KR20020086586A - Methods and apparatus for emi shielding - Google Patents

Abstract

The present invention relates to a method of manufacturing an electromagnetic interference shielding part for use in a non-conductive housing of an electronic device. In one embodiment, the shield may comprise an electrically nonconductive substrate, such as a thermoformable film, which is coated with an electrically conductive element, such as a stretchable ink or a mixture of stretchable film and conductive fibers. do. In one embodiment, a form in place (FIP) process may be used to form a compressible conductive peripheral gap gasket.

Description

EM eye shielding parts and manufacturing method {METHODS AND APPARATUS FOR EMI SHIELDING}

In general, the term “EMI” should be considered to refer to both EMI and Radio Frequency Interference (RFI) emissions. Further, the term "electromagnetic waves" should generally be considered to refer to electromagnetic waves and wireless high frequencies.

Electronic devices generate undesirable electromagnetic energy that can interfere with the operation of other electronic devices located in close proximity to the electronic device by EMI transmission via radiation and conduction during normal operation. The electromagnetic wave energy may be composed of a wide range of wavelengths and frequencies. To minimize EMI-related problems, an undesired electromagnetic wave energy source can be shielded and electrically grounded. The shield is designed to prevent both the entry and discharge of electromagnetic energy to the housing or other enclosure in which the electronic device is placed. However, such a sheath often has gaps or seams between neighboring access panels and peripheral entrances, so shielding is difficult to achieve effectively. This is because EMI can be transmitted through the gap of the envelope. In addition, where the sheath is a conductive metal sheath, this gap can suppress the desired Faraday cage effect by the discontinuous conductivity of the sheath, which impairs the efficiency of the ground conduction passage through the sheath. In addition, by presenting a level of conductivity in a gap that is significantly different from the gap in the envelope, the gaps can act as slot antennas, thereby making the envelope itself a secondary source of EMI.

Special EMI gaskets have been developed for gaps and perimeters to provide some EMI shielding while permitting the operation of the sheath and the access panel. In order to effectively shield EMI, the gasket must be able to establish a continuous conductive path across the gap in which the gasket is disposed, as well as be able to absorb or reflect EMI. Conventional metal gaskets made of copper with beryllium added are widely used for EMI shielding due to their high level of conductivity. However, due to the inherent electrical resistance of the gasket, some of the shielded electromagnetic field may induce a current in the gasket, in which case the gasket is required to form part of the conductive passageway that allows the induced current to flow to ground. . Failure to properly ground the gasket causes electromagnetic fields to radiate from the side of the gasket opposite the primary EMI field.

In addition to the desired high levels of conductivity and grounding, for gateway applications, EMI gaskets must be elastic to fill the various gap widths and to compensate for gate behavior and may also be caused by metal fatigue, applied compression, or other error behavior. It must be robust to withstand repeated door closures without failure. EMI gaskets also provide a minimum force resistance per unit length for entrance closure when the total length of the EMI gasket shielding a large entrance can easily exceed several meters, and with the nearest structure. It must be formed to ensure deep electrical contact. The gasket is also preferably resistant to galvanic corrosion, which can occur when dissimilar metals are in contact with each other for a long time. Due to the increasing shielding requirements, EMI gasket characteristics require very low resistance and consequently very high conductivity. Low cost, ease of manufacture, and ease of installation are also desirable properties for achieving a wide range of uses and commercial performance.

Conventional metal EMI gaskets, commonly referred to as “copper beryllium finger strips”, comprise a plurality of cantilevered or bridged fingers that form a linear slit. The fingers provide a springing action and a wiping action upon compression. Another type of EMI gasket includes closed-cell foam sponges. The hermetically sealed cell foam sponge has a metal wire mesh knitted over the sponge or a metallized fabric bonded to the sponge. The metal wire mesh can also be knitted over silicon tubing. Without foam or tubular inserts, strips of rolled metal wire mesh are also used.

