Flexible devices containing conductive traces with improved stretchability

Abstract

A flexible device including conductive traces with enhanced stretchability, as well as methods for making and using the same, is provided. A circuit die is disposed on a flexible substrate. The conductive traces are formed within channels on the flexible substrate and are in electrical contact with contact pads on the circuit die. A first polymer liquid flows within the channels and covers the free surfaces of the traces. The circuit die may also be surrounded by a cured product of a second polymer liquid.

Description

[Technical field]

[0001] The present disclosure relates to flexible devices including circuit dies with enhanced stretchability, and methods of making and using same. [Background technology]

[0002] Integrating solid semiconductor die with printing technology combines the computational power of semiconductor technology with the high throughput and form factor flexibility of web-based processes. However, a major challenge in flexible hybrid electronics manufacturing is aligning the semiconductor die to the electrically conductive traces on the moving web. Typical alignment mechanisms for wafer-based semiconductor devices cannot be easily transferred to web-based processes. Summary of the Invention

[0003] It is desirable to improve the stretchability, flexibility, or bendability of flexible devices including solid circuit dies where micrometer level alignment is achieved between the solid circuit die and conductive interconnects on a substrate, particularly on a movable stretchable flexible substrate. Briefly, in one aspect, the present disclosure describes a method for manufacturing a flexible device. The method includes providing a flexible substrate including an alignment region and one or more channels on a major surface thereof, the channels extending into the alignment region, providing a solid circuit die on the alignment region, the solid circuit die having one or more contact pads on its surface, forming one or more conductive traces in the channels to electrically contact the contact pads of the solid circuit die, and flowing a first polymer liquid into the channels to cover a free surface of the conductive traces.

[0004] In another aspect, the present disclosure describes a flexible device that includes a flexible substrate including an alignment region and one or more channels on a major surface thereof, the channels extending into the alignment region, a solid circuit die disposed on the alignment region, the solid circuit die having one or more contact pads on its surface, one or more conductive traces formed in the channels, the traces forming one or more electrical contacts with the contact pads of the solid circuit die, and a product of solidification of a first polymer liquid covering a free surface of the conductive traces. The product has a modulus of elasticity greater than that of the flexible substrate.

[0005] Various unexpected results and advantages are obtained in the exemplary embodiments of the present disclosure. One such advantage of the exemplary embodiments of the present disclosure is that the flexible devices / circuits described herein may exhibit enhanced stretchability and flexibility. The conductive traces in the channel may be covered by flowing a polymer liquid into the channel, which may eliminate the free surface of each of the conductive traces and reinforce the electrical contact between the conductive traces and the contact pads of the circuit die. Also, when the circuit die is received in the pocket of the flexible substrate, the circuit die may be surrounded by a polymer material having a higher elastic modulus than the elastic modulus of the material forming the pocket. Such a gradient of elastic modulus allows the flexible device / circuit to undergo a larger overall device strain without damaging or breaking the operable components.

[0006] The above is a summary of various aspects and advantages of exemplary embodiments of the present disclosure. The above "Summary" is not intended to describe each illustrated embodiment or every implementation of certain exemplary embodiments of the present disclosure. The following figures and "Description of the Preferred Embodiments" more particularly exemplify certain preferred embodiments that employ the principles disclosed herein. [Brief description of the drawings]

[0007] The present disclosure may be more fully understood from the following detailed description of various embodiments of the disclosure when considered in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 illustrates a top view of a substrate including multiple channels oriented into alignment areas for receiving a solid-state circuit die, according to one embodiment of the present disclosure. [Diagram 2] 2 is a top view of the substrate of FIG. 1 with a solid-state circuit die disposed on the alignment area according to one embodiment of the present disclosure. [Figure 3A] 2 is a side perspective view of a portion of the substrate of FIG. 1 in which a conductive liquid is provided to flow within a channel according to one embodiment of the present disclosure. [Figure 3B] FIG. 3B is a simplified cross-sectional view of the substrate of FIG. 3A, in which a conductive liquid is provided to flow within a channel, according to one embodiment of the present disclosure. [Figure 3C] FIG. 3B is a simplified cross-sectional view of the substrate of FIG. 3A where the conductive liquid has solidified to form conductive traces, according to one embodiment of the present disclosure. [Figure 3D] FIG. 3B is a simplified top view of the substrate of FIG. 3A, in which a conductive liquid is provided to flow within the channels, according to one embodiment of the present disclosure. [Figure 4A] FIG. 1 illustrates a top view of an article including a circuit die disposed on a substrate, where a conductive liquid is dispensed into a channel to form conductive traces and a first polymer liquid flows into the channel to cover the traces, according to one embodiment of the present disclosure. [Figure 4B] 4B is a cross-sectional view of the article of FIG. 4A taken along the transverse line 4B-4B. [Figure 4C] FIG. 4C is a cross-sectional view of the article of FIG. 4A taken along the transverse line 4C-4C. [Figure 4D] FIG. 4D is a cross-sectional view of the article of FIG. 4A taken along the transverse line 4D-4D. [Figure 4E] FIG. 4E is a cross-sectional view of the article of FIG. 4A taken along the transverse line 4E-4E. [Diagram 5] 1 is a perspective view of an article including an inlet channel and an outlet channel in fluid communication within a pocket, according to one embodiment. [Figure 6A] 1 is a cross-sectional view of an article including a circuit die disposed on a substrate, with channels on the substrate connecting to contact pads on a bottom surface of the circuit die, according to one embodiment. [Figure 6B] FIG. 6B is a cross-sectional view of the article of FIG. 6A, in which conductive ink flows into the channels, according to one embodiment. [Figure 6C] FIG. 6C is a cross-sectional view of the article of FIG. 6B where the conductive ink has solidified to form electrical contacts to the contact pads of the circuit die, according to one embodiment. [Figure 6D] FIG. 6D is a cross-sectional view of the article of FIG. 6C with a polymer liquid flowing through the channels to fill the void space below the circuit die, according to one embodiment. [Figure 7A] FIG. 2 is a top view of an article including a solid circuit die disposed in a pocket on a substrate with a gap therebetween filled with a polymer liquid, according to one embodiment. [Figure 7B] 7B is a cross-sectional view of the article of FIG. 7A taken along line 7B-7B according to one embodiment. [Figure 8A] 8A is a cross-sectional view of the flexible device 800 of FIG. 8B taken along line 8A-8A, according to one embodiment. [Figure 8B] FIG. 8B is a plan view of the flexible device 800 of FIG. 8A according to one embodiment. [Figure 8C] FIG. 8B is an exploded top view of the flexible device 800 of FIG. 8A with the overcoat removed, according to one embodiment. [Figure 8D] FIG. 8B is an exploded top view of the flexible device 800 of FIG. 8A with the overcoat and circuit die removed, according to one embodiment. [Figure 9A] FIG. 1 is a schematic diagram of an island structure for simulation, according to one embodiment. [Figure 9B] 13 is a plot of maximum tensile strain experienced by ink in a channel versus stiffness ratio from one simulation result. [Figure 10A] 1 is a plot of R / R0 versus strain for low modulus islands on a thick substrate. [Figure 10B] 1 is a plot of R / R0 versus strain for low modulus islands on a thin substrate. [Figure 10C] 1 is a plot of R / R0 versus strain for high modulus islands on a thick substrate. [Figure 11] 1 is a plot of local distortion versus global distortion for an example embodiment.

[0008] In the drawings, like reference numerals represent like elements. The above-identified drawings, which may not be drawn to scale, illustrate various embodiments of the present disclosure; however, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the disclosure content disclosed herein by illustrating exemplary embodiments, and not by express limitation. It should be understood that numerous other modifications and embodiments may be devised by those skilled in the art that are within the scope and spirit of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] With regard to the following glossary of defined terms, these definitions shall apply throughout this application, unless a different definition is provided in the claims or elsewhere in this specification.

[0010] Glossary Certain terms are used throughout this specification and claims, most of which are well known, but may require some explanation. It should be understood that:

[0011] The term "conductive liquid" refers to a liquid composition that can flow within a channel by capillary forces. The conductive liquids described herein can be solidified to form conductive traces. The conductive liquid may include any suitable electronic material that has desirable properties for use in forming conductive traces.

[0012] The term "liquid adhesive" refers to a liquid composition that includes a liquid carrier and one or more adhesives. The liquid adhesives described herein can be solidified to form an adhesive layer.

[0013] The term "elastic modulus" refers to Young's modulus, which is a measure of a material's ability to withstand a change in length under longitudinal tension or compression. Sometimes Young's modulus is referred to as the modulus of elasticity, which is equal to the longitudinal stress divided by the strain. A solid material may undergo elastic deformation when a small load is applied in compression or extension. The elastic deformation is reversible (i.e., the material returns to its original shape after the load is removed). At near zero stress and strain, the stress-strain curve may be linear, and the relationship between stress and strain is described by Hooke's law, which states that stress is proportional to strain. The proportionality factor is Young's modulus. The higher the modulus, the more stress is required to create the same amount of strain, and an idealized rigid body may have an infinite Young's modulus.

[0014] The term "adjacent" with respect to a particular layer means that the two layers are adjacent (i.e., adjacent) and in direct contact with one another, or are joined or attached to another layer in a position that is adjacent but not in direct contact with one another (i.e., there are one or more additional layers interposed between the layers).

[0015] With respect to the location of various elements in the disclosed coated articles, directional terms such as "on top of," "on," "above," "below," "on," "over," "overlying," "top," "underlying," and the like are used in this specification to refer to the relative location of an element with respect to a horizontally oriented, upward-facing substrate. However, unless otherwise indicated, it is not intended that the substrate or article should have any particular spatial orientation during or after manufacture.

[0016] The terms "about" or "approximately" with reference to a numerical value or shape mean ±5 percent of the numerical value or property or characteristic, but expressly include the exact numerical value. For example, a viscosity of "about" 1 Pa·sec refers to a viscosity between 0.95 and 1.05 Pa·sec, but also expressly includes a viscosity of exactly 1 Pa·sec. Similarly, a "substantially square" perimeter is intended to describe a geometry having four lateral edges, each lateral edge having a length that is between 95% and 105% of the length of any other lateral edge, but is also intended to include a geometry in which each lateral edge has the exact same length.

[0017] The term "substantially" with respect to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of the property or characteristic is exhibited. For example, a "substantially" transparent substrate refers to a substrate that transmits more radiation (e.g., visible light) than it does not transmit (e.g., absorbs and reflects). Thus, a substrate that transmits more than 50% of the visible light incident on its surface is substantially transparent, while a substrate that transmits 50% or less of the visible light incident on its surface is not substantially transparent.

[0018] As used herein and in the accompanying embodiments, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a microfiber containing a "compound" includes a mixture of two or more compounds. As used herein and in the accompanying embodiments, the term "or" is generally utilized in its sense including "and / or" unless the context clearly dictates otherwise.

[0019] As used herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5).

[0020] Unless otherwise indicated, all numbers expressing quantities or ingredients, property measurements, and the like used in the specification and embodiments are to be understood in all instances to be modified by the term "about". Accordingly, unless otherwise indicated, the numerical parameters set forth in the foregoing specification and the accompanying enumeration of embodiments may vary depending on the desired properties one of ordinary skill in the art would obtain using the teachings of the present disclosure. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques, which is not intended to limit the application of the doctrine of equivalents to the scope of the claimed embodiments.

[0021] Various exemplary embodiments of the present disclosure will be described below with specific reference to the drawings. Various modifications and changes may be made to the exemplary embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. Therefore, it should be understood that the embodiments of the present disclosure are not limited to the exemplary embodiments described below, but are governed by the limitations set forth in the claims and any equivalents thereof.

