts bent about the upper and lower projections, and the clip has a tab that extends through the slot and has a bent part that lies against the ground plane of the circuit board. Optionally, a second similar sheet metal clip is similarly mounted at a stationary position on the body and is exposed at the outside of the card opposite to the first mentioned clip with the clip also being connected to the ground plane thereby to enable static discharge of the ground plane. According to a second aspect of the invention there is provided a combination of an IC card as previously defined and an electronic device having a card-receiving slot with opposite sides, a rear end for initially receiving the card, and a front end, the device having a plurality of contacts at the front end, characterised in that the device has for the or each conductive clip a grounding terminal positioned to engage the clip and discharge any static charge on the card, which slot is deep enough as measured between front and rear ends to receive more than half of the length of the card, and the grounding terminal lies closer to the rear end than to the front end to thereby assure early discharge of any static charge on the card. The body of the card frame can be moulded of electrically conductive material, with the metal conductive region lying a distance rearward of the front of the card side. As a result, the grounding terminal first engages the moderately high resistance electrically conductive material of the body, for partial static discharge, and later engages the metal part of the conductive region for complete discharge. The card preferably has highly conductive regions at opposite sides of the card, and the electronic device preferably has a grounding terminal at opposite sides of the slot and positioned so both terminals simultaneously engage the highly conductive regions at opposite sides of the card. The invention will be best understood from the following description of embodiments of the invention when read in conjunction with the accompanying drawings, in which:- Figure 1 is an isometric view of an IC memory card in accordance with the present invention and an electronic device in the form of a laptop computer; Figure 2 is a sectional top view of the memory card and a portion of the electronic device of Figure 1; Figure 3 is an exploded isometric view of the memory card of Figure 2; Figure 4 is an isometric view of just the body of the frame of the memory card of Figure 3; Figure 5 is a partial sectional view of a memory card taken on the line 5 - 5 of Figure 2; Figure 6 is a side view of a combination of connector and circuit board assembly of the card of Figure 3; Figure 7 is an isometric view of a conductive clip constructed in accordance with another embodiment of the invention. Figure 8 is a partial sectional view of the clip of Figure 7 and of a memory card on which it is mounted, showing the clip during the process of mounting and showing a portion of a mounting tool therefor; and, Figure 9 is a partial sectional view of the clip and card of Figure 8, with the clip fully installed. Referring to Figure 1, this illustrates an IC (integrated circuit) memory card 10 of the present invention that is adapted to be inserted into a slot 12 of an electronic device 14, the particular device shown being a laptop computer. One style of electronic computer has a width and length of 21.25cm and 27.5cm (8.5 inches and 11 inches) respectively and a thickness T that is as small as possible, preferably a small fraction of 2.25cm (an inch). Such a laptop computer can be carried around in space designed to be occupied by ordinary sheets of paper or booklets. One source of concern in using memory cards, is that the card may have a considerable static electric charge, which must be dissipated prior to full insertion of the card into the electronic device, to avoid damage to components in the electronic device. Figure 2 shows the memory card 10 as it is being inserted into the slot 12 of the device 14. The memory card includes a frame 16 with forward and rearward ends 20,22 and opposite sides 24,26. A connector 30 is mounted at the forward end of the frame and has multiple socket contacts 32. The electronic device has multiple corresponding pin contacts 34 at the front end 36 of the slot, which fully engage the socket contacts when the card is fully inserted into the slot. Figure 3 shows details of the memory card 10, which includes the frame 16 and connector 30 that is mounted at the forward end of the frame. A circuit board assembly 40 that is mounted on the frame, includes a circuit board 42 and a plurality of circuit components 44 mounted on the board. Figure 6 illustrates how the rear ends 46 of the connector socket contacts 32 are connected to conductive tracks on the board 42. The frame 16 (Figure 3) includes an injection moulded body 50 and upper and lower electrically conductive covers 52,54 that can be mounted on the top and bottom of the frame body 50. The card is assembled by first installing the combination circuit board assembly 40 and connector 30 on the body 50. Then the upper and lower covers 52,54 are attached to opposite faces of the body. It is possible to mould the connector 30 as part of the frame, although the connector is usually manufactured separately. Figure 4 illustrates details of the moulded body 50. The body includes a pair of side beams 60,62 forming the opposite sides or side edges 24,26 of the card, and a rear beam 64 forming the rear end 22 of the card. The body also includes a pair of cross beams 66,68 which strengthen the body. The frame is provided with a pair of highly conductive regions 70,72 at opposite side edges 24,26 of the card. The highly conductive regions are formed by a pair of sheet metal clips 100,102 formed of material such as gold plated copper. The clips are preferably formed of material having a bulk resistivity that is no more than about one order of magnitude greater than that of copper (whose bulk electrical resistivity is 1.7 microhm-centimetre). The highly conductive regions 70,72 can be contacted by grounding terminals of the electronic device to completely discharge any static electric charge on the card prior to mating of signal contacts at the front of the card with corresponding contacts of the electronic device. As shown in Figure 2, the electronic device is constructed with a pair of grounding contactors or terminals 74,76 at opposite sides of the slot that are connected to a ground plane of the electronic