One problem with metal finger strips is that, in order to ensure a very low entrance closure force, for example, copper finger strips have a thickness of about 0.05 mm (0.002 inch) to about 0.15 mm (0.006 inch) It is made from thin stock. Therefore, when determining the size of a finger strip that is not installed, the height and width of the gap that is already installed, while ensuring proper electrical contact when installed and loaded, are artificially deformed due to overcompression of the finger and thereby Adjustments should be made to prevent the obtained strip error. To improve toughness, the alloy is formed by adding beryllium to copper. However, beryllium not only increases costs but is also considered a carcinogenic substance. Due to their thin structure, the finger strips become weak and can break if handled incorrectly or under heavy pressure. Finger strips also have thin and sharp edges, which are safety hazards for the device and maintenance personnel. Finger strips are also expensive to manufacture because of the costs associated with providing and improving tooling and rolling machines that supply pressure to form the required complex contours. In order to deal with manufacturing or performance issues, new mold presses must be purchased by modifying the design of the finger strip, and generally require improved costs associated with establishing a reliable and high yield manufacturing process. Nevertheless, despite the above limitations, metal finger strips are commercially accepted and widely used. If a manufacturing process is established, a large amount of finger strips can be produced at a relatively low cost.

Another problem with conventional finger strips is that EMI shielding is not effective as the clock speed of electronic products increases. As the clock speed increases, the wavelength of the generated EMI wave decreases. Thus, the waves can penetrate the smaller apertures of the skin and the EMI shield. At lower wavelengths, the slits formed in the finger shield can act as slot antennas, allowing the passage of EMI through the slits, thereby reducing the shielding effectiveness of the shield. Conventional finger strips with linear slits formed between the fingers are less effective in application.

Metallized fabric covered with foam gaskets prevents many device, performance and safety disadvantages of the finger strip. However, they can be relatively expensive to produce due to expensive raw materials. Nevertheless, EMI gaskets made from metallized fabrics with foam cores are particularly popular for devices that primarily consider performance.

As used herein, the term "metalized fabric" refers to those having one or more metal coating layers on a fabric, nonwoven, or open mesh carrier backing or substrate, and their equivalents. For example, US Pat. No. 4,900,618 to O'Connor et al., Incorporated herein by reference, US Pat. No. 4,910,072 to Morgan et al., US Pat. No. 5,075,037 to Morgan et al., And Cribb et al. See US Pat. No. 5,393,928. Metallized fabrics are commercially useful in various metal and fabric carrier support compositions. For example, pure copper on nylon carriers, nickel-copper alloys on nylon carriers, and pure nickel on polyester mesh carriers are registered trademarks of "Advanced Performance Materials" in St. Louis, Missouri. Flectron ^ⓡ can obtain a metallized material. Aluminum foil on polyester mesh carriers is available from "Neptco" located in Porterett, Rhode Island.

The choice of metal depends on the installation of the EMI shield. For example, certain metals may be selected due to the composition of the body metal adjacent to the shell to prevent galvanic corrosion of EMI shielding components that may increase electrical resistance and degrade electrical grounding performance. Metallized tapes are desirable for application convenience in addition to durability.

For example, metallized fabrics such as those described in O'Connor et al., Supra, are generally manufactured by electroless plating such as electroless precipitation of copper or other suitable metal on catalyzed fibers or film substrates. do. Thereafter, one or more additional layers of metal may be electrolessly deposited or electrolytically deposited on copper. By applying these additional layers, the underlying copper layer is prevented from corroding. However, this can increase the resistance, thereby reducing the conductivity and performance of the EMI gasket made in the form described above. On the other hand, an additional nickel layer on the copper provides a harder surface than the underlying copper layer.

The present invention relates to a method of manufacturing an electromagnetic interference (EMI) shielding component and an EMI shielding component manufactured by the method.

1 is a process diagram illustrating various methods of combining a moldable nonconductive substrate with a conductive coating and a FIP gap gasket in accordance with one embodiment of the present invention.

