Abstract:
A female edge connector is cut into a circuit board to reduce the connector size and therefore the distance the signal path is separated from the ground plane. Preferably, the female connector is a surface mount connector and is provided in two pieces. This allows the female connector to be attached to either side of the printed circuit board or can be connected to both sides if half of the connector is mounted on the opposite side of the board from the other. A male edge connector of a plug-in board can then be inserted through the aperture formed in the mother board to contact the female edge connector, providing very little distance between the ground planes of the plug-in board and the mother board. The distance between the two pieces of the female connector can be varied by changing the width of the aperture such that PC boards of various thicknesses can be accommodated.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to printed circuit board (PCB) connectors, and more particularly to high performance PCB edge connectors, systems and methods. 
     The use of electronics has become ubiquitous, finding its way into all manners and shapes of devices and appliances ranging from toasters to super-computers. Most electronic circuitry is now implemented with their active and passive devices coupled together by a printed circuit board (PCB). This is true whether the electronic circuitry being implemented is primarily analog in nature, digital in nature, or a hybrid of the two. 
     In its simplest form, a PCB is a relatively thin sheet of a dielectric (i.e. electrically non-conductive) material such as a resin-filled fiberglass. Metal lines or “traces” are typically formed on one or more surfaces of the fiberglass to provide electrical connections between the various components of the electronic circuit. 
     Printed circuit boards can be “one sided,” in which all of the traces are formed on one side of the dielectric sheet of material. PCBs can also be “two sided,” where traces are formed on both sides of the sheet of dielectric material. Furthermore, PCBs can be “multi-layer” where multiple dielectric layers are sandwiched between conductive layers, which may form traces or which may form grounds and/or power planes. With multi-layer boards it is common to provide electrical connections between various layers by the formation of “vias” (conductive plugs between metal layers) or through-holes through which conductors can be threaded. 
     Commonly, an electronic circuit implemented on a PCB is connected to other devices. These may be input/output devices, other electronic circuits supported on other PCBs, transmission lines, etc. While such devices could be connected directly to the PCB (such as being soldered to some of its traces or bonding pads), most commonly the connection to external devices or circuits is through a removable connector assembly. Electrical connectors of various types have been developed through the years for just this purpose. 
     FIGS. 1 and 2 illustrate a connection system of the prior art. This particular connection system is known as a single connector attachment or “SCA” and was primarily designed to replace the older Small Computer System Interface or “SCSI” connector design, which was not designed for modern high-frequency digital circuit operation. 
     In FIG. 1, a PCB  10  including traces,  12  formed on a dielectric body  14  has a male SCA connector  16  attached to its upper surface  18 . The male connector  16  includes a support  20  having a number of electrical contacts  22  and a surrounding shroud  24 . The SCA male connector  16  is also provided with a pair of alignment posts  26   a  and  26   b.    
     In FIG. 2, a PCB  28  provided with traces  30  on a dielectric substrate  32  includes a female SCA connector  34 . The female connector includes a slot  36  provided with a plurality of contacts  38 . The slot  36  is receptive to the support  20  such that when the support  20  engages with the slot  36  the contacts  22  of the male connector  16  engage with the contacts  38  of the female connector  34 . The shroud  24  of the male connector  16  surrounds the body  40  of the female connector  34 . The male connector  16  is guided into and locked in place with the female connector  34  by the alignment post  26   a  and  26   b  aligning with and engaging the alignment columns  42   a  and  42   b  of the female connector  34 . 
     The contacts  22  are in electrical contact with some of the traces  12  of the printed circuit board  10 . This can be accomplished with a surface mount technology (SMT) if the traces are formed on the same side of the printed circuit board as the male connector  16 , or with pin-through technology if the traces  12  are formed on the opposite side of the PCB  10  from the connector  16 . In the present example, a surface mount technology is illustrated. Likewise, the electrical contacts  38  connect to certain ones of the traces  30  at printed circuit board  28 . Thus, when the male connector  16  is engaged with the female connector  34 , the printed circuit boards  10  and  28  are in electrical communication. 
     It should be noted that while the SCA connectors are shown to be attached to two different PCB boards, one of the SCA connectors, such as the male SCA connector  16 , could, instead, be coupled to a cable, such as a ribbon cable. In this fashion, the SCA connector can be used to couple physically separated electronic devices. 
