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`US 20120236528Al
`
`c19) United States
`c12) Patent Application Publication
`Le et al.
`
`c10) Pub. No.: US 2012/0236528 Al
`Sep. 20, 2012
`(43) Pub. Date:
`
`(54) MULTILAYER EMI SHIELDING THIN FILM
`WITH HIGH RF PERMEABILITY
`
`(76)
`
`Inventors:
`
`John D. Le, Woodbury, MN (US);
`Robert C. Fitzer, North Oaks, MN
`(US); Charles L. Bruzzone,
`Woodbury, MN (US); Stephen P.
`Maki, North St. Paul, MN (US);
`Bradley L. Givot, St. Paul, MN
`(US); David A. Sowatzke, Spring
`Valley, WI (US)
`
`(21) Appl. No.:
`
`13/512,638
`
`(22) PCT Filed:
`
`Nov. 19, 2010
`
`(86) PCT No.:
`
`PCT/USl0/57372
`
`§ 371 (c)(l),
`(2), ( 4) Date:
`
`May 30, 2012
`
`300~
`
`Related U.S. Application Data
`
`(60) Provisional application No. 61/265,893, filed on Dec.
`2, 2009.
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`H0SK 9/00
`(2006.01)
`C23C 16106
`(2006.01)
`C23C 16156
`(2006.01)
`(52) U.S. Cl. ............ 361/818; 174/391; 427/58; 427/124
`ABSTRACT
`(57)
`
`A flexible multilayer electromagnetic shield is provided that
`includes a flexible substrate, a thin film layer of a first ferro(cid:173)
`magnetic material with high magnetic permeability disposed
`upon the substrate and a multilayer stack disposed upon the
`first ferromagnetic material. The multilayer stack includes
`pairs of layers, each pair comprising a polymeric spacing
`layer and a thin film layer of at least a second ferromagnetic
`material disposed on the spacing layer. At least one or more of
`the spacing layers includes an acrylic polymer. Also methods
`of making the flexible multilayer electromagnetic shield are
`provided.
`
`305
`
`302
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`Patent Application Publication
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`Sep.20,2012
`
`US 2012/0236528 Al
`
`100~
`
`105
`
`Fig.1
`
`200~
`
`205
`~~~~~~~~~~~~}208
`-----~---~---~~----204
`203
`202
`
`Fig. 2
`
`300~
`
`305
`
`302
`
`Fig. 3
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`Ex.1009
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`US 2012/0236528 Al
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`Sep.20,2012
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`1
`
`MULTILAYER EMI SHIELDING THIN FILM
`WITH HIGH RF PERMEABILITY
`
`FIELD
`
`[0001] Multilayer thin films are provided that have high RF
`permeability and can be useful for electromagnetic interfer(cid:173)
`ence shielding and suppression
`
`BACKGROUND
`
`[0002] Miniaturization of electronic devices and high fre(cid:173)
`quency electronic circuits have created a demand for compact
`and flexible electromagnetic interference/electromagnetic
`compatible (EMI/EMC) material that also can suppress the
`degrading effect of electromagnetic interference originating
`in the devices and circuits or originating in the environment.
`Additionally EMI/EMC materials can be needed to comply
`with the electromagnetic compatibility (EMC) specifications
`for EMI control. EMI control can include EMI shielding,
`absorption, and/or suppression. Electrically conducting
`materials can be utilized to primarily provide shielding of
`electromagnetic radiation.
`[0003] Lossy magnetic material with high permeability
`over a certain radio frequency (RF) range can also be useful to
`attenuate or suppress the high frequency common mode EMI
`noise on transmission lines as most noise frequency is usually
`higher than that of the circuit signal. For EMI suppression,
`ferrites are widely used. However, they are bulky and may not
`be suitable for compact devices or in products that have space
`limitations. Furthermore, the upper limit of frequency sup(cid:173)
`pression in ferrites is on the order of several hundred mega(cid:173)
`hertz (MHz).
