Patent Application
20230374289
Composition for use in the manufacture of an in-mould electronic (IME) component
The invention relates to a composition for use in the manufacture of an in-mould electronic (IME) component, a method of manufacturing the composition, a method of manufacturing an in-mould electronic (IME) component, and an in-mould electronic (IME) component.
Development of human-machine interfacing electronic devices, which are highly reliable, robust, lightweight, decorative, and three-dimensionally (3D) shaped, are in high-demand for the development of next-generation automotive, white goods or consumer electronics applications.
Film Insert Molding (FIM) is a process known to integrate graphics, labeling and components to the plastic parts during a molding process. It is a form of In-Mold Decorating (IMD) or In-mold Labeling (IML). The FIM process enables one to create single and decorated plastic parts in two-dimensional (2D) to curved and complex shaped, 3D designs, which are durable and lightweight, can be used for multiple applications. In a typical FIM process, decoration (color and light transmittance) and surface functionality (scratch, anti-reflection, anti-glare, gloss, matte, anti-fingerprint, etc.) of the thermoplastic films are designed as per the application necessity and are integrated to produce robust, complex shaped and decorative plastic parts. This technology is well known for producing decorative parts for automotive, handheld electronic devices and consumer products, while several recent examples show efforts of integrating with electronic functionality. One of the ways to prepare such structures are by injection molding of screen printed and/or thermoformed conductive and dielectric inks printed electronic circuitries.
There is a desire to produce 3D injection molded, light weight plastic structures capable of performing electronics functionalities. These structures can be produced by screen printing of interconnect circuitries on flexible polymer substrates such as, for example, polycarbonate (PC) and polyethylene terephthalate (PET); attaching/assembling electronic components to these screen printed circuitries; thermoforming to produce a 3D structures of such electronics devices and followed by pouring of liquid resins to the backside of the thermoformed structures by injection molding to produce a robust and solid plastic structures. Such structures can be designed to perform capacitive and resistive touch switch applications, for wireless or blue tooth connectivity, controlling volumes or light intensity and many such applications. These injection molded electronics structures are termed as In-Mold Electronics (IME) or Injection Molded Structural Electronics (IMSE) or Plastronics or Surface Electronics.
IME technology consists of the integration of several electronics and plastics manufacturing process steps: screen printing of electronic inks (conducting and dielectric inks), drying or curing of electronic inks, component attachment or electronic assembly using electronic adhesives, thermoforming and trimming to produce curved or 3D structures, and back filling of these curved or 3D structures with molten resins by injection molding.
Electronics functionalities can be integrated with FIM structures, either in two film or single film stacks. In two films stack, electronics ink printed plastic layers are prepared separately by screen printing of conducting or dielectric inks, which further are integrated with graphic ink coated decorated plastics during injection molding steps. Both decorative and electronic functions in a single layer film structure can be fabricated in a sequential fashion, starting by first screen printing of graphic ink layers followed by screen printing of electronic inks (conducting and dielectric inks) and components attachment using conducting or non-conducting adhesives, and then the whole stack is further thermoformed and back injection molded. Plastic substrates are typically PC or PET and injection molding resins are typically selected from polycarbonate (PC), polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyester, poly(methyl methacrylate) (PMMA), low density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and thermoplastic polyurethane (TPU) and the like.
Typical polymer Thick Film Inks (such as, Silver, Carbon etc. and UV/thermal curable dielectric inks) and conducting adhesives are used for the construction of flexible circuits on PC and PET substrates. Though, these inks are highly flexible, these inks cannot be thermoformed as they show discontinuity and cracking while thermoforming, and thus cannot be used for IME device fabrications.
There are several challenges that need to be solved to develop fully functional and reliable IME structures, since the fabrication of IME devices requires the integration of different processing conditions, screen printing, component assembly, thermoforming, trimming and injection molding. Materials property and processing conditions and parameters of each of these steps can further affect the performance of IME devices at different stages.
For example, to achieve superior thermoforming performance of a stack; all inks (graphic ink layers and electronic ink layers) and substrates need to be highly inter-compatible and to have similar thermal stability and modulus properties. Further, such intercompatibility and thermal stability of inks and substrates contributes significantly to the success of injection molding process, which governs the overall stability and reliability of such IME structure.
Accordingly, the following issues are relevant to compositions for use in the manufacture of an IME component:
One of the key requirements of electronic ink materials are their screen printability. For example, screen-printing of well-defined width, thickness and porosity controlled conductive traces are extremely important to construct, high performance interconnects to build circuitries, touch switches, illuminating devices and other similar devices. Similarly printing of uniform, pin-hole free, thin insulating or encapsulation films are important to construct multilayered circuitries, which often act as crossover dielectrics. Variation of deposit strcutures can signifncantly affect the eletrical fucntions of the IME and similar structures performance, thus would increase rejection rate during manufacturing. Similarly, precision dispensing, jetting, stencil printing, casting of conductive and nonconductive adhesives, encapsultants are required for assembling electronic component onto such interconnect structures.
Controlling rheology and viscosity of these formulations are one of the most important features and are responsible for depositing such defect-free conducting traces and non-conducting layers. Efficient drying and curing of these screen-printed materials would be crucial to minimize defects during thermoforming and injection molding process, thereby will increase the yield of overall IME process. Additionally, any printing and drying defects can also affect severally to the electrical and reliability performance of the 3D structural electronics or IME parts. Formulation optimizations with appropriate and compatible chemistry would be desirable to achieve fast and complete drying yet having longer screen-life while printing and providing other functional requirements, such as electrical conductivity, stretchability, and stability during injection molding. Longer screen life along with storage stability of these compositions are important for industrial applicability and manufacturability.
Intercompatibility of dielectric and conductive materials along with compatibility with different flexible polymer substrates, decorative inks, adhesives, encapsulants and injection molding resins are another one of the most important aspect for the manufacturing of IME and similar structures. Most often chemical functionalities of these materials are responsible for their compatibilities, while a perfect matching is the key for manufacturing of robust and high performing IME and similar structures, however, a non-compatible material will result a defective and non-reliable electronic device. Incompatible materials-set generate several errors, such as etching, dissolving, and delaminating of underneath layer on which another new layer is deposited.
Conductive electronic materials should have desirable electrical conductivities to construct electronics devices capable of switching, illuminating and touch functions. Further, higher electrical conductivities are desirable for the construction of structures those are capable of high-current carrying for performing wireless signal processing, blue-tooth connection, and ultra-high frequency sensing functions. The processing of such conductive electronic materials strictly needs to be below 150° C., as per the stability thresholds of most of the flexible substrates of choices for the manufacturing of IME and similar structures. Such conducting materials also need to maintain electrical path before and after thermoforming process without significant alteration of their electrical conductivity. It would also be important to control dielectric properties for effective insulation of high current, electrical devices. Additionally, such electrical conductors and dielectrics should have enough thermal stability to withstand injection molding processing conditions. To balance electrical properties and other functional requirements, such as thermoformability and injection molding stability, high-performance conductive and non-conductive polymer composites are needed to formulate.
