Patent Description:
Some electrical systems incorporate a number of electrical modules that are interconnected with one another via a backplane circuit board. Connectors on the modules facilitate insertion of the modules into complementary connectors on the backplane.

Each connector may be configured to couple one or more signals between the electrical module and the backplane. Signals transferred via the connector may be relatively high-frequency signals.

<CIT> discloses a circuit wafer with contact pads engaged by a connector. The electrical contact pad has a first region having a first length in a longitudinal direction, and a second region having a second length in the longitudinal direction that is greater than the first length. The connector includes electrodes wherein each electrode makes contact with a respective contact pad of the connector.

<CIT> discloses a circuit wafer with daughterboard contact pads wherein a contact pad may be engaged by a pair of arms of a connector. The rear of the daughterboard contact pads are connected to backplane contact pads by traces. The rear of the lower edge of the lowermost daughterboard contact pad is chamfered to the trace with the chamfer extending across most of the width of the contact pad.

<CIT> discloses a circuit board with a contact pad that is engaged by first and second arms of an electrical contact. The first contact arm has two points for contacting the contact pad which are separated by a first distance and the second contact arm has two points for contacting the contact pad which are separated by a second distance which is greater than the first distance.

The problem to be solved is that special care must be taken in the construction of the connector to minimize degradation of any signals communicated over the connector.

The solution is provided by a combination of a circuit wafer and a connector as claimed in claim <NUM>.

An electrical contact pad of the circuit wafer may include a first edge region connected to a trace, and an opposing edge region having a chamfered corner. The chamfered corner results in an increase of the impedance of the electrical contact pad, the contact pad typically being a low impedance region.

An electrical connector device may include a bottom housing; a plurality of the circuit wafers of the combination of the circuit wafer and the connector disclosed above disposed within the bottom housing; and a shroud that forms a top of the electrical connector device that is configured to engage the bottom housing to secure the plurality of circuit wafers between the bottom housing and the shroud.

<FIG> illustrates a perspective view of an electrical connector <NUM> formed in accordance with an exemplary embodiment. The electrical connector <NUM> may be one of many disposed on a specialized circuit module to facilitate electrically coupling signals on the circuit module with other circuit modules via a backplane circuit board of a product such RF test equipment and the like.

The connector <NUM> may correspond to a receptacle connector that is configured to be mounted on a circuit board <NUM> which in an exemplary embodiment is a daughter board. The connector <NUM> has a mating face <NUM> and a mounting face <NUM> that includes an interface for mounting the connector <NUM> to the circuit board <NUM>. In an exemplary embodiment, the mounting face <NUM> is substantially perpendicular to the mating face <NUM> such that the receptacle connector <NUM> interconnects electrical components that are substantially at a right angle to each other. The mating face <NUM> of the connector <NUM> defines a backplane connector interface. In one embodiment, the connector <NUM> may be used to interconnect a daughter board to a backplane circuit board. In other embodiments, the connector <NUM> may be configured to interconnect electrical components that are at other than a right angle to each other.

The connector <NUM> includes a dielectric housing <NUM> that has an upper housing portion <NUM> and a lower housing portion <NUM>. The upper housing <NUM> includes upper and lower shrouds <NUM> and <NUM>, respectively, that are proximate the mating face <NUM> of the connector <NUM>. Upper shroud <NUM> and lower shroud <NUM> extend forwardly from upper housing <NUM> in the direction of arrow A, which is also the mating direction of the connector <NUM>. The housing <NUM> includes end openings <NUM> at a first end <NUM> and a second end <NUM>. The upper housing <NUM> and lower housing <NUM> are coupled together, forming an open framework for holding a plurality of wafers <NUM> that are received into the housing <NUM> with a card edge connection. The upper shroud <NUM> and lower shroud <NUM> each include a plurality of slots <NUM> that position and align the wafers <NUM> to facilitate mating with a mating connector (not shown).

The wafers <NUM> include signal contact pads <NUM> and ground contact pads <NUM>, which may have a configuration that corresponds to the configuration of the various contact pad embodiments described above.

