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Title:
GROUND-POWER PLANE CONNECTOR
Document Type and Number:
WIPO Patent Application WO/1998/009354
Kind Code:
A1
Abstract:
A connector (10) is disclosed for interconnecting circuitry (28, 54) of two circuit boards (26, 52) which carry relatively high frequency signals. The receptacle connector (12) includes a central shield plate (22) and the mating plug connector (14) includes a central plate (50) that electrically engages the plate (22) at several points (146, 148, 162, 164) along its length. The plug and receptacle connectors (14, 12) each include an outer shield (172', 172) that substantially surrounds the rows of mated contact pairs (46, 18). The central plates (22 and 50) include a plurality of leads (34, 60) along their lengths that engage the outer shields (172, 172') and ground pads on the circuit boards (26, 52).

Inventors:
GRABBE DIMITRY
HASIRCOGLU ALEX
KORSUNSKY IOSIF
Application Number:
PCT/US1997/015014
Publication Date:
March 05, 1998
Filing Date:
August 26, 1997
Export Citation:
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Assignee:
WHITAKER CORP (US)
International Classes:
H01R12/50; H01R12/71; (IPC1-7): H01R23/72; H01R23/68
Foreign References:
EP0475067A21992-03-18
EP0321257A21989-06-21
US4734060A1988-03-29
US4762500A1988-08-09
EP0510869A21992-10-28
Attorney, Agent or Firm:
Anastasi, Salvatore (Suite 450 4550 New Linden Hill Roa, Wilmington DE, US)
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Claims:
CLAIMS:
1. An electrical connector (10) for interconnecting first and second electrical circuits (28, 54) on first and second circuit boards (26, 52) , respectively, said electrical circuits having both ground pads and signal pads, comprising: a housing having first and second matable housing parts (16, 44) with first and second longitudinal axes (20, 48) , respectively, each said first and second housing parts having a central opening (84,100) and first and second rows (78,80, 96,98) of openings (82) on opposite sides of said central opening extending parallel to said first axis (20) ; (b) a plurality of electrical contact pairs in said housing, each contact pair including first and second matable contacts (18) , 46) having a lead (30, 56) extending from each said contact, each of said first matable contacts (18) being in a respective opening (82) of said first and second rows (78, 80) of openings (82) of said first matable housing part (16) and each of said second matable contacts (46) being in a respective opening (82) of said first and second rows (96, 98) of openings (82) of said second matable housing part (44) , each of said leads (30) of said first matable contact adapted for electrical engagement with said first circuit (28) , and each of said leads (56) of said second matable contacts adapted for electrical engagement with said second circuit (54) , the connector characterized in that each said contact pair includes four points (116,118, 132,134) of electrical contact.
2. The connector according to claim 1 characterized in that each said first matable contact (18) includes a first base (110) and first and second spaced apart beams (112, 114) extending from said first base, and each said second matable contact (46) includes a second base (124) and third and fourth spaced apart beams (126,128) extending from said second base.
3. The connector according to claim 2 characterized in that each of said first, second, third, and fourth beams (112,114, 126,128) includes two contact surfaces arranged so that said contact surfaces (116, 118) of said first and second beams mate with said contact surfaces (134, 132) of said third and fourth beams, respectively.
4. The connector according to claim 3 characterized in that each of said first matable contacts (18) is a flat stamping, said first base (11) and first and second beams (112, 114) defining a plane (120) , said first and second beams extending cantilevered from said first base with opposing spaced edges, said contact surfaces (116, 118) of said first and second beams (112, 114) being on said opposing edges, and wherein each of said second matable contacts (46) is a flat stamping, said second base (124) and third and fourth beams (126, 128) defining a plane (136), said third and fourth beams spaced apart and extending cantilevered from said second base with opposing edges, said contact surfaces (134, 132) of said third and fourth beams (126, 128) being on said opposite edges.
5. The connector according to claim 4 characterized in that said lead (30) of each of said first matable contacts (18) extends from said first base (110) in a direction opposite that of said first and second beams (112, 114) , and wherein said lead (56) of each of said second matable contacts (46) extends from said second base (124) in a direction opposite that of said third and fourth beams (126, 128) .
6. The connector according to claim 5 characterized by a first central plate (22) disposed in said central opening (84) of said first housing (16) and a second central plate (50) disposed in said second housing (44) , said first central plate (22) having a plurality of pairs of first and second spaced apart central plate beams (142, 144) and said second central plate (50) having a plurality of third and fourth space apart central plate beams (156, 158) , each of said first and second central plates being a flat stamping, said first, second, third, and fourth central plate beams defining a common plane (150, 166) wherein each pair of said third and fourth central plate beams (156, 158) is in mated engagement with a corresponding pair of said first and second central plate beams (142, 144) at four points (162,164, 146,148) of electrical contact.
7. The connector according to claim 6 characterized by a plurality of leads (34) extending from said first central plate (22) adapted to be in electrical engagement with said ground pads of said first electrical circuit (28) , and a plurality of leads (60) extending from said second central plate (50) adapted to be in electrical engagement with said ground pads of said second electrical circuit (54) .
8. The connector according to claim 1 characterized by a first central plate (22) disposed in said central opening (84) of said first housing (16) and a second central plate (50) disposed in said second housing (44) , said first central plate (22) having a plurality of pairs of first and second spaced apart central plate beams (142, 144) and said second central plate (50) having a plurality of third and fourth space apart central plate beams (156, 158) , each of said first and second central plates being a flat stamping, said first, second, third, and fourth central plate beams defining a common plane (150, 166) , wherein each pair of said third and fourth central plate beams (156, 158) is in mated engagement with a corresponding pair of said first and second central plate beams (142, 144) at four points (162,164, 148, 146) of electrical contact.
9. The connector according to claim 8 characterized in that each of said first, second, third, and fourth central plate beams (142, 144, 156, 158) includes two contact surfaces arranged so that said contact surfaces (146, 148) of said first and second central plate beams (142, 144) mate with said contact surfaces (164, 162) of said third and fourth central plate beams (156, 158) . Respectively.
10. The connector according to claim 9 characterized in that one of said first and second base portions (140, 154) includes spaced openings (200) therethrough for controlling the characteristic impedance of said connector.
Description:
GROUND-POWER PLANE CONNECTOR The present invention relates to electrical connectors for carrying high speed signals in the interconnection of electrical circuits on circuit boards or in cables and more particularly to such connectors having low resistance contacts and an improved reference plane for controlling impedance.

