Abstract:
An electrical connector having electrical conductors in a plurality of rows is provided, wherein each of the plurality of rows includes a housing and a plurality of electrical conductors. Each electrical conductor has a first contact end connectable to a printed circuit board, a second contact end and an intermediate portion therebetween that is disposed within the housing. The housing includes a first region surrounding each of the plurality of electrical conductors, the first region made of insulative material and extending substantially along the length of the intermediate portion of the electrical conductors. The housing also includes a second region adjacent the first region and extending substantially along the length of the intermediate portion of the electrical conductors. The second region is made of a material with a binder containing conductive fillers.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     Reference to Microfiche Appendix 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to electrical connectors and more specifically to high speed electrical connectors. 
     2. Description of Related Art 
     Electrical connectors are widely used in the manufacture of electronic systems because they allow the system to be built in separate pieces that can then be assembled. Board-to-board connectors are widely used because sophisticated electronic systems are usually fabricated on multiple printed circuit boards. To assemble the electronic system, the printed circuit boards are electrically connected. 
     In the description that follows, the invention will be illustrated as applied to a board to board connector. In particular, the invention will be illustrated in connection with a backplane-daughter card interconnection system. Many electronic systems, such as computer servers or telecommunications switches are built using a backplane and multiple “daughter” cards. In such a configuration, the active circuitry of the electronic system is built on the daughter cards. For example, a processor might be built on one daughter card. A memory bank might be built on a different daughter card. The backplane provides signal paths that route electrical signals between the daughter cards. 
     Generally, electrical connectors are mounted to both the backplane and the daughter card. These connectors mate to allow electrical signals to pass between the daughter card and the backplane. 
     Because the electronic systems that use a backplane-daughter card configuration usually process much data, there is a need for the electrical connectors to carry much data. Furthermore, this data is generally transmitted at a high data rate. There is simultaneously a need to make the systems as small as possible. As a result, there is a need to have electrical connectors that can carry many high speed signals in a relatively small space. There is thus a need for high speed-high density connectors. 
     Several commercially available high-speed, high density electrical connectors are known. For example, U.S. Pat. No. 6,299,483 to Cohen et al. entitled High Speed High Density Electrical Connector is one example. Teradyne, Inc., the assignee of that patent, sells a commercial product called VHDM®. Another example may be found in U.S. Pat. No. 6,409,543 to Astbury, et al. entitled Connector Molding Method and Shielded Waferized Connector Made Therefrom. Teradyne, Inc., the assignee of that patent, sells a commercial product called GbX™. The foregoing patents arc hereby incorporated by reference. 
     Both of the above-described electrical connectors employ insert molding construction techniques, at least for the daughter card connectors. Subassemblies, called wafers, are formed around individual columns of signal contacts. The wafers are formed by molding a dielectric material around the metal signal contacts. The wafers are then stacked side by side to make a connector of the desired length. 
     One of the difficulties that results when a high density, high speed connector is made in this fashion is that the electrical conductors can be so close that there can be electrical interference between adjacent or nearby signal conductors. To reduce interference, and to otherwise provide desirable electrical properties, metal members are often placed between or around adjacent signal conductors. The metal acts as a shield to prevent signals carried on one conductor from creating “cross talk” on another conductor. The metal also impacts the impedance of each conductor, which can further contribute to desirable electrical properties. 
     Generally, the metal members are made from separate pieces of metal that are added to the connector. However, it has also been suggested that a metal coating be applied to the connector. Also, in some connectors, the base material of the housing is formed of metal, usually as a die cast part. Then, insulative members are inserted to preclude the signal conductors of the connector from being shorted by the metal housing. 
     A drawback of forming the shields from separate pieces of metal is that additional pieces are required to assemble the connector. The additional pieces increase the cost and complexity of manufacturing the connector. In some cases, shield pieces are stamped and formed to create tabs or projections that extend between adjacent signal conductors. This configuration reduces the number of separate pieces because the projections stay attached to the sheet, so only one additional piece is required. However, a drawback of forming a sheet with projections extending from it is that forming the projection leaves a hole in the sheet. Thus, while the projection increases shielding between signal conductors that are adjacent along a line running in one direction, leaving a hole in the shield sheet decreases shielding between signal conductors that are adjacent along a line running in an orthogonal direction. A further drawback of stamping and forming projections from a single shield member is that it is difficult to form projections that have bends or corners—which are often needed to follow contours of signal contacts in some connectors, such as right angle connectors. 