Typical choices to assemble electronics components, such as passives, LEDs, would be to use conductive and non-conductive adhesives, which also need to withstand thermoforming and injection molding process steps. Conductive and non-conductive adhesive compositions are also disclosed, which can be either stencil printed or dispensed for assembling passives, LEDs, QFP, QFN and similar other components.
To construct IME and similar structures, electronic materials are required to deposit on flexible polymer substrates to create 2D printed electronics structures by screen-printing and then converted into 3D form by the thermoforming process.
Thermoforming process of functional materials on various substrates opened to create new design, pattern in 3D forms which would not be possible with traditional printed circuit board technology. It is a process in which heat is utilized to soften the substrate above its glass transition/softening temperature and this temperature vary from substrate to substrate. High vacuum or pressure is also applied on soften plastics and given a specific size and shape during thermoforming process. Several other processing conditions, such as time and temperature of thermoforming process, design of tool i.e., depth or height of tool, vacuum pressure, etc. needs to optimize to get very good 3D parts. The challenges would be to design high-performing polymer composites, those could be screen printed and electrical properties of screen-printed traces (width and thickness) can be predictability control as a function of thermoforming strain and process conditions.
Additionally, aesthetic look before and after thermoforming, very good adhesion to above mentioned substrates before and after thermoforming i.e. delamination of ink should not take place on thermoforming, inter-compatibility with different inks such as dielectric for multilayer complex structure especially during thermoforming i.e. stack compatibility, flexibility and elongation so that they do not show cracks during thermoforming i.e. behavior of materials property during thermoforming, etc. Additionally, several other aesthetic defects, such as imprint of electronics circuitries (ghosting) should be avoidable, often arises due to the incompatibility of conducting and dielectric inks along with substrates or graphic ink coated substrates in combinations of in-appropriate selection of design parameters, thermoforming processing conditions and molds selections.
Stability during Injection Molding:
Screen-printed and thermoformed, flexible electronics structures are injection molded to provide structural stability, rigidity, and reliability requirements. Various resins, such as PC, ABS, ABS-PC blend, polyester, PP and TPU are used based on the performance requirements of IME and similar structures. The higher processing temperature and injection pressure are very harsh to the screen-printed circuitries, which needs to directly face the flow of the hot-injection-molding-resins. So, one of the key requirements for electronic materials, their thermal stability, as well as compatibility with incoming injection molding resin and high temperature adhesion to underneath substrates to resist any structural deformation and destructions. Often, such deformations and destructions of screen-printed features during injection molding are termed as “ink wash-off”. Ink wash-off is a serious factor that can lower the manufacturing yield of IME devices. Additionally, change of resistance before and after injection molding should also be minimum. Design of circuities along with materials composition are key to avoid ink wash-off during injection molding.
A typical IME devices need to pass several environmental tests, such as 85° C./85 RH, thermal aging, thermal cycling, illumination test, etc. The reliability of IME and similar structures are finally depended on the accuracy of all the above factors as discussed and compatibility of all materials, substrates, and components. A well-depth knowledge and iterations are needed to select different compatible raw materials to formulate and optimize a highly compatible electronics material. Selection and optimization of the ratios of appropriate inorganic fillers, polymeric resins, solvents, and functional additives are important to optimize such electronic compositions for the manufacturing of IME and similar structures.
The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.
In a first aspect, the present invention provides a composition for use in the manufacture of an in-mould electronic (IME) component, the composition containing a binder comprising:
Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any features indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.
The inventors have surprisingly found that the composition is particularly suitable for use in the manufacture of an IME component, for example as a conductive ink or a dielectric ink, and may result in the manufacture of IME components with superior robustness, environmental durability/ruggedness, mechanical flexibility, and improved operational life for electronics applications in comparison to conventional IME components.
As discussed in more detail below, the composition may comprise solid particles, such as conducting particles and non-conducting particles. The binder serves to “bind” these components of the composition together. When the composition comprises solid particles, then the binder may form the remainder of the composition together with any unavoidable impurities. When the composition does not contain solid particles, then the binder together with any unavoidable impurities may constitute the entire composition.
The term “melamine formaldehyde” as used herein may encompass a resin with melamine rings terminated with multiple hydroxyl groups derived from condensation products of two monomers, melamine, and formaldehyde. Melamine formaldehyde is sometimes referred to a “melamine formaldehyde resin”, “melamine resin” or simply “melamine”.
The term “thermoplastic resin” as used herein may encompass a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
The term “component” as used herein may encompass, for example, a part of an electronic component or an entire electronic component.
During a typical IME manufacturing method, a composition, such as a conductive ink or a dielectric ink, is printed on a thermoformable substrate. Prior to thermoforming, the composition is then dried, typically at an elevated temperature of up to 150° C., for example from 50 to 120° C., for a period of time to remove solvent from the composition. Without being bound by theory, it is considered that upon thermal heating of the composition of the present invention, e.g. using such typical drying temperatures and times, the melamine resin may react with the hydroxyl groups of the thermoplastic resins to form a “nitrogen-carbon-oxygen” linked, polymeric network.
Advantageously, once dried under such conditions, the binder of the present invention may exhibit two contradictory properties. At a normal operation temperature of an IME device (e.g. from about −20° C. to +50° C.) the binder may act like a thermoset showing exceptional strength, cohesion and interlayer adhesion, and a reasonable stretch-ability. However, at higher temperatures that are used during thermoforming, the binder may transform into a thermoplastic material that can be readily thermoformed into 3D structures without necking, breaking or delaminating.
Without being bound by theory, it is considered that these contradictory properties may result from the use of the cross-linking agent comprising melamine formaldehyde with the hydroxyl group-containing resins. In particular, it is considered that this advantageous balance of thermoplastic and thermoset properties is achieved by the occurrence of partial, i.e. not full, cross-linking. This is presumably because, in comparison to cross-linking agents used in conventional IME methods, melamine formaldehyde is a relatively “slow” cross-linking agent, and results in only partial cross-linking as a result of the drying temperatures and times used in a typical IME manufacturing method.
During a typical IME manufacturing process multiple thermoformable compositions are used so as to form the final component, e.g. conductive inks, dielectric inks, conductive adhesives, non-conductive adhesives, encapsulants, barrier layers etc. Advantageously, the compatibility of these materials can be improved when compositions of the present invention are used as a common platform. While each of these materials may of course include different species (e.g. conductive particles, non-conductive particles, etc.), the use of the common binder may ensure the inter-material (e.g. inter-ink) compatibility. As a result, problems with, for example, de-lamination of layers of different materials, may be reduced.
The compositions are compatible with conventional graphic ink-coated substrates, which is a desirable criteria for constructing highly functional IME structures and devices.
Flexible electronic circuits constructed using the composition may show excellent electrical performance.
The compositions may be highly compatible with injection-molding resins typically employed in an IME manufacturing method.