Electrical connectors for interconnecting circuitry on two circuit boards, typically in the computer and related industries usually contain a relatively large number of pins for interconnecting signals and a fewer number of pins for interconnecting to power and ground.

A typical prior art connector of this type, for example, is disclosed in United States Pat. No. 4,762,500 which issued August 9, 1988 to Dola et al .

This connector includes an insulating housing having two rows of closely spaced signal contacts and a central ground plate that extend between the two rows of signal contacts . The connector is impedance matched as closely as its structure allows, however, it is limited to interconnecting signals having rise times of more than 200 picoseconds. Further, this connector is relatively large having only 32 pins for signal interconnections. As the industry requires connectors having larger numbers of pins, due largely to increases in computer word length from 32 bits to 64 bits, to 128 bits and higher, necessarily these pins must be packed more closely together to remain within an acceptable overall package size and provide minimal propagation delay. The electrical characteristics of the connector become more important as the connector is miniaturized to meet the current trend of the industry and as the speed of the signals that are being interconnected increase. Such an increase in speed results in various well known problems such as crosstalk between signal contacts, signal integrity losses, reflections and ground bounce or

switching noise. Coaxial connectors and coaxial multicore connectors are able to interconnect these high speed signals while avoiding the above mentioned problems, however, such coaxial structures are difficult to miniaturize.

Further, the reliability of the electrical connections of the connector contacts is an important factor, especially in dusty or otherwise contaminated environments. There is an increasing demand in the industry for higher current carrying capacities of the ground and power buses with contact resistance under 10 milliohms. And frequently there is a requirement for a particular connector that can accommodate various distances between two parallel circuit boards, wherein present art connectors must be designed for a specific height to accommodate a specific distance between boards. Additionally, prior art connectors, such as the connector disclosed in the '500 patent, mentioned above, and United States Patent No. 4,734,060 which issued March 29, 1988 to Kawawada et al . , rely substantially upon the physical strength of the plastic housing to support the contacts and hold them in mated engagement.

