Method and system for printed circuits on substrates for stretchable electronic devices

Abstract

A method for fabricating a flexible or stretchable printed circuit includes providing a substrate including a polyethylene terephthalate (PET) support layer, a thermoplastic urethane (TPU) layer, and a hot melt adhesive (HMA) disposed between the PET and TPU layers, pre-shrunk processing the substrate, printing a resistive layer on the TPU layer of the substrate, printing an insulating layer on the resistive layer, removing the PET support layer, and transferring a portion of the substrate to the flexible or stretchable layer.

Description

[Technical Field]

[0001] Cross-reference to related patent applications This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 443,490, filed February 6, 2023, and International Application No. PCT / US23 / 29156, filed July 31, 2023, which claims the benefit of and priority to U.S. Provisional Patent Application No. 63,393,690, filed July 29, 2022, each of which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE DISCLOSURE The present disclosure relates generally to the fields of printed circuits, substrates, and stretchable electronic components. [Background technology]

[0003] There are various types of printed circuits for electronic systems that can provide effective performance under normal and extreme use conditions, but it is difficult to reliably electrically couple electronics mounted on stretchable or flexible substrate materials to rigid connectors using currently available electrical circuits. Summary of the Invention

[0004] Disclosed herein are methods and systems for fabricating flexible or stretchable printed circuits. For example, but not limited to, a substrate can be provided to receive the printed circuit and can be pre-shrunk to minimize degradation of fiducial alignment (registration) as each layer is printed. In some embodiments, a method for fabricating a flexible or stretchable circuit (e.g., heater) on a flexible or stretchable layer (e.g., fabric) includes pre-shrunking the substrate, printing the circuit onto the substrate, removing excess substrate, transferring the remainder of the substrate bearing the flexible or stretchable printed circuit (e.g., stretchable resistive heating element) to an adhesive element, and / or applying the resulting pattern to the flexible or stretchable layer (e.g., fabric).

[0005] The techniques and materials described herein enable the assembly of additively manufactured electronics such as flexible or stretchable circuits or resistive heating elements that can be heat pressed into, printed on, or included within or on materials used in products that benefit from the application of heat, such as, for example, textile elements, neoprene, leather, rubber, silicone, synthetic materials, clothing, seat covers, furniture, work equipment, athletic equipment, therapeutic products, medical products, wetsuits, blankets, etc.

[0006] In one general aspect, disclosed herein is a method for fabricating a flexible or stretchable printed circuit, comprising providing a substrate comprising a polyethylene terephthalate (PET) support layer, a thermoplastic urethane (TPU) layer, and a hot melt adhesive (HMA) disposed between the PET and TPU layers; pre-shrunk processing the substrate; printing a resistive layer on the TPU layer of the substrate; printing an insulating layer on the resistive layer; removing the PET support layer; and transferring a portion of the substrate to a flexible or stretchable layer.

[0007] In some embodiments, the PET support layer comprises a thickness of about 1 mil to 5 mils.

[0008] In some embodiments, the TPU layer comprises a thickness of about 1 mil to 5 mils.

[0009] In some embodiments, the HMA layer comprises a thickness of about 1 mil to 5 mils.

[0010] In some embodiments, the method further comprises applying electricity to the resistive layer to generate heat from the flexible or stretchable printed circuit.

[0011] In some embodiments, pre-shrunking the substrate comprises pre-shrunking the substrate at a temperature of about 100°C to about 200°C.

[0012] In some embodiments, pre-shrunking the substrate comprises pre-shrunking the substrate for a period of from about 30 seconds to about 10 minutes.

[0013] In some embodiments, the method further comprises printing a conductive layer between the resistive layer and the insulating layer.

[0014] In some embodiments, transferring a portion of the substrate to the flexible or stretchable layer comprises disposing a hot melt adhesive (HMA) layer on the flexible or stretchable layer.

[0015] In some embodiments, the flexible or stretchable layer is a fabric.

[0016] In one general aspect, disclosed herein is a stretchable printed circuit that includes a stretchable layer, a thermoplastic urethane (TPU) layer adhered to the stretchable layer using a hot melt adhesive, a resistive layer printed on the TPU layer, and an insulating layer printed on the resistive layer.

[0017] In some embodiments, the stretchable layer comprises a thickness of about 1 mil to 5 mils.

[0018] In some embodiments, the TPU layer comprises a thickness of about 1 mil to 5 mils.

[0019] In some embodiments, the hot melt adhesive comprises a thickness of about 1 mil to 5 mils.

[0020] In some embodiments, electricity is applied to the resistive layer to generate heat from the stretchable printed circuit.