Use of the composition may also reduce the occurrence of ink wash-out in comparison to compositions used in conventional IME methods.
Thermoformed and injection molded structures prepared using the compositions show excellent environmental reliability features, and thus are particularly suitable for IME applications for automotive, consumer electronics and white goods applications.
Advantageously, the composition may be stable at normal storage and ambient temperatures. Again, without being bound by theory, it is considered that this is due to the substantial absence of any cross-linking by the melamine formaldehyde at such temperatures.
The melamine formaldehyde preferably comprises hexamethoxymethyl melamine. Hexamethoxymethyl melamine is a particularly suitable cross-linking agent. In addition, hexamethoxymethyl melamine is soluble in most common organic solvents except aliphatic hydrocabons.
Suitable commercial melamine formaldehyde resins include, for example, Maprenal BF 891/77SNB, Maprenal MF 600/55BIB, Maprenal MF 650/55IB, Maprenal MF 800/55IB, CYMEL 370, CYMEL 373, and CYMEL 380. Maprenal MF 600/55BIB is an imino type, highly reactive, isobutylated melamine-formaldehyde resin.
The cross-linking agent may advantageously further comprise isocyanate and/or polyisocyanate and/or blocked polyisocyanate. Such species may increase the degree of cross-linking under the drying conditions employed in conventional IME manufacturing methods. This may be advantageous when the composition is required to have increased “thermoset” properties. A “blocked”, or “masked”, isocyanate may encompass an isocyanate that contains a protected isocyanate. The isocyanate functional group is typically masked through the use of a blocking agent producing a compound that is seemingly inert at room temperature yet yields the reactive isocyanate functionality at elevated temperatures.
Suitable isocyanates, polyisocyanates and blocked polyisocyanates include, for example, toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), Desmodur BL 3175A, Desmodur BL 3272 MPA, Desmodur BL 1100/1 and Vestanat B 1358A from Evonik. These can be used alone or in a combination of melamine formaldehyde resins. VESTANAT B 1358A comprises methyl-ether-ketone-oxime (MEKO) blocked cycloaliphatic polyisocyanate based on isophorone diisocyanate (IPDI).
The thermoplastic resin preferably comprises one or more of polyurethane resin, polyester resin, polyacrylate resin, polyvinyl ester resin, phenoxy resin and ketonic resin, i.e. a hydroxyl group containing polyurethane resin, polyester resin, polyacrylate resin, polyvinyl ester resin, phenoxy resin and/or ketonic resin. Such resins are particularly suitable for use in the present invention and under the drying conditions of a typical IME manufacturing method react with melamine formaldehyde to provide the desired degree of cross-linking.
These thermoplastic resins may be used alone or in combinations with other thermoplastic resins.
The polyurethane resin may comprise, for example, a reaction product of hydroxy terminated polyol, hydroxy terminated poly(ethylene oxide), hydroxy terminated poly(dimethylsiloxane) or trimethylolpropane ethoxylate with methylbenzyl isocyanate, (trimethylsilyl) isocyanate, 1-naphthyl isocyanate, 3-(triethoxysilyl) propyl isocyanate, phenyl isocyanate, allyl isocynate, butyl isocyanate, hexyl isocyanate, cyclohexyl isocyanate, furfuryl isocyanate, isophorone diisocyanate, hexamethylene diisocyanate, m-xylylene diisocyanate, 1,4-cyclohexylene diisocyanate, poly(propylene glycol), or tolylene 2,4-di-isocyanate. The polyurethane resin may comprise one or mixture of a thermoplastic polyurethane, such as Pearlstick series of polyurethane like Pearlstick 5701, Pearlstick 5703, Pearlstick 5707, Estane series of polyurethane like ESTANE FS M92B4P, Desmocoll series of polyurethane like Desmocoll 540/4, Desmocoll 400, Desmomelt series of polyurethane like Desmomelt 540/3, Desmomelt 540/4. The phenoxy resin is preferably a thermoplastic bisphenol-A based polyether containing polyester or polyacrylate or polyurethane compounds. Examples of suitable phenoxy resins containing polyester or poly acrylate or polyurethanes include phenoxy resins available under the tradenames LEN-HB, PKHW-35, PKHH, PKHA, PKHM-301 and PKHS-40. The polyester resin, polyacrylate resin and/or polyurethane resin may contain one or more of polyols, hydroxyls, amines, carboxyl acids, amides and aliphatic chains. The phenoxy resin contain polyester or polyacrylate or polyurethane or polyether or polyamide backbone.
The thermoplastic resin preferably comprises polyurethane resin, polyester resin and phenoxy resin. More preferably, the thermoplastic resin comprises:
Such thermoplastic resins, particularly in the amounts recited above, are particularly suitable for obtaining the desired degree of cross-linking with the melamine formaldehyde. The presence of polyurethane resin(s), particularly in the recited amount, may provide the dried composition with a desirable level of flexibility. The presence of polyester resin(s), particularly in the recited amount, may provide the dried composition with a desired degree of flexibility and also promote adhesion to the substrate. The presence of phenoxy resin(s), particularly in the recited amount, may promote adhesion to the substrate. The combination of these three resins, particularly in the recited amounts, may provide a favourable combination of high flexibility and high adhesion to the substrate.
Preferably, the thermoplastic resin:
In a preferred embodiment, the composition comprises:
based on the total amount of cross-linking agent and thermoplastic resin. Such amounts may help to provide the desired level of cross-linking under the drying conditions of conventional IME manufacturing methods.
The solvent preferably comprises one or more of a glycol ether acetate, a glycol ether, an ester, a ketone, an alcohol and a hydrocarbon. Such solvents may be particularly suitable for use in the present invention. Such solvents may be used alone or in combination. Such solvents may be particularly suitable for dissolving the thermoplastic resins and/or cross-linking agent, and may be particularly compatible with substrates and any functional fillers and/or additives in the composition. Such solvents may have a favourable combination of polarity, solvency properties (Hansen solubility parameters), compatibility with substrates, toxicity and other physical properties, such as boiling and flash points. Such solvents may improve the composition's storage stability, drying profile, drying stability during processing (e.g. on screen during screen printing), and reactivity with substrates and other printed ink layers (such as graphic inks or electronics inks layers). Such solvents may result in a homogeneous composition that will be stable upon storing and also satisfy performance requirements. Non-limiting examples of solvents include methanol, ethanol, 2-propanol, benzyl alcohol, ethylene glycol, propylene glycol, dipropylene glycol, 1,3-butane diol, 2,5-dimethyl-2,5-hexane diol, ethylene glycol methyl ether, ethylene glycol monobutyl ether, propylene glycol phenyl ether, diethylene glycol mono-n-butyl ether, propylene glycol n-propyl ether, dipropylene glycol methyl ether, terpineol, butyl carbitol, butyl carbitol acetate, glycol ether acetates, 2-(2-ethoxyethoxy)ethyl acetate, dipropylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, 2-Butoxyethyl acetate, carbitol acetate, propylene carbonate butyl carbitol, butyl cellosolve, heptane, hexane, cyclohexane, benzene, xylene, Cyrene, dibasic ester, isophorone, C11-ketone, and toluene.
