Hybrid flexible-rigid electrical interconnection system

Abstract

An electrical interconnection system is disclosed, comprising: i) an interconnection board comprising an intrinsically inelastic substrate having a first face and an opposite second face, and at least one electrically conductive track on and / or within at least a portion of the substrate; ii) a stretchable interconnect comprising an intrinsically elastic substrate comprising at least one recess or groove comprising at least one compliant electrically conductive element therein, the at least one recess or groove being configured to accommodate the at least one electrically conductive track of the interconnection board; and iii) at least one electrically conductive paste mass within the at least one recess or groove configured to electrically connect the at least one compliant electrically conductive element with the at least one electrically conductive track.

Description

TECHNICAL FIELD

[0001] The present invention is in the field of electronic and electrical devices. In particular, the present invention relates to hybrid (flexible / rigid) electrical interconnection systems, methods for producing the same, and low-profile, hybrid (flexible / rigid) multi-component electronic / electrical circuits and devices. BACKGROUND

[0002] In the field of wearable and implantable devices, soft and stretchable materials have been utilized to produce devices that can conform to complex static and dynamic 3D shapes. In particular, in the field of implantable neural interfaces, it has recently been shown that rigid materials, which are conventionally used as electronic substrates, despite being non-toxic, cause inflammatory reactions when implanted due to mechanical mismatch between the device and the soft host tissue. Using conformable, soft and stretchable materials, which are mechanically closer to the target tissue, can mitigate this side effect and permit safe and reliable implantation in the body.

[0003] Implantable devices consist of a substrate and a package, which generally dictate the mechanical signature of the device, depending on the shape and materials used, and embedded electrical tracks and interconnects that transmit electrical signals to and from a target location within the body of a subject. For the substrate, several material classes can be used, such as elastomers (silicone, polyurethane, natural rubber, etc.), hydrogels (polymer networks that can absorb large amounts of water), thermoset and thermoplastic plastics (polyimide, parylene C, etc.), and others. The embedded electrical interconnects must accompany the stretchable behavior of the substrate and package to guarantee device functionality. This is achieved by using intrinsically stretchable conductors (e.g. conductive polymers) or by engineering elasticity into rigid conductors (e.g. patterned metal spring structures) or embedded thin flexible interconnects in soft carriers. Multiple independent interconnects are typically included in the device design, so that multiple channels can target different locations on the tissue. The width of these electrical lines is typically tens to hundreds of micrometers, and is separated by gaps of the same size, with the goal of minimizing the overall size of the device. The typical number of parallel channels in implantable / wearable electronic devices is in the range of 8 to 128.

[0004] A prevalent challenge is the reliable connection of the numerous electronic circuits patterned on soft substrates to external hardware (such as stimulators or processing units) or implanted hardware (such as implanted pulse generators) due to the lack of established electronic packaging technology compatible with soft materials. The mechanics of soft substrates or carriers make them unsuitable for conventional connection technologies (i.e. surface mount rigid connectors, wire bonding, silicon packaging) which, if possible at all, would anyway make the device rigid. The most widely adopted connection scheme for soft electronic devices relies on connecting small wires to each individual channel on the substrate. This is both unreliable and labor intensive and imposes significant scaling limitations on the size of the connection points (from hundreds of microns to several millimeters) as the wiring process is almost impossible to scale down.

[0005] International patent application WO 2017 / 203441 describes a system for obtaining an electrical interconnection between an intrinsically stretchable conductor and a non-intrinsically stretchable conductor or between two intrinsically stretchable conductors. The system is particularly suitable for producing a device for neural stimulation and / or neural recording, implantable in the human or animal body, conformable and deformable. Despite the progress in the field of hybrid soft / rigid electrical interconnections, the described interconnection system presents some drawbacks that make it not optimal for implantable devices: in particular, the alignment between the various channels should be accurately performed during the manufacturing steps to assemble the various electrical channels / their tracks between them, which can bring quality problems during the manufacturing process and ultimately lead to electrical malfunctions; moreover, the external electrical conductors are joined to the interconnection system via known techniques such as welding, soldering, mechanical fastening or gluing with any kind of conductive glue. In one typical embodiment, the connection is made by means of through holes made on the electrical board, which are filled with a conductive material (e.g. tin), one end of the conductors being embedded in the conductive material. This gives rise to some problems related to the manufacturing burden, redistribution of stresses after elongation (strain) of the soft part of the interconnection system and increase of the bulky volume of the overall system, which is not desirable for implantable devices.

[0006] To date, to the best of the inventors' knowledge, there is still a lack of a method that is seamless in terms of foot print, reliable, scalable to a large number of channels and prevents the device from being excessively rigid at the connection points. SUMMARY

[0007] To solve and overcome at least some of the drawbacks of the prior art solutions mentioned above, the present inventors have developed a solution to seamlessly connect a soft electronic interface with non-extendable electrical devices, such as electrical panels, with improved features and capabilities.

[0008] It is an object of the present application to provide an electrical interconnection system that overcomes or at least reduces the drawbacks affecting the known solutions according to the prior art, outlined above.

[0009] In particular, it is a first object of the present application to provide an electrical interconnection system that is optimized in size and shape to be advantageously contained into thin form factor devices, and in particular compliant biomedical devices for permanent or temporary implantation inside the body of a subject.

[0010] It is a further object of the present application to provide a simple and reliable method for producing an electrical interconnection system having mixed elastic / non-elastic properties.

[0011] All these objects have been achieved, as described herein and in the appended claims, by the present application.

