Methods and systems of a printed circuit on a substrate for stretchable electronics

Abstract

A method for fabricating a flexible or stretchable printed circuit may include: providing a substrate comprising a polyethylene terephthalate (PET) support layer, a thermoplastic urethane (TPU) layer; and a hotmelt adhesive (HMA) layer disposed between the PET layer and the TPU layer; pre-shrinking the substrate; and printing a resistive layer on the TPU layer of the substrate, and printing an insulative layer on the resistive layer, removing the PET support layer; and transferring a portion of the substrate to a flexible or stretchable layer.

Description

METHODS AND SYSTEMS OF A PRINTED CIRCUIT ON A SUBSTRATE FOR STRETCHABLE ELECTRONICSCROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] 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 and priority to U.S. Provisional Patent Application No. 63,393,690 filed July 29, 2022, each of which is incorporated by reference herein in its entire disclosure.FIELD OF DISCLOSED SUBJECT MATTER

[0002] The present disclosure relates generally to the field of printed circuits, substrates, and stretchable electronic components.BACKGROUND

[0003] There are various types of printed circuits for electronic systems which can provide effective performance in normal and extreme use conditions. However, it is difficult to use currently available electrical circuits for reliably electrically coupling electronics provided on stretchable or flexible substrate materials to a rigid connector.SUMMARY

[0004] Disclosed herein include methods and systems for fabricating a flexible or stretchable printed circuit. For example, and without limitation, a substrate for receiving the printed circuit can be provided and pre-shrunk to minimize degradation of the fiducial alignment (registration) as each layer is printed. In some embodiments, the method of fabricating a flexible or stretchable circuit (e.g., a heater) on a flexible or stretchable layer (e.g., fabric) includes pre-shrinking the substrate, printing the circuit onto the substrate, removing excesssubstrate, transferring the remainder of the substrate with the flexible or stretchable printed circuits (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 allow for the assembly of additively manufactured electronics, for example, flexible or stretchable circuits or resistive heating elements, that can be heat pressed on, printed on, or included within or on materials used in items that benefit from the addition of heat, such as fabric elements, neoprene, leather, rubber, silicone, synthetic materials, clothing, seat covers, furniture, work gear, athletic gear, therapeutic items, medical items, wetsuits, blankets, and others.

[0006] In one general aspect, disclosed herein is a method for fabricating a flexible or stretchable printed circuit including: providing a substrate comprising a polyethylene terephthalate (PET) support layer, a thermoplastic urethane (TPU) layer; and a hotmelt adhesive (HMA) layer disposed between the PET layer and the TPU layer; pre-shrinking the substrate; printing a resistive layer on the TPU layer of the substrate, printing an insulative 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 from about 1 mil to 5 mil.

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

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

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

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

[0012] In some embodiments, pre-shrinking the substrate comprises: pre-shrinking the substrate for a period of time 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 insulative layer.

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

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

[0016] In one general aspect, disclosed herein is a stretchable printed circuit comprising: a stretchable layer; a thermoplastic urethane (TPU) layer adhered to the stretchable layer using a hotmelt adhesive; a resistive layer printed on the TPU layer; and an insulative layer printed on the resistive layer.

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

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

[0019] In some embodiments, the hotmelt adhesive comprises a thickness from about 1 mil to 5 mil.

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

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

[0022] In some embodiments, the TPU layer was pre-shrunk for a period of time from about 30 seconds to about 10 minutes.

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

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

[0025] In some embodiments, the stretchable layer is fabric.BRIEF DESCRIPTION OF THE DRAWINGS

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

[0027] FIG. 1A illustrates a view of a substrate, according to some embodiments.

[0028] FIG. IB illustrates a view of a flexible or stretchable printed circuit on a portion of the substrate as shown in FIG. 1A and a flexible or stretchable layer, according to some embodiments.

[0029] FIG. 2 illustrates a method for fabricating a flexible or stretchable printed circuit, according to some embodiments.

[0030] FIG. 3 illustrates views of a flexible or stretchable printed circuit, according to some embodiments.