The ground contact pads <NUM> have a length measured in the direction of arrow A that is greater than a corresponding length of the signal contact pads <NUM>. In one embodiment, the connector <NUM> is a high-speed connector that carries differential signals, and the signal contact pads <NUM> and ground contact pads <NUM> are arranged in an alternating pattern wherein pairs of signal contact pads <NUM> are separated by a ground contact pad <NUM>. For instance, the wafer 40A starts with a ground contact pad <NUM> adjacent the upper shroud <NUM> and ends with a pair of signal contact pads <NUM> adjacent the lower shroud <NUM>, whereas the adjacent wafer 40B begins with a pair of signal contact pads <NUM> adjacent the upper shroud <NUM> and ends with a ground contact pad <NUM> adjacent the lower shroud <NUM>. Due to their shorter lengths, the signal contact pads <NUM> on the wafer 40B may be hidden by the wafer 40A in <FIG>. However, the alternating nature of the pattern is revealed by the positioning of the ground contact pads <NUM>. The pattern of signal and ground contact pads alternates from wafer to wafer in the connector <NUM>. The connector <NUM> is modular in construction and, in the embodiment shown in <FIG>, includes twelve wafers <NUM> with a total of <NUM> differential signal pairs of contact pads. It is to be understood, however, that in alternative embodiments, a greater or fewer number of the wafers <NUM> may be used. The wafers <NUM> project from the shrouds <NUM> and <NUM> and may be vulnerable to damage from an electrostatic discharge (ESD). One purpose of the ground contact pads <NUM> is to provide ESD protection for the signal contact pads <NUM>.

<FIG> is a front view of an exemplary wafer <NUM> illustrating a wafer first side <NUM>. The wafer <NUM> includes a mating end <NUM> that has a forward mating edge or backplane edge <NUM>. The mating end <NUM> is configured to mate with a mating connector which may be a backplane connector (not shown). The wafer <NUM> also includes a mounting edge or daughter board edge <NUM> that is received in the lower housing <NUM> (<FIG>) at the interface with the circuit board <NUM> (<FIG>). The mounting edge <NUM> is substantially perpendicular to the mating edge <NUM>. The wafer <NUM> has chamfered corners <NUM> at the mating end <NUM> to facilitate the mating process with the mating connector.

In an exemplary embodiment, the wafer <NUM> is a printed circuit board wafer. The wafer <NUM> includes a number of signal and ground contact pads <NUM> and <NUM>, respectively, arranged along the mating edge <NUM> and a number of signal contact pads <NUM> and ground contact pads <NUM> along the mounting edge <NUM>.

Due to their shorter length, the signal contact pads <NUM> are recessed rearward from the wafer mating edge <NUM> with respect to the ground contact pads <NUM>. Conductive signal traces <NUM> interconnect the signal contact pads <NUM> and <NUM> on the mating edge and mounting edge <NUM> and <NUM>, respectively. Ground contact traces <NUM> interconnect the ground contact pads <NUM> at the mating edge <NUM> of the wafer <NUM> with ground contact pads <NUM> at the mounting edge <NUM>. However, there need not be a strict one-to-one relationship between ground contact pads <NUM> and <NUM>. The wafer <NUM> has contact pads <NUM>, <NUM>, <NUM>, and <NUM> and signal traces <NUM> only on the first side <NUM>.

While the contact pads <NUM> and <NUM> are illustrated as having generally rectangular shapes, in various preferred embodiments, the contact pads <NUM> and <NUM> may have an asymmetrical contact area and may have a generally asymmetrical shape to improve the impedance characteristics of the contact pads, as illustrated in <FIG>, <FIG>, and <FIG>.

<FIG> are perspective and top views, respectively, of electrical connectors <NUM> resting upon a contact pad <NUM>. Each electrical connector <NUM> includes a pair of contact arms 302a,b. Each arm 302a,b includes a pair of contact points 310a,b of which the contact points 310a,b of a first contact arm 302b are illustrated. As more clearly shown in <FIG>, the spacing between the contact points 310a,b of the first contact arm 302a is less than the spacing between the contact points 310a,b of the second contact arm 302b.

<FIG> illustrates a first exemplary contact pad embodiment <NUM> that may be utilized with the connector above. The contact pad <NUM> may include a first region 405a having a first length, D1, of between about <NUM> in a longitudinal direction of the contact pad <NUM>, and a second region 405b having a second length, D3, of about <NUM> in the longitudinal direction. The second length, D3, is greater than the first length, D1. In the exemplary implementation, the first region 405a is arranged to contact the first arm 302a of the connector <NUM>, and the second region 405b is arranged to contact the second arm 302b of the connector <NUM>.