However, the plastic will cold flow over time resulting in the displacement of the contacts and the lowering of the contact force.

What is needed is a compact connector having a relatively large number of signal contacts that provide high electromagnetic integrity and are sufficiently isolated from one another to interconnect relatively high speed signals, in the 50 picosecond range.

Further, higher current carrying capacities of the ground and power buses are needed with contact resistance under 10 milliohms. And a particular connector design should be easily altered to accommodate various distances between two parallel circuit boards without the necessity of completely redesigning the

connector. Additionally, the stored energy used to provide the necessary contact force when the connector halves are mated should be independent of the strength of the plastic housing. The contact forces should be contained within each individual contact body. An electrical connector is disclosed for interconnecting first and second electrical circuits on first and second circuit boards, respectively, wherein the electrical circuits having both ground pads and signal pads, comprising. A housing is provided having first and second matable housing parts with first and second longitudinal axes, respectively. Each of the first and second housing parts has a central opening and first and second rows of openings on opposite sides of the central opening extending parallel to the first axis. A plurality of electrical contact pairs are arranged in the housing, each contact pair including first and second matable contacts having a lead extending from each contact. Each of the first matable contacts is in a respective opening of the first and second rows of openings of the first matable housing part and each of the second matable contacts is in a respective opening of the first and second rows of openings of the second matable housing part. Each of the leads of the first matable contacts is adapted for electrical engagement with the first circuit, and each of the leads of the second matable contacts is adapted for electrical engagement with the second circuit. Wherein each contact mated pair includes four points of electrical contact.

The invention will now be described by way of example with reference to the accompanying figures of which:

FIGURE l is an isometric view of an electrical connector incorporating the teachings of the present invention;

FIGURES 2, 3 and 4 are front, side, and plan views, respectively, of the receptacle connector shown in Figure 1;

FIGURES 5, 6 and 7 are front, side, and plan views, respectively, of the plug connector shown in Figure l;

FIGURES 8 and 9 are plan and end views, respectively, of the first housing part shown in Figure 4;

FIGURES 10 and 11 are plan and end views, respectively, of the second housing part shown in Figure 7;

FIGURES 12, and 13 are front and side views, respectively, of the receptacle contact shown in Figure 4; FIGURES 14, and 15 are front and side views, respectively, of the plug contact shown in Figure 7;

FIGURES 16, 17, and 18 are front, side, and plan views, respectively, of the outer shield of the first and second housing parts shown in Figures 2 and 5; FIGURE 19 is a plan view similar to that of Figure 18 shown in another embodiment of the shield;

FIGURES 20 and 21 are front and end views, respectively, of the receptacle ground plate shown in Figure 4; FIGURES 22 and 23 are front and end views, respectively, of the plug ground plate shown in Figure 7;

FIGURE 24 is a cross-sectional view of the receptacle connector taken along the lines 24-24 of Figure 4;

FIGURE 25 is a cross-sectional view of the receptacle connector taken along the lines 25-25 of Figure 7;

FIGURE 26 is a cross-sectional view similar to the views shown in Figures 24 and 25 showing the two connector halves in mated engagement;

FIGURE 27 is a cross-sectional view taken along the lines 27-27 of Figure 26; and

FIGURE 28 is a plan view of an alternative central plate for both the receptacle and plug connectors. There is shown in Figure 1 an electrical connector 10 having a receptacle connector half 12 and a mating plug connector half 14. The receptacle connector 12, as best seen in Figures 2, 3, and 4, includes an insulating housing 16, two rows of receptacle contacts 18 on opposite side of a longitudinal axis 20 of the housing, and a central plate 22 that extend between the two rows of contacts along the axis. The receptacle connector 12 is shown surface mounted to a first circuit board 26 having a first circuit 28 thereon. Each of the contacts 18 includes a lead 30 that is in contact with respective signal pads 32 of the first circuit 28. The central plate 22 includes several leads 34 that extend downwardly, as viewed in Figures 2 and 3, through plated through holes 36 that are interconnected to either a ground or power plane of the first circuit.

