Patent Publication Number: US-10320098-B2

Title: High frequency BGA connector

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 62/492,003, filed on Apr. 28, 2017 and entitled “High Frequency BGA Connector,” which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     This application relates generally to interconnection systems, such as those including electrical connectors, used to interconnect electronic assemblies. 
     Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system as separate electronic assemblies, such as printed circuit boards (“PCBs”), which may be joined together with electrical connectors. A known arrangement for joining several PCBs is to have one PCB serve as a backplane. Other PCBs, called “daughterboards” or “daughtercards”, may be connected through the backplane. 
     A known backplane is a PCB onto which many connectors may be mounted. Conducting traces in the backplane may be electrically connected to signal conductors in the connectors so that signals may be routed between the connectors. Daughtercards may also have connectors mounted thereon. The connectors mounted on a daughtercard may be plugged into the connectors mounted on the backplane. In this way, signals may be routed among the daughtercards through the backplane. 
     Electrical connector designs have been adapted to mirror trends in the electronic industry. Electronic systems generally have gotten smaller, faster, and functionally more complex. Because of these changes, the number of circuits in a given area of an electronic system, along with the frequencies at which the circuits operate, have increased significantly in recent years. Current systems pass more data between PCBs and require electrical connectors that are electrically capable of handling more data at higher speeds than connectors of even a few years ago. 
     Electrical connectors typically include a dielectric connector housing supporting a plurality of electrical contacts. For example, electrical connectors can be constructed with arrays of electrical contacts having solder balls fused to mounting ends of the contacts. The mounting ends may be held in an array, creating a ball grid array (BGA) connector. 
     In a high density, high speed connector, electrical conductors may be so close to each other that there may be electrical interference between adjacent signal conductors. To reduce interference, and to otherwise provide desirable electrical properties, reference conductors are often placed between adjacent signal conductors. 
     BRIEF SUMMARY 
     Aspects of the present disclosure relate to improved high density, high speed interconnection systems. The inventors have recognized and appreciated techniques for configuring connector components to improve signal integrity for high frequency signals. These techniques may be used together, separately, or in any suitable combination. 
     Accordingly, some embodiments relate to a connector, comprising a housing comprising a plurality of pockets at a surface, and a plurality of contacts, each comprising a mating end, a mounting end opposite the mating end and disposed within at least a respective one of the plurality of pockets, and an intermediate portion that extends between the mating end and the mounting end. The connector may be configured for mounting to a circuit board with the surface of the housing facing the circuit board. Each of the plurality of pockets in the surface of the housing may comprise a floor surrounded by a wall having a first height in a direction perpendicular to the surface. For each of the plurality of contacts, the mounting end may comprise a space separating, in a direction parallel to the surface of the housing, first and second projections. The space may be separated from the floor of the respective pocket by a second distance in the direction perpendicular to the surface. The second distance may be less than the first height. At least one of the first and second projections may extend beyond the wall of the respective pocket in the direction parallel to the surface. 
     In some embodiments, an electrical connector is provided. The electrical connector may comprising a housing comprising a surface, and a plurality of contacts, each comprising a mating end, a mounting end opposite the mating end and exposed adjacent the surface of the housing, and an intermediate portion that extends between the mating end and the mounting end. The electrical connector may be configured for mounting to a circuit board with the surface of the housing facing the circuit board. For each of the plurality of contacts, the mounting end may have an edge joining a first surface and a second surface parallel to the surface of the housing, and the edge may have a concave region. Each of the plurality of contacts may have an anti-solder wicking coating on the first surface and the second surface adjacent the edge. The electrical connector may further comprise a plurality of solder masses preferentially fused to the concave regions of the plurality of contacts. 
     In another aspect, embodiments may relate to method of manufacturing a connector comprising a housing having a surface, and a plurality of contacts held by the housing, each having a mounting end exposed adjacent the surface. The mounting end of each of the plurality of contacts may have a width in a direction parallel to the surface of the housing and an edge spanning the width of the mounting end. The edge of the mounting end of each of the plurality of contacts may have a profile such that a length along the edge is longer than the width. The method may include applying solder flux to the edges of the mounting ends of the plurality of contacts. Subsequent to applying solder flux, a plurality of solder balls may be positioned adjacent the edges of the mounting ends of the plurality of contacts. The method may further include heating the plurality of solder balls such that solder melts to form solder masses attached to the mounting ends of the plurality of contacts. 
     The foregoing is a non-limiting summary of the invention, which is defined by the attached claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: 
         FIG. 1  is a perspective view of an electrical assembly constructed in accordance with some embodiments, including first and second electrical connectors mounted onto respective first and second printed circuit boards; 
         FIG. 2A  is a perspective view of an electrical connector, showing the mating interface, according to some embodiments; 
         FIG. 2B  is a plan view of the electrical connector in  FIG. 2A ; 
         FIG. 3A  is a perspective view of a set of electrical contacts of a plug electrical connector, according to some embodiments; 
         FIG. 3B  is a plan view of the set of electrical contacts in  FIG. 3A ; 
         FIG. 3C  is a side view of the set of electrical contacts in  FIG. 3A ; 
         FIG. 4A  is a perspective view of a set of electrical contacts of a receptacle electrical connector, according to some embodiments; 
         FIG. 4B  is a plan view of the set of electrical contacts in  FIG. 4A ; 
         FIG. 4C  is a side view of the set of electrical contacts in  FIG. 4A ; 
         FIG. 5A  is a perspective view of a set of electrical contacts of a plug electrical connector, schematically illustrating solder balls attached to the contact mounting ends, according to some embodiments; 
         FIG. 5B  is a plan view of the set of electrical contacts in  FIG. 5A ; 
         FIG. 5C  is a perspective view of a set of electrical contacts of a plug electrical connector schematically illustrating solder masses attached to the contact mounting ends, according to some embodiments; 
         FIG. 5D  is a plan view of the set of electrical contacts in  FIG. 5C ; 
         FIG. 6A  is a perspective view of a set of electrical contacts of a receptacle electrical connector, schematically illustrating solder balls attached to the contact mounting ends, according to some embodiments; 