     A drawback of coating metal onto a plastic is that there are no combinations of readily available and inexpensive metals and plastics that can be used. Either the metal does not adhere well to the plastic or the plastic lacks the desired thermal or mechanical properties needed to make a suitable connector. A further drawback of coating metal onto plastic is that available plating techniques are not selective. The portions of the connector housing which should not be conductive must be masked before the coating is applied. For example holes in the housing that hold signal contacts are often filled with plugs before coating, which are then removed after coating. A drawback of manufacturing connectors using a die cast metal housing is the complexity arising from the use of insulative inserts. Further, there is a limit to how thin features on a die cast part can be made. Generally, a die cast housing will have thicker parts. Using thicker housing parts is generally undesirable because it reduces the overall density of the connector. Die cast metals are more expensive than typical plastic parts. 
     It would be highly desirable to provide a connector with desirable electrical properties that is easy to manufacture and provides a high signal density. 
     BRIEF SUMMARY OF THE INVENTION 
     With the foregoing background in mind, it is an object of the invention to provide a high speed, high density electrical connector that is easy to manufacture. 
     The foregoing and other objects are achieved in an electrical connector that is molded from different types of material to form at least two regions of distinct electrical properties. One region is formed from material filled with conducting material to alter the electrical properties. 
     In a preferred embodiment, an electrical connector having electrical conductors in a plurality of rows is provided, wherein each of the plurality of rows includes a housing and a plurality of electrical conductors. Each electrical conductor has a first contact end connectable to a printed circuit board, a second contact end and an intermediate portion therebetween that is disposed within the housing. The housing includes a first region surrounding each of the plurality of electrical conductors, the first region made of insulative material and extending substantially along the length of the intermediate portion of the electrical conductors. The housing also includes a second region adjacent the first region and extending substantially along the length of the intermediate portion of the electrical conductors. The second region is made of a material with a binder containing conductive fillers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects, advantages, and novel features of the invention will become apparent from a consideration of the ensuing description and drawings, in which— 
     FIG. 1 is a sketch of an electrical connector as known in the prior art; 
     FIG. 2 is a sketch of a wafer of the electrical connector of FIG. 1; 
     FIG. 3 is a sketch of the wafer of FIG. 2 at a stage in its manufacture; 
     FIGS. 4A and 4B are cross sectional views of different embodiments of a wafer of an electrical connector made according to the invention; 
     FIG. 5 is a schematic illustration of a molding machine suitable for use in making a connector according to the invention; 
     FIG. 6 is a sketch of a prior art backplane connector; and 
     FIGS. 7A and 7B are views of a backplane connector made according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a two piece electrical connector  100  is shown to include a backplane connector  105  and a daughtercard connector  110 . The backplane connector  105  includes a backplane shroud  102  and a plurality of signal contacts  112 , here arranged in an array of differential signal pairs. In the illustrated embodiment, the signal contacts are grouped in pairs, such as might be suitable for manufacturing a differential signal electrical connector. A single-ended configuration of the signal contacts  112  is also contemplated in which the signal conductors are evenly spaced. In the prior art embodiment illustrated, the backplane shroud  102  is molded from a dielectric material. Examples of such materials are liquid crystal polymer (LCP), polyphenyline sulfide (PPS), high temperature nylon or polypropylene (PPO). All of these are suitable for use as binder materials in manufacturing connectors according to the invention. 
     The signal contacts  112  extend through a floor  104  of the backplane shroud  102  providing a contact area both above and below the floor  104  of the shroud  102 . Here, the contact area of the signal contacts  112  above the shroud floor  104  are adapted to mate to signal contacts in daugthercard connector  110 . In the illustrated embodiment, the mating contact area is in the form of a blade contact. 
     A tail portion of the signal contact  112  extends below the shroud floor  104  and is adapted to mating to a printed circuit board. Here, the tail portion is in the form of a press fit, “eye of the needle” compliant contact. However, other configurations are also suitable such as surface mount elements, spring contacts, solderable pins, etc. In a typical configuration, the backplane connector  105  mates with the daughtercard connector  110  at the blade contacts and connects with signal traces in a backplane (not shown) through the tail portions which are pressed into plated through holes in the backplane. 