[0031] FIG. 4 illustrates a diagram of a resistive heating element having flexible or stretchable printed circuits manufactured using the methods as described herein, according to some embodiments.

[0032] FIG. 5 illustrates results of an experiment measuring heat of an electrical connector assembly including the flexible or stretchable printed circuits as described herein, according to some embodiments.

[0033] FIG. 6 illustrates a flexible or stretchable substrate having a number of layers of flexible or stretchable printed circuits, according to some embodiments.

[0034] FIG. 7 illustrates graph lines for resistance of an electrode on a flexible or stretchable substrate with respect to a plurality of stretch cycles, according to some embodiments.

[0035] FIGS. 8A-8B illustrate graph lines for resistance of an electrode on a flexible or stretchable substrate when the flexible or stretchable substrate is in a stretched state, and also a relaxed state, according to some embodiments.

[0036] FIGS. 9A-9B illustrate the heat output of a flexible or stretchable printed circuit (e.g., resistive heater) on a flexible or stretchable substrate before and after a plurality of wash cycles, according to some embodiments.

[0037] FIGS. 10A-10B illustrate graph lines for resistance of and power output of an electrode on a flexible or stretchable substrate depending on a number of wash cycles, according to some embodiments.

[0038] The details of various embodiments of the methods and systems are set forth in the accompanying drawings and the description below.DETAILED DESCRIPTION

[0039] The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over, or on a second feature in the description that follows 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. In addition, the present disclosure may repeat reference numerals and / or letters in the variousexamples. 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 discussed.

[0040] In general, disclosed herein include methods and systems for fabricating a flexible or stretchable printed circuit. For example, and without limitation, a substrate for receiving the printed circuit can be provided and pre-shrunk to minimize degradation of the fiducial alignment (registration) as each layer is printed. In some embodiments, the method of fabricating a flexible or stretchable circuit (e.g., a heater) on a flexible or stretchable layer (e.g., fabric) includes pre-shrinking the substrate, printing the circuit onto the substrate, removing excess substrate, transferring the remainder of the substrate with the flexible or stretchable printed circuits (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).

[0041] The techniques and materials described herein allow for the assembly of additively manufactured electronics, for example, flexible or stretchable circuits or resistive heating elements, that can be heat pressed on, printed on, or included within or on materials used in items that benefit from the addition of heat, such as fabric elements, neoprene, leather, rubber, silicone, synthetic materials, clothing, seat covers, furniture, work gear, athletic gear, therapeutic items, medical items, wetsuits, blankets, and others.

[0042] As used in this description, the term “printing’' is intended to include all forms of printing and coating, including, but without limitation: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, 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; ink jet printing processes; direct write printing processes, jettable deposition processes and other similar techniques.

[0043] FIG. 1A illustrates a view of a substrate, according to some embodiments.

[0044] As shown in FIG. 1A, in general, the substrate includes a PET support layer (e.g., having a thickness of 4 mil), a hotmelt adhesive layer (e.g., with a thickness of 2 mil), and / or a thermoplastic urethane (TPU) layer (e.g., with a thickness of 4 mil). In some embodiments, the hotmelt adhesive (HMA) layer is disposed between the PET layer and the TPU layer.

[0045] In some embodiments, the PET support layer, the hotmelt adhesive layer, and / or the TPU layer includes a thickness from about 0.1 mil to about 10 mil. In some embodiments, the PET support layer, the hotmelt adhesive layer, and / or the TPU layer includes a thickness from about 0.5 mil to about 5 mil. In some embodiments, the PET support layer, the hotmelt adhesive layer, and / or the TPU layer includes a thickness from about 1 mil to about 4 mil. In some embodiments, the PET support layer, the hotmelt adhesive layer, and / or the TPU layer includes a thickness of about 1 mil, about 2 mil, about 3 mil, or about 4 mil.

[0046] In general, the PET Support layer (e.g., having a thickness of 4 mil) can provide enhanced thermal stability (e.g., when compared to the commonly-used Biaxially-Oriented Polypropylene (BOPP)). The support PET can also provide a coating to maximize the peelability of the print once dried, cooled, and cut (if applicable), resulting in easy release that allows for two-step transfer processes onto fabric or other flexible or stretchable layer.