[0012] In view of the drawbacks and / or problems affecting the electrical interconnection systems of the prior art, outlined above, according to the present application, there is provided an electrical interconnection system, comprising: i) an interconnection board comprising an intrinsically non-elastic substrate having a first face and an opposite second face, and at least one electrically conductive track located on and / or within at least a portion of said substrate; ii) a stretchable interconnection comprising an intrinsically elastic substrate comprising at least one recess or groove comprising at least one electrically conductive element therein, said at least one recess or groove accommodating said at least one electrically conductive track of said interconnection board; and iii) at least one electrically conductive paste mass located within said at least one recess or groove electrically connecting said at least one electrically conductive element with said at least one electrically conductive track; wherein said at least one recess or groove fully accommodates said at least one electrically conductive track of said interconnection board, so that said at least one electrically conductive track is fully embedded within said at least one electrically conductive paste mass.

[0013] A further object of the present application relates to a manufacture comprising the above electrical interconnection system.

[0014] In particular, according to the present application, an electrical interconnection system comprises:

[0015] i) an interconnection board comprising an intrinsically non-elastic substrate having a first face and an opposite second face, and at least one electrically conductive track located on and / or within at least a portion of said substrate;

[0016] ii) a stretchable interconnect comprising an intrinsically elastic substrate, the substrate comprising at least one well or groove comprising at least one electrically conductive element therein, the at least one well or groove configured to receive the at least one electrically conductive track of the interconnect board; and

[0017] iii) at least one electrically conductive bolus within the at least one well or groove configured to electrically connect the at least one electrically conductive element with the at least one electrically conductive track.

[0018] According to an embodiment, the at least one electrically conductive bolus consists essentially of a viscoelastic polymer configured to mechanically connect the at least one electrically conductive element with the at least one electrically conductive track.

[0019] According to an embodiment, the substrate of the interconnect board consists essentially of a flexible material.

[0020] According to an embodiment, the intrinsically inelastic substrate is planar at the interconnect site.

[0021] According to an embodiment, the at least one electrically conductive track of the interconnect board is on an elongate member of the intrinsically inelastic substrate.

[0022] According to an embodiment, the elongate member of the intrinsically inelastic substrate is planar.

[0023] According to an embodiment, the interconnect board comprises an array of elongate members, each of the elongate members comprising at least one electrically conductive track.

[0024] According to an embodiment, the stretchable interconnect comprises an array of wells or grooves, each well or groove comprising one of the at least one electrically conductive element therein.

[0025] According to an embodiment, the at least one well or groove is configured to completely receive the at least one electrically conductive track of the interconnect board, such that the at least one electrically conductive track is completely embedded within the at least one electrically conductive bolus.

[0026] According to an embodiment, the at least one electrically conductive element of the stretchable interconnect comprises a stretchable metal film.

[0027] According to an embodiment, the at least one electrically conductive element of the stretchable interconnect is embedded within the intrinsically elastic substrate.

[0028] According to one embodiment, the electrically conductive paste comprises a mixture of a soft polymeric material and a plurality of electrically conductive micrometer or nanometer particles, tube wires and / or sheets.

[0029] According to one embodiment, the encapsulation layer of adhesive and electrically insulating material encapsulates the opposite second face of the interconnection board and at least a portion of the stretchable interconnection, said at least a portion of the stretchable interconnection comprising at least a portion of the at least one recess or groove.

[0030] Preferably, the encapsulation layer consists substantially of an intrinsically elastic material.

[0031] According to one embodiment, the at least one electrically conductive track and / or the at least one electrically conductive element comprises an end configured to be electrically connectable to an external device.

[0032] The present application also relates to a manufactured article comprising an electrical interconnection system as disclosed above, for example a biomedical device configured to be temporarily or permanently implanted within the body of a subject.

[0033] Further embodiments of the present application are defined by the appended claims.

[0034] The above and other objects, features and advantages of the subject-matter presented herein will become more apparent from the studies of the following description in conjunction with the accompanying drawings, which show some preferred aspects of the subject-matter. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1a is a top view of an interconnection board according to one embodiment of the present application;

[0036] Figure 1b and Figure 1c are cross-sectional views taken at different points of the interconnection board of Figure 1a

[0037] Figure 2a is a top view of a stretchable interconnection according to one embodiment of the present application;

[0038] Figure 2b and Figure 2c are cross-sectional views taken at different points of the stretchable interconnection of Figure 2a

[0039] Figures 3a to 3e and Figures 4a to 4e schematically represent steps of a method for manufacturing an interconnection system according to the present application, and Figure 3f Figure 4f are cross-sections of the final manufactured system. Figures 3a to 3f Figures 4a to 4f ​​​​The main difference between the embodiments represented in Figure 3a ) or placed inside the substrate ( Figure 4a );

[0040] Figure 5a is a top view of an interconnection plate comprising an array of fingers, each finger comprising a conductive track thereon, according to an embodiment of the application;

[0041] Figure 5b and Figure 5c are cross-sectional views taken at different points of the interconnection plate of Figure 5a .

[0042] Figure 6a is a top view of a stretchable interconnect comprising an array of recesses or grooves, each recess or groove comprising a conductive element thereon, according to an embodiment of the application;

[0043] Figure 6b and Figure 6c are cross-sectional views taken at different points of the stretchable interconnect of Figure 6a .

[0044] Figures 7a to 7f , Figures 9a to 9f and Figures 11a to 11f schematically represent different embodiments of a method of manufacturing an interconnection system according to the application, and Figure 8 , Figure 10 and Figure 12 represent corresponding cross-sections of the system as finally manufactured, wherein the system comprises: an interconnection plate comprising an array of fingers, each finger being located in a corresponding recess or groove of a stretchable interconnect ( Figures 7a-7f and Figure 8 ); an interconnection plate comprising an array of fingers, all said fingers being located in a single recess or groove of a stretchable interconnect ( Figures 9a-9f and Figure 10 ); an interconnection plate comprising an array of fingers, said fingers being located in pairs in corresponding recesses or grooves of a stretchable interconnect ( Figures 11a-11f and Figure 12 );

[0045] Figure 13 schematically represents an electrical interconnection system according to the application, wherein at least one conductive track and / or said at least one conductive element comprises an end configured to be electrically connectable to an external device. DETAILED DESCRIPTION

