Temperature stabilization of convertible functional inks by blocking the conductive path.

Abstract

The ink stabilizing composition comprises a polymer network comprising an acrylate polymer and a plurality of high aspect ratio particles, each having an aspect ratio of from about 2:1 to about 30:1 and an average particle size of from about 0.5 to about 1.2 micrometers.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 254,230, filed Oct. 11, 2021, and U.S. Non - Provisional Patent Application No. 17 / 938,688, filed Oct. 7, 2022, which are hereby incorporated by reference in their entirety.

Background Art

[0002] The present disclosure relates to convertible inks, and more particularly, to temperature stabilization of convertible inks.

[0003] Convertible inks can be used to create electronic structures. Examples of convertible inks include composite materials that have an insulating or dielectric phase after curing but can be selectively converted to a conductive or resistive phase by methods such as heat treatment or laser sintering.

Summary of the Invention

[0004] According to one or more embodiments, an ink stabilization composition includes a polymer network including an acrylate polymer and a plurality of high - aspect - ratio particles each having an aspect ratio of about 2:1 to about 30:1 and an average particle size of about 0.5 to about 1.2 micrometers.

[0005] According to other embodiments, a stabilized ink includes a plurality of conductive particles, a plurality of insulating particles, a plurality of high - aspect - ratio stabilizing particles, and a polymer within voids between the plurality of conductive particles and the plurality of insulating particles. The stabilized ink is in an insulating phase.

[0006] Furthermore, according to some embodiments, a method for stabilizing a convertible ink includes arranging a stabilizing material on the convertible ink. The stabilizing material comprises a polymer network and a plurality of high aspect ratio particles, each having an aspect ratio of about 2:1 to about 30:1 and an average particle size of about 0.5 to about 1.2 micrometers. The convertible ink comprises a plurality of conductive particles and a plurality of insulating particles.

[0007] Further features and advantages are realized through the technology of this disclosure. Other embodiments and aspects of this disclosure are described in detail herein and are considered to be part of the claimed disclosure. Refer to the description and drawings for a better understanding of this disclosure, including its advantages and features.

[0008] To better understand this disclosure, the following brief description is to be seen in relation to the attached drawings and detailed description. Here, similar reference figures represent similar parts. [Brief explanation of the drawing]

[0009] [Figure 1A] This is a laser sintering method for converting the dielectric portion of convertible ink into a conductive portion; [Figure 1B] This is a magnified view of the dielectric portion of the convertible ink; [Figure 1C] This is a magnified view of the conductive path of the convertible ink after laser sintering; [Figure 2A] This shows the dielectric portion of the convertible ink; [Figure 2B] This shows the convertible ink after the stabilizing material layer has been applied; [Figure 2C] This demonstrates the blocking of the conductive path after coating with a stabilizing material layer and laser sintering; [Figure 3] This graph shows the change in resistance of convertible ink with and without a stabilizing layer; [Figure 4A] This is a top view of the patterning stabilization layer on the convertible ink layer; and [Figure 4B] This is a side view of Figure 4A. [Modes for carrying out the invention]

[0010] Convertible inks are composite materials that, after curing, have an insulating or dielectric phase, but can be selectively converted to a conductive or resistive phase by methods such as heat treatment or laser sintering. Convertible inks can include, for example, composite blends of conductive and insulating particles. Non-limiting examples of convertible inks include conductive metal nanoparticles (e.g., silver) and insulating nanoparticles (e.g., barium strontium titanate), which are blended in such a ratio that the ink contains an insulating phase after curing, but provides a conductive (and resistive) phase after high-temperature heat treatment (e.g., temperatures above 125 degrees Celsius), such as selective laser sintering with an ultraviolet laser. Selective laser sintering can be performed using most lasers, but lasers with wavelengths of 400-450 nanometers (nm) can provide optimal results. Since the surface plasmon resonance of silver (Ag) nanoparticles is approximately 400-450 nm, it should be noted that when using silver in a convertible ink, exciting the surface plasmon resonance of Ag nanoparticles will efficiently melt the silver nanoparticles due to the local heating caused by the surface plasmon resonance excitation. Furthermore, other lasers, such as the 830nm laser in particular, are also suitable for sintering silver nanoparticles to form conductive patterns. The laser wavelength used is tuned to match the conductive nanoparticles. For example, when gold nanoparticles are used, a 532nm laser can be used to excite the surface plasmon resonance of the gold. However, a laser of any wavelength may be used and tuned to the specific conductive nanoparticles.

