Patent Application
20120289095
This invention relates generally to electrical interconnection systems and more specifically to improved signal integrity in interconnection systems, particularly in high speed electrical connectors.
Electrical connectors are used in many electronic systems. It is generally easier and more cost effective to manufacture a system on several printed circuit boards (“PCBs”) that are connected to one another by electrical connectors than to manufacture a system as a single assembly. A traditional arrangement for interconnecting several PCBs is to have one PCB serve as a backplane. Other PCBs, which are called daughter boards or daughter cards, are then connected through the backplane by electrical connectors.
Electronic systems have generally become smaller, faster and functionally more complex. These changes mean that the number of circuits in a given area of an electronic system, along with the frequencies at which the circuits operate, have increased significantly in recent years. Current systems pass more data between printed circuit boards and require electrical connectors that are electrically capable of handling more data at higher speeds than connectors of even a few years ago.
One of the difficulties in making a high density, high speed connector is that electrical conductors in the connector can be so close that there can be electrical interference between adjacent signal conductors. To reduce interference, and to otherwise provide desirable electrical properties, shield members are often placed between or around adjacent signal conductors. The shields prevent signals carried on one conductor from creating “crosstalk” on another conductor. The shield also impacts the impedance of each conductor, which can further contribute to desirable electrical properties.
Other techniques may be used to control the performance of a connector. Transmitting signals differentially can also reduce crosstalk. Differential signals are carried on a pair of conducting paths, called a “differential pair.” The voltage difference between the conductive paths represents the signal. In general, a differential pair is designed with preferential coupling between the conducting paths of the pair. For example, the two conducting paths of a differential pair may be arranged to run closer to each other than to adjacent signal paths in the connector. No shielding is desired between the conducting paths of the pair, but shielding may be used between differential pairs. Electrical connectors can be designed for differential signals as well as for single-ended signals.
Examples of differential electrical connectors are shown in U.S. Pat. No. 6,293,827, U.S. Pat. No. 6,503,103, U.S. Pat. No. 6,776,659, and U.S. Pat. No. 7,163,421, all of which are assigned to the assignee of the present application and are hereby incorporated by reference in their entireties. Differential connectors with skew control are known. U.S. Pat. No. 6,503,103, for example, describes windows in an insulative housing above a longer leg of a differential pair of conductors. The windows increase the propagation velocity of an electrical signal carried by a longer conductor of the pair relative to propagation velocity of a signal carried by the shorter conductor. As a result, these windows reduce the differential propagation delay of a signal along the two legs, or “skew” of the pair.
An improved differential electrical connector is provided through improved skew control. Incorporation of features along an edge of a conductive element that forms a shorter element of a differential pair can reduce skew. The edge features may increase the electrical length of the shorter element of the pair, thereby removing skew from the pair. Such edge features can be effective even where structural requirements or other constraints on the design of a connector preclude the formation of windows or other modifications in an insulative housing for the connector or where the pair has an insufficient length for differences in dielectric constant of material surrounding the legs of the pair to equalize electrical length of the conductors of the pair.
Accordingly, in some embodiments, the edge features may be used in conjunction with other techniques for skew control, with different techniques being applied alone or in combination in different pairs within the connector. The edge features, for example, may be used in conjunction with selectively positioned regions of relatively higher and relatively lower dielectric constant material adjacent signal conductors of a differential pair that also reduce skew.
Edge features may be incorporated in connectors in which ground conductors are incorporated into columns between adjacent pairs of signal conductors. In some embodiments, edge features may be applied to equalize the electrical length of a set of edges, including the signal to signal edges of the pair of signal conductors and the signal to ground edges of each signal conductor in the pair. Parameters of the edge features may be varied from edge to edge to provide a consistent overall electrical length of all edges in the set. For example, the extent, amplitude, or repetition period of edge features may differ from edge to edge.
In one aspect, the invention relates to an electrical connector that has a plurality of conductive elements disposed in a plane. At least some of the conductive elements are group into pairs. For at least one pair, a first conductive member of the pair has an average centerline that traverses a longer physical length than an average centerline of the second conductive member of the pair. The first conductive member has a first edge and the second conductive member has a second edge disposed adjacent the first edge. The second edge has a second portion that is serpentine over a portion of the second conductive member.
In another aspect, the invention relates to a connector sub-assembly that has an insulative portion having a first surface and a second surface. Each of a plurality of conductive elements has a contact tail extending through the first surface, a mating contact portion extending through the second surface and an intermediate portion connecting the contact tail and the mating contact portion. The plurality of conductive elements forms a plurality of pairs. For a first pair of the plurality of pairs, the insulative portion has an opening preferentially positioned adjacent the first conductive element; and for a second pair of the plurality of pairs, the intermediate portion of the second conductive element has an edge with a plurality of arced segments adjacent the first conductive element of the second pair.
In yet a further aspect, the invention relates to a wafer for an electrical connector. The wafer has a support structure and a column of signal conductors held by the support structure. The column includes a plurality of pairs of signal conductors, each pair having a first signal conductor and a second signal conductor. The first signal conductor of each pair is longer than the second conductor of each pair. The first signal conductor and the second signal conductor of each pair are positioned for edge coupling of a differential signal along a first edge of the first signal conductor and a second edge of the second signal conductor. For at least one pair, the second edge of the signal conductor has a profile with a perimeter adapted to match the length of the first edge.