     Two-piece connectors such as the SCA connectors illustrated in FIGS. 1 and 2 have several advantages. For one, they are mechanically guided and secured which aids in the engagement and the retention of the engagement of the connector system. For another, since they are typically made from metal, they are well-shielded by, for example, the body of their connectors and by the shroud  24  of the male connector. This helps reduce electromagnetic radiation and, therefore, electromagnetic interference (EMI). However, these connectors suffer from a number of drawbacks including cost, size, and an impedance matching problems generated by the wide separation between the ground planes of the two electronic circuits being coupled together caused by the connectors. 
     Another connection technology of the prior art is illustrated in FIG.  3 . In this figure, a first PCB or “plug-in board”  44  includes a male edge connector portion  46 . This edge connector  46  is simply a portion of the PCB with a number of traces  48  that serve as contacts with contacts of a female edge connector. In this particular illustrated example, the edge connector has a first portion  50  and a second portion  52  separated by a slot  54 . There are also unslotted variants of edge connectors in the prior art. 
     The female edge connector  56  is preferably coupled to a PCB  58  having traces on its bottom surface  60  (not shown), traces can also be located on a top surface  59  of PCB  58 . Pins  62  of the female edge connector  56  extend through holes  64  drilled through the printed circuit board  58  and are soldered to traces or bonding pads at the end of traces on the bottom surface  60 . The female edge connector  56  is provided with a pair of slots  66  and  68  including a number of contacts  70  which couple to the pins  62 . 
     In operation, the first portion  50  of the male edge connector  46  engages the slot  66  of the female edge connector  56 , and the second portion  52  of the male edge connector  46  engages with the slot  68  of female edge connector  56 . In this way, the traces  48  of plug-in board  44  are in electrical contact with the contacts  70  and, therefore, the traces (not shown) of PCB  58 . 
     The edge connector technology illustrated in FIG. 3 has certain advantages, including the elimination of a separate male connector. This not only reduces cost, but it also brings the ground planes of the two PCBs closer together, which can be advantageous, particularly in high frequency applications. However, the ground planes are still separated by the body of the female edge connector  56 , thus reducing high-frequency performance. 
     An ever-increasing percentage of electronic circuitry is at least partially digital in nature. Furthermore, digital circuitry is operating at ever higher frequencies. For example, at the dawn of the computer age electronic circuitry was operating in the megahertz frequency range, while now it is not uncommon for circuitry to operate in the gigahertz and above frequency range. The operation of electronic circuitry at high frequencies creates a whole host of problems including EMI, cross coupling, data integrity, losses, reflections, etc. 
     One way of addressing the special needs of high frequency electronic circuit operation is the use of differential pairs to carry high frequency digital data. Differential pairs are typically labeled plus (+) or minus (−) where the plus line is used to carry the charge comprising the signal to the intended destination, and the minus line is used to carry the return charge. If two devices are communicating back and forth with each other, there may be a transmit differential pair and a receive differential pair to handle the two-way dialog. 
     The advantage of the differential pair is that the flux in the return line tends to cancel the flux in the transmission line. This reduces cross-coupling and radiation losses and, therefore, EMI as well. Differential routing is therefore a very desirable technique for use with digital electronic circuitry operating at high frequencies. 
     Routing high-speed differential signals on a circuit board can be accomplished by two philosophies; tightly coupled differential routing, or loosely coupled differential routing. Tightly coupled routing relies on the direct flux coupling between the differential pairs by placing the traces close enough to each other to achieve the desired differential impedance. The main drawback to this approach is that the slightest variation in trace spacing will cause a dramatic change in the differential impedance. This problem is unavoidable when the distance between the differential pairs must be altered to connect to an I.C. or connector. 
     Loosely coupled differential trace geometry places the differential signals much closer to the ground plane then the traces are to each other. This trace geometry relies on the ground plane as the main flux coupling media, and therefore is much less susceptible to trace spacing variation to control the impedance. Thus, in general, the use of loosely coupled differential traces are preferable over tightly coupled differential traces. The problem that occurs when using loosely coupled differential trace geometry is that when a differential pair passes through a connector system the ground plane is interrupted causing a significant impedance discontinuity. The problem of maintaining the flux coupling between a loosely coupled differential pair through any connector system is the main drawback to loosely coupled trace geometry. 