[0011] For example, Figure 1A shows a laser sintering method for converting the dielectric portion of a convertible ink to a conductive portion. After curing, the convertible ink becomes an insulating phase. Laser 110 converts the insulating portion 102 of the convertible ink to a conductive portion 106. Figure 1B is a magnified view of the dielectric portion 102 of the convertible ink, which contains a blend of conductive particles 122 and insulating particles 120. Figure 1C is a magnified view of the conductive portion 106, showing how the conductive paths of the convertible ink are formed after laser sintering or thermal sintering that fuses the conductive particles 122.

[0012] Convertible inks can be used as printable inks that are easily patterned and printed as films that can produce conductive traces by applying localized heat. However, it is desirable that the insulating material remains insulating after the traces have been patterned. However, depending on the application, subsequent thermal processes (e.g., soldering or other packaging processes) may unintentionally convert the desired pattern to a conductive state, rendering the patterning process ineffective.

[0013] Accordingly, this specification describes a stabilizing material, as well as methods for producing and using the same, which introduces high aspect ratio particles and three-dimensional polymer networks into convertible inks to prevent the formation of conductive paths within the film even after thermal exposure such as soldering or microelectronics packaging processes. The stabilizing material can be used as a patterned mask to selectively define conductive traces within the dielectric portion of the convertible ink. As used herein, the term "convertible ink" and other similar terms mean a composite of conductive and non-conductive particles that are converted from an insulating phase to a conductive / resistive phase by thermal sintering or laser sintering.

[0014] Figure 2A shows the dielectric portion of the convertible ink after curing, which includes a blend of conductive particles 224 and insulating particles 222 with an air gap 202 in between. Figure 2B shows the convertible ink after a stabilizing material layer has been applied to it. The stabilizing layer includes polymer 204 and high aspect ratio particles 260 that fill the air gap 202 in the convertible ink. Figure 2C shows the convertible ink after thermal exposure such as laser sintering or thermal sintering, and the blocking of the conductive pathway 230 by the high aspect ratio particles 260. Both polymer 204 and high aspect ratio particles 260 are necessary to prevent the formation of the conductive pathway 230.

[0015] The conductive particles 224 in the convertible ink include conductive metal particles. Non-limiting examples of conductive metal particles include silver particles, gold particles, copper particles, or combinations thereof.

[0016] In one or more embodiments, the conductive particles 224 are present in the convertible ink in an amount of about 55 to about 70 wt%. In other embodiments, the conductive particles 224 are present in the convertible ink in an amount of about 60 to about 65 wt%. Furthermore, in some embodiments, the conductive particles 224 are present in the convertible ink in an amount of about 62.5 wt%.

[0017] In some embodiments, the average diameter of the conductive particles 224 is about 20 to about 200 nanometers (nm). In other embodiments, the average diameter of the conductive particles 224 is about 80 to about 120 nm. However, in some embodiments, the average diameter of the conductive particles 224 is about 100 nm. To find a homogeneous distribution after curing, the average diameters of the conductive particles 224 and insulating particles 222 must be very close.

[0018] The insulating particles 222 in the convertible ink include insulating (dielectric) materials or alloys. Non-limiting examples of insulating particles 222 include barium strontium titanate particles. In one or more embodiments, the insulating particles 222 have a melting point of at least 700 degrees Celsius.

[0019] In some embodiments, the average diameter of the insulating particles 222 is from about 20 to about 200 nanometers (nm). In other embodiments, the average diameter of the insulating particles 222 is from about 80 to about 120 nm. Further, in some embodiments, the average diameter of the insulating particles 222 is about 100 nm.

[0020] In one or more embodiments, the insulating particles 222 are present in the convertible ink in an amount of about 30 to about 45 weight percent (wt%). In other embodiments, the insulating particles 222 are present in the convertible ink in an amount of about 35 to about 40 wt%. Further, in some embodiments, the insulating particles 222 are present in the convertible ink in an amount of about 37.5 wt%.

[0021] According to one or more embodiments, the conductive particles 224 are silver particles and the insulating particles 222 are barium strontium titanate particles.

