Patent Grant
7727017
The present invention relates generally to high speed connectors, and more particularly to high speed backplane connectors, with reduced crosstalk and improved performance.
High speed connectors are used in many data transmission applications particularly in the telecommunications industry. Signal integrity is an important concern in the area of high speed and data transmission for components need to reliably transmit data signals. The high speed data transmission market has also been driving toward reduced size components and increased signal density.
High speed data transmission is utilized in telecommunications to transmit data received from a data storage reservoir or a component transmitter and such transmission most commonly occurs in routers and servers. As the trend of the industry drives toward reduced size, the signal terminals in high speed connectors must be reduced in size and to accomplish any significant reduction in size, the terminals of the connectors must be spaced closer together. As signal terminal are positioned closer together, signal interference occurs between closely spaced signal terminals especially between pairs of adjacent differential signal terminals. This is referred to in the art as crosstalk and it occurs when the electrical fields of signal terminals abut each other and intermix. At high speeds the signal of one differential signal pair may influence and thereby cross-couple to an adjacent or nearby differential signal pair. This affects signal integrity of the entire signal transmission system. The reduction of crosstalk in high speed data systems is a key goal in the design of high speed connectors.
Previously, reduction of crosstalk was accomplished primarily by the use of shields positioned between adjacent sets of differential signal terminals. These shields were relatively large metal plates that act as an electrical reference point, or barrier, between rows or columns of differential signal terminals. These shields add significant cost to the connector and also increase the size of the connector. The shields may act as large capacitive plates to increase the coupling of the connector and thereby lower the impedance of the connector system. If the impedance is lowered because of the shields, care must be taken to ensure that it does not exceed or fall below a desired value at that location in the connector system. The use of shields to reduce crosstalk in a connector system requires the system designer to take into account their effect on impedance and their effect on the size of the connector.
Some have tried to eliminate the use of shields and rely upon individual ground terminals that are identical in shape and dimension to that of the differential signal terminals with which they are associated. However, the use of ground terminals the same size as the signal terminals leads to problems in coupling which may drive up the system impedance. The use of ground terminals similarly sized to that of the signal terminals requires careful consideration to spacing of all the terminals of the connector system throughout the length of the terminals. In the mating interface of high speed connector, impedance and crosstalk may be controlled due to the large amounts of metal that both sets of contacts present. It becomes difficult to match the impedance within the body of the connector and along the body portions of the terminals in that the terminal body portions have different configurations and spacing than do the contact portions of the terminals.
Notwithstanding the problems associated with the design of the terminals in high-speed connectors, the terminal launch area, i.e., the tail portions of the connector terminals, remains a concern to high speed connector designers, for in order to obtain maximum performance from a press fit mounting pin, the pin must be of a desired length and often takes up most if not all of the depth of the circuit board via into which it is inserted. These pins, when large in number, require a large press-in force. Large press-in forces may inadvertently lead to damage of the terminal tails or other parts of the connector.
The present invention is therefore directed to a high speed connector that overcomes the above-mentioned disadvantages and which uses extremely short length compliant pins as mounting portions of its connector terminals.
It is therefore a general object of the present invention to provide an improved connector for high speed data transmission which has reduced crosstalk and which operates reliably at high speeds.
Another object of the present invention is to provide a high speed connector for backplane applications in which a plurality of discrete pairs of differential signal terminals are arranged in pairs within columns of terminals, each differential signal pair being flanked by an associated ground shielded terminal in an adjacent column, the ground shield terminal having dimensions greater than that of one of the differential signal terminals so as to provide a large reference ground in close proximity to the differential signal pair so as to permit the differential signal pair to broadside couple to the individual ground shield facing it, the signal and ground shield terminals having mounting portions in the form of compliant, press-fit pins, the pins having a reduced length which permits backdrilling of the vias into which the mounting pins are inserted.