The preferably solvent comprises:
based on the total weight of the solvent.
Such amounts may be particularly suitable for providing the advantages described above.
The binder may preferably further comprise:
The presence of the thermosetting resin and curing catalyst may serve to form a three-dimensional thermoset network. This may be beneficial when the dried composition is required to have more “thermoset” properties. The thermosetting resin preferably comprises one or both of acrylic resin and epoxy resin, and may be cured using a thermal curing agent and/or a UV curing agent.
The thermosetting resin may contain, for example, a polyester or a polyacrylate or a polyether or a polyurethane or a polyamide backbone. The thermosetting resin may contain different combinations of monomer, dimer, trimer, tetramer, penta or hexamer and oligomers having epoxy, polyurethane, polyester, polyether, and acrylic backbones.
Examples of the epoxy resin include bisphenol-A epoxy, 4-vinyl-1-cyclohexene 1,2-epoxide, 3,4-epxoy cyclohexyl mehyl-3′,4′-epoxy cyclohexene carboxylate, 1,4-butanediol diglycidyl ether, trimethylolpropane triglycidyl ether, triglycidyl isocyanurate, epoxy siloxane, epoxy silane and phenol novolac epoxy. The epoxy resins may comprise one or a mixture of epoxy resins, such as EPON 862, DYCK-CH, JER 828, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidylether (DER 731), orho-Cresyl glycidyl ether (DER 723) and C12-C14 alkyl glycidyl ether (DER 721). One or more hardeners may be present, and such hardeners may be either amine such as butyl amine, N,N-diethyl amino ethanol, or amino ethanol, acid such as oleic acid, adipic acid, or glutaric acid, or anhydrides such as succinic anhydrides, phthalic anhydrides and maleic anhydride. Epoxy acrylates may also be used. (Meth)acrylates are produced by a ring opening reaction of 1,4-butanediol diglycidyl ether, bisphenol-A epoxy, 4-vinyl-1-cyclohexene 1,2-epoxide, 3,4-epxoy cyclohexyl mehyl-3′,4′-epoxy cyclohexene carboxylate, trimethylolpropane triglycidyl ether, triglycidyl Isocyanurate, epoxy siloxane, epoxy silane, phenol novolac epoxy with methacrylic acid. The epoxy acrylate may comprise one or more of epoxy backbone based (meth)acrylates such as Ebecryl 3503, Ebecryl 3201, Photomer 3005, Photomer 3316, Ebecryl 3411, and Ebecryl 3500, by way of example and not limitation. Polyurethane acrylates such as urethane acrylate, methacrylate terminated polyurethane and modified isocynate with hydroxy ethyl methacrylate may also be used. The urethane acrylate may comprise one or more of a urethane backbone based (meth)acrylate such as SUO2371, SUO-300, SUO-7620, Photomer 6891, SUO S3000, Ebecryl 8413, Ebecryl 230, Ebecryl 4833, Ebecryl 8411, Ebecryl 270, Ebecryl 8804, and Photomer-6628, by way of example and not limitation. Polyester acrylates such as fatty acid modified pentaerythritol acrylate, trimethylolpropane triacrylate and methacrylated monosaccharides may also be used. Polyether acrylates such as poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) methacrylate, poly(ethylene glycol) dimethacrylate may also be used. The polyester acrylate may comprise one or more of polyester backbone based (meth)acrylate such as Photomer-4006, Ebecryl 450, Photomer 5429, and Ebecryl 812, by way of example and not limitation. Non-limiting examples of monomer acrylates include, but are not limited to, methacrylic acid, 3-(trimethoxysilyl)propyl methacrylate, isoborynyl acrylate, tetrahydrofufuryl acrylate, poly(ethylene glycol) methyl ether acrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, 2-ethyl hexyl acrylate, butyl acrylate, isooctyl acrylate, methyl methacrylate, lauryl acrylate, dodecyl acrylate and tetrahydrofurfuryl acrylate. Non-limiting examples of dimer acrylates include dimer methacrylates such as poly(ethylene glycol) dimethacrylate, 1,6-bis(acryloyloxy)hexane, bisphenol A-ethoxylate dimethacrylate and neopentyl glycol diacrylate 1,3-butanediol diacrylate. Non-limiting examples of trimer acrylates include trimer methacrylates such as trimethylolpropane triacrylate, pentaerythritol triacrylate and 1,3,5-triacryloylhexahydro-1,3,5-triazine. Non-limiting examples of tetramer acrylates include pentaerythritol tetracrylate and di(trimethylolpropane) tetraacrylate. Non-limiting examples of penta or hexamer acrylates include dipentaerythritol penta-acrylate and dipentaerythritol hexa-acrylate. The siloxane acrylate may comprise one or more of siloxane backbone based (meth)acrylate such as BYK-UV3570, BYK-UV3575, BYK-UV3535, BYK-UV3530, BYK-UV3505, BYK-UV3500, Ebecryl 350, Ebecryl 1360, and SUO-S3000, by way of example and not limitation. The aliphatic acrylate may comprise one or more of hydrocarbon backbone based (meth)acrylate such as Ebecryl 1300, SAP-M3905, Ebecryl 525, and SAP-7700HT40, by way of example and not limitation.
The binder preferably further comprises one of more functional additives, preferably selected from one or more of surfactants, rheology modifiers, dispersants, de-foamers, de-tackifiers, slip additives, anti-sag agents, levelling agents, surface active agents, surface tension reducing agents, adhesion promoters, anti-skinning agents, matting agents, coloring agents, dyes, pigments and wetting agents. De-foamers may remove the foam from the binder, and de-tackifiers may remove tack from the binder. The surfactants may comprise anionic, cationic or non-ionic surfactants. Non-limiting examples include surfactants available under the tradenames SPAN-80, SPAN-20, Tween-80, Triton-X-100, Sorbitan, IGEPAL-CA-630, Nonidet P-40, Cetyl alcohol, FS-3100, FS-2800, FS-2900. FS-230, FS-30, BYK-UV3500/UV3505/077/UV3530, FS-34, Modaflow 2100, Omnistab LS 292, Omnivad-1116 and Additol LED 01. Rheology Modifiers are organic or inorganic additives that control the rheological characteristics of the formulation. These can be used alone or in a mixture. Examples of suitable rheology modifiers include, but are not limited to, those available under the tradenames THIXIN-R, Crayvallac-Super, Brij 35, 58, L4, O20, S100, 93, C10, O10, L23, O10, S10 and S20. Functional additive can also be coloring agents, dyes and pigments. Non-limiting examples of coloring agents, dyes and pigments include anthraquinone dyes, azo dyes, acridine dyes, cyanine dyes, diazonium dyes, nitro dyes, nitroso dyes, quinone dyes, xanthene dyes, fluorene dyes and rhodamine dyes. Non-limiting examples of antioxidants and inhibitors include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-p-cresol, butylhydroxytoluene, 3,5-di-tert-4-butylhydroxytoluene, Omnistab IC, Omnistab In 515/ 516, hydroquinone and phenothiazine.