The length, D1, of the first region 405a may be selected to facilitate contact with the two points of the first contact arm 302a, illustrated in <FIG>. The two points may be separated by a distance, D2, of about <NUM>. The length, D1, may be selected to be just large enough to accommodate variability in the location at which the points of the first contact arm 302a may contact the first region. For example, D1 may be <NUM>% larger than D2. Likewise, the length, D3, of the second region 405b may be selected to facilitate contact with the two points of the second contact arm 302b. The two points of the second arm 302b may be separated by a distance, D4, of about <NUM>. Distance D2 is smaller than distance D4. Thus, as illustrated, the regions may be sized accordingly to minimize the surface area of the contact pad as opposed to a traditional contact pad having a rectangular shape designed to make contact with all four points of the connector. This reduced surface area of the improved contact pad <NUM> increases the impedance of the contact pad <NUM> which in turn improves the impedance and frequency response characteristics at the location of the contact pad <NUM> as compared to typical contact pads which tend to correspond to low impedance regions.

<FIG> illustrates a second exemplary contact pad implementation <NUM> that may be utilized with a connector above having two contact arms. As illustrated, the contact pad <NUM> may include first and second regions 505a,b for contacting contact points of the arms of the connector. In the second implementation, the longitudinal lengths of the two regions 505a,b may be the same or different. In addition, the center axis of the two regions 505a,b may be offset from one another by a distance, O, of about <NUM>. Thus, as illustrated, the regions may be sized accordingly to minimize the surface area of the contact pad. The reduced surface area of the improved contact pad increases the impedance of the contact pad <NUM> which, in turn, improves the impedance and frequency response characteristics at the location of the contact pad <NUM> as compared to typical contact pads which tend to correspond to low impedance regions.

<FIG> illustrates an exemplary implementation of a differential pair of contact pads <NUM> and <NUM>, placed adjacent to one another, that may be utilized with a pair of the above-described connectors. The first contact pad <NUM> includes a first edge region <NUM> connected to a trace <NUM>. An opposing edge region <NUM> includes a chamfered corner <NUM>. The radius of the chamfered corner <NUM> may be about <NUM> times the radius of the other corners of the electrical pad, which may be less than about <NUM>. Applicant unexpectedly found that when the side of the contact pad <NUM> nearest the ground layer and opposite the trace side edge is chamfered, as illustrated, the impedance between the contact pads increases from <NUM>Ω with no chamfering to <NUM>Ω with chamfering, where an impedance of <NUM> ohms for the particular application was considered ideal.

In some implementations, the second contact pad <NUM> may chamfered on the edge <NUM> of the contact pad <NUM> nearest the first contact pad <NUM> at one or both ends, as illustrated. Applicant unexpectedly found that this modification further increases the impedance between the first contact pad <NUM> and the second contact pad <NUM>.

Claim 1:
A combination of a circuit wafer (<NUM>) and a connector (<NUM>),
the circuit wafer (<NUM>) including an electrical contact pad (<NUM>), the electrical contact pad comprising a first region (405a) having a first length (D1) in a longitudinal direction;
the electrical contact pad (<NUM>) includes a second region (405b) having a second length (D3) in the longitudinal direction that is greater than the first length (D1); and
the connector (<NUM>) including a first contact arm (302a) and a second contact arm (302b), the first region (405a) contacts the first contact arm (302a) of the connector (<NUM>) and the second region (405b) contacts the second contact arm (302b) of the connector,
characterized in that
the electrical contact pad (<NUM>) is a signal or ground pad;
the first length (D1) facilitates contact with two points (310a, 310b) of the first contact arm (302a), which are separated by a first distance (D2) wherein the first length (D1) of the first region (405a) is greater than the first distance (D2), and the second length (D3) facilitates contact with two points (310a, 310b) of the second contact arm (302b), which are separated by a second distance (D4) that is greater than the first distance (D2) wherein the second length (D3) of the second region (405b) is greater than the second distance (D4); and
the first region (405a) and the second region (405b) are joined by a chamfered region.