         FIG. 6B  is a plan view of the set of electrical contacts in  FIG. 6A ; 
         FIG. 6C  is a perspective view of a set of electrical contacts of a receptacle electrical connector, schematically illustrating solder masses attached to the contact mounting ends, according to some embodiments; 
         FIG. 6D  is a plan view of the set of electrical contacts in  FIG. 6C ; 
         FIG. 7A  is a perspective view of a plug electrical connector, partially cut away, mounted to a printed circuit board, according to some embodiments; 
         FIG. 7B  is an enlarged perspective view of circled region  7 B in  FIG. 7A ; 
         FIG. 8A  is a perspective view of an electrical connector, showing the mounting interface before attachment to a printed circuit board, according to some embodiments; 
         FIG. 8B  is an enlarged perspective view of circled region  8 B in  FIG. 8A ; 
         FIG. 8C  is a plan view of the electrical connector in  FIG. 8A ; 
         FIG. 9A  is a partial perspective view of an electrical connector, showing the mounting surface, according to some embodiments; 
         FIG. 9B  is a partial plan view of the electrical connector in  FIG. 9A ; 
         FIG. 9C  is an enlarged perspective view of circled region  9 C in  FIG. 9A ; 
         FIG. 10A  is a perspective view of an electrical connector, showing the mounting interface with fused solder masses, according to some embodiments; 
         FIG. 10B  is an enlarged perspective view of circled region  10 B in  FIG. 10A ; 
         FIG. 11A  is a perspective view of a printed circuit board, showing contact pads, according to some embodiments; 
         FIG. 11B  is an enlarged perspective view of circled region  11 B in  FIG. 11A ; 
         FIG. 12A  is an enlarged perspective view of circled region  12 A in  FIG. 3A  reversed 180 degrees, showing a mounting end of an electrical contact; 
         FIGS. 12B-12E  are cross-sectional views of alternative embodiments of circled region  12 B in  FIG. 12A , illustrating examples of alternative edge profiles; 
         FIGS. 13A-13C  are schematic illustration of successive steps in a method of manufacturing a connector described herein, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The inventors have recognized and appreciated connector designs that may increase the frequency of operation of connectors that are mounted to circuit assemblies, such as printed circuit boards, using solder balls. As a result, the connector may have very high density and operate at high frequencies, such as greater than 40 Gbps NRZ. In some embodiments, the connector may operate at 56 Gbps NRZ or higher. 
     One or more techniques may be used to reduce signal crosstalk. In some embodiments, the connectors may include a housing configured to position subsets of the solder balls close enough that, upon reflow of the solder balls to attach them to the mounting ends of the contacts in the connector or upon attachment of the connector to a circuit assembly, those subsets will fuse or otherwise be so closely spaced that they serve as a shield in the mounting interface of the connector. In accordance with some embodiments, the subsets may be attached to the mounting ends of wide contacts positioned within the connector to serve as reference conductors. Such a configuration may reduce crosstalk, or provide other desired characteristics, particularly for connectors with densely spaced signal conductors. 
     Some embodiments may relate to a connector including two types of contacts with the second type contacts being wider than the first type contacts. In some embodiments, the first type contacts may be designated as signal conductors and the second type contacts may be designated as reference conductors. One of ordinary skill in the art would recognize signal and reference conductors based on their shape and position within a connector. The mounting ends of the first type contacts may include two projections with the second projection being wider than the first projection. The mounting ends of the second type contacts may include at least four projections. The at least four projections may have the same width. The second projection of a first type contact may be adjacent to and extends towards an adjacent projection of a reference contact. 
     In some embodiments, a connector housing may comprise a surface configured to face a circuit board when the connector is mounted to the circuit board. The housing may include a plurality of pockets in the surface. The plurality of pockets may be arranged in a plurality of rows. Within each row, a first portion of the pockets may have a center-to-center spacing in a row direction from adjacent pockets of a first distance, and a second portion of the pockets have a center-to-center spacing from at least one adjacent pocket of a second distance, wherein the second distance is less than the first distance. For example, pockets receiving mounting ends of signal conductors may be spaced from each other by a greater distance than pockets receiving mounting ends of reference conductors. 
     In some embodiments, the pockets of the first portion may comprise a first region and a second region. The second region may include a slot that extends from the first portion towards an adjacent pocket in the second portion. Each first portion pocket may receive a mounting end of a first type contact, and each second type pocket may receive a portion of a mounting end of a second type contact. 
     In some embodiments, the connector may include solder masses within the pockets and fused to mounting ends of contacts. Solder masses within the second portion of the pockets may be fused to solder masses in at least one adjacent pocket of the second portion. 
     Alternatively or additionally, higher operating frequency may be achieved with contacts shaped to receive solder balls at their mounting ends but with lower inductance than conventional BGA-type connectors. In accordance with some embodiments, the mounting ends may include first and second projections separated by a space with the second projection being wider than the first projection. 
     In accordance with some embodiments, connectors may include contacts shaped to receive solder balls at their mounting ends so as to provide better signal integrity. Improvements in signal integrity may result from more uniform impedance of signal paths through the mounting interface. The mounting ends may be shaped to support a flux pin transfer approach for attaching solder balls to the contacts, which, in comparison to approaches using solder paste, may provide a smaller and more uniform amount of conductive material at the mounting interface for each signal contact. 
     A smaller amount of conductive material may result in smaller impedance discontinuities along the signal paths, which tend to degrade signal integrity. Smaller impedance discontinuities, in turn, enables other portions of the interconnection system to be reliably designed to account for the impedance of the mounting interface such that the impact of any impedance discontinuities may be lessened by compensating for those discontinuities in the design of other portions of the interconnection system. 
     In accordance with some embodiments, the mounting ends may have edges that are solder-wettable with surfaces joining the edges having a non-solder wettable coating. The mounting ends of at least some of the contacts may include projections that extend into pockets formed in a surface of a housing configured for mounting against the circuit assembly. These projections may have edges that are solder-wettable, which may aid in attachment of the solder balls to the contacts. The edges may be made solder-wettable by application of solder flux, such as through the use of a flux pin transfer technique. Alternatively or additionally, the edges may be made solder-wettable by coating a solder-wettable layer to the edges, such as a layer of copper, gold, nickel, nickel-vanadium alloy, or any other suitable materials in any suitable combinations. 