`
`SUMMARY
`
`[0004] Thus, there is a need for thin, flexible materials that
`have high magnetic permeability in the radiofrequency (RF)
`range. There is a need for materials that can suppress radiof(cid:173)
`requency energy over a wider range of frequencies than is
`currently available in ferrites. Soft magnetic alloys can pro(cid:173)
`vide higher permeability at higher frequencies. For example,
`alloys of NiFe, CoNbZr, FeCoB, nanocrystalline Fe-based
`oxides and nitrides, and boron-based amorphous alloy are
`useful in this regard. In today's wireless and compact elec(cid:173)
`tronics environment, there is also a need to be able to provide
`EMI control at high frequencies such as, for example, in the
`1-6 gigahertz (GHz) range. And in the electronics industry, as
`devices are becoming more compact, thinner is better.
`[0005]
`In one aspect, a flexible multilayer electromagnetic
`interference shield is provided that includes a flexible sub(cid:173)
`strate, a thin film layer of a first ferromagnetic material with
`a high magnetic permeability disposed upon the flexible sub(cid:173)
`strate, and a multilayer stack disposed upon the first ferro(cid:173)
`magnetic material, the multilayer stack comprises pairs of
`layers, each pair comprising a spacing layer and a thin film
`layer of a second ferromagnetic material disposed on the
`spacing layer. One or more of the spacing layers comprises an
`acrylic polymer. The spacing layer is preferably a dielectric
`layer or a non-electrically conductive material to suppress the
`Eddy current effect. The spacing layer can be made of a
`ferromagnetic material with relatively lower magnetic per(cid:173)
`meability.
`[0006]
`In another aspect, a method for making a flexible
`multilayer electromagnetic interference shield is provided
`that includes providing a substrate, vapor depositing a thin
`
`film layer of a first ferromagnetic material upon the substrate,
`vapor coating and curing an acrylic polymer upon the first
`ferromagnetic material to form a first polymeric spacing
`layer, and vapor depositing a thin film of a second ferromag(cid:173)
`netic material upon the first spacing layer.
`[0007]
`In this application:
`[0008]
`"adjacent" refers to layers in the provided filters that
`are in proximity to other layers. Adjacent layers can be con(cid:173)
`tiguous or can be separated by up to three intervening layers;
`[0009]
`"alloy" refers to a composition of two or more met(cid:173)
`als that have physical properties different than those of any of
`the metals by themselves;
`[0010]
`"contiguous" refers to touching or sharing at least
`one common boundary;
`[0011]
`"dielectric" refers to material that is less conductive
`than metallic conductors such as silver, and can refer to semi(cid:173)
`conducting materials, insulators, or metal oxide conductors
`such as indium-tin-oxide (ITO);
`[0012]
`"electromagnetic interference (EMI) shielding"
`refers to the reflection or absorption of at least one of the
`components of electromagnetic waves;
`[0013] The provided flexible multilayer electromagnetic
`shields can shield or/and suppress radiofrequency energy
`over a wide range of frequencies. By using thin layers of
`ferromagnetic material interlayered with spacing materials
`and by adjusting the numbers oflayers, thicknesses oflayers,
`and materials, electromagnetic interference control at high
`frequencies can be achieved, for example, in the 1-6 gigahertz
`range. Furthermore, by using vapor-condensed acrylic spac(cid:173)
`ing layers the provided shields can be manufactured in a
`continuous, roll-to-roll manner.
`[0014] The above summary is not intended to describe each
`disclosed embodiment of every implementation of the present
`invention. The brief description of the drawing and the
`detailed description which follows more particularly exem(cid:173)
`plify illustrative embodiments.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0015] FIG. 1 is a schematic of an embodiment of a pro(cid:173)
`vided electromagnetic shield.
`[0016] FIG. 2 is a schematic of an embodiment of a pro(cid:173)
`vided electromagnetic shield that includes a buffer layer dis(cid:173)
`posed upon the substrate.
`[0017] FIG. 3 is a schematic of an embodiment of a pro(cid:173)
`vided electromagnetic shield that includes a buffer layer and
`a multilayer stack comprising 4 layers.
