MXPA00009544A - Surface mount technology compatible emi gasket and a method of installing an emi gasket on a ground trace - Google Patents

Abstract

A surface mount technology compatible electromagnetic interference (EMI) gasket assembly includes an electrically conductive gasket material, a solderable electrically conductive support layer, and an adhesive or other mechanical assembly for affixing the electrically conductive gasket material to the support layer.

Description

MOUNTING SURFACE TECHNOLOGY COMFORTABLE WITH EMI PACKAGING AND AN INSTALLATION METHOD OF A EM PAQUE EMI IN A CONNECTION TO EARTH Field of the Invention The present invention generally relates to an improved electromagnetic interference (EMI) package. More particularly, the present invention relates to an EMI package which is compatible with the installation equipment of the mounting surface technology.

BACKGROUND OF THE INVENTION An EMI package is an interface conductive material, which is used to electrically connect an electrically conductive protector with a corresponding section of an electrical connection to ground. Such as a ground connection of a printed circuit board (PCB). Preferably, an EMI package must be highly electrically conductive and conformant. Said interface conductive material is required when joining surfaces of an electronic apparatus that are not dimensioned to fit exactly, such as the openings that are formed in the adjustment hook of the adjustment surfaces. These openings allow internal and external electromagnetic interference (EMI), which can cause the distortion of electronic devices.

Currently, EMI packaging is installed almost exclusively direct to a conductive surface. More particularly, the current manufacturing techniques for the installation of EMI packaging include the following: supplying a conductive paste or conductive liquid material directly on a conductive surface and curing the material supplied on-site; the die cutting of the conductive sheet material having an adhesive backing and then transferring, attaching and adhering the dimensioned material directly to the conductive surface; or mechanically fasten a conductive material to the conductive surface. Although the aforementioned manufacturing and installation techniques are effective in certain cases, the disadvantages associated with these installation and manufacturing techniques include compted, annoying labor and expensive automation equipment; and, the ineffective adhesion to certain conductive surfaces. Additionally, logistical comptions can be caused by multiple shipments and even duptes of parts and materials for processing among a diverse group of suppliers. As the installation of additional equipment for packaging EMI is generally undesirable and requires extensive manpower, technology machines for mounting surfaces (SMT) that are well known, high speed machines, which have a cast shaft in the electronics industry. For example, SMT machines are widely used to assemble printed circuit boards (PCBs) by cell phone manufacturers. As is well understood by those skilled in the art, SMT machines use a vacuum cadence at the end of a high-speed gantry system to collect and place the tape and reel components of the printed circuit boards fed onto the attenuators. of mounting surface on a printed circuit board. These attenuators are generally pre-prepared with solder paste and then sent through a reflow soldering iron (such as an infrared-IR furnace, steam phase or convection furnace) to melt the soldered tips, thereby forming a connection electrical and mechanical.

In an effort to eliminate the use of EMI packaging, "cans" were developed compatible with SMT machines, which are formed in a simple way, or metal protectors that can be soldered to a ground wire of a printed circuit board , thus forming, in effect, a network of electromagnetic induction (Faraday). Therefore, this serves to eliminate the packaging of the entire process. The disadvantages associated with the use of welded cans include, the difficulty in reworking the weld can; the inspection of the components beyond a welding that can be extremely difficult, and when desired in large cans, the lack of flat surface of the cans which prevents the formation of correct welded joints.

Alternatively, spring finger metal contacts can be used, which can be fed into the SMT machine; however, said spring finger metal contacts provide only separate grounding points between a cover, and a ground wire of a printed circuit board, and therefore, are not effective when operating frequencies continue to rise. . The above illustrates the known limitations that exist in the current EMI packaging, and the installation methods of the EMI packaging. Therefore, it will be appreciated that it would be advantageous to provide an improved EMI package focused on solving one or more of the limitations set forth above. Accordingly, a suitable alternative is provided which includes features that will be described in more detail below.