     In some embodiments, the mounting ends of the signal contacts may be shaped to lessen the impact of narrowed portions resulting from shaping the ends for solder ball attachment, which can also induce impedance discontinuities that may impact performance. The projections at the mounting ends of at least some of the contacts may be non-uniform in width, with one projection being wider than the other. Widening a projection in this way may decrease inductance of the mounting end of the contact, increasing the resonant frequency of the contacts to be outside the operating range of the connector. In a connector in which some contacts are designated as signal conductors and some are designated as reference conductors, the asymmetrical projections may be on at least the signal conductors, with the wider projections on the signal conductors extending toward an adjacent ground. 
       FIG. 1  illustrates an electrical assembly  10  constructed in accordance with some embodiments. Electrical assembly  10  includes a first electrical connector  100 , a first printed circuit board (PCB)  101 , a second electrical connector  200 , and a second PCB  201 . 
     Electrical connector  100  may include a connector housing  102 , an array of electrical contacts (not shown), a mounting surface  110 , and a mating interface (not shown). At least a portion of the connector housing may be made of any suitable dielectric material, such as plastic, so as to provide electrical isolation between electrical contacts. Additionally, the connector housing may include conductive or lossy portions, which in some embodiments may provide conductive or partially conductive paths between some of the electrical contacts. The electrical contacts may be made of any suitable electrically conductive material such as metal. The connector housing may be configured to support the array of electrical contacts. In some embodiments, the connector housing may be overmolded onto the electrical contacts. Alternatively, the electrical contacts may be stitched into the connector housing or otherwise supported by the connector housing as desired. 
     Each of the electrical contacts may include an intermediate portion that connects a mounting end to a mating end. The electrical contacts may have fusible elements, such as solder balls  108 , fused to their mounting ends such that the electrical connector  100  is placed in electrical communication with printed circuit board (PCB)  101  by conduction paths from the electrical contacts through the fusible elements to contact pads on a surface of the PCB. The fusible elements may be reflowed, such as through a conventional surface mount reflow operation, to electrically and mechanically affix the fusible elements to conductive pads on a surface of the PCB. 
     Connector housing  102  may have an array of pockets  106  in the mounting surface  110 . The connector is configured for attachment to a circuit assembly with the mounting surface facing the circuit assembly, which is the first PCB  101  in this example. Each pocket may be sized and positioned to at least partially receive a mounting end of an electrical contact and a respective solder mass, here illustrated as solder balls  108  attached to the mounting end of the electrical contact. Within each row, the contacts may be arranged in a repeating pattern such as a signal-signal-ground pattern, a ground-signal-signal pattern, or a signal-ground-signal pattern. The contacts may also be arranged in a repeating signal-signal-ground-ground pattern, a ground-signal-signal-ground pattern, or a signal-ground-signal-ground pattern. Each row of the array of pockets may also be arranged in a corresponding repeating pattern to receive the mounting ends of the contacts. 
     Electrical connector  200  may include a connector housing  202 , an array of electrical contacts  204 , a mounting surface (not shown), and a mating interface  212 . The array of electrical contacts  204  can be constructed the same or differently than the array of electrical contacts of the electrical connector  100 . The array of electrical contacts  204  may have fusible elements, such as solder masses (not shown), fused to their mounting ends such that the electrical connector  200  is placed in electrical communication with printed circuit board  201  by conduction paths from the electrical contacts through the solder masses to contact pads on a surface of the PCB. 
     Connector housing  202  may have an array of pockets in the mounting interface (not shown). The connector is configured for attachment to a circuit assembly with the mounting surface facing the circuit assembly, which is the second PCB  201  in this example. Each pocket may be sized and positioned to at least partially receive a mounting end of an electrical contact and a respective solder mass attached to the mounting end of the electrical contact. 
     In some embodiments, the electrical contacts may comprise first type contact  204 A and second type contact  204 B with the second type being wider than the first type along a direction parallel to the mounting surface. In some embodiment, the first type contacts may be designated as signal conductors and the second type contacts as ground conductors. The mounting end of each ground contact may occupy more pockets than the mounting end of each signal contact. In the embodiment illustrated, the mounting end of each signal contact is inserted into a single pocket while each ground contact has a plurality of mounting ends, here three, each with a corresponding pocket. It should be appreciated that ground conductors need not be connected to earth ground, but are shaped to carry reference potentials, which may include earth ground, DC voltages or other suitable reference potentials. The “ground” or “reference” conductors may have a shape different than the signal conductors, which are configured to provide suitable signal transmission properties for high frequency signals. One of ordinary skill in the art would recognize signal and reference conductors based on their shape and position. 
     In some embodiments, electrical connector  200  is configured to be mated with electrical connector  100  so as to be in electrical communication with electrical connector  100 . In some embodiments, electrical connector  200  may be constructed substantially identically to electrical connector  100 . 
       FIG. 2A  and  FIG. 2B  shows a perspective view and a plan view of the mating interface of electrical connector  220  respectively. Electrical connector  220  may include a plurality of electrical contacts  224 A,  224 B arranged into a plurality of rows extending in a row direction. 
     In some embodiments, electrical contacts  224 A may conduct signals and electrical contacts  224 B may conduct reference voltage levels and may additionally shield signals from crosstalk. Within each row, contacts  224 A may be arranged in pairs with contacts  224 B positioned between adjacent pairs such that the reference contacts may shape electric fields to avoid crosstalk induced in an adjacent row by constraining the fields around a single pair of signal contacts to be in the same row. Additionally, this arrangement may prevent undesired signal propagation along the row. In some embodiments, within each row, the electrical contacts may be arranged as a repeating pattern of sets of electrical contacts. One set of electrical contacts may include one electrical contact  224 B placed between two electrical contacts  224 A. In the illustrated embodiment, the width of one electrical contact  224 B is greater than the width of one electrical contact  224 A along the row direction. 
     At the mounting ends, an electrical contact  224 A may be spaced from an adjacent electrical contact  224 A by a distance  226 A and be spaced from an adjacent electrical contact  224 B by a distance  226 B. In some embodiments, distances  226 A and  226 B may be substantially equal. In another embodiments, space  226 B may be greater or less than space  226 A. Corresponding distances between the contacts for the intermediate portions and/or the mounting end may be the same as or different from distances  226 A,  226 B. 