Alternatively, the leads 34 may be bent over and surface mounted to appropriate pads, not shown. Similarly, the plug connector 14, as best seen in Figures 5, 6, and 7, includes an insulating housing 44, two rows of plug contacts 46 on opposite side of a longitudinal axis 48 of the housing, and a central plate 50 that extend between the two rows of contacts along the axis 48. The plug connector 14 is shown surface mounted to a second circuit board 52 having a second circuit 54 thereon. Each of the contacts 46 includes a lead 56 that is in contact with respective signal pads 58 of the second circuit 54. The central plate 50 includes several leads 60 that extend upwardly, as viewed in Figures 5 and 6, through plated through holes 62 that are interconnected to either a ground or power plane of the second circuit.

Alternatively, the leads 60 may be bent over and surface mounted to appropriate pads, not shown.

The receptacle housing 16, shown in Figures 8 and 9 and the plug housing 44, shown in Figures 10 and 11, are intermatable and similar in structure, as will be explained. The receptacle housing 16 includes a base portion 70 and several extensions 72 forming a first row and several extensions 74 forming a second row, as best seen in Figure 8. Each extension 72 and 74 extends upwardly from the base 70 and is, in the present example, molded integral with the base. Each extension 72 and 74 includes several openings 76, three in the present example, thereby forming a first row 78 of openings 76 and a second row 80 of openings 76. Each opening is arranged to receive a respective receptacle contact 18, as shown in Figure 4. A series of holes 82 are formed through the base portion 70 and evenly spaced along the rows 78 and 80, as shown in Figure 8. There is one hole 82 in each opening 76 and several holes 82 between each adjacent pair of extensions 72 and between each adjacent pair of extensions 74, for receiving a lead 30 of a receptacle contact 18. Each hole 82 includes a recess 88, as best seen in Figure 11, for a purpose that will be explained. Note that the extensions 72 and 74 are alternately spaced apart for a purpose that will be explained. The two rows of extensions 72 and 74 are spaced apart to form a central opening 84 therebetween, as best seen in Figure 9, for receiving the central plate 22, as shown in Figure 4. Several holes 86 are formed through the base 70 in alignment with the axis 20, as best seen in Figure 8, for receiving the leads 34. The plug housing 44 includes a base portion 90 and several extensions 92 forming a first row and several extensions 94 forming a second row, as best seen in Figure 10. Each extension 92 and 94 extends upwardly from the base 90 and is, in

the present example, molded integral with the base. Each extension 92 and 94 are substantially identical to the extensions 72 and 74 and include identically spaced openings 76 thereby forming a third row 96 of openings 76 and a fourth row 98 of openings 76. Each opening is arranged to receive a respective plug contact 46, as shown in Figure 7. As with the receptacle housing 16, the plug housing 44 includes two rows of spaced holes 82 formed through the base 90 on opposite sides of the axis 48 for receiving the leads 56 of the plug contacts 46.

The two rows of extensions 92 and 94 are spaced apart to form an opening 100 for receiving the central plate 50 in a manner similar to that of the opening 84. Several holes 86 are formed through the base 90 in alignment with the axis 48, as best seen in Figure 10, for receiving the leads 60.

The extensions 92 and 94 are substantially identical in size, shape, and spacing to the extensions 72 and 74, respectively, so that when the two housing parts are in mated engagement the extensions 94, except for the right most one as viewed in Figure 10, are received between adjacent pairs of the extension 72, the right most extension 94 being received in the right most space next to the extension 76. Similarly, the extensions 92, except for the left most one as viewed in Figure 10, are received between adjacent pairs of the extension 74, the left most extension 92 being received in the left most space next to the extension 74. When mated, the row 98 of extensions 94 interleaf with the row 78 of extension 72 thereby forming a continuous row of equally spaced openings 76, and the row 96 of extensions 92 interleaf with the row 80 of extensions 74 thereby forming another continuous row of equally spaced openings 76 on the opposite side of the axes 20 and 48. The base 90 of the plug housing 44 extends outwardly from the outer surfaces of the extensions 92 and 94 to

form a flange 102 that extend completely around the housing 44, for a purpose that will be explained.