The present invention accomplishes these and other objects by virtue of its unique structure. In one principal aspect, the present invention encompasses a backplane connector that utilizes a header connector intended for mounting on a backplane and a right angle connector intended for mounting on a daughter card. When the two connectors are joined together, the backplane and the daughter card are joined together, typically at a right angle.
The right angle connector, which also may be referred to as a daughter card connector, is formed from a series of like connector units. Each connector unit has an insulative frame formed, typically molded from a plastic or other dielectric material. This frame supports a plurality of individual connector units, each supporting an array of conductive terminals. Each connector unit frame has at least two distinct and adjacent sides, one of which supports terminal tail portions and the other of which supports the terminal contact portions of the terminal array. Within the body of the daughter card connector, the frame supports the terminals in a columnar arrangement, or array so that each unit supports a pair of terminal columns therein.
Within each column, the terminals are arranged so as to present isolated differential signal pairs. In each column, the differential signal terminal pairs are arranged edge to edge in order to promote edge coupling between the differential signal terminal pairs. The larger ground shield terminals are firstly located in an adjacent column directly opposite the differential signal terminal pair and are secondly located in the column adjacent (above and below) the differential signal terminal pairs. In this manner, the terminals of each differential signal terminal pair within a column edge couple with each other but also engage in broadside coupling to the ground shield terminals in adjacent columns facing that differential signal terminal pairs. Some edge coupling occurs between the terminals of the differential signal pairs and the adjacent ground shield terminals. The larger ground shield terminals, in the connector body, may be considered as arranged in a series of inverted V-shapes, which are formed by interconnecting groups of three ground shield terminals by imaginary lines and a differential signal terminal pair is nested within each of these V-shapes. In this manner, the terminals of each differential signal pair are isolated from coupling electrical noise into other differential signal pairs and isolated from having other differential signal pairs couple electrical noise into them. The in-column ground shields located above and below a given differential signal pair form a barrier in a vertical manner and the adjacent column ground shields form a horizontal barrier to electrical noise.
The frame is an open frame that acts as a skeleton or network, that holds the columns of terminals in their preferred alignment and spacing. In this regard, the frame includes at least intersecting vertical and horizontal parts and at least one bisector that extends out from the intersection to divide the area between the vertical and horizontal members into two parts. Two other radial spokes subdivide these parts again so as to form distinct open areas on the outer surface of each of the connector unit wafer halves. This network of radial spokes, along with the base vertical and horizontal members, supports a series of ribs that provide a mechanical backing for the larger ground shield terminals. The spokes are also preferably arranged so that they serve as a means for transferring the press-in load that occurs on the top of the daughter card connector to the compliant pin tail portions during assembly of the daughter card connector to the daughter card.
The connectors are provided with reduced length compliant mounting pins. The reduced length of these pins permits them to be arranged and fit within an envelope of space defined by an imaginary datum line drawn from a front edge of the daughter card connector and generally parallel to the base spoke member of the connector units. The reduce length of the mounting pins also permits a greater extent of back drilling to be performed on the daughter card circuit board. The reduced length of the shortened compliment pins of the present invention and consequential potential for reduced via length with appropriate backdrilling can reduce electrical stub length and improve high speed performance of the connectors upon which the novel compliant pins are used, whether the connectors be backplane connectors or input/output connectors or any other connector which are desired for high speed applications.
With the compliant pins of the present invention, a reduction in force needed to apply the connectors to their mounting circuit boards is obtained. The benefits of backdrilling are obtained and backdrilling is made easier. Further, increased electrical performance is obtained.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.
