Form-in-place EMI gaskets

Abstract

A form in place conductive gasket is disclosed. The gasket, foamed, gelled or unfoamed is made of one or more elastomer resins, such as silicone urethane and/or thermoplastic block copolymers and is either filled with a conductive filler and lined onto a desired substrate or lined onto the substrate unfilled and then coated with a conductive utrelayer, such as a silver filled elastomer or a conductive flocked layer. A process and system for making the gaskets are also disclosed.

What we claim:  
     
         1 .) An EMI shielded substrate comprising: 
 a.) a first electrically conductive substrate;    b.) a second electrically conductive substrate adjacent to the first substrate;    c.) a formed in place electrically conductive gasket formed on and bonded to a predetermined portion of the first substrate so as to provide an electrical connection and EMI shielding between the first and second substrates.    
     
     
         2 .) The structure of  claim 1  wherein the first substrate in an enclosure and the second substrate is a cover for the enclosure.  
     
     
         3 .) The structure of  claim 1  wherein the first and second substrates are formed of an electrically conductive material selected from the group consisting of metals, metal plated plastic, metal/plastic laminate and composites, coated plastisols and combinations thereof.  
     
     
         4 .) The substrate of  claim 1  wherein the gasket is formed of an erastomer resin and is rendered electrically conductive by the incorporation of one or more conductive fillers into the resin.  
     
     
         5 .) The substrate of  claim 1  wherein the gasket is formed of an inner and outer layer, at least the outer layer being electrically conductive.  
     
     
         6 .) The structure of  claim 1  wherein the gasket is formed of an elastomer and one or more electrically conductive fillers.  
     
     
         7 .) The structure of  claim 6  wherein the fillers are selected from the group consisting of noble metal-based fillers such as pure silver; noble metal-plated noble metals such as silver plated gold; noble metal-plated non-noble metals such as silver plated copper, nickel or aluminum, for example, silver plated aluminum core particles; noble-metal plated glass, plastic or ceramics such as silver plated glass microspheres, noble-metal plated alumina or noble-metal plated plastic microspheres; noble-metal plated mica; and other such noble-metal conductive fillers. Non-noble metal-based materials are also suitable, including non-noble metal-plated non-noble metals such as copper-coated iron particles or nickel plated copper; non-noble metals, e.g. copper, aluminum, nickel, cobalt; and non-metal materials such as carbon black and graphite and the elastomer is selected from the group consisting of EPDM copolymers, silicone rubbers, fluorosilicone rubbers, urethane rubbers, nitrile rubbers, butyl rubbers, elastomeric thermoplastics, and mixtures thereof.  
     
     
         8 .) The structure of  claim 1  wherein the gasket is formed of silicone gel containing one or more electrically conductive fillers.  
     
     
         9 .) The structure of  claim 1  wherein the gasket has a Shore A hardness of from about 5 to about 60, a force/deflection value of from about 0.2 pounds/inch to 15.0 pounds/inch, electrical resistance value of from about 0.005 ohms to 0.1 ohms, a compression set value of from about 5% to 50% and an EMI shielding effectivenss of from about 10 dbs to about 120 dbs at a frequency range from about 10 MHz to about 10 GHz.  
     
     
         10 .) An EMI shielded substrate comprising: 
 a.) a substrate having an electrically conductive surface;    b.) a cover for the substrate, the cover having an electrically conductive surface which corresponds to and is in register with the conductive surface of the substrate; and    c.) a formed in place electrically conductive gasket formed on and bonded to a predetermined portion of the condudtive surface of the substrate or cover so as to provide an electrical connection and EMI shielding between the substrate and cover upon the mating of the cover to the substrate.    
     
     
         11 .) The substrate of  claim 10  wherein the substrate and cover are formed of an electrically conductive material selected from the group consisting of metals, metal plated plastic, metal/plastic laminates and composites, electrically conductive coated plastics, and combinations thereof.  
     
