Shieldless, high-speed electrical connectors

Abstract

An electrical connector having a leadframe housing, a first electrical contact fixed in the leadframe housing, a second electrical contact fixed adjacent to the first electrical contact in the leadframe housing, and a third electrical contact fixed adjacent to the second electrical contact in the leadframe housing is disclosed. Each of the first and second electrical contacts may be selectively designated, while fixed in the lead frame housing, as either a ground contact or a signal contact such that, in a first designation, the first and second contacts form a differential signal pair, and, in a second designation, the second contact is a single-ended signal conductor. The third electrical contact may be a ground contact having a terminal end that extends beyond terminal ends of the first and second contacts.

Description

FIELD OF THE INVENTION

Generally, the invention relates to the field of electrical connectors. More particularly, the invention relates to an electrical connector having linear arrays of electrical contact leads wherein the connector is devoid of electrical shields between adjacent linear arrays.

BACKGROUND OF THE INVENTION

Electrical connectors provide signal connections between electronic devices using signal contacts. Often, the signal contacts are so closely spaced that undesirable interference, or “cross talk,” occurs between adjacent signal contacts. As used herein, the term “adjacent” refers to contacts (or rows or columns) that are next to one another. Cross talk occurs when one signal contact induces electrical interference in an adjacent signal contact due to intermingling electrical fields, thereby compromising signal integrity. With electronic device miniaturization and high speed, high signal integrity electronic communications becoming more prevalent, the reduction of cross talk becomes a significant factor in connector design.

One commonly used technique for reducing cross talk is to position separate electrical shields, in the form of metallic plates, for example, between adjacent signal contacts. The shields act to block cross talk between the signal contacts by blocking the intermingling of the contacts' electric fields. FIGS. 1A and 1B depict exemplary contact arrangements for electrical connectors that use shields to block cross talk.

FIG. 1A depicts an arrangement in which signal contacts S and ground contacts G are arranged such that differential signal pairs S+, S− are positioned along columns 101-106. As shown, shields 112 can be positioned between contact columns 101-106. A column 101-106 can include any combination of signal contacts S+, S− and ground contacts G. The ground contacts G serve to block cross talk between differential signal pairs in the same column. The shields 112 serve to block cross talk between differential signal pairs in adjacent columns.

FIG. 1B depicts an arrangement in which signal contacts S and ground contacts G are arranged such that differential signal pairs S+, S− are positioned along rows 111-116. As shown, shields 122 can be positioned between rows 111-116. A row 111-116 can include any combination of signal contacts S+, S− and ground contacts G. The ground contacts G serve to block cross talk between differential signal pairs in the same row. The shields 122 serve to block cross talk between differential signal pairs in adjacent rows.

Because of the demand for smaller, lower weight communications equipment, it is desirable that connectors be made smaller and lower in weight, while providing the same performance characteristics. Shields take up valuable space within the connector that could otherwise be used to provide additional signal contacts, and thus limit contact density (and, therefore, connector size). Additionally, manufacturing and inserting such shields substantially increase the overall costs associated with manufacturing such connectors. In some applications, shields are known to make up 40% or more of the cost of the connector. Another known disadvantage of shields is that they lower impedance. Thus, to make the impedance high enough in a high contact density connector, the contacts would need to be so small that they would not be robust enough for many applications.

The dielectrics that are typically used to insulate the contacts and retain them in position within the connector also add undesirable cost and weight.

Therefore, a need exists for a lightweight, high-speed electrical connector (i.e., one that operates above 1 Gb/s and typically in the range of about 10 Gb/s) that reduces the occurrence of cross talk without the need for separate shields, and provides for a variety of other benefits not found in prior art connectors.

SUMMARY OF THE INVENTION

An electrical connector according to the invention may include a plurality of differential signal contact pairs arranged along a first centerline or row, a second centerline or row, and a third centerline or row, the first centerline or row arranged adjacent and parallel to the second centerline or row and the third centerline or row arranged adjacent and parallel to the second centerline or row, (i) wherein each of the plurality of differential signal pairs comprises two electrical contacts; (ii) the two electrical contacts each define a broad side and an edge and are arranged broadside-to-broadside; (iii) each of the differential signal pairs arranged along the second centerline or row are offset from differential signal pairs arranged along the first centerline or row and the differential signal pairs arranged along the third centerline or row; (iv) the electrical connector is devoid of shields between the first centerline or row, the second centerline or row, and the third centerline or row; and (v) a ground contact is positioned at one end of the first centerline or row and on an opposite end of the second centerline or row.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B depict exemplary contact arrangements for electrical connectors that use shields to block cross talk.