`
`DETAILED DESCRIPTION
`
`[0018]
`In the following description, reference is made to
`the accompanying set of drawings that form a part of the
`description hereof and in which are shown by way of illus(cid:173)
`tration several specific embodiments. It is to be understood
`that other embodiments are contemplated and may be made
`without departing from the scope or spirit of the present
`invention. The following detailed description, therefore, is
`not to be taken in a limiting sense.
`[0019] Unless otherwise indicated, all numbers expressing
`feature sizes, amounts, and physical properties used in the
`specification and claims are to be understood as being modi(cid:173)
`fied in all instances by the term "about." Accordingly, unless
`indicated to the contrary, the numerical parameters set forth in
`the foregoing specification and attached claims are approxi(cid:173)
`mations that can vary depending upon the desired properties
`
`Ex.1009
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`US 2012/0236528 Al
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`sought to be obtained by those skilled in the art utilizing the
`teachings disclosed herein. The use of numerical ranges by
`endpoints includes all numbers within that range (e.g. 1 to 5
`includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within
`that range.
`[0020] With the growing trend of miniaturization and port(cid:173)
`ability of multifunctional high speed and high frequency per(cid:173)
`sonal electronic devices, such as mobile phone or personal
`digital assistant (PDA) devices, as well as near field commu(cid:173)
`nication (NFC) devices, there is a growing need for the con(cid:173)
`trol of electromagnetic interference (EMI) and electromag(cid:173)
`netic crosstalk. Meeting this need can be challenging.
`Radiated EMI noise may need to be controlled in such elec(cid:173)
`tronic devices in order to limit its degradative effects, such as,
`for example, extraneous noise in the radiofrequency (RF)
`spectrum, and health hazards in the environment. In addition
`compliance with governmental specification may require
`control of EMI and electromagnetic crosstalk. Materials are
`known that can provide EMI shielding and can suppress EMI
`emissions and thus control electromagnetic interference and
`n01se.
`[0021] Magnetic materials with high RF permeability can
`provide EMI shielding or suppression in miniaturized multi(cid:173)
`functional electronic devices. Thin conductive magnetic
`materials can be effective EMI shields for small devices due
`to their relatively thin skin depth and can be especially effec(cid:173)
`tive for near field magnetic shielding. Lossy magnetic mate(cid:173)
`rials can be used attenuate or suppress high frequency har(cid:173)
`monic noise, common-mode EMI noise on transmission
`lines, cables, and interconnects, or can be integrated into
`micro-scale semiconductor circuits. The advantage of using
`magnetic thin films to suppress EMI noise is related to their
`high RF impedance, which is proportional to the permeabil(cid:173)
`ity, frequency, volume/dimension of the magnetic material.
`Magnetic materials have a complex permeability, µ=µ'-iµ"
`that changes with frequency. Materials with a high RF per(cid:173)
`meability having a highµ" can be used to obtain high loss of
`unwanted high frequency noise with a relatively small vol(cid:173)
`ume of material. Materials with a highµ' can be used for near
`field magnetic shielding for NFC devices which, for example,
`can improve the reading range for high frequency radio fre(cid:173)
`quency identification tags (HF RFID tag) on metal surfaces as
`disclosed, for example, in U.S. Pat. No. 7,315,248 (Egbert).