[0047] In general, the Hotmelt Adhesive layer (e.g., having a thickness of 2 mil) can be tolerant of multiple wash cycles and bonds well to a variety of materials, such as polyester, poly-cotton, Lycra, ABS, polycarbonate, polyvinyl chloride (PVC), polyurethane, wood, leather, fiberglass, aluminum, copper, and steel.

[0048] In general, the TPU layer (e.g., having a thickness of 2 mil) can be the “print side” of the substrate (e.g., “ES1001”) and may be considered a high-melt TPU. In some embodiments, the TPU layer provides good elasticity for the substrate system.

[0049] FIG. IB illustrates a view of a substrate having a flexible or stretchable printed circuit on a flexible or stretchable layer, according to some embodiments.

[0050] FIG. 2 illustrates a method for fabricating a flexible or stretchable printed circuit, according to some embodiments.

[0051] At 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 hotmelt adhesive (HMA) layer disposed between the PET layer and the TPU layer. At step 220, the substrate is pre-shrunk. At step 230, a resistive layer is printed on the TPU layer of the substrate. At step 240, an insulative layer is printed on the resistive layer. At step 250, the PET support layer is removed from the substrate. At step 260, a portion of the substrate (e.g., the substrate without the PET support layer) is transferred to a flexible or stretchable layer.

[0052] For example, and without limitation, the method described herein can include printing processes for fabricating (e.g., assembling) a 5V fixed resistance heaters on fabric or other flexible or stretchable substrates.

[0053] This substrate may be pre-shrunk at 140°C (284°F) for 3 minutes to, as mentioned above, help ensure proper registration as layers are printed. Tighter tolerances may be accommodated by longer shrink time. For example, if registration tolerances are <1%, the substrate may be shrunk for 5 minutes, rather than 3 minutes.

[0054] In some embodiments, when the substrate comes out of the oven, it is clear, because the hot melt adhesive has melted and becomes optically clear. The high melt, high elastic TPU that is printed on also becomes active out of the oven. Waiting for the hot melt and TPU to re-crystallize can help prevent the TPU layer from clinging to the screen emulsion. In some embodiments, the waiting time is about 30 minutes. In some embodiments, allowing recrystallization may cause a haze to return to the substrate.

[0055] After pre-shrinking the substrate, a desired circuit topology may be printed on the substrate. Printing on TPU may be different from printing on PET / PI type substrates. TPU is absorbent and soft, while PET / PI won’t absorb solvent, and are hard. The soft and absorbent nature of TPU can cause pin holing due to the mesh pressing and deforming the TPU. Accordingly, pressure needs to be kept low.

[0056] In some embodiments, a printer such as an automatic screen printer (e.g., HMI Model 9156 manufactured by Hary Manufacturing Inc., Lebanon, NJ) is used for printing on the TPU layer. The squeegee takes a square stock, held in a diamond profile (e.g., provided in Tables 1-3 below), which means that printing occurs using a 45° angle of attack. Rectangular blade screen printing presses may need to use different angles of attack to determine the best parameters, such as 30°. Furthermore, using a chamfered or rounded edge on squeegees may help mitigate the effects of pin holing that printing on TPU can cause, and give a better laydown of ink.Printing A Resistive Laver Onto A TPU Laver

[0057] When printing a resistive layer onto the TPU layer, a stretchable heater ink such as the SE5025 Fixed Resistance Stretchable Heater Ink (e.g., manufactured by ACI Materals, Inc. of Goleta, California) may be used. The SE5025 ink can produce uniform heat and is suitable for printing both small and large heaters.

[0058] In some embodiments, exemplary conditions for printing this ink are listed in Table 1 below.Table 1. Printing Parameters for A Resistive Layer Onto A TPU Layer

[0059] In some embodiments, SE5025 is most consistent when using a double-stroke print. This is done with two consecutive print strokes. Some printers are configured to do a double print, others will have to have 2 print cycles, one right after the other.