Summary of the Invention The present invention is an advance in the art of EMI packaging beyond what has been known to date. In one aspect of the present invention, an EMI package compatible with the SMT machine is provided having a dimensionally sized electrically conductive package, which is adhered to the molding, fixed to an electrically conductive support material similarly sized. The dimensioned electrically conductive packing material and the electrically conductive support material are placed in an electrical contacting relationship with one another. The electrically conductive support material is of the type of material that effectively forms a bond with a welder. In an alternative embodiment of the present invention, the electrically conductive packaging material itself can be welded, completely eliminating the need for electrically conductive support material. The EMI package of the present invention is uniquely adapted to be installed, using a conventional tape and reel system compatible with the SMT. In such a system, the vacuum head (or fasteners) of the SMT machine collects and places the EMI gasket directly on the ground location, such as a location of a ground wire of a printed circuit board, which has been previously applied the welding paste. In an appropriate manufacturing case, the welder is reflowed so it links the EMI gasket to the ground connection. The EMI packaging assembly can be used individually, or in combination with other similar EMI packages with additional assemblies, in order to form a suitable conductive interface. The electrically conductive packing material can be manufactured from any suitable electrically conductive material, such as EMI packaging material of the GORE-SHIELD® brand, of the type GS500, GS3000 or GS5200, for example. Preferably, the means for fixing the electrically conductive packing material to the support layer comprises a conductive or non-conductive adhesive. The support layer can be manufactured from any suitable welding material. The solder paste can also be supplied in the support layer to effect the securing of the support layer to an object of interest, such as a ground connection, during reflow operations of the solder material. In one embodiment of the present invention, the electrically conductive packing material is manufactured from expandable particles blended in a metal composition, in a polytetrafluoroethylene (PTFE) composition and a conductive metal. Specifically, in one embodiment, the expandable particulate comprises, a polymer shell having a central core comprising a fluid material. The central core may include liquid or a gaseous material. The copolymer shell contains copolymers selected from a group consisting of vinyl chloride and vinylidene chloride; vinyl chloride and acrylonitrile; vinylidene chloride and acrylonitrile; methacrylonitrile and acrylonitrile; and styrene and acrylonitrile. In another embodiment, the expansive particulate comprises unexpanded microspheres containing a blowing agent, wherein the blowing agent comprises from 5 to 30% by weight of microspheres, and is selected from a group consisting of: ethane, ethylene, propane, butane, isobutane, isopentane, neopentane, acetylene, hexane and heptane. Alternatively, the blowing agent may include aliphatic hydrocarbons having an average number of molecules weight of at least 26, and a boiling point or atmospheric pressure of about the same temperature range or below the range of the softening point of the material. resinous of the polymeric shell. In another embodiment of the present invention, the electrically conductive packing material is manufactured from a mixture comprising: electrically conductive particulate; PTFE, in the form of paste, dispersion or powder; and microspheres in the form of a dry powder or solution. Specifically, the mixture is mixed in portions of at least 20 to 90% by volume of conductive particulate, 3 to 15% by volume of microspheres and from 5 to 70% of the volume of PTFE, and preferably 60% by volume conductive particulate, 6% volume of microspheres and 34% volume of PTFE. The electrically conductive particulate may be selected from a group consisting of: metal powder; metal beads; metal fiber and metal flakes. Alternatively, the electrically conductive particulate may be selected from a group consisting of: metals covered with metal; ceramics covered with metal; glass bubbles covered with metal; glass beads covered with metal; and mica flakes covered with metal. In another embodiment of the present invention, the electrically conductive packing material is fabricated from the polytetrafluoroethylene (PTFE) article having an elastomeric material, and electrically conductive particles intermixed therewith.

In another embodiment of the present invention, there is described a method of installing an electromagnetic interference (EMI) assembly assembly on an object of electrically conductive interest, wherein the EMI package assembly is of the type comprising an electrically conductive package, an electrically conductive welding support layer, and means for fixing the electrically conductive package to the support layer. This method comprises the steps of: (a) feeding a plurality of EMI packaging assemblies to a surface mount technology (SMT) machine; (b) collect and select the EMI packaging assembly with a vacuum head or machine fastener (SMT); (c) placing the selected EMI packing assembly on a conductive surface having a welding material placed therebetween; and, (d) reflowing the soldering material. In another embodiment of the present invention, a printable conductive colander adhesive, such as ETO-P EK E2101 manufactured by Epoxy Technology, Inc .; or similar, will serve to adhere the EMI packaging support layer (or the EMI packaging itself) to the ground connection of the printed circuit board. The adhesive, in a very similar way to the soldering material, can be applied with silk over the ground connection in the correct pattern on the ground connection. In this case, the need for the soldering material is completely eliminated, which has certain potential environmental advantages.