     The plurality of electrical contacts  224 A,  224 B may be arranged into at least two type of rows that extend along the row direction. In some embodiments, a first type row may be offset from a second type row by a distance in the row direction such that reference contacts  224 B in each row may be offset, in the row direction, toward signal contacts  224 A in an adjacent row. The offset distance may be a fraction of center to center spacing between signal contacts, depicted as distance  226 A, such as between 10% and 90% of the center-to-center spacing, between 20% and 80%, between 25% and 75%, or any value within such ranges. Alternatively, the distance may be a fraction of the signal to ground spacing, such as is represented by distance  226 B. That fraction may be, for example, between 15% and 95%, between 25% and 85%, between 30% and 80%, or any value within such ranges. In the illustrated embodiments, five first type rows and five second type rows are arranged in an alternating pattern. However, the electrical contacts can be configured into any numbers of rows and any types of rows in any pattern. 
     The inventors have recognized and appreciated that geometry of electrical contacts of the electrical connectors can improve signal integrity (SI) of an electrical assembly at high frequency. For example, a geometry at the mounting ends of the electrical contacts that provides a more uniform contact width at the mounting end than a conventional design in which the contact width is necked down to provide a solder ball attachment has a more uniform inductance along signal paths from a connector to a printed circuit board to which the connector is attached. The geometry at the mounting ends of the electrical contacts can also enable precise positioning of solder balls while reducing the need for solder paste, leading to ball attachments with less fusible material than conventional BGA-type connectors. Less mass at the mounting portion reduces changes of impedance along the signal path of a connector and enables more repeatable manufacturing processes, particularly for small solder balls, which reduces part-to-part variations. 
       FIGS. 3A to 3C  illustrates one set of electrical contact of a plug electrical connector, according to some embodiments, which may be a portion of a row. One set of electrical contact may include contact  304 A, contact  304 B which is a mirrored version of contact  304 A, and contact  304 C positioned between the contacts  304 A and  404 B. In some embodiments, electrical contacts  304 A and  304 B may conduct signals and electrical contacts  304 C may conduct reference potentials. The electrical contacts  304 A,  304 B, and  304 C may have respective mating ends  302 A,  302 B, and  302 C that may extend out from the mating interface  212 , respective opposed mounting ends  308 A,  308 B, and  308 C that may be disposed within pockets  106  in the mounting surface  110 , and respective intermediate portions  306 A,  306 B, and  306 C that may extend between the mating ends and the mounting ends. 
     The mounting end of an electrical contact  304 A may have a space  314  separating first and second projections  310 A,  310 B. The spaces may be formed by stamping the mounting ends of the contacts or any other suitable methods. The width of the second projection d 2  may be greater than the width of the first projection d 1 . In some embodiments, d 2  may be in the range of 20 mil to 60 mil, and d 1  may be in the range of 5 mil to 40 mil. In some embodiments, the second projection may project from intermediate portion  306 A that is adjacent to the electrical contact  304 C. In the embodiment illustrated, the spaces are rectangular. Such spaces increase the distance along the edge of electrical contact  304 A exposed at the mounting end. In accordance with some embodiments, portions of the contacts, including the mounting ends, may be coated with nickel or other metal that resists oxidation and/or undesired solder wicking. Such coatings may reduce the affinity of the solder to adhere to the mounting ends of the contacts. Whether or not such a coating is used, the edges of the mounting ends may be totally or partially coated with a solder flux that promotes adhesion of a solder ball to the electrical contact  304 A during a reflow operation. Additionally, the space provides a shape to the mounting end that tends to hold the solder ball in a desired position, centered in the center of the space. Further, the spaces increase the perimeter of the edge of the mounting end of the contact where a solder ball is fused to the contact. A rectangular space provides a suitable increase in the amount of exposed edge. However, it is not a requirement that the spaces are rectangular, and in some embodiments, different shapes may be used, such as triangular, dovetail, semi-circular, half-oval, or any other suitable opening shape. 
     As illustrated in the exemplary embodiment of  FIGS. 3A and 3B , the mounting end of an electrical contact  304 C may have pairs of projections  312  separated by spaces. Each of a pair of projections may be separated from the other by a distance d 7 . A pair of projections may be separated from an adjacent pair by a distance d 8 . In some embodiments, d 8  may be greater than d 7 . In some embodiments, the projections of a pair may have different widths. In some embodiments, the mounting ends of an electrical contact  304 C may include at least four projections. The at least four projections may have a same width. 
     In the illustrated embodiment, the electrical contacts  304 A,  304 B, and  304 C are configured as a plug contact. Thus, the mating ends  302 A,  302 B, and  302 C may define a blade with a thickness t 1 . The width of the mating end of an electrical contact  304 C d 6  may be greater than the width of the mating end of an electrical contact  304 A d 4 . In some embodiments, d 6  may be twice or three times of d 4 . 
     The width of the intermediate portion of an electrical contact  304 A d 3  may be substantially similar to the width of the mating end of the electrical contact  304 A d 4 . In some embodiments, d 4  may be greater than d 3 . In some embodiments, d 3  may be greater than 80% of d 4 , such as between 90% and 100%, or any value within such ranges. Similarly, the width of the body of an electrical contact  304 C d 5  may be substantially similar to the width of the mating end of the electrical contact  304 C d 6 . In some embodiments, d 6  may be greater than d 5 . In some embodiments, d 5  may be greater than 80% of d 6 , between 90% and 100%, or any value within such ranges. By having similar widths as the intermediate portion, the mating end and the solder ball attached to the mating end, electrical performance of the connector may be increased. 
     The inventors have recognized and appreciated that the edges at the mating end by having projections non-uniform in width creates larger contact surfaces. Moreover, this shape at the mating end can reduce inductance and thus impact the frequency at which resonance happens and result in a higher Q-factor. For example, in a non-limiting embodiment, the operation frequency of an electrical connector are increased to 56 GHz, such that the connector may operate at frequencies greater than 26 GHz. 
       FIGS. 4A to 4C  illustrates one set of electrical contact of a receptacle electrical connector, according to some embodiments, which may be a portion of a row. One set of electrical contact may include contact  404 A, contact  404 B which is a mirrored version of contact  404 A, and contact  404 C positioned between the contacts  404 A and  404 B. In some embodiments, electrical contacts  404 A and  404 B may conduct signals and electrical contacts  404 C may conduct reference potentials. The electrical contacts  404 A,  404 B, and  404 C may have respective mating ends  402 A,  402 B, and  402 C that may extend out from the mating interface  212 , respective opposed mounting ends  408 A,  408 B, and  408 C that may be disposed within pockets  106  in the mounting surface  110 , and respective intermediate portions  406 A,  406 B, and  406 C that may extend between the mating ends and the mounting ends. 