[0022] 1 is a top view of an article 100. Article 100 includes a substrate 2. Substrate 2 has a structured major surface 4. In some embodiments, substrate 2 can be a flexible substrate, such as a web of indefinite length polymeric material. The flexible substrate or web may be stretched (e.g., along a longitudinal direction and / or a transverse direction) as it moves along a web path. One or more channels 8 are formed on major surface 4. Each of channels 8 extends between a first end 102 and a second end 104 and extends toward an alignment region 6 configured to receive a solid-state circuit die.

[0023] In the illustrated embodiment of FIG. 1 , at least one of the first ends 102 of the channels 8 extends beyond each edge 61 of the alignment region 6 such that the channels 8 extend into the alignment region and have a portion at the first end 102 below the bottom surface of the received solid circuit die. In some embodiments, the alignment region 6 may include a pocket formed on the major surface 4. In some embodiments, the pocket may be a cavity including a bottom surface and one or more sidewalls. At least one of the channels 8 may extend into the cavity, e.g., extending across the sidewalls and having its first end 102 formed on the bottom surface of the pocket. It should be understood that the pocket may have a bottom surface flush with the major surface 4 of the substrate. In general, a pocket as described herein refers to an area on a substrate capable of receiving a circuit die.

[0024] Channels 8 are configured to allow fluid to flow primarily by capillary forces, for example, from second end 104 toward first end 102. In some embodiments, at least one of channels 8 or at least a portion of one channel may be open on the top. In some embodiments, at least one of channels 8 or at least a portion of one channel may be surrounded by a top wall. Although one alignment region and eight channels are shown in the embodiment of FIG. 1, it should be understood that any other number of pockets and / or channels may be formed on a substrate.

[0025] In some embodiments, the features on the substrate 2 (e.g., the channels 8 or the alignment regions 6) may include recesses formed in its major surface 4. In some embodiments, the features on the substrate 2 (e.g., the channels 8 or the alignment regions 6) may include embossments protruding from its major surface 4. In some embodiments, the features (e.g., the channels 8 or the alignment regions 6) may be formed by adding material onto the major surface 4. In some embodiments, the alignment regions 6 may be a portion of the major surface 4 of the substrate 2 that is flush with other portions of the major surface 4. In some embodiments, one or more alignment marks or fiducials may be formed on the alignment regions 6. When the solid circuit die is received on the alignment regions 6, the alignment marks or fiducials may be used to align the solid circuit die with the substrate 2 and the channels 8. The features (e.g., the channels and the alignment regions 6) may be formed by any suitable technique, including, for example, microreplication, hot embossing, molding, soft lithography, etching, 3D printing, and the like.

[0026] In some embodiments, the features (e.g., channel 8 or pockets in alignment region 6) may be made of the same material as substrate 2. The material of the channel may be referred to as the channel material. The material of the pocket may be referred to as the pocket material. In some embodiments, the channel material or pocket material may be different from the substrate material.

[0027] In some embodiments, the features (e.g., channels 8 or pockets in alignment regions 6) may have substantially the same depth. The top or bottom surfaces of adjacent features on substrate 2 may be substantially coplanar. In some embodiments, the features may have different depths. The top or bottom surfaces of adjacent features may not be coplanar. For example, one or more steps may be formed at the edges where the channels connect to the pockets.

[0028] In some embodiments, the substrate 2 may be a flexible substrate, e.g., a web of indefinite length material transported through a web path. The flexible substrate may include, for example, polyethylene terephthalate (PET), polyethylene, polystyrene, polyurethane, etc. The processes described herein may be performed on a roll-to-roll apparatus that includes one or more rollers for transporting the web along the web path. It is understood that in some embodiments, a portion of the substrate 2 may be rigid, e.g., made of materials including bakelite, acrylonitrile butadiene styrene (ABS), cured epoxy systems, etc. It is understood that the substrate 2 as a whole may be flexible and stretchable.

[0029] Substrate 2 may have a thickness of, for example, 2 mm or less, 1 mm or less, 500 micrometers or less, or 200 micrometers or less. Features (e.g., channels, pockets, etc.) formed on major surface 4 may have a minimum dimension of, for example, 500 micrometers or less, 300 micrometers or less, 100 micrometers or less, 50 micrometers or less, or 10 micrometers or less.

[0030] The alignment area 6 is configured to receive a solid circuit die 20, as shown in FIG. 2. The solid circuit die 20 includes one or more contact pads 22 disposed on a bottom surface 20b (see FIG. 4B). In some embodiments, the contact pads 22 may be partially embedded in the circuit die 20 or may have an exposed surface or portion adjacent an edge 23 of the circuit die 20. The contact pads of the circuit die 20 may be made of any suitable conductive material, such as, for example, metal. It should be understood that the contact pads may vary depending on the specific type of circuit die. Some contact pads may include protrusions, pegs, or feet that protrude from the casing of the circuit die. Some contact pads may include electroplated metal (e.g., Cu / Au) on the surface of the circuit die casing. In some embodiments, the contact pads may include metal bumps directly on the bare die surface.

[0031] In many applications, the solid-state circuit die may have its contact pads located on a surface thereof, e.g., a top or bottom surface, or a side surface. When the circuit die is placed in a pocket on the substrate, the circuit die may be positioned such that the major surface having the contact pads faces downward, i.e., the contact pads contact or are in close proximity to the bottom surface of the pocket. One or more channels formed on the substrate may extend into the pocket and reach the bottom contacts of the circuit die. Conductive traces may be formed in the channels and extend to make direct contact with the bottom contact pads of the solid-state circuit die.

[0032] 2, when circuit die 20 is placed in alignment region 6, contact pads 22 on edge 23 of circuit die 20 can be aligned with each channel 8. First ends 102 of channels 8 can extend into alignment region 6 to reach contact pads on the bottom surface of the circuit die, with a portion underneath the corresponding contact pads, such that fluid flowing within the channels can be automatically directed to the corresponding contact pads, primarily by capillary forces.

[0033] In some embodiments, the contact pads and channels may be aligned such that the contact pads may have exposed surfaces or portions that directly face the first ends 102 of the channels. For example, Figure 4B shows contact pads 22 formed on the bottom side 20b of circuit die 20, which may directly face the first ends 102 of respective channels 8a and 8c. For example, Figure 4E shows contact pads 22 formed on the side 26 of circuit die 20, which may directly face the corresponding channels 8b.

[0034] In some embodiments, the contact pads may have portions that face the channels. In some embodiments, the contact pads may not directly face the channels. Instead, the contact pads and channels may be aligned such that a fluid path can fluidly connect the channel to a corresponding contact pad. Fluid may flow through a fluid path in the channel toward a contact pad and directly contact that contact pad. It should be understood that the contact pads and channels may not have a one-to-one correspondence. The contact pads and channels may be aligned such that fluid flowing in one or more channels can be directed to one or more predetermined contact pads.

[0035] In some embodiments, the contact pad 22 may have a width that substantially matches the width of the channel 8. In some embodiments, the channel may have a width that is wider than the width of the contact pad aligned with the channel. The channel may have a width that is, for example, about 10%, about 30%, about 50%, about 70%, or about 90% wider than the width of the contact pad on the circuit die. For example, when the contact pad is about 200 micrometers wide, the channel may be selected to be about 300 micrometers wide. The wider channel allows the conductive trace formed in the channel to substantially cover the contact pad and provide good electrical contact between the conductive trace and the contact pad.

[0036] Circuit die 20 may include a circuit chip having one or more contact pads disposed along its edge 23. In some embodiments, circuit die 20 may include a rigid semiconductor die. In some embodiments, circuit die 20 may include a printed circuit board (PCB). In some embodiments, circuit die 20 may include a flexible printed circuit (FPC). It should be understood that circuit die 20 may be any suitable circuit die disposed on a substrate, the one or more contact pads of which are aligned with and connected to conductive traces on the substrate.

[0037] In some embodiments, when the circuit die 20 is received by the pocket in the registration region 6, the circuit die 20 may have a thickness that is substantially the same as the depth of the pocket or the depth of the channel. In some embodiments, the depth of the pocket may be such that the bottom of the solid circuit die within the pocket is located approximately in the neutral bending plane of the neutral construct.

[0038] In some embodiments, the circuit die 20 may be an ultra-thin chip having a thickness of, for example, about 2 micrometers to about 200 micrometers, about 5 micrometers to about 100 micrometers, or about 10 micrometers to about 100 micrometers. The depth of the pocket for receiving the circuit die may be, for example, 2 times, 4 times, 6 times, 8 times, or 10 times greater than the thickness of the circuit die. The depth of the pocket may be such that the solid circuit die may extend substantially along the neutral bending plane of the neutral construct when the solid circuit die is attached to the bottom surface of the pocket. This configuration may effectively reduce distortion of the solid circuit die when the substrate is bent.

[0039] In some embodiments, the ultra-thin circuit die may be mounted on a handle substrate to facilitate placement onto the alignment region 6. The handle substrate may be removed after the circuit die 20 is received in the alignment region 6.

[0040] In some embodiments, the circuit die 20 can be attached to the surface of the alignment region 6 by an adhesive. If the alignment region 6 includes a pocket, the circuit die 20 can be attached to the bottom surface of the pocket by an adhesive. Exemplary adhesives can include structural adhesives, acrylic adhesives, epoxy adhesives, urethane adhesives, and optical adhesives. In some embodiments, the adhesion can be achieved using, for example, a UV-curable polyurethane compound. The adhesive can be precisely applied to attach the circuit die 20 onto the surface of the alignment region 6 without blocking the channel 8. See also FIG. 4B. Here, the circuit die 20 is attached to the surface of the substrate 2 by an adhesive layer 12.

[0041] As shown in FIG. 4A, when the circuit die 20 is placed in the alignment region 6, a conductive liquid 16 can be dispensed into one or more of the channels 8a, 8b, 8c, or 8d. The conductive liquid 16 can be a liquid composition capable of flowing within the channels 8 primarily by capillary forces. The conductive liquid 16 can include, for example, a liquid carrier and one or more electronic materials, liquid metals or metal alloys, and the like. The conductive liquids described herein can be solidified to leave a continuous layer of conductive material that forms conductive traces within the channels. Suitable liquid compositions can include, for example, silver ink, silver nanoparticle ink, reactive silver ink, copper ink, conductive polymer ink, liquid metals or alloys (e.g., metals or alloys that melt at low temperature and solidify at room temperature), and the like.

[0042] The conductive liquid 16 can be delivered into the channel 8 by a variety of methods including, for example, inkjet printing, dispensing, microinjection, and the like. In some embodiments, one or more reservoirs can be provided adjacent to and in fluid communication with the channel 8. The reservoirs can be shaped to provide a convenient containment for the dispensed conductive liquid. The conductive liquid 16 can be disposed in the reservoirs by, for example, inkjet printing, dispensing such as piezo-dispensing, needle-dispensing, screen printing, flexographic printing, and the like. The conductive liquid 16 can move from the reservoirs to the channel 8 by capillary forces. The reservoirs can have a depth substantially the same as the depth of the channel 8. The reservoirs can have any desired shape and dimensions suitable for receiving the conductive liquid 16. In some embodiments, the reservoirs can have dimensions ranging from about 1 micrometer to about 1.0 mm, from about 5 micrometers to about 500 micrometers, or from about 50 micrometers to about 500 micrometers, for example. It should be appreciated that in some embodiments, the conductive liquid can be provided within the channel without the use of a reservoir.