In yet a further aspect, the invention relates to an electrical connector that has a plurality of conductive elements disposed in a column. The conductive elements can be organized into a plurality of groups, each group having at least a first conductive element, a second conductive element and a third conductive element. The first and second conductive element of each group form a pair, and the third conductive element of each group is adjacent to the pair. The conductive elements in each group having a set of edges, each set comprising a first edge on the first conductive element; a second edge on the second conductive element, the second edge adjacent the first edge; a third edge on the third conductive element; and a fourth edge on the first or second conductive element, the fourth edge being adjacent the third edge. A plurality of the edges in the set comprise features providing tortuosity, the degree of tortuosity of each edge being defined by a value of at least one parameter. At least one of the first or second edges has the features having a first value of the parameter, and at least one of the third or fourth edges has the features having a second value of the parameter.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
An electrical interconnection system with high speed, differential electrical connectors. The connector is assembled from wafers each containing a column of conductive elements, some of which form differential pairs. Skew control is provided for at least some of the pairs by providing a profile on an edge of the shorter signal conductor of the pair. The profile may contain multiple curved segments that effectively lengthen the signal conductor without significantly impacting its impedance. For connectors in which ground conductors are included between adjacent pairs of signal conductors, patterned segments of varying parameters may be included on edges of the signal conductors and ground conductors to equalize electrical lengths of all edges in a set of edges for which there is common mode or differential mode coupling as a signal propagates along each pair. Such features for skew control may be used in combination with other skew control features. The features used may vary depending on the location of the pair within the column.
This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
Referring to
Daughter card connector 120 is designed to mate with backplane connector 150, creating electronically conducting paths between backplane 160 and daughter card 140. Though not expressly shown, interconnection system 100 may interconnect multiple daughter cards having similar daughter card connectors that mate to similar backplane connections on backplane 160. Accordingly, the number and type of subassemblies connected through an interconnection system is not a limitation on the invention.
Backplane connector 150 and daughter connector 120 each contains conductive elements. The conductive elements of daughter card connector 120 are coupled to traces (of which trace 142 is numbered), ground planes or other conductive elements within daughter card 140. The traces carry electrical signals and the ground planes provide reference levels for components on daughter card 140. Ground planes may have voltages that are at earth ground or positive or negative with respect to earth ground, as any voltage level may act as a reference level.
Similarly, conductive elements in backplane connector 150 are coupled to traces (of which trace 162 is numbered), ground planes or other conductive elements within backplane 160. When daughter card connector 120 and backplane connector 150 mate, conductive elements in the two connectors mate to complete electrically conductive paths between the conductive elements within backplane 160 and daughter card 140.
Backplane connector 150 includes a backplane shroud 158 and a plurality conductive elements (see
Tail portions, shown collectively as contact tails 156, of the conductive elements extend below the shroud floor 514 and are adapted to be attached to a substrate, such as backplane 160. Here, the tail portions are in the form of a press fit, “eye of the needle” compliant sections that fit within via holes, shown collectively as via holes 164, on backplane 160. However, other configurations are also suitable, such as surface mount elements, spring contacts, solderable pins, etc., as the present invention is not limited in this regard.
In the embodiment illustrated, backplane shroud 158 is molded from a dielectric material such as plastic or nylon. Examples of suitable materials are liquid crystal polymer (LCP), polyphenyline sulfide (PPS), high temperature nylon or polypropylene (PPO). Other suitable materials may be employed, as the present invention is not limited in this regard. All of these are suitable for use as binder materials in manufacturing connectors according to the invention. One or more fillers may be included in some or all of the binder material used to form backplane shroud 158 to control the electrical or mechanical properties of backplane shroud 150. For example, thermoplastic PPS filled to 30% by volume with glass fiber may be used to form shroud 158.
In the embodiment illustrated, backplane connector 150 is manufactured by molding backplane shroud 158 with openings to receive conductive elements. The conductive elements may be shaped with barbs or other retention features that hold the conductive elements in place when inserted in the opening of backplane shroud 158.
As shown in
Daughter card connector 120 includes a plurality of wafers 1221 . . . 1226 coupled together, with each of the plurality of wafers 1221 . . . 1226 having a housing 260 (see
Wafers 1221 . . . 1226 may be formed by molding housing 260 around conductive elements that form signal and ground conductors. As with shroud 158 of backplane connector 150, housing 260 may be formed of any suitable material and may include portions that have conductive filler or are otherwise made lossy.
In the illustrated embodiment, daughter card connector 120 is a right angle connector and has conductive elements that traverse a right angle. As a result, opposing ends of the conductive elements extend from surfaces on perpendicular edges of the wafers 1221 . . . 1226.
Each conductive element of wafers 1221 . . . 1226 has at least one contact tail, shown collectively as contact tails 126, which can be connected to daughter card 140. Each conductive element in daughter card connector 120 also has a mating contact portion, shown collectively as mating contacts 124, which can be connected to a corresponding conductive element in backplane connector 150. Each conductive element also has an intermediate portion between the mating contact portion and the contact tail, which may be enclosed by or embedded within a wafer housing 260 (see
The contact tails 126 electrically connect the conductive elements within daughter card and connector 120 to conductive elements in a substrate, such as traces 142 in daughter card 140. In the embodiment illustrated, contact tails 126 are press fit “eye of the needle” contacts that make an electrical connection through via holes in daughter card 140. However, any suitable attachment mechanism may be used instead of or in addition to via holes and press fit contact tails.
In the illustrated embodiment, each of the mating contacts 124 has a dual beam structure configured to mate to a corresponding mating contact 154 of backplane connector 150. The conductive elements acting as signal conductors may be grouped in pairs, separated by ground conductors in a configuration suitable for use as a differential electrical connector. However, embodiments are possible for single-ended use in which the conductive elements are evenly spaced without designated ground conductors separating signal conductors or with a ground conductor between each signal conductor.