In addition to the elements recited herein, it will be understood that the composition and binder may comprise unavoidable impurities. Such unavoidable impurities, if present, are typically present in an amount of up to 1 wt. % of the composition or binder, more typically up to 0.5 wt. %, even more typically up to 0.1 wt. %, even more typically up to 0.05 wt. %.
In a preferred embodiment, the binder comprises:
Such a binder is particularly suitable for providing the composition with the advantages described above.
Preferably, the binder comprises a low level of:
In a preferred embodiment, the composition further comprises conductive particles, i.e. electrically conductive particles. This may enable the composition to be used as, for example, a conductive ink or a conductive adhesive.
The conductive particles preferably comprise metal particles, more preferably selected from one or more of silver particles, copper particles, brass particles, nickel particles, gold particles, platinum particles, palladium particles, metal alloy particles, silver-coated copper particles, silver-coated brass particles, silver-nickel alloy particles and silver-copper alloy particles. Such particles are particularly suitable for use in a conductive ink or conductive adhesive.
Alternatively, or in addition, the conductive particles preferably comprise non-metal particles, more preferably comprise carbon particles, preferably selected from one or more of graphite particles, graphite flakes, carbon black particles, graphene particles and carbon nanotubes. Such particles are particularly suitable for use in a conductive ink or conductive adhesive. The use of graphene may improve the mechanical, flexible and barrier properties of the composition. The combinations of graphene's unique mechanical, flexible and barrier properties may be highly beneficial for the preparation of flexible, mechanically robust, abrasion resistant and corrosion resistant carbon layers, thereby enhancing the operational life of an IME and similar structures. Additionally, incorporation of graphene to metal inks may enables the development of high-performing, low cost metal inks, with moderate electrical conductivities.
The conductive particles preferably have a mean particle size (d50) of from 0.5 to 30 μm, more preferably from 1 to 20 μm, even more preferably from 1.25 to 7 μm. The particle size may be determined, for example, using SEM, TEM, a laser scattering particle size analyser or a dynamic light scattering method. Such a particle size distribution may provide a favourable packing density, inter-particle interactions for targeted viscosity and electrical properties. The particular mean particle size may depend on the final application, for example fine line printing, thermoformable applications, e-textile, etc. and on the processing techniques.
The conductive particles preferably have a tap density of from 1 to 5 g/cc, more preferably from 1.5 to 4 g/cc. The tap density may be determined using a conventional tap density tester. The higher the tap density, the higher the percolation threshold for the electrical conductivity. Lower tap densities may make processing more difficult and may adversely affect the composition viscosity and rheology.
The conductive particles preferably have a surface area of from 0.3 to 2.1 m2/g or from 0.5 to 5 m2/g. This may make them more suitable for electronic applications. It may also help to provide the composition with favourable rheology and viscosity. The greater the surface area the greater the viscosity. Accordingly, higher surface areas may be more advantageous when the composition is used as a conductive adhesive, whereas lower surface areas may be more advantageous when the composition is used as a conductive ink. The surface area may be determined, for example, using a gas adsorption BET method.
The conductive particles preferably have an organic content of from 0.06 to 1.3 wt. % or from 0.01 to 3 wt. %. The organics may serve as an organic coating or capping agent. The organic coating may vary in chain length and may comprise a saturated or unsaturated fatty acid or ester, or a glycerol based derivative or amine or amide or phosphate or thiol. The organic coating may help the conductive particles to interact with polymers so as to remain in single phase. The organic content may be determined, for example by a gravimetric method. The amount of organic content on the filler particles (metal or metal oxide) are calculated by the loss of weight after heat treatment (200-700° C.).
The conductive particles preferably are in the form of one or more of flakes, spheres, irregularly shaped particles, nano-powders and nanowire. More preferably, the conductive particles are in the form of flakes. In comparison to spheres, flakes may have greater tendency for an interaction with the binder and adjacent particles. These features may help to achieve better adhesion to substrates and providing percolation threshold for the electrical conductivity.
Preferably, the conductive particles comprise a low level of:
In addition to the conductive fillers described above, the composition may preferably further comprise nano-sized silver particles or organo-silver compounds (AgMOC, such as silver neodecanoate and silver 2-ethylhexanoate). These may further enhance the electrical conductivities of the compositions.
The conductive fillers may comprise:
Such conductive fillers may be particularly suitable for producing transparent conducting films, printed resistive heaters, transparent heaters, and transparent flexible and circuit elements. The present invention also provides the use of such conductive fillers to manufacture such objects.
The composition preferably comprises:
Such amounts may provide a favourable level of conductivity together with the advantages of the binder described above.
In a preferred embodiment, the composition comprises:
In a preferred embodiment, the composition is in the form of a conductive ink. In other words, the present invention provides a conductive ink comprising the composition described herein. The conductive inks may advantageously be used to make electrical flexible and formable circuits, interconnects, attach components and parts, via-fills, etc. The conductive ink may also be used for thermal connections. The conductive inks may exhibit viscosity and rheology suitable for printing using, for example, screen, stencil, gravure and flexographic techniques to produce electronics interconnect circuitries on various polymeric substrates, such as PC and PET. Once thermally dried and/or cured, interconnect lines, pattern shapes and/or features (for example, trace width, pad width etc.) produced using such inks may be controlled to >100 μm and possesses excellent surface resistance <100 Ω/□/mil (when various carbon particles are only used as conducting fillers) or <100 mΩ/□/mil (when various metallic particles and/or flakes are used as conducting fillers) and have adhesion (as per ASTM standard >3B) suitable for manufacturing of flexible electronics circuits. These interconnect circuits produced using such inks may possess excellent thermoformability and are stable under injection-molding ink wash-out, and thus suitable for IME manufacturing.
In a preferred embodiment, the composition is in the form of a conductive adhesive. In other words, the present invention provides a conductive adhesive comprising the composition described herein. The conductive adhesive may exhibit viscosity and rheology characteristics suitable for printing (screen and stencil), dispensing, jetting and micro-dispensing techniques for assembling various components, packages, and LEDs to interconnect circuits produced by earlier disclosed conducting inks on various polymeric substrates, such as PC and PET. Once thermally dried or cured, these interconnect lines and pattern shapes and features can be controlled to >50 μm and possesses excellent surface resistance <100 Ω/□/mil (when various carbon particles are only used as conducting fillers) or <100 mΩ/□/mil (when various metallic particles and/or flakes are used as conducting fillers) and having adhesion (as per ASTM standard >3B) suitable for manufacturing of flexible electronics circuits. Assembled components and packages produced using such conductive adhesives may show high mechanical stability as evident by die-shear results. Circuits produced using such conductive adhesives may possess excellent thermoformability and may be stable under injection-molding ink wash-out, and are thus suitable for IME manufacturing.