In another embodiment of the present invention, a method of direct installation of an EMI package into an electrically conductive object of interest is described, wherein the EMI package is of the type that can be soldered directly to, without a solder support layer. The method comprises the steps of: (a) feeding a plurality of EMI packaging assemblies to a surface mount technology (SMT) machine; (b) the collection of a selected EMI packaging assembly with a vacuum head or machine fastener (SMT); (c) placing the selected EMI packing assembly on the conductive surface that has the welding material placed between them; and (d) reflowing the soldering material. In another embodiment of the present invention, the method of direct installation of an EMI package to an object of electrically conductive interest is described, without the use of welding (and, with or without the support layer). The method comprises the steps of: (a) feeding a plurality of EMI packages or packing assemblies to a surface mount technology (SMT) machine; (b) collecting a selected EMI gasket or packing assembly with a vacuum head or machine fastener (SMT); (c) placing the selected EMI gasket or packaging on the conductive surface that has an adhesive material placed between them; and (d) curing the adhesive material. Accordingly, one purpose of the present invention is to provide an EMI packaging assembly, which can be installed with a standard SMT machine. Another purpose of the present invention is to eliminate the need for specialized EMI packaging installation equipment. Another purpose of the present invention is to provide an EM I packaging installation method, which is simple and allows rapid design changes of the EMI package. Still another purpose of the present invention is to eliminate the need for soldered cans in the design and manufacture of electronic devices.

BRIEF DESCRIPTION OF THE DRAWINGS The above summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the accompanying drawings. For purposes of illustration of the present invention, the embodiments which are currently preferred are illustrated in the drawings. It should be understood, however, that the present invention is not limited to the non-precise distributions and instrumentalisations shown. In the drawings: Figure 1 is an enlarged elevation side view of an EMI packaging assembly of the present invention; Figure 1 A is a more amplified side elevation view of the EMI packaging assembly illustrated in Figure 1 with its component parts partially spaced apart; Figure 1 B is a front elevational view of the EMI packaging assembly illustrated in Figure 1 A; Figures 2 through 5 illustrate front views in elevation of EMI packaging assemblies having different shapes; Figure 6 is a perspective view of an EMI packaging assembly of the present invention; Figure 7 is a perspective view of an EMI packaging assembly illustrated in Figure 6 installed in a ground connection of a printed circuit board (PCB); Figure 8 is a perspective view of a tape and reel assembly used to feed the EMI packaging assemblies in the surface mount technology (SMT) machine (not illustrated); Figure 9 is an elevation view of a vacuum head of an SMT machine holding an EMI packaging assembly ready for installation; Figures 10 to 12 illustrate alternative embodiments of the present invention, in which a support layer of the EMI package assembly extends to form a pair of fingers in the form of a spring; and Figure 13 is a perspective view of a set of EMI packaging assemblies of the present invention.

