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Self-Contained, Self-Secured Grounding Spring Providing EMC Shielding Between Plastic And/Or Metal Covers And Enclosures

IP.com Disclosure Number: IPCOM000102245D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 6 page(s) / 200K

Publishing Venue

IBM

Related People

Dewitt, JR: AUTHOR [+3]

Abstract

This article describes the use of metal spring devices to provide a means for electrical continuity between a computer system unit enclosure and cover at multiple points along the enclosure/cover interface to satisfy electromagnetic compatibility (EMC) requirements.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Self-Contained, Self-Secured Grounding Spring Providing EMC Shielding Between Plastic And/Or Metal Covers And Enclosures

       This article describes the use of metal spring devices to
provide a means for electrical continuity between a computer system
unit enclosure and cover at multiple points along the enclosure/cover
interface to satisfy electromagnetic compatibility (EMC)
requirements.

      Because the trend in the industry is pushing towards faster and
higher frequency devices, and therefore higher magnitudes of EMI, the
design standards to accomplish acceptable EMC criteria continue to
rise.  Due to the increasing concern, the Federal Communications
Commission (FCC) and overseas organizations, have set, and are
enforcing, regulations to help maintain a clean electronic
environment.

      In the design of an electronic device, in order to maintain
this EMC criteria, it is necessary to shield the critical inner
components with a sealed enclosure of highly conductive material.
However, typical of most electronic devices, their packaging
incorporates removable covers which creates joints that corrupt the
machine's seal as well as its EMC integrity.  In order to maintain
the EMC at these joints, conductive contact between the cover and the
base enclosure must be made along the entire joint at distances of no
more than 1/20th of a signal's wavelength.  Typically, in today's
computers, this distance is approximately one inch.

      To overcome this design obstacle, industry has approached this
problem with a variety of mechanical fasteners and spring devices.
The most reliable, but the most impractical, would be a series of
screws along the perimeter of the joint.  This would insure the
required contact but would cause difficulties during
removal/installation of the covers.  The most typical solution used
by industry is through the use of finger stock strips stamped from
highly conductive material.  These strips are normally welded or heat
staked at the joint to a mating edge of the cover or base enclosure
and achieve contact through the fingers when the cover is assembled.
Functionally, these meet the requirements. However, when the joint is
exposed with the cover off, the spring fingers are susceptible to
damage and deformation through exposure.  The spring devices
disclosed herein are made of stainless steel and can be mounted to
either plastic or metal covers/enclosures and can be obtained in
strip form of any required length.  They are self-contained, offering
consistent spring contact and high resistance to deformation.

      Referring to the drawings, Fig. 1 is a perspective view showing
a system unit with its cover removed as viewed from above, to the
front and to the right.  Fig. 2 is a blownup sectional view showing
the mating edges of the unit cover and enclosure typical of the
entire cover perimeter.

      Fig. 3 isometrically shows an assembly view of the cover as
viewed from above, to th...