2 schematically illustrates a conductive coating on a thermoformable film.

3A-3C schematically illustrate simple thermoformed EMI shields and more complex thermoformed EMI shields in accordance with embodiments of the present invention.

4A-4C are process diagrams of the step of contouring a thermoformable film.

5 is a table summarizing the surface conductivity and shielding rate of conductive coatings made of various conductive materials and thermoformable materials.

6 schematically depicts a FIP process on a contoured substrate.

In the field of shielding parts for non-conductive enclosures such as molded plastic housings for mobile phones, computers, and the like, two technological developments have been carried out independently for many years. The first technology development is a form in place (FIP) process. For example, U. S. Patent No. 5,822, 729 discloses a method of making a casing that provides a screen for blocking electron radiation, which is incorporated herein by reference in its entirety. The purpose of the FIP process is to manufacture a conductive and compressible rubber-based EMI gasket that can be applied directly to the substrate to be shielded, thereby eliminating the step of attaching the EMI gasket to the product during the manufacturing process of the assembly facility. One problem with the FIP process is the need for relatively complex and expensive dispensing equipment for casting or molding equipment, or assembly equipment. The use of a single component can lead to very low utilization of the distribution device, resulting in a dangerous and potentially uneconomical situation.

The second technological development in the field of EMI shielding is the manufacture of conductive coatings, in particular stretchable conductive coatings, which are highly conductive which can be applied to films or other flexible substrates. And the flexible substrate is later shaped into the desired form without substantial deterioration of conductivity. For example, U.S. Patent No. 5,286,415 discloses a water-based polymer thick film conductive ink, and U.S. Patent No. 5,389,403 discloses a thick conductive ink of a water bran polymer. Thick Conductive Ink), which is incorporated herein by reference in its entirety. Located in Port Huron, Michigan, the "Acheson Colloids Company" can be stretched at relatively high elongation when coated on a thermoformable film, such as ^{Lexan® from} "General Electric". Products based on silver ink have been developed that maintain high electrical conductivity. The thermoformable film can be molded into a relatively complex three-dimensional shape known as "cans". Such thermoformable films with stretchable coatings can replace conventional metal cans as well as conductive coating and plating methods used in mobile phones and other nonconductive small sheaths. The thermoformable film and stretchable coating may also form part of a larger electronic package.

It is known to manufacture a complete EMI shield by combining a thermoformable film, a stretchable conductive coating and a FIP gasket, the EMI shield being easily manufactured and having a smaller assembly from a centralized location for installation into an electronic device. Can be shipped to the facility.

The EMI shield is made of an extensible conductive coating of a polymer thick film, which maintains high electrical conductivity even at high elongation and is applied to a thermoformable film in combination with a FIP gasket. The EMI shield and FIP gasket provide EMI shielding throughout the interior of a given structure.

For example, suitable thermoforming film comprises a LEXAN ^ⓡ and VALOX ^ⓡ produced by "General Electric Co. (General Electric company)" located in Massachusetts, Pittsfield. A stretchable conductive coating of polymer thick film has ^ⓡ Electrodag SP-405 manufactured by the "Acheson colo-rise Company (Acheson Colloids Company)" located in Michigan, Port Huron.

Thus, according to one embodiment, the present invention relates to a method of molding an EMI shield. The method comprises the steps of (a) providing a thermoformable film having a first side and a second side; (b) applying a stretchable conductive coating to the thermoformable film; (c) cutting the thermoformable film; (d) thermoforming the thermoformable film into a three-dimensional shape; And (e) applying a compressible EMI gasket to the thermoformable film, wherein steps (b) to (e) can be performed in any order.

According to another embodiment, the present invention relates to an EMI shield. The EMI shield includes a thermoformable film having a first side and a second side, wherein the thermoformable film is thermoformed into a three-dimensional shape; A stretchable conductive coating applied to the thermoformable film; And a compressible EMI gasket attached to the thermoformable film.