     The problem of impedance discontinuity through a loosely coupled differential connector system can be minimized through one of two methods: 1) create an artificial ground plane within the connector body; or 2) reduce the size of the uncoupled signal length to an extremely small distance to minimize the physical size, and therefore the magnitude, of the discontinuity. The first method, the artificial ground plane, has numerous previous implementations, most of which perform poorly or are very expensive. One example of this first method is the MICTOR (matched impedance connector) product of the TYCO company of Exeter, N.H. The second method has no known prior art because of the recent development of high-speed differential interfaces, and the recent understanding of the advantages of loosely coupled differential geometry. The problem with existing technology for physically small connector interfaces is either the designs are not robust enough for a hot swap environment, or they are designed for single ended signals and therefore have poor differential impedance control. 
     One company to address to this problem is the Molex Company of Lysle, Ill. The Molex connector, which can be purchased under the trademark betaphase or under the product name NextStep, includes a capton or flexible strip made in two layers with a ground plane underneath and connectors on top. The betaphase connector therefore carries the ground plane through the connector, reducing impedance matching problems. However the betaphase connector is extremely expensive, and would only be considered for the most critical of applications where cost was not considered to be a factor. 
     What the prior art does not address is a simple, inexpensive edge connector system for connecting a plug-in board to a mother board while maintaining the ground plane of the plug-in board in very close proximity to the ground plane of the mother board. The prior art has also not provided a female edge connector which can be configured to accommodate different thicknesses of plug-in board male edge connectors. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems inherent in prior art solutions with a variation on a card edge connector system which reduce the physical size, and therefore the magnitude, of the discontinuity. Reducing the distance of the signal path that is not directly over a ground plane is a primary goal of the present invention. 
     In the present invention, a female edge connector is cut into the circuit board to reduce the connector size and therefore the distance the signal path is separated from the ground plane. Preferably, the female connector is provided in two pieces. This is done, in part, so that the surface mount connector that can be attached to either side of the PCB or can even connect to both sides if one half the connector is mounted on the opposite side of the board from the other. This feature advantageously allows one controller (or other electronic circuit) to be routed on one side of the back plane, and a second controller (or other electronic circuit) can be routed on the other. For example, a disk interface can be made to connect to both sides of the back plane so it can connect to both controllers for redundancy (in this context, redundancy refers to a situation wherein if one controller fails, the disk interface is still connected to the other controller and therefore remains functional). Advantageously, the connector system of the present invention is preferably implemented with surface mount technology and with no vias or crossed traces on the printed circuit board to degrade performance. 
     A through-board PCB connector in accordance with the present invention includes an elongated body made from an electrically insulating material and a plurality of space contacts each made from an electrically conducting material. The elongated body has a first end, a second end, a top, a bottom, and inner side, and an outer side, and is preferably provided with a PC board alignment nub. Each of the contacts preferably includes a spring contact portion provided at the inner side of the body and a surface mount contact portion provided at the bottom of the body. The body is configured to be aligned with a connector aperture formed through a printed circuit board with the aid of the alignment nub to provide a through-board PCB edge connector. 
     Preferably, the body is a first body and the PCB edge connector further includes a second body made from an electrically insulating material which was also configured to be aligned with the connector aperture. Preferably, the first body is separated from the second body by a distance as appropriate, to achieve the desired space, to receive a male edge connector with plug-in board. 
     A printed circuit board with integral edge connector in accordance with the present invention includes a printed circuit board having a top surface and a bottom surface, an aperture formed through the printed circuit board from the top surface to the bottom surface to provide at least two edges which at least partially form a perimeter of the aperture, and a connector aligned with at least one of the edges. A PC board male edge connector can be inserted through the aperture of the printed circuit board and engage the connector to electrically couple the circuitry of a plug-in board to the circuitry of a mother board. Preferably, the aperture is rectangular and has two major edges and two minor edges, where the connector is aligned with a first one of the major edges. Also preferably, the connector is a first connector and a second connector is aligned with a second one of the major edges of the aperture. By controlling the separation between the first connector and the second connector PCBs of different thicknesses can be accommodated. 
     When the top surface of the PC board is provided with a first plurality of differential traces, and the bottom surface is provided with a second plurality of differential traces, the top surface can support the functionality of a first electronic circuit and the bottom surface can support the functionality of a second electronic circuit in such a fashion that no vias or through-holes are required through the printed circuit board to support the functionality of the first electronic circuit and the second electronic circuit. 
