Patent Publication Number: US-8979551-B2

Title: Low-profile mezzanine connector

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical connectors and more specifically, the present invention relates to a mezzanine connector having a low profile. 
     2. Description of the Related Art 
     Electrical connectors are used to allow electrical devices, such as substrates or printed circuit boards, to communicate with one another. A connector may be thought of as having two portions, one portion which connects to a first electrical device and the second portion which connects to a second electrical device to be put into communication with the first device. To connect the two electrical devices, the two portions of the connector are mated together. 
     Each connector includes one set of contacts in a first portion and a second set of contacts in a second portion to be connected with contacts of the first portion. This can be readily accomplished by providing a male connector and a female connector with corresponding sets of contacts that engage when the male and female connectors are mated. Further, the male and female connectors are easily connected and disconnected from each other to respectively electrically connect and disconnect the electrical devices to which they are connected. 
     Accordingly, each connector portion is connected to an electrical device through its contacts. The contacts are typically permanently connected to the electrical device. Further, the connector portions are typically secured to electrical devices by fusing the contacts to contact pads or other suitable structure provided on the electrical device. 
     Recently, there has been a trend toward miniaturization of most electrical devices. As electrical devices become smaller and more complex, the connectors used with these electrical devices must also become smaller and must be able to accommodate the more complex electrical devices. One problem with miniaturized connectors arises from the increased precision (i.e., tighter tolerances) of placement necessary to produce the proper positioning and connection of the connector contacts onto the electrical device. This problem is exacerbated by the ever-increasing input/output (I/O) density requirements demanded of the progressively smaller connectors by increasingly miniaturized electrical devices. As the number of contacts increases in each connector, it becomes more and more difficult to maintain desired levels of co-planarity, while maintaining connection of all of the contacts to a substrate. 
     In order to provide for a higher density of substrates, mezzanine connectors have been used. Mezzanine connectors are typically used to connect a first substrate to a second substrate in a parallel manner. A conventional mezzanine connector assembly includes a male connector to be mounted on one substrate, and a female connector to be mounted on another substrate. The male connector includes a plurality of contacts that each engages a corresponding contact on the female connector when the male connector and the female connector are mated, thereby establishing electrical contact between the two substrates. The individual electrical contacts in the male and female connectors are used to conduct electrical signals or electrical power. Examples of mezzanine connectors can be found in U.S. Pat. Nos. 6,702,590 and 6,918,776. 
     As the progression toward higher density continues, it has become useful to reduce the distance between substrates that are connected by mezzanine connectors by modifying the structure of the mezzanine connectors. However, conventional mezzanine connectors have a number of problems, as described below. 
     As shown in FIGS. 6 and 7 of U.S. Pat. No. 6,702,590, one problem with conventional mezzanine connectors is that the distance between the substrates is limited by the heights of the plug and the receptacle. That is, the plug is only partially inserted into the receptacle, such that the heights of both the plug and the receptacle significantly contribute to the overall height of the mated plug and receptacle and thus the distance between the substrates. 
     As shown in FIGS. 48 and 49 of U.S. Pat. No. 6,702,590, another problem with conventional mezzanine connectors is that reducing the heights of the plug and/or receptacle also reduces wipe distances of the contacts when the plug and receptacle are connected, which may negatively affect the performance and longevity of the electrical connection. A wipe distance between corresponding contacts refers to a distance between a first point where the corresponding contacts initially touch during mating of the plug and receptacle, and a second point where the contacts are positioned when the plug and the receptacle are fully mated. Along the wipe distance, oxides and other substances are wiped off of the corresponding contacts due to their physical engagement, thereby improving a mechanical connection between the contacts. A short wipe distance may cause poor electrical performance due to a weak mechanical connection between the corresponding contacts. 
     Furthermore, poor electrical performance in mezzanine connectors may result from a force normal to the mating direction of the plug and receptacle being insufficient to wipe off the oxides and other substances from the corresponding contacts. However, if the force normal to the mating direction of the plug and the receptacle is too great, one or more of the contacts may bend or buckle when the plug and receptacle are mated. Accordingly, proper alignment between the plug and the receptacle during mating is important to help ensure that the force normal to the mating direction of the plug and the receptacle is sufficient to wipe off the oxides and other substances from the corresponding contacts, yet insufficient to cause any of the contacts to bend or buckle. As an example, cantilevered contacts are particularly susceptible to variations in the force normal to the mating direction of the plug and the receptacle. 
