Grounding shroud for surface mounted electrical connector

Abstract: A conductive ground shroud (50) is for use with an electrical connector having a plurality of electrical terminals with surface mountable contact sections for electrically engaging circuitry on a circuit board. Shroud (50) includes a plate-like body (52) having first and second portions (54,62). The second portion (62) is configured to extend over the surface mountable contact sections when the shroud (50) is disposed on a housing The second portion (62) includes at least one contact section (70) for engagement to ground circuitry of the circuit board. The second portion further includes at least one elongated aperture (64) extending therethrough proximate the surface mountable contact sections. Upon disposing the shroud (50) on the connector, mounting the connector and shroud (50) to the circuit board and soldering the surface mountable contact sections to corresponding circuit pads on the board, aperture (64) permits sufficient heat generated during the soldering process to reach circuit pads to melt the solder thereby assuring electrical engagement of the contact sections with corresponding pads.

Description: The present invention relates to conductive shrouds used to provide a ground reference with respect to signal carrying pins in electrical connectors associated with the shroud and more particularly to a conductive shroud for use with a connector having surface mounted leads. As part of its effort to standardize the interface of the electronic equipment, the electronic industry has established pin assignments for some of the connectors that will be used in the interface. For various computer applications, it is desirable to interconnect memory cards. The Personal Computer Memory Card International Association (PCMCIA) has established standards for interconnecting memory cards. A sixty-eight pin connector, for example, is often used. This connector has sixty signal pins, four ground return pins and four DC voltage pins, all of which are preassigned by the industry in the standards. The connectors may be through hole mounted or surface mounted. The signal to ground ratio of an electrical connector is equal to the number of signal carrying pins divided by the number of ground return pins in the connector. For the purposes of the present disclosure the DC voltage pins can be considered similar in effect to the AC voltage ground pins, thus the signal to ground ratio of the sixty-eight pin connector is 7.5 to 1.0. Typically in computer applications multiple lines are simultaneously switched and all return current generated by this switching must be returned through one of the ground pins. The return current of eight or so signal pins, therefore, must be accommodated by a single ground pin. When the signal rise time is relatively slow, in the eight to ten nanosecond range, this presents no problem. When the rise time decreases i.e. to 1-3 nanoseconds, however, as in certain computer applications the induced voltage is increased resulting in "ground bounce" or common mode noise in the ground return pins. When the ground bounce reaches a high enough level, relative to the level of the signals, the systems may become unable to reliably read and respond to the signals thereby causing what is known in the industry as "false triggering". Since the pin assignments have been fixed by the industry, the signal to ground ratio cannot be altered. To reduce the adverse effects of the faster rise times a conductive shroud may be used to electrically interconnect the ground of the memory card to the ground of the equipment with which the card is being used. One such shroud and a related connector are disclosed in US-A-5,288,247. The shroud of the '247 patent is arranged to enclose the top of the connector and two sides thereof. The connector in this reference is top board mounted having terminal leads that are received in through holes of the circuit board. The shroud in the above reference is mounted on a board remote surface of the connector and is electrically connected to ground circuitry on a circuit board. The performance of the equipment is greatly improved by the use of such shrouds. To achieve a more uniformed distribution and flow of current, it is generally desirable that a ground shroud include a plurality of interconnections with the circuit board ground. One way of achieving this capability with top board mounted connectors is to provide a shroud of the type that has a plate-like section extending above the formed pins at the back of the connector and a back wall having a plurality of contact sections at desired locations therealong for engaging ground circuitry on the board. While a shroud of the type described above is suitable for top board mounted connectors having terminal members that have leads that are received in through holes on the circuit board, a problem arises when using this type of shroud with connectors having surface mounted leads. The top and back walls of the shroud prevent heat from reaching the solder paste or other material used for interconnecting the leads and circuit pads during the soldering process. Furthermore, the shroud walls prevent visual inspection of the soldered connections. Although a two step mounting process, that is, first soldering the connector with the surface mountable leads to the board and then securing the conductive shroud to the already mounted connector and soldering the shroud to respective ground circuitry is possible; the additional manufacturing steps are not cost effective. It is desirable, therefore, to provide a ground shroud for connectors having surface mountable leads that permits simultaneous mounting of the connector and shroud to the board and also allows visual inspection of the terminal leads after the soldering process is complete. The present invention consists in a connector and ground shroud assembly comprising an electrical connector having a housing with a plurality of electrical terminals disposed therein, said terminals including contact sections extending outwardly of the housing for electrically engaging circuitry on a circuit board; and a ground shroud adapted for electrically engaging ground circuitry of the circuit board for providing a ground reference for said terminals, said shroud including an electrically