[0021] In some embodiments, the TPU layer is preshrunk at a temperature of about 100° C. to about 200° C. prior to attachment to the stretchable layer.

[0022] In some embodiments, the TPU layer is preshrunk for a period of from about 30 seconds to about 10 minutes.

[0023] In some embodiments, the circuit further includes a conductive layer between the resistive layer and the insulating layer.

[0024] In some embodiments, the TPU layer is disposed on a polyethylene terephthalate (PET) support layer before being attached to the stretchable layer.

[0025] In some embodiments, the stretchable layer is a fabric.

[0026] Various objects, aspects, features, and advantages of the present disclosure will become more apparent and will be better understood by reference to the detailed description in conjunction with the accompanying drawings, in which like reference characters identify corresponding elements throughout. In the drawings, identical reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. The drawings are for illustrative purposes only and are not intended to limit the scope of the present disclosure. [Brief explanation of the drawings]

[0027] [Figure 1A] 1 shows a diagram of a substrate according to some embodiments. [Figure 1B] 1B shows a diagram of a flexible or stretchable printed circuit and a flexible or stretchable layer on a portion of the substrate shown in FIG. 1A, according to some embodiments. [Figure 2] 1 illustrates a method for fabricating a flexible or stretchable printed circuit, according to some embodiments. [Figure 3] 1 shows a diagram of a flexible or stretchable printed circuit according to some embodiments. [Figure 4] 1 shows a diagram of a resistive heating element having a flexible or stretchable printed circuit manufactured using the methods described herein, according to some embodiments. [Figure 5] 10 shows experimental results of thermal measurements of an electrical connector assembly including a flexible or stretchable printed circuit as described herein, according to some embodiments. [Figure 6] 1 illustrates a flexible or stretchable substrate having several layers of flexible or stretchable printed circuits according to some embodiments. [Figure 7] 1 shows a graph of the resistance of an electrode on a flexible or stretchable substrate over multiple extension cycles, according to some embodiments. [Figure 8] 8A-8B show graphs of the resistance of electrodes on a flexible or stretchable substrate when the flexible or stretchable substrate is in a stretched state and also when the flexible or stretchable substrate is in a relaxed state, according to some embodiments. [Figure 9] AB show the heat output of a flexible or stretchable printed circuit (eg, a resistive heater) on a flexible or stretchable substrate before and after multiple cleaning cycles, according to some embodiments. [Figure 10] 8A-8B show graphs of resistance and output of electrodes on a flexible or stretchable substrate in response to several cleaning cycles, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0028] The details of various embodiments of the methods and systems are set forth in the accompanying drawings and the description below.

[0029] The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to be limiting. For example, forming a first feature above or on a second feature in the following description may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. Furthermore, the present disclosure may repeat reference numerals and / or letters in various examples. This repetition is for the purpose of simplicity and clarity and does not, in itself, dictate a relationship between the various embodiments and / or configurations described.

[0030] In general, disclosed herein include methods and systems for fabricating flexible or stretchable printed circuits. For example, but not limited to, a substrate for receiving the printed circuit can be provided and pre-shrunk to minimize degradation of fiducial alignment (registration) as each layer is printed. In some embodiments, a method for fabricating a flexible or stretchable circuit (e.g., heater) on a flexible or stretchable layer (e.g., fabric) includes pre-shrunking the substrate, printing the circuit onto the substrate, removing excess substrate, transferring the remainder of the substrate bearing the flexible or stretchable printed circuit (e.g., stretchable resistive heating element) to an adhesive element, and / or applying the resulting pattern to the flexible or stretchable layer (e.g., fabric).

[0031] The techniques and materials described herein enable the assembly of additively manufactured electronics such as flexible or stretchable circuits or resistive heating elements that can be heat pressed into, printed on, or included within or on materials used in products that benefit from the application of heat, such as, for example, textile elements, neoprene, leather, rubber, silicone, synthetic materials, clothing, seat covers, furniture, work equipment, athletic equipment, therapeutic products, medical products, wetsuits, blankets, etc.

[0032] As used in this description, the term "printing" is intended to include all forms of printing and coating, including, but not limited to, patch die coating, slot or extrusion coating, slide or cascade coating, pre-metered coating such as curtain coating, roll coating such as knife-over-roll coating, forward and reverse roll coating, gravure coating, dip coating, spray coating, meniscus coating, spin coating, brush coating, air knife coating, screen printing processes, electrostatic printing processes, thermal printing processes, inkjet printing processes, direct writing printing processes, jettable deposition processes, and other similar techniques.

[0033] FIG. 1A shows a diagram of a substrate according to some embodiments.