In the embodiments illustrated, some conductive elements are designated as forming a differential pair of conductors and some conductive elements are designated as ground conductors. These designations refer to the intended use of the conductive elements in an interconnection system as they would be understood by one of skill in the art. For example, though other uses of the conductive elements may be possible, differential pairs may be identified based on positioning of those elements that provides preferential coupling between the conductive elements that make up the pair. Electrical characteristics of the pair, such as its impedance, that make it suitable for carrying a differential signal may provide an alternative or additional method of identifying a differential pair. As another example, in a connector with differential pairs, ground conductors may be identified by their positioning relative to the differential pairs. In other instances, ground conductors may be identified by their shape or electrical characteristics. For example, ground conductors may be relatively wide to provide low inductance, which is desirable for providing a stable reference potential, but provides an impedance that is undesirable for carrying a high speed signal.
For exemplary purposes only, daughter card connector 120 is illustrated with six wafers 1221 . . . 1226, with each wafer having a plurality of pairs of signal conductors and adjacent ground conductors. As pictured, each of the wafers 1221 . . . 1226 includes one column of conductive elements. However, the present invention is not limited in this regard, as the number of wafers and the number of signal conductors and ground conductors in each wafer may be varied as desired.
As shown, each wafer 1221 . . . 1226 is inserted into front housing 130 such that mating contacts 124 are inserted into and held within openings in front housing 130. The openings in front housing 130 are positioned so as to allow mating contacts 154 of the backplane connector 150 to enter the openings in front housing 130 and allow electrical connection with mating contacts 124 when daughter card connector 120 is mated to backplane connector 150.
Daughter card connector 120 may include a support member instead of or in addition to front housing 130 to hold wafers 1221 . . . 1226. In the pictured embodiment, stiffener 128 supports the plurality of wafers 1221 . . . 1226. Stiffener 128 is, in the embodiment illustrated, a stamped metal member. Though, stiffener 128 may be formed from any suitable material. Stiffener 128 may be stamped with slots, holes, grooves or other features that can engage a wafer.
Each wafer 1221 . . . 1226 may include attachment features 242, 244 (see
Contact tails 126 are grouped into signal conductor tails 2261 . . . 2264 and ground conductor tails 2361 . . . 2364. Similarly, mating contacts 124 corresponding to contact tails 126 are grouped into signal conductor contacts 2241 . . . 2244 and ground conductor contacts 2341 . . . 2344.
In some embodiments, housing 260 may be provided with openings, such as windows or slots 2641 . . . 2646, and holes, of which hole 262 is numbered, adjacent the signal conductors 420. These openings may serve multiple purposes, including to: (i) ensure during an injection molding process that the conductive elements are properly positioned, and (ii) facilitate insertion of materials that have different electrical properties, if so desired.
To obtain the desired performance characteristics, one embodiment of the present invention may employ regions of different dielectric constant selectively located adjacent signal conductors 3101B, 3102B . . . 3104B of a wafer. For example, in the embodiment illustrated in
As shown, slots 2641 . . . 2646 in housing 260 are formed adjacent as well as in between signal and ground conductors. For example, slot 2644 is formed between signal conductor 3104B and ground conductor 3304. In other embodiments that are shown in
The ability to place air, or other material that has a dielectric constant lower than the dielectric constant of material used to form other portions of housing 260, in close proximity to one half of a differential pair provides a mechanism to de-skew a differential pair of signal conductors. The time it takes an electrical signal to propagate from one end of the signal connector to the other end is known as the propagation delay. In some embodiments, it is desirable that each signal within a pair have the same propagation delay, which is commonly referred to as having zero skew within the pair. The propagation delay within a conductor is influenced by the dielectric constant of material near the conductor, where a lower dielectric constant means a lower propagation delay. The dielectric constant is also sometimes referred to as the relative permittivity. A vacuum has the lowest possible dielectric constant with a value of 1. Air has a similarly low dielectric constant, whereas dielectric materials, such as LCP, have higher dielectric constants. For example, LCP has a dielectric constant of between about 2.5 and about 4.5.
Each signal conductor of the signal pair may have a different physical length, particularly in a right-angle connector. In some embodiments, to equalize the propagation delay in the signal conductors of a differential pair even though they have physically different lengths, the relative proportion of materials of different dielectric constants around the conductors may be adjusted. In some embodiments, more air is positioned in close proximity to the physically longer signal conductor of the pair than for the shorter signal conductor of the pair, thus lowering the effective dielectric constant around the signal conductor and decreasing its propagation delay.
However, as the dielectric constant is lowered, the impedance of the signal conductor rises. To maintain balanced impedance within the pair, the size of the signal conductor in closer proximity to the air may be increased in thickness or width. This results in two signal conductors with different physical geometry, but a more equal propagation delay and more inform impedance profile along the pair.
Slots 2641 . . . 2644 are intersected by the cross section and are therefore visible in
Ground conductors 3301, 3302 and 3303 are positioned between two adjacent differential pairs 3401, 3402 . . . 3404 within the column. Additional ground conductors may be included at either or both ends of the column. In wafer 220A, as illustrated in
In the pictured embodiment, each ground conductor has a width approximately five times the width of a signal conductor such that in excess of 50% of the column width occupied by the conductive elements is occupied by the ground conductors. In the illustrated embodiment, approximately 70% of the column width occupied by conductive elements is occupied by the ground conductors 3301 . . . 3304. Increasing the percentage of each column occupied by a ground conductor can decrease cross talk within the connector.
Other techniques can also be used to manufacture wafer 220A to reduce crosstalk or otherwise have desirable electrical properties. In some embodiments, one or more portions of the housing 260 are formed from a material that selectively alters the electrical and/or electromagnetic properties of that portion of the housing, thereby suppressing noise and/or crosstalk, altering the impedance of the signal conductors or otherwise imparting desirable electrical properties to the signal conductors of the wafer.