[0046] The subject matter described below is illustrated by way of example and not limitation in the figures of the accompanying drawings in which: The subject matter of the present application is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this application. Rather, the inventors have contemplated that the subject matter might also be embodied in other ways, to include different steps or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. Moreover, although the terms "comprise", "comprises" and "comprising" are used herein, they do not exclude other elements. The use of the negative "not" in the phrases "not comprising" and "not comprising" does not exclude the presence of the elements mentioned in the phrases. The use of the indefinite article "an" does not exclude a plurality of elements. Similarly, the use of the indefinite article "a" does not exclude a plurality of elements, unless the context clearly requires that there be one and only one of the elements. The terms "comprise", "comprises" and "comprising" are not used in a restrictive sense, but are used in a permissive sense, i.e. they allow the possibility that the composition or method can include additional elements. The indefinite article "a" or "an" preceding the disclosure of a feature, structure or element does not exclude the presence of a plurality of such features, structures or elements. The disclosure of a single feature, structure or element does not exclude the presence of additional such features, structures or elements.

[0047] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this application belongs. Also, unless otherwise indicated herein, singular articles and singular pronouns are intended to encompass the plural forms as well. Unless otherwise indicated herein, the use of the term "about" in relation to a given value means that the value can vary from the given value by + / - 10%.

[0048] The following description will be better understood by way of the definitions below.

[0049] As used in the following description and claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Also, as used in the following description and claims, the term "or" means "and / or" unless the context clearly dictates otherwise. Similarly, the terms "comprise", "comprises", "comprising", "include", "includes" and "including" are interchangeable with respect to the inclusion of the recited elements. It will be further understood that the terms "comprise", "comprises", "comprising", when used in this specification, do not exclude the presence of other elements or steps. Furthermore, although the terms "comprise", "comprises" and "comprising" are used herein, these terms are used in their open-ended, conventional sense and are intended to cover a wide variety of embodiments.

[0050] Within the framework of the present disclosure, the expression "operatively connected" and similar expressions reflect the functional relationship between the various components of the device or system, in other words, the term means that the components are associated in such a way as to perform the specified function. The "specified function" can vary depending on the different components involved in the connection; for example, the specified function of an electrode operatively connected to a connection means is, for example, to deliver an electric current to a nerve to electrically stimulate it. The skilled person will easily understand and appreciate the specified function of each component of the device or system of the present invention and their association based on the present disclosure.

[0051] The expression "conductive track" refers to any film, path, stripe, strand, lead, etc. that is electrically conductive in nature. For the sake of clarity, the word "electrode" is used herein to denote the distal portion of the conductive track that is in direct contact with the subject's tissue. However, in embodiments of the present invention, the term "electrode" is used to denote the conductive track and its distal, terminal portion that is configured to interface with biological tissue. The conductive track according to the present disclosure is used to connect and / or close an electrical circuit, and is therefore typically an electrical connector or "interconnect". The conductive track is typically a metallic element that conducts electric current towards or away from the electrical circuit, but can be made of any suitable electrically conductive material, including but not limited to metals such as Au, Pt, Al, Cu, etc., as well as any alloys, oxides and / or combinations thereof; electrically conductive polymeric materials; composite materials such as polymeric materials embedded with metallic particles and / or metallic strands or stripes, including insulating materials functionalized with electrically conductive flakes or fibers, e.g. carbon-filled polymers; liquid metals, including alloys or oxides thereof, such as gallium; electrically conductive inks; and any suitable combination thereof. The components of the electrode can be fabricated using micro-lithography and / or micro-integrated electronic devices and other techniques readily available in the art.

[0052] The expression "membrane" or "membranes" relates to the thin form factor of the elements of the device of the application, such as the support substrate and / or the conductive tracks. In general, "membrane" or "membranes" as used herein relates to a layer of material having a thickness that is much smaller than the other dimensions, for example at least one fifth compared to the other dimensions. Typically, a membrane is a solid layer having a top surface and a bottom surface, having any suitable shape, and having a thickness that is typically in the order of nanometers, micrometers or even millimeters, depending on the needs and circumstances, for example the manufacturing steps used to produce it. In some embodiments, the membranes according to the application have a thickness comprised between 1 nm and 10 mm, such as between 1 nm and 10 nm, between 20 nm and 100 nm, between 5 pm and 5 mm, between 5 pm and 1 mm, between 10 pm and 1 mm, between 5 pm and 500 pm, between 50 pm and 500 pm, between 50 pm and 150 pm, between 100 pm and 500 pm, or between 200 pm and 500 pm. When referring to thin electrode membranes, they can have a thickness comprised between 1 nm and 500 pm, such as between 20 nm and 200 nm or between 50 nm and 100 nm. These dimensions are considered optimal in the framework of the application because of the stretchability and mechanical compliance of the device that is to be engaged with the body tissue.

[0053] When referring to electrically conductive elements such as electrodes, tracks and / or interconnects, the term "compliant" refers to the behavior of said electrically conductive element to adapt to the shape change of the support to which it adheres, without significantly impairing the mechanical and / or electrical properties. The term "compliant" is intended to encompass any conformable structure that is compressible, reversibly compressible, elastic, flexible, bendable, stretchable or any combination thereof. Examples of compliant electrodes known in the art include metallic thin films, including patterned electrodes, out-of-plane buckled electrodes and corrugated membranes, metallic-polymer micro / nano-composites, carbon powder, carbon grease, conductive rubber or conductive paint, a review of which is provided in Rosset and Shea (Applied Physics A, February 2013, vol. 110, no. 2, 281-307), which is incorporated herein by reference in its entirety. As will be apparent to those skilled in the art, a built-in multilayer or stack of several layers of any of the above polymeric materials, composite materials, metallic materials and / or oxide materials and combinations thereof are encompassed in the definition of compliant interconnects. Preferably, but not limited to, the electrodes, tracks and / or interconnects according to the present application are compliant by nature. Preferably, but not limited to, the electrodes, tracks and / or interconnects according to the present application are stretchable by nature. In some embodiments, stretchable electrodes as described in international patent applications WO 2004 / 095536, WO 2016 / 110564 and / or WO 2018 / 100005 Al, which are incorporated herein by reference in their entirety, can be used.