     As shown in FIG. 1 of U.S. Pat. No. 6,918,776, an additional problem with conventional mezzanine connectors is that the distance between the substrates is also limited due to both the plug and the receptacle being mounted on the surface of substrate. That is, a distance between each of the plug and the receptacle and a surface of each of the substrates contributes to the distance between the substrates. 
     A further problem with conventional mezzanine connectors is the use of multiple folded contacts in the plug and receptacle that require the width of the connector to be much wider. For example, the Panasonic P5KF series of mezzanine connectors have contacts that are folded over multiple times, which causes these connectors to have a substantial width. 
     SUMMARY OF THE INVENTION 
     To overcome the problems described above, preferred embodiments of the present invention provide a low-profile mezzanine connector with a long contact wipe distance. 
     A mezzanine connector according to a preferred embodiment of the present invention includes a first connector including a pass-through hole and a first plurality of contacts arranged around the pass-through hole, the first connector arranged to be connected to a first substrate such that the first plurality of contacts are connected to the first substrate and a second connector including a beam and a second plurality of contacts arranged around the beam, the second connector arranged to be connected to a second substrate such that the second plurality of contacts are connected to the second substrate. The pass-through hole extends fully through the first connector in a mating direction of the first connector and the second connector, and the beam of the second connector is arranged to extend into the pass-through hole of the first connector when the first connector and the second connector are mated such that each of the first plurality of contacts engages with a respective one of the second plurality of contacts 
     The first connector is preferably arranged to fit into a cut-out of the first substrate. The first connector preferably includes recessed portions and a main body that are arranged to fit into the cut-out of the first substrate. At least one of the first connector and the second connector preferably includes at least one post to engage with at least one corresponding post hole in the first or second substrate. 
     A wipe distance of the first plurality of contacts and the second plurality of contacts is preferably about 0.6 mm or greater. A distance between the first substrate and the second substrate is preferably about 2 mm or less. A wipe distance of the first plurality of contacts and the second plurality of contacts is preferably greater than a distance between the first substrate and the second substrate. 
     The first connector is preferably soldered to the first substrate, and the second connector is preferably soldered to the second substrate. A portion of each of the first plurality of contacts is preferably arranged to be soldered to the first substrate and preferably includes a ribbed or multi-planar area that limits the flow of solder, and a portion of each of the second plurality of contacts is preferably arranged to be soldered to the second substrate and preferably includes a ribbed or multi-planar area that limits the flow of solder. 
     The first plurality of contacts is preferably arranged in at least one row, and the second plurality of contacts is preferably arranged in at least one row. The beam of the second connector preferably touches the first substrate when the first connector is mated with the second connector. A bottom surface of the beam of the second connector is preferably parallel or substantially parallel to a bottom surface of the first connector. 
     The first connector preferably includes at least one first retention tab, and the second connector preferably includes at least one second retention tab. The at least one first retention tab is preferably arranged to be connected to the first substrate, and the at least one second retention tab is preferably arranged to be connected to the second substrate. A height of each of the first plurality of first contacts is preferably equal to or greater than a height of the at least one first retention tab, and a height of each of the plurality of second contacts is preferably equal to or greater than a height of the at least one second retention tab. 
     A receptacle connector according to a preferred embodiment of the present invention includes a plurality of contacts and a pass-through hole. The plurality of contacts is arranged in at least one row along the pass-through hole. The pass-through hole extends fully through the receptacle connector such that when the receptacle connector mates with another connector, a bottom surface of the another connector is co-planar or substantially co-planar to a bottom surface of the receptacle connector. 
     The receptacle connector is preferably arranged to fit to a cut-out of a substrate. The receptacle connector preferably includes recessed portions and a main body that are arranged to fit into the cut-out of the substrate. The pass-through hole preferably extends along the receptacle connector between a first retention tab and a second retention tab of the receptacle connector. 