In the embodiment illustrated in
Materials that conduct, but with some loss, over the frequency range of interest are referred to herein generally as “lossy” materials. Electrically lossy materials can be formed from lossy dielectric and/or lossy conductive materials. The frequency range of interest depends on the operating parameters of the system in which such a connector is used, but will generally be between about 1 GHz and 25 GHz, though higher frequencies or lower frequencies may be of interest in some applications. Some connector designs may have frequency ranges of interest that span only a portion of this range, such as 1 to 10 GHz or 3 to 15 GHz or 3 to 6 GHz.
Electrically lossy material can be formed from material traditionally regarded as dielectric materials, such as those that have an electric loss tangent greater than approximately 0.003 in the frequency range of interest. The “electric loss tangent” is the ratio of the imaginary part to the real part of the complex electrical permittivity of the material.
Electrically lossy materials can also be formed from materials that are generally thought of as conductors, but are either relatively poor conductors over the frequency range of interest, contain particles or regions that are sufficiently dispersed that they do not provide high conductivity or otherwise are prepared with properties that lead to a relatively weak bulk conductivity over the frequency range of interest. Electrically lossy materials typically have a conductivity of about 1 siemans/meter to about 6.1×107 siemans/meter, preferably about 1 siemans/meter to about 1×107 siemans/meter and most preferably about 1 siemans/meter to about 30,000 Siemens/meter. In some embodiments material with a bulk conductivity of between about 25 Siemens/meter and about 500 Siemens/meter may be used. As a specific example, material with a conductivity of about 50 Siemens/meter may be used.
Electrically lossy materials may be partially conductive materials, such as those that have a surface resistivity between 1 Ω/square and 106 Ω/square. In some embodiments, the electrically lossy material has a surface resistivity between 1 Ω/square and 103 Ω/square. In some embodiments, the electrically lossy material has a surface resistivity between 10 Ω/square and 100 Ω/square. As a specific example, the material may have a surface resistivity of between about 20 Ω/square and 40 Ω/square.
In some embodiments, electrically lossy material is formed by adding to a binder a filler that contains conductive particles. Examples of conductive particles that may be used as a filler to form an electrically lossy material include carbon or graphite formed as fibers, flakes or other particles. Metal in the form of powder, flakes, fibers or other particles may also be used to provide suitable electrically lossy properties. Alternatively, combinations of fillers may be used. For example, metal plated carbon particles may be used. Silver and nickel are suitable metal plating for fibers. Coated particles may be used alone or in combination with other fillers, such as carbon flake. In some embodiments, the conductive particles disposed in the lossy portion 250 of the housing may be disposed generally evenly throughout, rendering a conductivity of the lossy portion generally constant. In other embodiments, a first region of the lossy portion 250 may be more conductive than a second region of the lossy portion 250 so that the conductivity, and therefore amount of loss within the lossy portion 250 may vary.
The binder or matrix may be any material that will set, cure or can otherwise be used to position the filler material. In some embodiments, the binder may be a thermoplastic material such as is traditionally used in the manufacture of electrical connectors to facilitate the molding of the electrically lossy material into the desired shapes and locations as part of the manufacture of the electrical connector. However, many alternative forms of binder materials may be used. Curable materials, such as epoxies, can serve as a binder. Alternatively, materials such as thermosetting resins or adhesives may be used. Also, while the above described binder materials may be used to create an electrically lossy material by forming a binder around conducting particle fillers, the invention is not so limited. For example, conducting particles may be impregnated into a formed matrix material or may be coated onto a formed matrix material, such as by applying a conductive coating to a plastic housing. As used herein, the term “binder” encompasses a material that encapsulates the filler, is impregnated with the filler or otherwise serves as a substrate to hold the filler.
Preferably, the fillers will be present in a sufficient volume percentage to allow conducting paths to be created from particle to particle. For example, when metal fiber is used, the fiber may be present in about 3% to 40% by volume. The amount of filler may impact the conducting properties of the material.
Filled materials may be purchased commercially, such as materials sold under the trade name Celestran® by Ticona. A lossy material, such as lossy conductive carbon filled adhesive preform, such as those sold by Techfilm of Billerica, Mass., US may also be used. This preform can include an epoxy binder filled with carbon particles. The binder surrounds carbon particles, which act as a reinforcement for the preform. Such a preform may be inserted in a wafer 220A to form all or part of the housing and may be positioned to adhere to ground conductors in the wafer. In some embodiments, the preform may adhere through the adhesive in the preform, which may be cured in a heat treating process. Various forms of reinforcing fiber, in woven or non-woven form, coated or non-coated, may be used. Non-woven carbon fiber is one suitable material. Other suitable materials, such as custom blends as sold by RTP Company, can be employed, as the present invention is not limited in this respect.
In the embodiment illustrated in
To prevent signal conductors 3101A, 3101B . . . 3104A, and 3104B from being shorted together and/or from being shorted to ground by lossy portion 250, insulative portion 240, formed of a suitable dielectric material, may be used to insulate the signal conductors. The insulative materials may be, for example, a thermoplastic binder into which non-conducting fibers are introduced for added strength, dimensional stability and to reduce the amount of higher priced binder used. Glass fibers, as in a conventional electrical connector, may have a loading of about 30% by volume. It should be appreciated that in other embodiments, other materials may be used, as the invention is not so limited.
In the embodiment of
In some embodiments, the lossy regions 336 and 3341 . . . 3344 of the housing 260 and the ground conductors 3301 . . . 3304 cooperate to shield the differential pairs 3401 . . . 3404 to reduce crosstalk. The lossy regions 336 and 3341 . . . 3344 may be grounded by being electrically connected to one or more ground conductors. This configuration of lossy material in combination with ground conductors 3301 . . . 3304 reduces crosstalk between differential pairs within a column.