`[0022] Shielding against EMI is commonly accomplished
`by reflecting and/or absorbing the incident electromagnetic
`waves. A large impedance mismatch between the incident
`medium and the shielding material can lead to relatively high
`reflectance. As a wave passes through shielding material, its
`amplitude is attenuated exponentially as a function of skin
`depth. Due to cost constraints most EMI shielding materials
`operate simply by reflection. However, many applications can
`benefit by absorption of the EMI since reflected EMI can also
`cause additional interference. Non-magnetic metals such as
`silver, gold, copper, and aluminum, can have high electrical
`conductivities and can be useful for EMI shielding. However,
`the metals which are ferromagnetic can be less electrically
`conductive but can have much higher magnetic permeabilities
`than other metals. As such, they can be useful for shielding
`against EMI and particularly for shielding against the mag(cid:173)
`netic component ofEMI. Shielding materials with high mag(cid:173)
`netic permeability and high electrical conductivity can
`develop low surface impedance with thinner skin depth that
`can help to attenuate and to reflect incident waves. In order to
`absorb EMI it is important to reduce or eliminate eddy cur-
`
`rents to allow the incident EMI waves to penetrate the shield(cid:173)
`ing material. Permalloy, which is an alloy of approximately
`19 mole% Fe and 81 mole% Ni, and has zero magnetostric(cid:173)
`tion, is a very useful, versatile, and relatively inexpensive
`material with high magnetic permeability. Permalloy alloy
`can have from about 18 mole% to about 20 mole% Fe and
`from about 80 mole% to about 82 mole% Ni. By zero mag(cid:173)
`netostriction it is meant that the permeability does not change
`with stress.
`[0023] Magnetic thin films with high RF permeability can
`be lossy in a high-frequency range, especially in the gigahertz
`frequency range, where most of the bulk and the composite
`ferrite materials have only a small loss generation per thick(cid:173)
`ness, can be advantageous for suppression applications.
`[0024] Thin ferromagnetic films are known to exhibit the
`highest possible RF permeability of known magnetic materi(cid:173)
`als. However, with the increase of film thickness, the RF
`permeability can degenerate because of both effects of eddy
`currents and out-of-plane magnetization. For these effects to
`be reduced, films that include multiple layers of thin ferro(cid:173)
`magnetic layers can be useful. Multilayer constructions of
`alternating layers of materials with high magnetic permeabil(cid:173)
`ity and non-magnetic spacing layers have been previously
`disclosed, for example, in U. S. Pat. No. 5,083,112 (Pi(cid:173)
`otrowski et al.) and U.S. Pat. No. 5,925,455 (Bruzzone et al.)
`as well as in an article authored by C. A. Grimes, "EMI
`shielding characteristics of permalloy multilayer thin films",
`IEEE Aerospace Applications Conj Proc., IEEE, Computer
`Society Press Los Alamitos, IEEE, California, USA (1994),
`pp. 211-221. For example, multilayer, thin film, electronic
`article surveillance systems which are used for protecting
`store merchandise and library books can have multiple layers
`of a magnetic thin film, such as Permalloy, interspaced with a
`film, such as an inorganic oxide of silicon or aluminum.
`[0025] A flexible multilayer electromagnetic interference
`shield is provided that includes a flexible substrate. The sub(cid:173)
`strate is typically a polymer film. Typical substrates can be
`smooth or textured, uniform or non-uniform and flexible.
`Polymer films can be suitable for roll-to-roll manufacturing
`processes. Substrates can also contain other coatings or com(cid:173)
`pounds, for example, abrasion-resistant coatings (hardcoats).
`Substrates can include flexible plastic materials including
`thermoplastic films such as polyester ( e.g., PET), polyimide,
`polyolefin, polyacrylate ( e.g., poly(methyl methacrylate ),
`PMMA), polycarbonate, polypropylene, high or low density
`polyethylene, polyethylene naphthalate, polysulfone, poly(cid:173)
`ether sulfone, polyurethane, polyamide, polyvinyl butyral,
`polyvinyl chloride, polyvinylidenefluoride (PVDF), fluori(cid:173)
`nated ethylene propylene (FEP), and polyethylene sulfide;
`and thermoset films such as epoxy, acrylate, cellulose deriva(cid:173)
`tives, polyimide, polyimide benzoxazole, polybenzoxazole,
`and high T g cyclic olefin polymers. Typically, the substrate
`can have a thickness of from about 0.01 mm to about 1 mm.
`Substrates can also be metal foils, flexible printed circuits,
`printed circuit boards, or any other article on which the mul(cid:173)
`tilayer construction can be formulated on or applied to.
