Dual read-out SIMM socket for high speed electrical applications

Abstract: A dual readout socket (10) for establishing electrical contact with electrically isolated traces on opposite surfaces of a single in-line memory module comprises an elongate insulating housing (12) having a longitudinal slot (14) for receiving the module, and slots (16) in which the signal terminals (13) and ground terminals (15) are retained. The terminals (13, 15) have contact springs (64) projecting into the module receiving slot (14) for contacting the traces of the module. The housing (12) has a central wall (28) which receives a ground plane (81). The signal terminals (13) are insulated from the ground plane (81) by the walls of the ground plane receiving slot (84) whereas these walls have openings (92) through which contact members (58) of the ground terminals (15) project, into electrical contact with the ground plane (81). The signal terminals (13) have leads (36a, 36b) and the ground plane (81) has leads (85). The leads of the signal terminals and of the ground plane, are inserted through holes (82) on a mother card substrate (80) and are connected to signal conductors and ground conductors, respectively, on the substrate (80).

Description: This invention relates to a socket for establishing electrical contact with electrically isolated traces on opposite surfaces of a single in-line memory module (SIMM). A single in-line memory module provides a high density, low profile single in-line package for electronic components such as dynamic random access memory integrated circuit components. A plurality of these components can be mounted in line on a circuit panel, the height of which is little more than the length of the components themselves. Such a circuit panel can be mounted on a printed circuit board daughter-card for mounting to a printed circuit board mother card. Such a daughter card with the circuit panels mounted thereon is known as a single in-line memory module. US-A-4,973,270 discloses a socket known as an SIMM socket for use in mounting such a module to a mother board. The modules with which such sockets are intended to be used, have circuit traces on both sides thereof. The traces on one side are, however, electrically connected to the traces on the other side, the traces on both sides of the module being in direct alignment with each other. Accordingly, the socket of US-A-4,973,270 has terminals having opposed beams which are commoned to a single lead, the opposed beams being for making electrical contact to each of a pair of commoned traces, one on each surface of the module. The need has arisen for a socket for connection to electrically isolated circuits on opposite surfaces a single in-line memory module. Such a socket is known as a dual read out socket (see, for example, US-A-5 082 459). There is disclosed in US-A-3 871 728, a dual read-out socket for establishing electrical contact with electrically isolated traces on opposite surfaces of a single in-line memory module, the socket comprising an elongate insulating housing having a longitudinal slot for receiving the module, terminal receiving slots extending transversely of, and opening into, the module receiving slot on both of opposite sides thereof, electrical terminals retained in the terminal receiving slots each having a contact spring having a contact surface extending into the module receiving slot for establishing said electrical contact with said traces, the terminals comprising signal terminals having leads for connection to external conductors, and a ground plane received in a ground plane receiving slot defined by the housing, the signal terminals being electrically isolated by the housing from the ground plane. Electrical connection between ground contacts and the ground plane in this assembly is established via a ground layer in the circuit board to which the connector is mounted. The need has also arisen for selected terminals for such a dual read out socket to be connected to ground in such a way as to enhance the capabilities of such a dual read-out socket for high speed electrical application. A dual read out socket, according to the present invention, is accordingly characterized in that the ground plane receiving slot communicates with selected ones of the terminal receiving slots, said terminals further comprising ground terminals retained in said selected terminal receiving slots, each ground terminal having a contact member in electrical contact with the ground plane. Such a dual read out socket can conveniently and rapidly be mounted to a mother card by connecting the signal terminals to respective signal conductors of the mother card and the ground plane to a ground conductor, or ground conductors of the mother card. Both the signal terminals and the ground plane maybe provided with leads which can be inserted through the respective pre-drilled holes of the mother card and which project a direction way from the module receiving slot. In the interest of economy the ground and signal terminals may be identical, excepting that the ground terminals need not be provided with leads. Conveniently the signal terminals have retention posts for engaging side walls of the ground plane receiving slot and the contact members of the ground terminals are identical with these retention posts. Communication between the module receiving slot and the selected terminal receiving slots can be established by providing the walls of the ground plane receiving slot with access openings for the contact members of the ground terminals. In the interest of rapid assembly of the dual read out socket, a single ground plane receiving slot may extend throughout the length of the housing and may receive a single ground plane of the same length as the ground plane receiving slot. In the interest of contact density, the terminals are preferably uniplanar whereby the centre to centre spacing of the terminal receiving slots lengthwise of the housing need not exceed 0.75 mm. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is an isometric view of a high speed, dual read-out, single in line memory module socket according to an embodiment of the present invention; Fig. 2 is an end view of the socket shown in section through slots therein which receive ground terminals; Fig. 3 is a similar view to that of Fig. 2 but being shown in section through slots which receive signal terminals; Fig. 4 is a top plan view of the socket; Fig. 5 is a side view of the ground and signal terminals when connected together in strip form; Fig. 6 is a view taken on the lines 6-6 of Fig. 4, showing the signal terminals; Fig. 7 is a view taken on the lines 7-7 of Figure 4 showing the ground terminals; Fig. 8 is a side view of a ground plane of the socket; and Fig. 9 is a side view of an alternative embodiment of the ground plane. A dual readout SIMM (single in line memory module) socket 10 shown in Figure 1 includes a housing 12 and a plurality of signal terminals 13 and ground terminals 15, which are shown in detail in Figures 5-7. The housing 12 , which is molded from an insulating plastics material, for example a liquid crystal polymer, defines SIMM panel receiving slots 14 and parallel rows of terminal receiving slots 16 extending at right angles to, and opening into the panel receiving slots 14. At each end of the housing 12 there is provided a panel support member 18 having a groove 20 for receiving and retaining a SIMM panel (not shown) therein. The grooves 20 are aligned with the slots 14. As shown in Figures 2 and 3 , terminal receiving slots 16 are defined by transverse walls 22 and side walls 26 of the housing 12. The walls 22 serve electrically to isolate terminals disposed in slots 16 which are adjacent to one another lengthwise of the housing 12. The transverse walls 22 support terminal retaining bars 24 extending between the walls 22. The bars 24 are parallel to, and are inwardly spaced from, the sidewalls 26 and a centerwall 28 midway between the walls 26. Each bar 24 defines, in co-operation with the side wall 26 which is proximate thereto, a vertically open ended retention slot 27. The slots 16 open into the top surface 30 and the bottom surface 32 of the housing 12 as well as into respective panel receiving slots 14. A blind slot 84 in the centre wall 28 extends along the length of the housing 12 and opens into the bottom surface 32 of the housing as best seen in Figure 3. The slot 84 communicates with respective terminal receiving slots 16 which are to receive ground terminals 15, by way of openings 92 in the wall 28, as shown in Figure 2. As will best be apparent from Figure 4, the terminal receiving slots 16 open towards each other on opposite sides of the panel receiving slots 14. According to the present embodiment, adjacent terminal slots 16 in the lengthwise direction of the housing 12 have a centre line spacing of 0.75 mm, although such spacing may be smaller, for example 0.5 mm. Figure 5 shows a pair of terminals 13 and a pair of terminals 15 connected by way of slugs 35 to a common carrier strip 34 in strip form. The strip of terminals 13 and 15 was manufactured by stamping and forming a single strip of sheet metal stock, for example, of phosphor bronze, by means of a progressive stamping and forming operation. As shown in Figure 5, each signal terminal 13 comprises leads 36a and 36b depending from a lower edge 38 of a base section 44 of the terminal 13. The lead 36a depends from one end 40 of the base section 44 of the terminal 13, the lead 36b depending from the other end 42 of the section 44. The ground terminals 15 are identical with the signal terminals 13, and so bear the same reference numerals, excepting that the terminals 15 are devoid of the leads 36a and 36b. A first retention post 48 upstands from the upper edge 50 of the base section 44 at the end 40, the post 48 having retention barbs 52 on both edges thereof. A second retention post 58 upstands from the upper edge 50 at the end 42 of the base section 44 and has a retention barb 60 on its outer edge 62 only. A contact spring 64 extends upwardly from the upper edge 50 of the base section 44 and is located just inwardly of the first retension post 48. The contact spring 64 is substantially S-shaped and terminates in a depending contact arm 68 having proximate to its free end 70, an inwardly bowed contact surface 72. Before being fully assembled to the housing 12, as shown in Figures 6 and 7, the terminals 13 and 15 were separated from the carrier strip 34 by shearing away the slugs 35 connecting them to the carrier strip 34, the terminals of each pair of terminals 13 and 15 were separated from one another by shearing out respective slugs 44a connecting the terminals of the pairs and the two pairs of terminals 13 and 15 were separated from each other by shearing out a slug 44a' connecting said two pairs. Further to this one of the leads 36a and 36b was severed from each terminal 13 as will be apparent from Figure 6. As shown in Figure 6, each terminal 13 is retained in a respective slot 16 by means of its first retention post 48 forced into a respective slot 