In another embodiment, the stretchable conductive coating includes a stretchable film and conductive fibers. In another embodiment, the glass transition temperature of the stretchable film is lower than the glass transition temperature of the thermoformable film.

1 shows process embodiments for manufacturing an EMI shield.

In a first step, the EMI shield is made from a thermoformable film such as ^{Lexan® from} "General Electric." The thermoformable film may consist of small sheets or large sheets or long, continuous reels, depending on the size of the product required. Generally, a moldable film can be used, and additionally, an unmolded film can be used when the desired shape is flat.

To form the thermoformable film is formed "Acheson colo-rise Company (Acheson Colloids Company)," Conductive Coatings stretchable, by coating as a possible elongation of a conductive ink such as Electrodag SP-405 ^ⓡ of. The extensible ink may be any extensible ink in the case of a 3-D shape, and any conductive ink (or paint or plating) in the case of a 2-D shape. The extensible inks may include flexographic printing, screen printing, gravure printing, offset printing, letter press printing, pad printing, The film can be applied by various printing or film coating methods, such as slot coating, flood coating, spray coating, and jet coating.

Depending on the shape of the portion used during the forming process, a significant amount of elongation of the EMI shield is possible where the geometrical features of the EMI shield are concentrated. This in turn may exert excessive stress on the stretchable ink. Too much elongation of the extensible ink leads to breakage of the conductive layer, which in turn leads to loss of conductivity and shielding loss. Ideally, the conductive layer can be infinitely stretched over the entire portion. In practice, usually highly conductive materials tend to be fragile and such stretching is difficult. In addition, the best extensible materials are generally not conductive enough to be used as conductive shields.

In another embodiment, conductive fibers and stretchable films may be combined to form the stretchable conductive coating. The extensible film can be selected from materials that generally have a lower glass transition temperature than the thermoformable film, and in one embodiment, may be a polymer. The polymer selected for use with the conductive fiber may be very thermoplastic to be almost liquid, thereby making the bonded polymer very flexible to the change in geometry caused by thermoforming of the thermoformable film. A conductive fibrous layer is created, on the other hand, the conductive fibers continue to interact with negligible conductivity losses. 2 shows a stretchable conductive coating 20 on a thermoformable film 30.

In one embodiment, the conductive fiber may be located on the thermoformable film and the stretchable film may be located on top of the conductive fiber. The arrangement of the thermoformable film, the conductive fiber, and the stretchable film may be laminated such that the conductive fiber is integrated with the stretchable film. In another embodiment, the stretchable film can be treated with fibers that can mix with the conductive fiber. A fiber mixture of conductive fibers and the extensible film may be deposited onto the thermoformable film at a temperature at which the extensible film fibers at least partially melt.

The conductive fiber material is stainless steel fiber of "Baeckert", Naslon-SUS316L of "Nippon Seisen" in Osaka, Japan, "sol" in St. Louis, Missouri Panex Chopped Fiber-PX33CF1000-01 from "Zoltex Corporation" and X-Static Silver Nylon Fiber from "Instrument Specialties" located in Scranton, Pennsylvania. The bulk conductivity of the material is less than about 50 milliohm-cm, preferably less than 25 milliohm-cm, and more preferably less than about 10 milliohm-cm as determined by Mil-G-83528 paragraph 4.6.11 / ASTM 991. As long as the outer surface of the fiber is sufficiently coated with metal, any fiber of at least about 3.175 mm (0.125 inch) in length and less than about 0.254 mm (0.01 inch) in diameter can be used. Pure bulk fibers can also be used if the bulk resistivity is below about this value. Additionally, other conductive materials that can be used include silver load particles, silver / copper flakes, silver / nylon fibers, silver carbon fibers, tin on copper flash, and tin.