[0034] 1A, the substrate typically includes a PET support layer (e.g., having a thickness of 4 mils), a hot melt adhesive layer (e.g., having a thickness of 2 mils), and / or a thermoplastic urethane (TPU) layer (e.g., having a thickness of 4 mils). In some embodiments, the hot melt adhesive (HMA) layer is disposed between the PET layer and the TPU layer.

[0035] In some embodiments, the PET support layer, hot melt adhesive layer, and / or TPU layer comprises a thickness of about 0.1 mil to about 10 mils. In some embodiments, the PET support layer, hot melt adhesive layer, and / or TPU layer comprises a thickness of about 0.5 mil to about 5 mils. In some embodiments, the PET support layer, hot melt adhesive layer, and / or TPU layer comprises a thickness of about 1 mil to about 4 mils. In some embodiments, the PET support layer, hot melt adhesive layer, and / or TPU layer comprises a thickness of about 1 mil, about 2 mils, about 3 mils, or about 4 mils.

[0036] Generally, a PET support layer (e.g., having a thickness of 4 mils) can provide enhanced thermal stability (compared to, for example, commonly used biaxially oriented polypropylene (BOPP)). The support PET can also provide a coating to maximize the release ability of the print once dried, cooled, and cut (if applicable), resulting in easy release that enables a two-step transfer process to fabric or other flexible or stretchable layer.

[0037] Generally, a hot melt adhesive layer (e.g., having a thickness of 2 mils) can withstand multiple washing cycles and adheres well to polyester, polycotton, Lycra, ABS, polycarbonate, polyvinyl chloride (PVC), polyurethane, wood, leather, fiberglass, aluminum, copper, and steel.

[0038] Generally, the TPU layer (e.g., having a thickness of 2 mils) may be the "print side" of the substrate (e.g., "ES1001") and may be considered a high melting point TPU. In some embodiments, the TPU layer provides good elasticity to the substrate system.

[0039] FIG. 1B shows a diagram of a flexible or stretchable printed circuit and a substrate having a flexible or stretchable layer, according to some embodiments.

[0040] FIG. 2 illustrates a method for fabricating a flexible or stretchable printed circuit, according to some embodiments.

[0041] In step 210, a substrate is provided. In some embodiments, the substrate includes a polyethylene terephthalate (PET) support layer, a thermoplastic urethane (TPU) layer, and a hot melt adhesive (HMA) layer disposed between the PET and TPU layers. In step 220, the substrate is pre-shrunk. In step 230, a resistive layer is printed onto the TPU layer of the substrate. In step 240, an insulating layer is printed onto the resistive layer. In step 250, the PET support layer is removed from the substrate. In step 260, a portion of the substrate (e.g., the substrate without the PET support layer) is transferred to a flexible or stretchable layer.

[0042] For example, without limitation, the methods described herein may include a printing process for fabricating (e.g., assembling) a 5V fixed resistive heater on a fabric or other flexible or stretchable substrate.

[0043] The substrate can be pre-shrunk at 140°C (284°F) for 3 minutes to help ensure proper registration when the layers are printed, as described above. Longer shrink times can accommodate tighter tolerances. For example, if the registration tolerance is <1%, the substrate can be shrunk for 5 minutes instead of 3 minutes.

[0044] In some embodiments, when the substrate is removed from the oven, it is transparent because the hot melt adhesive melts and becomes optically clear. The high melting point, high modulus TPU printed on the surface also activates upon removal from the oven. Waiting for the hot melt and TPU to recrystallize can help prevent the TPU layer from sticking to the screen emulsion. In some embodiments, the waiting time is about 30 minutes. In some embodiments, allowing recrystallization can cause the substrate to regain its haze.

[0045] After the substrate is pre-shrunk, the desired circuit topology can be printed onto the substrate. Printing on TPU can be different from printing on PET / PI type substrates. TPU is absorbent and soft, while PET / PI does not absorb solvents and is stiff. The flexible and absorbent nature of TPU can cause pinholes as the mesh presses against and deforms the TPU. Therefore, pressure must be kept low.

[0046] In some embodiments, a printer such as an automated screen printer (e.g., HMI Model 9156 manufactured by Harry Manufacturing Inc. of Lebanon, NJ) is used to print the TPU layer. The squeegee takes a square piece of stock held in a diamond shape (e.g., as shown in Tables 1-3 below), which means printing is done using a 45° angle of attack. A rectangular blade screen printer may need to use a different angle of attack, such as 30°, to determine optimal parameters. Additionally, using a chamfered or rounded edge on the squeegee can help reduce the effect of pinholes that can occur when printing on TPU and improve ink adhesion.