[0043] In some embodiments, the conductive liquid 16 can be placed directly on the surface area adjacent to the channel 8. The conductive liquid 16 can then be automatically collected by the channel 8 from the surrounding area by capillary forces. In some embodiments, the surrounding area of ​​the second end 104 can be selectively treated or patterned to increase the collection of the conductive liquid 16 to the second end 104 of the channel 8. Suitable surface treatment or patterning methods include, for example, high definition, flexographic printing, screen printing, gravure printing, and the like. It should be understood that any suitable method can be used to deliver the conductive liquid 16 to the distal end of the channel 8. The conductive liquid 16 can be deposited by any suitable technique, such as, for example, printing, pouring, funneling, microinjection, and the like.

[0044] When the conductive liquid 16 is delivered to the channel 8, it may be routed through the channel 8, for example, from the second distal end 104 toward the first end 102, primarily by capillary forces. In some embodiments, the conductive liquid 16 may be delivered to fill the channel 8 from a point between the distal end 104 and the first end 102. Without wishing to be bound by theory, it is believed that several factors may affect the ability of the conductive liquid 16 to move through the channel 8 by capillary action. Such factors may include, for example, channel dimensions, viscosity of the conductive liquid, surface energy, surface tension, drying, etc. These factors are described in U.S. Pat. No. 9,401,306 (Mahajan et al.), which is incorporated herein by reference.

[0045] Channel 8 can have any suitable dimensions (e.g., width, depth, or length), which can be determined in part by one or more of the factors discussed above. In some embodiments, channel 8 can have a width or depth in the range of, for example, about 0.01 micrometers to about 500 micrometers, about 0.05 micrometers to about 200 micrometers, or about 0.1 micrometers to about 100 micrometers.

[0046] 3A-3D, as the conductive liquid 16 moves by capillary action into the channel 8 from the second end 104 toward the first end 102, the sidewall 84 and bottom wall 82 of the channel 8 may be wetted by the conductive liquid 16 to form one or more bent menisci. It should be appreciated that the conductive liquid 16 may be dispensed in an amount that covers a portion of the sidewall 84 adjacent the bottom wall 82. The top surface 32 of the conductive liquid 16 has a convex crescent shape. An edge 34 of the top surface 32 may act as a pinned contact line during ink 16 flow. The front surface 36 of the ink 16 also has a convex crescent shape. An edge 36' of the front surface 36 may act as a leading edge that directs the flow forward. The formation of the meniscus may create a pressure gradient that may drive the flow in the capillary with viscous resistance provided by friction at the capillary walls.

[0047] The conductive liquid 16 in the channel 8 can solidify to form a conductive trace 30 that is deposited in the channel and directly contacts a contact pad on the bottom surface 20b of the circuit die 20. The conductive trace 30 has a free surface 32'. See also Figures 4B-4E. Suitable processes that can be used to enhance the solidification of the conductive liquid 16 can include curing or evaporation, for example, by heat or radiation. During the solidification process, the pinned contact lines 34 can begin to flow the liquid from the center of the channel 8 toward the sidewall 84. The volume of the conductive liquid 16 can be reduced by removing the liquid carrier from the conductive liquid. The thickness of the deposited solid material can depend on the solid amount of the conductive liquid 16. In some embodiments, the deposited solid material can have a thickness of, for example, about 0.01 micrometers to about 200 micrometers, about 0.05 micrometers to about 100 micrometers, or about 0.1 micrometers to about 10 micrometers.

[0048] As conductive liquid 16 moves through channel 8 by capillary action and reaches its first end 102, conductive liquid 16 may wet the portion of circuit die 20 exposed to channel 8. Conductive liquid 16 may wet and spread to cover corresponding contact pads 22 disposed on the surface of circuit die 20.

[0049] In some embodiments, the alignment region 6 may be a pocket, and as shown in FIG. 4A, the side 23 of the circuit die 20 and the sidewall 18 of the pocket 6 may have a gap 38 formed therebetween. The gap 38 may facilitate attachment of the circuit die 20 to the pocket 6. In some embodiments, the gap 38 may have a width of, for example, about 10 to about 500 micrometers, about 10 to about 200 micrometers, or about 10 to about 100 micrometers. As the conductive liquid 16 flows through the channel 8 and into the alignment region 6, the edge of the top surface of the conductive liquid may still act as a pinned contact line and may prevent some of the conductive liquid 16 from flowing into the gap 38. See also FIG. 3A and FIG. 3B.

[0050] 4B and 4D, when an edge of the top surface of the conductive liquid contacts the bottom surface 20b of the circuit die 20, the conductive liquid 16 can wet the portion of the bottom surface 20b of the circuit die 20 exposed to the channel 8. The conductive liquid 16 can wet and spread to cover the contact pads 22 on the bottom surface 20b of the circuit die 20. In this manner, the conductive traces 30 can be formed in the channel that directly contacts the contact pads of the solid circuit die 20. When the channel 8 extends under the circuit die 20, the conductive traces 30 can directly contact the contact pads 22 on the bottom surface 20b of the circuit die 20, while the free surface 32' can form an air gap space 33' below the circuit die 20. See FIG. 4D.

[0051] 4E, as the conductive liquid 16 moves through the channel 8b by capillary action and reaches the first end 102, the front side of the conductive liquid 16 can wet the side 26 of the circuit die 20 exposed to the channel 8. The conductive liquid 16 can wet and spread over the exposed portion 26, covering the side contact pad portion 24, and continue to move over the edge of the major surface 21, covering the edge portion 222 of the contact pad 22 on the major surface 21. In some embodiments, the front side of the conductive liquid 16 can be pinned to the edge portion 222 of the contact pad 22. The conductive liquid 16 may not move further over the major surface 21 of the circuit die 20, which can leave a major portion of the contact pad 22 uncovered by the conductive liquid 16. After solidification, the conductive trace 30 can be formed with a free surface 32'.

[0052] In some embodiments, the substrate can have an alignment feature shaped to receive an electronic component and at least one channel shaped to extend toward an area corresponding to one of the contacts when the electronic component is placed in the alignment feature. A conductive liquid can be dispensed into the channel such that the conductive liquid flows by capillary forces in the channel toward and wets the contacts. The conductive liquid can be solidified to form a conductive trace in the channel. In some embodiments, the at least one channel further includes an enlarged portion shaped to provide a convenient containment for dispensed adhesive ink or conductive liquid. For example, one end of the channel can be in fluid communication with a reservoir to facilitate delivery of the liquid.

[0053] In the present disclosure, the liquid or ink delivered into the channel can be automatically aligned with the circuit die by wetting the alignment features on the substrate and various surfaces of the circuit die (e.g., walls of the channel, sidewalls of the pocket, sides of the circuit die, etc.) via capillary forces. The flow of the liquid on the various capillary surfaces can be automatically induced by capillary forces, eliminating the need to use a fluid pump to pump the fluid towards the circuit die. After automatic alignment, the liquid or ink can be further solidified or dried to form a solid continuous layer. This process can be repeated to form a multi-layer structure aligned with the solid circuit die on the substrate.

[0054] In some embodiments, once the conductive traces are formed and automatically aligned with the contact pads on the circuit die, the traces can be connected to other parts of the circuit, or to other circuits or devices. In some embodiments, additional metal traces (e.g., Cu traces) can be patterned in alignment with the conductive traces. In some embodiments, the conductive traces can be connected to antenna coils of electronic devices, such as receivers or transmitters. The processes described herein can be used to fabricate a variety of chip-based circuits / devices, including, for example, radio frequency identification (RFID) tags, near field communication (NFC) circuits, Bluetooth circuits, Wi-Fi circuits, microprocessor chips, and the like.

[0055] It is desirable to improve the stretchability, flexibility, or bending of the chip-based circuits / devices because the conductive traces in the channels may crack when the circuits / devices are subjected to bending or rotational stress or strain. In some embodiments, void spaces near the electrical contact between the conductive traces and the contact pads of the circuit die (e.g., void space 33' under the circuit die 20 in FIG. 4D) may make the electrical contact weaker in the context of stress or strain. In the present disclosure, the conductive traces in the open channels, which may cover the free surface of the traces, may be reinforced by backfilling the channel with a product of solidified polymer liquid. The polymer liquid in the channel may be caused to flow and flow in the void space under the circuit die to at least partially fill the void space, which may reinforce the electrical contact formed between the traces and the contact pads of the circuit die. The circuit / device backfilled with the curable polymer may eliminate the void space under the free surface of the conductive traces and the circuit die, such that the circuit / device may resist cracking at much higher overall strains. Thus, flexible devices including the circuit dies described herein can exhibit enhanced stretchability, flexibility, or bending.

[0056] 4C-4E, by forming the conductive traces 30 in the channel 8, the conductive traces 30 have a free surface 32' that may have a crescent shape in the channel. A first polymer liquid 40 is then dispensed into the channel 8 and flows through the channel primarily by capillary forces, covering the free surface 32' of the conductive traces 30. The first polymer liquid 40 can be delivered to the channel 8 by a variety of methods including, for example, inkjet printing, dispensing, microinjection, coating, etc.

[0057] As shown in FIG. 4D, the circuit die 20 has contact pads 22 on its bottom surface 20b. The channel 8c extends below the bottom contact pads 22. As the first polymer liquid 40 flows into the void space 33′ below the circuit die 20, the polymer liquid 40 can wet and spread over the free surface 32′ of the conductive traces 30 to at least partially fill the void space 33′. As shown in FIG. 4E, the contact pads 22 have sides 24 disposed on the side surfaces 26 of the circuit die 20. As the first polymer liquid 40 flowing in the channel 8b approaches the side surfaces 26 of the circuit die 20, the first polymer liquid 40 can wet and spread over the free surfaces 32′ of the conductive traces 30 to cover the electrical contacts formed between the traces 30 and the sides 24 of the contact pads 22 adjacent the edges 222 of the contact pads 22. In some cases, first polymer liquid 40 may wet and spread over contact pads 22 on major surface 21 of circuit die 20 .

[0058] In some embodiments, the first polymer liquid may include, for example, a UV curable polymer. Exemplary polymer liquids may include UV acrylates, heat curable epoxies, two-part epoxies, and the like. In some embodiments, the first polymer liquid may include poly(thiol-ene) that may be made by free radical polymerization of a multifunctional thiol and a multifunctional ene (vinyl-terminated compound). In one example prepared herein, the first polymer liquid was an optical adhesive commercially available under the trade name NOA-73 from Norland Products, Inc. (CRANBURY, NJ, USA).

[0059] The first polymer liquid 40 may then be solidified to form a product 40'. Suitable processes that may be used to enhance the solidification of the first polymer liquid 40 may include, for example, curing or evaporation, by heat or radiation. In some embodiments, the first polymer liquid may include a UV-curable polymer, and the polymer layer 40' may be a product of curing the UV-curable polymer. The channel 8 may be at least partially filled with the product 40'. In some embodiments, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the volume of the channel 8 may be filled with the product 40'.

[0060] In some embodiments, the product of the cured UV-curable polymer may have a modulus of elasticity in the range of, for example, 0.1 MPa to 10 GPa. The pocket material may include, for example, an acrylate, a urethane, a silicone, or an epoxy, which may have a modulus of elasticity in the range of, for example, 0.1 MPa to 10 GPa. In some embodiments, the product 40' has a modulus of elasticity higher than the modulus of elasticity of the material forming the channel 8 on the flexible substrate 2. In some embodiments, the product of the cured UV-curable polymer may have a modulus of elasticity in the range of, for example, 0.1 MPa to 10 GPa. The channel material may include, for example, an acrylate, a urethane, a silicone, or an epoxy, which may have a modulus of elasticity in the range of, for example, 0.1 MPa to 10 GPa. In some embodiments, the channel material may include a poly(thiol-ene), which may be made by free radical polymerization of a multifunctional thiol and a multifunctional ene (vinyl-terminated compound).