`[0026] Flexible substrates can also be releasable polymer
`webs such as paper coated with a release liner. Releaseable
`polymer webs are well known to those of ordinary skill in the
`art of coatings. Flexible substrates can also include thin poly(cid:173)
`mer coatings on releaseable polymer web. Thin polymer coat(cid:173)
`ings can be epoxy coating, acrylic coating, and can be ther(cid:173)
`moplastic, thermoset, or photo-curable material. When the
`substrates are releasable polymer webs, the webs can be
`
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`3
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`separated from the rest of the construction yielding ultra-thin
`products at application. An adhesive can be used to attach the
`multilayer construction to an electronic device after it has
`been removed from a releaseable polymer web.
`[0027] The provided flexible multilayer electromagnetic
`interference shield includes a thin film layer of a first ferro(cid:173)
`magnetic material with a high magnetic permeability dis(cid:173)
`posed upon the flexible substrate. These materials typically
`include ferromagnetic materials such as Permalloy as dis(cid:173)
`cussed above. Other ferromagnetic materials and alloys com(cid:173)
`prise iron, cobalt, or nickel can be used, including FeN. A
`multilayer stack is disposed upon the first ferromagnetic
`material. The multilayer stack includes pairs oflayers. Each
`pair includes a spacing layer and a thin film of at least a second
`ferromagnetic material disposed upon the spacing layer. One
`or more of the ferromagnetic material layers may be of the
`same or different compositions and may have the same or
`different thicknesses. Each of the thin film layers of ferro(cid:173)
`magnetic materials have a thickness from about 10 nanom(cid:173)
`eters (nm) to about 1 micrometer (µm), from about 20 nm to
`about 500 nm, or even from about 30 nm to about 200 nm.
`[0028] The spacing layers can include at least one acrylic
`polymer. One or more of the spacing layers can include an
`acrylic polymer. If more than one spacing layer includes an
`acrylic polymer, each spacing layer may include an acrylic
`polymer having the same or different composition. Further(cid:173)
`more, the thicknesses of each of the layers can be the same or
`different. For example, the layers can include one or more
`acrylic polymer spacing layers having a thickness of from
`about 10 nm to about 50 µm, from about 10 nm to about 1 µm,
`or even from about 50 nm to about 500 nm. In the provided
`shields, the multilayer stack can include from 2 to about 100,
`from about 4 to about 50, from about 6 to about 30, from about
`6 to about 20, or even from about 6 to about 12 pairs oflayers.
`There may be more than one multilayer stack in the provided
`shields. If there are multiple multilayer stacks there can be
`additional spacing layers ( one or more) in between each of the
`multilayer stacks.
`[0029] The provided flexible multilayer electromagnetic
`interference shields can also include a buffer layer between
`the substrate and either the thin film layer of a first ferromag(cid:173)
`netic material with a high magnetic permeability or the mul(cid:173)
`tilayer stack polymer coating can be utilized for adjust
`mechanical properties of the multilayer coating. Polymer
`coatings can also be used as a stress-buffered layer for the
`multilayer stack to improve adhesion of the stack coating and
`substrate, to eliminate curling, and to enable multilayer con(cid:173)
`structions having a large number of bilayers, which, without
`the buffer coating would be limited to a few bilayer stacks
`without delaminating and curling. For EMI shield applica(cid:173)
`tion, polymer coatings can be also used as spacer layers to
`improve durability and flexural fatigue of the coating, espe(cid:173)
`cially for EMI shielding of flexible printed circuit, where
`flexural endurance is required.
`[0030] The polymer buffer layer can also be engineered to
`induce various degrees of crack patterns in the multilayer
`coating, therefore, minimize surface conductance, which can
`minimize reflection loss and Eddy current effects where
`desirable for EMI suppression application. Patterning the
`multilayer coating can also help to suppress eddy currents for
`RFID application. Useful buffer layers include thermoset
`epoxy coatings. The epoxy coatings can be coated on release
`liner or polymer liner, and kept uncured until multilayer stack
`deposition. Heat and stress of multilayer stack deposition can
`
`induce the epoxy and multilayer stack to crack, which can
`help to minimize the coating stress, curling and delamination.