     The mounting end of an electrical contact  404 A may have a space  414  separating first and second projections  410 A,  410 B. The width of the second projection d 42  may be greater than the width of the first projection d 41 . In some embodiments, d 42  may be in the range of 20 mil to 60 mil, and d 41  may be in the range of 5 mil to 40 mil. In some embodiments, the second projection may project from intermediate portion  406 A that is adjacent to the electrical contact  404 C. In the embodiment illustrated, the spaces are rectangular. Such spaces increase the distance along the edge of electrical contact  404 A exposed at the mounting end. In accordance with some embodiments, that edge may be coated with a solder flux that promotes adhesion of a solder ball to the electrical contact  404 A during a reflow operation. Additionally, the space provides a shape to the mounting end that tends to hold the solder ball in a desired position, centered in the center of the space. A rectangular space provides a suitable increase in the amount of exposed edge. However, it is not a requirement that the spaces are rectangular, and in some embodiments, different shapes may be used, such as triangular, dovetail, semi-circular, half-oval, or any other suitable opening shape. 
     The mounting end of an electrical contact  404 C may have pairs of projections  412  separated by spaces. Each of a pair of projection may be separated from the other by a distance d 47 . A pair of projections may be separated from an adjacent pair by a distance d 48 . In some embodiments, d 48  may be greater than d 47 . In some embodiments, the projections of a pair may have different widths. In some embodiments, the mounting ends of an electrical contact  404 C may include at least four projections. The at least four projections may have a same width. 
     In the illustrated embodiment, as described in U.S. Pat. No. 6,042,389, which is incorporated by reference as if set forth in its entirety herein, the electrical contacts  404 A,  404 B, and  404 C are configured as a receptacle contact. Each of the mating ends  402 A,  402 B, and  402 C may include at least one pair of cantilevered spring arms  416 A and  416 B that each extend out from a respective intermediate portion. Each spring arm  416 A,  416 B may be resiliently supported by the respective intermediate portion and may extend out from the respective intermediate portion to a respective free distal tip  416 . 
     The width of the intermediate portion of an electrical contact  404 C d 45  may be greater than the width of the body of an electrical contact  404 A d 43 . In some embodiments, d 45  may be twice or three times of d 43 . 
     The inventors have recognized and appreciated that intentionally placing solder spheres close enough so that they bridge together when heated above their melting temperature will create an elongated solder mass or shield, which reduces signal crosstalk more efficient than the shield formed by individual solder spheres. 
       FIGS. 5A-5B  illustrates a set of electrical contacts  504 A,  504 B of a plug electrical connector, schematically illustrating solder balls  502 A,  502 B attached to the mounting ends. In some embodiments, the diameter of the solder balls may be in the ranges of 4 mil to 30 mil, 10 mil to 25 mil, or any value within these ranges. The solder balls may be made of lead, tin, copper, silver, bismuth, indium, zinc, antimony, traces of other metals, and any combination thereof. The electrical contacts may have gold plating down to plug blade  506 . As a result, the gold zone is very close to the tips with solder balls. If solder balls touch gold, it will wick. To prevent solder balls from wicking, the electrical contacts may have nickel plating at their mounting ends, including projections  510 A,  510 B, and  512 . However, the coating used, in some embodiments, may be non-wettable with solder. Nonetheless, the edges of spaces  514  of the mounting ends of the contacts may be solder wettable as the result of a coating, such as of solder flux. The surfaces joining the edges of the spaces may have a non-solder wettable coating. As a result, solder balls may be precisely positioned in the vicinity of the spaces. 
     In some embodiments, a method of manufacturing of a connector including a plurality of contacts  504 A,  504 B held by a housing comprising a plurality of pockets in a surface, wherein the connector is configured for attachment to a circuit assembly with the surface facing the circuit assembly, the method may include: 1) applying solder flux to the edges of the contacts; 2) positioning a plurality of solder balls adjacent the edges of the contacts; and 3) heating the plurality of solder balls such that solder melts to form solder masses that attach to the mounting ends of the plurality of contacts. A schematic example of the manufacturing method is illustrated in  FIGS. 13A-13C . 
     In some embodiments, during the heating step, the signal solder balls  502 A may remain disconnected from each other and from the reference solder balls  502 B and form solder masses  508 A ( FIGS. 5C-D ). In some embodiments, during the heating step, the reference solder balls  502 B may also remain disconnected from each other and from the signal solder balls  502 A. In other embodiments, during the heating step, the reference solder balls  502 B may fuse with at least one adjacent reference solder ball and form solder masses  508 B ( FIGS. 5C-D ). Each of solder masses  508 A,  508 B has a height, a width, and a length. The solder masses may be elongated such that the length is a multiple of the width. In some embodiment, the lengths of solder masses  508 A are less than the lengths of solder masses  508 B. In some embodiment, each of solder masses  508 B may have a volume and/or mass that is equal to a combined mass of a plurality of solder masses  508 A. By the term “equal”, it is meant to be within variations expected in the manufacturing process, such as within +/−10%, +/−5%, or any value within the ranges. 
       FIGS. 6A-B  illustrates a set of electrical contacts of a receptacle electrical connector, schematically illustrating solder balls  602 A,  602 B attached to the mounting ends.  FIGS. 6C-D  illustrates a set of electrical contacts of a receptacle electrical connector, schematically illustrating solder masses  608 A,  608 B attached to the mounting ends. The difference between  FIGS. 6A-D  and  FIGS. 5A-D  is that electrical contacts in  FIGS. 6A-D  are configured as receptacle type while electrical contact in  FIGS. 5A-D  are configured as plug type. The mounting ends of the contacts in  FIGS. 5A-D  and  FIGS. 6A-D  may be the same. Similar processes may be used to attach solder balls  602 A and  602 B to the mounting ends and form solder masses  608 A and  608 B. For the brevity of the writing, descriptions are not repeated herein. 