[0061] In some embodiments, the material filling the channels or pockets (e.g., product 40') may have a preferred upper limit for its modulus. If the modulus is greater than the upper limit, the filling material may have a low elongation to break. The elongation to break, also known as the break strain or tensile elongation at break, is the ratio of the increased length to the initial length after the material breaks at a particular temperature. It is related to the ability of the material to resist a change in shape without cracking. For example, a filling material with a modulus above a certain upper limit may break when the flexible substrate is bent to a certain level.

[0062] In some embodiments, while bending a substrate having a thickness H to a bending radius R, the outer surface of the substrate is bent at a radius of approximately H / (2 * R). If the backfilled channel or pocket is outside the substrate, the material (e.g., polymer) used for backfilling must withstand that amount of strain without breaking. This means that the filler material may require a breaking elongation greater than a certain value. If the substrate thickness is 25 micrometers, 50 micrometers, 100 micrometers, 200 micrometers, or 1000 micrometers, the corresponding required bending radius may be 1 mm, 5 mm, 10 mm, 25 mm, 50 mm, 100 mm, and the corresponding required breaking elongation may be 2%, 3%, 5%, 10%, or even greater than 100%. In general, a filler material (e.g., polymer) with a higher modulus may have a lower breaking elongation. The selection of a backfill material for an application requiring a specific elongation in stretching or bending to a specific radius and with a specific substrate thickness must involve a balance between modulus and breaking elongation.

[0063] In some embodiments, the fluid channels on the flexible substrate may include inlet and outlet channels that are fluidly connected. A first polymer liquid may flow into the inlet channel and wet and spread within the channel on the free surface of the conductive trace. FIG. 5 is a perspective view of an article 400 including one or more pairings of inlet and outlet channels formed on a substrate 2, according to one embodiment. Each pairing of inlet and outlet channels 402i and 402o has respective ends that extend across sidewall 64a or sidewall 64b into pocket 6 and are fluidly connected within pocket 6 to form an internal channel 403. Internal channel 403 has an "L" shape. Another pairing of inlet and outlet channels 404i and 404o has respective ends that extend across sidewall 64a into pocket 6 and are fluidly connected within pocket 6 to form an internal channel 405. Internal channel 405 has a "U" shape. While the embodiment of FIG. 5 shows pairing of inlet and outlet channels in fluid communication within the pocket, it should be understood that in some embodiments, two or more inlet channels can be in fluid communication with one outlet channel, and in some embodiments, one inlet channel can be in fluid communication with two or more outlet channels. It should also be understood that some inlet or outlet channels are not in fluid communication to avoid shorting between different contact pads. In some embodiments, the channels may have a width, for example, in the range of about 5 to about 500 micrometers.

[0064] When the circuit die is placed in the pocket 6, the bottom contacts of the circuit die may be aligned with a portion of the internal channel 403 or the internal channel 405. The conductive liquid may flow, primarily by capillary forces, through the inlet channel 402i or the inlet channel 404i into the internal channel 403 or the internal channel 405 and directly contact the bottom contact pads of the solid circuit die. Excess liquid may flow out of the pocket through the outlet channel 402o or the outlet channel 404o. The inlet and outlet channels (e.g., 402i and 402o, or 402i and 402o) are in fluid communication through the respective internal channels (e.g., 403 or 405), which may help ensure a continuous flow of liquid without trapping air in the internal channels. In this manner, a strong contact may be formed between the conductive liquid and the bottom contact pads of the solid circuit die.

[0065] 5, at least a portion of the internal channel 403 or internal channel 405 extends below the circuit die 20 such that electrical contact is made between the contact pads 22 and the conductive liquid within the internal channel 403 or internal channel 405. It should be understood that the internal channel (e.g., 403 or 405) formed by fluidly connecting the inlet and outlet channels can have a variety of configurations or shapes, such as, for example, a "U" shape, an "L" shape, a straight shape, a curved shape, etc., so that the conductive traces formed within the internal channel can have strong contact with the bottom contact pads 22 of the circuit die 20.

[0066] In some embodiments, the interior channel 403 or the interior channel 405 can be shaped such that the bottom contact pads 22 of the circuit die 20 are disposed within the outer edges 403e and 405e of the interior channel 403 and the interior channel 405, respectively. When the circuit die 20 is attached to the bottom surface 62 of the pocket 6 with liquid adhesive, the outer edges 403 and 405e of the channels can stop (e.g., by pinning) the movement of the liquid adhesive (e.g., from the center of the pocket 6 toward the contact pads 22) and prevent possible contamination of the contact pads 22.

[0067] In some embodiments, a conductive liquid can flow through an inlet channel (e.g., 402i or 404i) into a channel (e.g., inner channel 403 or inner channel 405) and solidify to form a conductive trace in the channel. For example, the conductive trace can be formed by evaporating a solvent of the liquid conductive ink. During the solidification process, the conductive material can be deposited on the sidewalls and bottom of the channel and on a portion of the bottom surface of the circuit die located above the channel. In this process, the conductive material can conformally contact with the contact pads on the circuit die. The solidification process may leave some void space in the channel below the circuit die. See, for example, void space 33' in FIG. 4D. The void space can be filled by flowing a first polymer liquid into the channel through an inlet or outlet channel. The first polymer liquid can wet and spread over the free surface of the conductive trace in the channel, mainly by capillary forces, and flow into the void space, at least partially filling the channel and the void space.

[0068] In the illustrated embodiment of FIG. 5 , alignment region 6 includes a pocket or cavity. It should be understood that alignment region 6 can have other configurations. In some embodiments, alignment region 6 can be a portion of major surface 4 of substrate 2 that is coplanar with other portions of major surface 4. In some embodiments, one or more alignment marks or fiducials can be formed on alignment region 6. When a solid circuit die is received on alignment region 6, the alignment marks or fiducials can be used to align the solid circuit die with substrate 2 and channel 8.

[0069] In some embodiments, the circuit die can be attached to the alignment region 6 by a liquid adhesive. In some embodiments, the liquid adhesive can be provided in a fluid channel in the alignment region for die attachment. In some embodiments, one or more reservoirs can be formed on the alignment region 6 to receive liquid adhesive that can flow from the reservoir into the adhesive channel primarily by capillary forces to bond the circuit die 20 to the alignment region 6. The adhesive channel or reservoir is not in fluid communication with the channel to allow the conductive liquid to flow and form the conductive traces. One or more fiducials are provided on the flexible substrate to precisely align the circuit die 20 with the channel.

[0070] In some embodiments, the liquid adhesive can be dispensed prior to placing the circuit die 20 in the pocket 6. In some embodiments, the liquid adhesive can be delivered to the pocket 6 as one droplet in the center of the pocket 6 or as multiple droplets in a specific pattern depending on the size and details of the circuit die 20. An isolated reservoir can also be placed at the bottom of the circuit die 20 to capture and pin the liquid adhesive in place. Once the circuit die 20 is placed on top of the liquid adhesive, the adhesive can wet the space between the circuit die 20 and the pocket 6 while being pinned to the edges of the channels (e.g., outer edges 403e and 405e of inner channel 403 and inner channel 405 in FIG. 5) underneath the circuit die 20. This adhesive patterning scheme can help attach the circuit die 20 to the pocket 6 without contaminating the contact pads on the circuit die 20.

[0071] The liquid adhesive can then be solidified to form an adhesive layer, such as adhesive layer 612 in Figures 6A-6D. Suitable processes that can be used to enhance solidification of the adhesive ink 40 include curing or evaporation, for example, by heat or radiation. In some embodiments, the liquid carrier of the liquid adhesive can be evaporated, leaving the adhesive material to form the adhesive layer. Once the liquid carrier is removed, the remaining adhesive material can form the adhesive layer.

[0072] 6A-6D illustrate a manufacturing process for a flexible device, according to some embodiments. A solid circuit die 20 is attached to an alignment region 6 of a flexible substrate via an adhesive layer 612. Channels 602 and 604 are formed on a major surface of the flexible substrate and extend below the contact pads 22 on the bottom surface of the circuit die 20. In some embodiments, the channels 602 and 604 can be inlet and outlet channels, respectively. A conductive liquid 16 flows into the channel primarily by capillary forces, wetting and spreading on the sides of the channel and the contact pads 22. The conductive liquid 16 is then solidified to form conductive traces 30 in the channel 22, including electrical contacts 30c that directly contact the contact pads 22 of the circuit die 20. Solidifying the conductive liquid 16 in the channels 602 and 604 can form a void space 33′ below the circuit die 20.

[0073] A first polymer liquid 40 may be provided to flow within the channels to at least partially fill the void spaces 33'. The first polymer liquid 40 may wet and spread over the free surfaces of the conductive traces 30 and cover the electrical contacts 30c formed between the traces 30 and the contact pads 22 adjacent the edges 222 of the contact pads 22. The first polymer liquid 40 may then be solidified to form a polymer layer 40'.

[0074] FIG. 7A is a top partial view of an article 700 including an oversized pocket 6' on a flexible substrate to receive a solid-state circuit die 20', according to one embodiment. FIG. 7B is a cross-sectional view of the article 700. The pocket 6' is formed on the substrate 2 and has a size larger than the size of the solid-state circuit die 20'. The solid-state circuit die 20' is disposed in the pocket 6' facing down to a bottom surface 62' of the pocket 6'. The bottom contact pads 22' of the circuit die 20' can be aligned with channels 710 extending into the pocket 6'. The channels 710 can include one or more inlet channels, outlet channels, etc. In the illustrated embodiment, the solid-state circuit die 20' is attached to the bottom surface 62' of the pocket 6' by an adhesive layer 712, which can be formed by solidifying a liquid adhesive.

[0075] Once the solid circuit die 20' is placed in the pocket 6', conductive traces 730 can be formed in the channels 710, for example, by flowing a conductive fluid into the channels 710 and solidifying the conductive fluid. The free surfaces of the conductive traces 730 can be covered by a product 740 by solidifying the first polymer liquid. The product 740 can at least partially fill the channels 710 and the void spaces beneath the bottom contact pads 22 of the circuit die 20'.

[0076] In the illustrated embodiment of FIGS. 7A-7B, there is a gap 720 between a sidewall or edge of the solid circuit die 20′ and a sidewall of the pocket 6′. In some embodiments, the gap 720 may refer to the in-plane distance between the sidewall of the pocket and the circuit die edge on the bottom surface 62 of the circuit die. The gap 720 may be larger than the tolerance required to place the circuit die in the pocket. For example, a typical tolerance may be, for example, about 10 to about 20 micrometers, generally less than about 50 micrometers. In some embodiments, the gap 720 may be at least 3 times, at least 5 times, at least 7 times, at least 10 times, or at least 20 times larger than the required tolerance. In some embodiments, the gap 720 may be, for example, in the range of about 100 micrometers to about 2 mm or more.

[0077] In the illustrated embodiment of FIGS. 7A-7B, the gap 720 is filled with product 722 by solidifying the second fluid polymer. In some embodiments, after forming the conductive traces in the channel 710, a second polymer liquid can be dispensed and flowed in the void space of the gap 720 to at least partially fill the gap 720, primarily by capillary forces. In some embodiments, the second polymer liquid can include, for example, a UV-curable polymer. Exemplary polymer liquids can include UV-curable acrylates, heat-curable epoxies, two-part epoxies, and the like. In some embodiments, the second polymer liquid can include a poly(thiol-ene) that can be made by free radical polymerization of a multifunctional thiol and a multifunctional ene (vinyl-terminated compound). In one example prepared herein, the second polymer liquid was an optical adhesive commercially available under the trade name NOA-73 from Norland Products, Inc. (CRANBURY, NJ, USA). The second polymer liquid may be delivered to the gap 720 by a variety of methods including, for example, inkjet printing, dispensing, microinjection, coating, and the like.