[0060] In some embodiments, the method includes hand stirring the ink thoroughly before printing. This step can shear thins easily, reduce the number of setup prints and / or reach a steady state viscosity.

[0061] In some embodiments, the method includes Checking prints against a backlight to look out for pinholes in the wet film and adjust squeegee pressure or angle of attack until free of pin holes.Printing A Conductive Laver Onto The TPU Layer

[0062] After the resistive ink is printed and dried, a conductive ink may then be applied, such as the SEI 109 Stretchable Printed Silver Conductor Ink (e.g., manufactured by ACI Materials, Inc. of Goleta, California). In some embodiments, the layer of conductive ink selves as a “buss bar,” that is, it conducts current from a current source and through the resistive ink, which results in heat. The SEI 109 ink provide superior conductivity and is capable of stretching to 150% of its original length without breakage.

[0063] In some embodiments, exemplary conditions (e.g., printing parameters) for printing this ink are hsted in Table 2 below.Table 2. Printing Parameters for A Conductive Layer Onto A TPU Layer

[0064] In some embodiments, SEI 109 is most consistent when using a double-stroke print. This is done with two consecutive print strokes. Some printers are configured to do a double print, others will have to have 2 print cycles, one right after the other.

[0065] In some embodiments, the method includes hand stirring the ink thoroughly before printing. This step may shear thins less easily than other inks, and may take more time mixing. This step can reduce the number of setup prints and to reach a steady state viscosity.

[0066] In some embodiments, the method includes checking prints against a backlight to look out for pinholes in the wet film and adjust squeegee pressure or angle of attack until free of pin holes.Printing A Insulative Laver Onto The TPU Laver

[0067] After the conductive ink is printed and dried, one or more layers of insulator ink may be printed, such as the SE3104 Stretchable Insulator Ink, manufactured by ACI Materials, Inc. of Goleta, California. The SE3104 ink protects the underlying layers from abrasion and environmental degradation and is tolerant of multiple wash cycles. Exemplary conditions for printing this ink are listed in Table 3 below.Table 3. Printing Parameters for A Insulative Layer Onto A TPU Layer

[0068] In some embodiments, SE3104 is most consistent when using a single-stroke print.

[0069] In some embodiments, the method includes Hand stirring the ink thoroughly before printing. This step may shear thins easily. This step can help reduce the number of setup prints and to reach a steady state viscosity.

[0070] In some embodiments, the method includes checking prints against a backlight to look out for pinholes in the wet film and adjust squeegee pressure or angle of attack until free of pin holes.

[0071] In some embodiments, there may be very small amounts of residual solvent in the SE3104 after final layer and will need a final 3 min pass in the oven. If part is going to be heat bonded to fabric, it will remove these trace amounts of solvents without an additional pass. Once the part is done printing, the TPU substrate can be trimmed around the heater pattern to remove excess TPU. This increases the breathability of the end product and greatly reduced mechanical stresses while in use. This TPU substrate may 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 made for heat transfer processing. The sheet is laid over top and pressed onto print. It is then flipped over, and the PET support is peeled away, leaving the print adhesive side out, ready to be bonded to fabric. The transferred part is placed on fabric in the heated shirt press and bonded using temperature and pressure.

[0072] In some embodiments, the insulator ink layer may be replaced by another layer of TPU. That is, a resistive ink layer is printed on a first TPU substrate. A conductive layer can be printed over the first TPU layer and a second TPU layer can be deposited over the conductive layer.

[0073] In some embodiments, the layer of conductive ink may be omitted. In these embodiments, an insulator layer is deposited directly over the resistive ink layer. In these embodiments, the resistive ink layer conducts sufficient current from a current source to generate heat.

[0074] Further to FIGS. 1A, IB, and 2, in some embodiments, the PET support layer comprises a thickness from about 1 mil to 5 mil.

[0075] In some embodiments, the TPU layer comprises a thickness from about 1 mil to 5 mil. In some embodiments, the HMA layer comprises a thickness from about 1 mil to 5 mil.