[0047] Printing a resistive layer onto a TPU layer When printing a resistive layer onto the TPU layer, a stretchable heater ink such as SE5025 Fixed Resistance Stretchable Heater Ink (e.g., manufactured by ACI Materials, Inc. of Goleta, California) can be used. SE5025 ink can generate uniform heat and is suitable for printing both small and large heaters.

[0048] In some embodiments, exemplary conditions for printing this ink are listed in Table 1 below. [Table 1]

[0049] In some embodiments, the SE5025 is most consistent when using double-stroke printing, which is done in two consecutive print strokes. Some printers are configured to do double printing, while others require two print cycles, one immediately following the other.

[0050] In some embodiments, the method includes thoroughly hand stirring the ink before printing, which allows it to shear thin easily, reduce the number of set-up prints, and / or reach a steady-state viscosity.

[0051] In some embodiments, the method involves checking the print against a backlight to locate pinholes in the wet film and adjusting the squeegee pressure or angle of attack until the pinholes disappear.

[0052] Printing a conductive layer onto the TPU layer After the resistive ink is printed and dried, a conductive ink such as SE1109 Stretchable Printed Silver Conductor Ink (e.g., from ACI Materials, Inc. of Goleta, California) can then be applied. In some embodiments, the conductive ink layer acts as a "bus bar," i.e., it conducts current from a current source through the resistive ink and generates heat. SE1109 ink provides excellent electrical conductivity and can be stretched up to 150% of its original length without breaking.

[0053] In some embodiments, exemplary conditions (eg, printing parameters) for printing this ink are listed in Table 2 below. [Table 2]

[0054] In some embodiments, SE1109 is most consistent when using double-stroke printing, which is done in two consecutive print strokes. Some printers are configured to do double printing, while others require two print cycles, one immediately following the other.

[0055] In some embodiments, the method includes thoroughly hand-stirring the ink before printing. This step may be less shear-thinning than other inks and may take more time to mix. This step reduces the number of setup prints and allows a steady-state viscosity to be reached.

[0056] In some embodiments, the method involves checking the print against a backlight to locate pinholes in the wet film and adjusting the squeegee pressure or angle of attack until the pinholes disappear.

[0057] Printing an insulating layer onto a TPU layer After the conductive ink is printed and dried, one or more layers of an insulator ink, such as SE3104 Stretchable Insulator Ink manufactured by Applied Cavitation Inc. of Goleta, California, can be printed. SE3104 ink protects the underlying layers from abrasion and environmental degradation and withstands multiple washing cycles. Exemplary conditions for printing this ink are listed in Table 3 below. [Table 3]

[0058] In some embodiments, the SE3104 is most consistent when using single-stroke printing.

[0059] In some embodiments, the method includes thoroughly hand stirring the ink before printing. This step can facilitate shear thinning of the flakes. This step can reduce the number of setup prints and help reach a steady-state viscosity.

[0060] In some embodiments, the method involves checking the print against a backlight to locate pinholes in the wet film and adjusting the squeegee pressure or angle of attack until the pinholes disappear.

[0061] In some embodiments, a very small amount of solvent may remain in the SE3104 after the final layer, necessitating a final 3-minute pass in an oven. When the part is thermally bonded to the fabric, these traces of solvent are removed without an additional pass. Once the part is printed, the TPU substrate can be trimmed around the heater pattern to remove excess TPU. This increases the breathability of the final product and significantly reduces mechanical stress during use. This TPU substrate can be laser cut. In some embodiments, a Zing Orbit CNC kiss cutter is used to remove excess TPU. Once the part is cut, it is transferred to an adhesive tape designed for the heat transfer process. A sheet is placed on top and pressed onto the print. The sheet is then flipped over, and the PET support is peeled off, leaving the print adhesive side out, ready to be bonded to the fabric. The transferred part is placed on top of the fabric in a heated shirt press and bonded using temperature and pressure.

[0062] In some embodiments, the dielectric ink layer may be replaced with another TPU layer. That is, a resistive ink layer may be printed on a first TPU substrate. A conductive layer may be printed on top of the first TPU layer, and a second TPU layer may be deposited on top of the conductive layer.

[0063] In some embodiments, the conductive ink layer may be omitted. In these embodiments, the insulator layer is deposited directly on the resistive ink layer. In these embodiments, the resistive ink layer conducts sufficient current from a current source to generate heat.

[0064] With reference to Figures 1A, 1B, and 2, the PET support layer comprises a thickness of about 1 mil to 5 mils.

[0065] In some embodiments, the TPU layer comprises a thickness of about 1 mil to 5 mils. In some embodiments, the HMA layer comprises a thickness of about 1 mil to 5 mils.

[0066] In some embodiments, electricity is applied to the resistive layer to generate heat from the flexible or stretchable printed circuit.