27 so that the barbs 52 of the post 48 frictionally engage the proximate side wall 26 and the associated bar 24. Further retention of each terminal 13 is provided by its second retention post 58 forced against the centre wall 28, given that the width of the slot 16 is slightly less than the length of the base section 44 of the terminal 13, so that the barb 60 of the post 58 frictionally engages the centre wall 28. The contact arm 68 of the contact spring 64 extends into the panel receiving slot 14 with the bowed contact surface 72 of the arm 68 innermost of the slot 14. As shown in Figure 7 each ground terminal 15 is retained in its respective slot 16 in a manner similar to that in which each signal terminal 13 is retained in its slot 16, excepting that the retention post 58 of the terminal 15 extends through a respective opening 92 in the centre wall 28 so that the outside edge 62 of the post 58 makes electrically conductive contact with a ground plane 81 when seated in the slot 84 as described below. Preferably, the pairs of terminals 13 and the pairs of terminals 15 are disposed in alternate respective pairs of opposed slots 16. The terminals 13 and 15 may, however, be disposed in the slots 16 in any other selected arrangement needed for their mating with appropriate signal and ground traces on the SIMM panel to be received in the slots 14. Figures 6 and 7 show the socket 10 mounted on a substrate, which may, for example, be a back plane, printed circuit board or other like device. As shown in Figure 6, the right hand terminal 13 has a single lead 36a, the left hand terminal 13 having a single lead 36b, each lead 36a and 36b having been inserted through a pre-drilled hole 82 in the substrate 80. The leads 36a and 36b are soldered to signal conductors (not shown) on the substrate 80. The ground plane 81 which has been stamped from a sheet of electrically conductive material, and which is uniplanar, comprises an elongate, substantially rectangular body 87 from one longitudinal edge 86 of which depend leads 85, one at each end of the body 87. The ground plane 81 has a leading edge 88 opposite to the edge 86. The body 87 of the ground plane 81 is inserted into the slot 84 in the centre wall 28 of the housing 12 with the edge 88 of the body 87 leading. As shown in Figure 6, the body 87 is insulated by the walls of the slot 84 from the retention posts 58 of the terminals 13, whereas as shown in Figure 7, since the posts 58 of the terminals 15 extend through the openings 92 of the wall 28, the body 87 of the ground plane 81 is gripped between the posts 58 as described above. The leads 85 of the ground plane 81 are inserted through pre-drilled holes 82 in the substrate 80 and are soldered to a ground conductor, or ground conductors, thereon, this being done either before the insertion of the body 87 into the slot 84 or afterwards. The body 87 is preferably retained by an interference fit in the slot 84. As will be apparent, a substantial number of ground planes 81 must be provided, since a ground plane 81 is only long enough to common only a few of the pairs of ground terminals 15. As shown in Figure 9, however, a ground plane 81 of indefinite length may be provided for commoning all of, or a substantial number of, pairs of terminals 15. In Figure 9 the reference numerals are the same as those of Figure 8, but with the addition of a prime symbol. When the leading margin of a SIMM panel is inserted into the slots 14, the lateral edges of the panel being guided to the grooves 20, predetermined signal and ground traces on opposite sides of the panel engage opposite and electrically isolated contact surfaces 72 of the terminals 13 and 15 and are thereby electrically connected to predetermined conductors on the substrate 80. The leads 36a and 36b of the terminals 13 and the leads 85 or 85' of the ground plane 81 or 81', may conveniently be staggered for insertion through predetermined holes 82 in the substrate 80. In order to enable the preferred alternate arrangement of the terminals 13 and 15, mentioned above, the centre wall 28 between every other pair of opposed slots 16 is provided with the openings 92. Instead of the leads 36a and 36b the terminals 13 may be provided with conventional surface mount leads for soldering to conductors on the upper surface of the substrate 80. The socket 10 may, instead of having slots 14 for receiving a single panel, be provided with parallel slots so that the SIMM socket can be mated with two SIMM panels. The strip of terminals 13 and 15 as shown in Figure 5 is of particular use with such an embodiment of the socket. The terminals can thus be loaded into the housing by partially inserting each pair of terminals 13 and 15 into respective terminal receiving slots in the socket, severing the carrier strip 34 from the terminals by shearing out the slugs 35, separating the terminals of each pair by shearing out the slugs 44a, separating the two pairs of terminals 13 and 15 by shearing out the slug 44a', severing a selected lead 36a or 36b and finally driving the terminals home into their terminal receiving slots. Where the socket 10 has, as in the embodiment described above, slots 14 for receiving only one panel, two such sockets 10 could be loaded with the terminals, with the sockets 10 arranged in side by side relationship, by the method just described. A single socket 10 could be loaded with terminals 13 and 15 by loading one pair of terminals into their slots 16 and the other pair of terminals into their slots 16 after severing the two pairs of terminals.