`Other materials for buffer layers can include acrylics and
`thermoplastic adhesives.
`[0031] Each pair in the multilayer stack can include a spac(cid:173)
`ing layer. If there is more than one magnetic layer in the
`multilayer stack then one or more of the spacing layers
`includes an acrylic polymer. Typically the acrylic polymer
`can be crosslinked. Crosslinked polymer layers are important
`during the fabrication of the multilayer stacks. As discussed
`later, one efficient way of making the multilayer stacks (and
`the shields, in some cases) is to alternate deposition of the
`magnetic materials with vapor condensation polymerization
`of the acrylic spacing layers. It has been unexpectedly found
`that crosslinked acrylic polymer systems made by vapor con(cid:173)
`densation polymerization of monomer systems are able to
`withstand the heat of subsequent vapor deposition of metallic
`coatings. The processes used to make the provided multilayer
`shields is discussed later in this specification and is exempli(cid:173)
`fied in the example section.
`[0032] Useful crosslinked polymeric layers can be formed
`from a variety of organic materials. Typically, the polymeric
`layer is crosslinked in situ atop substrate or the previously
`deposited layer. If desired, the polymeric layer can be applied
`using conventional coating methods such as roll coating ( e.g.,
`gravure roll coating) or spray coating ( e.g., electrostatic spray
`coating), then crosslinked using, for example, UV radiation.
`Typically, the polymeric layer can be formed by flash evapo(cid:173)
`ration, vapor deposition, and crosslinking of a monomer.
`Volatilizable acrylamides (such as those disclosed in U. S.
`Pat. Pub!. No. 2008/0160185 (Endle et al.)) and (meth)acry(cid:173)
`late monomers are typically used in such a process, with
`volatilizable acrylate monomers being especially preferred.
`Fluorinated (meth)acrylates, silicon (meth)acrylates and
`other volatilizable, free radical-curing monomers can be
`used. Coating efficiency can be improved by cooling the
`support. Particularly preferred monomers include multifunc(cid:173)
`tional (meth)acrylates, used alone or in combination with
`other multifunctional or monofunctional (meth)acrylates,
`such as phenylthioethyl acrylate, hexanediol diacrylate,
`ethoxyethyl acrylate, phenoxyethyl acrylate, cyanoethyl
`(mono )acrylate, isobornyl acrylate, isobornyl methacrylate,
`octadecyl acrylate, isodecyl acrylate, lauryl acrylate, ~-car(cid:173)
`boxyethyl acrylate, tetrahydrofurfuryl acrylate, dinitrile
`acrylate, pentafluorophenyl acrylate, nitrophenyl acrylate,
`2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, 2,2,
`2-trifluoromethyl(meth)acrylate, diethylene glycol diacry(cid:173)
`late,
`triethylene glycol diacrylate,
`triethylene glycol
`dimethacrylate, tripropylene glycol diacrylate, tetraethylene
`glycol diacrylate, neopentyl glycol diacrylate, propoxylated
`neopentyl glycol diacrylate, polyethylene glycol diacrylate,
`tetraethylene glycol diacrylate, bisphenolA epoxy diacrylate,
`1,6-hexanediol dimethacrylate, trimethylol propane triacry(cid:173)
`late, ethoxylated trimethylol propane triacrylate, propylated
`trimethylol propane triacrylate, 2-biphenyl acrylate, tris(2-
`hydroxyethyl)-isocyanurate triacrylate, pentaerythritol tria(cid:173)
`crylate, phenylthioethyl acrylate, naphthloxyethyl acrylate,
`EBECRYL 130 cyclic diacrylate (available from Cytec Sur(cid:173)
`face Specialties, West Paterson, N.J.), epoxy acrylate
`RDX80095 (available from Rad-Cure Corporation, Fairfield,
`N.J.), CN120E50 and CN120C60(both available from Sar(cid:173)
`tomer, Exton, Pa.), and mixtures thereof. A variety of other
`
`Ex.1009
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`4
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`curable materials can be included in the crosslinked poly(cid:173)
`meric layer, e.g., vinyl ethers, vinyl naphthylene, acryloni(cid:173)
`trile, and mixtures thereof.