[0067] In some embodiments, the substrate is preshrunk at a temperature of about 100°C to about 200°C.

[0068] In some embodiments, the substrate is preshrunk for a period of about 30 seconds to about 10 minutes.

[0069] In some embodiments, the method (eg, FIG. 2) further includes printing a conductive layer between the resistive layer and the insulating layer.

[0070] In some embodiments, transferring a portion of the substrate to the flexible or stretchable layer comprises disposing a hot melt adhesive (HMA) layer on the flexible or stretchable layer.

[0071] In some embodiments, the flexible or stretchable layer is a fabric.

[0072] 3 shows a fabricated flexible or stretchable printed circuit, according to some embodiments. In some embodiments, the circuit is printed (e.g., pressed) onto a substrate for between 1 second and about 100 seconds at a press temperature between about 25° C. and about 300° C., after which a portion of the substrate is removed and the remainder of the substrate is transferred (e.g., attached to an adhesive) to a flexible or stretchable layer (e.g., fabric).

[0073] In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature between about 25°C and about 300°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature between about 50°C and about 275°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature between about 75°C and about 250°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature between about 100°C and about 225°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature between about 125°C and about 200°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature between about 150°C and about 175°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 50°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 75°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 100°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 125°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 150°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 175°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 200°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 225°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 250°C. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at a press temperature of about 275°C. In some embodiments, the circuit is printed (eg, pressed) onto the substrate at a press temperature of about 300°C.

[0074] In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 1 second and about 100 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 5 seconds and about 90 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 5 seconds and about 80 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 10 seconds and about 70 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 10 seconds and about 60 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 15 seconds and about 50 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 15 seconds and about 40 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 15 seconds and about 30 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for a period of between 15 seconds and about 20 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 1 second. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 5 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 10 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 15 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 20 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 25 seconds. In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 30 seconds.In some embodiments, the circuit is printed (e.g., pressed) onto the substrate at the press temperature for about 10 seconds, 11 seconds, 12 seconds, 13 seconds, 14 seconds, 15 seconds, 16 seconds, 17 seconds, 18 seconds, 18 seconds, 20 seconds, 21 seconds, 22 seconds, 23 seconds, 24 seconds, or 25 seconds.

[0075] FIG. 4 shows a diagram of one embodiment of a resistive heating element having a flexible or stretchable printed circuit fabricated according to the methods described herein.

[0076] FIG. 5 shows the results of an experiment to measure the heat of an electrical connector assembly including a printed circuit, according to some embodiments.

[0077] The experiment shown in FIG. 5 indicates that the electrical connector assembly 10 provided sufficient power to the heating element 34 to maintain a temperature above 110°F for at least 90 minutes. Furthermore, observation of the infrared images indicates that the connector housings 11a-11g remained at ambient temperature, indicating that the electrical bond was sufficiently formed to avoid or substantially reduce heat buildup over time. In some embodiments, the electrical connector assembly 10 has a temperature below ambient temperature, or the temperature of the heating element 34, during the period when the external power source is in operation. In some embodiments, the electrical connector assembly 10 has a temperature below ambient temperature, or the temperature of the heating element 34, when the electrical connector assembly 10 is in use by a user. For example, the electrical connector assembly 10 can be at ambient temperature while charging or during use for 1 minute to 24 hours. In some embodiments, the usage time may depend on the external power source (e.g., a battery). In some embodiments, the heater 34 can be used for a longer period of time at a much lower power than when the heater 34 operates at a higher temperature. A detailed description of the assembly 10 is provided in International Application Publication No. WO2024 / 026149, the entire disclosure of which is incorporated herein by reference.

[0078] FIG. 6 illustrates one embodiment of an electrical structure 36 (or flexible or stretchable substrate) that provides a resistive heater. In some embodiments, the resistive heater can be, for example, fixed and / or stretch-resistant. As shown in FIG. 6 , in brief overview, the electrical structure 36 can include multiple layers. For example, the electrical structure 36 can include a base thermoplastic polyurethane (TPU) film 84, which can be disposed on an adhesive layer 79 that is spread over a fabric 76. A fixed-resistivity stretchable heater ink 88 (or heating element) is disposed on the TPU layer 84, and a stretchable printed silver conductor 90 is disposed at least partially on the heater ink 88. In some embodiments, the heating element 88 is covered using a stretchable insulating ink 93.