[0076] In some embodiments, electricity is applied to the resistive layer for generating heat from the flexible or stretchable printed circuit.

[0077] In some embodiments, the substrate is pre-shrunk at a temperature from about 100 °C to about 200 °C.

[0078] In some embodiments, the substrate is pre-shrunk for a period of time from about 30 seconds to about 10 minutes.

[0079] In some embodiments, the method (e.g., FIG. 2) further includes printing a conductive layer between the resistive layer and the insulative layer.

[0080] In some embodiments, transferring a portion of the substrate to a flexible or stretchable layer comprises: disposing the hotmelt adhesive (HMA) layer onto the flexible or stretchable layer.

[0081] In some embodiments, the flexible or stretchable layer is fabric.

[0082] FIG. 3 illustrates a fabricated flexible or stretchable printed circuit, according to some embodiments. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of between about 25 °C to about 300 °C for a period of time between 1 second and about 100 seconds, followed by removing a portion of the substrate and transferring the rest of the substrate (e.g., attaching the rest of the substrate to an adhesive) to a flexible or stretchable layer (e.g. fabric).

[0083] In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of between about 25 °C to about 300 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of between about 50 °C to about 275 C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of between about 75 °C to about 250 C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of between about 100 °C to about 225 C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of between about 125 °C to about 200 C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of between about 150 °C to about 175°C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 50 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 75 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 100 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 125 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 150 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 175 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 200 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 225 °C. In someembodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 250 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 275 °C. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature of about 300 °C.

[0084] In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 1 second and about 100 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 5 seconds and about 90 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 5 seconds and about 80 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 10 seconds and about 70 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 10 seconds and about 60 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 15 seconds and about 50 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 15 seconds and about 40 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 15 seconds and about 30 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for a period of time between 15 seconds and about 20 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 1 second. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 5 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 10 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 15 seconds.In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 20 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 25 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 30 seconds. In some embodiments, the circuit is printed (e.g., pressed) on a substrate at a press temperature for about 10, 11, 12, 13, 14, 15, 16, 17, 18, 18, 20, 21, 22, 23, 24, or 25 seconds.

[0085] FIG. 4 illustrates a diagram of one embodiment of a resistive heating element having flexible or stretchable printed circuits manufactured according to the methods described herein.

[0086] FIG. 5 illustrates results of an experiment measuring heat of the electrical connector assembly including the printed circuits, according to some embodiments.

[0087] The experiment illustrated in FIG. 5, shows that an electrical connector assembly 10 supplied sufficient power to the heating element 34 to maintain a temperature in excess of 1 10 degrees Fahrenheit for at least 90 minutes. Further, observation of the infrared images shows that a connector housing 11 a- 11g remained at an ambient temperature, showing the electrical coupling was sufficiently formed to avoid or substantially reduce heat buildup over time. In some embodiments, the electrical connector assembly 10 has an ambient temperature or a temperature below a temperature of the heating element 34 during a period of time of the external power source being in an operative state. In some embodiments, the electrical connector assembly 10 has an ambient temperature or a temperature below a temperature of the heating element 34 when the electrical connector assembly 10 is used by a user. For example, the electrical connector assembly 10 can have an ambient temperature, during charging or use for 1 minute to 24 hours. In some embodiments, use time can depend on the external power source (e.g., a battery). In some embodiments, the heater 34 can be used at very low power for longer periods of time in comparison to when the heater 34 runs at hottertemperatures. Detailed descriptions of the assembly 10 can be found in InternationalApplication Publication No. WO 2024 / 026149, the entire disclosure of which is incorporated by reference herein.

[0088] FIG. 6 illustrates an embodiment of an electrical structure 36 (or the flexible or stretchable substrate) providing a resistive heater. In some embodiments, the resistive heater that can be, for example, fixed and / or stretch-tolerant. As shown in FIG. 6, and in brief overview, the electrical structure 36 can include a plurality of layers. For example, the electrical structure 36 can include a base thermoplastic polyurethane (TPU) film 84 that can be disposed on, for example, an adhesive layer 79 that is spread over a fabric 76. A fixed resistance 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 over the heater ink 88. In some embodiments, the heating element 88 is covered using a stretchable insulator ink 93.

