Patterned electrically conductive features on a particle-containing porous substrate

Abstract

Patterns of conductive material bonded to a porous polymer matrix composite by an adhesive layer are described. The porous polymer matrix composites comprise a plurality of particles interconnected by an open pore network of a thermoplastic polymer. The pattern of conductive material may be located on the side of the adhesive layer opposite the porous polymer matrix or located between the adhesive layer and the porous polymer matrix. Methods of making and using such articles are also described.

Description

PA102311W003PATTERNED ELECTRICALLY CONDUCTIVE FEATURES ON A PARTICLECONTAINING POROUS SUBSTRATEFIELD

[0001] The present disclosure relates to articles having patterned electrically conductive features adhesively bonded to porous substrates. The substrates include a plurality of particles distributed within a porous polymeric network. Methods of creating patterned conductive features on such particle-containing porous substrates are also described.SUMMARY

[0002] Briefly, in one aspect, the present disclosure provides porous polymer matrix composites comprising a plurality of particles interconnected by an open pore network of a thermoplastic polymer. The porous polymer matrix has a thickness extending from a first major surface of the porous polymer matrix to a second major surface of the porous polymer matrix. The porous polymer matrix composite comprises 50 to 98 weight percent of the particles based on the total weight of the porous polymer matrix composite. The porous polymer matrix composites also include a first adhesive layer comprising a first major surface and a second major surface; and a pattern of a first conductive material on the first major surface of the first adhesive layer. Either the first major surface of the first adhesive layer or the second major surface of the first adhesive layer is bonded to the first major surface of the porous polymer matrix, forming the porous polymer matrix composites.

[0003] In another aspect, the present disclosure provides methods of making articles. Such methods comprise contacting a pattern of a conductive material with a first major surface of a first adhesive layer and bonding either the first major surface of the first adhesive layer or a second major surface of the first adhesive layer to a first major surface of a porous polymer matrix composite comprising a plurality of particles interconnected by an open pore network of a thermoplastic polymer.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIGS. 1-6 are elevational cross-sectional views of composite articles according to various embodiments.

[0005] FIG. 7A is an SEM image of a cross-section of a porous polymeric substrate at 500x magnification.

[0006] FIG. 7B is an SEM image of a surface of a porous polymeric substrate at 500x magnification.

[0007] FIG. 8 illustrates a template useful to create a pattern of conductive material.

[0008] FIG. 9 is an optical image of a pattern of conductive material on a porous polymeric substrate.DETAILED DESCRIPTION

[0009] Electrical insulators with high and low dielectric constants (Dk) have many uses in electromagnetic applications. For example, many electronic devices employ capacitors for energy storage and power delivery, which require dielectric mediums of high Dkand low dielectric loss factor (Df). Alternatively, many radio-frequency (RF) antennas minimize signal latency, distortion, and loss by employing dielectric materials with low Dkand low Df. The exact dielectric specification depends on the specific application, making composite materials with tunable properties important for RF control and signal integrity

[0010] Polymeric binders have a relatively low dielectric constant, typically about 2 to 4; therefore, large amounts of high-dielectric particles (e.g., ceramics) are often incorporated into a polymer matrix when a high electric field density is important (e.g., in capacitive or self-resonant devices). For applications requiring a low dielectric constant, a film with significant void space is often desired, while additional particles may be incorporated to improve mechanical properties. In some applications, the desired Dkis as close to the Dkof air, i.e., 1, as possible, necessitating composite materials with as high of a pore volume as is achievable, while other applications require specific low Dkvalues, necessitating a specific control of the pore volume fraction. United States Patent No. US 11,732,104 B2 (“Polymer Matrix Composites Comprising Dielectric Particles and Methods of Making the Same”) describes a polymer matrix composite comprising a porous polymeric network structure and a plurality of particles. The dielectric properties can be adjusted by varying the compositions and amounts of particles used, and by controlling the void volume in the composite.

[0011] In some cases, planar conductive features such as traces, microstrips, interdigitated capacitors, spiral inductors, antenna elements, and terminations are often patterned onto dielectric substrates for circuit-based applications such as signal handling, power generation, antennas, and capacitive touch sensors. The impedance of these conductive features is an explicit function of the Dkof the dielectric substrate, making tunable composite materials important for optimizing circuit design, geometry, and performance.