The receptacle contact 18, as best seen in Figures 12 and 13, includes a base 110, the lead 30 extending from one side of the base, and two spaced apart resilient beams 112 and 114 extending cantilevered from the other side of the base. Each beam has two contact surfaces 116 and 118, the surface 116 adjacent the free end of the beam and the surface 118 adjacent the base 110. The two contact surfaces 116 of the two beams 112 and 114 are in opposing relationship, and the two contact surfaces 118 are in opposing relationship. The receptacle contact 18 is stamped from a flat sheet of material so that the base 110, lead 30, and two beams 112 and 114 define a common plane 120, as shown in

Figure 13. The openings 76 are sized to closely receive the receptacle contact 18 and hold it in proper alignment yet there is sufficient clearance for the beams 112 and 114 to deflect during mating. However, the walls of the openings will prevent over deflection to help assure that the contacts are not inadvertently damaged. The plug contact 46, as best seen in Figures 14 and 15 includes a base 124 that extends into the recess 88 of the base 124. The lead 56 extends from one side of the base 124 and two resilient beams 126 and 128 extending cantilevered from the other side of the base. The two beams join the base 124 at a shank 130. Each beam has two contact surfaces 132 and 134, the surface 132 adjacent the free end of the beam and the surface 134 adjacent the base 110. The two contact surfaces 132 of the two beams 126 and 128 are on opposite sides of the contact, and the two contact surfaces 134 are also on opposite sides. The plug contact 46 is stamped from a flat sheet of material sc that the base 124, lead 56, shank 130, and two beams 126 and 128 define a common plane 136, as shown in Figure 15. The two beams 126 and

128 are sized so that when the plug connector is mated with the receptacle connector, as shown in Figure 26, the two contact surfaces 132 are in electrical engagement with the two contact surfaces 118, and the two contact surfaces 134 are in electrical engagement with the two contact surfaces 116, thereby providing four points of contact for each mated pair of receptacle and plug contacts 18 and 46. The resiliency in the two beams 112 and 114 provide sufficient stored energy, when mated, to provide the necessary amount of force to provide good electrical contact between the contact surfaces 116 and 134 with relatively low resistance. Similarly, the resiliency in the two beams 126 and 128 provide sufficient stored energy, when mated, to provide the necessary amount of force to provide good electrical contact between the contact surfaces 118 and 132 with relatively low resistance. The base 124 has a length LI that corresponds to the depth of the recess 88, both of which can be varied in size to produce a plug connector 14 having a desired height, indicated as H in Figure 6, so that when mated with the receptacle connector 12 will accommodate a given space between the first and second circuit boards 26 and 52. That is, the overall height of the connector 10 can be easily controlled by simply controlling the length LI of the base 124 and the corresponding depth of the recess 88. Additionally, a similar adjustment must be made to the base of the central plate 50, as will be explained below.

The central plate 22 that is in the receptacle connector 12, as best seen in Figures 20 and 21, includes an elongated base 140 having several leads 34 extend from one side of the elongated base, and several pairs of spaced beams 142 and 144 extending cantilevered from the opposite side thereof. Each beam 142 and 144 has two contact surfaces 146 and 148, the surface 146 adjacent the free end of the beam and the surface 148