     A connector assembly according to a preferred embodiment of the present invention includes a first connector including a pass-through hole and a first plurality of contacts arranged along the pass-through hole, a second connector including a beam and a second plurality of contacts arranged along the beam, a first substrate, and a second substrate. The first connector is arranged to be connected to the first substrate such that the first plurality of contacts is connected to the first substrate. The first connector includes a pass-through hole extending fully through the first connector in a mating direction of the first connector and the second connector. The second connector is arranged to be connected to the second substrate such that the second plurality of contacts is connected to the second substrate. The beam of the second connector is arranged to engage the pass-through hole of the first connector when the first connector and the second connector are connected such that each of the first plurality of contacts engages with a respective one of the second plurality of contacts. 
     The first substrate and the second substrate preferably each include a cut-out or a recess. The first connector is preferably arranged to fit to the cut-out or the recess of the first substrate. The second connector is preferably arranged to fit to the cut-out or the recess of the second substrate. 
     Accordingly, the preferred embodiments of the present invention provide a relatively narrow mezzanine connector with a low stack height and long wipe lengths for contacts. 
     The above and other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are perspective views of a mezzanine connector in accordance with a preferred embodiment of the present invention. 
         FIGS. 2A and 2B  are perspective views of the mezzanine connector of  FIGS. 1A and 1B  connecting two substrates. 
         FIG. 3A  is a cross-sectional end view of the mezzanine connector of  FIGS. 1A and 1B . 
         FIG. 3B  is a cross-sectional end view of the mezzanine connector of  FIGS. 1A and 1B  connecting the two substrates of  FIGS. 2A and 2B . 
         FIG. 4A  is a cross-sectional perspective view of the mezzanine connector of  FIGS. 1A and 1B . 
         FIG. 4B  is a cross-sectional perspective view of the mezzanine connector of  FIGS. 1A and 1B  connecting the two substrates of  FIGS. 2A and 2B . 
         FIGS. 5A and 5B  are perspective views of a mezzanine connector in accordance with a preferred embodiment of the present invention. 
         FIG. 6A  is a perspective view of the plug of the mezzanine connector of  FIGS. 5A and 5B  mounted on a substrate. 
         FIG. 6B  is a perspective view of the receptacle of the mezzanine connector of  FIGS. 5A and 5B  mounted on to a substrate. 
         FIG. 6C  is a perspective view of the mezzanine connector of  FIGS. 5A and 5B  connecting two substrates. 
         FIG. 6D  is a perspective view of the substrate of  FIG. 6B . 
         FIG. 7A  is a cross-sectional end view of the mezzanine connector of  FIGS. 5A and 5B  prior to the plug being attached to the receptacle. 
         FIG. 7B  is a cross-sectional end view of the mezzanine connector of  FIGS. 5A and 5B  connecting two substrates. 
         FIG. 8  is a cross-sectional perspective view of the mezzanine connector of  FIGS. 5A and 5B . 
         FIG. 9  is a cross-sectional end view of the mezzanine connector of  FIGS. 5A and 5B  connecting two substrates. 
         FIG. 10  is a cross-sectional end view of the mezzanine connector of  FIGS. 5A and 5B  prior to the plug being attached to the receptacle. 
         FIG. 11  is a cross-sectional end view of the mezzanine connector of  FIGS. 5A and 5B  connecting two substrates. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to  FIGS. 1A to 9 . Note that the following description is in all aspects illustrative and not restrictive, and should not be construed to restrict the applications or uses of the present invention in any manner. 
       FIGS. 1A to 4B  show a mezzanine connector  100  according to a preferred embodiment of the present invention. 
       FIGS. 1A and 1B  are perspective views of the mezzanine connector  100  according to a preferred embodiment of the present invention.  FIGS. 2A and 2B  are perspective views of the mezzanine connector  100  of  FIGS. 1A and 1B  connecting a first substrate  130  to a second substrate  140 .  FIG. 3A  is a cross-sectional end view of the mezzanine connector  100  of  FIGS. 1A and 1B .  FIG. 3B  is a cross-sectional end view of the mezzanine connector  100  connecting the first substrate  130  and the second substrate  140 .  FIG. 4A  is a cross-sectional perspective view of the mezzanine connector  100  of  FIGS. 1A and 1B .  FIG. 4B  is a cross-sectional perspective view of the mezzanine connector  100  connecting the first substrate  130  and the second substrate  140 . 