[0054] As used herein, the term "stretchable" refers to the elastic behavior of an article. In particular, a stretchable article can withstand an elongation or multi-directional strain, including between 1 and 500%, preferably at least 5%, such as about 50%, about 100% or about 200% of its size at rest, without breaking or losing its physical and / or mechanical properties, which represents an advantage in those contexts and / or body structures in which several cycles of mechanical stress over time can be foreseen.

[0055] In the framework of the present application, "physical and / or mechanical properties" refer by way of example to the stress-strain behavior, the elastic modulus, the strain at break, the conformability to curved surfaces, the compliance to soft surfaces, the thickness, the area and the shape, which in a group of embodiments according to the present application must be as similar as possible to those found in the tissues of the body of a subject.

[0056] Within the framework of the present application, the expression "intrinsically inelastic material" must be understood to mean a material that, once subjected to a strain (pressure, stress, stretching, twisting, etc.), breaks or permanently deforms, i.e. does not regain its original shape and size in a spontaneous and / or natural manner. On the contrary, an "intrinsically elastic material" is a material that, once subjected to a strain, regains its original shape and size in a spontaneous and / or natural manner.

[0057] The term "subject" as used herein refers to an animal, including birds and mammals. For example, mammals contemplated by the present application include humans, primates, domesticated animals such as cows, sheep, pigs, horses, laboratory rodents, and the like.

[0058] As used herein, "treatment" and "treating" and the like generally mean obtaining a desired physiologic effect. The effect can be prophylactic in terms of preventing or partially preventing a disease, symptom or condition thereof, or therapeutic in terms of a partial or complete cure of a disease, condition, symptom or adverse effect attributed to the disease. The term "treatment" as used herein covers any treatment of a disease in a mammal, particularly in a human, and includes: (a) preventing the disease from occurring in a subject that can be predisposed to the disease but has not yet been diagnosed as having it, e.g., based on family history, state of overweight or age; (b) inhibiting the disease, i.e., arresting its development; or relieving the disease, i.e., causing the disease and / or its symptoms or conditions to regress, such as improvement or remediation of damage. The terms "diagnosing", "diagnostic" and the like refer to identifying the presence or nature of a pathological condition in a subject.

[0059] With reference to Figures 1 to Figure 12 The present application is characterized by an electrical interconnection system comprising:

[0060] i) an interconnection plate 100 comprising an intrinsically inelastic substrate 101 having a first face 102 and an opposite second face 103, and at least one electrically conductive track 104 located on or in at least a portion of said substrate 101; Figures 1a to 1c

[0061] ii) a stretchable interconnection piece 200 comprising an intrinsically elastic substrate 201 comprising at least one recess or groove 202 comprising at least one electrically conductive element 203 therein, said recess or groove 202 being configured to accommodate said at least one electrically conductive track 104 of said interconnection plate 100 (see, for example, Figures 2 to 4); and

[0062] ​iii) at least one electrically conductive paste blob 300, said electrically conductive paste blob 300 being located within said recess or groove 202 and configured to electrically connect said electrically conductive element 203 with said interconnect board electrically conductive tracks 104 (see e.g. Figures 3a to 3f or Figures 4a to 4f ). In embodiments of the application, the system further comprises an encapsulation layer 400 of adhesive and electrically insulating material located on both the second face 103 of the interconnect board 100 and the stretchable interconnect 200 (see e.g. Figures 3a to 3f or Figures 4a to 4f ).

[0063] For example, with reference to Figure 3f , the interconnect board 100 is housed in the recess or groove 202, the first face 102 facing the substrate 201, i.e. towards the bottom of the recess or groove 202, the electrically conductive tracks 104 facing the electrically conductive element 203. The opposite second face 103 of the interconnect board 100 is arranged at the aperture of the recess or groove 202, e.g. protruding from the aperture. The encapsulation layer 400 encapsulates the opposite second face 103 of the interconnect board 100 with at least a portion of the recess of the groove 202 at its aperture, so as to enclose the interconnect board 100 in the recess or groove 202. The remaining portion of the recess or groove 202 can be free of the encapsulation layer 400.

[0064] The substrate 101 of the interconnect board 100 can have a predetermined length extending from one side 101a to an opposite side 101b, the first surface 102 and the second surface 103 being arranged along the predetermined length. The substrate 101 can have different thicknesses at portions 101c, 101d thereof arranged at different distances from one lateral side 101a and the electrically conductive tracks 104 can be exposed from the first surface 102 at one of the portions 101c thereof having a thickness smaller than the other portion 101d thereof in which the electrically conductive tracks 104 are not exposed.

[0065] To address the drawbacks affecting the state of the art, one of the key inventive concepts characterizing the system of the present application relies on the presence of individual electronic contacts on the intrinsic elastic substrate 201 of the hybrid elastic / non-elastic electrical interconnection system, implemented as recesses or grooves 202 comprising at least one electrically conductive element 203 therein, patterned in the elastic substrate 201. By adjusting the design of the electrically conductive tracks 104 located on the intrinsic non-elastic substrate 101 of the mating interconnection board 100 to match the size (width and gap) of the recesses or grooves 202 at the preliminary planning stage, the electrically conductive tracks 104 can be easily placed on the elastic device substrate, as the electrically conductive tracks 104 are self-aligned with the walls 204 of the recesses 202 structure. Advantageously, in the case where more than one electrically conductive track 104 is present, in one embodiment, each electrically conductive track 104 is seated inside a recess 202 and isolated from each other by the recess walls 204.