device. As the card is inserted into the slot, the grounding terminals 74,76 wipe against the highly conductive regions 70,72 at opposite side edges 24,26 of the card to establish contact therewith. The conductive regions of the card are connected to the ground potential of circuitry on the circuit board. As a result, when the grounding terminals engage the conductive regions of the card, the terminals discharge any electrical charge on the card, prior to mating of the contacts 32,34 on the card and the electronic device. It is not unusual for a static electric charge on a card to have a potential of a few thousand volts, and such a voltage can create a spark that jumps a gap of 6mm (one-quarter inch). Accordingly, it is desirable that a terminal engages a conductive card region before the card and device contacts are as close as 6mm (one-quarter inch). Figure 5 illustrates some details of the connection of the circuit board assembly 40 and an electrically conductive region 70 (Figure 4) of the frame. The circuit board 42 of the assembly includes a ground plane 80 of electrically conductive material such as metal foil, which is connected to grounded locations of the electronic components on the board. The ground plane lies on the opposite faces 82,84 of the board adjacent to the edges 85 of the board. A clip 100 extends around the entire side 106 of the body, around the moulded material 112 thereof. When the card is assembled as shown in Figure 5, the ground plane 80 lies facewise against a surface 86 of the clip, to ground the clip. As a result, when a grounding terminal 74 contacts the clip, the ground plane of the circuit board is quickly established at the same potential as ground in the electronic device. The bottom cover 54 has a horizontally-extending face 90 and has an edge portion 92 that is bent to extend largely vertically. The edge of the edge portion bears against the ground plane at 80, to ensure that the lower cover 54 is maintained at the same potential as the ground plane of the circuit board and the conductive regions. The top cover 52 also has a face 94 and a bent edge portion 96 whose edge contacts the conductive clip to keep the upper cover grounded. The construction of the electronic device with the grounding terminals 74,76 that engage conductive regions at opposite sides of the card, instead of at its opposite faces, enables the electronic device to be made thinner. That is, each ground terminal such as 74 requires appreciable space beyond the card surface that it engages, and by using space along the width or length of the card instead of along its thickness, the electronic device may be constructed so that it is very thin. It is possible to use a single ground terminal such as 74 instead of two of them, to simplify the electronic device and reduce its cost. However, tests that have been conducted show that symmetrical grounding is highly desirable, in that unsymmetrical discharge of the static charge on the card can result in damage to the circuitry in the card. Thus, it is preferred to arrange the two grounding terminals 74,76 so that each engages an opposite clip 100, 102 at the same time to symmetrically discharge static electricity from the card. The moulded frame body 50 (Figure 4) can be formed of dielectric material (a resistivity more than 10⁵ times that of copper), so static discharge occurs only when the ground terminals engage the clips. However, it may be preferred to construct the moulded body material 112 of electrically conductive material, although with a bulk conductivity of less than one-half and preferably less than one-tenth that of the material of the clip 100. Such conductive body is connected to the ground potential of the clip and of the circuit board. In such an arrangement, the ground terminals 74,76 (Figure 2) initially engage a ground moderate resistivity material as they engage the opposite sides 24,26 of the card. The advantage is that static discharge is more gradual in that it occurs over a longer period of time, resulting in smaller discharge current and less possibility of damage to the card and electronic device. The presence of the high conductivity clips 100,102 ensures that all of the static charge is discharged prior to mating of the contacts at the front end of the card in the event that there is a large static charge on the card. The provision of an all conductive body has the additional advantage of guarding against EMI (electromagnetic interference). Figures 7 - 9 illustrate another clip 120 which is formed of thin sheet metal that is initially bent in the shape shown in Figure 7. The clip includes an outer side 121 that will lie at the outer surface of the memory card body, upper and lower parts 122,124 that will lie around the upper and lower surfaces of the body, and a contact tab 126. The clip is initially installed as shown in Figure 8 on the body 130 of the memory card frame, with the contact tab at 126A extending through a slot 128 in the body side beam 129, and bent down along a board-support surface 132 of the body. Then, a tool 134 is used to bend the upper part 122 tightly around a body lip 136 to securely hold the clip in place. Figure 9 shows the circuit board assembly 40 installed, with the ground plane 80 thereof lying facewise against the bent part 127A of the tab 126A of the clip to electrically connect them. The upper and lower clip parts at 122A, 124A lie about upper and lower projections 140,142 of the body side beam 129. It may be noted that the card in Figures 8 and 9 is in an orientation upside-down from that of Figure 5. Thus, the invention provides a memory card that can be inserted into the slot of an electronic device, which ensures discharge of any static charge on the card prior to mating of the contacts of the card and device. The card has an electrically conductive metal region mounted on the moulded body of the card frame and connected to a ground plane of the card circuit board, and the electronic device has at least one grounding terminal positioned to engage the conductive region. The conductive region lies at a side edge of the card to minimise the require height of the electronic device. Preferably, opposite sides of the card have conductive clips and the device has a pair of grounding terminals for engaging them. The body of the frame can be formed primarily of electrically conductive material of higher resistance than the clips, to gradually discharge the static charge, with the clips quickly discharging any remaining charge.