     An electronic system in accordance with the present invention includes a plug-in board having a male edge connector, a mother board having a top surface and an opposing bottom surface, and provided with an aperture formed therethrough to provide at least two edges which at least partially form a perimeter for the aperture. A female connector is aligned with at least one of the edges, whereby the male edge connector of the plug-in board can be inserted through the aperture of the mother board and engage the female connector. Preferably, the mother board is provided with a pair of alignment holes extending at least partially through the mother board and the female connector is provided with a pair of alignment pins adapted to engage the alignment holes to align the female connector with the aperture. 
     A method for making a printed circuit board with integral edge connector includes forming an aperture through a printed circuit board from a top surface to a bottom surface and aligning a female edge connector with the aperture whereby a PCB male edge connector can be inserted through the aperture of the printed circuit board to engage with the female edge connector. Preferably, the method also includes forming a pair of alignment holes through the printed circuit board near to the aperture to aid in the alignment of the female edge connector with the aperture. 
     Even more preferably, the female edge connector comes in two parts, i.e., a first female edge connector and a second female edge connector such that two opposing side of the plug-in boards male edge connector can be contacted simultaneously when it is inserted into the aperture. The first and second female edge connectors can be both electrically coupled to the same side of the mother board, or to opposite sides of the mother board. 
     A method for connecting a plug-in board with a mother board in accordance with the present invention includes providing a mother board with an aperture and a female edge connector aligned with the aperture, providing a plug-in board with a male edge connector configured to extend through the aperture, and inserting the male edge connector through the aperture such that it engages the female edge connector. 
     As will be apparent from the preceding descriptions, the through-board PCB edge connector, system, and method provide a number of distinct advantages over the prior art. For one, the ground planes of the plug-in board and the mother board can be separated by a very small distance, e.g. a few thousandths of an inch, which improves high-frequency performance of the system in a dramatic fashion. Furthermore, the connector system is relatively inexpensive in comparison to connection systems of the prior art. So further, the current connection system is much more flexible in design than the prior art, and can be used to accommodate plug-in boards of various sizes, configurations, and thicknesses. 
     These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed descriptions and a study of the various figures of the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 illustrate the male and female portions, respectively, of a prior art SCA connector; 
     FIG. 3 is a perspective view illustrating a plug-in card edge connector system of the prior art; 
     FIG. 4 is a perspective view illustrating a through-board PCB edge connector, system, and method in accordance with the present invention; 
     FIGS. 5 and 6 are perspective views of a female edge connector in accordance with the present invention as seen from opposing sides; 
     FIG. 7 is an elevational view of the outer side of the female edge connector illustrated in FIGS. 5 and 6; 
     FIG. 8 is an inner side elevational view of the female edge connector of FIGS. 5 and 6; 
     FIG. 9 is an end-view of the female edge connector of FIG. 8, the left and elevational view being a mirror image thereof; 
     FIG. 10 is a broken-perspective view of a male edge connector used with the present invention; 
     FIG. 11 is a top plan view of the male edge connector of FIG. 10; 
     FIG. 12 illustrates a female edge connector in accordance with present invention attached to a mother board in a first configuration; 
     FIG. 13 is a cross-sectional view taken along line  13 — 13  of FIG. 12; 
     FIG. 14 is a top plan view of a female edge connector configuration attached to a mother board in accordance with the present invention; 
     FIG. 15 is a cross-sectional view taken along line  15 — 15  of FIG. 14; 
     FIG. 16 is a top plan view of a female edge connector in a third operational configuration in accordance with the present invention; 
     FIG. 17 is a cross-sectional view taken along line  17 — 17  of FIG. 16; 
     FIG. 18 is an inner side elevational view of an alternate embodiment for a female edge connector in accordance with the present invention; 
     FIG. 19 is a perspective view of four of the female connectors illustrated in FIG. 18 engaged with an aperture of a PCB; 
     FIG. 20 is a top plan view of the female edge connector illustrated in FIG. 19; and 