conductive plate-like body having a first portion disposed on a board remote surface of the connector housing, and a second portion extending over the contact sections and having at least one second contact section extending therefrom for engagement with the ground circuitry of the circuit board; the assembly being characterized in that the contact sections of the terminals are surface mountable contact sections and the second portion of the shroud includes one or more elongated apertures extending therethrough proximate the surface mountable contact sections, whereby upon mounting the housing and shroud to the circuit board and soldering the surface mountable contact sections to corresponding circuit pads on the board, said aperture(s) permit(s) sufficient heat generated by a board remote source during the soldering process to reach the circuit pads and melt the solder thereby assuring electrical engagement of the terminals with the circuitry on the board. In one preferred embodiment, the second shroud portion includes a plurality of apertures or slots extending in the same direction as the terminal leads. The slots preferably extend across the top plate surface and partially down the back wall of the shroud. The first shroud portion may include at least one contact section adapted to engage a ground contact of a mating electrical device. The present invention has the advantage of allowing the shroud and connector to be soldered to a circuit board simultaneously. A further advantage of the present invention is that the aperture allows for visual inspection of the surface mount terminals and circuit pads after the soldering process has been completed. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: FIGURE 1 is a perspective view of a shroud made in accordance with the invention exploded from a connector having surface mounted terminals, the connector being exploded from a circuit board to which the connector and shroud are to be mounted. FIGURE 2 is a cross-sectional view of the assembled shroud and connector. FIGURE 3 is a perspective view of the front of the shroud of Figure 1. FIGURE 4 is a perspective view taken from the back of the shroud of Figure 1. FIGURE 5 is a view similar to Figure 4 with the shroud mounted on the connector of Figure 1. FIGURE 6 is a view of the assembly of Figure 5 taken from the board, mounting surface of the connector. FIGURE 7 shows the connector of Figure 5 mounted to one side of a circuit board and having a second shrouded surface mount connector exploded from the bottom of the circuit board for a stacked configuration. FIGURE 8 is a perspective view of the shroud used with the second or bottom board surface mounted connector. FIGURE 9 shows a stacked assembly of connectors having surface mounted leads and ground shrouds. FIGURE 10 is a cross-sectional view of the assembly of Figure 9. Electrical connector assembly 20 of the present invention includes electrical connector 22 and a shroud 50. For purposes of illustrating the invention connector 22 is shown as a top board surface mounted connector for a card reader. It is to be understood that the improved shroud of the present invention may also be used with receptacle connectors to be mated with shielded or unshielded plug connectors. When using a connector assembly with memory cards as identified by PCMCIA standards, the memory cards need to be oriented in a specific direction. The embodiment shown herein is for memory cards having the ground contacts on their upper surfaces. In some applications the assembly may also include an eject mechanism for the card proximate the circuit board. The connectors shown herein can be used in combination with numerous ejector mechanisms as known in the art. Referring now to Figures 1 to 6, the connector 22 of the present invention includes a housing 24 having a first major or board remote side 26 and an opposed second major or board proximate side 28, and opposed minor sides 30 together defining a card receiving mouth 32. A portion of the card receiving mouth 32 defines a card receiving space 34. A plurality of electrical terminals 36 are disposed within the housing 24, the terminals 36 having first and second connecting portions 38,40 respectively. The first connecting portions 38 extend into the card receiving space 34 and are adapted for mating with complementary terminals of a memory card (not shown). The second connecting portions 40 include as contacts at leading ends 42 adapted for being surface mounted to respective circuit pads 84 of a circuit board 80, as best seen in Figure 1. In the embodiment as illustrated, connector 22 further includes card guide arms 44 extending outwardly thereof for receiving a card. The housing is preferably made from high temperature dielectric materials that can withstand soldering temperatures in the range of 230°C, such as liquid crystal polymers and other materials known in the art. The structure of shroud 50 can best be understood with reference to Figures 3 and 4. Conductive shroud 50 is a unitary member including a top plate surface 52 having first portion 54 and a second portion 62. First portion 54 includes a plurality of spring fingers 56 extending from the leading edge 55 thereof. Spring fingers 56 are adapted to be received in card receiving mouth 32 as seen in Figure 2 and electrically engage ground contacts on the memory card inserted into the mouth 32. Fingers 56 are of the type disclosed in the previously discussed patents. Shroud 50 includes side walls 58 extending from the first portion 54. Shroud 50 further includes lower flanges 60 extending from the side walls 58 adapted to extend beneath the connector housing 24 as seen in Figure 6. The flanges 60 may serve as additional conductive pads that can be secured and referenced to ground electrical potential by being electrically connected to corresponding pads on a circuit board as discussed in US-A-5,288,247. Second portion 62 of shroud 50 further includes a back wall 66 having a plurality of terminal members 70 extending downwardly therefrom for electrical engagement with ground circuits in the circuit board. Terminal members 70 are held in true position by the strap-like section 68 of second shroud portion 62. For purposes of illustration, terminal members 70 are shown as leads that are received in through-holes of a