As shown in
Material that flows through openings in the ground conductors allows perpendicular portions 3341 . . . 3344 to extend through ground conductors even though a mold cavity used to form a wafer 220A has inlets on only one side of the ground conductors. Additionally, flowing material through openings in ground conductors as part of a molding operation may aid in securing the ground conductors in housing 260 and may enhance the electrical connection between the lossy portion 250 and the ground conductors. However, other suitable methods of forming perpendicular portions 3341 . . . 3344 may also be used, including molding wafer 320A in a cavity that has inlets on two sides of ground conductors 3301 . . . 3304 Likewise, other suitable methods for securing the ground contacts 330 may be employed, as the present invention is not limited in this respect.
Forming the lossy portion 250 of the housing from a moldable material can provide additional benefits. For example, the lossy material at one or more locations can be configured to set the performance of the connector at that location. For example, changing the thickness of a lossy portion to space signal conductors closer to or further away from the lossy portion 250 can alter the performance of the connector. As such, electromagnetic coupling between one differential pair and ground and another differential pair and ground can be altered, thereby configuring the amount of loss for radiation between adjacent differential pairs and the amount of loss to signals carried by those differential pairs. As a result, a connector according to embodiments of the invention may be capable of use at higher frequencies than conventional connectors, such as for example at frequencies between 10-15 GHz.
As shown in the embodiment of
Lossy material may also be positioned to reduce the crosstalk between adjacent pairs in different columns.
As illustrated in
Each of the wafers 320B may include structures similar to those in wafer 320A as illustrated in
The housing for a wafer 320B may also include lossy portions, such as lossy portions 250B. As with lossy portions 250 described in connection with wafer 320A in
In the embodiment illustrated, lossy portion 250B may have a substantially parallel region 336B that is parallel to the columns of differential pairs 3405 . . . 3408. Each lossy portion 250B may further include a plurality of perpendicular regions 3341B . . . 3345B, which extend from the parallel region 336B. The perpendicular regions 3341B . . . 3345B may be spaced apart and disposed between adjacent differential pairs within a column.
Wafers 320B also include ground conductors, such as ground conductors 3305 . . . 3309. As with wafers 320A, the ground conductors are positioned adjacent differential pairs 3405 . . . 3408. Also, as in wafers 320A, the ground conductors generally have a width greater than the width of the signal conductors. In the embodiment pictured in
Ground conductor 3309 is narrower to provide desired electrical properties without requiring the wafer 320B to be undesirably wide. Ground conductor 3309 has an edge that faces differential pair 3408. Accordingly, differential pair 3408 is positioned relative to a ground conductor similarly to adjacent differential pairs, such as differential pair 3308 in wafer 320B or pair 3404 in a wafer 320A. As a result, the electrical properties of differential pair 3408 are similar to those of other differential pairs. By making ground conductor 3309 narrower than ground conductors 3308 or 3304, wafer 320B may be made with a smaller size.
A similar small ground conductor could be included in wafer 320A adjacent pair 3401. However, in the embodiment illustrated, pair 3401 is the shortest of all differential pairs within daughter card connector 120. Though including a narrow ground conductor in wafer 320A could make the ground configuration of differential pair 3401 more similar to the configuration of adjacent differential pairs in wafers 320A and 320B, the net effect of differences in ground configuration may be proportional to the length of the conductor over which those differences exist. Because differential pair 3401 is relatively short, in the embodiment of
For example, differential pair 3406 is proximate ground conductor 3302 in wafer 320A. Similarly, differential pair 3403 in wafer 320A is proximate ground conductor 3307 in wafer 320B. In this way, radiation from a differential pair in one column couples more strongly to a ground conductor in an adjacent column than to a signal conductor in that column. This configuration reduces crosstalk between differential pairs in adjacent columns.
Wafers with different configurations may be formed in any suitable way.
To facilitate the manufacture of wafers, signal conductors, of which signal conductor 420 is numbered, and ground conductors, of which ground conductor 430 is numbered, may be held together on a lead frame 400 as shown in
The wafer strip assemblies shown in
Although the lead frame 400 is shown as including both ground conductors 430 and the signal conductors 420, the present invention is not limited in this respect. For example, the respective conductors may be formed in two separate lead frames. Indeed, no lead frame need be used and individual conductive elements may be employed during manufacture. It should be appreciated that molding over one or both lead frames or the individual conductive elements need not be performed at all, as the wafer may be assembled by inserting ground conductors and signal conductors into preformed housing portions, which may then be secured together with various features including snap fit features.
In the embodiment illustrated in
Each of the beams includes a mating surface, of which mating surface 462 on beam 4601 is numbered. To form a reliable electrical connection between a conductive element in the daughter card connector 120 and a corresponding conductive element in backplane connector 150, each of the beams 4601 . . . 4608 may be shaped to press against a corresponding mating contact in the backplane connector 150 with sufficient mechanical force to create a reliable electrical connection. Having two beams per contact increases the likelihood that an electrical connection will be formed even if one beam is damaged, contaminated or otherwise precluded from making an effective connection.
Each of beams 4601 . . .4608 has a shape that generates mechanical force for making an electrical connection to a corresponding contact. In the embodiment of
In the illustrated embodiment, the ground conductors adjacent broadening portions 4801 and 4802 are shaped to conform to the adjacent edge of the signal conductors. Accordingly, mating contact 4341 for a ground conductor has a complementary portion 4821 with a shape that conforms to broadening portion 4801. Likewise, mating contact 4342 has a complementary portion 4822 that conforms to broadening portion 4802. By incorporating complementary portions in the ground conductors, the edge-to-edge spacing between the signal conductors and adjacent ground conductors remains relatively constant, even as the width of the signal conductors change at the mating contact region to provide desired mechanical properties to the beams. Maintaining a uniform spacing may further contribute to desirable electrical properties for an interconnection system according to an embodiment of the invention.