[0012] Generally, the articles of the present disclosure comprise a porous polymer matrix composite comprising a plurality of particles held in a porous polymer matrix and a pattern of conductive material adhesively bonded to at least one major surface of the porous polymer matrix composite. The articles can enable independent process control of the dielectric substrate and the conductive features, overcoming challenges associated with applying traditional circuit-board fabrication techniques (e.g., as high-temperature process steps like sintering, drying, and solder reflow) to porous polymer composites. Additionally, it may be difficult to achieve acceptable adhesion of a conductive material directly to the porous polymer matrix. By using an adhesive to bond the conductive features to the porous polymer matrix, the articles of the present disclosure allow the practitioner to decouple the electrical properties of the conductive material from the ability to attach the conductive pattern to the porous polymer matrix.

[0013] The porous polymeric matrix, which may also be described as a porous polymeric network, may be a porous phase separated polymeric network. Generally, the porous polymeric matrix includes a porous polymeric network structure comprising a plurality of interconnected strands. The polymeric matrix is a continuous network structure (e.g., the polymer matrix is open- celled with continuous voids or pores) and forms interconnections between the voids extending throughout the structure. The geometry of the strands is not particularly limited and may include one or more of, e.g., fibrils, nodules, nodes, open cell walls, leafy laces, spheres, lattices, or honeycombs. Such porous network stmctures are distinguished from a solid matrix material or a closed cell foam comprising primarily isolated voids.

[0014] In some cases, the porous polymeric matrix may include a 3-dimensional reticular structure that includes an interconnected network of polymeric fibrils. In some cases, individual fibrils may have an average width in a range from 10 nanometers to 5 micrometers, as may be measured by microscopy. In some cases, finer fibrils may be useful, e.g., 10 to 1000 nm or 10 to 500 nm. In some cases, larger fibrils may be useful, e.g., 500 nm to 5 micrometers or 1 to 5 micrometers. Generally, the porous polymer matrices may include both fine and large fibrils as well as other features such as nodes, e.g., where fibrils intersect.

[0015] Regardless of the structure, the polymeric matrix is porous, i.e., it has a porosity of at least 25%. In some cases, the polymeric matrix has a porosity of at least 30%, or even at least 40%. In some cases, the polymeric matrix has a porosity of 25 to 80%, e.g., 25 to 70%, 30 to 60% or even 30 to 50%. The porosity can be determined from the measured and theoretical density of the composite, as described below.

[0016] The porous polymeric matrix also has continuous open cell voids or pores forming interconnections between the polymer strands, extending through the structure and interconnecting with the particles. The pore structure may be open, enabling fluid communication from an interior region of the polymeric network structure to an exterior surface of the polymeric network structure and / or between a first surface of the polymeric network structure and an opposing second surface of the polymeric network structure. In some embodiments, the porous polymeric matrix may be comprised of closed cell voids. In some cases, the pore size can range from 0.01 micrometers to 100 micrometers, e.g., 0.05 to 50 micrometers, 0.5 to 40 micrometers, or 1 to 20 micrometers. The pore size can be determined by various porosimetry techniques, e.g., (bubble point, mercury porosimetry) or via microscopy, e.g., (scanning electron microscopy).

[0017] Generally, the polymer comprises at least one thermoplastic polymer. As used herein, the term “polymer” includes both homopolymers and copolymers (e.g., block copolymers or random copolymers). Thermoplastic polymers are generally characterized as being partially crystalline and exhibiting a melting point. In some cases, the thermoplastic polymer may have a melting point in a range from 120 to 350 °C, e.g., from 120 to 300 °C, 120 to 250 °C, or even 120 to 200 °C. The melting point of the thermoplastic polymer can be measured by known techniques in the art (e.g., the on-set temperature measured in a differential scanning calorimetry (DSC) test, conducted with a 5 to 10 mg sample, at a heating scan rate of 10 °C / min., while the sample is under a nitrogen atmosphere).

[0018] The selection of the thermoplastic polymer(s) may depend on a variety of process and end use factors and is not particularly limited. Suitable thermoplastic polymers include polyolefins, polyurethanes, polyesters, polyethers, polycarbonates polyimides, polysulphones, polyether sulphones, polyphenylene oxides, polyacrylates (e.g., thermoplastic polymers formed from the polymerization of monomer(s) containing an acrylate functional group), polymethacrylates (e.g., thermoplastic polymers formed from the polymerization of monomer(s) containing a methacrylate functional group), styrene and styrene-based random and block copolymer, chlorinated polymers, and fluorinated polymers. Certain polymers may be particularly well-suited to dielectric applications, e.g., polyolefins, polylactic acids, poly(ethylene-co-chlorotrifluoroethylene), polyvinylidene fluoride, and polytetrafluoroethylene. Suitable thermoplastic polymers also include a mixture of at least two thermoplastic polymer types (e.g., a mixture of polyethylene and polypropylene or a mixture of polyethylene and poly aery late).