`[0033] The polymeric spacing layer can be crosslinked in
`situ after it is applied. In some embodiments, the crosslinked
`polymeric layer can be formed by flash evaporation, vapor
`deposition and crosslinking of a monomer as described
`above. Exemplary monomers for use in such a process
`include volatilizable (meth)acrylate monomers. In a specific
`embodiment, volatilizable acrylate monomers are employed.
`Suitable (meth)acrylates will have a molecular weight that is
`sufficiently low to allow flash evaporation and sufficiently
`high to permit condensation on the support. If desired, the
`polymeric spacing layers can also be applied using conven(cid:173)
`tional coating methods such as roll coating ( e.g., gravure roll
`coating) or spray coating ( e.g., electrostatic spray coating),
`then crosslinked using, for example, UV radiation.
`[0034] The smoothness and continuity of the multi-layer
`construction and its adhesion to the substrate or buffer layer
`can be enhanced by appropriate pretreatment of the support.
`A typical pretreatment regiment involves electrical discharge
`pretreatment of the support in the presence of a reactive or
`non-reactive atmosphere ( e.g., plasma, glow discharge,
`corona discharge, dielectric barrier discharge or atmospheric
`pressure discharge); chemical pretreatment; flame pretreat(cid:173)
`ment; or application of a nucleating layer such as the oxides
`and alloys described in C. A. Grimes, "EMI shielding char(cid:173)
`acteristics of permalloy multilayer thin films", IEEE Aero(cid:173)
`space Applications Conj Proc., IEEE, Computer Society
`Press Los Alamitos, IEEE, California, USA (1994), pp. 211-
`221. Typical nucleating or undercoat layers for ferromagnetic
`materials can include Cu, CuAl metal, silicon, silicon nitride
`and Co 21Cr79 , as well as other nucleating agents known to
`those of ordinary skill in the art. These pretreatments can help
`ensure that the surface of the support will be receptive to the
`subsequently applied metal layer. Plasma pretreatment is par(cid:173)
`ticularly preferred for certain embodiments.
`[0035] Various functional layers or coatings can be added
`to the provided electromagnetic shields to alter or to improve
`their physical or chemical properties. Such layers or coatings
`can include, for example, low friction coatings (see for
`example, U.S. Pat. No. 6,744,227 (Bright et al.)), slip par(cid:173)
`ticles to make the filter easier to handle during manufacturing;
`and adhesives such as pressure-sensitive adhesives.
`[0036] The magnetic or spacing layers can be patterned
`using a variety of techniques including laser ablation, dry
`etching, and wet etching. In some embodiments, the provided
`[0037] EMI shield multilayer stack can be patterned by
`providing a resist with a pattern. The resist can include hydro(cid:173)
`carbon waxes, positive photoresists, negative photoresists or
`any other resist or masking known to those of ordinary skill in
`the art of patterning and masking After applying the resist, the
`multilayer stack can be immersed in an etching tank and
`exposed to an etching solution to remove the exposed metal or
`metal alloy layer.Useful etchants include, for example, aque(cid:173)
`ous HCl, aqueous HNO3 , and aqueous I2 :KI. After etchant
`exposure, the multilayer stack can be rinsed with water, dried,
`and used in further operations.
`[0038] Flexible, multilayer electromagnetic shielding con(cid:173)
`structions can be designed and fabricated that include a plu(cid:173)
`rality of thin films of high permeability magnetic layers,
`separated by thin films of dielectric layers. These multilayer
`constructions can have excellent RF permeability as well as
`high frequency response. By using a layered design, ferro-
`
`magnetic resonance frequencies can be tuned to absorb from
`the megahertz to the gigahertz range. Overall magnetic prop(cid:173)
`erties including real and imaginary part of permeability, fer(cid:173)
`romagnetic resonance, and impedance are a function of
`parameters such as layer design (thickness of magnetic and
`polymeric spacing layer), number of layers, process condi(cid:173)
`tions (aligned magnetic field, process temperature, etc.), and
`the nature of the substrate. Such dynamic relationships
`between the thickness of the ferromagnetic layers, spacing
`layers, and number of layers have not been previously estab(cid:173)
`lished.