[0089] Still referring to the FIG. 6, and in greater detail, the base TPU film 84 may be printed onto the fabric 76 and customized to satisfy the performance requirements for the smart textile material used for various applications. For example, TPUs 84 extruded with polyester provide resistance to chemicals and oils while materials extruded with polyether TPUs 84 offer flexibility and tear resistance. In some embodiments, TPUs 84 extruded with polycaprolactone are hydrolysis resistant are useful for applications with prolonged water exposure. In some embodiments, the TPU film 84 may include metals to provide a metallic color to the fabric. In still other embodiments, the TPU film 84 may include various materials to enhance antistatic properties.

[0090] In some embodiments, the resistive elements 88 can be disposed on the TPU film 84. In some embodiments, the resistive elements are printed over the TPU film 84. In one embodiment, the resistive elements are printed using materials such as SE5025, that is a stretchable, resistive ink manufactured by Applied Cavitation Inc. of Goleta, California. Insome embodiments, the resistive elements such as SE5025 is designed for heating applications integrated onto elastomeric substrates. When cured, the ink such as the SE5025 material has a set resistance value and offers enhanced flexibility and stretchability. In some embodiments, the SE5025 material provides an enhanced adhesion to the TPU layer 84 and other elastomeric substrates.

[0091] The conductive component 90 can include silver traces 90a and / or a busbar system 90b. In some embodiments, the conductive component 90 can be disposed at least partially over the resistive elements 88. In some embodiments, the silver traces 90a and the busbar system 90b are printed on the resistive elements 88. In some embodiments, a stretchable silver conductor can be disposed on the TPU film 84. For example, the silver conductor is printed over the TPU film 84. In one embodiment, the silver conductor elements, such as the traces 90a and the busbar system 90b elements, are printed using an ink such as the SEI 109 material. The conductive component material can be a stretchable silver ink such as SEI 109 manufactured by Applied Cavitation Inc. of Goleta, California. In some embodiments, the conductive component material is a silver- filled conductor for printed interconnects for devices on elastomeric substrates. After drying, the ink has an enhanced conductivity and offers enhanced elongation and flexibility. In some embodiments, the SEI 109 material has superior 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.

[0092] In some embodiments, a stretchable carbon conductive element 92 can be disposed over the silver conductive elements 90. For example, the carbon elements 92 are printed on the silver conductive elements 92. In one embodiment, the carbon elements 92 are printed using an ink such as the SE1502 material, that is a stretchable, carbon conductormanufactured by Applied Cavitation Inc. of Goleta, California. In some embodiments, the SEI 502 material is a carbon filled conductor for printed circuitry and / or devices on elastomeric substrates. The SEI 502 material can be dried at low temperatures to accommodate sensitive substrates and devices. After curing, the ink has sufficient conductivity and offers enhanced elongation and flexibility. In some embodiments, the SE1502 material limits silver migration when applied over silver traces, e.g., over a conductive component 90.

[0093] 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, an insulator layer 93 is disposed at least partially over the conductive silver traces 90a and the busbar system 90b. In some embodiments, the insulator layer 90 is printed on the silver traces 90a. In some embodiments, an insulator layer 93 is disposed at least partially over the resistive elements such as SE5025. In one embodiment, the insulator layer 90 is printed using an ink such as a 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 ink cured with an ultraviolet (UV) light; the SE3104 material is stretchable when cured. In some embodiments, the SE3104 material can be used as an insulator and / or crossover dielectric. When cured, the ink displays enhanced durability and flexibility, as well as high insulation resistance.

[0094] The printed circuit described herein can be utilized in various settings. For example, they can be used in outerwear, base layers, 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 / orfabric(s) for pain management. Automotive applications include seat warming, steering wheel warming, defrosting applications, and / or warming of interior panels.