[0019] In some cases, the thermoplastic polymer comprises polyethylene (e.g., ultra-high molecular weight polyethylene, UHMWE) or polypropylene (e.g., ultra-high molecular weight polypropylene, UHMWP). As used herein, ultrahigh molecular weight polymers have a numberaverage molecular weight of at least 0.5 x 10^ grams / mole, e.g., 1 x 10^ to 8 x 10^ grams / mole. The number average molecular weight can be measured by techniques known in the art (e.g., gel permeation chromatography (GPC)). GPC may be conducted in a suitable solvent for the thermoplastic polymer, along with the use of narrow molecular weight distribution polymer standards (e.g., narrow molecular weight distribution polystyrene standards).

[0020] The porous polymer matrix composite further includes a plurality of particles. The interconnected polymeric stmctures may adhere directly to the surface of the particles and act as a binder for the particles. In this regard, the space between adjacent particles (e.g., particles or agglomerate particles) may include porous polymeric network structures, as opposed to a solid matrix material, thereby providing the desired porosity.

[0021] Generally, the particles are dispersed within the polymeric network structure and held in place by the porous polymer network, which requires at least some minimal contact between the particles and the polymeric matrix. However, the external surfaces of the individual particles (e.g., individual particles or individual agglomerates of particles) may be mostly uncontacted or uncoated by the polymer, partially coated by the polymer, or even fully coated by, e.g., embedded in, the polymer. In some cases, no greater than 50% of the external surface area of the particles is in direct contact with the polymer. In some cases, not greater than 40, 30, 25, 20, 10, 5, or even not greater than 1%, based on the total surface area of the external surfaces of the individual particles is in contact with polymeric network structure.

[0022] Any suitable electrically insulating particles may be used. In some cases, solid, hollow, or porous particles may be used. The particle may include organic and / or inorganic materials. For example, in some cases, solid glass beads or hollow glass microspheres (HGM) may be used. In some cases, solid or hollow ceramic particles, including but not limited to barium titanate, alumina, titania, boron nitride, silicon nitride, and zirconia. In some cases, solid or hollow polymeric particles may be used. In some cases, porous particles, i.e., particles comprising open or closed cell pores, may be used. In some cases, the particles may be surface treated. For example, glass beads and HGM may be surface treated with silanes, organic coatings, metal oxides, or combinations thereof.

[0023] In some cases, dielectric particles may be used. Typical dielectric particles comprise inorganic materials such as ceramics and glass. Exemplary ceramic dielectric particles include those comprising at least one of barium titanate, alumina, or titania. Exemplary glass dielectric particles include hollow glass microspheres coated with at least one of a metal and a metal oxide, often both.

[0024] The porous polymer matrix composites comprise high loadings of the particles, e.g., at least 50 weight percent particles based on the total weight of the particles and the polymer. In somecases, the porous polymer matrix composite comprises 50 to 98 wt.%, e.g., 50 to 90 wt.%, or even 50 to 80 wt.% of the particles.

[0025] The porous polymer matrix composites have a high void volume. The total void volume includes the void volume contributed by the pores or voids in the polymer matrix and the void volume associated with the hollow or porous particles, if any.

[0026] Generally, the porous polymer matrix composites have a total percent void volume of at least 60%, e.g., at least 70% or even at least 80%, based on the total volume of the composite. In some cases, the composites have a total percent void volume of 60 to 95%, e.g., 70 to 95%, 80 to 95%, or even 80 to 90%, based on the total volume of the composite. Both open-cell and closed-cell porosity can be measured using gas pycnometry.

[0027] The porous polymer matrix composites have a low density. The low density is achieved by the pores or voids in the polymer matrix and the void volume associated with the hollow or porous particles, if any. Generally, the porous polymer matrix composites have density of less than 0.20 g / cc, e.g., less than 0.15 g / cc, or even less than 0.10 g / cc. In some cases, the composites have a density of 0.05-0.2 g / cc, e.g., 0.08-0.15 g / cc, 0.1-0.15 g / cc, or even 0.1 to 0.13 g / cc, based on the Archimedes density measurements of the entire composite according to the following formula:D =Mc,CA(MCIA~MC,W) / DW’ wherein: DQ = density of the porous polymer matrix composite;Me A= mass°f ^e porous polymer matrix composite measured in air;= mass of the porous polymer matrix composite measured submerged in water; and D\y = density of water.