     
         12 .) The substrate of  claim 10  wherein the gasket is formed of an elastomer resin and is rendered electrically conductive by the incorporation of one or more conductive fillers into the resin.  
     
     
         13 .) The substrate of  claim 10  wherein the gasket is formed of an inner and outer layer and wherein at least the outer layer being electrically conductive.  
     
     
         14 .) A form-in-place EMI gasket comprising a composition formed of a silicone resin, one or more conductive fillers, a curing agent for the resin wherein the composition, when mixed and applied to a substrate, will create a form stable, form-in-place gasket capable of providing EMI shielding of from about 20 dBs to about 80 dBs over a frequency range from 10 MHz to 10 GHz.  
     
     
         15 .) The gasket of  claim 14  wherein the silicone resin is a silicone gel.  
     
     
         16 .) An EMI gasket comprising a composition formed of: 
 a.) a first component which is a primary polymer having end groups that are capable of chemically reacting with each other in the presence of moisture to form a derivative polymer having a longer average chain length than said primary polymer;    b.) a second component which is a noncross-linked elastomer that is not substantially chemically reactive with itself or with said first component; and    c.) a third component which is one or more electrically conductive fillers, wherein when said first, said second, said third components are intimately mixed, said composition, when maintained in the absence of moisture and other active hydrogen donor materials, being readily extrudable and otherwise conventionally moldable thermoplastic composition but, upon exposure to moisture, becoming essentially thermoset.    
     
     
         17 .) The gasket of  claim 16  wherein the first component has a polyester backbone and isocyanate or trialkoxysilyl end groups, and the second component is selected from the group consisting of a styrene-isoprene-styrene block polymer, a styrene-butadiene-styrene block polymer, an isoprene homopolymer, a polyvinyl chloride, polyisobutylene, styrene-ethylene-butylene-styrene, or ethylene-propylene rubber and the third component is selected from the group consisting of noble metal fillers; noble metal-plated noble metals; noble metal-plated non-noble metals; noble-metal plated glass, plastic or ceramics noble-metal plated mica; non-noble metals, non-noble metal-plated non-noble metals; and non-metal materials such as carbon black and graphite and combinations thereof.  
     
     
         18 .) A system for forming EMI shielded enclosures comprising: 
 a.) a support platform;    b.) a compound applicator nozzle located above and in register with the platform;    c.) a supply of electrically conductive compound connected to the applicator nozzle; and    d.) a drive mechanism for moving the nozzle or platform relative to each other in one or more directions of travel.    
     
     
         19 .) The system of  claim 18 , further comprising a second drive mechanism.  
     
     
         20 .) The system of  claim 18  further comprising a curing chamber for curing of the compound after application.  
     
     
         21 .) The system of  claim 20  wherein the chamber is selected from the group consisting of hot air ovens, infrared ovens, light chambers, moisture chambers or combinations thereof.  
     
     
         22 .) The system of  claim 18  further comprising a computer for controlling preprogrammed, respective movements of the nozzle relative to the table so as to create a predetermined gasket configuration.  
     
     
         23 .) A process for forming a form-in-place conductive EMI shielding gasket or a substrate comprising the steps of: 
 a.) providing a substrate to be gasketed;    b.) providing a supply of conductive gasket material;    c.) applying the material to the substrate's surface in a predetermined pattern; and    d.) curing the material in place upon the substrate.    
     
     
         24 .) The process of  claim 23  further comprising applying a primer to the substrate before step (c).  
     
     
         25 .) The process of  claim 23  wherein the gasketing material is formed of a conductive filled resin, the resin being selected from the group consisting of silicone, urethanes, thermoplastic elastomers and mixtures thereof; the fillers being selected from the group consisting of noble metal fillers; noble black and graphite and combinations thereof; and the substrate is an electrically conductive material selected from the group consisting of metals, metal composites, metal coated plastics and metal laminates.  
     
     
         26 .) The process of  claim 23  wherein the curing occurs via a curing agent, a cross linking agent, heat, light, moisture or combinations thereof.