In a preferred embodiment, the composition further comprises non-conductive particles. Such compositions may be used to make, for example, electrical flexible and formable circuits, interconnects, attach components and parts, and via-fills. Such compositions may be used for mechanical and thermal connections.
The non-conductive particles preferably comprise organic non-conductive particles, preferably selected from one or more of cellulose, wax (for example, Ceraflour 991, Ceraflour 929 and Ceraflour 920 from BYK), polymer microparticles, non-conductive carbon particles and graphene oxide.
Alternatively, or in addition, the non-conductive particles preferably comprise inorganic non-conductive particles, preferably selected from one or more of mica, silica (SiO2), fumed silica, talc, titanium dioxide (TiO2), alumina, barium titanate (BaTiO3) zinc oxide (ZnO) and boron nitride (BN), optionally wherein the inorganic non-conductive particles are submicron to micron sized (e.g. from 5 to 50000 nm, preferably from 10 to 30000 nm).
Organic non-conductive particles may increase the homogeneity of the composition but may have lower dielectric strength in comparison to inorganic non-conductive particles. Inorganic non-conductive particles may increase the dielectric strength but may result in decreased homogeneity in comparison to organic non-conductive particles. Thus, it may be preferable to functionalize the non-conductive particles with a functional group such as, for example, carboxylic acid, amine or alcohol to enable them to be better dispersed very well through interaction with the polymer system. The organic coating may vary in chain length and may comprise a saturated or unsaturated fatty acid or ester, or a glycerol based derivative or amine or amide or phosphate or thiol. This may also help to improve the long-term storage stability of the composition.
The non-conductive particles preferably exhibit a mean particle size (d50) from 1 to 30 μm or less than or equal to 10 μm. Higher ratio of very small particle size distributions increases the viscosity and makes the processing difficult, whereas presence of higher distribution of very larger particle size distributions lowers the viscosity, creates problem of slumping.
The non-conductive particles may be in the form of flakes and/or spheres and/or irregularly shaped particles. Preferably, the non-conductive particles are in the form of flakes and/or irregularly shaped particles. This is because, in comparison to spheres, flakes and irregularly shaped particles may have improved adhesion to a substrate and may have a reduced propensity to delaminate during a thermoforming process.
The non-conductive particles preferably have a low ionic content, preferably substantially zero.
Preferably, the non- conductive particles comprise a low level of:
The composition preferably comprises:
Such amounts may provide a favourable level of dielectric properties together with the advantages of the binder described above.
In a preferred embodiment, the composition comprises:
and the binder comprises:
In a preferred embodiment, the composition is in the form of a dielectric ink. In other words, the present invention provides a dielectric ink comprising the composition described herein.
In a preferred embodiment, the composition is in the form of a non-conductive adhesive. In other words, the present invention provides a non-conductive ink comprising the composition described herein.
In a preferred embodiment, the composition is in the form of an encapsulant. In other words, the present invention provides an encapsulant comprising the composition described herein.
Once dried/cured, the binder of the dielectric ink, non-conductive adhesive and encapsulant may possess excellent dielectric properties and may be highly flexible and moderately stretchable, have superior adhesion and compatibility with other ink materials (e.g. silver and carbon) and substrates and have excellent weather resistance (moisture, gas and chemicals). The dielectric ink, non-conductive adhesive and encapsulant may possess excellent thermoformability and may be stable under injection-molding ink wash-out, thus be suitable for IME manufacturing. The viscosity and rheology of the dielectric ink, non-conductive adhesive and encapsulant may be suitable for printing using, for example, screen, stencil, gravure or flexographic techniques; spraying; dispensing; and jetting techniques to produce insulating layers for protecting conducting interconnect circuitries on various polymeric substrates, such as PC and PET. Once thermally dried or cured, the dielectric coating thickness can be controlled to >1 μm and may possess excellent dielectric break-down voltages (>100 V) and may have adhesion (as per ASTM standard >3B) suitable for manufacturing of flexible electronics circuits. The encapsulating coating layers may provide protection of conducting circuitries from environments, such as moisture and gasses.
The composition may preferably further comprise a colorant and/or dye and/or pigment, and may be the form of a graphic ink. In other words, the present invention provides a graphic ink comprising the composition described herein. The dye and/or pigment may form part of the functional additives discussed above.
In a further aspect, the present invention provides a method of manufacturing the composition described herein, the method comprising:
The advantages and preferably features of the first aspect apply equally to this aspect.
In a further aspect, the present invention provides a method of manufacturing an in-mould electronic (IME) component, the method comprising:
wherein preparing the blank comprises forming one or more structures on a thermoformable substrate, each structure formed by a method comprising:
The term “thermoforming” as used herein may encompass a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product. The sheet is typically heated in an oven to a high-enough temperature that permits it to be stretched into or onto a mold and cooled to a finished shape. Its simplified version is vacuum forming. A pressure may be applied during the thermoforming. The thermoforming may comprise high-pressure thermoforming.
Drying the composition is carried out at a temperature of from 20 to 150° C., preferably from 30 to 130° C., for from 0.5 to 60 minutes, preferably for from 1 to 30 minutes.
Preferably two or more structures are formed. Use of the composition as disclosed herein ensures that the one or more structures, for example one or more layers in a multilayer stack, are compatible with each other.
The one or more structures are preferably selected from a conductive layer, a wire, a dielectric layer, an encapsulant layer, a graphic layer and a barrier layer.
The one or more structures preferably comprises a multilayer stack.
The one or more structures preferably comprises a printed circuit board.
Disposing the composition preferably comprises printing the composition, more preferably screen-printing the composition.
The substrate preferably comprises polycarbonate (PC) and/or polyethylene terephthalate (PET). The composition as described herein is compatible with, and forms strong adhesion with, such materials. Such materials also exhibit favourable thermoforming properties.
The thermoforming is preferably carried out at a temperature of from 140° C. to 210° C. Such a temperature is particularly suitable for thermoforming, and the composition described herein may be stable at such a temperature. The thermoforming may comprise vacuum thermoforming. In a preferred embodiment, the vacuum thermoforming is carried out at a pressure of from 0.25 MPa to 0.4 MPa. In another preferred embodiment, the high-pressure thermoforming is carried out at a pressure of from at a pressure ranging from 6 MPa to 12 MPa.
Preferably, the method further comprises attaching one or more electronic devices to the blank using a conductive adhesive or a non-conductive adhesive, the conductive adhesive being the composition described herein, wherein the attaching takes place before and/or after thermoforming.
Preferably, the method further comprises, after thermoforming, applying a layer of resin to the substrate using injection moulding, preferably wherein the resin comprises one or more of polycarbonate (PC), polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyester, poly(methyl methacrylate) (PMMA), low density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and thermoplastic polyurethane (TPU). Other similar resins may also be used. Such a layer of resin may provide the final IME component with favourable mechanical and/or aesthetic properties.
