Abstract:
A method and structure of an electrical connector is provided for tuning the impedance of the terminals in the connector. The connector includes a dielectric housing having a plurality of terminal-receiving passages. A plurality of terminals are shaped from sheet metal material, with each terminal having a contact portion at one end and a terminating portion at an opposite end. The contact portion has a contact area which engages a mating terminal of a complementary mating connecting device. The contact portion, except for the contact thereof, or the tail portion, is selectively trimmed to a given size to vary the plate area of the contact portion or the tail portion to adjust the impedance of the terminal. This may be done by removing sections of the contact portion from the contact edges or by forming holes in the contact portions. Alternatively, to adjust impedance, a drive shoulder of the terminal may be located at a position to lengthen or shorten the contact portion or tail portion.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to the art of electrical connectors and, particularly, to a method and structure for controlling the impedance in electrical connectors by controlling the impedance of the terminals of the connectors. 
     BACKGROUND OF THE INVENTION 
     In high speed electronic equipment, it is desirable that all components of an interconnection path be optimized for signal transmission characteristics, otherwise the integrity of the system will be impaired or degraded. Such characteristics include risetime degradation or system bandwidth, crosstalk, impedance control and propagation delay. Ideally, an electrical connector would have little or no effect on these characteristics of the interconnection system. In other words, the system would function as if circuitry ran through the interconnection without any effect on the system. However, such an ideal connector is impractical or impossible, and continuous efforts are made to develop electrical connectors which have as little effect on the system as possible. 
     Impedance and inductance control are concerns in designing an ideal connector. This is particularly true in electrical connectors for high speed electronic equipment, i.e., involving high frequencies. An example of one such connector is a board-mounted connector adapted for mounting on a printed circuit board and for mating with a complementary second connector. The connector includes a dielectric housing in which a plurality of terminals are mounted. Each terminal includes a contact portion, such as a contact blade, and a terminating portion, such as a terminal tail. 
     One exemplary obstacle to providing a consistent impedance across an electrical connection occurs when contact portions of terminals are mounted in a spaced-apart relationship in the dielectric housing of an electrical connector. The contact portions of terminals typically have a broad plate area relative to the rest of the terminal to assure adequate and reliable contact. The contact portions which are separated by a dielectric increase the capacitance of the terminals at the contact portions. Because impedance is inversely related to capacitance, the increase in capacitance causes an impedance drop in the terminals, thereby greatly disrupting the characteristic impedance through the overall electrical system. 
     This phenomena is illustrated in FIG. 22 in which impedance (Z) is plotted over distance along a terminal in a connector to provide an impedance curve for a conventional terminal. Z o  is the average or characteristic impedance of the terminal over the distance of the terminal. The dip at Z min  is the lowest impedance exhibited over the terminal at the contact portion. The greater the capacitance increase at the contact portion, the greater the impedance drop with respect to the characteristic impedance Z o  and the greater the connector affects the electrical performance of the electrical system. Conversely, the peak at Z max  represents the increased impedance of the tail portion at the end of the terminal which has a smaller plate area relative to the contact portion. 
     The invention is directed to a method and structure for tuning the impedance of an electrical connector, such as the connector described above, so as to adjust the impedance of the terminal and/or to minimize the range of deviation from the characteristic impedance of the system. The invention is specifically directed to tuning the connector by trimming or removing a section of the terminals of the connector. 
     SUMMARY OF THE INVENTION 
     An object, therefore, of the invention is to provide a new and improved method and structure for tuning the impedance of an electrical connector by selectively trimming a section of the terminals of the connector. 
     In the exemplary embodiment of the invention, generally, the connector includes a dielectric housing having a plurality of terminals mounted in the housing. Each terminal includes a contact portion at one end thereof and a terminating portion at an opposite end thereof. Each terminal has a contact area for mating to a respective terminal of a complementary connector to comprise a mated terminal pair. 
     The invention contemplates a method and structure in which a desired impedance is determined for each terminal in the connector. The contact area of the contact portion of each terminal is determined. The contact portion, except for the contact area thereof, is selectively trimmed to a given size to reduce the plate area of the contact portion according to the determination of the desired impedance of the terminals. By reducing the plate area of the contact portion, the capacitance at the contact portion of the terminal is reduced to increase the impedance Z min  at the contact portion, thereby increasing the characteristic or average impedance Z o  of the terminal. This procedure also has the result of diminishing the range of deviation of the impedance from the characteristic or average impedance Z o  for the terminal. By increasing Z min  , Z o  is increased and brought closer to Z max  which is determined by the terminal tail. 