[0066] Another advantage of the design presented by the present application is the significant reduction of the bulk of the interconnection system, particularly in terms of thickness: as the electrically conductive tracks 104 of the interconnection board 100 end up inside the matching recesses or grooves 202 of the stretchable interconnect 200, the interconnection board 100 and the interconnect 200 result in coplanar and are not coupled in a stacked configuration. The arrangement thus obtained allows for a significant reduction of the size of the overall system compared to the solutions known in the art, creating a seamless hybrid soft / rigid interconnection. Without being bound by any theory, it is believed that the proposed configuration further allows for a more uniform distribution of the post-elongation stress strain along the stretchable portion of the electrical interconnection system, thus reducing the risk of failure due to breakage.

[0067] The stretchable interconnect 200 can be manufactured with methods known in the art, such as microfabrication and photolithography, as will become apparent in the following description. The intrinsic elastic substrate 201 is first provided on a temporary substrate such as a rigid silicon wafer. The substrate 201 is substantially composed of a soft polymer matrix made of a soft polymer material or a combination of many soft polymer materials - which can be biocompatible materials whenever required, to accommodate biomedical applications. The term "soft" is intended herein to encompass any material that is compressible, reversibly compressible, elastic, flexible, stretchable, or any combination thereof. In particular, a soft material comprises a material that has a small Young's modulus (typically < 100 MPa, such as between 0.01 and 100 MPa), provides large elongation upon strain stress, typically more than 5% of the elongation of the soft structure at rest. In this way, the obtained device is highly compliant upon experiencing deformation even for thicknesses of a few millimeters to a few centimeters.

[0068] In a preferred embodiment of the application, the soft material is preferably stretchable in more directions, i.e. elastically deformable after elongation. The stretchability of the support 201 is provided by the material, which is generally made of a composition; in this context, in a preferred embodiment, the support substrate 201 is generally made of a soft polymer material or a combination of many soft polymer materials - which can be biocompatible materials - or coated with a soft polymer material or a polymer material of a hydrogel, or made of a composite material. Examples of suitable materials for constituting the soft polymer matrix of the substrate 201 are, for example, thermoset plastics or thermoplastic plastics such as styrene butadiene styrene (SBS) or styrene ethylene butylene styrene (SEBS), soft foams such as polyurethane - including reticulated polyurethane, polyvinyl chloride (PVC), neoprene, non-crosslinked neoprene, crosslinked polyethylene, polyether, ethylene-vinyl acetate (EVA), polyethylene-vinyl acetate (PEVA), polypropylene glycol (PPG), latex, elastomeric materials such as silicone rubber (e.g. polydimethylsiloxane PDMS) or fluorosilicone rubber, thermoplastic elastomers such as styrene block copolymers (SBC), ethylene propylene diene monomer (EDPM) rubber, butyl rubber, nitrile rubber, or a combination of any of the foregoing.

[0069] Thus, in a preferred embodiment of the application, the support 201 has a Young's modulus comprised between about 1 kPa and 1 GPa, such as, for example, between about 100 kPa and about 1 GPa, between about 100 kPa and about 1 GPa, between about 5 MPa and about 1 GPa, between about 100 kPa and about 100 MPa, between about 100 kPa and about 5 MPa, between about 10 kPa and about 300 kPa or between about 10 kPa and about 10 MPa, preferably between about 1 MPa and about 10 MPa, which is a suitable range of values matching the Young's modulus of many biological tissues and surfaces to avoid mechanical mismatch between said tissues and biomedical devices and / or for mimicking physical and / or mechanical properties of body tissues.

[0070] In a second step, at least one electrically conductive element 203 is provided on the substrate 201. By way of example, the electrically conductive element 203 can be provided by depositing a metal such as Au, Pd, Pt, Ir or alloys thereof on at least one surface of a solidified soft and stretchable elastomer material such as PDMS via physical vapor deposition such as thermal evaporation or sputtering, chemical vapor deposition, spray coating, lamination, cluster ion implantation or supersonic cluster beam implantation. The term "solidified" is used herein to refer to toughening or hardening of a polymeric material by cross-linking of the polymer chains induced by electron beam, heat and / or chemical additives such as cross-linking agents, as well known to the person skilled in the art. When the additives are activated by ultraviolet radiation, the process is also referred to as UV-curing. In this non-limiting and combinable embodiment, the at least one electrically conductive element 203 comprises or consists of a stretchable metal thin film having a thickness comprised between 10 nm and 80 nm, having a track width comprised between 50 pm and 300 pm.

[0071] Additionally or alternatively, the at least one electrically conductive element 203 can substantially consist of a composite material deposited on the surface of the solidified soft material by, for example, spray coating, sputtering, screen printing or inkjet printing, such as a metal and / or carbon-based ink and paste. The composite material can alternatively consist of a soft polymer matrix "doped" or embedded with micro- or nano-particles, such as carbon nanotubes or micro / nano-particles, gold micro / nano-particles, platinum micro / nano-particles, etc.

[0072] Additionally or alternatively, the at least one electrically conductive element 203 can substantially consist of a liquid metal or an alloy thereof, preferably one of gallium and gallium-based alloys, deposited on the surface of the solidified soft material by, for example, physical vapor deposition, chemical vapor deposition, spray coating, thermal evaporation / condensation, direct writing screen printing, doctor blading or inkjet printing. Combinations of any of the above solutions are also conceivable.

[0073] In a third step, at least a portion of the electrically conductive element 203 is encapsulated into the same or a different soft matrix consisting essentially of a soft polymer material. To this end, a soft curable material is provided in such a way that the electrically conductive element 203 is embedded according to methods known in the art, such as overmolding, spraying, dispensing (pouring), molding, compression molding, dip coating, etc. Preferably, the electrically conductive element 203 is encapsulated into the same or a different soft matrix and this latter is subsequently patterned by, for example, photolithography to 1) expose the electrically conductive element 203 through vias and 2) create a recess or groove 202 bounded by walls 204 resulting from the patterning process. The result at the end of those steps is that the substrate 201 comprises at least one recess or groove 202 comprising therein at least one electrically conductive element 203: thus, the encapsulation covers everywhere the substrate except one end of the stretchable interconnect 202 where a "pad" from the electrically conductive element 203 is used for electrical contact. The dimensions of the recess or groove 202 are chosen to accommodate at least one electrically conductive track 104 of the interconnect board 100 as will be detailed later in the description.