[0078] The second polymer liquid may be solidified to form product 722. In some embodiments, product 722 has a higher modulus of elasticity than the modulus of the material forming pocket 6' on flexible substrate 2. In some embodiments, the product of the cured UV curable polymer may have a modulus of elasticity in the range of, for example, 0.1 MPa to 10 GPa. The pocket material may include, for example, an acrylate, a urethane, a silicone, or an epoxy, which may have a modulus of elasticity in the range of, for example, 0.1 MPa to 10 GPa.

[0079] In the present disclosure, in some embodiments, a circuit die can be received in a pocket of a flexible substrate, and the circuit die can be surrounded by a polymeric material having a higher modulus than the modulus of the material forming the pocket. Such a modulus gradient can help a flexible device / circuit to withstand significantly larger overall device strains, as indicated by the arrows shown in FIG. 7B. In contrast, in a device / circuit without such a modulus gradient, the overall device strain can result in high local strains near the circuit die, channels, or cavities. Because the conductive traces are not as stretchable as the substrate, the local strains can crack and break the device even at relatively low overall strains. The present disclosure provides a material modulus gradient to address these issues. It should be understood that various configurations of modulus materials and modulus gradients can be utilized to manage device strains to improve stretchability, flexibility, and bendability.

[0080] Figure 8A is a cross-sectional view of a flexible device 800 including an island structure 10 on a flexible substrate 2' according to one embodiment. Figure 8B is a plan view of the flexible device 800 of Figure 8A. Figure 8C is an exploded plan view of the flexible device 800 of Figure 8A with the overcoat removed. Figure 8D is an exploded plan view of the flexible device 800 of Figure 8A with the overcoat and circuit die removed. The flexible device 800 includes an island structure 10 disposed on a flexible substrate 2'.

[0081] The flexible substrate 2' may comprise any stretchable, flexible, elastic material, such as, for example, polyurethane, rubber, epoxy, polyethylene terephthalate (PET), polyethylene, polystyrene, etc. In one example prepared in this application, Very High Bond (VHB) tape, commercially available under the trade name Very High Bond (VHB) Tape 4910 from 3M Company, St. Paul, MN, was used as the flexible substrate. It should be understood that in some embodiments, a portion of the substrate 2' may be rigid, and the substrate 2' as a whole may be flexible and stretchable. The flexible and stretchable substrate 2' may have an elastic modulus E1, for example, in the range of 0.1 MPa to 10 GPa.

[0082] The island structure 10 includes a channel layer 810 disposed on a flexible substrate 2'. The channel layer 810 can be made of a relatively stiff polymeric material having a modulus of elasticity E2 greater than the modulus of elasticity E1 of the flexible substrate. The modulus of elasticity E2 can be in the range of, for example, 0.1 MPa to 10 GPa, 1 MPa to 10 GPa, or 5 MPa to 10 GPa. The channel layer 810 can be made of a UV curable material, a thermosetting material, a reactive material, or any other suitable material, so long as it has a modulus of elasticity appropriate for the desired properties.

[0083] In some embodiments, suitable materials for the channel layer 810 may include an optical adhesive, such as an optical adhesive available under the trade name NOA-73 from Norland Products, Inc. (CRANBURY, NJ, USA). The channel layer material may include a two-part UV-curable epoxy, such as an epoxy available under the trade name DP100 from 3M Company, St. Paul, MN. The channel layer material may include one or more of a stretchable epoxy, a UV-curable polyurethane, or an acrylic material, and the like. In some embodiments, the channel layer material may include a poly(thiol-ene), which may be made by free radical polymerization of a multifunctional thiol and a multifunctional ene (vinyl-terminated compound).

[0084] Without wishing to be bound by theory, in some embodiments, it may be desirable for the channel layer materials described herein to have both a high modulus (e.g., greater than 100 MPa) and low brittleness (e.g., acceptable elongation properties). Such properties may be achieved using a composition that includes a urethane (meth)acrylate polymer and a high Tg monomer.

[0085] In some embodiments, the material of the channel layer can include, for example: i) a urethane (meth)acrylate polymer comprising the reaction product of an aliphatic polyester, polycarbonate, or polyether diol, a diisocyanate, and a hydroxy-functional methacrylate; ii) Monofunctional (meth)acrylate monomers, wherein a cured homopolymer of at least one monofunctional (meth)acrylate monomer has a Tg of at least 60°C.

[0086] In some embodiments, the urethane component is a urethane (meth)acrylate polymer. Such polymers are the reaction products of (e.g., aliphatic) polycarbonate, polyester, or polyether diols, (e.g., aliphatic and / or aromatic) diisocyanates, and (e.g., aliphatic and / or aromatic) hydroxy-functional (meth)acrylates. Polycarbonate diols typically have the following formula: H(O-R1-OC(=O)) m -O-R2-OH wherein R1 and R2 in each (O-R1-OC(=O)) repeat unit are each independently an aliphatic, alicyclic, or aliphatic / alicyclic alkylene group, the average number of carbon atoms in the combination of all R1 and R2 groups is 4 to 10, and m is an integer from 2 to 23. In other words, R1 and / or R2 in some repeat units may have a carbon number less than 4 (e.g., 2 or 3), which is sufficient for the repeat units to have a carbon number high enough that the average carbon number of R1 and R2 in all repeat units in the polycarbonate diol of formula (I) falls within any of the following ranges: 4 to 10, or 4 to 6, 4 to 7, 4 to 8, 4 to 9, 5 to 7, 5 to 8, 5 to 9, 5 to 10, 6 to 8, 6 to 9, 6 to 10, 7 to 9, 7 to 10, or 8 to 10. In selected embodiments, at least one of R1 or R2 is -CH2CH2CH(CH3)CH2CH2-, -(CH2)6-, or -(CH2)4-, preferably a combination of -CH2CH2CH(CH3)CH2CH2- and -(CH2)6-.

[0087] In some embodiments, any of the polycarbonate diols has a number average molecular weight (Mn) greater than 1,000 grams / mole (g / mol), or the weighted average of all polycarbonate diols present in the component has a Mn greater than 1,000 g / mol, where Mn is determined by OH number. Stated differently, if the component contains a single polycarbonate diol, the polycarbonate diol has a Mn greater than 1,000 g / mol. If the component contains two or more polycarbonate diols, the Mn of at least one of the polycarbonate diols can be 1,000 g / mol or less, provided that the weighted average of all the Mn values ​​of the two or more polycarbonate diols is greater than 1,000 g / mol. For example, a component containing two polycarbonate diols may include a 1:2 molar ratio of a first polycarbonate diol having an Mn of about 500 g / mol to a second polycarbonate diol having an Mn of about 1,500 g / mol, resulting in a weighted average Mn of 1,167 g / mol. In certain embodiments, the polycarbonate diol (or the weighted average of all polycarbonate diols present in the component) has a number average molecular weight of 1,500 g / mol or greater.

[0088] In some embodiments, the polyester diol typically has the following formula: H[(O-R3-OC(=O)-R4-C(=O)] m -O-R3-OH The wherein R3 and R4 are independently straight or branched chain or ring-containing alkylene groups, which optionally contain heteroatoms such as oxygen. R3 and R4 independently contain 2 to 40 carbon atoms. The subscript "m" is typically at least 2, 3, 4, 5, 6, or 7. The subscript "m" is typically no greater than 50, 45, 40, 35, 30, 25, 20, or 15. In some embodiments, R3 and R4 are alkylene.

[0089] Representative polyester diols can include, for example, neopentyl glycol adipate diol, butanediol adipate diol, 3-methyl-1,5-pentanediol adipate diol, and 3-methyl-1,5-pentanediol sebecate diol, and dimer acid-based polyols in which the dimer acid is derived from the dimerization of two 18-carbon diacids, such as linoleic acid.

[0090] In some embodiments, such as the diols described above, the polyester diol can include a single R3 group (eg, neopentyl or 3-methyl-1,5-pentyl) and a single R4 group (eg, adipate).

[0091] In other embodiments, the aliphatic polyester diols can be prepared from two or more diols and two or more acids, in which the diols can contain two or more different R3 groups and two or more different R4 groups, such as in the case of ethylene glycol-hexanediol / adipate-azelate copolyester diol.

[0092] In other embodiments, the polyester diol typically has the following formula: H[-O-R6-C(=O)] n -O-R5-O-[C(=O)-R6-O] o -H The wherein R5 and R6 are independently straight or branched chain or ring-containing alkylene groups, which optionally contain heteroatoms such as oxygen, and which alkylene groups independently contain 2 to 40 carbon atoms. The subscripts "n" and "o" (i.e., the letter o) are typically independently at least 4, 5, or 6. The subscripts "n" and "o" are typically independently no more than 25, 20, or 15.

[0093] One representative polyester diol of this type is polycaprolactone diol, available, for example, from Perstorp. In this embodiment, R6 is a C5 alkylene group and R5 is the residue of an alcohol, such as, for example, ethylene glycol, butylene glycol, diethylene glycol, and the like.

[0094] In some embodiments, at least one of R3 or R4 in formula 1 and at least one of R5 and R6 in formula 2 are independently a straight-chain or branched-chain or ring-containing alkylene group containing at least 4, 5, or 6 carbon atoms.

[0095] In some embodiments, each of the R and R groups of formula 1 is independently an alkylene group containing at least 4, 5, or 6 carbon atoms. In some embodiments, each of the R and R groups of formula 2 is independently an alkylene group containing at least 4, 5, or 6 carbon atoms.

[0096] The values ​​of m, n, and o are selected such that the molecular weight (Mn) of the diol is at least 500, 600, 700, 800, 900, or 1000 g / mol. In some embodiments, the molecular weight (Mn) of the diol is at least 1100, 1200, 1300, 1400, or 1500 g / mol. In some embodiments, the molecular weight (Mn) of the diol is at least 1600, 1700, 1800, 1900, or 2000 g / mol. In some embodiments, the molecular weight (Mn) of the diol is no greater than 10,000, 9,000, 8,000, 7,000, 6,000, 5000, 4000, or 3000 g / mol. If the molecular weight is too low, the elongation may be insufficient (i.e., less than 15-20%). The values ​​of m, n, and o can vary widely due to the range of carbons in the R3, R4, R5, and R6 groups.

[0097] Polyether diols typically have the following formula: H[-O-R7] q-OH, where each R7 in each [-O-R7] repeat unit is independently an aliphatic, cycloaliphatic, or aliphatic / cycloaliphatic alkylene group of 2 to 10 carbon atoms. In some embodiments, the polyether polyol comprises poly(ethylene oxide), poly(propylene oxide), or poly(tetramethylene oxide) units. Of these types, poly(tetramethylene oxide) diols are preferred.

[0098] Preferably, no more than 20% of the q groups have 2 or 3 carbons. The value q is selected such that the molecular weight (Mn) of the diol is at least 500, 600, 700, 800, 900, or 1000 g / mol. In some embodiments, the molecular weight (Mn) of the diol is at least 1100, 1200, 1300, 1400, or 1500 g / mol. In some embodiments, the molecular weight (Mn) of the diol is at least 1600, 1700, 1800, 1900, or 2000 g / mol. In some embodiments, the molecular weight (Mn) of the diol is no more than 10,000, 9,000, 8,000, 7,000, 6,000, 5000, 4000, or 3000 g / mol. If the molecular weight is too low, elongation may be insufficient (i.e., less than 15-20%).