In the course of this detailed description, reference will be frequently made to the attached drawings in which:
Turning to
Each connector unit 112, in the preferred embodiment of the invention, takes the form of a wafer that is formed by the wedding, or marriage, of two waflets or halves 121, 122 together. The right hand wafer halve 122 is illustrated open in
The terminals 113 are separated into distinct signal terminals 113-1 and ground shield terminals 113-2. The ground shield terminals 113-2 are used to mechanically separate the signal terminals into signal terminal pairs across which differential signal will be carried when the connectors of the invention are energized and operated. The ground shield terminals 113-2 are larger than each individual signal terminal 113-1 and are also larger in surface area and overall dimensions than a pair of the signal terminals 113-1 and as such, each such ground shield terminal 113-2 may be considered as an individual ground shield disposed within the body of the connector unit 112. Within each wafer halve, the ground shield terminals 113-2 are separated from each other by intervening spaces. These spaces contain a pair of signal terminals 113-1, which are aligned with the ground shield terminals 113-2 so that all of the terminals 113 are arranged substantially in a single line within the column of terminals.
These signal terminals 113-1 are intended to carry differential signals, meaning electrical signals of the same absolute value, but different polarities. In order to reduce cross-talk in a differential signal application, it is wise to force or drive the differential signal terminals in a pair to couple with each other or a ground(s), rather than a signal terminal or pair of terminals in another differential signal pair. In other words, it is desirable to “isolate” a pair of differential signal terminals to reduce crosstalk at high speeds. This is accomplished, in part, by having the ground shield terminals 113-2 in each terminal array in the wafer halves offset from each other so that each pair of signal terminals 113-1 opposes, or flanks, a large ground terminal 113-2. Due to the size of the ground shield terminal 113-2, it primarily acts as an individual ground shield for each differential signal pair it faces within a wafer (or connector unit). The differential signal pair couples in a broadside manner, to this ground shield terminal 113-2. The two connector unit halves 121, 122 terminal columns are separated by a small spacing so that for most of their extent through the connector unit, the terminals in one column of the connector unit are separated from the terminals in the other column of the connector unit by air with a dielectric constant of 1. The ground shield terminal 113-2 also acts, secondarily, as a ground shield to the terminals of each differential signal pair 113-1 that lie above and below it, in the column or terminals. The nearest terminals of these differential signal terminal pairs edge couple to the ground shield terminal 113-2. The two terminal columns are also closely spaced together and are separated by the thickness of the interior spokes, and this thickness is about 0.25 to 0.35 mm, which is a significant reduction in size compared to other known backplane connectors.
Such a closely-spaced structure promotes three types of coupling within each differential signal channel in the body of the daughter card connector: (a) edge coupling within the pair, where the differential signal terminals of the pair couple with each other; (b) edge coupling of the differential signal terminals to the nearest ground shield terminals in the column of the same wafer half; and, (c) broadside coupling between the differential signal pair terminals and the ground shield terminal in the facing wafer half. This provides a localized ground return path that may be considered, on an individual signal channel scale as having an overall V-shape when imaginary lines are drawn through the centers on the ground shield terminal facing the differential signal pair into intersection with the adjacent ground shield terminal that lie on the edges of the differential signal pair. With this structure, the present invention presents to each differential signal terminal pair, a combination of broadside and edge coupling and forces the differential signal terminal pair into differential mode coupling within the signal pair.
The ground shield terminal 113-1 should be larger than its associated differential signal pair by at least about 15% to 40%, and preferably about 34-35%. For example, a pair of differential signal terminals may have a width of 0.5 mm and be separated by a spacing of 0.3 mm for a combined width, SPW, of 1.3 mm, while the ground shield terminal 113-2 associated with the signal pair may have a width of 1.75 mm. The ground shield terminals 113-2 in each column are separated from their adjacent signal terminals 113-1 by a spacing S, that is preferably equal to the spacing between signal terminals 113-1, or in other words, all of the terminals within each column of each wafer half are spaced apart from each other by a uniform spacing S.
The large ground shield terminal serves to provide a means for driving the differential signal terminal pair into differential mode coupling, which in the present invention is edge coupling in the pair, and maintaining it in that mode while reducing any differential mode coupling with any other signal terminals to an absolute minimum.