[0028] The thickness of the porous polymer matrix composite may be selected to meet specific needs. In some cases, thin composites may be desired, e.g., a thickness of no greater than 5000 micrometers, e.g., no greater than 2000 micrometers or even no greater than 1000 micrometers. In some non-limiting cases, the thickness may be from 50 to 5000 micrometers, e.g., 100 to 2000 micrometers, 200 to 1500 micrometers, or even 500 to 1000 micrometers.

[0029] Methods of making the porous polymer matrix composites of the present disclosure are described in detail in United States Patent No. US 11,732,104 B2. For example, the porous polymer matrix composite may be produced by an induced phase separation of a miscible thermoplasticpolymer-solvent solution. In some cases, the induced phase separation is at least one of thermally induced phase separation or solvent induced phase separation.

[0030] For example, in one method, the polymer matrix composites can be prepared by combining (e.g., mixing orblending) a thermoplastic polymer, a solvent, and a plurality of particles to provide a slurry; forming the slurry into an article (e.g., a layer); heating the article in an environment to retain at least 90 to 100 percent by weight of the solvent in the article, based on the weight of the solvent in the article, solubilizing at least 50 and up to 100 percent of the thermoplastic polymer, based on the total weight of the thermoplastic polymer; inducing phase separation of the thermoplastic polymer from the solvent to provide the polymer matrix composite, and removing up to 100% by weight of the solvent.

[0031] In another method, the polymer matrix composites can be prepared by combining (e.g., mixing or blending) a thermoplastic polymer, a solvent for the thermoplastic polymer, and a plurality of particles to form a miscible thermoplastic polymer-solvent solution; inducing phase separation of the thermoplastic polymer from the solvent to provide the polymer matrix composite, and removing up to 100% by weight of the solvent.

[0032] In some cases, the phase separation is induced thermally (e.g., via thermally induced phase separation (TIPS)). In some cases, the phase separation is induced chemically (e.g., via solvent induced phase separation (SIPS)). However, other forms of phase separation may also be used.

[0033] A 500x magnification SEM images of an exemplary porous polymeric matrix composite are shown in FIG. 7A (cross-section) and FIG. 7B (surface). The porous polymeric matrix composite comprises particles 100 bound by a highly porous network of polymer fibrils 110 interconnected at nodes 120 forming an open pore structure. Collectively, the fibrils and nodes may be referred to as strands. As shown, only a very minor portion of the particle surface area is in contact with the polymer strands.

[0034] While this structure provides the desired electrical properties for supporting the planar conductive features of the present disclosure, direct patterning and / or curing of conductive materials, such as conductive inks, on such a structure presents many challenges. For example, the major surfaces of the porous polymeric matrix composite are uneven, with surface roughness and nonuniformities larger than the typical thicknesses of the desired conductive ink layers. For example, surface roughness may exceed 10, 25, or even 50 micrometers. In addition, the surface and bulk structure are highly porous, and the composites can be very brittle. As a result, it is very difficult to provide high fidelity, planar conductive patterns on the surfaces. For example, liquid inks can spread and distort the desired pattern. Higher viscosity inks typical of conductive inks and pastes may limitspreading, but often require higher pressures to transfer, which can itself cause spreading and damage to the fragile matrix. In addition, the higher pressures may cause the inks to conform to the rough surfaces, further distorting the patterns. Similar technical problems can arise for other conductive materials, such as vapor-deposited or electroplated metal layers, or free-standing metal foils.

[0035] Also, when direct printed, the high curing and sintering temperatures required for some conductive inks can change the porous substrate’s electrical and mechanical properties, for example changing the porous polymer network morphology or decreasing the dielectric composite’s tensile strength. In addition, due to the highly porous composite structure, there is limited area available for binding the conductive material to the surface of the composite, which can result in poor adhesion, printing gaps, and flaking.

[0036] The present inventors discovered that conductive materials could be directly bonded to the surfaces of the porous polymeric composites with an adhesive. In some cases, the materials can be applied (e.g., printed) directly on the adhesive. In other cases, the materials may be applied (e.g., printed) on a release layer. An adhesive can then be coated on or laminated to the material and release layer and, when peeled off, cleanly remove the material layer by transferring it to the adhesive. In either case, the adhesive and conductive material are then laminated to a major surface of the porous polymer matrix.