     The backplane shroud  102  further includes side walls  108  which extend along the length of opposing sides of the backplane shroud  102 . The side walls  108  include grooves  118  which run vertically along an inner surface of the side walls  108 . Grooves  118  serve to guide the daughter card connector  110  into the appropriate position in shroud  102 . Running parallel with the side walls  108  are a plurality of shield plates  116 , located here between rows of pairs of signal contacts  112 . In a presently preferred single ended configuration, the plurality of shield plates  116  would be located between rows of signal contacts  112 . However, other shielding configurations could be formed, including having the shield plates  116  running between the walls of the shrouds, transverse to the direction illustrated. In the prior art, the shield plates are stamped from a sheet of metal. 
     Each shield plate  116  includes one or more tail portions, which extend through the shroud base  104 . As with the tails of the signal contacts, the illustrated embodiment has tail portions formed as an “eye of the needle” compliant contact which is press fit into the backplane. However, other configurations are also suitable such as surface mount elements, spring contacts, solderable pins, etc. 
     The daughtercard connector  110  is shown to include a plurality of modules or wafers  120  that are supported by a stiffener  130 . Each wafer  120  includes features which are inserted into apertures (not numbered) in the stiffener to locate each wafer  120  with respect to another and further to prevent rotation of the wafer  120 . 
     Referring now to FIG. 2, a single wafer is shown. Wafer  120  is shown to include dielectric housings  132 ,  134  which are formed around both a daughtercard shield plate ( 10 , FIG. 3) and a signal lead frame. As described in the above-mentioned U.S. Pat. No. 6,409,543, wafer  120  is preferably formed by first molding dielectric housing  132  around the shield plate, leaving a cavity. The signal lead frame is then inserted into the cavity and dielectric housing  134  is then overmolded on the assembly to fill the cavity. 
     Extending from a first edge of each wafer  120  are a plurality of signal contact tails  128 , which extend from the signal lead frame, and a plurality of shield contact tails  122 , which extend from a first edge of the shield plate. In the example of a board to board connector, these contact tails connect the signal conductors and the shield plate to a printed circuit board. In the preferred embodiment, the plurality of shield contact tails and signal contact tails  122  and  128 , respectively, on each wafer  120  are arranged in a single plane. 
     Here, both the signal contact tails  128  and the shield contact tails  122  are in the form of press fit “eye of the needle” compliants which are pressed into plated through holes located in a printed circuit board (not shown). In the preferred embodiment, it is intended that the signal contact tails  128  connect to signal traces on the printed circuit board and the shield contact tails connect to a ground plane in the printed circuit board. In the illustrated embodiment, the signal contact tails  128  are configured to provide a differential signal and, to that end, are arranged in pairs. 
     Near a second edge of each wafer  120  are mating contact regions  124  of the signal contacts which mate with the signal contacts  112  of the backplane connector  105 . Here, the mating contact regions  124  are provided in the form of dual beams to mate with the blade contact end of the backplane signal contacts is  112 . The mating contact regions are positioned within openings in dielectric housing  132  to protect the contacts. Openings in the mating face of the wafer allow the signal contacts  112  to also enter those openings to allow mating of the daughter card and backplane signal contacts. 
     Provided between the pairs of dual beam contacts  124  and also near the second edge of the wafer are shield beam contacts  126 . Shield beam contacts are connected to daughter card shield plate  10  (FIG. 3) and are preferably formed from the same sheet of metal used to from the shield plate. Shield beam contacts  126  engage an upper edge of the backplane shield plate  116  when the daughter card connector  110  and backplane connector  105  are mated. In an alternate embodiment (not shown), the beam contact is provided on the backplane shield plate  116  and a blade is provided on the daughtercard shield plate between the pairs of dual beam contacts  124 . Thus, the specific shape of the shield contact is not critical to the invention. 
     FIG. 3 shows a wafer at an intermediate step of manufacture. The shield plate  10  is shown still attached to a carrier strip  310 . In a preferred embodiment, shield plates will be stamped for many wafers on a single sheet of metal. A portion of the strip of metal will be retained as a carrier strip. The individual components can then be more readily handled. When manufacturing is completed, the finished wafers  120  can then be severed from the carrier strip and assembled into daughter card connectors. 