Returning to
The bottom spoke 131 and the front spoke 133 are joined together at their ends at a point “O” which is located at the forward bottom edge of the connector units 112. From this junction, a radial spoke 137 extends away and upwardly as shown in a manner to bisect the area between the base and vertical spoke 135 into two parts, which, if desired, may be two equal parts or two unequal parts. This radial spoke 137 extends to a location past the outermost terminals in the connector unit 112. Additional spokes are shown at 138, 139 & 140. Two of these spokes, 138 and 139 are partly radial in their extent because they terminate at locations before the junction point “O” and then extend in a different direction to join to either the vertical front spoke 135 or the base spoke 131. If their longitudinal centerlines would extend, it could be seen that these two radial spokes emanate from the junction point “O”. Each terminus of these two part-radial spokes 138, 140 occurs at the intersection with a ground shield rib 142, the structure and purpose of which is explained to follow. The radial spokes are also preferably arranged in a manner, as shown in
The ribs 142 of the support frame provide the ground shield terminals with support but also serve as runners in the mold to convey injected plastic or any other material from which the connector unit support frames are formed. These ribs 142 are obviously open areas in the support frame mold and serve to feed injected melt to the spokes and to the points of attachment of the terminals to the support frame. The ribs 142 preferably have a width RW that is less than the ground shield terminal width GW. It is desired to have the width of the rib 142 less than that of the ground shield terminals 113-2 so as to effect coupling between the edge of a differential signal terminal pair facing the edge of the ground shield terminal 113-2 and its rib 142 so as to deter the concentration of an electrical field at the ground terminal edges, although it has been found that the edges of the rib 142 can be made coincident with the edges of the ground shield terminals 113-2. However, keeping the edges of the ribs 142 back from the edges of the ground shield terminals 113-2 facilitates molding of the connector units for it eliminates the possibility of mold flash forming along the edges of the ground shield terminal and affecting the electrical performance thereof. The ground shield terminal also provides a datum surface against which mold tooling can abut during the molding of the support frames. As shown in
As shown in
The opposing connector unit wafer half 121 as shown in
This structural change is effected so as to minimize any impedance discontinuity that may occur because of the sudden change in dielectric, (from air to plastic). The signal terminals 113-1 are narrowed while a rectangular window 170 is cut through the ground shield terminals 113-2. These changes increase the edge coupling physical distance and reduce the broadside coupling influence in order to compensate for the change in dielectric from air to plastic. In the area of the window, a portion of the metal of the large ground shield terminal is being replaced by the plastic dielectric in the window area and in this area, the widths of the signal terminals 113-1 are reduced to move their edges farther apart so as to discourage broadside coupling to the ground shield terminal and drive edge coupling between the differential signal terminals 113-1. This increase in edge spacing of the signal terminals 113-1 along the path of the open window 170 leads the differential signal terminal pair to perform electrically as if they are spaced the same distance apart as in their regular width portions. The spacing between the two narrowed signal terminals is filed with plastic which has a higher dielectric constant than does air. The plastic filler would tend to increase the coupling between the signal terminal pair at the regular signal terminal pair edge spacing, but by moving them farther apart in this area, electrically, the signal terminal pair will react as if they are the same distance apart as in the regular area, thereby maintaining coupling between them at the same level and minimizing any impedance discontinuity at the mounting areas.