[0095] The following test samples of the printed conductor transferred onto flexible or stretchable substrate 36 were used. The samples were printed with a 200.0016 Stainless Steel Mesh. Sample dimensions were 76.2mm in length by 2.0mm in width (e.g., 38.1 Squares). The following tests were performed: case 1 having the flexible or stretchable substrate 36 formed of the SEI 109 material on 4-mil TPU; case 2 having the flexible or stretchable substrate 36 formed of the SEI 109 material on 4-mil TPU with three layers and an insulator formed of the SE3104 material; case 3 having the flexible or stretchable substrate 36 formed of the SEI 109 material on 4-mil TPU with three layers and the insulator formed of SE3104 material, bonded to fabric with, e.g., 3 mil hot-melt adhesive.

[0096] The following methods were used for testing. Method 1 for cases 1 through 3 achieved 20% Elongation (15.2mm displacement), 20% 01 elongation rate (15.2mm / s), 5000 cycles. Method 2 for case 1 achieved 50% Elongation (38.1mm displacement), 20% elongation rate (15.2mm / s), 500 cycles. Method 3 for case 1 achieved 100% Elongation (76.2mm displacement), 20%01elongation rate (15.2mm / s), 50 cycles.

[0097] FIG. 7 illustrates a resistance (measured in Ohms) with respect to the number of stretch cycles when, for example, the flexible or stretchable substrate 36 can be 20% stretched, e.g., 20% 01 elongation rate (15.2mm / s), having 5000 cycles. In some embodiments, having the measured performance for 5000 cycles, a maximum resistance in the stretched condition for a printed conductor transferred onto flexible or stretchable substrate 36 formed of the SEI 109 material on 4-mil TPU is illustrated by a curve 55a (or graph line). A lowest resistance for a printed conductor transferred onto a flexible or stretchable substrate 36 in a relaxed state is illustrated by a curve 53a (or graph line).

[0098] A maximum resistance in the stretched condition for a printed conductor transferred onto flexible or stretchable substrate 36 formed of the SEI 109 material on 4 mil TPU having three layers and the insulator formed of the SE3104 material is illustrated by a curve 56a (or graph line). A lowest resistance for such flexible or stretchable substrate 36 at the relaxed state is illustrated by a curve 60a (or graph line).

[0099] A maximum resistance in the stretched condition for a printed conductor transferred onto flexible or stretchable substrate 36 having the flexible or stretchable substrate 36 formed of the SEI 109 material on 4-mil TPU having three layers and the insulator formed of the SE3104 material, bonded to the fabric 76 with, e.g., 3 mil hot melt adhesive is illustrated by a curve 58a (or graph line). A lowest resistance for such flexible or stretchable substrate 36 in the relaxed state is illustrated by a curve 62a (or graph line).

[0100] FIG. 8A illustrates a resistance (measured in Ohms) with respect to the number of stretch cycles when, for example, the printed conductor transferred onto flexible or stretchable substrate 36 can be 50% stretched, having 20%01elongation rate (15.2mm / s), 500 cycles. For example, a curve 55b (or graph line) shows a maximum resistance in the stretched state. For example, a curve 53b (or graph line) shows a lowest resistance in the relaxed state for such a printed conductor transferred onto flexible or stretchable substrate 36.

[0101] FIG. 8B illustrates a resistance (measured in Ohms) with respect to the number of stretch cycles when, for example, the printed conductor transferred onto flexible or stretchable substrate 36 can be 100% stretched, having 20%05elongation rate (15.2mm / s), having 50 cycles. For example, a curve 55c (or graph line) shows a maximum resistance in the stretched state. For example, a curve 53c (or graph line) shows a lowest resistance in the relaxed state for such flexible or stretchable substrate 36.

[0102] Fig. 9A and Fig. 9B illustrate at least a partial view of the heater 34 of the printed conductor transferred onto flexible or stretchable substrate 36 before and after a washmethod, according to some embodiments. The following conditions can be set for testing: a front load washer, a delicate cycle having a laundry bag, a medium to low water temperature, an unscented liquid high efficiency (HE) laundry detergent, the flexible or stretchable substrate 36 can be washed with delicate and cotton items, hang dry technique was used. Fig. 9A illustrates at least a partial view of the heater 34 before the heater 34 can be washed. Fig. 9B illustrates at least a partial view of the heater 34 after the heater 34 had undergone fifteen wash cycles.