     In FIG. 3, dielectric housing  132  is shown molded over a shield. Insert molding is known in the art and is used in the connector art to provide conductors within a dielectric housing. In this prior art connector, dielectric material is molded over the majority of the surface of shield  10 . Additionally, the dielectric is largely on the upper surface of shield, leaving the lower surface of the shield exposed. 
     Tabs  322  on the shield plate are visible because dielectric housing  132  is molded to leave windows  324  around tabs  322 . Likewise, holes  22  and  24  are visible because no dielectric housing has been molded around them. 
     Various features are molded into dielectric housing  132 . Cavity  350  bounded by walls  352  is left generally in the central portions of the housing  132 . Channels  324  are formed in the floor of cavity  350  by providing closely spaced projecting portions of dielectric housing. Channels  324  are used to position signal conductors. Also, openings  326  are molded to allow a mating contact area for each signal contact. The front face of dielectric housing  132  creates the mating face of the connector and contains holes to receive the mating contact portion from the backplane connector, as is known in the art. The walls of opening  326  protect the mating contact area. 
     To complete the manufacture of the prior art connector shown in FIG. 3, a signal lead frame is inserted into cavity  350 . Cavity  350  is then filled with additional dielectric material to form dielectric housing  134 , thereby locking the signal conductors into the wafer. Holes  22  and  24  represent openings through which stabilizers, sometimes called “pinch pins,” can be inserted into the part as dielectric housing  134  is being molded. The pinch pins hold the signal lead frame in place as the part is being molded. 
     According to the invention, a similar molding process will be used. However, different types of material will be used in molding the housing pieces of each wafer. In particular, in addition to the dielectric material used in the prior art, a material with different electromagnetic properties is used to form a portion of the housing for the wafer. In particular, portions of the housing will be formed from material that selectively alters the electrical properties of the housing, thereby suppressing cross talk, altering the impedance of the signal conductors or otherwise imparting desirable electrical properties to the connector. In the preferred embodiment, some portion of the material used to mold the connector housing will be an insulator and some portion will have a higher conductivity. 
     In accordance with the preferred embodiment, prior art molding material will be used to create the portions of the connector housing that need to be non-conducting to avoid shorting out signal contacts or otherwise creating unfavorable electrical properties. Also, in the preferred embodiment, those portions of the connector housing for which no benefit is derived by using a material with different electromagnetic properties are also made from prior art molding materials, because such materials are generally less expensive and mechanically stronger than the electromagnetic materials to be described below. 
     Prior art electrical connector molding materials are generally made from a thermoplastic binder into which non-conducting fibers are introduced for added strength, dimensional stability and to reduce the amount of higher priced binder used. Glass fibers are typical, with a loading of about 30% by volume. 
     In a preferred embodiment of the invention, electromagnetic fillers are used in place of or in addition to the glass fibers for portions of the connector housing. The fillers can be conducting or can be ferroelectric, depending on the electrical properties that are desired from the material. 
     To simulate a metal shield insert, it is preferable that a conducting filler be used. Examples of suitable conducting fillers are stainless steel fibers, carbon fibers, nanotube material, carbon flake or nickel-graphite powder. Blends of materials might also be used. 
     In a preferred embodiment, the binder is loaded with conducting filler between 10% and 80% by volume. More preferably, the loading is in excess of 30% by volume. Most preferably, the conductive filler is loaded at between 40% and 60% by volume. 
     When fibrous filler is used, the fibers preferably have a length between 0.5 mm and 15 mm. More preferably, the length is between 3 mm and 11 mm. In one contemplated embodiment, the fiber length is between 3 mm and 8 mm. 
     In one contemplated embodiment, the fibrous filler has a high aspect ratio (ratio of length to width). In that embodiment, the fiber preferably has an aspect ratio in excess of 10 and more preferably in excess of 100. 
     Filled materials can be purchased commercially, such as materials sold under the trade name Celestran® by Ticona. Or, suitable material could be custom blended as sold by RTP Company. 
     Preferably, the binder material is a thermoplastic material that has a reflow temperature in excess of 250° C. and more preferably in the range of 270-280° C. LCP and PPS are examples of suitable material. In the preferred embodiment, LCP is used because it has a lower viscosity. Preferably, the binder material has a viscosity of less than 800 centipoise at its reflow temperature without fill. More preferably, the binder material has a viscosity of less than 400 centipoise at its reflow temperature without fill. 