[0099] In some embodiments, the urethane (meth)acrylate polymer has the formula [ka] The wherein A has the formula -OC(=O)C(R1)=CH2, where R1 is H or alkyl of 1 to 4 carbon atoms (e.g., methyl), p is 1 or 2, Q is a polyvalent organic linking group, and R di is the residue of a diisocyanate, and R dOH is the residue of a polyester, polycarbonate, or polyether polyol, and r is an average of 1 to 15.

[0100] Such urethane (meth)acrylate polymers have the following formula: [ka] is represented by wherein A has the formula -OC(=O)C(R1)=CH2, where R1 is H or alkyl of 1 to 4 carbon atoms (e.g., methyl), p is 1 or 2, Q is a polyvalent organic linking group as described below, and R di is the residue of a diisocyanate, and R dOH is the residue of a polyester, polycarbonate polyol, or polyether, and r is, on average, 1 to 15. In some embodiments, r is, on average, at least 2, 3, 4, or 5. In some embodiments, A is a methacrylic functional group, such as methacrylate. A variety of diisocyanates can be used to prepare urethane (meth)acrylate polymers. In an exemplary embodiment, useful diisocyanates are represented by the formula R di (NCO)2, where R di is the aliphatic and / or aromatic moiety between the isocyanate groups. Upon reaction, R di is also commonly referred to as the residue of a diisocyanate. A variety of polyols can be used in the preparation of urethane (meth)acrylate polymers. In an exemplary embodiment, a useful polymer polyol is represented by the formula R dOH (OH)2, where R dOH is what remains after the hydroxyl groups are removed from the polymer polyol. In some embodiments, R dOH is the residue of a polyol including, for example, a polyester, polycarbonate, or polyether diol.

[0101] In some embodiments, Q is a straight or branched chain or ring-containing aliphatic (e.g., divalent) linking group, such as alkylene. In other embodiments, Q is an aromatic (e.g., divalent) linking group, such as arylene, aralkylene, and alkarylene. Q can optionally contain heteroatoms, such as O, N, and S, and combinations thereof. Q can also optionally contain heteroatom-containing functional groups, such as carbonyl or sulfonyl, and combinations thereof. Q typically contains 20 or fewer carbon atoms.

[0102] In some embodiments, Q is an alkylene, typically containing up to 12, 10, 8, or 6 carbon atoms. In some embodiments, Q is a C2, C3, or C4 alkylene group. In some embodiments, p is 1.

[0103] The urethane (meth)acrylate polymers described herein (e.g., containing polymerized units of aliphatic polycarbonate diols or polyester diols) are the primary difunctional (e.g., di(meth)acrylate) components of the free radically polymerizable resin composition. The total amount of urethane (meth)acrylate polymers is typically at least 25, 30, 35, or 40 weight percent based on the total weight of the free radically polymerizable resin (e.g., excluding inorganic components such as fillers). The total amount of urethane (meth)acrylate polymers is typically no more than 70, 65, or 60 weight percent.

[0104] Oligomers, which are reaction products of hydroxy-functional (meth)acrylates and diisocyanates (excluding polycarbonate diols or polyester diols), have been found to be by-products of the polymerization reaction of the components in certain embodiments. To remove such by-products, it is possible to purify the polyurethane methacrylate polymer. Alternatively, additional by-products such as oligomers may be added to the polymerization reaction product, especially when a particular reaction produces a small amount of one or more by-products. It has been discovered that some by-product components can improve at least one of the modulus or degree of crosslinking after the photopolymerizable composition has cured.

[0105] For example, the photopolymerizable composition may have the formula: [ka] (wherein Q, p, and R1 are the same as above, and R di is a residue of a diisocyanate as defined above. Typically, as described above, this compound is produced during polymerization of the components together. In certain embodiments, this compound is added to the photopolymerizable composition, particularly when a less than desired amount of such compound is produced by polymerization of the components. In any embodiment, the compound may advantageously improve crosslinking during the photopolymerization reaction, increasing the modulus or the photopolymerization product, or both. Regardless of whether the compound is formed during polymerization of the components, added separately to the photopolymerizable composition, or both, in some embodiments the compound is present in an amount of 0.05 weight percent (wt %) or more, 0.1 wt % or more, 0.5 wt % or more, 1 wt %, 1.5 wt % or more, 2 wt % or more, 3 wt % or more, 4 wt % or more, 5 wt % or more, 6 wt % or more, 7 wt % or more, 8 wt % or more, or 9 wt % or more based on the weight of the polymerizable composition, and 20 wt % or less, 18 wt % or less, 16 wt % or less, 14 wt % or less, 12 wt % or less, or 10 wt % or less based on the weight of the polymerizable composition. Stated another way, the compound may be present in the photopolymerizable composition in an amount of 0.05 to 20 weight percent (wt %), 1.5 to 12 wt %, 2.5% to 12 wt %, 5% to 15 wt %, 5% to 12 wt %, 7% to 15 wt %, 7% to 12 wt %, or 5 to 20 wt %, based on the weight of the polymerizable resin composition.

[0106] In selected embodiments, the compound is: [ka]

[0107] In another embodied synthetic route, typically in the presence of a catalyst, a urethane (meth)acrylate polymer is the reaction product of a (e.g., aliphatic) polycarbonate diol or polyester diol, as described above, with a (e.g., aliphatic and / or aromatic) isocyanate-functional (meth)acrylate.

[0108] In an exemplary embodiment, the isocyanate-functional (meth)acrylate has the following formula: (A) p -Q-NCO, In the formula, A and Q are the same as above.

[0109] Isocyanate-functional (meth)acrylates include, for example, isocyanatoethyl methacrylate, isocyanatoethoxyethyl methacrylate, isocyanatoethyl acrylate, and 1,1-(bisacryloyloxymethyl)ethyl isocyanate, available commercially from Showa Denko (Tokyo, Japan).

[0110] Such urethane (meth)acrylate polymers have the following formula: (A) p -Q-NHC(O)OR dOH -OC(O)NH-Q-(A) p is represented by In the formula, A, p, Q and R dOH is the same as above. In some embodiments, A is a methacrylate functional group. This material can be used as the primary difunctional (e.g., di(meth)acrylate) component of the free radically polymerizable resin composition or as an additional component.

[0111] In some embodiments, the photopolymerizable composition comprises one or more "high Tg" monofunctional (meth)acrylate monomers, i.e., a cured homopolymer of such monofunctional (meth)acrylate monomers has a Tg of at least 60, 65, 70, 75, 80, 85, or 90° C. In some embodiments, the polymerizable composition comprises at least one monofunctional (meth)acrylate monomer, such that a cured homopolymer of such monofunctional (meth)acrylate monomers has a Tg of at least 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, or 190° C. The Tg of the homopolymer of the monofunctional (meth)acrylate monomer is typically about 260° C. or less. For example, 1-adamantyl methacrylate decomposes at about 260° C. In some embodiments, the Tg of a homopolymer of a monofunctional (meth)acrylate monomer is less than or equal to 255, 250, 245, 240, 235, 230, 225, 220, 215, 210, 205, or 200° C.

[0112] In some embodiments, the high Tg monofunctional (meth)acrylate monomer comprises a cyclic moiety. The cyclic moiety can be aromatic, although in typical embodiments, the cyclic moiety is alicyclic. Suitable monofunctional (meth)acrylate monomers include, but are not limited to, for example, 3,3,5-trimethylcyclohexyl (meth)acrylate, butyl-cyclohexyl (meth)acrylate, 2-decahydronaphthyl (meth)acrylate, 1-adamantyl (meth)acrylate, 1-adamantyl acrylate, dicyclopentadienyl (meth)acrylate, dicyclopentadienyl acrylate, bornyl (meth)acrylate, bornyl acrylate, isobornyl (meth)acrylate, isobornyl acrylate, dimethyl-1-adamantyl (meth)acrylate, dimethyl-1-adamantyl acrylate, 3-tetracyclo[4.4.0.1.1]dodecyl methacrylate, and 3-tetracyclo[4.4.0.1.1]dodecyl acrylate.

[0113] The high Tg monofunctional (meth)acrylate monomers are typically at least 25, 30, 35, or 40 wt % based on the total weight of the free radically polymerizable resin (e.g., excluding inorganic components such as fillers). The total amount of high Tg monofunctional (meth)acrylate monomers is typically no more than 75, 70, 65, or 60 wt %.

[0114] The polymerizable composition may optionally include other difunctional (meth)acrylate monomers or polymers. Suitable free radically polymerizable multifunctional reactant diluents include di-, tri-, or other polyacrylates and methacrylates. The other difunctional (meth)acrylate monomers or polymers may include the by-products mentioned above, as well as the reaction products of diisocyanates with hydroxy-functional (meth)acrylates.

[0115] In some embodiments, the channel layer 810 may have a multi-layer structure. For example, the channel layer 810 may include a rigid polymer layer laminated with a relatively softer polymer layer that can bond the rigid polymer layer onto a flexible substrate. The rigid polymer layer may include, for example, PET. The relatively softer polymer layer may include, for example, an adhesive. It should be understood that the multi-layer structure may include any suitable material for the channel layer described herein.

[0116] The channel layer 810 includes one or more surface channels 812 formed on its exposed surface 811 and one or more via channels 814 fluidly connected to at least one of the surface channels 812. See FIG. 8A and FIG. 8C-D. At least one of the via channels 814 extends vertically through the channel layer 810 to access a conductive material 25 on the flexible substrate 2′. The conductive material 25 may be part of a circuit (e.g., an antenna circuit) formed on the flexible substrate 2′. The surface channels 812 and the via channels 814 may be formed by any suitable mechanical, chemical, or optical technique, including, for example, high definition, hot embossing, molding, soft lithography, etching, 3D printing, laser drilling, and the like.

[0117] In some embodiments, the channel layer 810 may be a microreplicated structure formed by a microreplication process. The liquid in which the microreplication structure is created may be a curable photocurable material, such as an acrylate that can be cured by UV light. Those skilled in the art will appreciate that other coating materials, such as polymerizable materials, may be used, and the choice of material depends on the particular properties desired for the microreplication structure. For example, if a flexible circuit board is being made, the coating material may include a conductive or insulating polymer. In some embodiments, the coating material includes an electroplating masking material and / or a non-conductive or insulating polymer.

[0118] Conductive traces 830 are formed in the surface channels 812 and the via channels 814 and are formed to make electrical contact with the conductive material 25 on the flexible substrate 2' below the island structures 10. The conductive traces 830 can be formed by any suitable process described herein. For example, the conductive traces 830 can be formed by flowing the conductive liquid 16 of FIG. 3A into the surface channels 812. The conductive liquid 16 can also flow into the via channels 814 and contact the conductive material 25. The conductive liquid 16 can then be solidified to form the conductive traces 830.

[0119] The conductive traces 830 in the surface channel 812 have respective free surfaces 832 that may be covered to protect the conductive traces 830 and their corresponding contacts, as further described above. In some embodiments, the conductive traces 830 may be reinforced by backfilling the channel with a product 816 of solidified polymer liquid. The polymer liquid may flow into the channel along the free surfaces 832 and form a protective cover layer thereon after solidification. The polymer liquid may be the same polymer liquid as the first polymer liquid 40 of Figures 4C-4E or may be the same material of the channel layer 810. In some embodiments, the product 816 may have an elastic modulus E4 that is greater than the elastic modulus E2 of the channel layer 810.