Such stretchable film materials include polypropylene and polyethylene fibers or films, both available from "Dow Chemicals". As long as the thermoplastic polymer has a glass transition temperature lower than the support polymer shield, for example at least 20 ° C. or less, other suitable polymers for the stretchable film are polystyrene, acrylonitrile-butadiene- Styrene (acrylonitrile-butydiene-styrene (ABS)), styrene-acrylonitrile (SAN), polycarbonate, polyester, and polyamide. In addition, silicone materials may also be used for the stretchable film.

The extensible conductive coating may be made by mixing polyethylene and / or polypropylene fibers with the conductive fibers to calender or laminate the composite material with the thermoformable film. Other methods of applying the extensible conductive coating to the thermoformable film include wet coating, carding, plating, coating, flocking, dry laid screening, and vacuum metal / ion sputter techniques. Include.

The method of applying the conductive fiber material, the various combinations and substitutions of the material for the extensible film, and the extensible conductive coating made of the extensible film and the conductive fiber to the thermoformable film are desirable surface conductivity of EMI shields. And shielding rate can be selected.

In some embodiments, the conductive coating can be applied to both sides of the thermoformable film. In another embodiment, the conductive coating can be applied to one side of the thermoformable film. The conductive coating may be applied uniformly, or may be applied in a predetermined pattern such as a grid. In another embodiment, the conductive coating can be applied to separate areas or areas.

In the second step, the resulting coating film is cut into 2-D shapes. Any cutting method known to those skilled in the art may be used, such as water jet cutting, laser cutting, die-cutting, hot wire cutting, and the like. The film is delivered to produce a single shape or a plurality of similar or different shapes, which shapes can be held together by a sprue.

Next, in a third step, the cut film is thermoformed into the desired 3-D shape. Any thermoforming method known to those skilled in the art can be used. The complexity of the 3-D shape can vary considerably from simple boxes formed by a single rectangular draw to multiple chamber parts with different chamber sizes and depths. Embodiments are shown in FIGS. 3A-3B.

4A-4C illustrate a thermoforming, positive forming method. The thermoformable film 30 and the extensible conductive coating 20 were heated with a heater 50 to soften the thermoformable film 30 and the extensible conductive coating 20. The thermoformable film 30 and the extensible conductive coating 20 were then applied to a mold 60 and stretched in vacuo 70 to conform the thermoformable film 30 and the conductive coating 20 to the mold 60. After sufficient cooling, the contoured thermoformable film 30 and stretchable conductive coating 20 are removed from the mold 60.

Finally, using the FIP dispensing apparatus shown in FIG. 6 and described below, conductive elastomeric gaskets were dispensed onto the coated thermoformable film in a desired pattern. The FIP gasket is generally applied around a perimeter, edge, lip, or other similar structure; However, in more complex parts, the FIP gasket can be applied to inner or outer sidewalls, dividers, or other similar surfaces formed with structures adjacent to the final assembled part or housing.

In addition to using the FIP method of making the elastomeric gasket, other gaskets known to those skilled in the EMI shielding art can be used. For example, the gasket may be another conductive polymer including, but not limited to, foam gaskets wrapped with metallized fabrics, metal fingers, knitted gaskets, printable foaming inks, and the like. Can be. In some cases, the finished part may comprise a gasket in a separate environment, for example a polyurethane gasket.

The finished trimmed shielding element is then transferred to an assembly facility whereby a complete shielding function is achieved by simply placing the single part on the shell. 1, 3C, and 4 show cross sections of shielded composite embodiments.

The four general process steps need not be performed in any particular order, and in fact can be performed in any order. For example, the FIP gasket can be applied before or after coating, cutting or molding. Similarly, the coating can be applied before or after cutting, molding, or applying the FIP gasket.

FIG. 5 is a table summarizing the results of surface conductivity and shield effectiveness test for various conductive coatings. The table shows the conductive material, the main material of the extensible film, and the manufacturing method of applying the conductive coating to the thermoformed film. The table also shows the thickness of the conductive coating and exemplary draw amounts of the conductive coating. The results of testing the surface conductivity and the shielding rate are shown for both the non-molded conductive layer after applying the extensible conductive coating to the thermoformable film and the molded conductive layer after the three-dimensional molding of the EMI gasket. According to the test results, the surface conductivity generally increases after the conductive layer is three-dimensionally molded. In addition, according to the test results, except for Ag particle ink in general, the shielding rate SE remains relatively constant before or after three-dimensional molding.