FIG. 2 depicts a conductor arrangement in which signal pairs are arranged along centerlines.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Certain terminology may be used in the following description for convenience only and should not be considered as limiting the invention in any way. For example, the terms “top,” “bottom,” “left,” “right,” “upper,” and “lower” designate directions in the figures to which reference is made. Likewise, the terms “inwardly” and “outwardly” designate directions toward and away from, respectively, the geometric center of the referenced object. The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import.

Any or all of the following factors may be considered in determining a suitable contact arrangement for a particular connector design:

a) Less cross talk has been found to occur where adjacent contacts are edge-coupled (i.e., where the edge of one contact is adjacent to the edge of an adjacent contact) than where adjacent contacts are broad side coupled (i.e., where the broad side of one contact is adjacent to the broad side of an adjacent contact) or where the edge of one contact is adjacent to the broad side of an adjacent contact. The tighter the edge coupling, the less the coupled signal pair's electrical field will extend towards an adjacent pair and the less towards the unity height-to-width ratio of the original I-shaped theoretical model a connector application will have to approach. Edge coupling also allows for smaller gap widths between adjacent connectors, and thus facilitates the achievement of desirable impedance levels in high contact density connectors without the need for contacts that are too small to perform adequately. For example, it has been found that a gap of about 0.3-0.4 mm is adequate to provide an impedance of about 100 ohms where the contacts are edge coupled, while a gap of about 1 mm is necessary where the same contacts are broad side coupled to achieve the same impedance. Edge coupling also facilitates changing contact width, and therefore gap width, as the contact extends through dielectric regions, contact regions, etc.;

b) It has also been found that cross talk can be effectively reduced by varying the “aspect ratio,” i.e., the ratio of column pitch (i.e., the distance between adjacent columns) to the gap between adjacent contacts in a given column;

c) The “staggering” of adjacent columns relative to one another can also reduce the level of cross talk. That is, cross talk can be effectively limited where the signal contacts in a first column are offset relative to adjacent signal contacts in an adjacent column. The amount of offset may be, for example, a full row pitch (i.e., distance between adjacent rows), half a row pitch, or any other distance that results in acceptably low levels of cross talk for a particular connector design. It has been found that the optimal offset depends on a number of factors, such as column pitch, row pitch, the shape of the terminals, and the dielectric constant(s) of the insulating material(s) around the terminals, for example. It has also been found that the optimal offset is not necessarily “on pitch,” as was often thought. That is, the optimal offset may be anywhere along a continuum, and is not limited to whole fractions of a row pitch (e.g., full or half row pitches).

d) Through the addition of outer grounds, i.e., the placement of ground contacts at alternating ends of adjacent contact columns, both near-end cross talk (“NEXT”) and far-end cross talk (“FEXT”) can be further reduced.

e) It has also been found that scaling the contacts (i.e., reducing the absolute dimensions of the contacts while preserving their proportional and geometric relationship) provides for increased contact density (i.e., the number of contacts per linear inch) without adversely affecting the electrical characteristics of the connector.

By considering any or all of these factors, a connector can be designed that delivers high-performance (i.e., low incidence of cross talk), high-speed (e.g., greater than 1 Gb/s and typically about 10 Gb/s) communications even in the absence of shields between adjacent contacts. It should also be understood that such connectors and techniques, which are capable of providing such high speed communications, are also useful at lower speeds. Connectors according to the invention have been shown, in worst case testing scenarios, to have near-end cross talk of less than about 3% and far-end cross talk of less than about 4%, at 40 picosecond rise time, with 63.5 mated signal pairs per linear inch. Such connectors can have insertion losses of less than about 0.7 dB at 5 GHz, and impedance match of about 100.+−0.8 ohms measured at a 40 picosecond rise time.

Alternatively, as shown in FIG. 2, differential signal pairs may be arranged along rows and first, second, and third centerlines CL1, CL2, and CL3. As shown in FIG. 2, each row 511-516 comprises a repeating sequence of two ground conductors and a differential signal pair. First row 511 comprises, in order from left to right, two ground conductors G, a differential signal pair S1+, S1−, and two ground conductors G. Row 512 comprises in order from left to right, a differential signal pair S2+, S2−, two ground conductors G, and a differential signal pair S3+, S3−. The ground conductors block cross talk between adjacent signal pairs. In the embodiment shown in FIG. 2, arrangement of 36 contacts into rows provides only nine differential signal pairs collectively alone first centerline CL1, second centerline CL2, and third centerline CL3.