Claims: A dual readout socket (10) for establishing electrical contact with electrically isolated traces on opposite surfaces of a single in-line memory module, the socket (10) comprising an elongate insulating housing (12) having a longitudinal slot (14) for receiving the module, a terminal receiving slot (16) extending transversely of, and opening into, the module receiving slot (14) on both of opposite sides thereof, electrical terminals (13, 15) retained in the terminal receiving slots (16) each having a contact spring (64) having a contact surface (72) extending into the module receiving slot for establishing electrical contact with a respective one of said traces, said terminals comprising signal termminals (13) having leads (36a, 36b) for connection to external conductors, and a ground plane (81) received in a ground plane receiving slot (84) defined by the housing (12), the signal terminals (13) being electrically isolated by the housing (12) from the ground plane (81); characterized in that the ground plane receiving slot communicates with selected ones of said terminal receiving slots (16), said terminals (13, 15) further comprising ground terminals (15) in said selected terminal receiving slots (16), each ground terminal(15) having a contact member (58) in electrical contact with the ground plane (81). A socket as claimed in claim 1, characterized in that the ground plane receiving slot (84) is aligned with the module receiving slot (14) and opens in a direction away therefrom to receive the ground plane (81), side walls of the ground plane receiving slot (84) having openings (92) through which the contact members (58) of the ground terminals (15) extend. A socket as claimed in claim 1 or 2, characterized in that the signal terminals (13) have retention posts (58) engaged with the side walls of the ground plane receiving slot (84), the retention posts (58) being identical with the contact members (58) of the ground terminals (15). A socket as claimed in claim 1, 2, or 3, characterized in that the ground plane receiving slot (84) is defined by a central longitudinal wall (28) of the housing (12) connected to the base of the module receiving slot (14) and extending between the contact springs (64) of the terminals (13, 15) on each side of the module receiving slot (14). A socket as claimed in any one of the preceding claims, characterized in that the terminal receiving slots (16) are arranged in pairs of opposed terminal receiving slots (16), the terminal receiving slots (16) of each pair being disposed on opposite sides of the module receiving slot (14), the terminals retained in the slots (16) of each pair both being either signal terminals (13) or ground terminals (15), the pairs of signal terminals (13) alternating with the pairs of ground terminals (15) lengthwise of the housing (12). A socket as claimed in any one of the preceding claims, characterized in that the ground plane (81) has leads (85) projecting from the housing (12) in a direction away from the module receiving slot (14). A socket as claimed in any one of the preceding claims, characterized in that the ground plane receiving slot (84) and the ground plane (81) extend along the full length of the housing (12). A socket as claimed in any one of the preceding claims, characterized in that the centre to centre spacing of the terminals (13, 15) lengthwise of the housing (12) does not exceed 0.75 mm.

Inventors: BILLMAN TIMOTHY BRIAN, THRUSH ROGER LEE, BILLMAN, TIMOTHY BRIAN, THRUSH, ROGER LEE
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1993
Main classification: H01R23
IPC codes: H01R12, H01R13, H01R24, H01R43