`[0039]
`In general, thin ferromagnetic films are known to
`exhibit very high microwave permeability. Among the ele(cid:173)
`ments, only cobalt, iron and nickel are strongly ferromag(cid:173)
`netic. With the increase of.film thickness, the RF permeability
`degenerates because of both effects of eddy currents and
`out-of-plane magnetization. For these effects to be reduced,
`laminates or multilayer of thin ferromagnetic layers are use(cid:173)
`ful. However, since the permeability of multi-layer construc(cid:173)
`tions are additive, with the use of inorganic spacing layer the
`permeability can degrade noticeably with the number oflay(cid:173)
`ers, possibly due to surface quality, internal stress, and limi(cid:173)
`tation of thickness coating of spacing layer. The use of poly(cid:173)
`meric spacing layers can help to smooth the surface, to lower
`interlayer stress, and, at thicker spacings, to avoid magnetic
`coupling between layers.
`[0040] Some embodiments of provided electromagnetic
`shields are illustrated in the Figures. FIG. 1 is a schematic
`drawing of one embodiment 100 and includes substrate 102
`upon which is disposed first electromagnetic material 104.
`Multilayer stack 108 that includes two spacer layers 105 and
`two layers of second ferromagnetic material 107 are disposed
`upon first ferromagnetic layer 104. At least one of spacing
`layers 105 includes an acrylic polymer.
`[0041] FIG. 2 is a schematic illustration of.another embodi(cid:173)
`ment of a provided electromagnetic shield. Electromagnetic
`shield 200 includes substrate 202 upon which is disposed
`buffer layer 203. Buffer layer 203 can reduce stress in the
`article when it is flexed which may be needed in order to
`prevent layers from flaking off. Disposed upon buffer layer
`203 is first ferromagnetic layer 204. It is within the scope of
`this disclosure that, in another embodiment, first ferromag(cid:173)
`netic layer 204 may be directly disposed upon the substrate,
`and buffer layer 203 may be disposed between first ferromag(cid:173)
`netic layer204 and multilayer stack 208. Multilayer stack 208
`includes two spacer layers 205 and two layers of second
`ferromagnetic material 207 are disposed upon first ferromag(cid:173)
`netic layer 204.
`[0042] FIG. 3 is a schematic illustration of yet another
`embodiment. Electromagnetic shield 300 includes substrate
`302 upon which is disposed buffer layer 303. In this embodi(cid:173)
`ment, first electromagnetic layer 304 is disposed upon buffer
`layer 303 upon which is disposed multilayer stack 308. Mul(cid:173)
`tilayer stack 308 includes three spacer layers 305 and three
`layers of second ferromagnetic material 307.
`[0043] The provided EMI shields can be used to isolate
`electronic devices that are sensitive to electromagnetic inter(cid:173)
`ference-particularly in application where the magnetic
`component of the electromagnetic interference needs to be
`suppressed. For example, EMI shields can be effective for
`improving reading range RFID systems attached to conduc(cid:173)
`tive objects and can help to miniaturize the RFID tag. For
`shielding ofRFID tags on conductive objects such as metals,
`the signal frequency should be considerably lower than the
`
`Ex.1009
`APPLE INC. / Page 6 of 9
`
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`US 2012/0236528 Al
`
`Sep.20,2012
`
`5
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`onset of ferromagnetic resonance. The magnetic shield,
`which is relatively electrically non-conductive at the tag oper(cid:173)
`ating frequency, helps to confine the magnetic field energy
`and reduce the amount of energy coupled to the conductive
`substrate which results in higher signal returned to the R