     As disclosed herein, the contact area of the contact portion of each terminal is generally centrally located between side edges of the contact portion. All or part of the side edges may be trimmed to adjust the impedance or, alternatively, apertures or recesses may be formed in the contact portion on opposite sides of the contact area. Still further, the contact portion defines a front end of the terminal, and the front end may be trimmed to vary the impedance. Furthermore, a rear section of the contact portion may also be trimmed to vary the impedance. Preferably, the terminals are formed by stamping the terminals from sheet metal material, and the contact portions can be trimmed during the stamping operation. 
     The invention also contemplates selectively trimming the tail portion of the terminal to adjust the plate area of the tail portion. By reducing the plate area of the tail portion, the capacitance is decreased and the impedance Z max  of the terminal at the tail portion is increased, and the deviation of the impedance at the contacting interface area is increased thereby increasing the characteristic impedance Z o . By increasing the impedance Z max  at the tail portion, relative to the characteristic impedance Z o  and Z min , the range of deviation between Z max  and Z min  is expanded. 
     This invention also contemplates adding plate area to the tail portion to adjust the impedance. By enlarging the plate area of the tail portion, the capacitance of the tail portion is increased and impedance Z max  at the tail portion is decreased to decrease the characteristic impedance Z o . By reducing the impedance Z max  at the tail portion relative to Z o  and Z min , the range of deviation between Z max  and Z min  is contracted along the length of the terminal. 
     Another embodiment of the invention contemplates a terminal having a drive shoulder between the contact portion and the terminating portion of the terminal, to facilitate inserting the terminal into its respective terminal-receiving passage in the connector housing. The drive shoulder is selectively located at a given position longitudinally of the terminal to vary the relative plate areas of the contact portion and the terminating portion as necessary to achieve a desired impedance in the terminal and/or minimize the deviation of the impedance from the characteristic impedance of the electrical system. 
     Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with its objects and the advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which: 
     FIG. 1 is a perspective view of one type of electrical connector assembly with which the invention is applicable; 
     FIG. 2 is a top plan view of the board-mounted connector of the assembly in FIG. 1; 
     FIG. 3 is a side elevational view of the board-mounted connector; 
     FIG. 4 is an end elevational view of the board-mounted connector, looking at the mating end thereof; 
     FIG. 5 is a vertical section, on an enlarged scale, taken generally along line  5 — 5  of FIG. 4 without the shield; 
     FIG. 6 is a horizontal section taken generally along line  6 — 6  of FIG. 5; 
     FIG. 7 is a plan view of a conventional terminal for mounting in the connector of FIG. 1, still in an intermediate form and connected to a carrier strip during manufacture; 
     FIG. 8 is a side elevational view of the conventional terminal of FIG. 7; 
     FIG. 9 is a side elevational view of the conventional terminal of FIGS. 7 and 8, after the terminal is formed to its ultimate configuration; 
     FIG. 10 is an enlarged sectional view of the terminal of FIG. 7 mated with the terminal of the complementary connector of FIG. 1; 
     FIG. 11 is a fragmented plan view of the contact portion of the conventional terminal; 
     FIG. 12 is a fragmented plan view of a terminal for mounting in the connector of FIG. 1, with the contact portion selectively trimmed to a particular configuration in accordance with one embodiment of the present invention; 
     FIG. 13 is a fragmented plan view of a terminal for mounting in the connector of FIG. 1 with the contact portion trimmed to an alternative configuration in accordance with an alternative embodiment of the present invention; 
     FIG. 14 is a fragmented plan view of a terminal for mounting in the connector of FIG. 1 with entire side edges of the contact portion trimmed in accordance with an additional embodiment of the present invention; 
     FIG. 15 is a fragmented plan view of a terminal for mounting in the connector of FIG. 1 with entire side edges of the contact portion trimmed in accordance with an additional embodiment of the present invention; 
     FIG. 16 is a fragmented plan view of a terminal for mounting in the connector of FIG. 1 with the contact portion selectively trimmed to a particular configuration in accordance with a further embodiment of the present invention; 
     FIG. 17 is a plan view of a terminal for mounting on the connector of FIG. 1, but with a wider tail portion than that of the conventional terminal of FIG. 7; 
     FIG. 18 is a plan view of a terminal for mounting on the connector in FIG. 1, but with sections added to the tail portion; 
     FIG. 19 is a plan view of a terminal for the mounting on the connector of FIG. 1, but with a more narrow tail portion than that of the terminal in FIG. 7; 
     FIG. 20 is a plan view of a terminal for mounting on the connector in FIG. 7, but with the drive shoulder of the terminal at a different location than that of the terminal in FIG. 7; 
     FIG. 21 is a vertical section view of the connector of FIG. 5 but mounting the terminal of FIG. 20; 
     FIG. 22 is a graph plotting impedance as a function of time or distance of a terminal. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in greater detail, and first to FIG. 1, the invention is embodied in an electrical connector assembly, generally designated  20 , which includes a first or board-mounted connector, generally designated  22 , and a second or mating connector, generally designated  24 . Board-mounted connector  22  is mounted on the top surface of a printed circuit board  26 , and mating connector  24  is terminated to a multi-conductor electrical cable  28 . Mating connector  24  is a conventional connector and will not be described in detail herein except to state that the connector mounts a plurality of terminals  58  which are terminated to the conductors of cable  28  and which mate with the terminals of board-mounted connector  22 . The terminals  52  shown in FIGS. 1-11 of the connector  22  are initially described as conventional terminals to highlight the invention. 