Some or all of the construction techniques employed within daughter card connector 120 for providing desirable characteristics may be employed in backplane connector 150. In the illustrated embodiment, backplane connector 150, like daughter card connector 120, includes features for providing desirable signal transmission properties. Signal conductors in backplane connector 150 are arranged in columns, each containing differential pairs interspersed with ground conductors. The ground conductors are wide relative to the signal conductors. Also, adjacent columns have different configurations. Some of the columns may have narrow ground conductors at the end to save space while providing a desired ground configuration around signal conductors at the ends of the columns. Additionally, ground conductors in one column may be positioned adjacent to differential pairs in an adjacent column as a way to reduce crosstalk from one column to the next. Further, lossy material may be selectively placed within the shroud of backplane connector 150 to reduce crosstalk, without providing an undesirable level attenuation for signals. Further, adjacent signals and grounds may have conforming portions so that in locations where the profile of either a signal conductor or a ground conductor changes, the signal-to-ground spacing may be maintained.
The conductive elements of backplane connector 150 are positioned to align with the conductive elements in daughter card connector 120. Accordingly,
Ground conductors 5301 . . . 5305 and differential pairs 5401 . . . 5404 are positioned to form one column of conductive elements within backplane connector 150. That column has conductive elements positioned to align with a column of conductive elements as in a wafer 320B (
Ground conductors 5302, 5303 and 5304 are shown to be wide relative to the signal conductors that make up the differential pairs by 5401 . . . 5404. Narrower ground conductive elements, which are narrower relative to ground conductors 5302, 5303 and 5304, are included at each end of the column. In the embodiment illustrated in
As can be seen, each of the ground contacts has a mating contact portion shaped as a blade. For additional stiffness, one or more stiffening structures may be formed in each contact. In the embodiment of
Each of the wide ground conductors, such as 5302 . . . 5304, includes two contact tails. For ground conductor 5302 contact tails 6561 and 6562 are numbered. Providing two contact tails per wide ground conductor provides for a more even distribution of grounding structures throughout the entire interconnection system, including within backplane 160 because each of contact tails 6561 and 6562 will engage a ground via within backplane 160 that will be parallel and adjacent a via carrying a signal.
As with the stamping of
In the embodiment illustrated, each of the narrower ground conductors, such as 5301 and 5302, contains a single contact tail such as 6563 on ground conductor 5301 or contact tail 6564 on ground conductor 5305. Even though only one ground contact tail is included, the relationship between number of signal contacts is maintained because narrow ground conductors as shown in
As can be seen in
As can be seen from
Likewise, signal conductors have projections, such as projections 664 (
To facilitate use of signal and ground conductors with complementary portions, backplane connector 150 may be manufactured by inserting signal conductors and ground conductors into shroud 510 from opposite sides. As can be seen in
A column of conductive elements is held within the housing of wafer 720.
In the example of
In the embodiment illustrated, signal conductor 7442B is longer than signal conductor 7442A in pair 7422 Likewise, signal conductor 7443B is longer than signal conductor 7443A in pair 7423. To reduce skew, the propagation speed of signals through the longer signal conductor may be increased relative to the propagation speed in the shorter signal conductor of the pair. Selective placement of regions of material with different dielectric constant may provide the desired relative propagation speed.
In the embodiment illustrated, for each of the pairs 7422 and 7423, a region of relatively low dielectric material may be incorporated into wafer 720 in the vicinity of each of the longer signal conductors. In the embodiment illustrated, regions 7102 and 7103 are incorporated into wafer 720. In contrast, the housing of wafer 720 in the vicinity of the shorter signal conductor of each pair creates regions of relatively higher dielectric constant material. In the embodiment of
Similarly to that described above, and as shown in
Regions of lower dielectric constant material and higher dielectric constant material may be formed in any suitable way. In embodiments in which the insulative portions of the housing for wafer 720 are molded from plastic filled with glass fiber loaded to approximately 30% by volume, regions 7122 and 7123 of higher dielectric constant material may be formed as part of forming the insulative portion of the housing for wafer 720. Regions 7102 and 7103 of lower dielectric constant material may be formed by voids in the insulative material used to make the housing for wafer 720. An example of a connector with lower dielectric constant regions formed by voids in an insulative housing is shown in
However, regions of lower dielectric constant material may be formed in any suitable way. For example, the regions may be formed by adding or removing material from region 7102 and 7103 to produce regions of desired dielectric constant. For example, region 7102 and 7103 may be molded of material with less or different fillers than the material used to form region 7122 and 7123.
Regardless of the specific method used to form regions of lower dielectric constant, in some embodiments, those regions are positioned generally between the longer signal conductor and an adjacent ground conductor. For example, region 7102 is positioned between signal conductor 7442B and ground conductor 7302. Likewise, region 7103 is positioned between signal conductor 7443B and ground conductor 7303.
The inventors have appreciated that positioning regions of lower dielectric constant material between the longer signal conductor of a differential pair and an adjacent ground is desirable for reducing skew. While not being bound by any particular theory of operation, the inventors theorize that the common mode components of the signal carried by a differential pair may be heavily influenced by differences in the length of the conductors of the pair caused by curves in the differential pair. In the example of
The reasons why common mode components of a signal are most heavily influenced by skew are illustrated in
As can be seen in
Common mode components propagating in region 7603 must cover a distance that is generally proportional to the radius of curvature R4. The distance that a common mode component travels through region 7601 is proportional to the radius of curvature R1. Therefore, skew in the common mode components will be proportional to the difference (R4−R1).
In contrast, the difference in path lengths traveled by the differential mode components traveling through region 7602 is proportional to the difference in the radii of curvature defining the boundaries of region 7602. In the configuration of
As can be seen by comparing
More generally, material of a lower dielectric constant positioned in region R (
It is not necessary that the entire region R be occupied by material of a lower dielectric constant. In some embodiments, the region of lower dielectric constant material, such as region 7102, does not extend to the distal edge 732 of an adjacent ground conductor. Rather, the region of lower dielectric constant material extends no farther the midpoint of the ground conductor.