     The mezzanine connector according to a preferred embodiment of the present invention includes a receptacle  110  (a male connector) and a plug  120  (a female connector). 
     The receptacle  110  preferably includes receptacle contacts  112  which may be connected to respective connection pads  131  on the first substrate  130 . For simplicity, not all of the receptacle contacts  112  are shown in  FIGS. 1A-4B . Preferably, the receptacle contacts  112  are arranged in two rows to be parallel or substantially parallel, within manufacturing tolerances, with respect to each other. The receptacle contacts  112  and the connection pads  131  are preferably connected, for example, by solder. As a particular example, a reflow solder operation may be used to connect the receptacle contacts  112  to the connection pads  131 . Preferably, portions of the receptacle contacts  112  arranged to connect to the connection pads  131  have ribbed or multi-planar shapes to help prevent the flow of solder into a wipe area of the receptacle contacts  112 . Further, solder may flow to retaining arms of the receptacle contacts  112  that are press-fit into corresponding holes in the receptacle  110 , thereby helping secure the receptacle contacts  112  to the receptacle  110  and preventing the solder from flowing to the wipe area of the receptacle contacts  112 . 
     Retention tabs  116  arranged at ends of the receptacle  110  help to secure the receptacle  110  to the first substrate  130 , particularly during mating and un-mating with the plug  120 . Preferably, each of the receptacle contacts  112  has a height equal to or greater than the retention tabs  116 . Receptacle posts  119  arranged on a receptacle mounting surface of the receptacle  110  and post holes  139  of the first substrate  130  position the receptacle  110  when the receptacle  110  is mounted to the first substrate  130  to help ensure proper alignment between the receptacle contacts  112  and the connection pads  131  and proper orientation of the receptacle  110  with respect to the substrate to which the receptacle  110  is connected. 
     The plug  120  preferably includes plug contacts  122  which may be connected to respective connection pads  141  on the second substrate  140 . For simplicity, not all of the plug contacts  122  are shown in  FIGS. 1A-4B . Preferably, the plug contacts  122  are arranged in two rows to be parallel or substantially parallel, within manufacturing tolerances, with respect to each other. The plug contacts  122  and the connection pads  141  are preferably connected, for example, by solder. As a particular example, a reflow solder operation may be used to connect the plug contacts  122  to the connection pads  141 . Preferably, portions of the plug contacts  122  arranged to connect to the connection pads  141  have ribbed or multi-planar shapes to help prevent the flow of solder into a wipe area of the plug contacts  122 . Further, solder may flow to retaining arms of the plug contacts  122  that are press-fit into corresponding holes in the plug  120 , thereby helping secure the plug contacts  122  to the plug  120  and preventing the solder from flowing to the wipe area of the plug contacts  122 . 
     Retention tabs  126  arranged at ends of the plug  120  help to secure the plug  120  to the second substrate  140 , particularly during mating and un-mating with the receptacle  110 . Preferably, each of the plug contacts  122  has a height equal to or greater than the retention tabs  126 . Plug posts  129  arranged on a plug mounting surface of the plug  120  and post holes  149  of the second substrate  140  position the plug  120  when the plug  120  is mounted to the second substrate  140  to help ensure proper alignment between the plug contacts  122  and the connection pads  141  and proper orientation of the plug  120  with respect to the substrate to which the plug  120  is connected. 
     The receptacle  110  includes a pass-through hole  111  arranged to receive a beam  121  of the plug  120  when the plug  120  is mated with the receptacle  110 . A surface of the beam  121  facing the first substrate  130  may be in close proximity to, or may even touch, the first substrate  130 . Preferably, the surface of the beam  121  facing the first substrate  130  is parallel or substantially parallel, within manufacturing tolerances, to a bottom surface of the receptacle  110 . The receptacle contacts  112  are exposed at the pass-through hole  111 , and the plug contacts  122  are exposed at the beam  121 . Thus, the receptacle contacts  112  and the plug contacts  122  are connected when the beam  121  is inserted into the pass-through hole  111 . 
