In electronics systems, many devices and techniques have been developed to provide electrostatic discharge (ESD) protection and to provide electromagnetic containment (EMC) or electromagnetic interference (EMI) shielding. Such protection is necessary in systems incorporating printed circuit boards housed within modules where the modules are mounted parallel to each other in a cabinet and connected to a common backplane.
In such systems, each module can be slid in or out of the cabinet. Each module is electronically connected to the backplane through engagement of pins projecting from the backplane with connectors attached to the module. As a module is slid into the cabinet along card guides, the pins of the backplane engage the connectors of the module, just prior to the module being completely slid into the cabinet.
When a user pushes a module into a cabinet, any static built up in the user may be discharged onto the module. It is important that this static be discharged from the module prior to the connectors of the module making contact with the pins of the backplane. Otherwise, the static will travel through the backplane pins toward electronic components connected to those pins and may damage those components.
Another concern associated with such systems is electromagnetic wave energy generated by electronic components within the modules. It is desirable to contain electromagnetic wave energy generated within each module; otherwise the emissions may adversely affect or interfere with the operation of other electronic components.
One technique for providing ESD protection is for the user to wear a wrist strap. Before the user touches a module, the user must attach the wrist strap to a grounded portion of the cabinet to discharge any static built up in the user. However, there are several concerns associated with this technique. First, it requires the user to wear an appropriate wrist strap. Second, it requires the user to remember to attach the wrist strap to the grounded portion of the cabinet before making contact with the module.
EMC is achieved in respect of a module by forming the module with a conductive outer housing providing an EMI shield extending along five sides. The rear side, however, has to be left unshielded because it is provided with connectors which engage with the pins from the backplane. As a result of the fashion in which the backplane pins engage with the connectors of the module, there is a gap between the rear side and the backplane. If no precautions are taken for EMC, electromagnetic wave energy could escape through this gap.
To address this problem, it is known to adhere gaskets along shelves of the cabinet to essentially bridge the gap between the module and the backplane. However, such gaskets tend to have an open end (ie: an end which is not held down) or and end which may not be technically open, but is only loosely held down. After the module has slid over such a gasket a number of times, the open end (or the end that is loosely held down) tends to snag against the moving module, thereby often damaging the gasket.
One technique for providing both ESD protection and EMC, without the user having to wear a wristband, has been suggested in U.S. Pat. No. 5, 311,408, which issued to Ferchau on May 10, 1994 for "Electronic Assembly with Improved Grounding and EMI Shielding." This patent describes a pin (an alignment pin) grounded to the backplane which makes contact with the module just prior to the connector pins of the backplane connecting with the connectors of the module. Thus, the module is grounded prior to the engagement of the pins of the backplane with the connectors of the module. The patent requires an additional separate gasket to provide EMI shielding. However, the assembly described in this patent requires numerous specially designed parts, some of which require relatively precise adjustment to ensure proper engagement of the various parts. It would be desirable to provide ESD protection and EMC without the necessity of using many parts and without requiring involved installation to ensure relatively precise interaction of the various parts.