     Referring to FIGS. 2-6 in conjunction with FIG. 1, board-mounted connector  22  is a shielded connector and includes an outer box-like shield  30  which is a one-piece structure stamped and formed of sheet metal material. The shield has integral feet portions  32  for insertion into appropriate holes  34  in the printed circuit board. The feet portions may be connected to appropriate ground traces on the printed circuit board. A dielectric housing or insert  35  is mounted within shield  30  and includes a forwardly projecting tongue or mating portion  36 . As best seen in FIGS. 5 and 6, in which the housing  35  of board mounted connector  22  is shown without shield  30 , a plurality of terminal-receiving passages  50  extend from a rear of the housing  35  to a front of the mating portion  36 , both above and below the mating portion  36 . At the rear of the housing  35  the passages  50  comprise a bore  50   a.  On the mating portion  36 , the passages comprise a floor  51  bounded by lateral walls  53 . The passages  50  are exposed between lateral walls  53  at the mating portion  36 . A step  51   a  is provided in the floor  51  at a front end of the mating portion  36 . The dielectric insert is unitarily molded of plastic material or the like and has a pair of board-mounting posts  38  for insertion into appropriate mounting holes in the printed circuit board. 
     The shield  30  is hollow for receiving a mating plug end  40  of second connector  24 , and the plug end of the second connector has a socket for receiving forwardly projecting mating portion  36  of the dielectric insert of board-mounted connector  22 . When the connectors are mated, a plurality of inwardly biased, cantilevered grounding arms  42  of shield  30  of board-mounting connector  22  make positive engagement with a circumferential shield  44  (FIG. 1) of mating connector  24 . 
     The dielectric housing or insert  35  of board-mounted connector  22  is shown in FIGS. 5 and 6 without shield  30  to facilitate an illustration of the mounting of a plurality of terminals, generally designated  46 , on the housing. The conventional terminals include contact portions  52  which are mounted in terminal-receiving passages  50  of the dielectric housing or insert  35 . The contact portion  52  includes a body portion  48  disposed in the bore  50   a  to retain the terminal  46  in the passage  50 . The contact ends or portions  52  are disposed in vertical alignment above and below the forwardly projecting mating portion  36  of the housing. Each conventional terminal includes a terminating end or tail portion  54  which projects out of a mouth  49  of the terminal-receiving passage at the rear of the housing, with the tail portion terminating in a foot  56  which is connected, such as by soldering, to an appropriate circuit trace on printed circuit board  26 . 
     FIGS. 7 and 8 show one of the conventional terminals  46  in intermediate form after the terminal is stamped and partially formed from conductive sheet metal material, but with the terminal still connected by a web  60  to a carrier strip  62  during manufacture. It can be seen that contact portion  52  and tail portion  54  are stamped at opposite ends of the terminal  46  and the contact portion  52  is wider than the tail portion  54 . The contact portion  52  includes a forward tip  43 . Foot portion  56  at the distal end of tail portion  54  is offset from the tail portion during the stamping and forming operation, as seen in FIG.  8 . Skiving teeth  64  for contact portion  52 , teeth  65 ,  66  for body portion  48  and teeth  68  for tail portion  54  are formed during the stamping operation, for skiving into the plastic material of housing  35  to facilitate securing the terminal and its respective portions in the housing. Teeth  64 ,  65  and  66  skive into lateral walls  53  of terminal passages  50 . Teeth  65  are cut on two edges from body portion  48  and are upwardly deformed. Upon insertion of the terminal  46  into terminal passages  50 , teeth deflect to provide additional retention. First and second lateral edges  55   a  and  55   b  of terminals  46  are disposed at lateral walls  53  when mounted in terminal passages  50 . Although the terminals  46  are described herein to be mounted in the housing  35  by insertion into terminal passageways, the terminals  46  of the present invention may be mounted in the housing  35  or a housing of a different connector to which the invention is applicable by insert-molding. 