     FIG. 21 is a top plan view similar to the top plan view of FIG. 20 except that the female edge connector is made from a unitary body rather than in four sections. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1,  2 , and  3  were discussed in reference to the prior art. In FIG. 4, an exploded, perspective view of a through-board PCB edge connector system  100  is illustrated. The system  100  includes a mother board  102  and one or more plug-in boards  104   a ,  104   b , and  104   c . Plug-in boards  104   a - 104   c  are sometimes referred to as “daughter boards.” Each of the plug-in boards  104   a ,  104   b , and  104   c  include a male edge connector portion  106   a ,  106   b , and  106   c , respectively, which, as will appreciated by those skilled in the art, is simply an extension of the respective plug-in board. These male edge connectors  106   a - 106   c  are adapted to engage the slots  108   a ,  108   b , and  108   c , respectively, of female edge connectors  110   a ,  110   b , and  110   c , respectively, in accordance with the present invention. As will be discussed in greater detail subsequently, the female edge connectors  110   a - 110   c  can vary in configuration in accordance with a preferred split-connector design of the present invention. The female edge connectors  110   a - 110   c  are preferably aligned with apertures formed through the mother board  102  by alignment pins  112  which extend through holes drilled through the mother board  102 . When the male edge connectors  106   a - 106   c  are operationally engaged with the female edge connectors  110   a - 110   c , electronic circuitry on plug-in boards  104   a - 104   c  can be electrically connected to electronic circuitry on mother board  102 . The design and manufacture of plug-in boards such as plug-in boards  104   a - 104   c  are well known to those skilled in the art and will not be discussed herein in any detail. Likewise, the basic construction and manufacturing of mother boards, such as mother board  102 , is well known to those skilled in the art, and the modification of the mother board  102  to accommodate the female edge connectors  110   a - 110   c  will become apparent to those skilled in the art upon a reading of the following detailed descriptions and a study of the drawings. 
     In FIG. 5, a unitary female edge connector  114  is illustrated in a perspective drawing. This female connector  114  is also shown in a perspective view in FIG. 6 after it has been rotated  180  degrees around a central axis A. The female edge connector  114  is, in the currently described referred embodiment, one component of the female card edge connectors  110   a - 110   c  illustrated in FIG.  4 . However, as will be discussed in greater detail subsequently, the connector  114  can also be used on its own. Therefore, as used herein, a “female connector” shall refer to a single connector, such as connector  114 , or a collection (i.e., two or more) of the connectors, such as connector  114 . 
     With reference to both FIGS. 5 and 6, female edge connector  114  includes an elongated body  116  made from an electrically insulating material, such as a polyvinylcloride (PVC) plastic material. Other insulating or “dielectric” materials suitable for elongated body will be well known to those skilled in the art. The elongated body  116  has a first end  118 , a second end  120 , a top  122 , a bottom  124 , an inner side  126 , and an outer side  128 . The elongated body  116  is further preferably provided with a pair of alignment pins or “nubs”  130   a  and  130   b . The alignment pins and their operation will be discussed in greater detail subsequently. 
     The female edge connector  114  also includes a number of spaced contacts  132 . As can be best seen in FIG. 6, these contacts engage aperture  134  of the body  116  a~and are carried by body  116 . Each of the contacts  132  are made from an electrically conducting material has preferably a “springy” metal such phosphor bronze. Other suitable materials will be apparent to those skilled in the art. The electrically conducting material can be plated with one or more other materials, as also will be appreciated by those skilled in the art. 
     Preferably each contact includes a spring contact portion  136  provided at the inner side  126  of the body  114  and a surface mount contact portion  138  provided at the bottom  124  of the body  114 . While the contacts  132  are currently described as being made from a single piece of electrically conducting material, they can also be formed by two or more pieces that are electrically coupled together, as will be appreciated by those skilled in the art. Preferably, the spring portion  136  is plated with, for example, nickel or gold, and the surface mount contact portion  138  is plated with Sn/Pb plating to aid in the soldering process. Additional drawings of the female edge connector of FIGS. 5 and 6 can be seen in FIG. 7 which is an elevational view of the outer side of the female edge connector and FIG. 8 which is an inner side elevational view of the female edge connector. 
     Some typical dimensions of the female edge connector  114  include a diameter of the base  131  of nubs  130   a  and  130   b , which is approximately 40 mils. Width of contacts  132  as depicted by distance Z is approximately 25 mils and a spacing  133  between the contacts  132  is approximately 50 mils, as defined by distance Y. The female edge connector  114  is also approximately 1,370 mils long between each end contact as defined by distance X. Distance X is can obviously vary as it is a function of the number of contacts  132  present on a female edge connector  114 . Finally, distance W is approximately 175 mils and defines a height of the female edge connector  114 . It should be re-emphasized that these are sample dimensions and a female edge connector  114  of varying dimensions can be constructed and still fall within the scope of the present invention. 