There are many ways to form a gasket in place. For example, as shown in FIG. 6, method 100 is an embodiment of manufacturing an EMI shield made of conductive particles and a foamable mixture. In one embodiment, conductive particles 105, such as chopped metal fibers or metallized polymer fibers, are added to the foamable mixture component. The component of the effervescent mixture may be the polyol component 110 and the isocionate component 115 of the urethane mixture. The polyol component 110, the isocyanate component 115, and the conductive particles 105 are mixed in one or more mixing heads 125 to produce a urethane mixture having a complete network of conductive particles 120.

The urethane mixture having a complete network of conductive particles 120 is then treated by available means to produce a conductive EMI gasket having the desired size and shape. In one embodiment, the urethane mixture having a complete network of conductive particles 120 is distributed directly through the nozzle 130 onto the surface 135 of the electrical envelope 140 using the xyz positioning system so that the mixture 120 is foamed and cured. The EMI gasket is molded in place.

A FIP EMI gasket can be made of a conductive foam, wherein the conductive element is introduced into the foam matrix before molding by adding an organometallic compound to the foam chemical matrix.

In addition, various forms of carbon may be added to the urethane foam chemical precursor to produce foams having a surface resistivity of 100 to 1000 ohms / squre. However, these materials have limited use in EMI shielding applications due to their relatively high resistivity. The new method produces a conductive foam having a bulk resistivity of less than 10 ohms / squre, which is a silver plated glass sphere, a sintered metal particle having a bulk resistivity of less than about 10 ^-5 ohm-cm (e.g. Cu , Al, Ni, Ag), and by incorporating higher conductive materials into foam chemical precursors comprising silver plated copper particles. Other conductive materials include nonmetallic materials referred to as conductive polymers. Such materials include materials such as poly-analine.

Another method of producing a conductive foam is to produce the conductive element in the foaming process by reacting the organometallic compound during the foaming process. This is accomplished by introducing a reducing agent into one of the chemical precursors of at least two of the foams before foaming. One such compound is copper acetate, but any metal compound may be used that is compatible with one of the chemical foam precursors.

Examples of chemical foam systems that can be used include a very wide range of urethane foams, including polyester and polyether types. Chloroprene, commonly known as neoprene rubber foam, can also be used.

Those skilled in the art to which the present invention pertains may make modifications, changes, and other implementations described herein without departing from the spirit and scope of the present invention.

The present invention provides a method of manufacturing an EMI shielding component used in a non-conductive housing of an electronic device, and provides an EMI shielding component having good conductivity and shielding ratio.

Claims (29)