[0079] Still referring to FIG. 6 , in more detail, the base TPU film 84 can be printed onto the fabric 76 and customized to meet the performance requirements of smart textile materials used in various applications. For example, polyester-extruded TPU 84 provides resistance to chemicals and oils, while polyether-extruded TPU 84 provides flexibility and tear resistance. In some embodiments, polycaprolactone-extruded TPU 84 is hydrolysis-resistant, making it useful for applications with prolonged exposure to water. In some embodiments, the TPU film 84 may include metal to provide a metallic color to the fabric. In yet other embodiments, the TPU film 84 may include various materials to enhance antistatic properties.

[0080] In some embodiments, the resistive element 88 can be disposed on the TPU film 84. In some embodiments, the resistive element is printed on the TPU film 84. In one embodiment, the resistive element is printed using a material such as SE5025, a stretchable resistive ink manufactured by Applied Cavitation Inc. of Goleta, California. In some embodiments, resistive elements such as SE5025 are designed for integrated heating applications on elastomeric substrates. When cured, inks such as the SE5025 material have a set resistivity and provide enhanced flexibility and stretchability. In some embodiments, the SE5025 material provides enhanced adhesion to the TPU layer 84 and other elastomeric substrates.

[0081] The conductive component 90 can include silver traces 90a and / or a bus bar system 90b. In some embodiments, the conductive component 90 can be at least partially disposed on the resistive element 88. In some embodiments, the silver traces 90a and bus bar system 90b are printed on the resistive element 88. In some embodiments, a stretchable silver conductor can be disposed on the TPU film 84. For example, the silver conductor is printed on the TPU film 84. In one embodiment, the silver conductor elements, such as the traces 90a and bus bar system 90b elements, are printed using an ink such as SE1109 material. The conductive component material can be a stretchable silver ink, such as SE1109, manufactured by Applied Cavitation Inc. of Goleta, California. In some embodiments, the conductive component material is a silver-filled conductor for printed interconnects of devices on elastomeric substrates. After curing, the ink has enhanced conductivity and provides improved elongation and flexibility. In some embodiments, the SE1109 material has excellent adhesion to thermoplastic urethane (TPU) materials. In some embodiments, the conductive component material can be used in stretchable electronics and e-textile applications to power components and / or devices and transmit signals from embedded devices and / or sensors.

[0082] In some embodiments, a stretchable carbon conductive element 92 can be disposed on top of the silver conductive element 90. For example, the carbon element 92 is printed on the silver conductive element 92. In one embodiment, the carbon element 92 is printed using an ink such as SE1502 material, a stretchable carbon conductor manufactured by Applied Cavitation Inc. of Goleta, California. In some embodiments, the SE1502 material is a carbon-filled conductor for printed circuits and / or devices on elastomeric substrates. The SE1502 material can be dried at low temperatures to accommodate sensitive substrates and devices. After curing, the ink has sufficient conductivity to provide improved elongation and flexibility. In some embodiments, the SE1502 material limits silver migration when applied to silver traces, such as on conductive component 90.

[0083] In some embodiments, an insulator layer 93 is applied. In some embodiments, the insulator layer is printed at least partially on the carbon conductive elements 92. In some embodiments, the insulator layer 93 is disposed at least partially on the conductive silver traces 90a and bus bar system 90b. In some embodiments, the insulator layer 90 is printed on the silver traces 90a. In some embodiments, the insulator layer 93 is disposed at least partially on the resistive elements, such as SE5025. In one embodiment, the insulator layer 90 is printed using an ink such as SE3104 material. The SE3104 material is a stretchable, printable insulator manufactured by Applied Cavitation Inc. of Goleta, California. In some embodiments, the SE3104 material is a screen-printable, thermally cured ink and / or an ultraviolet (UV) light cured ink. The SE3104 material is stretchable once cured. In some embodiments, the SE3104 material can be used as an insulator and / or crossover dielectric. Upon curing, the ink exhibits improved durability and flexibility, as well as high insulation resistance.

[0084] The printed circuits described herein can be utilized in a variety of contexts. For example, the printed circuits can be used in outerwear, substrates, gloves, socks, and / or chairs for outdoor activities. Military applications of the smart textiles described herein include outerwear, gloves, seats, and / or other gear. Therapeutic applications include braces, wraps, pads, bedding, and / or fabric(s) for pain management. Automotive applications include heated seats, heated steering wheels, defrosting applications, and / or heated interior panels.

[0085] The following test samples of printed conductors transferred to a flexible or stretchable substrate 36 were used. The samples were printed on 200.0016 Stainless Steel Mesh. The sample dimensions were 76.2 mm long by 2.0 mm wide (e.g., 38.1 squares). The following tests were conducted: Case 1, which had a flexible or stretchable substrate 36 formed from SE1109 material on 4 mil TPU; Case 2, which had a flexible or stretchable substrate 36 formed from SE1109 material on 4 mil TPU with three layers and an insulator formed from SE3104 material; and Case 3, which had a flexible or stretchable substrate 36 formed from SE1109 material on 4 mil TPU with three layers and an insulator formed from SE3104 material bonded to a fabric with, for example, a 3 mil hot melt adhesive.