A comparison of
For example, region 7603 (
Incorporating regions of lower dielectric constant material may alter other properties of the differential pairs in wafer 720. For example, the impedance of signal conductor 7442B may be increased by a region of lower dielectric constant material 7102. To compensate for an increase of impedance, the width of a signal conductor adjacent a region of lower dielectric constant may be wider than the corresponding signal conductor of the pair. For example,
Positioning material of relatively lower dielectric constant adjacent curved regions has the benefit of offsetting effects of different length conductors as those effects occur. Consequently, signal components associated with each signal conductor of the pair stay synchronized throughout the entire length of the differential pair. In such an embodiment, the differential pair may have an increased common mode noise immunity, which can reduce crosstalk. Of course, equalizing the total propagation delay through the signal conductors of a differential pair is desirable even if the signal components are not synchronized at all points along the differential pair. Accordingly, the material of relatively lower dielectric constant may be placed in any suitable location or locations.
In the embodiments described above, regions of relatively lower dielectric constant are formed by incorporating into the housing of wafer 720 regions of material that has a lower dielectric constant than other material used to form the housing. However, in some embodiments, a region of relatively lower dielectric constant may be formed by incorporating material of a higher dielectric constant outside of that region.
For example,
However, in the embodiment illustrated, regions 9101 and 9102 are formed of the same material used to form the insulative portion of housing 940. Nonetheless, regions 9101 and 9102 have a relatively lower dielectric constant than the material surrounding the shorter signal conductors because of the incorporation of regions 9121 and 9122. In the embodiment illustrated, regions 9121 and 9122 have a higher dielectric constant than the material used to form the insulative portion 940. As described earlier, in some embodiments, regions 9121 and 9122 may be formed adjacent to conductive elements, but not directly in between, as shown in
Regions 9121 and 9122 may be formed in any suitable way. For example, they may be formed by incorporating fillers or other material into plastic that is molded as a portion of the housing of wafer 920. However, any suitable method may be used to form regions 9121 and 9122.
The embodiment of
Though selective positioning of material of different dielectric constant may compensate for skew, other techniques may be used instead of or in addition to this technique. In some embodiments, skew control may be provided for one or more of the differential pairs by providing a shaped profile on edges of the shorter signal conductor of a differential pair. The profile may include multiple arcuate segments that serve to effectively lengthen the signal conductor without a significant impact in its impedance. A comparison of
In contrast,
When signal conductors 1010 and 1012 are used to carry a differential signal, the differential mode component of that signal will propagate predominantly as energy between edges 1014 and 1016. By equalizing the physical length of those edges, the electrical length of the conductors carrying the differential signal is also equalized. As a result, skew may be reduced. In this regard, in addition to reducing skew by adjusting the propagation speed of signals through signal conductors of varying length by suitably placed dielectric materials, skew may reduced in another manner by effectively lengthening the electrical path length of one or more of the signal conductors. The corresponding contact tail and mating contact portion of the second signal conductor may remain the same, despite the existing serpentine region that are intermediate to the contact regions.
Signal conductors that exhibit a serpentine region are not limited to a particular shape. In some cases, signal conductors may exhibit a shape that has a substantially irregular profile, such as, for example, in a zig-zagged configuration.
For some embodiments, the serpentine region may be substantially sinusoidal in profile. In some embodiments, the serpentine region incorporates a number of alternating concave and convex segments. In some cases, concave and convex segments may have an average height or amplitude normal to the edge of the second signal conductor of between 0.05 mm and 0.3 mm. In more specific cases, concave and convex segments may have an average height or amplitude normal to the edge of the second signal conductor of between 0.1 mm and 0.2 mm. In other embodiments, concave and convex segments may alternate in such a fashion to produce a frequency of oscillation. In some cases, a period of alternating concave and convex segments may be less than 2 mm. In more specific cases, a period of alternating concave and convex segments may be less than 1 mm. In an oscillating path, as the amplitude or frequency increase, the path length of the conductor will also increase, allowing a desired edge length to be achieved by varying one or more parameters.
It can be appreciated that the serpentine region may conform to any suitable shape, provided that the effective electrical path length of the signal conductor is as appropriately desired for effective functioning of the differential pair, and the invention is not limited to the shapes disclosed herein. Though, smooth segments have fewer electrical discontinuities than segments with abrupt angles, which provides better signal integrity than a conductor with angular features. Accordingly, the serpentine region may incorporate any sort of irregular shape.
Additionally, the serpentine feature for skew control presented herein may be used in combination with other skew control features, including incorporating regions or openings of low dielectric constant that may be located adjacent to signal conductors within differential pairs. In this respect, an additional motivation for effectively lengthening the signal conductors in the manner presented is in incorporating serpentine regions for signal conductors in rows where it may be less practical to include a window of suitable length.
A combination of techniques for skew compensation m may be employed on the same differential pair when a single technique does not provide adequate skew compensation. In some embodiments, skew compensation techniques may be combined by using different techniques for different differential pairs in a connector. For example, in a right angle connector, pairs in a column of signal conductors may be compensated differently, depending on the position within the column. Incorporating air pockets or other regions of low dielectric material adjacent a longer conductor of a pair may adequately compensate for skew in the outer, longer rows in the column. Because signal conductors in those rows extend across a longer distance, there are more places along the length of the conductor in which regions of relatively low dielectric constant material may be incorporated.
Conversely, for inner rows in a column, the signal conductors are shorter, leaving few locations in which pockets of air may be incorporated adjacent the longer signal conductor of the pair. Further, structural considerations may preclude introducing pockets of air in those locations. Accordingly, in some embodiments, skew compensation may be provide by using pockets of air to compensate for skew in the outer, longer rows of a column and a tortuous profiles may be incorporated into edges of signal conductors in the signal conductors in the shorter rows in the columns.