     At this point, it should be noted that contact portion  52  of each conventional terminal  46  has an elongated raised boss  70  formed during the stamping and forming operation of the terminal. This raised boss defines the contact area of the contact portion which engages a complementary contact of one of the terminals mounted in mating connector  24 . These raised bosses are effective to increase the positive forces of engagement between the mating terminals of the respective connectors and enhance the rigidity of the terminal. However, it should be understood that the invention is applicable for other types of terminals which may not include such raised bosses, but which have defined and determinable contact areas which, preferably, should not be disturbed during trimming of the terminals. 
     FIG. 9 shows one of the conventional terminals  46  after the terminal has been stamped and formed as described above in relation to FIGS. 7 and 8, and with the terminal further formed for insertion into dielectric housing  35  (FIG.  5 ). In other words, the final shape of the terminal in FIG. 9 corresponds to that shown in FIG.  5 . Either before or after the terminal is so formed, web  60  and carrier strip  62  (FIG. 7) are severed from the terminal along line  72  (FIG.  7 ). Therefore, a drive shoulder is formed at line  72  to facilitate insertion of the terminal into its respective terminal-receiving passage in housing  35 . 
     FIG. 10 shows a contacting interface area  59  at which contact portions  52  of conventional terminals  46  mate with terminals  58  of the complementary mating connector  24 . The mating of terminal  46  and terminal  58  comprise a completed mated terminal pair  61 . FIG. 4 illustrates that the terminals  46  are mounted on the top surface of the insert  35  and the terminals  46  are mounted on the bottom surface of the insert  35 . Contact portions  52  of pairs of terminals  46  oppose each other on top and bottom surfaces of the insert  35 . Because the pairs of contact portions  52  have relatively large plate areas opposed to each other in close proximity and are separated by a dielectric they increase the capacitance of the terminals  46  at the contact portions  52 . The increased capacitance results in an impedance drop from the average impedance of the terminal  46  which increases the range of deviation of impedance across the terminal. This phenomena is shown in the impedance curve in FIG. 22 wherein the dip at Z min  represents the impedance at the contact portion  52 . Conversely, the tail portion  54  has relatively small plate area of metal opposed to an adjacent tail portion  54  and a greater inductance and, therefore, a greater impedance, represented by the hump at Z max . 
     FIG. 11 shows a conventional contact portion  52 , including a contact area  70 , without any trimming and corresponding to the depiction of FIG.  7 . FIGS. 12-20 show terminals of the present invention which have a similar configuration as the conventional terminal  46  but further modified to adjust the impedance across the contact portion  52  in accordance with the present invention. FIGS. 12-16 show various schemes for trimming contact portions  52   a - 52   e  of the terminals to effectively reduce the plate area of the contact portions to achieve a desired impedance across the contact portion or to minimize the impedance drop at the contact portion  52 . The portions removed are shown in phantom in the Figures. 
     FIG. 12 shows one scheme for reducing the plate area of the contact portion  52   a  to reduce the capacitance and increase the impedance at the contact portion  52   a.  Specifically, side sections  74  of contact portion  52   a  of terminal  46   a  have been removed all the way to the contact area  70 . In addition, corner sections  76  at the distal or insertion end of the contact portion have been removed. Still further, a central section  78  has been removed at the distal end of the contact portion. As a result, a significant area of contact portion  52   a  has been removed or trimmed away to significantly reduce the overall plate area of the contact portion  52 . It should be noted that contact area  70  which engages the mating terminal is undisturbed. Metal may be removed as necessary to obtain a desired impedance at the contact portion  52   a  while preserving adequate provision for mechanical functions such as terminal retention, contacting engagement and robustness. Some of these considerations may not be as important if the terminals  46  are insert-molded in the housing  35 . Additionally, the hump in the contact area  70  lends robustness to the terminal  26  and enhances the interengagement of the contact with the mating terminal  58 . It is contemplated that these sections  74 ,  76 ,  78  will be removed from the contact portion  52  during the initial stamping process. However, the removal of these sections  74 ,  76 ,  78  may be performed later in the construction of the terminal. 