[0074] According to Figure 4a to 4f In one embodiment exemplarily depicted in FIG. 2, at least one electrically conductive element 203 of the stretchable interconnect 200 is embedded into the intrinsically elastic substrate 201. Preferably, the electrically conductive element 203 embedded into the intrinsically elastic substrate 201 consists of a soft polymer matrix doped with or embedded with micro- or nano-particles such as carbon nanotubes or micro / nano-particles, gold micro / nano-particles, platinum micro / nano-particles, etc.

[0075] As for the stretchable interconnect of the present invention, the interconnect board 100 according to the present disclosure can be manufactured with methods known in the art. The interconnect board 100 according to the present invention comprises an intrinsically inelastic substrate 101 and at least one electrically conductive track 104 located thereon, for example on at least a first face 102 and / or on an opposite second face 103. Additionally or alternatively, said electrically conductive track 104 can be embedded within said substrate 101 and exposed or partially exposed by means of a via, possibly a metalized via. The electrically conductive track 104 can be passivated on at least a portion thereof with the same material or a different material constituting the substrate 101, and the via can be opened to access the electrically conductive portion of the track 104. In some preferred embodiments, the substrate 101 of the interconnect board 100 is substantially composed of a flexible material. In this context, the term "flexible" refers to a bendable, intrinsically inelastic material, such as for example a plastic, a thermoplastic (e.g. polyimide or parylene), a liquid crystal polymer (LCP), a thin glass fiber composite in epoxy resin (e.g. FR4), and the like. A flexible substrate 101 is of particular interest for interconnect systems implemented into biomedical implants / devices such as neural interfaces, as it can reduce mechanical mismatch between the device parts and the body tissue (such as for example the cortex), while being compliant and sufficiently resistant to avoid the risk of mechanical failure.

[0076] Preferably, and still within the scope of the present invention, said interconnect board intrinsically inelastic substrate 101 is planar at least at the interconnect site, in other words at least at the portion of the substrate where the electrically conductive track 104 is located, and its function is to establish an electrical connection with the counterpart of the stretchable interconnect 200. This configuration allows the possibility to reduce the form factor of the final assembly in terms of thickness, i.e. once the at least one electrically conductive track 104 is coupled with the stretchable interconnect 200, so that the track 104 is located within the assigned recess or groove 202. Moreover, according to some embodiments, the stretchable interconnect 200 is planar.

[0077] In embodiments, the at least one electrically conductive track 104 of the interconnect board 100 is located on an elongated member 1000 of the intrinsically inelastic substrate 101, which can be a planar elongated member. A plurality of elongated members 1000 or an array of elongated members 1000 is envisaged in embodiments of the invention, possibly arranged in a matrix (1000)2. Figures 5a to 5c), each elongated member 1000 comprising at least one electrically conductive track 104 thereon / in which, said array can allow multiplexing the functions of the final interconnection system, thus providing a plurality of separate channels. The array of elongated members 1000 can be hereinafter referred to as "fingers". According to the above embodiment, the stretchable interconnect 200 comprises a substrate 201 having a plurality of recesses or grooves 202 or an array of recesses or grooves 202, said recesses or grooves 202 comprising at least one electrically conductive element 203 therein, the recesses 202 being configured to accommodate a matching electrically conductive track 104 Figures 6a to 6c ), depending on the needs and the environment. In Figure 7a 、 Figure 7b 、 Figure 7c 、 Figure 8 、 Figure 9a 、 Figure 9b 、 Figure 9c 、 Figure 10 、 Figure 11a 、 Figure 11b 、 Figure 11c and Figure 12 depict some exemplary embodiments of an array configuration and of an interconnection system according to the present application obtainable therefrom.

[0078] With reference to Figures 3a to 3c and Figures 4a to 4c , two non-limiting embodiments of a manufacturing method of an interconnection system according to the present application are shown, as well as one embodiment of said system depicted in cross-section. Figures 3a-3c and Figures 4a-4c the main difference between the embodiments shown in Figure 3a ) or placed within the substrate 201 Figure 4a . In a first step Figure 3a or Figure 4a ), a stretchable interconnect 200 is provided, better shown in Figure 2a as a top view.

[0079] In a second step Figure 3b or Figure 4b ), at least one electrically conductive paste blob 300 is located within the recesses or grooves 202. The electrically conductive paste blob 300 is configured to electrically connect the electrically conductive element 203 with the interconnection board electrically conductive track 104. In some embodiments, said at least one electrically conductive paste blob 300 substantially consists of a viscoelastic polymer configured to mechanically connect said electrically conductive element 203 with said interconnection board electrically conductive track 104. This configuration facilitates the mechanical linkage of the different elements composing the system, thus reducing the mechanical mismatch between the "soft" and "rigid" components of the final assembly.

[0080] In one embodiment, the conductive paste 300 comprises a mixture of a flexible polymer material and a plurality of conductive micron or nanoparticles, leads, and / or sheets. Typically, the element consists of: micron or nanoparticles, leads, and / or sheets of metallic materials selected from silver (e.g., silver powder), gold, platinum, etc., and oxides and / or combinations thereof; carbon powder, carbon nanotubes, graphene nanosheets, etc.