[0022] To prepare the convertible ink, the conductive particles 224 and the insulating particles 222 are combined in a solvent(s) and optionally with one or more additives. Non-limiting examples of solvents include 1-methoxy-2-propanol, ethylene glycol, or any combination thereof. In one or more embodiments, the solvent is a glycol solvent.

[0023] Next, the mixture of the conductive particles 224 and the insulating particles 222 in the solvent(s) and optional additives is cured by applying heat. After curing, the convertible ink remains in an insulating / dielectric phase and contains only the conductive particles 222 and the insulating particles 224.

[0024] Curing is performed, for example, by heating for a certain period of time. The temperature and time of curing vary depending on the composition of the convertible ink. According to one or more embodiments, curing is performed by heating at a temperature of about 75 degrees Celsius to about 125 degrees Celsius. In other embodiments, curing is performed by heating at a temperature of about 80 degrees Celsius to about 100 degrees Celsius.

[0025] Once the convertible ink is formed and cured, a stabilizing material layer is applied and cured with ultraviolet light.

[0026] The stabilizing layer contains polymer 204 and high aspect ratio particles 260 that fill the air gap 202 in the convertible ink (see Figure 2B). Figure 2C shows the blockage of the conductive path 230 by the convertible ink and high aspect ratio particles 260 after heat treatment such as ultraviolet laser sintering. The relatively large high aspect ratio particles 260 reduce the ratio of conductive particles 224 to insulating particles 222 in the initially cured convertible ink. The relatively large high aspect ratio particles 260 further hinder the adhesion of conductive particles 224 during heat sintering when the conductive path 230 is formed.

[0027] According to one or more embodiments, the high aspect ratio particles 260 are hexagonal boron nitride particles. In some embodiments, the high aspect ratio particles 260 have an aspect ratio of about 2:1 to about 30:1. In other embodiments, the high aspect ratio particles 260 have an aspect ratio of about 10:1 to about 20:1.

[0028] According to one or more embodiments, the high aspect ratio particles 260 have an average diameter of about 0.5 to about 1.2 micrometers. In other embodiments, the high aspect ratio particles 260 have an average diameter of about 0.8 to about 1.0 micrometers.

[0029] In one or more embodiments, the high aspect ratio particles 260 are present in the stabilization layer in an amount of about 5 to about 20 wt%. In other embodiments, the high aspect ratio particles 260 are present in the stabilization layer in an amount of about 12 to about 15 wt%.

[0030] According to one or more embodiments, the polymer 204 that fills the air gap 202 in the convertible ink is an acrylate polymer. Other non-limiting examples of polymers include trimethylolpropane ethoxylate triacrylate, urethane acrylate, epoxy acrylate, polyester acrylate, or any combination thereof. In some embodiments, polymer 204 is a triacrylate polymer, which creates a strong three-dimensional polymer network as a result of three unsaturated sites. The three-dimensional polymer network created by polymer 204 fills the air gap 202 and minimizes the reflow of conductive particles 224.

[0031] The polymer 204, which forms a three-dimensional network, can withstand high temperatures without decomposing. In some embodiments, the polymer 204 can withstand temperatures of approximately 100°C to approximately 250°C without decomposing. In other embodiments, the polymer 204 can withstand temperatures of approximately 200°C to approximately 225°C without decomposing.

[0032] To form a stabilizing layer, one or more photoinitiators are combined with polymer 204 precursors (i.e., oligomers and / or monomers), high aspect ratio particles 260, and one or more optional additives, such as one or more photoinitiators. If any of the one or more optional additives are added, they are added in amounts of approximately 0.25 to 5 wt%. This combination is mixed until no aggregation is observed.

[0033] In one or more embodiments, the polymer precursor (e.g., oligomers and / or monomers) is present in the stabilizing layer in an amount of about 70 to about 89 wt%. In other embodiments, the polymer precursor (e.g., oligomers and / or monomers) is present in the stabilizing layer in an amount of about 80 to about 85 wt%.

[0034] Non-limiting examples of photoinitiators include 1-hydroxycyclohexylphenyl ketone, phenylbis(2,4,6,7-trimethylbenzoyl)phosphine oxide, 2-methyl-4'-(methylthio)-2-morpholinopropionphenone, benzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, benzyldimethyl ketal, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanoate, or any combination thereof.