Detailed Description of the Invention Referring now to the drawings, wherein the similar reference characters designate the corresponding parts in the different Figures, a packing assembly is generally indicated with the number 20 in Figures 1, 1 A and 1 B electromagnetic interference (EMI) of the present invention. As will be explained in more detail below, the EMI 20 packaging assembly can be installed with a standard surface mount technology machine, thus eliminating the need for specialized EMI packaging installation equipment. Figure 1 A shows an amplified side view of an EMI packaging assembly 20, reflecting a preferred embodiment of the present invention. Specifically, the EMI packaging assembly comprises an electrically conductive packing material 22, an electrically conductive welding support layer 24, means (adhesive 26) for fixing the electrically conductive packing material 22 to the support layer 24, and a layer of welding 28 which secures the complete assembly to a conductive surface, such as a ground connection 30 of a printed circuit board 32 (see Figures 1 and 7, which illustrate the printed circuit board 32). One type of electrically conductive packaging material which may be particularly suitable for use in the present invention is the EMI packaging material of the GORE-S HIELD® brand, of the type GS500, GS3000 or GS5200 marketed by W. L. Gore & Associates, Inc of Newark, Delaware. Other suitable electrically conductive packaging materials will be described in greater detail below. The term "weldable", as used in the present invention, will mean a fusion material, bonding or metallurgical bonding with welding to form an electrically conductive connection, connection or interface. The electrically conductive packing material 22 may be rectangular in its cross-sectional view (from one side) as illustrated; however, it can also be round, oval, pointed, wavy, etc. Other shapes of the cross sections of the gaskets 22 are illustrated in Figures 2 through 5, wherein Figure 2 illustrates a rectangular cross section, Figure 3 illustrates a triangular cross section, Figure 4 illustrates a cross-section curve or decreasing and Figure 5 a cross-section in half rectangular shape and half round. Sometimes, the shape of the electrically conductive package is deliberately formed to achieve a desired result, such as the decrease in force required to compress the EMI packaging material with a cover (not shown). This allows smaller screws or even springs to be used to secure the cover to the printed circuit board 32. It should be noted that suitable means for fixing the metal support layer 24 to the electrically conductive mounting material 22 includes, but is not limited to non-conductive adhesives, electrically conductive adhesives, molding or mechanical means, such as a barb assembly, or retaining clips. In the cases in which the adhesive 26 is employed, any suitable adhesive can be used to adhere or fix the electrically conductive packing material 22 to the support layer 24, insofar as the electrical opening is maintained between them. In one embodiment, an electrically conductive, pressure-sensitive acrylic adhesive filled with particles can be used. This adhesive is laminated to the package in the form of a transversal roller, but can be applied directly to the package, or applied in some other way. In fact, the adhesive itself is not necessary to fix the package to the support layer. The present invention only requires some means to electrically and mechanically connect the package to the support layer. The electrically conductive pressure sensitive adhesive is an example to achieve this fixation; however, the adhesive could also be thermal, thermoplastic, etc. Also, the adhesive may not necessarily be electrically conductive, if the backing layer 24 can be made to mechanically touch the gasket 22 in some areas to maintain an electrical path along the z-axis "A". (Figures 1 to 3). Additionally, the electrically conductive packing material 22 can be molded directly to the support material and mechanically secured in some other way (such as with support tests, etc.), thereby eliminating the overall need for an adhesive 26. Any As the case may be, the fastening means must have the ability to withstand the reflow temperatures of the weld and retain its mechanical and electrical properties. The backing layer 24 must impart sufficient hardness to the electrically conductive packing material 22 to allow the assembly to be effectively processed with the SMT machines. Therefore, the support layer 24 can be made of a variety of different materials, such as plastic or metal; however, if it is plastic, it should be chromed with a solderable material such as copper, nickel, gold, silver, tin, etc. If the support layer 24 is made of metal, it should be easily welded, or chromed with a similar metal, such as those described above. The preferred chromium materials are gold, nickel and tin, and are used extensively in the industry. Also the support layer 24 can have any thickness, especially if desirable, that fills an existing aperture in a design. In this way, the thickness of the package 22 can be maintained in a standard thickness, while the thickness of the support layer 24 is modified to accommodate the different designs. Also, the backing layer 24 need not be rectangular in cross section, as would occur if the part were pressed or cut from a sheet metal material. For example, the support layer 24 can be molded into a trapezoidal, parallelogram, etc .; depending on the application. Whichever material the backing layer 24 is made of, it must have the ability to withstand the reflow temperatures of the weld. Figure 6 illustrates an example of assembly of the EMI package 20 contemplated by the present invention. Figure 7 shows a typical printed circuit board 32, with several packing assemblies 20 installed in various locations on the ground wires 30. The assembly 20 is dimensioned as shown only for purposes of illustration, therefore, the assembly 20 can easily be made wider, thicker, longer, thinner, etc. , depending on an application. In the case illustrated in Figure 7, the assemblies 20 are hypothetically shown to be installed strategically in desired locations. Referring now to Figures 8 and 9, Figure 8 illustrates a typical tape and reel section 36, used to feed the EMI packaging assembly 20 into the SMT machine. The assemblies 20 are received in bags 38, which are positioned to allow a vacuum head 40 (Figure 9) of a SMT machine (not illustrated) to have quick and accurate access and collect the assemblies 20 from their respective bags. 38 for placement. This process is illustrated in Figure 9, which reveals a cropped view of the vacuum head 40 in the SMT machine, holding a packing assembly 20 ready for installation. The ground wire 30, in Figure 9, has already been prepared with a sieved welding packing pattern 28, to fit with the support box 24 of the assembly 20. Once the assembly 20 is deposited on the ground wire 30 , the welder is reflowed by any suitable means such as a reflow oven of the welder, for example. Figures 10 through 12 illustrate a pair of alternative embodiments of the present invention. As illustrated in the same, a support layer 24 is extended to act in the shape of a finger similar to a spring 42, which provides an improved metal-to-metal configuration. This extra contact of the support layer 24 provides a lower strength for the entire complete assembly 20 than without it, because the metal or chrome generally has better conductivity than the electrically conductive packing material 22. Used in this configuration, the assembly 20 has the ability to provide improved performance on an assembly that has no extra contacts. In the Figures of the drawings, one embodiment (Figure 10) shows a pair of spring fingers 42 bent at their ends, while the other embodiment (illustrated in Figures 1 1 and 12) shows a single finger 42 at the center. Other configurations similar to those illustrated in Figures 10 to 12 are additionally contemplated. Finally, Figure 13 illustrates a set of assemblies of five EMI 20 pack assemblies, of varying thicknesses, used in combination. This configuration could be used to combat bending in the decks, which have a tendency to deviate from the printed circuit board 32 between the deck adjustment locations. This can provide improved performance on a set of packaging assemblies with identical thicknesses. As stated above, any suitable electrically conductive material can be used in the construction of an EMI package 20 compatible with a SMT machine in accordance with the teachings of the present invention. The embodiments of the suitable conductive packing materials provided below are indicated for purposes of illustration only and are not intended to limit the scope of the present invention.