(a) providing a thermoformable film comprising a first side and a second side; (b) applying a stretchable conductive coating to the thermoformable film; (c) cutting the thermoformable film; (d) thermoforming the thermoformable film into a three-dimensional shape; And (e) applying a compressible EMI gasket to the thermoformable film, wherein steps (b) to (e) may be performed in any order. The method of claim 1, wherein the thermoformable film of step (a) is drawn from a roll. 2. The method of claim 1 wherein step (b) of applying a stretchable conductive coating to the thermoformable film is selected from the group consisting of a printing process and a film coating process. 4. The group of claim 3, wherein the group consisting of a printing process and a film coating process includes flexograph printing, screen printing, gravure printing, offset printing, iron plate printing, pad printing, slot coating, fluid coating, spray coating, and jet printing. Molding method, characterized in that. The method of claim 1, wherein applying (b) applying the extensible conductive coating to the thermoformable film comprises applying the extensible conductive coating to at least one of the first side and the second side of the thermoformable film. Molding method characterized in that. 6. The method of claim 5, wherein the stretchable conductive coating is applied substantially uniformly to at least one of the first side and the second side of the thermoformable film. The method of claim 5, wherein the stretchable conductive coating is selectively applied to at least one region on at least one of the first side and the second side of the thermoformable film, and the stretchable conductive coating is selectively applied to the other regions. Molding method characterized in that not applied to. The method of claim 1 wherein the EMI gasket of step (d) is selected from the group consisting of a conductive elastomer, a fabric wrapped foam, a metal finger, a polyurethane, and a knitted gasket. The method of claim 1, wherein applying the EMI gasket to the thermoformable film comprises: Mixing the foamable material and the conductive particles to form a foam mixture having a complete network of conductive particles; And Processing the foam mixture having a complete network of conductive particles to form the EMI gasket. 10. The method according to claim 9, wherein said foamable material is a polyol component and an isocyanate component forming a urethane foam mixture. 11. The method of claim 10, wherein processing the urethane foam mixture having a complete network of conductive particles to form the EMI gasket comprises forming the urethane having a complete network of conductive particles such that the EMI gasket is formed in place. Moving the surface of the thermoformable film in relation to a nozzle supporting the foam. 10. The method of claim 9, wherein the conductive particles are selected from the group consisting of silver plated glass spheres, sintered metal particles, silver plated copper particles, and conductive polymers. The method of claim 12, wherein the sintered metal particles have a bulk resistivity of less than about 10 ⁻⁵ ohm-cm. The method of claim 1, wherein the stretchable conductive coating comprises conductive fibers and a stretchable film. A product manufactured according to the molding method of claim 1. (a) a thermoformable film comprising a first side and a second side, thermoformed into a three-dimensional shape; (b) a stretchable conductive coating applied to the thermoformable film; And and (c) a compressible EMI gasket attached to said thermoformable film. 17. The shield of claim 16, wherein the stretchable conductive coating is applied to at least one of the first side and the second side of the thermoformable film. 18. The shield of claim 17, wherein the stretchable conductive coating is applied substantially uniformly to at least one of the first side and the second side of the thermoformable film. 18. The EMI of claim 17, wherein the conductive coating is selectively applied to at least one region on at least one of the first and second sides of the thermoformable film and not selectively applied to the other region. Shielding parts. 18. The EMI shield of claim 16, wherein the compressible EMI gasket comprises a mixture of foamable material and conductive particles to form a foam mixture having a complete network of conductive particles. 21. The shield of claim 20 wherein the foamable material is a polyol component and an isocyanate component forming a urethane foam mixture. 21. The EMI shield of claim 20, wherein the conductive particles are selected from the group consisting of silver plated glass spheres, sintered metal particles, silver plated copper particles, and conductive polymers. The EMI shield of claim 22, wherein the sintered metal particles have a bulk resistivity of less than about 10 ⁻⁵ ohm-cm. 17. The shield of claim 16, wherein the stretchable conductive coating comprises conductive fibers and a stretchable film. A stretchable conductive coating comprising conductive fibers and a stretchable film. 27. The method of claim 25, wherein the conductive fiber is selected from the group consisting of stainless steel fibers, silver metallized fibers, silver loads, silver / copper flakes, silver / nylon fibers, silver carbon fibers, tin on copper flash, and tin. A stretchable conductive coating, characterized in that. 27. The stretchable conductive coating of claim 25, wherein the outer surface of the conductive fiber is coated with a metal sufficient for the bulk conductivity of the material per ASTM 991 to be less than about 10 milliohm-cm. 27. The group of claim 25, wherein said stretchable film is comprised of polypropylene, polyethylene, polystyrene, acrylonitrile-butadiene-styrene, styrene-acrylonitrile, polycarbonate, polyester, and polyamide A stretchable conductive coating, characterized in that selected from. 25. The EMI shield of claim 24, wherein said stretchable film has a lower glass transition temperature than said thermoformable film.