     The viscosity of the molding material when filled can not be made arbitrarily high. Preferably, the material has a viscosity low enough to be molded with readily available molding machinery. 
     When filled, the molding material preferably has a viscosity below 2000 centipoise at its reflow temperature and more preferably a viscosity below 1500 centipoise at its reflow temperature. It should be appreciated that the viscosity of the material can be decreased during molding operation by increasing its temperature or pressure. However, binders will break down and yield poor quality parts if heated to too high a temperature. Also, commercially available machines are limited in the amount of pressure they can generate. If the viscosity in the molding machine is too high, the material injected into the mold will set before it fills all areas of the mold. 
     In connectors for which the conductive plastic material is molded to act as a shield, preferably, the binder is filled to provide a surface resistivity of less that 10 5  Ω/sq. More preferably, the surface resistivity is less than 10 2  Ω/sq. Resistivity might also be expressed as a bulk or volume resistivity. Preferably, the volume resistivity is less than 10 Ω-cm and more preferably less than 1 Ω-cm and more preferably less than 0.8 Ω-cm. 
     The use of plastics filled with electromagnetic materials for a portion of the connector housing allows electromagnetic interference between signal conductors to be reduced. In a preferred embodiment, housing  132  is molded with materials that contains conductive filler. If sufficiently conductive, the conductive filler acts like an extension of the shield plate  10 . Even if not fully conductive, the filled plastic can absorb signals radiating from the signal conductors that would otherwise create crosstalk. 
     FIG. 4 shows a portion of wafer  120  that has been molded with two types of material according to the invention. In FIG. 4A, housing  132  is shown formed from a material with conductive filler. Housing  134  is formed from an insulator with little or no conductive fillers. 
     Housing  132  is electrically in contact with shield  10 , which will preferably be grounded in a connector system. Therefore, housing  132  is preferably grounded. To increase the electrical connection between housing  132  and shield plate  10 , projections can be provided from shield plate  10 . FIG. 4A shows, as an example, tab  460  bent out of the plane of shield plate  10  and projecting into housing  132 . 
     If sufficiently conductive, housing  132  acts as an extension of shield  10 . Projections  414 A,  414 B . . . are positioned between adjacent signal conductors used to carry different signals. They therefore provide shielding between the signal conductors. Significantly, because projections  414 A,  414 B . . . are molded from plastic, they can be in almost any shape and can follow the contours of the signal conductors  410 A,  410 B . . . through the connector. 
     In the embodiment of FIG. 4A, wafer  120  is designed to carry differential signals. Thus, each signal is carried by a pair of signal conductors. And, preferably, each signal conductor is closer to the other conductor in its pair than it is to a conductor in an adjacent pair. For example, a pair of signal conductors  410 A and  410 B carry one differential signal and signal conductors  410 C and  410 D carry another differential signal. Thus, projection  414 B is positioned between these pairs to provide shielding between the adjacent differential signals. 
     Projection  414 A is at the end of the column of signal conductors in wafer  120 . It is not shielding adjacent signals in the same column. However, having shielding projections at the end of the row helps prevent cross-talk from column to column. 
     To prevent signal conductors  410 A,  410 B . . . from being shorted together through conductive housing  132 , a second molding step is used to create insulative portions such as  450 A and  450 B in the housing. Once the signal conductors arc inserted, further dielectric material is molded over the part to finish housing  134 . 
     FIG. 4B shows an alternative implementation of wafer  120 ′. Wafer  120 ′ is designed for single ended signals. Therefore, a projection, such as  414 B,  414 C,  414 D . . . is positioned between adjacent signal conductors, which are relatively uniformly spaced. In FIG. 4B, insulative portions  452 A,  452 B . . . are molded between the projections  414 B,  414 C,  414 D . . . to ensure that the signal conductors are not shorted to the conducting portions of the housing. 
     FIG. 5 is a simplified sketch of a machine to make a connector according to the invention. Molding machine  500  is a two-shot molding machine, generally as known in the art. Such machines arc used for things such as molding knobs, toohbrushes or buttons in two colors of plastic. 