[0037] In some cases, the adhesive may be bonded such that the conductive material is positioned between the adhesive layer and a major surface of the porous polymer matrix. In some cases, the opposite side of the adhesive is laminated to a major surface of the porous polymer matrix so that the conductive material remains exposed to the surrounding atmosphere. In either case, a protective layer may be applied by, e.g., coating or laminating, to protect the conductive material against damage due to oxidation or abrasion. The protective layer can also add stiffness, depending on its composition. For example, a polymeric film may be laminated to the adhesive layer on the side opposite the porous polymer matrix. The specific configuration may depend on the desired electromagnetic properties of the matrix, adhesive layer, protective layer, and any additional layers or materials in the application.

[0038] Advantageously, having the conductive material facing toward the porous polymer matrix can help minimize the dielectric constant (Dk) by avoiding the interposition of a high- dielectric adhesive layer. As a further benefit, this option provides greater flexibility in layer configuration, including broader spacing ranges between the conductive material and the substrate.

[0039] In some embodiments, the conductive material can be at least partially embedded within the adjacent adhesive layer. In some embodiments, the conductive material is fully embedded within the adjacent adhesive layer, such that the conductive material and adhesive layer have coplanar major surfaces. Benefits of embedded configurations include the reduction of adhesive thickness for reduced dielectric properties as well as the enablement of thinner composites overall.

[0040] The foregoing embodiments are exemplified by FIGS. 1-6. FIG. 1 shows a composite article 10 comprised of a release layer 12, a conductive layer 14 disposed on the release layer 12 according to a desired two-dimensional pattern (which may be discontinuous), and an adhesive layer 16 disposed on the release layer 12 and the conductive layer 14. The conductive layer 14 is embedded flush with the adhesive layer 16 such that the major surfaces of the conductive layer 14 and adhesive layer 16 that face the release layer 12 are coplanar with each other.

[0041] FIG. 2 shows a composite article 20 with a similar construction, in which a similar conductive layer 24 is disposed on release layer 22 and an adhesive layer 26 is laminated onto both layers 22, 24. As evident in this figure, lamination can produce some voids adjacent to the features of the conductive layer 24, but otherwise this method is capable of providing a layer configuration that is similar to that depicted in FIG. 1.

[0042] FIG. 3 shows a composite assembly 30 obtained by peeling the release layer 12 away from the composite article 10 of FIG. 1 and then adhesively bonding the remaining layers onto a porous polymer matrix 32. As shown, the conductive layer 34 is fully embedded in the composite assembly 30 between the porous polymer matrix 32 and the adhesive layer 36, with the major surface of the porous polymer matrix 32 facing toward the conductive layer 34 and adhesive layer 36 being generally planar.

[0043] FIG. 4 shows a composite assembly 40 obtained using a similar method as described above, except the remaining layers of composite article 10 are inverted before being adhesively bonded to the porous polymer matrix 32. This results in a configuration in which the conductive layer 44 is exposed at the top of the composite assembly 40 and spaced apart from porous polymer matrix 42 by adhesive layer 46.

[0044] FIG. 5 shows a composite assembly 50 obtained using a similar method to that described above for the composite assembly 30 in FIG. 3, except the composite article 20 was used instead of the composite article 10. As before, the conductive layer 54 is fully embedded in the composite assembly 50 between the porous polymer matrix 52 and the adhesive layer 56.

[0045] Finally, FIG. 6 shows a composite assembly 60 according to yet another variant where an adhesive layer 66 is bonded to porous polymer matrix 62 and a patterned conductive layer 64 isdisposed on the exposed major surface of adhesive layer 66. The conductive layer 64 protrudes from the exposed major surface of the adhesive layer 66, making the exposed major surface of the composite assembly 60 non-planar. This can occur, for example, when there is lamination of an adhesive onto a release liner to peel the structure off. In these instances, some wetting of the adhesive up the sides of the conductive features may occur. It can be appreciated that this configuration provides a high degree of separation between the conductive layer 64 and the porous polymer matrix 62.

[0046] Although the adhesive is not particularly limited, in some cases a pressure sensitive adhesives may be preferred. The use of a pressure sensitive adhesive can facilitate the adhesion of the ink to the adhesive and the adhesive to the porous substrate without requiring heating or curing steps. However, in some cases thermally, radiation, or solvent activated, or curable adhesives may be used.

[0047] Generally, any pressure sensitive adhesive (PSA) may be used. The selection of the PSA may depend on the selection of the conductive material, the thermoplastic polymer(s), and the particles to which the PSA should bond. Suitable PSA include, but are not limited to, silicones, rubbers, and acrylates, including methacrylates.