[0120] The stiffness ratio between the substrate 2′ and the channel layer 810 is defined as follows: (E * t2) / (E1 *t1), where E1 and E2 are the elastic moduli of the substrate 2' and the channel layer 810, respectively, and t1 and t2 are their respective thicknesses as shown in FIG. 8A. In the present disclosure, it has been found that a higher stiffness ratio results in a lower maximum tensile strain experienced by the channel layer or conductive traces within the channel, and the stiffer and thicker the channel layer 810 is compared to the substrate 2', the more stretchable and stronger the structure will be. In practice, the conductive traces 830 within the channel 812 tend to break at relatively low strains (1-3%). The safety window W for the maximum tensile strain experienced by the conductive traces (e.g., about 3% or less) may depend on the overall in-plane strain imposed on the substrate 2'. For example, a preferred stiffness ratio may be at least 5 or more to accommodate a maximum 5% overall strain imposed on the substrate, a preferred stiffness ratio may be at least 5 or more, at least 7 or more, or at least 9 or more to accommodate a maximum 20% overall strain imposed on the substrate, and a preferred stiffness ratio may be at least 15 or more to accommodate a maximum 50% overall strain imposed on the substrate. The overall in-plane distortion is about 5% to about 50%, (E2 * t2) / (E1 * The required lower limits for the ratios of t1) are, respectively, about 5 to about 15. This is further explained with reference to FIG. 9B below.

[0121] In some embodiments, one or more optional circuit dies may be provided on the island structure 10. The conductive traces 830 may be electrically contacted to corresponding contact pads of the circuit die in various ways described herein. In the illustrated embodiment of FIG. 8A, the island structure 10 further includes a pocket 6 for receiving the solid circuit die 20. The solid circuit die 20 is attached to the bottom surface of the pocket 6 via an adhesive layer 712, which may be formed by solidifying a liquid adhesive. As shown in FIG. 8D, a conductive liquid (conductive liquid 16 in FIG. 6B) may flow into a channel 812U below the circuit die to contact corresponding contact pads on the circuit die. The conductive traces may be reinforced by backfilling the void space with a product of solidified polymer liquid 816 in a manner similar to that shown in FIGS. 6A-6D. A product of solidified fluid polymer 722 may be used to fill the gap between the solid circuit die 20 and the pocket 6 after the formation of electrical contact between the conductive traces 830 and corresponding contact pads of the circuit die.

[0122] In the illustrated embodiment of Figures 8A-8B, an overcoat 820 is provided over the channel layer 810. In some embodiments, the overcoat 820 has a thickness t3 and may be made of one or more barrier materials to prevent penetration by water or other ambient factors from the underlying conductive traces or circuit die. In some embodiments, the overcoat 820 may be made of a material having an elastic modulus E3 greater than the elastic modulus E1 of the flexible substrate 2' and less than the elastic modulus E2 of the channel layer 810. It should be understood that the overcoat 820 may be made of any suitable protective material, such as, for example, a barrier having an adhesive surface for adhering to the channel layer 810.

[0123] The operation of the present disclosure will be further described in conjunction with the following embodiments. These embodiments are provided to further illustrate various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications can be made while remaining within the scope of the present disclosure.

[0124] List of Exemplary Embodiments It should be understood that any one of embodiments 1 to 13, 14 to 20, 21 to 26, and 27 to 35 can be combined.

[0125] Embodiment 1 is a method for producing a flexible device, the method comprising: providing a flexible substrate including an alignment region and one or more channels on a major surface thereof, the channels extending into the alignment region; providing a solid-state circuit die on the alignment area, the solid-state circuit die having one or more contact pads on a surface thereof; forming one or more conductive traces within the channel so as to make electrical contact with contact pads of the solid state circuit die; Flowing a first polymer liquid into the channel so as to cover the free surfaces of the conductive traces.

[0126] Example 2 is the method of example 1, wherein flowing the first curable polymer further comprises filling cavities in the channel beneath the solid-state circuit die with the first polymer liquid primarily by capillary forces.

[0127] Embodiment 3 is the method of embodiment 1 or 2, wherein the first polymer liquid comprises a UV-curable polymer.

[0128] Embodiment 4 is the method of any one of embodiments 1-3, further comprising solidifying the first polymer liquid.

[0129] Example 5 is the method of example 4, wherein the solidified product of the first polymer liquid has a modulus of elasticity greater than the modulus of elasticity of the flexible substrate.

[0130] Embodiment 6 is the method of any one of embodiments 1 to 5, wherein the alignment region includes a pocket for receiving the solid-state circuit die, and the pocket is oversized such that a gap exists between an edge of the pocket and the solid-state circuit die.

[0131] Embodiment 7 is the method of embodiment 6, further comprising flowing a second polymer liquid into the gap so as to at least partially fill the gap.

[0132] Example 8 is the method of example 7, further comprising solidifying the second polymer liquid, wherein a product of the solidified second polymer liquid has a modulus greater than the modulus of the flexible substrate.

[0133] Embodiment 9 is the method of embodiment 5, wherein the second polymer liquid comprises a UV-curable polymer.

[0134] Example 10 is a method according to any one of Examples 1 to 9, wherein forming the one or more conductive traces comprises disposing a conductive liquid in a channel and causing the conductive liquid to flow in the channel primarily by capillary forces.

[0135] Example 11 is the method of example 10, further comprising solidifying the conductive liquid.

[0136] Example 12 is the method of any one of Examples 1-11, wherein the channel comprises an inlet channel and an outlet channel in fluid communication, and the first polymer liquid flows into the inlet channel.

[0137] Example 13 is the method of any one of Examples 1 to 12, wherein providing the solid-state circuit die on the alignment area includes attaching the solid-state circuit die on the alignment area with an adhesive.

[0138] Embodiment 14 is a flexible substrate including an alignment region and one or more channels on a major surface thereof, the channels extending into the alignment region; a solid-state circuit die disposed on the alignment area, the solid-state circuit die having one or more contact pads on a surface thereof; one or more conductive traces formed within the channel, the traces making one or more electrical contacts with contact pads of the solid state circuit die; and a solidified product of the first polymer liquid covering the free surface of the conductive trace, the product having a modulus of elasticity greater than the modulus of elasticity of the flexible substrate.

[0139] Embodiment 15 is the device of embodiment 14, wherein the solidified product of the first polymer liquid at least partially fills the cavity in the channel beneath the solid-state circuit die.

[0140] Embodiment 16 is the device of embodiment 14 or 15, wherein the product comprises a product of curing a UV-curable polymer.

[0141] Embodiment 17 is a device described in any one of embodiments 14 to 16, wherein the alignment area includes a pocket for receiving a solid circuit die, and the product of solidifying the second polymer fluid at least partially fills the gap.

[0142] Example 18 is the device of example 17, wherein the product comprises a cured product of a UV-curable polymer, the product having a modulus of elasticity greater than the modulus of elasticity of the flexible substrate.

[0143] Embodiment 19 is a device described in any one of embodiments 14 to 18, wherein the channel includes an inlet channel and an outlet channel that are fluidly connected, and the product of the solidified first polymer liquid extends from the inlet channel into the outlet channel.

[0144] Example 20 is the device of any one of Examples 14-19, wherein the solid-state circuit die is attached to the alignment area by an adhesive.

[0145] Embodiment 21 is a method for manufacturing a flexible device, the method comprising: Providing a flexible substrate having circuitry thereon; providing an island structure on a flexible substrate for at least partially covering a circuit thereon, the island structure including one or more surface channels on an exposed surface thereof and one or more via channels in fluid communication with at least one of the surface channels and extending vertically through the island structure; forming one or more conductive traces in the surface channel and the via channel to make electrical contact with circuitry on the flexible substrate beneath the island structure; Providing a first polymer liquid in the surface channel to cover the free surfaces of the conductive traces therein.

[0146] Example 22 is the method of example 21, wherein the island structure has an elastic modulus E2 greater than the elastic modulus E1 of the flexible substrate.

[0147] Embodiment 23 is the method of embodiment 21 or 22, further comprising providing an overcoat over the island structures.

[0148] Example 24 is the method of any one of Examples 21-23, further comprising flowing a first polymer liquid into the surface channels and the via channels and solidifying the first polymer liquid.

[0149] Example 25 is the method of any one of Examples 21 to 24, further comprising providing a solid circuit die in the island structure, flowing a second polymer liquid to at least partially surround the solid circuit die, and solidifying the second polymer liquid.

[0150] Example 26 is a method according to any one of embodiments 21 to 25, wherein forming the one or more conductive traces comprises disposing a conductive liquid in a channel, causing the conductive liquid to flow in the channel primarily by capillary forces, and solidifying the conductive liquid.

[0151] Embodiment 27 is a flexible substrate having circuitry thereon; an island structure on the flexible substrate for at least partially covering a circuit thereon, the island structure including one or more surface channels on an exposed surface thereof and one or more via channels in fluid communication with at least one of the surface channels; one or more conductive traces formed within the surface channel and the via channel to make electrical contact with circuitry on the flexible substrate beneath the island structure; and a solidified product of the first polymer liquid covering the free surface of the conductive trace.

[0152] Embodiment 28 is a device described in embodiment 27, wherein the flexible substrate has an elastic modulus E1 and a thickness t1, the island structure has an elastic modulus E2 and a thickness t2, and the ratio of (E2×t2) / (E1×t1) is greater than 7.

[0153] Embodiment 29 is a device according to embodiment 27 or 28, in which the flexible substrate has an elastic modulus E1 and a thickness t1, the island structure has an elastic modulus E2 and a thickness t2, and when the overall in-plane strain on the flexible substrate is from about 5% to about 50%, the required lower limit for the ratio (E2×t2) / (E1×t1) is from about 5 to about 15, respectively.

[0154] Embodiment 30 is the device of any one of embodiments 27-29, further comprising providing an overcoat over the island structures.

[0155] Embodiment 31 is a device according to any one of embodiments 27 to 30, wherein the product has an elastic modulus E4 greater than the elastic modulus E2 of the islands.

[0156] Embodiment 32 is the device of any one of embodiments 27-31, wherein the first polymer liquid comprises a UV-curable polymer.

[0157] Embodiment 33 is a device described in any one of embodiments 27 to 32, wherein the island structure further includes a pocket for receiving a solid circuit die, and the product of solidifying the second polymer fluid at least partially surrounds the periphery of the solid circuit die.

[0158] Embodiment 34 is the device according to any one of embodiments 27 to 33, wherein the island structure is: i) a urethane (meth)acrylate polymer comprising the reaction product of an aliphatic polyester, polycarbonate, or polyether diol, a diisocyanate, and a hydroxy-functional methacrylate; ii) a monofunctional (meth)acrylate monomer, wherein a cured homopolymer of at least one monofunctional (meth)acrylate monomer has a Tg of at least 60°C.

[0159] Embodiment 35 is a method for preparing a urethane (meth)acrylate polymer having the formula [ka] where A has the formula -OC(=O)C(R1)=CH2, where R1 is H or alkyl of 1 to 4 carbon atoms (e.g., methyl), p is 1 or 2, Q is a polyvalent organic linking group, and R di is the residue of a diisocyanate, and R dOH is a residue of a polyester, polycarbonate, or polyether polyol, and r average is 1 to 15.

[0160] Example of an island structure These examples are merely illustrative and are not intended to unduly limit the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, each numerical parameter should be construed by at least applying ordinary rounding techniques in light of the number of reported significant digits, but this is not intended to limit the application of the doctrine of equivalents to the scope of the claims.