circuit board. It is to be understood that these leads may be surface mountable leads as well as the leads of the connector. The shroud is preferably made from a highly conductive material, such as phosphor-bronze or the like as known in the art. The second shroud portion 62, as best seen in Figures 3 and 4 includes a plurality of apertures 64 or slots extending in the same direction as the terminal members 36. The slots 64 preferably extend rearwardly from the first plate portion 54 and partially down the back wall 66 of the shroud, ending at strap-like section 68. The slots 64 overly portions of the terminals 36 that extend outwardly of the housing 24 and are sufficient in number to permit visual inspection of the underlying connecting portions 40 and in particular contacts 42 when the shroud is disposed on the housing 24. In assembling top board surface mounted connector 20, plate portion 52 of shroud 50 is placed over the board remote surface 26 of housing 24, the spring fingers 56 are slid into position within the card receiving mouth 32 and side edges 58 and flange 60 are wrapped around the housing 24. In mounting connector 20 to top board surface 82, the surface mounted leads are brought into engagement with corresponding circuit pads 84 and terminal member leads 70 are inserted into the corresponding through-holes 86 as shown in Figure 2. As known in the art, the circuit pads 84 and through holes 86 are provided with solder paste or the like prior to mounting the connector and shroud assembly 20 to the board 80. The mounted assembly is then passed through an infrared oven at about 230°C using standard soldering procedures. The elongated apertures or slots 64 enable heat to reach the solder paste on the circuit pads causing it to melt thereby effecting electrical interconnection. For purposes of this disclosure, the term solder paste is to be understood to include conductive adhesives and the like that may be used to effect mechanical and electrical interconnect between the leading ends 42 and pads 84. After the soldering process has been completed. the slots 64 permit visual inspection of the soldered connections. Memory card assemblies are often used in stacked relationship. One method of stacking the connectors is by mounting memory cards on opposed surfaces 82, 88 of a circuit board 80 as shown in Figures 7-10. Figure 7 shows a connector assembly 20 as previously described mounted to a first or top major surface 82 of circuit board 80 and having a second connector assembly 120 exploded from the second or bottom major surface 88. The structure of the ground shrouded connector 120 differs from the ground shrouded structure of connector assembly 20 as previously described. In order to keep the memory cards on both sides of the stacked assembly oriented in the same direction, that is with the ground contacts on the upper surface thereof, the shroud 150 for assembly 120 is attached to the board proximate surface 28 of the connector housing 24, rather than the board remote surface 26 of the connector housing 24 as previously described. Thus the shroud 150 has terminal members 170 extending upwardly from the main body portion 154, and requires no further structure to extend over the terminals. The details of the structure of shroud 150 are shown in Figure 8. Shroud 150 includes a top plate surface 152 having side walls 158 and flanges 160. The leading edge 155 of plate section 152 includes spring fingers 156 which operate in the same manner as previously described. The terminal members 170 of shroud 150 are adapted to be received in the through-holes 92 of circuit board 80 as seen in Figures 1. Figures 9 and 10 show the assembled stacked card assembly with a respective terminal leads 42 secured to the circuit pads 84, 90 on the opposed surfaces 82, 88 of circuit board 80 and respective ground terminal members 70, 170 in their respective through holes 86, 92.

Claims: A connector and ground shroud assembly comprising an electrical connector (22) having a housing (24) with a plurality of electrical terminals (36) disposed therein, said terminals (36) including contact sections (42) extending outwardly of the housing (24) for electrically engaging circuitry on a circuit board (80); and a ground shroud (50) adapted for electrically engaging ground circuitry of the circuit board (80) for providing a ground reference for said terminals (36), said shroud (50) including an electrically conductive plate-like body (52) having a first portion (54) disposed on a board remote surface (26) of the connector housing (24), and a second portion (62) extending over the contact sections (42) and having at least one second contact section (70) extending therefrom for engagement with the ground circuitry of the circuit board (80); the assembly being characterized in that the contact sections of the terminals (36) are surface mountable contact sections (42) and the second portion (62) of the shroud (50) includes one or more elongated apertures (64) extending therethrough proximate the surface mountable contact sections (42), whereby upon mounting the housing (24) and shroud (50) to the circuit board (80) and soldering the surface mountable contact sections (42) to corresponding circuit pads (84) on the board, said aperture(s) (64) permit(s) sufficient heat generated by a board remote source during the soldering process to reach the circuit pads (84) and melt the solder thereby assuring electrical engagement of the terminals (36) with the circuitry on the board (80). An assembly according to claim 1, in which the first shroud portion includes at least one contact section (56) adapted to engage a ground contact of a mating electrical device. An assembly according to claim 1 or 2, in which the second portion (62) of the shroud body (52) terminates in a back wall (66) having terminal members (70) extending therefrom for electrical engagement with ground circuits of the circuit board, said second portion including a plurality of the elongated apertures (64) extending from the top surface of the second portion and partially down the back wall.

Inventors: KAUFMAN JOHN W, ROOT JOHN A, SCHROEDER JAMES L, KAUFMAN, JOHN W., ROOT, JOHN A., SCHROEDER, JAMES L.
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1995
Main classification: H01R23
IPC codes: H01R13, H01R12, H05K9, H01R24