[0048] The adhesive may be provided as a single-coated tape, a double-coated tape, or an adhesive transfer tape. Generally, a single coated tape has an adhesive permanently bonded to one surface of a carrier (e.g., paper, polymeric film), while a double-coated tape has an adhesive layer permanently bonded to opposing surfaces of the carrier. Generally, an adhesive transfer tape differs in that the adhesive layer is removably -bonded to a surface of a carrier, e.g., a release liner. In some cases, the tape may have a pattern-coated adhesive. In such cases, the conductive ink may be applied in registration with the adhesive pattern. The adhesive can be applied via either a wet or dry process. For example, the adhesive may be coated onto the patterned conductive material, then solidified to create an adhesive-backed tape, or it may be laminated as an already solidified tape.

[0049] If a single-sided tape is used, the conductive material may be directly patterned on the adhesive layer or laminated against and transferred to the adhesive layer. The adhesive layer may then be bonded to the surface of the porous substrate with the conductive pattern located between the porous substrate and the adhesive layer. The carrier would then overlay the adhesive layer. In some embodiments, the adhesive layer is patterned on a carrier and, in the final construction, the carrier extends over the adhesive in some areas and over air in other areas where there is no adhesive. In these constructions, the conductive material can be disposed on either side of the carrier.

[0050] If a double-sided tape is used, the conductive material may be directly patterned on a first adhesive layer or laminated against and transferred to the first adhesive layer. In some cases, the patterned side may then be laminated to a surface of the porous substrate with the conductive pattern located between the porous substrate and the first adhesive layer. In this construction, the second adhesive layer can be adhered to any desired surface or film. Alternatively, the second adhesive layer could be laminated to the porous substrate, leaving the conductive pattern exposed. In such cases, a carrier may be coated on or laminated to the first adhesive layer, covering the conductive pattern. As before, the conductive material can be disposed on either side of the carrier layer.

[0051] If an adhesive transfer tape is used, the conductive material may be applied directly to or transferred to the exposed surface of the adhesive layer. This adhesive surface may then be adhered to the porous substrate, positioning the conductive pattern between the surface of the porous substrate and the adhesive layer. The transfer tape carrier may then be removed, exposing the opposite surface of the adhesive and, optionally, an additional layer may be applied. Alternatively, after applying or transferring the conductive pattern to the exposed surface of the adhesive layer, a protective layer may be applied to cover the conductive pattern. This structure may then be removed from the tape carrier and adhered to the surface of the porous substrate via the second surface of the transfer adhesive. Optionally, the conductive material is first patterned on a carrier, overcoated with adhesive layer, and then both are transferred to the porous substrate.

[0052] Generally, a conductive pattern may be adhered to one or both major surfaces of the porous polymeric network. The patterns may be the same or independently selected.

[0053] Useful conductive inks may include any material suitable for producing patterns of conductive material. Such inks may contain metal particles such as nanoparticles, flakes, or wires of any suitable metal or alloy. Exemplary inks may include at least one of silver and copper. The ink may contain organic conductors, such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (“PEDOT:PSS”), carbon, or graphene. The conductive ink may include any suitable solvent, including water, or may be solvent-free. The conductive ink may include any suitable binders, dispersants, and / or surfactants. The conductive ink may be solidified via evaporation of a volatile component (such as a solvent) or via a reaction, for example a free-radical reaction initiated by UV light, or both (i.e. an ink may include both a solvent and a reactive component)

[0054] Generally, the method of applying, e.g., printing, the pattern of conductive ink is not particularly limited. The selected method should be capable of achieving the desired resolution and may be required to be compatible with patterning on a pressure sensitive adhesive surface. Suitableapplication methods include inkjet printing, flexographic printing, gravure printing, stencil printing and screen printing.

[0055] Alternatives to using a conductive ink are also possible. For example, a pattern of conductive material can be fabricated directly by various approaches. One approach involves vacuum deposition techniques such as evaporation or sputtering, where a conductive material is vaporized in a vacuum chamber and deposited onto a substrate, forming a thin conductive layer. Electroplating is another method, where a metal is deposited onto a substrate by passing an electric current through a solution containing metal ions, resulting in a conductive coating. Additionally, calendaring involves passing metal coils through rollers to achieve a desired thickness and surface finish, producing a continuous conductive layer. Each of these methods allows for the creation of a conductive layer with specific properties tailored to the intended application. Free standing metal layers, such as metal foils, can also be procured from various commercial sources.