     Molding machine  500  has three molding chambers  510 A,  510 B and  510 C. Each molding chamber is made of a lower chamber, such as  512 A, and an upper chamber, such as  514 A. Upper chamber  514 A is moveable, allowing the upper and lower chamber to separate. As is traditional in the molding art, mold pieces separate to allow removal of molded parts or to place conducting members into the chamber to prior to injection of molding material to insert mold the conducting members into the molding material. 
     In the illustrated embodiment, the lower chambers  512 A,  512 B and  512 C are identical. Each lower chamber has a mold cavity that has the same contour as the lower portions of the part to be molded. Upper chamber  514 A is shaped to mate with any of the lower chambers and form a mold cavity that ha contour matching the desired contour of the part being molded after one type of molding material has been applied. For example, in the case of a wafer as shown in FIG. 4, mold chamber  510 A has a contour that matches shield  10  with housing  132  molded on it—but without housing  134  in place. 
     Mold chamber  510 B has a contour that matches the upper surface of housing  132  with inserts  450 A and  450 B in place. 
     Mold chamber  510 C has a contour that matches the contour of the finished part. To provide this result, upper chamber  514 B will have a different shape than upper chamber  514 A. In the example of FIG. 4, mold chamber  510 C will have a contour that matches the contour of the finished wafer  120  with a shield  10 , housing  132  and  134  in place. 
     Molding machine  500  includes feed systems  520 A,  520 B and  520 C. As in a conventional molding machine, each of the feed systems provides molding material into a mold cavity. In a preferred embodiment that uses a thermoplastic material as a binder, each feed system includes a hopper of materials in pellet form. 
     In this preferred configuration, material is dispensed from the hopper and heated to a liquid state. The feed system then injects the liquid material into the mold cavity. For example, and auger screw can be used to provide the required force to inject the material. In FIGS. 4 5 , the material passes through nozzles  522 A,  522 B or  522 C into a respective mold chamber  510 A,  510 B or  510 C. 
     In the mold cavity, the material rapidly cools to below its set point. The mold can then be opened. Parts molded in chamber  510 A and  510 B are only partially complete. To finish molding parts from chamber  510 A, the partially finished part is left in lower chamber  512 A. Lower chamber  512 A is then moved below upper chamber  514 B. Thus, the partially molded part is in chamber  510 B. Additional material can be added to the part. The partially finished part can then be rotated below upper chamber  514 C to complete the operation. 
     In the illustrated embodiment, lower mold chamber  512 A is mounted on a moving member and moves with the partially molded part into position to form mold chamber  510 B. Here, lower mold chamber  512 A rotates on a turntable-like device. However, other forms of moving members could be used. 
     For example, a moving member that provided linear motion might be preferred. A shuttle is a suitable moving member that provides linear motion. In some cases, a shuttle-type arrangement would be preferable. Where wafers are formed on carrier strips, it is preferable that the parts move in a straight line so that a “reel to reel” manufacturing line can be set up. In such a line, numerous shield plates would be stamped from a long strip of metal. As part of the stamping, a carrier strip would be left and each of the shield plates would be attached to the carrier strip. The strip would be wound on a reel. The reel would feed shields one at a time into chamber  510 A. For each cycle of the molding machine, a new shield would be fed into chamber  510 A and a finished part would emerge from chamber  510 B. The finished parts, still on their carrier strips, could then be wound on another reel. 
     In the illustrated embodiment, feed system  520 A feeds molding material filled with conducting fibers. Depending on the length of fibers used in the filler and the filler content in the binder, such a material is likely to have a higher viscosity than materials traditionally used to mold connector housings. Consequently, greater pressure might be required. 
     Feed system  520 A must generate sufficient force to inject the filled material. In practice, empirical data is gathered to determined the appropriate settings for molding machine  500 . However, it is expected that the feed system providing conductor filled plastic will deliver material at a higher pressure. 
     Furthermore, nozzle  522 A, which delivers the conductor filled plastic at higher pressure will have a larger orifice. Furthermore, the combination of higher pressure and conductive fillers, which could be abrasive, is likely to cause additional wear in feed system  520 A. To counteract these problems, nozzle  522 A is preferably made of a hardened material, such as carbide steel. 