[0103] FIG. 10A illustrates a graph line 72 of resistance (in Ohms) of the heater 34 of the flexible or stretchable substrate 36 with respect to the number of wash cycles.

[0104] FIG. 10B illustrates a graph line 74 of power output (in Watts) of the heater 34 of the flexible or stretchable substrate 36 with respect to the number of wash cycles.

[0105] The term “coupled” and variations thereof includes the joining of two members directly or indirectly to one another. The term “electrically coupled” or “in communication” and variations thereof includes the joining of two members directly or indirectly to one another through conductive materials (e.g., metal or copper traces). Such joining (for both terms “coupled” and “electrically coupled”) may be stationary (e.g., permanent or fixed) or moveable (e.g., removable or releasable). Such joining (for both terms “coupled” and “electrically coupled”) may be achieved with the two members coupled directly with or to each other, with the two members coupled with each other using a separate intervening member and any additional intermediate members coupled with one another, or with the two members coupled with each other using an intervening member that is integrally formed as a single unitary body with one of the two members. If “coupled” or variations thereof are modified by an additional term (e.g., directly coupled), the generic definition of “coupled” provided above is modified by the plain language meaning of the additional term (e.g., “directly coupled” means the joining of two members without any separate interveningmember), resulting in a narrower definition than the generic definition of “coupled” provided above. Such coupling may be mechanical, electrical, or fluidic.

[0106] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

[0107] It should be noted that certain passages of this disclosure can reference terms such as “first” and “second” in connection with subsets of transmit spatial streams, sounding frames, response, and devices, for purposes of identifying or differentiating one from another or from others. These terms are not intended to merely relate entities (e.g., a first device and a second device) temporally or according to a sequence, although in some cases, these entities can include such a relationship. Nor do these terms limit the number of possible entities that can operate within a system or environment. It should be understood that the systems described above can provide multiple ones of any or each of those components and these components can be provided on either a standalone machine or, in some embodiments, on multiple machines in a distributed system.

[0108] While the foregoing written description of the methods and systems enables one of ordinary skill to make and use embodiments thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The present methods and systems shouldtherefore not be limited by the above described embodiments, methods, and examples, but by all embodiments and methods within the scope and spirit of the disclosure.

Claims

CLAIMS1. 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 hotmelt adhesive (HMA) layer disposed between the PET layer and the TPU layer; pre-shrinking the substrate; printing a resistive layer on the TPU layer of the substrate, printing an insulative layer on the resistive layer, removing the PET support layer; and transferring a portion of the substrate to a flexible or stretchable layer.

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

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

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

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

6. The method of claim 1, wherein pre- shrinking the substrate comprises: pre-shrinking the substrate at a temperature from about 100 °C to about 200 °C.

7. The method of claim 1, wherein pre-shrinking the substrate comprises: pre-shrinking the substrate for a period of time from about 30 seconds to about 10 minutes.

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

9. The method of claim 1, wherein transferring a portion of the substrate to a flexible or stretchable layer comprises: disposing the hotmelt adhesive (HMA) layer onto the flexible or stretchable layer.

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

11. A stretchable printed circuit comprising: a stretchable layer; a thermoplastic urethane (TPU) layer adhered to the stretchable layer using a hotmelt adhesive; a resistive layer printed on the TPU layer; and an insulative layer printed on the resistive layer.

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

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

14. The circuit of claim 11, wherein the hotmelt adhesive comprises a thickness from about 1 mil to 5 mil.

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

16. The circuit of claim 11, wherein prior to adhering to the stretchable layer, the TPU layer is pre-shrunk at a temperature from about 100 °C to about 200 °C.

17. The circuit of claim 16, wherein TPU layer was pre-shrunk for a period of time from about 30 seconds to about 10 minutes.

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

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

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

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