[0035] A stabilizing material layer is applied to the surface of the dielectric phase convertible ink. Once applied, the stabilizing layer prevents the formation of conductive paths that would otherwise convert the ink to a conductive phase under heat treatment (see Figure 3).

[0036] A stabilizing layer is formed on the curable convertible ink layer. In some embodiments, the stabilizing layer is patterned as a mask. Figures 4A and 4B are top and side views, respectively, of a patterned stabilizing layer 402 on a convertible ink layer 404, which is a curable dielectric phase. When a portion of the stabilizing layer 402 is removed and a selected portion of the convertible ink underneath is exposed, the uncovered portion is selectively heat-treated, for example by laser sintering, to form a selected conductive portion 406. The stabilizing layer 402 protects the unexposed portion of the convertible ink layer 404. [Examples]

[0037] Example 1: Formulation of the stabilizing layer Examples of stabilization layer formulations are shown in Table 1 below. [Table 1]

[0038] Place the oligomer, boron nitride, and photoinitiator into a glass jar lined with aluminum foil. Next, stir the jar for 2 hours in 10-second on-off cycles. Check the sample for agglomeration every minute. If agglomeration is present, mix the mixture by hand until it breaks down. The final mixture should be free of visible agglomeration. [Examples]

[0039] Example 2: Change in resistance measurement Thermal stability tests were conducted on convertible inks of barium strontium silver titanate. The convertible inks were laser-sintered, and Figure 3 shows a graph illustrating the change in resistance of the convertible inks with and without a stabilizing layer. When the convertible ink was protected by a stabilizing layer (UV96), the resistance did not change significantly. However, when the stabilizing layer was absent, the measured resistance changed significantly, indicating that the insulating material was completely converted into a conductor.

[0040] The following definitions and abbreviations should be used in the interpretation of the claims and specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains,” or “containing,” or any other variation thereof, are intended to extend to non-exclusive inclusion. For example, a composition, mixture, process, method, article, or apparatus containing a list of elements is not necessarily limited to these elements alone, and may include other elements not expressly enumerated, or other elements specific to such composition, mixture, process, method, article, or apparatus.

[0041] Furthermore, the term “typical” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “typical” should not necessarily be construed as being preferable or superior to other embodiments or designs. The terms “at least one” and “one or more” are understood to include any integer one or more, i.e., 1, 2, 3, 4, etc. The term “multiple” is understood to include any integer two or more, i.e., 2, 3, 4, 5, etc. The term “connection” may include indirect and direct “connections.”

[0042] References in the specification such as “one embodiment,” “embodiment,” and “exemplary embodiment” indicate that the described embodiment may include certain features, structures, or characteristics, but not all embodiments may include or may not include such features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment. In addition, if certain features, structures, or characteristics are described in relation to an embodiment, it is presented that, whether explicitly described or not, the influence of such features, structures, or characteristics in relation to other embodiments is within the knowledge of those skilled in the art.

[0043] For the purposes of the following explanation, the terms “up,” “down,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” and their derivatives shall be those of the structures and methods described, as oriented in the drawings. The terms “lying on top,” “on top,” “located on top,” or “located above” mean that a first element, such as a first structure, is located on a second element, such as a second structure, and an intervening element, such as an interface structure, may be located between the first and second elements. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected at the interface of the two elements without any intermediate conductive, insulating, or semiconductor layer.

[0044] The terms “approximately,” “substantially,” and “nearly,” and their variations, are intended to include the degree of error relating to the measurement of a particular quantity based on equipment available at the time of filing. For example, “approximately” may include a range of ±10%, 9%, 8%, 7%, 6%, or 5%, 4%, 3%, 2%, or 1% of a given value.

[0045] All means or step-plus-function elements in the following claims are intended to include any structures, materials, or actions for performing a function in combination with other specifically claimed elements. While the descriptions in this disclosure have been presented for illustrative and explanatory purposes, they are not intended to be exhaustive or to limit the disclosure in a detailed form. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of this disclosure. The selection and description of embodiments have been made to best illustrate the principles and practical applications of this disclosure and to enable other those skilled in the art to understand the various embodiments, along with various modifications suitable for specific intended uses.