It can be understood that a column arrangement of differential signal pairs results in a higher density of signal contacts than does a row arrangement. However, for right angle connectors arranged into columns, contacts within a differential signal pair have different lengths, and therefore, such differential signal pairs may have intra-pair skew. Similarly, arrangement of signal pairs into either rows or columns may result in inter-pair skew because of the different conductor lengths of different differential signal pairs. Thus, it should be understood that, although arrangement of signal pairs into columns results in a higher contact density, arrangement of the signal pairs into columns or rows can be chosen for the particular application.

Regardless of whether the signal pairs are arranged into rows or columns, each differential signal pair has a differential impedance Z.sub.0 between the positive conductor Sx+ and negative conductor Sx− of the differential signal pair. Differential impedance is defined as the impedance existing between two signal conductors of the same differential signal pair, at a particular point along the length of the differential signal pair. As is well known, it is desirable to control the differential impedance Z.sub.0 to match the impedance of the electrical device(s) to which the connector is connected. Matching the differential impedance Z.sub.0 to the impedance of electrical device minimizes signal reflection and/or system resonance that can limit overall system bandwidth. Furthermore, it is desirable to control the differential impedance Z.sub.0 such that it is substantially constant along the length of the differential signal pair, i.e., such that each differential signal pair has a substantially consistent differential impedance profile.

The differential impedance profile can be controlled by the positioning of the signal and ground conductors. Specifically, differential impedance is determined by the proximity of an edge of signal conductor to an adjacent ground and by the gap between edges of signal conductors within a differential signal pair.

Through the use of air as the primary dielectric, a lightweight, low-impedance, low cross talk connector can be provided that is suitable for use as a ball grid assembly (“BGA”) right-angle connector. Typically, a right angle connector is “off-balance, i.e., disproportionately heavy in the mating area. Consequently, the connector tends to “tilt” in the direction of the mating area. Because the solder balls of the BGA, while molten, can only support a certain mass, prior art connectors typically are unable to include additional mass to balance the connector. Through the use of air, rather than plastic, as the dielectric, the mass of the connector can be reduced. Consequently, additional mass can be added to balance the connector without causing the molten solder balls to collapse.

A desired differential impedance Z₀ depends on the system impedance and may be 100 ohms or some other value. Typically, a tolerance of about 5 percent is desired; however, 10 percent may be acceptable for some applications. It is this range of 10% or less that is considered substantially constant differential impedance.

In an embodiment of the invention, each contact may have a contact width W of about one millimeter, and contacts may be set on 1.4 millimeter centers C. Thus, adjacent contacts may have a gap width GW between them of about 0.4 millimeters. The IMLA may include a lead frame into or through which the contacts extend. The lead frame may have a thickness T of about 0.35 millimeters. An IMLA spacing IS between adjacent contact arrays may be about two millimeters. Additionally, the contacts may be edge-coupled along the length of the contact arrays, and adjacent contact arrays may be staggered relative to one another.

Generally, the ratio W/GW of contact width W to gap width GW between adjacent contacts will be greater in a connector according to the invention than in prior art connectors that require shields between adjacent contact arrays. Such a connector is described in published U.S. patent application 2001/0005654A1. Typical connectors, such as those described in application 2001/0005654, require the presence of more than one lead assembly because they rely on shield plates between adjacent lead assemblies. Such lead assemblies typically include a shield plate disposed along one side of the lead frame so that when lead frames are placed adjacent to one another, the contacts are disposed between shield plates along each side. In the absence of an adjacent lead frame, the contacts would be shielded on only one side, which would result in unacceptable performance.

Because shield plates between adjacent contact arrays are not required in a connector according to the invention (because, as will be explained in detail below, desired levels of cross-talk, impedance, and insertion loss may be achieved in a connector according to the invention because of the configuration of the contacts), an adjacent lead assembly having a complementary shield is not required, and a single lead assembly may function acceptably in the absence of any adjacent lead assembly.