[0081] In the third step ( Figures 3c to 3e or Figures 4c to 4e The intrinsically inelastic substrate 101 of the interconnect plate 100, including conductive tracks 104, is placed in a receiving recess 202 in a manner that establishes a strong physical and electrical connection with the stretchable interconnect 200. For this purpose, the conductive tracks 104 are embedded in conductive paste clumps 300, which, depending on the need and environment, may be substantially composed of a viscoelastic polymer configured to mechanically connect the conductive elements 203 of the stretchable interconnect 200 to the conductive tracks 104 of the interconnect plate. The viscoelastic polymer of clump 300 may initially be in liquid or semi-solid form and is subsequently cured once the conductive tracks 104 are in plane within the recess 202 by means known in the art, such as photopolymerization, chemical polymerization, or heat (e.g., curing in an oven at 80°C for 1 hour). Clump 300 may contain reactive chemicals that act as crosslinking agents (e.g., photoinitiators) to aid, accelerate, and / or enhance the curing process. Therefore, within the framework of this disclosure, the "paste" also includes a soft solid material produced by a curing process of one or more initial non-soft solid precursors. In one embodiment, the at least one recess or groove 202 is configured to completely accommodate the at least one conductive track 104 of the interconnect 100, such that the at least one conductive track 104 is completely embedded within the at least one conductive paste mass 300. In other embodiments, the at least one recess or groove 202 is configured to completely accommodate the at least one conductive track 104 and the intrinsically inelastic substrate 101 including the at least one conductive track 104.

[0082] In the last, optional step ( Figure 3f or Figure 4f), the electrical interconnection system is encapsulated with an encapsulation layer 400 of adhesive and electrically insulating material, which is located on the second face 103 of the interconnection board 100 and on the stretchable interconnection 200. In order to maintain the flexibility and stretchability of the final assembly as much as possible, said encapsulation layer 400 is preferably substantially composed of an intrinsically elastic material, for example an elastomeric material such as silicone rubber, polybutyl rubber, polyurethane, thermoplastic vulcanizate products, etc., in accordance with the general spirit of the present application. The encapsulation layer 400 not only guarantees the mechanical robustness of the entire system, but also avoids the risk of short circuits with the surrounding environment and / or with several components of the system.

[0083] In a preferred embodiment, in the electrical interconnection system according to the present application, said at least one electrically conductive track 104 and / or said at least one electrically conductive element 203 comprises an end configured to be electrically connectable to an external device (s). Figure 13 As will be apparent, as an "electrical interconnection" system of the system of the present application, the elements constituting the system should create a suitable electrical connection between at least two elements. For reasons that will become apparent in the description below, the two elements can be electrical, electronic or electromechanical external devices, or one of these elements can be a tissue, organ or other part of the body of a subject, as in the case of biomedical devices for body interfacing.

[0084] As will be apparent to the person skilled in the art, the interconnection system of the present application can be used and implemented to connect "soft" components and "rigid" components of a system, device, etc. An aspect of the present application thus relates to an article of manufacture comprising an electrical interconnection system as described herein. Articles of manufacture that can enjoy the application described herein include medical devices and biomedical devices, including implantable devices, wearable devices, such as "smart" clothing (shirts, hats, shoes, etc. embedded with electronic components), wristbands, thin form factor articles of manufacture, such as (flexible) displays, furniture embedded with electronic components, such as chairs, etc.

[0085] In particular, as expected, the electrical interconnection system can advantageously be used and incorporated in biomedical devices, in particular devices configured to be temporarily or permanently implanted in the body of a subject, in the framework of the present application. The term "subject" as used herein refers to a mammal or even a bird. For example, the mammals contemplated by the present application include humans, primates, domesticated animals such as cows, sheep, pigs, horses, laboratory rodents, etc. Within the meaning of the present application, a "fixed implant" defines a biomedical device that can comply with established and / or custom surgical procedures and that can be present in the body without generating adverse biological reactions over an extended period of time, such as for example more than 7 days. Still within the meaning of the present application, a "removable implant" defines a biomedical device that can comply with established and / or custom surgical procedures and that can be present in the body for a limited amount of time, such as for example the time of the surgery.

[0086] Advantageously, in the framework of biomedical devices, the electrical interconnection system of the present application can primarily allow 1) to reduce the form factor of the device comprising the system, 2) to optimize the distribution of mechanical stresses along the device after a deflection stimulus (e.g. swelling, shrinking, bending, twisting, twisting, linear or area strain), and 3) to better comply with the mechanical properties of the surrounding biological tissue, thereby reducing mechanical mismatch and thus adverse reactions (e.g. inflammatory or fibrotic reactions) in the subject.

[0087] The biomedical devices according to the present application can be used for sensing, measuring and / or monitoring physiological and / or physiopathological parameters in a subject in need thereof, with the aim of treating the subject. Advantageously, the interconnection system of the present application can be implemented into devices that are prone to physical and / or mechanical stresses, such as deflection after implantation. For example, neural interfaces for the treatment of central and / or peripheral nervous system disorders comprise a group of devices that are typically comprised into this aspect according to the present application. Alternatively, electrode array implants intended to interface with the surface of soft tissues such as the heart, the liver, the intestinal tract, the bladder, the retina, etc. are also comprised into this aspect of the present application. By way of example, microelectrode arrays are particularly suitable for use as neural interfaces with the spinal cord, the brain or peripheral nerves or soft biological tissues, for example for the purpose of stimulating and / or recording neural or cardiac activity, as well as for monitoring hippocampal electrical activity following traumatic brain injury or bladder afferent activity, or even for stimulating the electric potential of excitable cells, etc., and can advantageously benefit from the interconnection electrical system of the present application.

[0088] Example

[0089] In one implemented, non-limiting example according to the present application, an interconnection electrical system has been manufactured and incorporated into a biomedical device.

[0090] The comb structure 100, implemented as a flexible PCB (FPCB) - comprising a plurality of fingers, each having a conductive track 104 made of a thin film of metallic material - has been placed on a soft interconnect 200 so that each finger 1000 sits in its assigned channel 202: the fingers of the comb automatically self-align to the walls of the recess structure on the device and are isolated from each other by the recess walls.

