SHIELDING DEVICE FOR VENTILATION PANELS OF ELECTRONIC INSTRUMENTS AND METHOD FOR MANUFACTURE THEREOF

Abstract: An electrical connector comprises a dielectric housing having a terminal receiving cavity and an aperture extending into the housing at an angle with respect to the cavity and open to the cavity. A terminal which is insertable into the cavity has a component mounting surface which is arranged to be aligned with the aperture when the terminal is disposed in the cavity. The terminal and the cavity are configured with cooperating surfaces which guide the terminal during insertion into the cavity such that the component mounting surface does not contact the housing during the insertion, whereby contamination of the component mounting surface is prevented. A method for manufacturing an electromagnetic shielding device suitable for air flow vents of electronic instruments comprises forming a honeycomb and applying a conductive coating thereto.

Description: SHIELDING DEVICE FOR VENTILATION PANELS OF ELECTRONIC INSTRUMENTS AND METHOD FOR MANUFACTURE THEREOF Most electronic instruments and systems consume power thereby generating heat. The heat must be dissipated in some form to maintain acceptable and stable operating temperatures for the electronic instrument. Air flowing over the heat generating components is a common method of dissipating heat. Air flow may be natural flow or forced by way of a fan. It is known that electronic systems are both susceptible to and generate electromagnetic radiation. It is desirable to shield electronic instruments to reduce electromagnetic interference and to reduce electromagnetic emissions. There is a need, therefore, for an electromagnetic shielding device that permits air flow with sufficient volume to cool electronic instruments and systems. Known solutions include metal honeycomb comprising corrugated metal foil strips that are glued, braised, or welded in stacks. The corrugated strips are joined at two points to create a cell, each cell having a hexagonal cross section. Braised or welded honeycombs must be made from brass or steel and are expensive to manufacture. Glued honeycombs may be made of the less expensive aluminum strips, but the glue in prior art is insulating and provides sufficient conductivity in one direction only. Glued honeycomb joints do not conduct electricity in a direction perpendicular to the strip of foil and can result in electromagnetic leakage. Omnidirectional conductivity provides optimum performance rendering glued joints less desirable than the welded or braised joints. There is a need, therefore for a less expensive electromagnetic interference and emission shielding device for air flow vents. U.S. Patent #5,032,689 discloses conventional EM1/RFI shielding vent filter media including honeycomb structures, woven screen panels and expanded or perforated metal. All structures disclosed are believed to be metal in order to provide the necessary conductive feature. Expanded metal is disclosed as the preferred media. Disadvantageously, it is difficult to easily control the cell sizes and cell depth of the media in expanded metal and woven screen. Cell size and cell depth together determine air flow volume, cut-off frequency, and attenuation at the cutoff frequency. There is a need, therefore, for a filter media capable of cost effective manufacture wherein the cutoff frequency and attenuation may be reliably controlled. It is an object of the present invention to fabricate a low cost electromagnetic interference and emission shielding device suitable for air flow vents of electronic instruments and systems. A method of manufacturing an electromagnetic shielding device comprises the steps of forming a plastic honeycomb and applying a conductive coating thereto. A method of fabricating an electromagnetic shielding device comprises the steps of forming a plastic honeycomb, cutting the honeycomb to a desired dimension, disposing a frame around a perimeter of the honeycomb and applying a conductive coating to the honeycomb and frame. It is an advantage of the present invention that an electromagnetic shielding device has a lower fabrication cost than prior art solutions. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a honeycomb comprising an array of polycarbonate tubes according to the teachings of the present invention. Figure 2 is a cross section of the array pictured in Figure 1 of the drawings. Figure 3 is a perspective view of a iTra e and honeycomb for use with an electromagnetic shielding device according to the teachings of the present invention. Figure 4 is a cross sectional view of the frame and honeycomb pictured in Figure 3. An electromagnetic shielding device is made by applying a conductive coating to a honeycomb (1) . In a preferred embodiment the honeycomb (1) comprises an array of polycarbonate tubes (2) as shown in Figure 1, each tube (2) creating a cell of the honeycomb. The tubes (2) are stacked in staggered lines so that each single tube (2) internal to the array has a joint (3) in common with each of six adjacent tubes (2) . The array is formed by cutting polycarbonate tubes (2) to a uniform and appropriate length. The tubeb (2) are vibrated against a planar member. The vibration results in a configuration comprising staggered lines (4) of tubes (2) stacked on top of each other. The center of each tube (2) is collinear with the center of adjacent tubes (2) in a single direction to form the line (4) . The planar member acts as an alignment guide to create a planar face for the honeycomb (1) . The stacked array of loose tubes (2) is captivated to retain alignment and is immersed in a dissolving solution sufficient to partially dissolve the tubes (2) . The array of partially dissolved tubes (2) is removed from the solution and permitted to cure. Curing of the partially dissolved tubes (2) creates the joint (3) at each point on the tube (2) that touches an adjacent tube (2) . The array (1) of tubes resolidifies in fixed relation to each other to create the honeycomb (1) . An embodiment of the honeycomb (l) for use in a preferred embodiment of an electromagnetic shielding device according to the teachings of the present invention is available from Plascore under the name PC Polycarbonate Honeycomb core. The resulting honeycomb (1) can be cut to appropriate dimensions for mounting over an air flow vent in an electronic instrument. The appropriately dimensioned honeycomb (1) fits into a frame (5) that enables mounting of the shielding device over an air flow vent of an electronic instrument for fixed attachment thereto. With specific reference to Figures 3 and 4 of the drawings, the frame (5) is substantially rectangular and has mounting holes (6) around the perimeter of the frame (5) . Each side of the frame (5) comprises a length of polycarbonate material extruded to form a C-shaped cross section as illustrated in Figure 4 of the drawings. Distal ends (7) of the C of the cross section are separated by a distance larger than the thickness of the honeycomb (1) . Frame (5) further comprises compression stop (10) and integral gasket (11) . Each of four lengths comprising the sides of the frame (5) are disposed over the honeycomb (1) to complete the structure of the framed shielding device. The honeycomb (1) and frame (5) are then plated with a conductive coating. The honeycomb (1) and frame (5) are preferably plated with a first layer of copper to provide electrical conductivity. The copper plated honeycomb (1) and frame (5) are then plated with a second layer of nickel to resist corrosion. The copper plating provides conductivity in the X and Y directions simultaneously. The coated frame (5) and honeycomb (1) are mounted over an air flow vent using threaded screws (8) in mounting holes (6) . The integral gasket (11) with the conductive coating is interposed between the frame (5) and the chassis of the electronic instrument. For insertion into an electronic instrument, integral gasket (11) faces the air flow vent of the electronic instrument and contacts a perimeter of the vent opening. Due to its cantilevered configuration, the gasket (11) is cammed toward the electronic instrument as the mounting screws (8) are tightened. The resulting force of the biased gasket (11) provides a positive contact when the shielding device is mounted to the instrument. The compression stop (10) provides for a positive stop to prevent overstressing the integral gasket (11) . The biased conductive gasket assures conductivity from the honeycomb (1) through the frame and to chassis which is important for effective shielding. A forward facing side (9) of the frame (5) flares outwardly slightly to create a lead-in for the honeycomb (1) . As the honeycomb (1) is forced into the opening of the frame's (5) cross section, the honeycomb (1) enters an area wherein the thickness of the honeycomb is slightly greater than the opening of the C and is compressed. This compression provides a frictional retention between the honeycomb and the frame. The inner diameter of each cell of the honeycomb (1) determines the cut off frequency for which the shielding device may be used. The most desirable inner diameter dimension for the tubes of a shielding device according to the teachings of the present invention is selected based upon the wave length of a desired cut off frequency and the desired attenuation for the cut off frequency. A high cutoff frequency suggests a small inner diameter for each cell. A large volume of air flow necessary to maintain a stable operating temperature suggests a large inner diameter for each cell. Specifically a 40dB attenuation at 90 GHz is achieved using a 1/16 inch inner diameter and 2 inch depth for each cell. Other advantages of the invention are apparent from the detailed description by way of example, and from accompanying drawings, and from the spirit and scope of the appended claims.