The injection moulding is preferably carried out at a temperature of from 170 to 330° C. Such a temperature is particularly suitable for injection moulding, and the composition described herein may be stable at such a temperature.
The in-mould electronic (IME) component preferably comprises a capacitive touch switch or a resistive touch switch. In comparison to conventional capacitive touch switches and resistive touch switches, such a capacitive touch switch and resistive touch switch may exhibit improved performance and/or reliability.
The in-mould electronic (IME) component preferably comprises one or more of a display, a light/lamp, a sensor, an indicator and a haptic/touch feedback device.
The in-mould electronic (IME) component preferably comprises one or more of a transparent conducting film, printed resistive heater, transparent resistive heater, transparent capacitive touch-based device, and transparent flexible and circuit element. In such case, preferably the composition comprises conductive fillers may comprising conducting, metallic nanowires and/or conducting carbon nanotubes and carbon nanofibers; and/or conducting polymers; and/or conducting graphene flakes, as described above.
In a further aspect, the present invention provides in-mould electronic (IME) component manufactured according to the method described herein. In comparison to conventional IME components, the IME component may exhibit improved performance and/or reliability.
In a further aspect, the present invention provides an in-mould electronic (IME) component comprising the composition described herein. As will be appreciated, the composition will have undergone at least partial cross-linking. In comparison to conventional IME components, the IME component may exhibit improved performance and/or reliability.
The in-mould electronic (IME) component preferably comprises a capacitive touch switch or a resistive touch switch. In comparison to conventional capacitive touch switches and resistive touch switches, such a capacitive touch switch and resistive touch switch may exhibit improved performance and/or reliability.
The in-mould electronic (IME) component preferably comprises one or more of a display, a light/lamp, a sensor, an indicator and a hepatic/touch feedback device. In comparison to conventional, display, a light/lamp, a sensor, an indicator and a hepatic/touch feedback device such a display, a light/lamp, a sensor, an indicator and a hepatic/touch feedback device may exhibit improved performance and/or reliability.
The in-mould electronic (IME) component preferably comprises one or more of a transparent conducting film, printed resistive heater, transparent resistive heater, transparent capacitive touch-based device, and transparent flexible and circuit element. In such case, preferably the composition comprises conductive fillers may comprise conducting, metallic nanowires and/or conducting carbon nanotubes and carbon nanofibers; and/or conducting polymers; and/or conducting graphene flakes, as described above.
The invention will now be further described by reference to the following numbered clauses:
33. The composition for electronic assembly of any of clauses 18 to 32 printed on a suitable graphic ink or decorative ink, which have been applied on to a polymer substrate, such as polycarbonate (PC), polyethylene terephthalate (PET), can be thermoformed to form curved, 2.5D and 3D structure, injection molded to form in-mold electronics (IME) and similar structures.
The invention will now be described in relation to the following non-limiting drawings in which:
The invention will now be described in relation to the following non-limiting examples.
Key attributes of various fillers (conductive and non-conductive) used in the examples are set out in Table 1 below.
Several compositions were prepared by dissolving mixture of thermoplastic polyester resins, polyurethane resins and phenoxy resins having hydroxyl functional groups in mixture of different category of solvents at 70-100° C. The reaction mixtures were cooled to room temperature followed by addition of functional additive package, containing surfactants, rheology modifier, dispersants, defoaming agents and wetting agents. Reactive cross-linkers and/or other acrylics or epoxy curing agents were then mixed well with the above polymer resin mixtures. The compositions were further mixed with several different conductive particles for the preparation of conductive inks, coatings and adhesive compositions. The conductive particles were mixed using an orbital mixer (1000 rpm for 1 min for 3 cycles). Certain compositions were also milled in a three-roll mill for a few minutes to obtain to obtain a homogeneous paste.
Example 1 to Example 14 and Example 19 to Example 26 below are conductive compositions prepared without a thermosetting resin. Example 15 to Example 18 are conductive compositions prepared using a thermosetting resin and corresponding curing catalyst.
Compositions having the components specified in Tables 2-6 below were prepared as per the process described in Example 1 above.
Several compositions were prepared by dissolving mixture of thermoplastic polyester resins, polyurethane resins and phenoxy resins having hydroxyl functional groups in mixture of different category of solvents at 70-100° C. The reaction mixtures were cooled to room temperature followed by addition of functional additive package, containing surfactants, rheology modifier, dispersants, defoaming agents and wetting agents. Reactive cross-linkers and/or other acrylics or epoxy curing agents were then mixed well with the above polymer resin mixtures. The compositions were further mixed with several different conductive particles for the preparation of conductive inks, coatings and adhesive compositions. The conductive particles were mixed using an orbital mixer (1000 rpm for 1 min for 3 cycles). Certain compositions were also milled in a three-roll mill for a few minutes to obtain to obtain a homogeneous paste.
Example 27 to Example 36 and Example 41 to Example 61 below are conductive compositions prepared without a thermosetting resin. Example 37 to Example 40 are conductive compositions prepared using a thermosetting resin and corresponding curing catalyst.
30.1 weight % of mixture talc and organic filler and 69.9 weight % of polymer solution of was mixed together using an orbital mixer at 1000 rpm for 1 min for 3 cycles to obtain a homogeneous paste. The viscosity of the paste was found to be in the range of 11000-15000 cP and is suitable for the screen printing.
Compositions having the components specified in Tables 7-11 below were prepared as per the process described in Example 27 above.
indicates data missing or illegible when filed
Conductive and Dielectric compositions disclosed above are characterized thoroughly and tested for screen printing, electrical performances, compatibility among different inks and substrates (PC and PET), tested for adhesion and stability under different accelerated environmental testing conditions. These inks further tested for thermal stability, thermoforming, and injection molding stability.
For example, Table 12 below summarizes various characteristics and testing performance attributes of conducting compositions as described in Example 1 to Example 26.
Further, Table 13 below summarizes various characteristics and testing performance attributes of non-conducting compositions as described in Example 27 to Example 61.
Intercompatibility of conductive and nonconductive materials along with compatibility with different flexible polymer substrates, decorative inks, adhesives, encapsulants and injection molding resins are important aspects for the manufacturing of IME and similar structures.
Compatibility of Wet Silver Ink Compositions with Various PC Substrates
The wet silver ink compositions are highly compatible with various PC substrates. The compatibility of wet silver inks (Example 1, 17, 23 and 25) with PC film substrates (Makrafol DE1.4) was investigated, with microscopic images of screen printed patterns (1000 μm line) of wet silver inks being captured at different time intervals (immediately, i.e., 0 min, 1, 2, 3, 5 and 15 min) before drying using a jet dryer. These results depict very good compatibility of silver inks with PC substrates.
Inter-Compatibility of Silver Ink and Dielectric Ink Compositions, and Compatibility with Various Nascent and Graphic Coated PET and PC Substrates
The disclosed silver ink and dielectric ink compositions are highly intercompatible and compatible with various nascent and graphic coated PET and PC substrates.