[0086] The following methods were used for testing: Method 1 for Cases 1-3 achieved 20% elongation (15.2 mm displacement), 20% elongation rate (15.2 mm / sec), and 5000 cycles. Method 2 for Case 1 achieved 50% elongation (38.1 mm displacement), 20% elongation rate (15.2 mm / sec), and 500 cycles. Method 3 for Case 1 achieved 100% elongation (76.2 mm displacement), 20% o1 The elongation rate (15.2 mm / sec) and 50 cycles were achieved.

[0087] 7 shows the resistance (measured in ohms) versus the number of extension cycles when flexible or stretchable substrate 36 is allowed to elongate by 20%, e.g., at 20% elongation (15.2 mm / sec) and has 5000 cycles. In some embodiments, the maximum resistance in the extended state for a printed conductor transferred to flexible or stretchable substrate 36 formed from SE1109 material on 4 mil TPU, with a measured performance of 5000 cycles, is shown by curve 55a (or graph line). The minimum resistance for a printed conductor transferred to flexible or stretchable substrate 36 in the relaxed state is shown by curve 53a (or graph line).

[0088] The maximum resistance in the stretched state of a flexible or stretchable substrate 36 formed from SE1109 material on 4 mil TPU having three layers and a printed conductor transferred to an insulator formed from SE3104 material is shown by curve 56a (or graph line). The minimum resistance of such a flexible or stretchable substrate 36 in the relaxed state is shown by curve 60a (or graph line).

[0089] The maximum resistance in the stretched state of a flexible or stretchable substrate 36 formed from SE1109 material on a 4 mil TPU having three layers and a printed conductor transferred to an insulator formed from SE3104 material, for example, bonded to a fabric 76 with a 3 mil hot melt adhesive, is shown by curve 58a (or graph line). The minimum resistance of such a flexible or stretchable substrate 36 in the relaxed state is shown by curve 62a (or graph line).

[0090] FIG. 8A shows, for example, a printed conductor transferred to a flexible or stretchable substrate 36, with a 20% o1(15.2 mm / sec) for 500 cycles, showing the resistance (measured in ohms) versus the number of extension cycles at which 50% elongation is possible. For example, curve 55b (or graph line) shows the maximum resistance in the extended state. For example, curve 53b (or graph line) shows the lowest resistance in the relaxed state of such a printed conductor transferred to a flexible or stretchable substrate 36.

[0091] FIG. 8B shows, for example, a printed conductor transferred to a flexible or stretchable substrate 36, with a 20% o5 (15.2 mm / sec) and 50 cycles to reach 100% elongation. For example, curve 55c (or graph line) shows the maximum resistance in the stretched state. For example, curve 53c (or graph line) shows the minimum resistance in the relaxed state of such a flexible or stretchable substrate 36.

[0092] 9A and 9BB show at least partial views of a printed conductor heater 34 transferred to a flexible or stretchable substrate 36 before and after a washing process, according to some embodiments. For testing, the following conditions can be established: a front-loading washing machine, a delicate cycle with a wash bag, medium to low water temperature, unscented liquid high-efficiency (HE) laundry detergent, the flexible or stretchable substrate 36 was washed with delicate cotton items, and a line-drying method was used. FIG. 9A shows at least a partial view of the heater 34 before it can be washed. FIG. 9B shows at least a partial view of the heater 34 after it has undergone 15 wash cycles.

[0093] FIG. 10A shows a graph 72 of the resistance (in ohms) of the heater 34 of the flexible or stretchable substrate 36 versus the number of cleaning cycles.

[0094] FIG. 10B shows a graph 74 of the power output (in watts) of the heater 34 of the flexible or stretchable substrate 36 versus the number of cleaning cycles.

[0095] The term "coupled" and variations thereof include joining two members directly or indirectly to one another. The terms "electrically coupled" or "in communication" and variations thereof include joining two members directly to one another or indirectly through a conductive material (e.g., a metal or copper trace). Such joining (for both "coupled" and "electrically coupled") may be static (e.g., permanent or fixed) or movable (e.g., removable or releasable). Such joining (for both "coupled" and "electrically coupled") may be achieved when two members are directly connected to one another or when two members are connected to one another using separate intervening members and any additional intermediate members connected to one another, or when two members are connected to one another using an intervening member integrally formed with one of the two members as a single unit. When "coupled" or variations thereof are modified by additional terms (e.g., directly coupled), the general definition of "coupled" given above is modified by the plain linguistic meaning of the additional terms (e.g., "directly coupled" means joining two members without a separate intervening member), resulting in a narrower definition than the general definition of "coupled" given above. Such coupling may be mechanical, electrical, or fluid.