[0091] The channels 202 are filled with conductive paste 300 - for example by stencil printing - prior to or after placement of the comb, to provide an intrinsically elastic electrical contact between the flexible structure 100 and the stretchable interconnect 200 on the device. Once placed, the FPCB is fixed in place and electrically isolated by a silicone sealant 400 to lock the components in place and provide mechanical stability against the substrate. Because the fingers 1000 are not rigidly connected to the soft substrate 200, the assembly can maintain elasticity to allow flexing and stretching, while the conductive paste 300 maintains the electrical contact function. The other end of the FPCB is connected to external hardware via a standard connector or cable. The overall thickness of the interconnect system is therefore limited only by the thickness of the soft substrate and the encapsulation, as the fingers sit inside the recess.

[0092] Although in this demonstration the soft device is manufactured using processes adapted from the semiconductor industry, this technology can be applied to any encapsulation material that can be machined with the required recess / wall structure. In this example, the thickness of the substrate and encapsulation are both equal to 200 pm. The pad-to-pad pitch can be on the order of hundreds of microns, for example 500 pm, and is limited by the resolution of the patterning / machining process. The length of the channels (recesses 202) is approximately 1 mm. The overall thickness of the FPCB can be approximately 100 pm, depending on the manufacturing process. The thickness of the metallic thin film is 23 nm. This technology is independent of the metallization material, as long as a compatible conductive paste is available.

[0093] This connection structure can be scaled up in the number of channels and down in size - as this depends only on the resolution of the metallic tracks (by photolithography) and the substrate patterning (laser machining). Furthermore, the flexible printed circuit board can be extended to be used as a narrow strip of flat ribbon cable carrying all the channels, or terminated in small leads that can be soldered and bundled together using conventional techniques (as the limitations imposed by the soft material do not apply). Furthermore, small active electronic chips can be integrated in the vicinity of the fingers using standard electronic packaging techniques, in order to provide enhanced functionality to the device.

[0094] While the application has been disclosed with reference to certain preferred embodiments, many modifications, alterations, and variations will be apparent to those skilled in the art in light of the foregoing disclosure. Accordingly, it is intended that the present application be construed as including all such modifications, alterations, and variations as come within the scope and spirit of the present application and the following claims.

Claims

1. An electrical interconnection system, comprising: i) Interconnect plate (100) including intrinsically inelastic substrate (101) having a first side (102) and an opposing second side (103), and at least one conductive track (104) located on and / or within at least a portion of the substrate (101); ii) A stretchable interconnect (200) comprising an intrinsically resilient substrate (201) including at least one recess or groove (202) including at least one conductive element (203) therein, the at least one recess or groove (202) receiving the at least one conductive track (104) of the interconnect plate (100); as well as iii) At least one conductive paste ball (300) is located in the at least one recess or groove (202) and electrically connects the at least one conductive element (203) to the at least one conductive track (104); The at least one recess or groove (202) completely accommodates the at least one conductive track (104) of the interconnect plate (100), such that the at least one conductive track (104) is completely embedded in the at least one conductive paste (300).

2. The electrical interconnection system according to claim 1, wherein the at least one conductive paste (300) is composed of a viscoelastic polymer configured to mechanically connect the at least one conductive element (203) to the at least one conductive track (104).

3. The electrical interconnection system according to claim 1 or 2, wherein the substrate (101) of the interconnection board (100) is composed of a flexible material.

4. The electrical interconnect system according to claim 1 or 2, wherein the intrinsically inelastic substrate (101) is planar at the interconnect location.

5. The electrical interconnection system according to claim 1 or 2, wherein the at least one conductive track (104) of the interconnection board (100) is located on an elongated member (1000) of the intrinsically inelastic substrate (101).

6. The electrical interconnect system of claim 5, wherein the elongated member (1000) of the intrinsically inelastic substrate (101) is planar.

7. The electrical interconnection system of claim 5, wherein the interconnection board (100) comprises an array of elongated members (1000), each of the elongated members comprising at least one conductive track (104).

8. The electrical interconnect system of claim 7, wherein the stretchable interconnect (200) comprises an array of recesses or grooves (202), each recess or groove (202) comprising one of the at least one conductive element (203) therein.

9. The electrical interconnect system according to claim 1 or 2, wherein the at least one recess or groove (202) completely accommodates the intrinsically inelastic substrate (101).

10. The electrical interconnect system according to claim 1 or 2, wherein the at least one conductive element (203) of the stretchable interconnect (200) comprises a stretchable metal film.

11. The electrical interconnect system according to claim 1 or 2, wherein at least one conductive element (203) of the stretchable interconnect (200) is embedded within the intrinsically elastic substrate (201).

12. The electrical interconnection system according to claim 1 or 2, wherein the conductive paste (300) comprises a mixture of a soft polymer material and a plurality of conductive micron or nanoparticles, leads and / or sheets.

13. The electrical interconnect system according to claim 1 or 2 further includes an encapsulation layer (400) of adhesive and electrical insulating material, the encapsulation layer encapsulating the opposing second surface (103) of the interconnect plate (100) and at least a portion of the stretchable interconnect (200), the at least a portion of the stretchable interconnect (200) including at least a portion of the at least one recess or groove (202).

14. The electrical interconnection system of claim 13, wherein the encapsulation layer (400) is composed of an intrinsically elastic material.

15. The electrical interconnection system according to claim 1 or 2, wherein the at least one conductive rail (104) and / or the at least one conductive element (203) includes an end configured to be electrically connected to an external device.

16. The electrical interconnection system according to claim 1 or 2, wherein, The substrate (101) of the interconnect board (100) has a predetermined length extending from one side (101a) to the opposite side (101b) and a predetermined width extending from the side of the substrate (101) that connects the one side (101a) to the opposite side (101b), and the first surface (102) as a first surface and the second surface (103) as a second surface are arranged along the predetermined length. The at least one conductive track (104) is located on the portion of the substrate (101) excluding the side surface.

17. An article comprising an electrical interconnection system according to any one of claims 1 to 16.

18. The manufacture of claim 17, wherein the manufacture is a biomedical device configured to be temporarily or permanently implanted in the body of a subject.

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