Adhesion tests (tested as per ASTM F1842-09) to demonstrate the compatibility of dried Silver and Dielectric Inks with various polymer film substrates (PC, PET and graphic coated PC film substrates) were carried out. Table 14 below summarizes the representative adhesion test results of silver ink (Example 2) and dielectric ink (Example 33 and 34) on various nascent PET (MacDermid Autotype AHU5, CT5 and HT5), nascent PC (Makrafol DE1.4) and graphic ink printed on PC (MacDermid Autotype XFG2502L-HTR952) film substrates. Table 4 also summarizes representative adhesion test results of silver ink (Example 2) on dielectric ink (Example 33 and 34) coated on various nascent PET (MacDermid Autotype AhU5, CT5 and HT5), nascent PC (Makrafol DE1.4) and graphic ink printed on PC (MacDermid Autotype XFG2502L-HTR952) film substrates.
Adhesion tests were also carried out on the following:
All these samples show 5B adhesion test results as per ASTM F1842-09.
The disclosed silver ink and dielectric ink compositions are highly robust and stable when tested at different accelerated environmental test conditions as per JEDEC 22-A101 (Environmental Testing, 85° C/85 RH) and IEC 60068-2-2 (Thermal Aging Test/Dry Heat Test). A typical test structure consisted of 500 μm lines of conducting silver circuit traces prepared by screen printing on nascent PC and drying by jet drying. Electrical resistances of these lines are measured before and after exposing to either 85° C/85 RH or 110° C. for 100-1000 h. Also, a stack of Dielectric Ink//Silver Ink//Dielectric Ink samples were also prepared and electrical resistances conducting silver circuit traces were measured. Further, adhesion of these inks was tested as per as per ASTM F1842-09 after exposing these samples to either 85° C./85 RH or 110° C. for 100 -1000 h.
Table 5 summarizes percentage of change of electrical resistance (% AR, calculated as per Equation 1) of the representative test structures prepared using Silver Ink (Example 10) and a stack of Dielectric Ink (Example 47)//Silver Ink (Example 10)//Dielectric Ink (Example 47) on nascent PC (Makrafol DE1.4) after exposing to 85° C/85 RH or 110° C. for 100h.
Percentage of change of electrical resistance (%JR)=[Resistance after−Resistance before/Resistance before] (Equation 1)
Adhesion testing of the above reliability test structures after exposure to environmental testing conditions were conducted as per ASTM F1842-09 and results are summarized in Table 15.
Stack of Screen-Printed Silver Layer//Dielectric Layer//Graphic Layer coated Thermoformable PC Substrate
One of the key attribute of the conductive and non-conductive compositions is the thermoformability. This is particularly important for IME and similar applications. To assess thermoformability of the 2D circuit traces, formed into 3D circuits/devices, a cone structure test vehicle was employed. To determine the thermoforming attribute of the traces an in-house developed procedure referred to as ‘Cone Formability Test Procedure’ was used. In this procedure, conductivity of a series of circuit traces is measure on a flat polymeric substrate. After forming, change in electrical resistance along with other failure mechanisms is used to assess the degree of thermoformability. This test structure has straight line traces with 150 μm, 300 μm, 500 μm and 1000 μm line widths. These flat line structures are thermoformed into a cylindrical conical shape that can be positive or negative. During thermoforming, various traces experience stretching that can vary from 0 to 58%. Key performance metric that determines thermoformability to be stretched without breaking or delaminating from the substrate and preferably with a low change in electrical resistance.
Thermoforming attributes of silver inks were evaluated as per the ‘Cone Formability Test Procedure’ as described previously. In a typical process, silver ink was printed on a thermoformable polymer substrate (eg. PC or PET) and electrical resistances of the conducting test circuits were measured before and after thermoforming process to record the change of resistance at various % strain.
Compatibility and Thermoforming Attribute of Silver Inks with Various PC Substrates
Compatibility and thermoforming attribute of silver inks with various PC substrates were evaluated as per the ‘Cone Formability Test Procedure’ as described previously. In a typical process, silver ink was printed on different types of thermoformable PC substrate (DE as Makrafol DE1.4, V3 as MacDermid Autotype XFG250 M HCL V3, and 2L as MacDermid Autotype XFG250 2L substrates) as well as graphic Ink coated PC substrate (GCPC as MacDermid Autotype XFG2502L-HTR952). Since, graphic ink coated PC substrate (GCPC) was found mildly conducting, to avoid shorting, a layer of Dielectric Ink (Example 33) was printed before printing of Silver inks. Electrical resistances of the Silver conducting test circuits were measured before and after thermoforming process to record change of resistance at various % strain. After forming, change in electrical resistance along with other failure mechanisms is used to assess the degree of thermoformability. For example,
Compatibility and thermoforming attribute of a two-stack, Dielectric and Silver Inks were evaluated as per the ‘Cone Formability Test Procedure’ as described previously. A typical two-stack circuit assembly was prepared by first printing of a Dielectric ink layer (Barrier Dielectric layer) on a thermoformable polymer substrate (eg. PC or PET) followed by printing of conducting silver circuit traces. The electrical resistances of the Silver conducting test circuits were measured before and after thermoforming process to record the change of resistance at various % strain.
Silver Ink (Example 11) printed on Dielectric Ink (Example 35), before and after thermoforming, respectively. The resistance before (
Compatibility and thermoforming attribute of a three-stack dielectric and silver inks were evaluated as per the ‘Cone Formability Test Procedure’ as described previously. A typical three-stack circuit assembly was prepared by first printing of a dielectric ink layer (barrier dielectric layer) on a thermoformable polymer substrate (eg. PC or PET), next printing of conducting silver circuit traces and followed by printing of another Dielectric ink layer (Protection layer). The electrical resistances of the conducting Silver test circuits were measured before and after thermoforming process to record the change of resistance at various % strain.
Thermoformable Conductive Compositions used as Conductive Adhesive to Attach Various SMD Components
Thermoformable conductive compositions disclosed in Example 1 to Example 26 can also be used as conductive adhesive to attach various SMD components, LED etc. to thermoformable conductive silver ink circuit traces. Viscosities of these formulations can be optimized to either dispose these conductive adhesives by dispensing or stencil printing. Compatibility of the thermoformable conductive adhesives with Silver Ink and substrates are very crucial to fabricate IME structures.
Thermoforming attribute of a representative conductive circuit structure, where components (such as, SMD 1206 Chip or SMD 1206 LED) are attached using conductive adhesive (Example 7) on Silver Ink (Example 10) on a thermoformable PC substrate (DE as Makrafol DE1.4), were evaluated as per the ‘Cone Formability Test Procedure’ as described previously. A typical assembly was prepared by first printing of a Silver ink (Example 10) conducting circuit traces on a thermoformable polymer substrate (DE), next dispensing of Example 7 and followed by component attachments of SMD 1206 Chip and SMD 1206 LED). Electrical continuity of these conducting circuit structure was checked by supplying electric current before and after thermoforming. For example,
The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/025396 | 10/7/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63088530 | Oct 2020 | US |
