Electrical connectors – Electromagnetic or electrostatic shield – Multi-part shield body
Reexamination Certificate
1999-08-26
2001-05-29
Donovan, Lincoln (Department: 2832)
Electrical connectors
Electromagnetic or electrostatic shield
Multi-part shield body
C439S108000
Reexamination Certificate
active
06238245
ABSTRACT:
This invention relates generally to electrical connectors used to interconnect printed circuit boards and more specifically to such connectors designed to carry many high speed signals.
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 which are then joined together with electrical connectors. A traditional arrangement for joining several printed circuit boards is to have one printed circuit board serve as a backplane. Other printed circuit boards, called daughter boards, are connected through the backplane.
A traditional backplane is a printed circuit board with many connectors. Conducting traces in the printed circuit board connect to signal pins in the connectors so that signals may be routed between the connectors. Other printed circuit boards, called “daughter boards” also contain connectors that are plugged into the connectors on the backplane. In this way, signals are routed among the daughter boards through the backplane. The daughter cards often plug into the backplane at a right angle. The connectors used for these applications contain a right angle bend and are often called “right angle connectors.”
Connectors are also used in other configurations for interconnecting printed circuit boards, and even for connecting cables to printed circuit boards. Sometimes, one or more small printed circuit boards are connected to another larger printed circuit board. The larger printed circuit board is called a “mother board” and the printed circuit boards plugged into it are called daughter boards. Also, boards of the same size are sometimes aligned in parallel. Connectors used in these applications are sometimes called “stacking connectors” or “mezzanine connectors.”
Regardless of the exact application, electrical connector designs have generally needed to mirror trends in the electronics industry. Electronic systems generally have gotten smaller and faster. They also handle much more data than systems built just a few years ago. These trends mean that electrical connectors must carry more and faster data signals in a smaller space without degrading the signal.
Connectors can be made to carry more signals in less space by placing the signal contacts in the connector closer together. Such connectors are called “high density connectors.” The difficulty with placing signal contacts closer together is that there is electromagnetic coupling between the signal contacts. As the signal contacts are placed closer together, the electromagnetic coupling increases. Electromagnetic coupling also increases as the speed of the signals increase.
In a conductor, the amount of electromagnetic coupling is indicated by measuring the “cross talk” of the connector. Cross talk is generally measured by placing a signal on one or more signal contacts and measuring the amount of signal coupled to another signal contact. The choice of which signal contacts are used for the cross talk measurement as well as the connections to the other signal contacts will influence the numerical value of the cross talk measurement. However, any reliable measure of cross talk should show that the cross talk increases as the speed of the signals increases and also as the signal contacts are placed closer together.
A traditional method of reducing cross talk is to ground signal pins within the field of signal pins. The disadvantage of this approach is that it reduces the effective signal density of the density of the connector.
To make both a high speed and high density connector, connector designers have inserted shield members between signal contacts. The shields reduce the electromagnetic coupling between signal contacts, thus countering the effect of closer spacing or higher frequency signals. Shielding, if appropriately configured, can also control the impedance of the signal paths through the connector, which can also improve the integrity of signals carried by the connector.
An early use of shielding is shown in Japanese patent disclosure 49-6543 by Fujitsu, Ltd. dated Feb. 15, 1974. U.S. Pat. Nos. 4,632,476 and 4,806,107—both assigned to AT&T Bell Laboratories—show connector designs in which shields are used between columns of signal contacts. These patents describe connectors in which the shields run parallel to the signal contacts through both the daughter board and the backplane connectors. Cantilevered beams are used to make electrical contact between the shield and the backplane connectors. U.S. Pat. Nos. 5,433,617; 5,429,521; 5,429,520 and 5,433,618—all assigned to Framatome Connectors International—show a similar arrangement. The electrical connection between the backplane and shield is, however, made with a spring type contact.
Other connectors have the shield plate within only the daughter card connector. Examples of such connector designs can be found in U.S. Pat. Nos. 4,846,727; 4,975,084; 5,496,183; 5,066,236—all assigned to AMP, Inc. An other connector with shields only within the daughter board connector is shown in U.S. Pat. No. 5,484,310, assigned to Teradyne, Inc.
From the number of patents that describe connectors using shielding to reduce cross talk, it will be appreciated that the placement and connection of the shields can have a great effect on the electrical performance of the connector. The specific configuration of the shielding can also have a significant impact on the mechanical properties of the connector. For example, the manner in which the electrical connection is made to the shield can influence whether there is “stubbing” when the connectors are mated. Stubbing means that one contact gets caught on another contact. When there is stubbing, one of the contacts is usually damaged, requiring that the connector be repaired or replaced.
It would be highly desirable to have a shield arrangement that is highly effective at reducing the cross talk between signal contacts. It would be also highly desirable if the shielding arrangement were mechanically robust. It would also be desirable if that connector were easy to manufacture. It would further be highly desirable to control signal reflections by controlling the geometry of the shields and signal contacts for impedance matching the connection.
SUMMARY OF THE INVENTION
With the foregoing background in mind, it is an object of the invention to provide a high speed, high density connector.
It is a further object to provide a high performance connector that allows all of its signal contacts to be used for carrying signals.
It is also an object to provide an electrical connector that is mechanically robust.
It is a further object to provide a connector that is easy to manufacture.
The foregoing and other objects are achieved in an electrical connector having shield plates between rows of signal contacts in both the daughter board and backplane connectors. The shield plates in the backplane connector have torsional contacts. The torsional contacts significantly reduce the chance of stubbing. They also provide a highly desirable pattern of current flow through the shields, which increases their effectiveness at reducing inductive coupling between signal contacts and the resulting cross talk.
REFERENCES:
patent: 4869677 (1989-09-01), Johnson et al.
patent: 5904594 (1999-05-01), Longueville et al.
patent: 486298 (1991-11-01), None
Allen Steven J.
Cohen Thomas
Stokoe Philip T.
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