Claims: CLAIMS 1. An electromagnetic shielding device for air flow vents having a honeycomb structure characterized in that: the honeycomb comprises an array of plastic tubes having a conductive coating disposed thereon. 2. An electromagnetic shielding device as recited in claim 1, wherein said honeycomb has a first layer of copper thereon. 3. An electromagnetic shielding device as recited in claim 2, wherein said copper coated honeycomb has a second layer of nickel thereon. 4. An electromagnetic shielding device as recited in claims 1, 2 or 3 and further comprising a plastic frame enclosing a perimeter of said honeycomb, said honeycomb and frame having a first layer of copper thereon. 5. An electromagnetic shielding dev.ice as recited in claim 4, wherein said frame has a gasket integral to said frame. 6. A method of manufacturing an electromagnetic shielding device comprising the steps of: (1) forming a plastic honeycomb and, applying a conductive coating to said honeycomb. 7. A method of manufacturing an electromagnetic shielding device comprising the steps of forming a plastic honeycomb, cutting the honeycomb to a desired dimension, disposing a frame around a perimeter of said honeycomb wherein the improvement comprises the step of: applying a conductive coating to said honeycomb and said frame. 8. A method of manufacturing an electromagnetic shielding device as recited in claims 6 or 7, wherein the step of applying a conductive coating to said honeycomb further comprises the step of electroplating said honeycomb with copper. . A method of manufacturing an electromagnetic shielding device as recited in claim 8, and further comprising the step of electroplating said copper coated honeycomb with nickel„ 10. A method of manufacturing an electromagnetic shielding device as recited in claims 6, 7, 8 or 9 wherein the step of forming a plastic honeycomb further comprises: assembling an array of plastic tubes, vibrating said tubes against a planar member, partially dissolving said tubes, and curing said partially dissolved tubes to create said honeycomb. 11. A method of manufacturing an electromagnetic shielding device as recited in claim 10 wherein each tube comprises a hollow polycarbonate cylindrical member.

Inventors: PEREGRIM WALTER ANDREW, PEREGRIM, WALTER, ANDREW
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1997
Main classification: H05K9
IPC codes: H05K9