     FIG. 13 shows another scheme of trimming contact portion  52   b  by again removing corner sections  76  and central section  78  at the distal end of the contact portion. However, elongated holes  80  have been stamped out of the contact portion on opposite sides of contact area  70 , and a round hole  82  has been stamped out of the body portion  48  at the inner end of contact area  70  of terminal  46   b.  Again, the result is the removal of significant metal plate area from the contact portion  52   b  to reduce the capacitance and, thereby, to increase the impedance of the terminals  46   b  at the contact portions  52   b.    
     It should be noted that it is not necessary to remove metal from both sides of the contact area  70 , so that the terminal  46  remains longitudinally symmetrical. Sections of the contact portion  52  may be selectively removed from only one side of the contact area  70  to obtain desired electrical characteristics with respect to adjacent mated terminal pairs. 
     FIG. 14 shows an additional scheme for reducing the area of terminal  46   c.  Side sections  74   a  of the contact portion  52   c  have been removed all the way to the front end of the terminal  46   c.  Skiving teeth  64   a  are disposed on the narrowed front end of the contact portion  52   c.    
     FIG. 15 shows a further scheme for reducing the area of terminal  46   d.  Side sections  74   b  of the entire contact portion  52   d  and the body portion  48   b  have been removed. The elongated raised boss  70   a  of the contact area is lengthened to provide additional structural rigidity to the thinner terminal  46   d.  In addition to skiving teeth  64   a  disposed on the front end of the narrowed contact portions  52   d,  skiving teeth  66   a  are also disposed on the narrowed contact portion  46   d.    
     FIG. 16 shows a further scheme for reducing the area of the terminal  46   e.  Side sections  74   c  of contact portion  52   e  have been removed to define opposite, side recessed sections  74   c  bounded by front and rear edges. The rear edges rearwardly diverge at angles on opposite sides of the terminal  46   e.  Moreover, elongated hole  82   a  is fashioned in body portion  48   c.  It may be preferable to trim sections to have radiused corners  49  as shown in FIG. 16 to reduce electromagnetic field concentration points. 
     When the terminals  46   a - 46   e  are mounted in terminal cavities, the first edge  55   a  of the terminal  46  is disposed at the first lateral wall  53  of the cavity  50  and the second edge  55   b  of the terminal  46  is disposed at the second lateral wall  53  of the cavity  50 . A gap in the contact portions  52   a - 52   e  of terminals  46   a - 46   e  is provided between an edge of the terminal at the boundary of the recessed section and the adjacent first and second lateral walls to expose a portion of the floor  51  of the terminal cavity  50  where a section of the contact portion  52   a - 52   e  has been trimmed away. 
     FIGS. 17-20 show another scheme for varying the impedance of terminals  46   f - 46   i.  In FIG. 17, tail portion  54   f  of the terminal  46   f  has been made wider than tail portion  54  shown in FIG.  7 . Increasing the tail width decreases the impedance of the terminal and also reduces the extent of the impedance deviation from the contact portion  52 . FIG. 18 shows an additional way to increase the plate area of the tail portion  54   g  in terminal  46   g  by adding sections  57  of metal to the edges thereof. 
     Conversely, tail portion  54   h  of terminal  46   h  in FIG. 19 has been made more narrow than tail portion  54  in FIG.  7 . Reducing the plate area of the tail portion increases the impedance of the terminal and will increase the deviation of the impedance from the characteristic impedance at the contact portion. By narrowing and widening the tail portions, the plate areas of the tail portions can be varied to correspondingly adjust the impedance of the terminals. 
     Finally, FIG. 20 shows a terminal  46   i  in which the drive shoulder  72   i  has been moved rearwardly (to the right) versus the location of drive shoulder  72   i  in FIG.  7 . This increases the plate area of the contact portion  52   i  at the body portion  48   i  which, in turn, again will decrease the impedance of the respective terminals. In other words, the axial location of drive shoulder  72   i  can be varied to, correspondingly, adjust the metal plate area of the contact portion and the plate area distribution of the terminal to adjust the impedance of the terminal and the deviation of the impedance at the contact portion  52 . FIG. 21 shows terminal  46   i  mounted in the housing  35  with the drive shoulder  72   i  spaced remotely from the mouth  49  of the terminal-receiving passage  50  as compared to terminal  46  in FIG.  5 . 
     It will be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.