ELECTRICALLY CONDUCTING PACKAGING MATERIALS A first electrically conductive packing material 22 can be manufactured from an electrically conductive polymer matrix of the type described in detail in FIG.

U.S. Patent No. 5,431, 571, which is incorporated herein by reference. A second suitable electrically conductive packing material 22 can be manufactured from an electrically conductive packing material of the type described in detail in FIG.

U.S. Patent No. 5,286,568, which is incorporated herein by reference. A third suitable electrically conductive packing material 22 can be manufactured from the material of the type described in detail in U.S. Patent No. 5,604,026, which is incorporated herein by reference. A fourth suitable electrically conductive packing material 22 can be an electrically conductive polytetrafluoroethylene (PTFE) article, which has an expandable particulate mixed in the PTFE and the conductive material composition. Specifically, the expandable particulate exhibits intumescence to the application of heat. The expandable particulate is not homogeneous, for example they are not polymeric tips, but rather comprises a polymer shell having a central core comprising a fluid material. An additional feature is that the general dimensions of the expansive particulate increases with the heat at a specific temperature. The hollow polymeric expansive particulate, which is useful, includes those materials comprising a polymer shell and a core of at least one other material, either liquid or gaseous, and more preferably, a liquid material at room temperature, in which it is the polymeric shell, essentially insoluble. A liquid core is advantageous because the degree of expansion is directly related to the volume change of the core material at the expansion temperature. For a gaseous core material, it is expected that the expansion volume can be approximated from the general gas laws. However, the expandable particulate comprising a liquid core material offers the opportunity to provide much larger volume changes, especially in those cases where phase changes take place (for example, the liquid volatilizes in, or near the expansion temperature). A preferred expandable polymeric particulate (also called microspheres, microballoons and microbubbles) may have shells comprising copolymers, such as vinyl chloride and vinylidene chloride and copolymers of vinyl chloride and acrylonitrile, copolymers of vinylidene chloride and acrylonitrile, copolymers of methacrylonitrile and acrylonitrile, and copolymers of styrene and acrylonitrile The additional materials which are worth mentioning are methylmethacrylate copolymers containing about 2% by weight of styrene, copolymers of methylmethacrylate and up to 50% by weight of ethyl methacrylate and copolymers of methyl methacrylate and up to about 70% by weight of orthochlorostyrene The unexpanded microspheres contain fluid, preferably a volatile liquid, for example a blowing agent, which is conventional for microspheres of the type described herein. is 5% to 30% by weight d e the microsphere. The microspheres can be added in different ways, such as dry particles, wet pastes, or in a suspension, for example in an alcohol, such as isopropanol. Desirably, the unexpanded particles have a size range of from about 0.1 microns to about 600 microns, preferably from 0.5 microns to 200 microns, and more preferably from 1 microns to 100 microns. The expanded particulate can have a size in a range of from about 0.12 micrometers to 1000 micrometers, preferably from 1 micrometer to 600 micrometers. After expansion, the volume of the expanded particulate increases by a factor of at least 1.5, preferably by a factor of at least 5, and more preferably by a factor of at least 10, and may still be a factor. as high as approximately 100. Suitable microspheres are commercially available from Nobel Industries of Sundsvall, Sweden, under the trademark EXPANCEL®. These microspheres can be obtained in a variety of sizes and shapes, with expansion temperatures that are generally in a range of 80 ° C to 130 ° C. A typical EXPANCEL® microsphere has an average initial diameter of 9 to 17 micrometers, and an average expanded diameter of 40 to 60 micrometers. According to Nobel Industries, the microspheres have an unexpanded real density of 1250 to 1300 kg / m3, and an expanded density of less than 20 kg / m3. It should be understood that the use of the term "expansive energy particulate" as used in the present invention is intended to comprise any elastic hollow container filled with a volatile liquid, which is adapted to expand. Although presently obtained microspheres are essentially ball-shaped particles, adapted to expand, when exposed to an energy source, it should be understood that said microspheres are quite elastic in their expanded form and can be compressed and released ( for example, through extrusion), to achieve the expansion required for the present invention. Additionally, it may be possible to form such products in a variety of different forms, such as tubes, ellipses, cubes, particles, etc. As such, the term "expansive energy particulate" is intended to include all applicable forms and uses of these products known at this time or developed subsequently. A large variety of blowing and lifting agents can be enclosed within the polymer shell of the expandable microspheres. These may be volatile liquid forming agents, such as aliphatic hydrocarbons including ethane, ethylene, propane, butane, isobutane, isopentane, megapentane, acetylene, hexane, heptane or mixtures of one or more of said aliphatic hydrocarbons, preferably having a number molecular weight average of at least 26, and a boiling point at atmospheric pressure, of about the same temperature range and below the range of the softening point of the resinous material of the polymeric shell, when they are saturated with the agent of Blown particular used. The EXPANCEL® microspheres, of type DU091, can be used. This product comprises a colorless dry powder with a particle size in a range of between 10 and 40 micrometers. The shell of these microspheres comprises acrylonitrile while the volatile liquid comprises isopentane. It has been found that by mixing a dry preparation of EXPANCEL® microspheres with a dispersion of PTFE in a similar polymer and then heating the resulting composition, the polymer will undergo expansion in three dimensions to achieve a fibrillated PTFE matrix. According to this embodiment, a precursor material comprising an electrically conductive particulate; PTFE in the form of paste, dispersion or powder; microspheres in the form of dry powder or solution, is mixed in proportions of at least 20 to 90 percent volume of conductive particles from 3 to 15 volume percent of EXPANCEL® microspheres, and from 5 to 70% volume of PTFE with proportions of 60% volume of conductive particulate, 6% volume of EXPANCEL® microspheres, and 34% volume of PTFE being preferred in a form comprising, at least in part, electrically conductive flakes. The mixing can be carried out by any suitable means, including dry mixing of the powders, wet mixing, co-coagulation of the aqueous dispersions, and paste filling, and high-cut mixing, etc. The term "volume percent", as used in the present invention, should mean a percentage of the volume of the precursor material.