[0056] Patterning of the conductive layer can be achieved in various ways. Patterning can be accomplished in situ by masking the substrate prior to coating. Masking involves applying a resist material to the foil in a desired pattern, followed by etching or deposition processes to remove or add material only in unmasked areas, thereby creating the pattern. Die cutting is another method, in which a continuous metal layer is provided and a die used to mechanically cut the foil into specific shapes and patterns. Photolithography can also be employed, using light to transfer a geometric pattern from a photomask to a light-sensitive chemical photoresist on the substrate. Each of these techniques can enable precise control over the patterning of conductive layers for the provided articles and methods.

[0057] Patterned metal layers can be provided using any known method. Useful methods of providing and transferring patterns of conductive material are known and described, for example, in U.S. Patent Publication Nos. 2023 / 0049504 (Velamakanni et al.) and 2023 / 0382151 (Johnston et al.).

[0058] Generally, any desired conductive pattern may be produced and may be selected by the desired electrical properties of the final device. For example, the patterns may include lines, grids, circles, and polygons, as well as irregular, and even random or arbitrary shapes.

[0059] In some cases, thin features are desired. For example, in some cases, the conductive ink pattern has a thickness of no greater than 50 micrometers, e.g., no greater than 30, or even no greater than 10 micrometers. For example, some applications desire thickness from 1 to 50 micrometers, e.g., 1 to 25 micrometers or even 3 to 15 micrometers. However, thinner or thicker features may be used.Example

[0060] A porous polymer matrix composite was produced using the following approach, as outlined in US 11,732,104. A mixture of 83 wt. % solvent (ISOPAR G isoparaffinic hydrocarbon fluid from Exxon Mobil, Houston, Texas), 4.6 wt. % ultrahigh molecular weight polyethylene powder (GUR 2126, with average molecular weight of 4.2 x 10^ g / mol, from Celanese, Dallas, Texas), and 12.4 wt. % hollow glass microspheres (KI glass bubbles, 65 micrometer average diameter, 0.125 g / cc average density, from 3M Company, Saint Paul, MN), were blended together using an air mixer and a prop blade. A quantity of approximately 100 mL of the resulting mixture was then poured onto a first sheet of PET film and a second piece of PET film was laminated on top to produce a thin liquid layer. This laminate was placed in an oven at 150 °C for approximately five minutes, after which the sample was removed from the oven and allowed to cool slightly. The top PET film was then removed, and the sample was put back in the oven for an additional 10 minutes at 150 °C to evaporate the solvent.

[0061] The resulting porous polymeric matrix contained 72.9 wt.% of the hollow glass microspheres (i.e., the dialectic particles) based on the total weight to of the polymer and particles. This porous polymer matrix composite was 0.878 mm (34.6 mils) thick, had a Gurley air flow of 139.1 sec / 50 cm^, a bubble point pressure of 45.3 kPa (6.57 psi) as measured with a 60 / 40 IPA / water wetting solution, an Archimedes density of 0.115 g / cc, a coefficient to thermal expansion (CTE) of 24.3 um / (um«°C), a dielectric constant (Dk) of 1.125 and a dissipation factor (Df ) of 0.00095.

[0062] A flat bed nickel stencil was fabricated by Sefar, Depew NY) with an open hole pattern. As shown in FIG. 8, the pattern comprised an array of hexagonal openings 200. Each hexagonal opening had a major axis, A, and a side length, S. The openings were aligned in a hexagonal array with a vertical spacing, V, and pattern pitch (P). The dimensions of the stencil are summarized in Table 1.

[0063] A sheet of release liner (RF032 release liner from SK microworks America, Convington, GA) was taped to a flat glass surface with the release-treated side (i.e., the release layer) facing up. The flat bed stencil was placed on the release surface. A conductive ink (silver paste 125-13(LP), purchased from Creative Materials, Ayer, MA) was placed on the stencil, and a 2.5 cm thick squeegee was used to press the ink through the stencil and onto the release surface. The stencil was removed, and the printed construction was placed in an oven at 150 °C for approximately five minutes to dry the ink.

[0064] A piece of acrylic adhesive, double-sided tape (Double-Sided Tape, Permanent, Clear from 3M Company, Saint Paul, MN) was laminated to the top of the dried conductive ink and thenpeeled off, cleanly removing the printed silver ink from the release surface. The double-sided tape with the pattern of conductive ink was then laminated to the major surface of the porous polymeric matrix composite with the ink positioned between the adhesive and the porous polymeric matrix composite. The resulting construction is shown in FIG. 9.