       FIGS. 7A-B  illustrate a perspective view of an electrical assembly formed by mounting a plug electrical connector  700 , partially cut away, to PCB  701  through solder masses. In some embodiments, connector  700  may be constructed substantially identical to connector  100  or  200 . In some embodiments, connector  700  may include contact sets substantially identical to contact sets shown in at least one of  FIGS. 3A-C ,  FIGS. 4A-C ,  FIGS. 5A-D , and  FIGS. 6A-D . 
     The method of forming the electronic assembly may comprise 1) inserting a plurality of contacts  704 A and  704 B into housing  702  such that the mounting ends of the plurality of contacts are disposed in respective pockets in a mounting surface of the housing; 2) applying solder flux to the edges of the contacts; 3) positioning a plurality of solder balls adjacent the edges of the contacts; 4) heating the plurality of solder balls such that solder melts to form solder masses that attach to the mounting ends of the plurality of contacts; 5) positioning the solder masses to face and align with contact pads on surface  703  of PCB  701 ; and 6) heating the solder masses such that solder melts to form solder masses  708 A and  708 B that attach to the contact pads such that conduction paths are formed from signal contacts  704 A through solder masses  708 A to contact pads connecting to signal traces in the PCB, and from reference contacts  704 B through solder masses  708 B to contact pads connecting to reference planes in the PCB.  FIGS. 11A-B  illustrate a perspective view of a printed circuit board showing contact pads on a surface of the PCB. 
       FIGS. 8A-8C  show a perspective view of electrical connector  800 , including a connector housing  802 , an array of electrical contacts (not shown) held by the housing, solder masses  808 A-C attached to mounting ends of respective contacts, a mating interface (not shown), and a mounting surface  810 . In some embodiments, connector  800  may include contacts as pictured in  FIGS. 7A-B  or contact sets shown in at least one of  FIGS. 3A-3C ,  FIGS. 4A-4C ,  FIGS. 5A-5D , and  FIGS. 6A-6D . 
     Connector housing  802  may have an array of pockets  806  that are in the mounting surface  810 . Each pocket may be sized and positioned to expose a mounting end of an electrical contact and to at least partially receive the mounting end of the contact and a respective solder mass attached to the mounting end of the electrical contact. The array of pockets  806  may be arranged in at least two rows that extend along a row direction. In the illustrated embodiments, the electrical contacts are arranged into 10 rows with 33 contacts per row, some of which are configured as signal contacts and some of which are configured as ground contacts. In the illustrated embodiment, within each row, the contacts are arranged with pairs of signal contacts with an attached solder mass  808 A between adjacent ground contacts with an attached solder masses  808 B. The ends of each row may have a single ground contact with an attached solder mass  808 C. The pairs of signal contacts may be configured to carry high speed differential signals. The single ground contacts at the end of the row may be used for any suitable purpose, such as for low speed control signals. However, the pockets can be configured into any number of rows and columns. 
     The pockets may be offset relative to corresponding pockets in adjacent rows along the row direction by a distance s 1 . In some embodiments, s 1  may be in the range of 0.5 mm to 1.5 mm, such as 1.2 mm, or any other value within the range. This offset positions the mounting ends of the reference contacts  808 B 1 - 808 B 3  in a first row r 1  such that they can provide shielding between the mounting ends of the pairs of signal conductors p 1  and p 2  in rows r 2  and r 3  on either side of the first row. By having the mounting ends of the reference contacts close together, the effectiveness of that shielding is enhanced. In some embodiments, the solder balls of the reference contacts are so closely spaced that they are fused into a unitary solder mass to provide more effective shielding, for example,  508 B in  FIG. 5C or 608B  in  FIG. 6C . However, in the embodiment illustrated, the spacing is illustrated as s 4  in  FIG. 8B . The inventors have surprisingly found that, despite a relatively small separating between connector  800  and a substrate to which it is mounted, this positioning of solder balls on reference contacts materially improves performance of the connector. 
     In some embodiments, pockets  806 A may receive signal contacts  224 A and pockets  806 B may receive reference contacts  224 B. The centers of pockets  806 A may be isolated from the centers of adjacent pockets  806 A by a distance s 5  and from the centers of adjacent pockets  806 B by a distance s 2 ; the centers of pockets  806 B may be isolated from the centers of adjacent pockets  806 B by a distance s 3 . In some embodiments, s 2  may be in the range of 0.5 mm to 1.5 mm, preferably 1.15 mm, or any value within the range; s 3  may be in the range of 0.5 mm to 1.5 mm, preferably 1.12 mm, or any value within the range; and s 5  may be in the range of 0.5 mm to 2 mm, preferably 1.2 mm, or any value within the range. 
     The pockets in a row may be arranged as a repeating pattern of sets of pockets  806 A,  806 B corresponding to the sets of electrical contacts they receive. In the illustrated embodiment, a set of pockets include two pockets  806 A separated by three pockets  806 B aligned in the row direction. When the solder balls are heated above their melting temperature, such as occurs when the colder balls are fused to the mounting ends of the contacts, the solder balls held by  806 A may remain disconnected to adjacent solder balls while the solder balls held by pockets  806 B may combine with adjacent solder balls held by pockets  806 B and form an elongated solder mass or shield such as  708 B. However, the number of pockets  806 B can be placed together is not limited to three, for example, two or four pockets  806 B may be placed together continuously. 
     The inventors have recognized and appreciated that geometry of the pockets assist in holding the solder masses within desired regions. In the illustrated example of  FIG. 8C , the pockets are diamond-shaped, diagonals of which are aligned with the row direction. Though the solder masses may extend from the pockets in a direction perpendicular to the mounting surface, in the row direction, the solder masses are substantially within the perimeters of the pockets. However, the pockets may have different shapes, such as rhombus, oval, circular, square, rectangular, etc. In the illustrated embodiment, all the pockets have equal shape and size, but other embodiments are possible. 
       FIGS. 9A-9C  show a partial perspective view of an electrical connector  900 . The connector may include a connector housing  902  having a surface  903 , a plurality of electrical contacts  904 A,  904 B held by the housing, and a plurality of solder balls  908  attached to mounting ends of the contacts. Connector housing  902  may include an array of pockets  906  and  926  in the surface  903 . The connector is configured for attachment to a circuit assembly with the surface  903  facing the circuit assembly. 