adjacent the base 140. The two contact surfaces 146 of the two beams 142 and 144 are in opposing relationship, and the two contact surfaces 148 are in opposing relationship. The central plate 22 is stamped from a flat sheet of material so that the leads 34, base 140, and beams 142 and 144 define a plane 150, as shown in Figure 21. The opening 84 of the receptacle housing 16 is sized to closely receive the central plate 22 and hold it in proper alignment, as shown in Figure 4. The central plate 50 that is in the plug connector 14, as best seen in Figures 22 and 23, includes an elongated base 154 having several leads 60 extend from one side of the elongated base, and several pairs of spaced beams 156 and 158 extending cantilevered from the opposite side thereof. Each pair of beams 156 and 158 join the base 154 at a shank 160. Each beam has two contact surfaces 162 and 164, the surface 162 adjacent the free end of the beam and the surface 164 adjacent the base 154. The two contact surfaces 162 of the two beams 156 and 158 are on opposite sides, and the two contact surfaces 164 are also on opposite sides. The central plate 50 is stamped from a flat sheet of material, similar to that of the central plate 22, so that the base 154, lead 60, shank 160, and two beams 156 and 158 define a plane 166, as shown in Figure 23. The two beams 156 and 158 are sized so that when the plug connector is mated with the receptacle connector, as shown in Figure 27, the two contact surfaces 162 are in electrical engagement with the two contact surfaces 148, and the two contact surfaces 164 are in electrical engagement with the two contact surfaces 146, thereby providing four points of contact for each mated pair of receptacle and plug central plate contacts. The resiliency in the two beams 142 and 144 provide sufficient stored energy, when mated, to provide the necessary amount of force to provide good electrical

contact between the contact surfaces 146 and 164 with relatively low resistance. Similarly, the resiliency in the two beams 156 and 158 provide sufficient stored energy, when mated, to provide the necessary amount of force to provide good electrical contact between the contact surfaces 148 and 162 with relatively low resistance. The base 154 has a length L2 that corresponds to the length LI of the base 124 of the plug contact 46. The length of L2 is varied in size to correspond to the length LI to produce a plug connector 14 having a desired height, indicated as H in Figure 6, as explained above with respect to the plug contact 46.

When the length L2 is relatively large, the surface area of the base 154 may become large enough to cause substantial capacitive coupling. In such cases apertures, not shown, may be formed through the base 154 at desired intervals to add inductance, permitting compensation of transmission parameters and better control of the desired characteristic impedance of the connector 10. Alternatively, the base 110 of the receptacle contact 18 and the base 140 of the central plate 22 may be lengthened to increase the height of the receptacle connector 12 to accommodate the space between the two circuit boards. See for example Figure 28 where the central plate 50 is shown in mated engagement with a central plate 22' including a base 140' having a length of L3. In this example the central plate 22 ' is similar to the central plate 22 except that the length of the base 140' is substantially longer and will affect the characteristic impedance of the connector 10. Slots 200 are formed through the base 140' in adjacent rows of alternating directions as shown. This effectively lengthens the current path, indicated by the dashed line 202 thereby increasing the self inductance. By manipulating the length of this current path the impedance can be easily controlled.

The receptacle connector 12 includes an outer shield 172, shown in Figures 16, 17, and 18, having four sides 174, 176, 178, and 180 that completely surround the receptacle housing 16, associated receptacle contacts 18, and central plate 22, as shown in Figure 4. The outer shield 172 includes a bottom 182 having a series of holes therethrough that correspond to the position of the leads 30 and 34. The outer shield 172 is made of electrically conductive material, such as copper or brass, and may be produced by deep drawing in the usual manner. A series of holes 184 are formed through the bottom 182 and spaced along the axis 20, as best seen in Figure 18, and are sized to be an interference fit with the leads 34 of the central plate 22. When the central plate 22 is inserted into the opening 84, the leads 34 enter the holes 184 and slightly deform the metal surrounding the holes, thereby making good electrical contact. When the leads 34 are interconnected to the ground of the first circuit, then the outer shield 172 is also interconnected to the ground of the first circuit. There are two rows of holes 186 and 188 formed through the bottom 182 on each side of the axis 20, as shown in Figure 18, for receiving the leads 30 of the receptacle contacts 18. The holes 186 are clearance holes that are sufficiently large so that the leads 30 pass through without electrical contact. The holes 188, on the other hand, are an interference fit with the leads 30 so that when the leads 30 enter the holes 188 they slightly deform the metal surrounding the holes, making good electrical contact, thereby grounding these receptacle contacts. Note that each hole 186 is in alignment with the center of two adjacent holes 188 so that when all of the contacts 18 are inserted into the receptacle housing 16 and their leads inserted through the bottom 182, each receptacle contact 18 having its lead in a hole 186 will