[0065] The dimensions of the transferred conductive ink pattern were measured using optical microscopy. These measured dimensions are compared to the stencil patterns in Table 1. As shown, excellent feature fidelity was maintained when the conductive ink pattern was transferred to the foam.Table 1: Feature fidelity measurements in millimeters.

[0066] In addition, as shown in FIG. 9, the transferred ink pattern 300 (dark hexagons) has sharp edges 310 and no visible voids. Note, the white lines 320 are wrinkles in the adhesive layer overlaying the ink pattern and the porous polymer composite 340, not a defect in the ink pattern.

Claims

What is Claimed is:

1. An article comprising a porous polymer matrix composite comprising a plurality of particles interconnected by an open pore network of a thermoplastic polymer, where in the porous polymer matrix has a thickness extending from a first major surface of the porous polymer matrix to a second major surface of the porous polymer matrix, wherein the porous polymer matrix composite comprises 50 to 98 weight percent of the particles based on the total weight of the porous polymer matrix composite; a first adhesive layer comprising a first major surface and a second major surface; and a pattern of a first conductive material on the first major surface of the first adhesive layer; wherein either the first major surface of the first adhesive layer or the second major surface of the first adhesive layer is bonded to the first major surface of the porous polymer matrix.

2. The article of claim 1, wherein the first conductive material comprises a first conductive ink.

3. The article of claim 2, wherein the first major surface of the first adhesive layer is bonded to the first major surface of the porous polymer matrix and the first conductive ink is positioned between the first adhesive layer and the porous polymer matrix.

4. The article of claim 3, further comprising a cover film bonded to the second major surface of the first adhesive layer.

5. The article of claim 1, wherein the second major surface of the first adhesive layer is bonded to the first major surface of the porous polymer matrix.

6. The article of claim 5, further comprising a cover film bonded to the second major surface of the first adhesive layer and the first conductive ink is positioned between the first adhesive layer and the cover film.

7. The article according to any one of the preceding claims, further comprising a second adhesive layer comprising a first major surface and a second major surface; and a pattern of a second conductive material on the first major surface of the second adhesive layer; wherein either the first major surface of the second adhesive layer or the second major surface of the second adhesive layer is bonded to the second major surface of the porous polymer matrix.

8. The article according to claim 7, wherein the second conductive material comprises a second conductive ink.

9. The article according to any one of claims 2-8, wherein the first conductive ink comprises silver.

10. The article according to any one of claims 2-9, wherein the pattern of the first conductive ink comprises an array of discrete elements.

11. The article according to any one of the preceding claims, wherein the thermoplastic polymer comprises at least one of a polyester, a polyolefin, a polyimide, or a fluoropolymer.

12. The article of claim 11, where the thermoplastic polymer comprises an ultrahigh molecular wight polyethylene or an ultrahigh high molecular weight polypropylene.

13. The article according to any one of the preceding claims, wherein the particles are selected from the group consisting of hollow glass microspheres and ceramic particles.

14. The article of claim 13, wherein the particles comprise hollow glass microspheres.

15. The article of claim 14, wherein hollow glass microspheres are coated with at least one of a metal and a metal oxide.

16. The article according to any one of the preceding claims, wherein the porous polymer matrix composite comprises 50 to 80 weight percent of the particles based on the total weight of the porous polymer matrix composite.

17. The article according to any one of the preceding claims, wherein porous polymer matrix composite has a density of 0.05 to 0.2 grams per cubic centimeter.

18. The article according to claim 17, wherein porous polymer matrix composite has a density of 0.08 to 0.15 grams per cubic centimeter.

19. A method of making an article comprising contacting a pattern of a conductive material with a first major surface of a first adhesive layer and bonding either the first major surface of the first adhesive layer or a second major surface of the first adhesive layer to a first major surface of a porous polymer matrix composite comprising a plurality of particles interconnected by an open pore network of a thermoplastic polymer.

20. The method of claim 19, wherein contacting the pattern of the conductive material with the first major surface of a first adhesive layer comprises forming the pattern of conductive material on a release surface, contacting the first major surface of the first adhesive layer with the pattern of conductive material and the release surface, and removing the first adhesive layer and the conductive material from the release surface.

21. The method of claim 19, wherein contacting the pattern of the conductive material with the first major surface of a first adhesive layer comprises forming the pattern of conductive material directly on the first major surface of the first adhesive layer.

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