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Flexible Electrically Conductive EMI Envelope Enclosure for Printed Circuit Cards

IP.com Disclosure Number: IPCOM000031489D
Original Publication Date: 2004-Sep-27
Included in the Prior Art Database: 2004-Sep-27
Document File: 3 page(s) / 334K

Publishing Venue

IBM

Abstract

Construction of Electromagnetic (EMC) and electrostatic discharge (ESD) enclosures for computing equipment encounters various problems due to effectiveness against electromagnetic radiation, ease-of-implementation, and increased manufacturing and bill of material costs. These problems are compounded for small form factors found in mobile computing devices. The available space within the plastic enclosure leaves little room to form a tight fitting rigid metal shield (such as stainless steel). Other electrically conductive plating methods such as copper spray represent environmental hazards. The solution to these problems is a novel enclosure that is flexible, conforms to the dimension of a printed circuit board (PCB), and completely seals the PCB with no slot openings or gaps in electrical conductivity.

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Flexible Electrically Conductive EMI Envelope Enclosure for Printed Circuit Cards

     The basic implementation of the flexible enclosure uses conductive foil with or with out mylar backing for electrical insulation. A single piece of material is cut and folded, then seam sealed with perforations to provide electrical conductivity; in essence a three dimensional envelope. The seams can have adhesive applied for further mechanical robustness as required. See figure 1. The foil envelope is designed to confirm to the dimensions of the required printed circuit board and will have apertures positioned to coincide with externally mating connectors or switches.

      A conductive clip is used to connect the foil envelope with the PCB connectors to electrically seal this opening; see figure 2. A major source of intermittency in ESD (Electro Static Discharge) and EMC (Electromagnetic Compatibility) performance is lack of positive contact between I/O connector housings and the conductive enclosure. The conductive clip is designed to squeeze the flexible material together with the I/O connector faces. A rigid metal I/O connector bracket attached to the PCB connectors aids in this contact between the two surfaces.

      The enclosure may be fabricated to confirm to the topology of the assembled PCB to provide minimum clearance within an outer plastic or non conductive enclosure; see figure 3 and 4. The flexible conductive envelope is ideally suited for small form factor devices which do not re...