have a grounded receptacle contact 18 on each side. This, coupled with the outer shield 172 and the central ground shield 22, provides substantial isolation for the receptacle contacts that are not grounded. In the case where the signals being transmitted through the receptacle contacts 18 are configured as differential pairs, then all of the holes through the bottom 182 for the leads 30 will be clearance holes 186, as shown in Figure 19. In this case none of the leads 30 will contact the outer ground shield 174. While only two configurations of holes 186 and 188 are shown in Figures 18 and 19, it will be understood that any combination of clearance holes 186 and interference holes 188 may be utilized to achieve a desired purpose. For example, the receptacle contacts on adjacent opposite sides of one or more particular signal contacts may be grounded in this manner, independent of other contacts and whether or not the other contacts are grounded, thereby creating near coaxial conditions for only desired signal contacts. Similarly, the plug connector 14 includes an outer shield 172' which is similar to the outer shield 172. The outer shield 172 * is sized slightly larger to receive the plug housing 44 having the peripheral flange 102. It will be understood that the hole configuration of the bottom 182' of the outer shield 172' will be identical to the hole configuration of the bottom 182 of the outer shield 172. That is, when the bottom 182 has the hole configuration shown in Figure 18 or any variation thereof, so does the bottom 182' and when the bottom 182 has the hole configuration shown in Figure

19, so does the bottom 182'. In cases where interference holes 188 are utilized in the outer shields 172 and 172', a lead 30 or 56 extending through a hole 188, if desired, may be cut off short so that it will not reach the circuit board, thereby obviating the need to provide a solder pad on the circuit board for the

lead. The leads 34 and 60 of the central plates 22 and 50 assure a short ground path for the contacts of such leads 30 and 56.

As shown in Figures 24, 25, and 26, the plug connector 14 is mated to the receptacle connector 12 by simply aligning them vertically and bring them together in the usual manner. The central plates 50 and 22 interengage and make electrical contact first, followed by the plug contacts 46 engaging the receptacle contacts 18 and making electrical contact last. When the two connector halves are fully mated, as shown in Figures 26 and 27, each of the plug and receptacle contact pairs 46 and 18 make electrical contact at four point, as described above, thereby establishing a good low resistance connection. Similarly, as shown in Figure 27, the contact surfaces 162 and 164 of the central plate 50 electrically interconnect to the contact surfaces 146 and 148 of the central plate 22, thereby establishing a reference plane separating the two rows of contacts on opposite sides of the axes 20 and 48.

The peripheral flange 102 of the plug housing 44 and the outer shield 172 ' are sized so that the outer shield 172' will slip over the outer shield 172, as shown in Figure 26. The facing surfaces of the two outer shields 172 and 172' may have features, such as bumps or raised portions, that electrically interconnect the two outer shields to provide additional ground paths. In the present case, for example, the walls of the outer shield 172, as shown in Figures 2 and 3, has a series of slits 192 in the sides 174 and 178 thereby forming resilient fingers 194. Similar slits may be formed in the sides 176 and 180, as desired. A small projection or bump 196 is formed in each finger 194 projecting outwardly so that it contacts the inner surface of the shield 172 ' when the receptacle and plug connectors 12 and 14 are mated. This prevents radiation either into or out of

the connector thereby enhancing the signal integrity of the connector. In the case of the contact configuration wherein every other plug and receptacle contact 46 and 18 are grounded to their respective outer shield 172 and 172 ' , that is when the hole configuration shown in

Figure 18 is used, the combination of the short ground paths between the signal contacts provided by the central plate, the interposed grounded contacts, and the outer shield provides a connector capable of interconnecting high speed signals having rise times of about 50 picoseconds. Each of the mated plug and receptacle contacts 46 and 18 are substantially surrounded by ground members thereby creating a near coaxial environment having the benefits of coaxial construction without the detriments of bulky structures. An important advantage of the present invention is that simplified tooling for producing both halves of the bus and the signal contacts results in lower tooling costs and lower parts costs, yet produces a superior performance connector. Additionally, the connector design can accommodate different board spacings while providing substantially improved signal integrity. Impedance adjustments can be easily made by providing appropriate apertures in the central plates.