The electrically conductive particulate entangled within the resulting PTFE precursor is the main component thereof. The electrically conductive particulate may include, but not limited to, metal powder, metal beads, metal fiber or metal flakes, and may be a metal-coated particulate, such as metal-covered metals, metal-covered ceramics, metal-covered glass bubbles , glass beads covered with metal or mica flakes covered with metal. Preferred conductive metals in the particulate form include, but are not limited to silver, nickel, aluminum, copper, stainless steel, graphite, carbon, gold or platinum. Preferred metal coatings include silver, nickel, copper or gold. Additionally, a combination of two or more conductive particulates can be used. The average size of the conductor flakes can be from about 1 μm to about 200 μm, preferably from about 1 μm to about 100 μm, and more preferably from about 20 μm to about 40 μm. The average size of the conductive powders can be from about 0.5 μm to about 200 μm, preferably from about 0.5 μm to about 100 μm, and more preferably from about 2 μm to about 60 μm.

The aqueous dispersion of PTFE used in the production of the PTFE precursor of the present embodiment should be a milky white suspension of PTFE particulate. Generally, the aqueous PTFE dispersion will contain about 20% to about 70% by weight solids, with the main proportion of said solids being PTFE particles having a particle size in the range of 0.05 microns to about 5.0 microns. Said aqueous dispersions of PTFE can be commercially available in E. l. DuPont de Nemours Company, for example, under the trademark TEFLON® 3636, which is from 18% to 24% by weight of solids, being for most PTFE particles from about 0.05 microns to about 5.0 microns. A thickness of the precursor material described above can be, for example, in a range from about 5 thousandths to about 125 thousandths. Upon heating of the precursor metal, the thickness increases due to expansion of the expandable particulate by energy. The amount of expansion observed depends on several factors, including the percentage of present weight of the expandable energy particulate, the type of expandable energy particle, the molecular weight of the polymeric shell of the expandable energy particle, the roughness, the matrix of PTFE that maintains next to the precursor material. The general thickness of the material of this embodiment can be in a range of from approximately at least 10 thousandths, and preferably from 10 to 100 thousandths, and more preferably from 20 to 60 thousandths, other thicknesses can be achieved. The temperatures necessary for the thermal expansion step to occur depends on the type of polymer comprising the shell of the microsphere and the particular blowing agent used. The general temperature range is from about 40 ° C to about 220 ° C, preferably from 60 ° C to 200 ° C, more preferably from 80 ° C to 190 ° C. In addition to the article of the compound, which has been described above, an alternative embodiment can be made by adding to the precursor material, elastomeric material, such as a silicone elastomer material (eg, dimethylsiloxane). In one embodiment of the present invention, this is accomplished by composing the clot of the fine powder filled with the dimethylsiloxane. An appropriate dimethylsiloxane is Sylgard® of type 1 -4105 or Q1-4010, which can be obtained from Dow Corning. It may also be suitable to use silicone dioxide reinforced with silicone material such as Q3-661, which can also be obtained from Dow Corning. The siloxane is added on a weight basis by weight, and can be diluted with a solvent, such as mineral spirits, for example. In general, the siloxane can be added in amounts ranging from 1% to about 50%, preferably from 5% to about 20%, and more preferably from 10% to about 15%. Other suitable elastomeric materials include, but are not limited to, silicone rubbers, fluorosilicone elastomers, fluorocarbon elastomers, perfluoro elastomers, other fluoroelastomer or polyurethane materials. Subsequently, this precursor material is heated in a range from about 130 ° C to about 190 ° C, not only to achieve the expansion of the precursor material, but to catalyze the siloxane to a cured condition. The resulting article is a continuous and compressible PTFE electrically conductive compound, including a silicone elastomer placed within the article of the compound in a batch mode. The addition of the elastomer material produces a compound with increased z-axis strength, tensile strength and elongation. It also provides some range of elasticity and increases the temperature range of the material that can be used. These desired properties are achieved without sacrificing electrical conductivity, or the softness / compression capacity of the composite article. A fifth suitable electrically conductive