     As shown in  FIGS. 1A to 4B , the above-described arrangement of the receptacle  110  and the plug  120  provides a stable physical connection between the receptacle  110  and the plug  120 . 
     Furthermore, the above-described arrangement of the receptacle  110  and the plug  120  provides a long wipe distance between the receptacle contacts  112  and the plug contacts  122 , thereby cleaning oxides and other substances from the contacts  112 ,  122  when the plug  120  is inserted into the receptacle  110 . Preferably, the wipe distance between the receptacle contacts  112  and the plug contacts  122  is between about 0.6 mm and about 0.9 mm. However, the wipe distance between the receptacle contacts  112  and the plug contacts  122  is not limited thereto, and may be about 1 mm or more. Accordingly, an improved mechanical and electrical connection between the receptacle contacts  112  and the plug contacts  122  may be achieved. 
     Moreover, the above-described arrangement of the receptacle  110  and the plug  120  provides a small spacing between the first substrate  130  and the second substrate  140 , thus allowing a denser arrangement of substrates. Preferably, a distance between the first substrate  130  and the second substrate  140  is between about 2 mm and about 4 mm. 
       FIGS. 5A to 8  show a mezzanine connector  200  according to another preferred embodiment of the present invention. 
       FIGS. 5A and 5B  are perspective views of a mezzanine connector  200  in accordance with a preferred embodiment of the present invention.  FIG. 6A  is a perspective view of the plug  220  of the mezzanine connector  200  of  FIGS. 5A and 5B  mounted on a second substrate  240 .  FIG. 6B  is a perspective view of the receptacle  210  of the mezzanine connector  200  of  FIGS. 5A and 5B  mounted on a first substrate  230 .  FIG. 6C  is a perspective view of the mezzanine connector  200  of  FIGS. 5A and 5B  connecting the first substrate  230  with the second substrate  240 .  FIG. 6D  is a perspective view of the first substrate  230 .  FIG. 7A  is a cross-sectional end view of the mezzanine connector  200  of  FIGS. 5A and 5B  prior to the plug  220  being mated with the receptacle  210 .  FIG. 7B  is a cross-sectional end view of the mezzanine connector  200  of  FIGS. 5A and 5B  after the plug  220  is mated with the receptacle  210 .  FIG. 8  is a cross-sectional perspective view of the mezzanine connector  200  of  FIGS. 5A and 5B . 
     The receptacle  210  preferably includes receptacle contacts  212  which may be connected to respective connection pads  231  of a first substrate  230 . Preferably, the receptacle contacts  222  are arranged in two rows to be parallel or substantially parallel, within manufacturing tolerances, with respect to each other. The receptacle contacts  212  and the connection pads  231  are preferably connected, for example, by solder. As a particular example, a reflow solder operation may be used to connect the receptacle contacts  212  to the connection pads  231 . Preferably, portions of the receptacle contacts  212  arranged to connect to the connection pads  231  have ribbed or multi-planar shapes to help prevent the flow of solder into a wipe area of the receptacle contacts  212 . Further, solder may flow to retaining arms of the receptacle contacts  212  that are press-fit into corresponding holes in the receptacle  210 , thereby helping secure the receptacle contacts  212  to the receptacle  210  and preventing the solder from flowing to the wipe area of the receptacle contacts  212 . 
     The plug  220  preferably includes plug contacts  222  which may be connected to respective connection pads  241  of a second substrate  240 . Preferably, the plug contacts  222  are arranged in two rows to be parallel or substantially parallel, within manufacturing tolerances, with respect to each other. The plug contacts  222  and the connection pads  241  are preferably connected, for example, by solder. As a particular example, a reflow solder operation may be used to connect the plug contacts  222  to the connection pads  241 . Preferably, portions of the plug contacts  222  arranged to connect to the connection pads  241  have ribbed or multi-planar shapes to help prevent the flow of solder into a wipe area of the plug contacts  222 . Further, solder may flow to retaining arms of the plug contacts  222  that are press-fit into corresponding holes in the plug  220 , thereby helping secure the plug contacts  222  to the plug  220  and preventing the solder from flowing to the wipe area of the plug contacts  222 . 