     Each of the pockets  926  may include a floor  918  surrounded by a wall  916  having a first height h 1  in a direction perpendicular to the surface  903 . Each of the pockets  906  may further include a first region  906 A and a second region/slot  906 B that extends from the first region  906 A towards an adjacent pocket  926 . The first region  906 A of a pocket  906  may be configured similarly to a pocket  926 . In the illustrated example, the first regions  906   a  and pockets  926  are diamond-shaped having diagonals aligned with the row direction. However, they can have different shapes, such as rhombus, oval, circular, square, rectangular, etc. 
     Each pocket may be sized and positioned to at least partially receive a mounting end of an electrical contact  904 A or  904 B. Solder balls  908  may extend into respective pockets and fused to mounting ends within the pockets. The mounting end of the electrical contact may include a space  914  separating first and second projections  910 A and  910 B along a direction parallel to the surface  903 . The space is disposed above the floor  918  of the pocket at a second distance h 2  in the direction perpendicular to the surface  903 . In some embodiments, the second height may be less than the first height. In some embodiments, at least one of the first and second projections extends, in a direction perpendicular to the mounting surface of the connector housing, beyond the wall of the respective pocket. For example, in the illustrated embodiment, projection  910 B is wider than projection  910 A and extends beyond the wall  916  of the pocket in the direction parallel to the surface  903 . 
     In some embodiments, pockets  906  may be designated to receive contacts  904 A which may conduct signals and may be arranged as differential pairs  920 . Pockets  926  may be designated to receive contact  904 B that may conducts reference potentials and are positioned between adjacent signal pairs. A projection of contacts  904 A may extend beyond the wall of the respective pocket and towards an adjacent projection of a contact  904 B within the same row. 
       FIGS. 10A-10B  illustrate a perspective view of an electrical connector  1000 , showing solder masses  1004 A,  1004 B received by pockets  1006 A,  1006 B in the mounting surface  1010  of connector housing  1002 , according to some embodiments. The difference between  FIGS. 10A-B  and  FIGS. 8A-C  is that solder balls received by pockets  1006 B fuse with solder balls in adjacent pockets  1006 B and form elongated solder masses  1004 B when heating solder balls such that solder melts to form solder masses attached to the mounting ends of the contacts. 
     Each solder mass  1004 A or  1004 B may have a height perpendicular to the mounting surface  1010 , a width, and a length in a row direction which may be a multiple of the width. The length of a solder mass  1004 A may be less than the length of a solder mass  1004 B. The mass of individual solder mass  1004 A may equal the mass of an individual solder ball. Individual solder mass  1004 A may be received by a pocket  1006 A. The mass of individual solder mass  1004 B may equal a combined mass of at least two solder balls. Solder mass  1004 B may be received by at least two pockets  1006 B. In the illustrated embodiment, the mass of solder mass  1004 B equal to a combined mass of three solder balls. And individual solder mass  1004 B is received by three pockets  1006 B. In some embodiments, solder masses  1004 A may be attached to signal contacts, and solder masses  1004 B may be attached to reference contacts. 
     Pockets  1006 A,  1006 B may be arranged in a plurality of rows. Within each row, pockets  1006 A may have a center-to-center spacing in the row direction from adjacent pockets of a first distance, and pockets  1006 B may have a center-to-center spacing in the row direction from at least one adjacent pocket  1006 B of a second distance. The second distance may be less than the first distance. In some embodiments, pockets  1006 A may hold signal contacts and pockets  1006 B may hold reference contacts. 
       FIGS. 11A-11B  illustrate a perspective view of a printed circuit board (PCB)  1001 . PCB  1001  may have surface pads for surface mounting of a connector according to some embodiments as described herein. The PCB may be formed as a multi-layer assembly manufactured from stacks of dielectric sheets. Some or all of the dielectric sheets may have a conductive film on one or both surfaces. Some of the conductive films may be patterned, using lithographic or laser printing techniques, to form conductive traces that are used to make interconnections between circuit boards, circuits and/or circuit elements. Others of the conductive films may be left substantially intact and may act as ground planes or power planes that supply the reference potentials. The dielectric sheets may be formed into an integral board structure such as by pressing the stacked dielectric sheets together under pressure. 
     The PCB may include contact pads  1104 A and  1104 B on a surface  1103 . Each contact pad may be sized and positioned corresponding to a solder mass of a connector to be mounted to the PCB. The contact pads may be arranged in rows. Within each row, the contact pads may be arranged in a repeating signal-signal-ground pattern, a ground-signal-signal pattern, or a signal-ground-signal pattern. The contact pads may also be arranged in a repeating signal-signal-ground-ground pattern, a ground-signal-signal-ground pattern, or a signal-ground-signal-ground pattern. In some embodiments, contact pads  1104 A may connect to signal traces and contact pads  1104 B may connect to reference planes. Contact pads  1104 B may be wider than contact pads  1104 A. The contact pads within each row may be offset relative to corresponding contact pads in adjacent rows such that contact pads  1104 B in each row are offset, in the row direction, towards contact pads  1104 A in an adjacent row. 
       FIG. 12A  is an enlarged perspective view of circled region  12 A in  FIG. 3A  reversed 180 degrees, showing a mounting end  1200  of an electrical contact. In the illustrated embodiments, the mounting ends may be shaped to facilitate a manufacturing process that provides improved electrical performance of the connector in one or more ways, including reducing impedance discontinuities at the mounting interface or reducing manufacturing defects from mis-positioned solder balls. Such results may be achieved with a mounting end with an edge profile that supports a solder-flux transfer process, avoiding the variability and impedance-lowering effect of a process using solder paste in the pockets. The profile may be created to provide a relatively large edge length relative to the width of the contact. Positioning of the solder ball may be achieved by having a central portion of that profile lower than the lateral portions, such that the solder ball is positioned by the lowered portion. In the illustrated examples, that lowered portion may be created by a space between projections at the sides of the mounting end. 
     In the illustrated embodiment, the mounting end  1200  includes a space  1214  separating projections  1210 A and  1210 B. Edge  1202  of the mounting end of the contact may be joined by surfaces  1204 . In the embodiment of  FIG. 12A , the projections at the lateral portions of the mounting end are generally rectangular, as is the space between them. Nonetheless, upon reflow, a solder ball placed between the projections  1210 A and  1210 B may adhere to the edge of the mounting end, centered between  1210 A and  1210 B. 