packing material 22 includes an electrically conductive polytetrafluoroethylene (PTFE) article which has an elastomeric material and electrically conductive particles intermixed therein. Specifically, the conductive packing material of this embodiment is defined by a plurality of electrically conductive particles and the PTFE in the form of paste, dispersion or powder. The electrically conductive particles and the PTFE are mixed in proportions to achieve a mixture containing from about 50% to 90% of the volume of electrically conductive particles. The mixing can be carried out by any suitable means, including the dry mixture of the powders, the wet mixture, the co-coagulation of the aqueous dispersions and the paste filler or the high-cut mixing, for example. The term "volume percent" as used in the present invention, shall mean a percentage of the total volume of a material or mixture. The electrically conductive particles entangled within the resulting compound is a major component thereof. The electrically conductive particles may include, but are not limited to, metal powder, metal beads, metal fiber or metal flakes, or the particles may be defined by a metal-covered particulate, such as metal covered metals, covered ceramics metal, metal-covered glass bubbles, metal-covered glass beads or metal-covered mica flakes. Preferred conductive materials in particulate form include, but are not limited to silver, nickel, aluminum, copper, stainless steel, graphite, carbon, gold or platinum. Preferred metal coatings include silver, nickel, copper or gold. Additionally, a combination or mixture of two or more of the above may be employed. The average size of the conductor flakes can be from about 1 μm to about 200 μm, preferably from about 1 μm to about 100 μm, and more preferably from about 20 μm to about 40 μm. The average size of the conductive powders can be from about 0.5 μm to about 200 μm, and more preferably from about 2 μm to about 100 μm. The aqueous dispersion of the PTFE used in the production of the article of the electrically conductive compound of this embodiment can be a milky white aqueous suspension of PTFE particles. Generally, the aqueous PTFE dispersion will have a content of from about 20% to about 70% by weight of solids, with the main portion of said solid PTFE particles having a particle size ranging from about 0.05 microns to approximately 5.0 micrometers. Said aqueous suspensions of PTFE have currently been marketed by E. l. DuPont de Nemours Company, for example, under the trademark TEFLON® 3636, in which it is from 18% to 24% by weight of solids, with the majority being PTFE particles of about 0.0 micrometers to about 5.0 micrometers. An elastomeric material, such as a silicone elastomeric material (eg, dimethylsiloxane) is placed inside the conductive packing material. This is accomplished by composing a clot filled with fine powder of PTFE and electrically conductive particles with the elastomeric material. A suitable dimethylsiloxane is Sylgard® of type 1 -4105, or Q1 -4010, which is available from Dow Corning. (It may also be appropriate to use silicone dioxide reinforced silicone material such as Q3-661, which can also be obtained from Dow Corning.). The elastomeric material, such as dimethylsiloxane, is added on a weight basis by weight, and can be diluted with a solvent, such as mineral alcohol. In general, the absorbent material can be added in amounts ranging from about 1% to about 75%, preferably from 5% to about 20%, and more preferably from about 10% to about 15%. Other suitable elastomeric materials include, but are not limited to, silicone rubbers, fluorosilicone elastomers, fluorocarbon elastomers, perfluoro elastomers, fluoroelastomers, polyurethane or ethylene-propylene (EPDM). After the addition of the elastomeric material, the composite article is heated in a range from about 130 ° C to about 190 ° C, to catalyze the elastomeric material in a cured condition. The resulting composite article is a continuous electrical conductive composite article having a main body, which can be sized in any suitable shape and thickness. The addition of the elastomeric material produces a continuous electrical conductive compound with increased z-axis strength and tensile strength. The elastomer also provides a degree of elasticity. These desired properties are achieved without sacrificing electrical conductivity. Although some exemplary embodiments of the present invention have been described in detail, those skilled in the art will readily appreciate that many modifications are possible, without departing materially from the novel teachings and disadvantages, which have been described in the present application. Accordingly, it is intended that all such modifications be included within the scope of the present invention, as defined by the appended Claims.