It can be appreciated that regions of varying dielectric constant may be located at any suitable position along a signal conductor and that edges with tortuosity may be formed with any suitable parameters. In some embodiments, regions of varying dielectric constant may be spaced apart from one another by any appropriate distance. In other embodiments, a signal conductor may include one region that is serpentine in profile and another region, along the same signal conductor, that may incorporate an adjacent area with a different dielectric constant. In this regard, through a combination of the techniques described, the effective electrical length can be suitably varied by adjusting the physical length of the signal conductor path through the serpentine arrangement and/or the propagation delay of electrical signals through appropriately placed dielectrics.
It should be understood that openings can be interpreted to be a region of a different dielectric constant, including, for example, but not limited to an air pocket of open space, plastic, or polymer with filler material.
The techniques described that may provide skew control can be appropriately varied, such as by adjusting the geometry of the serpentine regions or modifying the nature and amount of dielectric constant adjacent a signal conductor. In addition, the location of the dielectric relative to signal and ground conductors may also shift in neighboring differential pairs to compensate for differences in skew based on the position of a pair within a column. In this regard, for longer differential pairs, openings may be centered substantially over the first signal conductor, the first signal conductor being longer than the second signal conductor in the differential pair. For shorter differential pairs, openings may be shifted so that they are centered more between the first signal conductor and the corresponding ground for the differential pair.
In some aspects, where openings formed adjacent to conductive elements do not include an opening portion that is formed directly between conductive elements, serpentine regions with greater path length may be incorporated to further limit skew effects. For some embodiments, serpentine regions with greater path length may be included along with openings without an opening portion formed directly between conductive elements where conductive elements have a shorter average centerline path length as compared to other conductive elements.
As an example of a further variation in techniques for providing skew compensation, serpentine edges may be introduced to compensate for skew in both differential and common mode components of signals carried by a pair of conductive elements. In some embodiments, multiple edges in a set may have serpentine profiles, but one or more parameters of the edges may be varied to provide both common mode and differential mode skew compensation.
Such a pattern gives rise to sets of edges for which profiles may be selected to equalize both common mode and differential mode skew. In the example of
As described above, compensation for differential mode skew may be achieved by equalizing the electrical length of edges ES2S1 and ES1S2. In this example, signal conductor 1244B has an average center line that traverses a path that is short than the average center line of signal conductor 1244A. Accordingly, differential mode skew may be equalized by incorporating serpentine features into edge ES2S1 that effectively lengthens edge ES2S1 such that it has approximately the same length as edge ES1S2.
Common mode skew may be compensated by forming edges EG21 and ES2G2 with serpentine features such that each edge has approximately the same electrical length. Additionally, edge ES1G1 should be formed with serpentine features such that it has approximately the same electrical length as edge EG11. Moreover, edge EG21 may be formed with serpentine features that provide edge EG21 with approximately the same length as edge EG11.
Further, the lengths of the edges may be selected to reduce differences in propagation delay between the differential and common mode components. Such compensation may be provided by equalizing any length disparities within each set of edges. In the example of
As described above, parameters such as distance over which the pattern is applied or the amplitude or frequency of the pattern may be varied to increase the amount of tortuosity of an edge and thereby control the amount by which the physical length of the edge is altered by the pattern. In the embodiment of
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art.
As one example, a connector designed to carry differential signals was used to illustrate selective placement of material to achieve a desired level of delay equalization. The same approach may be applied to alter the propagation delay in signal conductors that carry single-ended signals.
Also, as described above, varying degrees of tortuosity may be achieved by varying parameters of features incorporated along the edges of conductive elements. Examples of parameters that can be varied or given. Though, any suitable parameter may be varied to control the length of an edge. Moreover, more than one parameter may be varied from edge to edge. For example, short, inner row conductors may have serpentine features with an amplitude and frequency that is greater than the amplitude and frequency of similar features in longer, outer row conductors.
Also, columns of conductive elements were illustrated by embodiments in which all conductive elements were positive along a centerline of the column. In some scenarios, it may be described to offset some conductive elements relative to the centerline of the column. Accordingly, a column of conductors may refer generally to and conductors that, in cross section, are arranged in a first direction pattern that has one conductor and multiple conductors along a second, transverse direction.
Further, although many inventive aspects are shown and described with reference to a daughter board connector, it should be appreciated that the present invention is not limited in this regard, as the inventive concepts may be included in other types of electrical connectors, such as backplane connectors, cable connectors, stacking connectors, mezzanine connectors, or chip sockets.
As a further example, connectors with four differential signal pairs in a column were used to illustrate the inventive concepts. However, the connectors with any desired number of signal conductors may be used.
Also, impedance compensation in regions of signal conductors adjacent regions of lower dielectric constant was described to be provided by altering the width of the signal conductors. Other impedance control techniques may be employed. For example, the signal to ground spacing could be altered adjacent regions of lower dielectric constant. Signal to ground spacing could be altered in an suitable way, including incorporating a bend or jag in either the signal or ground conductor or changing the width of the ground conductor.
Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
This application is a continuation of U.S. patent application Ser. No. 12/700,291, filed on Feb. 4, 2010, entitled “DIFFERENTIAL ELECTRICAL CONNECTOR WITH IMPROVED SKEW CONTROL,” which claims the benefit under 35 U.S.C. §119(e) to Provisional Application Ser. No. 61/149,799, filed on Feb. 4, 2009, entitled “DIFFERENTIAL ELECTRICAL CONNECTOR WITH IMPROVED SKEW CONTROL.” These applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 61149799 | Feb 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12700291 | Feb 2010 | US |
| Child | 13444593 | US |