     FIG. 9 is an end view taken along line  9 — 9  of FIG. 7 which has been increased in size to provide additional detail. Overall, the body in cross section is L-shaped with a top portion  140  and a downwardly extending leg  142 . The alignment pins, such as alignment pin  130   b , also extend downwardly from the top portion  140 . As described previously, the contacts  132  are provided within slots or apertures  134  in the body  122  and have a spring contact portion  136  and a surface mount contact portion  138 . As can be seen in this view, the contact  132  is substantially J-shaped. That is, the spring-contact portion  136  is a curved portion of the overall shape, and the surface mount contact  138  is a straight portion of the overall J-shape. An end portion  144  near to the spring contact portion  136  is bent to engage a stop  146  to help anchor the contact in place. The distance S between the inner surface  148  of inner side  126  and the outer surface  150  of leg portion  142  shall be referred to as the “spring beam” distance, which is the limiting distance between the ground plane of a mother board to which the connector  114  is attached and a plug-in board having a male connector engaged with the contact  132 . An example distance S is approximately 15 mils. 
     There are a number of ways that the connector  114  can be manufactured, as will be appreciated by those skilled in the art. One preferred method is by injection molding, but other standard methodologies can be used as well. Further, while it is preferred that the body  116  be of unitary construction, it can be also fabricated in separate pieces and joined in a suitable fashion. Likewise the contacts  132  are preferably formed in a unitary fashion but can also be made from separate pieces that are electrically coupled together. 
     FIG. 10 is a broken, perspective view of the male card edge connector  106   a  of plug-in board  104   a  of FIG.  4 . FIG. 11 is a top plan view of the connector taken along lines  11 — 11  of FIG.  10 . As mentioned previously, the manufacture and use of male card edge connectors is well known to those skilled in the art. Connector  106   a  is a protrusion from the edge  150  of plug-in board  106   a  and includes a number of traces  152 . These traces are typically made from copper although they may be coated with a conductive material such as gold. If traces  152  can be considered to be on the “top” surface of the plug-in board  104   a , then similar traces (not shown) can also be provided on the bottom surface  156  of the plug-in board  104   a . The end  158  of the male connector  106   a  is chamfered to aid in its insertion into the slot of the female connector. This chamfering or beveling is preferably inwardly from all four edges of the end  156  such that the engagements with one or more of the edges with the slot of female connector will urge the male connector  106   a  towards the center of the slot. That is, there are two end bevels  160   a  and  160   b , a top bevel  160   c , and a bottom bevel  160   d . The mother board  104   a  is of traditional PC board design and manufacture. 
     FIG. 12 is a top plan view of the female connector configuration  110   c  of FIG.  4 . It will be noted that this configuration is created by using a pair of female edge connectors  114 , labeled here  114   a  and  114   b . FIG. 13 is a cross-sectional view taken along line  13 — 13  of FIG. 12 with the male edge connector  106 c as can be seen in this figure. The connector  114   b  is inserted into an aperture A in the PC board  102  from a bottom surface  162 , and the female edge connector  114   a  is inserted into the aperture A from a top surface  164 . The alignment pins  112  of the connectors  114   a  and  114   b  are engaged with holes  166  drilled through the mother board  102 . The alignment pins help to properly position and orient the female connectors  114   a  and  114   b  with the aperture to provide a slot  108   c  of the proper width for the male edge connector  106   c.    
     It should be specifically noted that this two piece or “split” two-sided connector design can accommodate plug-in boards of various thicknesses. The slot  108   c  can, for example, be widened by forming a larger aperture A and by properly locating the holes  166  for the alignment pins  112 . While it is preferred to use alignment pins and holes for this alignment process because of the great accuracy that can be achieved in the location of drill holes, it should be noted that the pin or “nub” can have a number of different equivalents. For example, the nub could engage with-a surface mounted stop or alignment rather than a through-hole. Alternatively, the connector itself could be used for alignment with one or more of the edges of the aperture A. It should be noted that the connectors  114   a  and  114   b  are preferably surface-mounted components. These components can be coupled to traces or contacts or pads on the printed circuit board by techniques well known to those skilled in the art. For example, a stainless steel stencil can be used to put down a paste on the pads on the printed circuit boards at the right locations and then the stencil is removed and the components are installed. The paste is a combination of solder and flux. When exposed to higher temperatures in a “IR” reflow process, the solder melts and the flux causes the components to be drawn into place. Thus, once the connectors  114   a  and  114   b  are soldered to the mother board  102 , these components are rigidly held in place. While the pins  112  may provide additional mechanical support as the male edge connector  106   c  is inserted into the female connector  110   c , they are not technically required once the components have been soldered to the mother board  102 . 