[0096] The foregoing outlines features of some embodiments so that those skilled in the art may better understand aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use this disclosure as a basis for designing or modifying other processes and structures to carry out the same purposes and / or achieve the same advantages as the embodiments presented herein. Those skilled in the art should also recognize that such equivalent structures do not depart from the spirit and scope of the present disclosure, and that those skilled in the art may make various changes, substitutions, and alterations therein without departing from the spirit and scope of the present disclosure.

[0097] It should be noted that certain sections of this disclosure may refer to terms such as "first" and "second" in connection with transmit spatial streams, sounding frames, responses, and subsets of devices for the purpose of identifying or distinguishing one from another or other. These terms are not intended to simply associate entities (e.g., a first device and a second device) in time or sequence, although in some cases these entities may include such a relationship. These terms also do not limit the number of possible entities that may operate within a system or environment. It should be understood that the above-described system may provide multiple components of any or each of these components, and that these components may be provided either on a standalone machine or, in some embodiments, on multiple machines in a distributed system.

[0098] While the foregoing written description of the method and system will enable one skilled in the art to make and use the best embodiment thereof, one skilled in the art will understand and recognize that there are variations, combinations, and equivalents of the specific embodiments, methods, and examples herein. Thus, the present method and system should not be limited by the above-described embodiments, methods, and examples, but rather by all embodiments and methods within the scope and spirit of the present disclosure.

Claims

1. 1. A method for fabricating a flexible or stretchable printed circuit, comprising: providing a substrate including a polyethylene terephthalate (PET) support layer, a thermoplastic urethane (TPU) layer, and a hot melt adhesive (HMA) layer disposed between the PET layer and the TPU layer; shrink-proofing the substrate; printing a resistive layer onto the TPU layer of the substrate; printing an insulating layer onto the resistive layer; removing the PET support layer; transferring a portion of the substrate to a flexible or stretchable layer; The method comprising:

2. The method of claim 1 , wherein the PET support layer comprises a thickness of about 1 mil to 5 mils.

3. The method of claim 1 , wherein the TPU layer comprises a thickness of about 1 mil to 5 mils.

4. The method of claim 1 , wherein the HMA layer comprises a thickness of about 1 mil to 5 mils.

5. The method of claim 1 , further comprising applying electricity to the resistive layer to generate heat from the flexible or stretchable printed circuit.

6. The shrink-proofing of the substrate includes: shrink-proofing the substrate at a temperature of about 100°C to about 200°C; The method of claim 1 , comprising:

7. The shrink-proofing of the substrate includes: pre-shrunk said substrate for a period of about 30 seconds to about 10 minutes; The method of claim 1 , comprising:

8. printing a conductive layer between the resistive layer and the insulating layer; The method of claim 1 further comprising:

9. Transferring a portion of the substrate to a flexible or stretchable layer includes: disposing said hot melt adhesive (HMA) layer on said flexible or stretchable layer; The method of claim 1 , comprising:

10. The method of claim 1 , wherein the flexible or stretchable layer is a fabric.

11. 1. A stretchable printed circuit comprising: An elastic layer; a thermoplastic urethane (TPU) layer attached to the stretchable layer using a hot melt adhesive; a resistive layer printed on the TPU layer; an insulating layer printed on the resistive layer; 1. The stretchable printed circuit comprising:

12. The circuit of claim 11 , wherein the elastic layer comprises a thickness of about 1 mil to 5 mils.

13. The circuit of claim 11, wherein the TPU layer comprises a thickness of about 1 mil to 5 mils.

14. The circuit of claim 11, wherein the hot melt adhesive layer comprises a thickness of about 1 mil to 5 mils.

15. The circuit of claim 11 , wherein electricity is applied to the resistive layer to generate heat from the stretchable printed circuit.

16. 12. The circuit of claim 11, wherein the TPU layer is preshrunk at a temperature of about 100°C to about 200°C before being attached to the stretchable layer.

17. 17. The circuit of claim 16, wherein the TPU layer is preshrunk for a period of about 30 seconds to about 10 minutes.

18. The circuit of claim 11 further comprising a conductive layer between the resistive layer and the insulating layer.

19. 12. The circuit of claim 11, wherein the TPU layer is disposed on a polyethylene terephthalate (PET) support layer prior to attachment to the stretchable layer.

20. The circuit of claim 11 , wherein the stretchable layer is a fabric.

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