Claims (12)

R E I V I N D I C A C I O N S Having described the present invention, it is considered as novelty and, therefore, the content of the following CLAIMS is claimed as property:

1 . An electromagnetic interference packing (EMI) assembly compatible with surface mounting technology (SMT), which comprises: an electrically conductive packing material; a solderable electrically conductive support layer; and means for fixing the electrically conductive packing material to the electrically conductive, weldable support layer.

2. The packaging assembly as described in Claim 1, further characterized in that said electrically conductive material comprises at least in part polytetrafluoroethylene.

3. The packaging assembly as described in Claim 1, further characterized in that said electrically conductive packing material is manufactured from an elastomer impregnated with a material selected from a group consisting of silver, nickel, chromium-plated copper, glass covered with silver, graphite-nickel and coal.

4. The packaging assembly as described in Claim 1, further characterized in that said means for securing the electrically conductive packing material to the electrically conductive weldable support layer comprises adhesive.

5. The packaging assembly as described in Claim 4, further characterized in that said adhesive is a conductive adhesive.

6. The packaging assembly as described in Claim 4, further characterized in that said adhesive is made of an electrically conductive adhesive material sensitive to pressure.

7. The packing assembly as described in Claim 1, further characterized in that said electrically conductive, weldable support layer is fabricated from a chromated plastic material with a metal selected from a group consisting of copper, nickel, gold and silver.

8. The packing assembly as described in Claim 1, further characterized in that said electrically conductive, weldable support layer is made of a metal chromed with a metal selected from a group consisting of nickel, gold, silver, copper and tin.

9. The packing assembly as described in Claim 1, further characterized in that it additionally includes a solder material placed on a surface of said solderable electrically conductive support layer.

10. The packaging assembly as described in Claim 1, further characterized in that said weldable electrically conductive support layer has at least one end that terminates beyond the electrically conductive packing material by defining said end, a similar finger to a spring.

1. The packing assembly as described in Claim 1, further characterized in that said electrically conductive packing material is manufactured from an expandable particulate mixed within the polytetrafluoroethylene (PTFE) and the metal conductive composition.

12. A method of installing an electromagnetic interference packing (EMI) assembly on a conductive surface, said EMI packaging assembly being of the type comprising an electrically conductive packing material, a solderable electrically conductive support layer, and media for attaching the conductive package to the support layer, said method comprising the steps of: a) feeding the selected EMI packaging assembly to a surface mount technology (SMT) machine; b) the collection of the selected EM I packing assembly with a vacuum head or machine fastener (SMT); c) the placement of the selected EMI packaging assembly on a conductive surface; d) welding the packing assembly EM I to the conductive surface.