[0046] While preferred embodiments have been described, those skilled in the art should understand that various improvements and enhancements, both now and in the future, can be made as described in the following claims. These claims should be interpreted as maintaining adequate protection over the disclosure described initially.

Claims

1. A polymer network containing an acrylate polymer, Multiple high aspect ratio particles of one type, each having an aspect ratio of 2:1 to 30:1 and an average diameter of 0.5 to 1.2 micrometers, A composition for stabilizing ink, comprising: The ink comprises a plurality of conductive particles and a plurality of insulating particles. A composition for stabilizing an ink, wherein the polymer network and the plurality of high aspect ratio particles prevent the formation of conductive paths in the ink, which are selectively converted from an insulating phase to a conductive or resistive phase upon thermal exposure, thereby keeping the ink in an insulating phase.

2. The composition for stabilizing an ink according to claim 1, wherein the acrylate polymer is a triacrylate polymer.

3. The composition for stabilizing the ink according to claim 1, wherein the acrylate polymer is trimethylolpropane ethoxylate triacrylate, urethane acrylate, epoxy acrylate, polyester acrylate, or any combination thereof.

4. The composition for stabilizing the ink according to claim 1, wherein each of the plurality of high aspect ratio particles has an aspect ratio of 10:1 to 20:

1.

5. The composition for stabilizing the ink according to claim 1, wherein each of the plurality of high aspect ratio particles has an average diameter of 0.8 to 1.0 micrometers.

6. The composition for stabilizing the ink according to claim 1, wherein each of the plurality of high aspect ratio particles is boron nitride.

7. A composition for stabilizing the ink according to claim 1, further comprising a photoinitiator.

8. A stabilized ink comprising convertible ink and stabilizing material, The aforementioned convertible ink is Multiple conductive particles, Multiple insulating particles, Includes, The stabilizing material is Multiple high-aspect-ratio stabilized particles of one type, each having an aspect ratio of 2:1 to 30:1 and an average diameter of 0.5 to 1.2 micrometers, A polymer network in the gap between the plurality of conductive particles and the plurality of insulating particles, Includes, The polymer network and the plurality of high aspect ratio stabilizing particles prevent the formation of conductive paths in the convertible ink, which is selectively converted from an insulating phase to a conductive phase or a resistive phase by thermal exposure, thereby making the convertible ink an insulating phase, the stabilized ink.

9. The stabilized ink according to claim 8, wherein the polymer network comprises an acrylate polymer.

10. The stabilized ink according to claim 9, wherein the acrylate polymer is a triacrylate polymer.

11. The stabilized ink according to claim 9, wherein the acrylate polymer is trimethylolpropane ethoxylate triacrylate, urethane acrylate, epoxy acrylate, polyester acrylate, or any combination thereof.

12. The stabilized ink according to claim 8, wherein each of the plurality of high aspect ratio stabilized particles has an aspect ratio of 10:1 to 20:

1.

13. The stabilized ink according to claim 8, wherein each of the plurality of high aspect ratio stabilized particles has an average diameter of 0.8 to 1.0 micrometers.

14. The stabilized ink according to claim 8, wherein the plurality of high aspect ratio stabilizing particles are boron nitride.

15. A method for stabilizing convertible ink, This includes placing a stabilizing material on a convertible ink, The stabilizing material comprises a polymer network and a plurality of high aspect ratio particles of one type, each having an aspect ratio of 2:1 to 30:1 and an average diameter of 0.5 to 1.2 micrometers. The convertible ink comprises a plurality of conductive particles and a plurality of insulating particles, The method wherein the polymer network and the plurality of high aspect ratio particles prevent the formation of conductive paths in the convertible ink, which is selectively converted from an insulating phase to a conductive phase or a resistive phase by thermal exposure, thereby making the convertible ink an insulating phase.

16. The method according to claim 15, wherein the polymer network comprises an acrylate polymer.

17. The method according to claim 16, wherein the acrylate polymer is a triacrylate polymer.

18. The method according to claim 16, wherein the acrylate polymer is trimethylolpropane ethoxylate triacrylate, urethane acrylate, epoxy acrylate, polyester acrylate, or any combination thereof.

19. The method according to claim 15, wherein each of the plurality of high aspect ratio particles is boron nitride.

20. The method according to claim 15, wherein the stabilizing material further comprises a photoinitiator.

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