     With additional reference to FIG. 13, a male edge connector  106   c  seemed to be operationally engaged with the female edge connector  110   c . As can be seen, the contact  132   b  of connector  114   b  couples traces from one side of male connector  106   c  to traces on the bottom of the mother board  102 , while the contact  132   a  electrically couples traces from the other side of the male contact  106   c  to the top surface  164  of the mother board  102 . It should be also noted that the spring beam length S is the distance between the ground planes on the mother board  102  and on the plug-in board  104   c  which can be as small as a few millimeters. It should also be noted that the male connector  106   c  extends entirely through the mother board  102  such that an end portion of the male connector  106   c  extends a distance E beyond the bottom surface  162  of the mother board  102 . An example distance E is approximately  62  mils and depends on how far end portion  106   c  goes beyond the bottom surface  162  of the mother board  102 . 
     FIG. 14 is a top plan view of the connectors in accordance with the present invention configured as female connector  110   a  of FIG.  4 . The description of FIG. 14 in the cross-section  15 — 15  as shown in FIG. 15 is very similar to the description made previously-with respective FIGS. 12 and 13. In the embodiments of FIGS. 14 and 15, however, all of the contacts  132   b  of connector  114   b  are in contact with traces on the top surface  164  of mother board  102  as well as all of the contacts  132   a  of connector  114   a . In other words, the connector  114   b  has been flipped over from the bottom side  162  to the top side  164  of the mother board  102  such that all of the traces from both sides of the male connector  106   a  are electrically coupled to traces on the top surface  164  of PC board  102 . The bottom surface  162  can therefore be a solid ground plane, if desired, which is separated from a ground plane of the plug-in board  104   a  by only the spring beam distance S. 
     FIG. 16 is a top plan view of a female edge connector  110   b  of FIG. 4 in a third operational configuration in accordance with the present invention. The description of FIG. 16 in the cross section  17 — 17  as shown in FIG. 17 is similar to the description made previously with respective FIGS. 14 and 15. In the embodiments of FIGS. 14 and 15, however, all of the contacts  132   a  of connector s  114   a  and  114   b  are in contact with traces on the bottom surface  162  of mother board  102 . In other words, both connectors  114   a  and  114   b  have been flipped over from the top side  164  to the bottom side  162  of the mother board  102  such that all of the traces from both sides of the male connector  106   b  are electrically coupled to traces on the bottom-surface  162  of PC board  102 . 
     FIG. 18 is an inner side elevational view of an alternate embodiment for a female edge connector  114   a  in accordance with the present invention. Also included are contacts  132 , as previously described in FIGS. 5 and 6, as well as inner side surface  172  and outer side surface  174 . FIG. 19 is a perspective view of four of the female connectors  114   a  illustrated in FIG. 18 engaged with an aperture  170  of a PCB  102 . As can be seen, the four female connectors  114   a  are disposed such that each inner side surface  172  is exposed. In this configuration, the set of female edge connectors  114   a  are receptive to an analogously shaped male edge connector (not shown). FIG. 20 is a top plan view of the female edge connector  114   a  engaged in an aperture  170  of a PCB  101 , as illustrated in FIG.  19 . Advantageously, this embodiment offers circuit board/connector design flexibility since one does not necessarily need to be constrained in one particular direction when adding contacts  132 . It will be appreciated by one skilled in the art that the four female edge connector embodiment could also employ a pair of parallel female edge connectors of a length different from the other pair of parallel female edge connectors, e.g. a rectangle. 
     FIG. 21 shows a top plan view similar to the top plan view of FIG. 20 of a variation of the four female edge connector embodiment wherein the female edge connector  176  is made from a unitary body rather than in four sections. Some possible uses for the four female edge connector embodiment includes, but is not limited to, high-frequency and special microwave installations. 
     From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.