[0161] Material Overview All parts, percentages, ratios, etc. in the examples and elsewhere in the specification are by weight unless otherwise noted. Solvents and other reagents used were available from Sigma-Aldrich Chemical Company (Milwaukee, WI) unless otherwise noted. Additionally, Table 1 provides the abbreviations and sources for all materials used in the following examples.

[0162] [Table 1]

[0163] Test Method The following test methods were used in evaluating some of the embodiments of the present disclosure.

[0164] Simulation Method A commercially available finite element analysis software, ANSYS Mechanical APDL 17.1 (Ansys Inc., Pittsburgh PA, USA), was used to simulate the deformation of the island structure with the configuration shown in Fig. 9A. The modeling results were then analyzed with the design of experiments (DOE) method using DOE analysis software, ISight 5.8 (Dassault Systemes Simulia Corp., Providence RI, USA).

[0165] The mathematical model utilizes symmetry considerations and plane strain elements (typically at least 5 elements through the thickness, fine mesh near the interface) to simulate the island structure of FIG. 9A with fixed lengths (51 mm for substrate 91 and 25.4 mm for island 92). The model calculates the tensile principal strains in the surface channel 93 by applying displacements to the model ends, where the displacements reached 20%, 30%, 40% and 50% of the applied strain. The parameterized model was used to automatically generate a full factorial DOE around the input parameters: elastic modulus and thickness of substrate 91 (elastic modulus E1 ranges from about 0.5 to about 1.8 MPa, thickness t1 ranges from about 0.25 to about 1 mm), elastic modulus and thickness of island 92 (elastic modulus E2 ranges from about 10 to about 1300 MPa, thickness t2 ranges from about 0.127 to about 0.381 mm), and the length of channel 93 ranges from about 12 to about 20 mm.

[0166] Simulation results FIG. 9B is a plot of the maximum tensile strain experienced by the ink in channel 93 versus stiffness ratio according to several simulation results. The stiffness ratio is defined as: (E * t2) / (E1 * t1), where E1 and E2 are the elastic moduli of the substrate 91 and the islands 92, respectively, and t1 and t2 are the thicknesses of the substrate 91 and the islands 92, respectively. The plot in FIG. 9B examines the maximum strain vs. stiffness ratio for an imposed global in-plane strain of 5% to 50% on the substrate 91, as shown in FIG. 9B. Simulations show that the maximum strain decreases as the stiffness ratio increases, indicating that the more stiff and thick the islands 93 are compared to the substrate 91, the more stretchable and stronger the structure will be. For example, since the ink in the channels 93 and the interfaces within the structure tend to break at relatively low strains (1-3%), a preferred stiffness ratio may be at least 20 or more to accommodate an imposed global strain of up to 50%. The safety window W for the maximum tensile strain experienced by the ink (e.g., about 3% or less) may depend on the global in-plane strain imposed on the substrate 91. When the global in-plane strain is about 20%, (E2 * t2) / (E1* The ratio of (E2t1) is greater than about 7. The overall in-plane distortion is about 5% to about 50%, and (E2t2) is greater than about 7. * t2) / (E1 * The lower limit of the ratio of t1) is about 5 to about 15.

[0167] Since the stiffness ratio depends on the product of the layer's elastic modulus and thickness, the plot in Figure 9B can also be used to minimize the overall device thickness by specifying how high the island elastic modulus will endure when both the substrate and islands are as thin as possible for a thin device. For example, if both the substrate 91 and islands 92 are about 100 micrometers thick, the island material can have an elastic modulus at least 20 times greater than that of the substrate, creating a robust stretchable device that can withstand an overall applied strain of 50%.

[0168] Sample-I Samples with two-layer island structures, as shown in Figure 9A, were prepared to demonstrate the improved stretchability. Islands of NOA and DP100 were replicated on VHB substrates with different thicknesses for various island structures. The microchannels within the island structures were filled with conductive ink, and the resistance change (R / R0) across the channel was measured while straining the VHB substrate.

[0169] FIG. 10A is a plot of R / R0 versus strain for low modulus islands (NOA) on a thick substrate (VHB tape). FIG. 10B is a plot of R / R0 versus strain for low modulus islands (NOA) on a thin substrate (VHB tape). FIG. 10C is a plot of R / R0 versus strain for high modulus islands (DP100 epoxy) on a thick substrate (VHB tape). The thickness ratio (t2 / t1), modulus ratio (E2 / E1) and stiffness ratio (E2 * t2) / (E1 * 10A to 10C, where E1 and E2 are the elastic moduli of the substrate 91 and the islands 92, respectively, and t1 and t2 are the thicknesses of the substrate 91 and the islands 92, respectively.

[0170] Comparing Figures 10A-B, the modulus ratio (E2 / E1) remains constant while the thickness ratio (t2 / t1) increases. This increases the stiffness ratio from 2.4 to 10.2. The sample shown in Figure 10A breaks at about 5% strain (a sharp increase in R / R0), while the sample shown in Figure 10B withstands up to 35% strain on the substrate. This confirms the trend shown by the simulation in Figure 9B, as the device can withstand higher strains at higher stiffness ratios. Comparing Figures 10A and 10C, the modulus ratio (E2 / E1) increases while the thickness ratio (t2 / t1) decreases. The overall stiffness ratio increases because the DP100 epoxy has a significantly higher modulus than that of NOA. The sample in Figure 10C was able to withstand higher strains (although the DP100 islands are thinner). This therefore demonstrates that the thin device with island structures described herein can minimize total thickness by manipulating the elastic modulus ratio.

[0171] Sample-II: PE2-PE4 All parts, percentages, ratios, etc. in the examples and elsewhere in this specification are by weight unless otherwise noted. Table 2 below lists the materials used in Sample-II.

[0172] [Table 2]

[0173] 4 IPDI / 2 C-2050 / 2 HEMA(PE-1) A 3 L, 3-neck round bottom flask was charged with 1176.57 g of C-2050 (1.195 equiv., 984.5 hydroxide equivalents (OH EW), heated to approximately 58° C.), then 265.57 g of IPDI (2.390 equiv.), 0.640 g of BHT (400 ppm), and 0.40 g of BiN (250 ppm). The reaction was heated under dry air to an internal set point of 105° C. (maximum temperature reached was approximately 120° C.). At 1 hour 35 minutes, 157.86 g of HEMA (1.2130 equiv., 130.14 MW, 1.5% excess) was added via the addition funnel at a steady rate over 20 minutes. At approximately 2.75 hours of total reaction time, an aliquot was checked by Fourier transform infrared spectroscopy (FTIR) and found to be 2265 cm -1 No -NCO peak was found in the eluate and the product was isolated as a clear viscous material.

[0174] Samples PE2-PE4 were prepared by mixing the following materials in Table 3, all given in grams:

[0175] [Table 3]

[0176] Samples with two-layer island structures as shown in Figure 9A were prepared to demonstrate improved stretchability. Flat islands (~3 to ~4 mils thick) of NOA and PE2, PE3 & PE4 (details below) were created on VHB substrates. Briefly, a droplet of island material was dispensed onto the VHB substrate, a PET liner was placed on the droplet, and the droplet was spread evenly on the substrate. The island material was then fully solidified by a two-step UV curing process through the liner. The liner was then removed and black powder was spotted on the islands to aid in local strain mapping using digital image correlation (DIC). The results of the local strain experienced by the islands observed by these materials in response to a globally applied strain are plotted as shown in Figure 11. When fully cured, none of the islands in PE2, PE3 & PE4 reach a local strain greater than 4% for a global strain of up to 30%. The local strain in these materials is less than 7% for a local strain of up to 52%. On the other hand, the NOA islands experience local strains of over 10% relative to a global strain of 30%.

[0177] Throughout this specification, references to "one embodiment," "a particular embodiment," "one or more embodiments," or "an embodiment" mean that the particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one of the particular exemplary embodiments of the disclosure, regardless of whether the term "embodiment" is preceded by the term "embodiment." Thus, the appearances of phrases such as "in one or more embodiments," "in a particular embodiment," "in one embodiment," or "in an embodiment" in various places throughout this specification do not necessarily refer to the same particular exemplary embodiments of the disclosure. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0178] Although several exemplary embodiments have been described in detail herein, it will be understood that those skilled in the art will be able to easily conceive modifications, variations, and equivalents of these embodiments upon comprehension of the above description. It should therefore be understood that the present disclosure is not unduly limited to the exemplary embodiments described thus far. In particular, as used herein, the recitation of numerical ranges by endpoints is intended to include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). In addition, all numbers used herein are intended to be modified by the term "about." Furthermore, all publications and patents referenced herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. Various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims.

Claims

1. providing a flexible substrate including an alignment region and one or more channels on a major surface thereof, the channels extending into the alignment region, each channel having a bottom wall and a sidewall adjacent to the bottom wall; providing a solid-state circuit die on the alignment area, the solid-state circuit die having one or more contact pads on a surface thereof; forming one or more conductive traces within the channel to electrically contact the contact pads of the solid-state circuit die, the conductive traces having a surface covering the bottom wall and a portion of the side wall of the channel and a free surface; flowing a first polymer liquid over the free surfaces of the conductive traces in the channel so as to cover the free surfaces of the conductive traces; solidifying the first polymer liquid to form a solidified product covering the free surfaces of the conductive traces and having a higher elastic modulus than the flexible substrate; A method for manufacturing a flexible device, comprising:

2. 10. The method of claim 1, wherein flowing the first polymer liquid further comprises filling a cavity in the channel beneath the solid-state circuit die with the first polymer liquid primarily by capillary forces.

3. 2. The method of claim 1, wherein the registration area includes a pocket for receiving the solid-state circuit die, the pocket being oversized such that a gap exists between an edge of the pocket and the solid-state circuit die.

4. The method of claim 3 , further comprising flowing a second polymer liquid into the gap so as to at least partially fill the gap.

5. a flexible substrate including an alignment area and one or more channels on a major surface thereof, the channels extending into the alignment area, each channel having a bottom wall and a sidewall adjacent to the bottom wall; a solid-state circuit die disposed on the alignment area, the solid-state circuit die having one or more contact pads on a surface thereof; one or more conductive traces formed within the channel, the traces making one or more electrical contacts with the contact pads of the solid state circuit die, the conductive traces having a surface covering a bottom wall and a portion of the side wall of the channel, and a free surface; a solidified product of a first polymer liquid covering a free surface of the conductive trace; and wherein the product has a modulus of elasticity greater than a modulus of elasticity of the flexible substrate.

6. The device of claim 5 , wherein the product of solidifying the first polymer liquid at least partially fills a cavity in the channel beneath the solid-state circuit die.

7. 6. The device of claim 5, wherein the alignment area includes a pocket for receiving the solid-state circuit die, a gap exists between an edge of the pocket and the solid-state circuit die, and a product of solidified second polymer fluid at least partially fills the gap.

8. The device of claim 7 , wherein the product comprises a cured product of a UV curable polymer, the product having a modulus of elasticity greater than a modulus of elasticity of the flexible substrate.

9. a flexible substrate having circuitry thereon; an island structure on the flexible substrate for at least partially covering the circuitry thereon, the island structure including a channel layer including one or more surface channels on an exposed surface thereof and one or more via channels in fluid communication with at least one of the surface channels, each surface channel having a bottom wall and a sidewall adjacent to the bottom wall, and each via channel having a sidewall; one or more conductive traces formed within the surface channel and the via channel to electrically contact the circuitry on the flexible substrate beneath the island structure, the conductive trace having a surface covering the bottom wall and a portion of the sidewall of the surface channel and a sidewall of the via channel, and a free surface; a product of solidification of a first polymer liquid covering a free surface of the conductive trace, the product having a higher elastic modulus than the channel layer; A flexible device comprising:

Images