In summation, the present invention can be a scalable, inverse two-piece backplane connector system that is based upon an IMLA design that can be used for either differential pair or single ended signals within the same IMLA. The column differential pairs demonstrate low insertion loss and low cross-talk from speeds less than approximately 2.5 Gb/sec to greater than approximately 12.5 Gb/sec. Exemplary configurations include 150 position for 1.0 inch slot centers and 120 position for 0.8 slot centers, all without interleaving shields. The IMLAs are stand-alone, which means that the IMLAs may be stacked into any centerline spacing required for customer density or routing considerations. Examples include, but are certainly not limited to, 2 mm, 2.5 mm, 3.0 mm, or 4.0 mm. By using air as a dielectric, there is improved low-loss performance. By taking further advantage of electromagnetic coupling within each IMLA, the present invention helps to provide a shieldless connector with good signal integrity and EMI performance. The stand alone IMLA permits an end user to specify whether to assign pins as differential pair signals, single ended signals, or power. At least eighty Amps of capacity can be obtained in a low weight, high speed connector.

It is to be understood that the foregoing illustrative embodiments have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the invention. Words which have been used herein are words of description and illustration, rather than words of limitation. Further, although the invention has been described herein with reference to particular structure, materials and/or embodiments, the invention is not intended to be limited to the particulars disclosed herein. Rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may affect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects.

Claims

1. An electrical connector, comprising: a plurality of differential signal contact pairs arranged along a first centerline, a second centerline, and a third centerline, the first centerline arranged adjacent and parallel to the second centerline and the third centerline arranged adjacent and parallel to the second centerline,wherein (i) each of the plurality of differential signal pairs comprises two electrical contacts; (ii) the two electrical contacts each define a broadside and an edge and are arranged broadside-to-broadside along at least a majority of the length of the signal pair; (iii) each of the differential signal pairs arranged along the second centerline are offset from differential signal pairs arranged along the first centerline and the differential signal pairs arranged along the third centerline; (iv) the electrical connector is devoid of shields between the first centerline, the second centerline, and the third centerline; (v) a ground contact is positioned at one end of the first centerline and on an opposite end of the second centerline; and (vi) adjacent rows of the signal pairs are staggered in a row direction that is perpendicular to a line direction along which the centerlines extend such that no signal pair of one row aligns with any signal pair of an adjacent row in the line direction.

2. The electrical connector of claim 1, wherein a 0.3 to 0.4 mm gap is defined between each of the two electrical contacts.

3. The electrical connector of claim 1, wherein one of the plurality of differential signal pairs has an impedance of 100Ω, plus or minus ten percent.

4. The electrical connector of claim 1, further comprising ground contacts arranged along the first centerline, the second centerline, and the third centerline.

5. The electrical connector of claim 1, wherein the plurality of differential signal contact pairs arranged along the first centerline terminate in solder balls.

6. The electrical connector of claim 1, further comprising a second ground contact arranged at one end of the second centerline.

7. The electrical connector of claim 6, wherein the ground contact and the second ground contact are arranged on opposite ends of the first centerline and the second centerline.

8. An electrical connector comprising: a plurality of differential signal contact pairs arranged along a first row, a second row, and a third row, the first row arranged adjacent and parallel to the second row and the third row arranged adjacent and parallel to the second row,wherein (i) each of the plurality of differential signal pairs comprises two electrical contacts; (ii) the two electrical contacts each define a broadside and an edge and are arranged broadside-to-broadside along at least a majority of the length of the signal pair; (iii) each of the differential signal pairs arranged along the second row are offset from differential signal pairs arranged along the first row and the differential signal pairs arranged along the third row; (iv) the electrical connector is devoid of shields between the first row, the second row, and the third row; (v) a ground contact is positioned at both ends of the first row and at both ends of the third row; and (vi) adjacent rows of the signal pairs are staggered in a first direction along which the rows extend such that no signal pair of one row aligns with any signal pair of an adjacent row in a second direction that is perpendicular to the first direction.

9. The electrical connector of claim 8, wherein a 0.3 to 0.4 mm gap is defined between each of the two electrical contacts.

10. The electrical connector of claim 8, wherein one of the plurality of differential signal pairs has an impedance of 100Ω, plus or minus ten percent.

11. The electrical connector of claim 8, further comprising additional ground contacts arranged along the second row.

12. The electrical connector of claim 8, wherein the plurality of differential signal contact pairs arranged along the first centerline terminate in solder balls.