     The receptacle  210  includes a pass-through hole  211  arranged to receive a beam  221  of the plug  220  when the plug  220  is mated with the receptacle  210 . A surface of the beam  221  facing the first substrate  230  may be in close proximity to, or may even touch, the first substrate  230 . Preferably, the surface of the beam  221  facing the first substrate  230  is co-planar or substantially co-planar, within manufacturing tolerances, to a bottom surface of the receptacle  210 . The receptacle contacts  212  are exposed at the pass-through hole  211 , and the plug contacts  222  are exposed at the beam  221 . Thus, the receptacle contacts  212  and the plug contacts  222  are connected when the beam  221  is inserted into the pass-through hole  211 . Furthermore, the receptacle  210  includes recesses  219  so that a main body  215  of the receptacle  210  fits into a cut-out  239  of the first substrate  230 .  FIG. 6D  shows a perspective view of the first substrate  230 . 
     As shown in  FIGS. 5A to 8 , the above-described arrangement of the receptacle  210  and the plug  220  provides a stable physical connection between the receptacle  210  and the plug  220 . 
     Furthermore, the above-described arrangement of the receptacle  210  and the plug  220  provides a long wipe distance between the receptacle contacts  212  and the plug contacts  222 , thereby cleaning oxides or other substances from the contacts  212 ,  222  when the plug  220  is inserted into the receptacle  210 . Preferably, the wipe distance between the receptacle contacts  212  and the plug contacts  222  is between about 0.8 mm and 1.2 mm. However, the wipe distance between the receptacle contacts  212  and the plug contacts  222  is not limited thereto, and may be greater than 1.2 mm. Accordingly, an improved mechanical and electrical connection between the receptacle contacts  212  and the plug contacts  222  may be achieved. 
     Moreover, the above-described arrangement of the receptacle  210  and the plug  220  provides a small spacing between the first substrate  230  and the second substrate  240 , thus allowing a denser arrangement of substrates. Preferably, a distance between the first substrate  230  and the second substrate  240  is between about 1 mm to about 6 mm. 
     While preferred embodiments of the present invention show the receptacle  210  preferably being fit into a cut-out  239  of the first substrate  230 , the first substrate may be provided with a recess that does not extend through the first substrate instead of a cut-out  239  in order to fit the plug  220 .  FIG. 9  is a cross-sectional end view of the mezzanine connector  200  of  FIGS. 5A and 5B  connecting a first substrate  230 ′ with a recess  239 ′ to a second substrate  240 . For example, the recess  239 ′ may be included in the first substrate  230 ′ if the first substrate  230 ′ is a relatively thick substrate, if it is desired to include routing in the first substrate  230 ′ under the mezzanine connector  200 , or if electrical traces are included on a side of the first substrate  230 ′ that is opposite to the mezzanine connector  200 . Using recess  239 ′ allows for some routing underneath the recess  239 ′ that would not be available if a cut-out  239  was used. 
     Also, the plug  220  may be fitted into a cut-out or recess  280  of the second substrate  240  as shown in  FIGS. 10 and 11 , in addition to or as an alternative to the receptacle  210  being fit into the cut-out  239  or recess of the first substrate  230 . Furthermore, the receptacle  110  and the plug  120  may be respectively fitted to cut-outs or recesses in the first substrate  130  and the second substrate  140 . Using cut-outs or recesses in both the first substrate  130 ,  230  and the second substrate  140 ,  240  could allow the distance between the first substrate  130 ,  230  and the second substrate  140 ,  240  to be less than 1 mm. Accordingly, as a result of a mezzanine connector according to the preferred embodiments of the present invention being fitted into a cut-out or a recess of at least one substrate, wipe distances of the contacts  112 ,  122 ,  212 ,  222  can be greater than or equal to the distance between the first substrate  130 ,  230  and the second substrate  140 ,  240 . 
     Also, receptacle posts may be arranged on the receptacle  210 , and post holes may be arranged on the first substrate  230  to position the receptacle  210  when the receptacle  210  is mounted to the first substrate  230  to help ensure proper alignment between the receptacle contacts  212  and the connection pads  231  and proper orientation of the receptacle  210  with respect to the substrate to which the receptacle  210  is connected. Similarly, plug posts may be arranged on the plug  220 , and post holes may be arranged on the second substrate  240  to position the plug  220  when the plug  220  is mounted to the second substrate  240  to help ensure proper alignment between the plug contacts  222  and the connection pads  241  and proper orientation of the plug  220  with respect to the substrate to which the plug  220  is connected. 