     Other parts of molding machine  500  exposed to the conductor filled plastic are also likely to experience excessive wear and can likewise be made of hardened materials and might be made easily replaceable. For example, carbide mold inserts might be used to reduce wear and also to allow easy replacement. 
     Turing to FIGS. 6 and 7, an example of application of the invention to a backplane connector is shown. FIG. 6 shows a prior art backplane connector  605 . Backplane connector  605  has a shroud  610 . To enhance shielding, shroud  610  is die cast of metal. 
     Shields  616  may make direct electrical contact to the metal housing, as both are intended to be connected to ground in operation. However, signal conductors  612  would be shorted out if inserted directly into the metal housing. Insulative spacer member  620  is inserted into shroud  610  to prevent signal conductors  612  from being shorted out by the conducting housing of backplane connector  605 . 
     The implementation shown in FIG. 6 has the drawback of being made of relatively expensive die cast parts and has separate pieces that add cost to the assembly operation. Using the molding technique according to the invention, a connector providing similar performance can be achieved at a lower cost. 
     FIG. 7A shows a portion of backplane connector  605  in cross section. Housing  632  is molded of conventional connector molding material. For example, the thermoplastic PPS filled to 30% by volume with glass fiber might be used. 
     In molding housing  632  a recessed area is left for housing  634 . However, the recessed area includes lands  710  (FIG. 7B) that contain areas for receiving signal conductors  612 . 
     In a second molding step, the recessed area is filled with molding material with conductive filler. Examples of the materials and fillers that might be used for housing  634  are given above. 
     FIG. 7A shows a projection  650  from shield  616  into the conductive portion  634 . The projection enhances the electrical conductivity between the shield and the conducting plastic portions. The projection could be in any convenient form, such as a tab or a bend in the shield. 
     FIG. 7B shows a top view of the portion of backplane connector  605  shown in FIG.  7 A. Lands  710  are visible in this view. Also, it can be seen that housing  634  is in contact with shields  616 , grounding housing  634  through the ground contacts of shields  616 . 
     Alternatives 
     Having described one embodiment, numerous alternative embodiments or variations can be made. 
     For example, it was described that parts being molded with molding material with different electrical properties are moved from molding station to molding station. It is possible that the parts could be stationary at a molding station with two different material inlets. 
     As another example, the invention was described as applied to a backplane-daughter card connector. Conductive features might be built into connectors in any configuration, such as stacking connectors or other board to board connectors or in phone jacks or cable connectors. Moreover, the invention was illustrated as applied to both the backplane and daughter card pieces of the connector. It could be used with either or both. 
     Also, a two step molding operation is described in connection with the backplane connector and a three step operation is described in connection with daughter card wafers  120 . Other types of molding operations might be used. A single step molding might be used in cases where the entire housing is to be conducting. Alternatively, three or more molding steps might be performed. Such a process might be employed where the finished shape of the part is more complicated than can be molded in two steps or where materials with more than two different properties are required in the finished product. 
     Further, it was shown in FIG. 4A that a conductive housing is molded and then an insulative housing is molded. Thereafter, the signal contacts are inserted and a second insulative layer is applied to lock the signal contacts into place. Application of the second insulative layer could be done as a true molding operation using a mold with a cavity shaped to match the desired final contour of the part. Alternatively, a simpler form of “molding” might be used in which the first two operations leave a cavity. Once the signal contacts are inserted into this cavity the second insulative layer is “molded” by putting material into this cavity and leveling it off to leave a smooth upper surface. In this process, a full cavity mold is not required to shape the final part. 
     FIG. 5 shows a molding machine that has two mold chambers operating simultaneously. For each cycle of the molding machine, a part is being molded with the first type material and another part is being molded with the second type of material. One complete part can therefore emerge from mold chamber  510 B each cycle. As shown, there is no loss of efficiency from having a two step molding operation. It would be possible, however, to manufacture parts with molding steps done sequentially rather than simultaneously. Sequential molding equipment might be lower cost, but would have lower throughput. 
     Also, it should be appreciated that preferred lengths and aspect ratios of fibers are described. It should be appreciated that all fibers in a batch will not have precisely uniform properties. Thus, when reference is made to an upper or lower limit on properties of fibers or other materials, it should be appreciated that not every fiber will meet this limit. Rather, the limits should be interpreted as meaning that most of the fibers meet that limitation. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.