The body portions 113c of the ground and signal terminals 113-1 and 113-2 have irregular coplanar shapes which permit the tail portions 113a of the signal and ground contacts 113-1 and 113-2 to be disposed with a uniform pitch, while enabling the above-described positional relationship of differential signal pairs of terminals 113-1 in facing relation to a respective larger ground terminal 113-2 in an adjacent column of an opposing connector unit half. It can be seen that the body portions 113c of the signal and ground terminals 113-1, 113-2 of each column of terminals are aligned in coplanar relation to each other with the body portions of the terminals in one column of each connector unit being half disposed a uniform predetermined distance “t” with respect to the body portions of the terminals of the other column of the connector unit half. (
Notwithstanding the non-uniform spacing of the center lines 113d of body portions 113c of the signal and ground terminals 113-1, 113-2, the mounting tail portions 113a of the ground and signal contacts are disposed in a uniform array of columns and rows for more versatile and efficient usage. To this end, the tail portions 113a of the signal and ground terminals 113-1, 113-2 are laterally offset from the respective longitudinal center line 113d of the terminal by predetermined different distances, and the signal and ground contacts 113-1, 113-2 are formed with recesses or necks that facilitate mounting of the terminals in laterally nested relation to each other where necessary a uniform spacing or pitch between the tail portions 113a of the terminals of each column. In the illustrated embodiment, as viewed in
To facilitate positioning of the tail portions with such uniform pitch, each of the signal and ground terminals 113-1, 113-2 in this case is formed with a lateral recess or neck 113e on a lateral or edge side thereof sufficient to permit the required offsetting and nesting of the tail portions 113a. In the embodiment shown in
The tail portions 113a of each column of signal and ground contacts 113-1, 113-2 are separated from the tail portions 113a of an adjacent columns of terminals by a uniform transverse spacing different than the transverse spacing between the body portions 113c of the terminals of each connection unit. In the illustrated embodiment, the tail portion 113a of each signal and ground terminal 113-1, 113-2 is supported by a transverse, substantially horizontal flange portion 113f (
Hence, it can be seen that the tail portions 113a of the ground and signal terminals of the connector units are disposed in a uniform array, comprising equally spaced columns of tail portions 113a with the tail portions of each column also being equally spaced. In the illustrated embodiment, particularly
In an important aspect of the present invention, the mounting tail portions 113a of the terminals 113 have a reduced length that provides for reduced capacitance and reduced electrical stub length in a reduced length via. The mounting pins 113a are “mini” or smaller-size than conventional compliant pin allowing for smaller board vias and increased depth back-drilling in the daughter card circuit board and in the backplane circuit board. This reduced dept also assists in minimizing via capacitance and loading. The reduced depth is about a 1.0 mm pin length which is a substantial reduction in length from conventional compliant mounting pins which are about 2.0 to 1.77 to as low as 1.6 mm in length, meaning a reduction of between about 37% to about 50%. This reduction in depth reduces the length of the via needed to support the pin and allows one to increase the height (depth) of the backdrilling in the via, if desired.
The press fit pins of the present invention 113a are preferably only about 1 mm long (the length LN shown in
The term “length” as used here in is defined as the distance LN shown in
After the vias are drilled into a circuit board, they are plated and the plating can add a thickness to the inner surface of the vias and reduce its diameter. Typically with a 0.46 mm (18 mils) via, the plating will add about 1.0 to 1.5 to 2.0 mils to the inner surface so that a 18 mil diameter hole will reduce down to 14.5 mils (0.37 mm) in diameter. A conventional via drilled at a 22.5 mil (0.572 mm) diameter will reduce down to 18 mils (0.46 mm) in diameter after plating. The surface area that is formed within the via is reduced by almost 50% with reduced width vias used with reduced width pins of the invention, such as 1.44 mm.sup.2 (1.0 mm depth and 0.457 mm drill bore to obtain a plated through hole diameter of 0.37 mm) vs. 2.87 mm.sup.2 (1.6 mm depth and 0.572 mm drill bore to obtain a plated through hole diameter of 0.46 mm). This reduction in the electrical surface outside of and surrounding the reduced size pin reduces capacitive coupling of the outer via surfaces to other outer via surfaces.
As shown in
While the preferred embodiment of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims.
This application claims the domestic benefit of U.S. Provisional Application No. 60/936,374, filed on Jun. 20, 2007, the disclosure of which is herein incorporated by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20090011642 A1 | Jan 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60936374 | Jun 2007 | US |