     In the embodiment of  FIG. 12A , the projections are set back from the lateral-most portion of the mounting end. In an alternative embodiment, there may be no setback.  FIG. 12B  is cross-sectional views of circled region  12 B in  FIG. 12A , illustrating non-limiting alternative profiles of  1206 . The mounting end may include a width W 1  in a direction parallel to a mounting surface of a connector described herein. Edge  1202  may span the width W 1  but have a length L 1  along the edge. L 1  may be longer than W 1  due to the profile of the edge. Edge  1202  may be coated with a solder wettable layer. Surfaces  1204  may have non-solder wettable coating. As a result, a solder ball to be mounted to the mounting end may be shaped by and preferentially adhere to the mounting end. 
       FIGS. 12C-12E  illustrate alternative edge profiles  1208 ,  1212  and  1216  of edge  1202 . As can be seen, the edge profile may be triangular, semi-circular, or may have other suitable shapes that increase the length of the exposed edge. These profiles may be symmetrical, but need not be. 
       FIGS. 13A-13C  are illustrate a method of manufacturing a connector described herein, according to some embodiments. One electrical contact  1316  of an array of contacts of the connector is illustrated. Dashed line  1322  illustrates an exemplary geometry of a pocket in a mounting surface of the connector, in which mounting end  1320  of the contact may be disposed. The method may include: 
     Step  1302 : applying solder flux  1308  to the edges  1314  of contact  1316  using pin transfer  1310 ; 
     Step  1304 : positioning solder ball  1312  adjacent the edges of the contact; and 
     Step  1306 : heating the plurality of solder balls such that solder melts to form solder mass  1318  that attach to the mounting end  1320  of the contact. 
     As can be seen in  FIG. 13C , once the solder ball has reflowed, it is preferentially adhered to locations where solder flux was applied, which in this example leads to the solder mass being preferentially adhered to an edge of the contact. In the embodiment illustrated, the solder ball may be centered within the space between projections defining the mounting end of the contact. 
     Of significance, because solder paste is not required to attach the solder ball, the mass of fusible material in the pocket may be reduced, reducing the capacitance, and therefore increasing the impedance at the mounting interface of the connector. Such a configuration may reduce impedance discontinuities in the signal paths, which may provide improvements in connector performance. Additionally, as the volume of solder paste is harder to control than the volume of a solder ball, direct attachment of a solder ball to an edge, without use of solder paste, for example, leads to more uniformity from contact to contact or connector to connector. Such uniformity can improve electrical performance of the connection system. Uniformity may also promote co-planarity of the solder masses, which may improve mechanical robustness of the connections to a printed circuit board when a connector is mounted to the printed circuit board. 
     Although details of specific configurations of electrical contacts and housings are described above, it should be appreciated that such details are provided solely for purposes of illustration, as the concepts disclosed herein are capable of other manners of implementation. In that respect, various connector designs described herein may be used in any suitable combination, as aspects of the present disclosure are not limited to the particular combinations shown in the drawings. 
     Having thus described several embodiments, it is to be appreciated various alterations, modifications, and improvements may readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only. 
     High speed connectors are described herein. The speed of a connector may be determined using known measurement techniques by which the highest operating frequency at which a connector exhibits an electrical characteristic within a desired limit. The frequency range of interest may depend on the operating parameters of the system in which such a connector is used, but may generally have an upper limit between about 15 GHz and 60 GHz, such as 25 GHz, 30 GHz or 40 GHz, although higher frequencies or lower frequencies may be of interest in some applications. Some connector designs may have frequency ranges of interest that span only a portion of this range, such as 1 to 10 GHz or 3 to 15 GHz or 5 to 35 GHz. 
     The operating frequency range for an interconnection system may be determined based on the range of frequencies that can pass through the interconnection with acceptable signal integrity. Signal integrity may be measured in terms of a number of criteria that depend on the application for which an interconnection system is designed. Some of these criteria may relate to the propagation of the signal along a single-ended signal path, a differential signal path, a hollow waveguide, or any other type of signal path. Two examples of such criteria are the attenuation of a signal along a signal path or the reflection of a signal from a signal path. 
     Other criteria may relate to interaction of multiple distinct signal paths. Such criteria may include, for example, near end cross talk, defined as the portion of a signal injected on one signal path at one end of the interconnection system that is measurable at any other signal path on the same end of the interconnection system. Another such criterion may be far end cross talk, defined as the portion of a signal injected on one signal path at one end of the interconnection system that is measurable at any other signal path on the other end of the interconnection system. 
     As specific examples, it could be required that signal path attenuation be no more than 3 dB power loss, reflected power ratio be no greater than −20 dB, and individual signal path to signal path crosstalk contributions be no greater than −50 dB. Because these characteristics are frequency dependent, the operating range of an interconnection system is defined as the range of frequencies over which the specified criteria are met. 
     Designs of an electrical connector are described herein that improve signal integrity for high frequency signals, such as at frequencies in the GHz range, including up to about 25 GHz or up to about 40 GHz, up to about 50 GHz or up to about 60 GHz or up to about 75 GHz or higher, while maintaining high density, such as with a spacing between adjacent mating contacts on the order of 3 mm or less, including center-to-center spacing between adjacent contacts in a column of between 1 mm and 2.5 mm or between 2 mm and 2.5 mm, for example. Spacing between columns of mating contact portions may be similar, although there is no requirement that the spacing between all mating contacts in a connector be the same. It should be appreciated, however, that connectors as described herein might be configured to meet other requirements. 
     Furthermore, although many inventive aspects are shown and described with reference to a connector having a mezzanine configuration, it should be appreciated that aspects of the present disclosure is not limited in this regard, as any of the inventive concepts, whether alone or in combination with one or more other inventive concepts, may be used in other types of electrical connectors, such as right angle connectors, cable connectors, stacking connectors, I/O connectors, chip sockets, etc. 
     The present disclosure is not limited to the details of construction or the arrangements of components set forth in the foregoing description and/or the drawings. Various embodiments are provided solely for purposes of illustration, and the concepts described herein are capable of being practiced or carried out in other ways. Also, the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof herein, is meant to encompass the items listed thereafter (or equivalents thereof) and/or as additional items. 
     Moreover, it should be appreciated that certain dimensions, said to be “equal” need not be precisely the same. Manufacturing tolerances and the precision of the system being constructed impact what one of skill in the art would consider to be “equal.” However, differences within +/−10% generally will be regarded as equal.