     Moreover, while preferred embodiments of the present invention show the receptacle  110  preferably including a pass-through hole for the beam  121  of the plug  120 , one or more pass-through holes may be provided in the plug  120  to allow for insertion of a corresponding component of the receptacle  110 , for example, to further reduce the distance between the first substrate  130  and the second substrate  140 . 
     According to the preferred embodiments of the present invention, an initial point of contact between the receptacle contacts  112 ,  212  and the plug contacts  122 ,  222  during mating of the plugs  120 ,  220  to the receptacles  110 ,  210  is arranged at a side of the receptacles  110 ,  210  closest to the second substrates  140 ,  240  and a side of the plugs  120 ,  220  closest to the first substrates  130 ,  230 . Furthermore, a resting point of contact between the receptacle contacts  112 ,  212  and the plug contacts  122 ,  222  when the plugs  120 ,  220  are fully mated with the receptacles  110 ,  210  is arranged at a side of the receptacles  110 ,  210  closest to the first substrates  130 ,  230  and a side of the plugs  120 ,  220  closest to the first substrates  130 ,  230 . 
     Preferably, the retention tabs  116  and  126  are electrically isolated from the receptacle contacts  112  and the plug contacts  122 , such that the retention tab  116  of the receptacle  110  is not electrically connected with the plug  120 , and the retention tab  126  of the plug  120  is not electrically connected with the receptacle  110 . 
     Furthermore, while preferred embodiments of the present invention have been described above with respect to substrates, a mezzanine connector according to the preferred embodiments of the present invention may be used to connect any electrically conductive materials including, for example, printed circuit boards or other types of circuit substrates. 
     Additionally, while preferred embodiments of the present invention show the beams  121 ,  221  as preferably having substantially rectangular cuboid shapes, for example, the beams  121 ,  221  may have other shapes. The beams  121 ,  221  may have rounded edges, may have a triangular or trapezoidal cross-section, may be discontinuous along the length of the mezzanine connector, etc. Furthermore, the contacts  112 ,  122 ,  212 ,  222  may have shapes other than those shown in  FIGS. 1-9 , for example, cantilevered contacts, folded contacts, spring contacts, bellow contacts, etc., and the beams  121 ,  221  may be adjusted according to the shapes of the contacts  112 ,  122 ,  212 ,  222 . Respective sizes and shapes of the beams  121 ,  221  and the contacts  112 ,  122 ,  212 ,  222  may be selected to provide an appropriate force normal to the mating direction of the receptacles  110 ,  210  and the plugs  120 ,  220 . 
     The beams  121 ,  221  may also have lengths that are longer than the heights of the receptacles  110 ,  210 , such that a portion each of the beams  121 ,  221  extends past the receptacles  110 ,  210  when the plugs  120 ,  220  are mated with the receptacles  110 ,  210 . Accordingly, the beams  121 ,  221  may extend into or through the first substrates  130 ,  230 , for example, to mate with another of the receptacles  110 ,  210  that is arranged on an opposite side of the first substrates  130 ,  230  or with another of the receptacles  110 ,  210  that is arranged on another substrate. As another example, the beams  121 ,  221  may be arranged to pass through the first substrates  130 ,  230  before connecting to the receptacles  110 ,  210 . 
     According to preferred embodiments of the present invention, the receptacles  110 ,  210  and the plugs  120 ,  220  may include, as an insulating material, any thermoplastic material, thermoset material, ceramic material, glass, or similar dielectric material. Further, the contacts  112 ,  122 ,  212 ,  222  may include any copper alloy material. 
     Moreover, while preferred embodiments of the present invention show the substrates  130 ,  140 ,  230 ,  240  arranged in a parallel or substantially parallel manner, within manufacturing tolerances, the mezzanine connectors  100 ,  200  may be applied to other arrangements of substrates. For example, the plug  220  could be arranged at the edge of a substrate to provide an edge mount connection with the receptacle  210 , in which the substrates are perpendicular or substantially perpendicular, within manufacturing tolerances. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.