Claims: An IC card (10) which includes a frame (16) comprising a moulded body (50,130) having opposite sides (24,26) and forward and rearward ends (20,22) and a circuit board assembly (42) which lies in the frame and which includes a board (40) having a ground plane (80) and a plurality of circuit components (44) mounted on the board, the card being constructed to be inserted into a slot (12) of an electronic device (14) until card contacts (32) at the front end of the card mate with device contacts (34) in the device, characterised in that a sheet metal clip (100,120) of material which has a higher bulk conductivity than the body, is mounted at a stationary position by securement around a side of the body and is exposed at the outside of the card, with the clip being in contact with the ground plane (80), thereby to enable early static discharge of the ground plane in cooperation with a grounding contact in the electronic device. An IC card as claimed in claim 1, characterised in that the body (50) has a pair of side beams (60,62,129) that each form one of the sides (24,26), in that the sheet metal clip (100,120) extends at least partially around a first of the side beams (60) and in that the circuit board has opposite faces (82,84) and edges (85), with a first of the circuit board edges (85) lying adjacent to a first of the body edges (24), and the ground plane (80) of the circuit board including a portion lying on one of the board faces (84) and against a portion of the clip (100,120) which clip lies against the body side beam (60). An IC card as claimed in claim 1, characterised in that the body (50) has a pair of side beams (129), with a first of the side beams having upper (140) and lower (142) projections and having a slot (128) and in that the sheet metal clip (120) has upper (122A) and lower (124A) parts bent about the upper and lower projections, and the clip has a tab (126A) that extends through the slot (128) and has a bent part (127A) that lies against the ground plane (80) of the circuit board (140). An IC card as claimed in any one of claims 1 to 3, characterised in that a second similar sheet metal clip (102,120) is similarly mounted at a stationary position on the body (50) and is exposed at the outside of the card opposite to the first mentioned clip (100,120) with the clip also being connected to the ground plane (80) thereby to enable static discharge of the ground plane. An IC card as claimed in any one of the preceding claims, characterised in that the moulded body (50,130) is formed from an electrically conductive material having a conductivity less than one half of the conductivity of the material of the clip (100, 120) thereby to enable initial static discharge during insertion of the card into a slot by cooperation between the moulded body and the grounding contact in the electronic device. An IC card as claimed in claim 5, characterised in that the conductivity of the moulded body (50,130) is less than one tenth of the conductivity of the material of the clip (100, 120). The combination of an IC card (10) as claimed in any one of the preceding claims and an electronic device (14) having a card-receiving slot (12) with opposite sides (80,82), a rear end for initially receiving the card, and a front end (36), the device having a plurality of contacts (34) at the front end, characterised in that the device has for the or each conductive clip (100, 102, 120) a grounding terminal (74, 76) positioned to engage the clip and discharge any static charge on the card, which slot is deep enough as measured between front and rear ends to receive more than half of the length of the card, and the grounding terminal lies closer to the rear end than to the front end to thereby assure early discharge of any static charge on the card. A combination as claimed in claim 7, characterised in that the electronic device (14) has for the or each conductive clip (100, 102, 120) a terminal (74, 76) positioned to engage the clip and discharge any static charge on said card before any of the card contacts (32) approach within 6mm (one-quarter inch) of any of the device contacts (34).

Inventors: MACGREGOR DUNCAN DAVID, PERKINS CARL CURTISS, MACGREGOR, DUNCAN DAVID, PERKINS, CARL CURTISS
Applicants: INTEL CORP, ITT, INTEL CORPORATION, ITT INDUSTRIES, INC. (A DELAWARE CORPORATION)
Application year: 1992
Main classification: H01R13
IPC codes: G11C5, G06K19, G06F3, B42D15, G06K17, H01R13, H01R12