Silver nanoparticle-based ink

Abstract

The present invention relates to ink formulations based on silver nanoparticles that can be advantageously used for electromagnetic interference ("EMI") shielding coatings of semiconductor chips, particularly epoxy molding compound ("EMC") chips. In particular, the present invention relates to such ink formulations based on silver nanoparticles, which inks are stable, have improved electrical conductivity, and are particularly suitable for application by spraying.

Description

[Technical Field]

[0001] The present invention relates to ink formulations based on silver nanoparticles that can be advantageously used for electromagnetic interference ("EMI") shielding coatings of semiconductor chips, particularly epoxy molding compound ("EMC") chips. In particular, the present invention relates to such ink formulations based on silver nanoparticles, which inks are stable, have improved electrical conductivity, and are particularly suitable for application by spraying.

[0002] The present invention also relates to the use of the ink in the field of electromagnetic interference ("EMI") shielding coating by spraying the ink onto semiconductor chips, particularly epoxy molding compound ("EMC") chips. [Background technology]

[0003] Similar inks have already been described by the applicant in patent applications WO 20160184979(A1) published on 24 November 2016 and WO 2020120252(A1) published on 18 June 2020, which inks are particularly suitable for application by serigraphy and inkjet, respectively.

[0004] The development of conductive nanoparticles offers new applications and allows many new uses to be envisaged. Nanoparticles have a very large surface area / volume ratio, and substituting their surface with surfactants entails a change in certain properties and the possibility of dispersing them.

[0005] Their small size may result in quantum confinement effects in some cases. The term "nanoparticle" is used when at least one of the particle's dimensions is 250 nm or less. If a nanoparticle does not have a defined shape, it can be a bead (1 to 250 nm), a rod (L<200 to 300 nm), a wire (hundreds of nanometers or even a few microns), a disk, a star, a pyramid, a tetrapod, a cube, or a crystal.

[0006] Several processes have been developed for the synthesis of conductive nanoparticles, among which the following may be mentioned, but in a non-exhaustive list: - physical processes: chemical vapor deposition (CVD), when a substrate is exposed to volatilized chemical precursors that react or decompose on its surface. This process generally leads to the formation of nanoparticles whose morphology depends on the conditions used; thermal evaporation; molecular beam epitaxy, when the atoms that make up the nanoparticles collide with the substrate at high speed (where they become bonded); gas flow morphology; - Chemical or physicochemical processes: microemulsions; laser pulses in solutions when solutions containing precursors are irradiated with laser light. Nanoparticles are formed in solutions along the laser beam; synthesis by microwave irradiation; surfactant-assisted oriented synthesis; ultrasound-mediated synthesis; electrochemical synthesis; organometallic synthesis; synthesis in alcoholic media.

[0007] Physical syntheses consume more starting materials with significant losses. They are generally time-consuming and require high temperatures, making them unattractive for industrial-scale production. This makes them unsuitable for certain substrates, such as flexible substrates. Furthermore, synthesis is carried out directly on the substrate within a compact framework. These manufacturing methods have proven relatively rigid and do not allow for manufacturing on large substrates. However, they may be perfectly suitable for producing silver nanoparticles used in the ink formulations according to the present invention.

[0008] Chemical synthesis has many advantages. First, it works in solution; the conductive nanoparticles thus obtained are already dispersed in a solvent, facilitating their storage and use. In many cases, the nanoparticles are not bound to a substrate at the end of the synthesis, which allows for greater flexibility in their use. This opens the way to the use of substrates of different sizes and properties. These methods also allow for better control of the starting materials used, reducing losses. Correct adjustment of the synthesis parameters results in better control of the synthesis and growth rate of the conductive nanoparticles. This also ensures good batch-to-batch reproducibility and good control of the final morphology of the nanoparticles. The ability to chemically produce nanoparticles quickly and in large quantities while maintaining a certain degree of flexibility in terms of the product makes industrial-scale production possible. The production of dispersed conductive nanoparticles opens up many possibilities for their customization. Therefore, it is possible to adjust the nature of the stabilizers present on the nanoparticle surface according to the intended application. In particular, various methods exist for wet deposition. In all cases, particular attention must be paid to the physical properties of the ink, such as surface tension or viscosity. The adjuvants used in the formulation of nanoparticle-based inks allow them to comply with the requirements of the deposition method. However, surface ligands also influence these parameters, and their selection proves to be crucial. Therefore, it is important to have a holistic view of the ink in order to combine all the involved elements (nanoparticles, solvents, ligands, and adjuvants) and obtain a product that is compatible with the target application. Summary of the Invention

[0009] It is an object of the present invention to overcome one or more of the shortcomings of the prior art by providing an ink suitable for non-contact spraying and improved homogeneous coating for use as an electromagnetic interference ("EMI") shielding coating. The ink is characterized by a set of improved properties, among which the following are mentioned by way of example: - greater stability, e.g., greater stability over time than current inks, and / or - non-toxicity of the solvent and nanoparticles, and / or - Improved surface tension, and / or - preservation of the intrinsic properties of the nanoparticles after application by spraying, and / or - better annealing (homogeneity of the deposit), and / or - improved adhesion on the substrate, and / or - No bubbles / foaming after spraying, and / or - Excellent electrical conductivity with annealing temperatures typically between 120°C and 220°C.

[0010] While the inks described in WO 2016 / 184979 A1 and WO 2020120252 A1 already meet many of the requirements set out above, the Applicant has now succeeded in developing new ink compositions which make it possible to further improve both their performance and their ability to be sprayed, in particular for use in the field of electromagnetic interference ("EMI") shielding coating by spraying said inks onto semiconductor chips, in particular epoxy molding compound ("EMC") chips.

[0011] ink Therefore, the present invention provides at least - 25% by weight or more of silver nanoparticles; - 15% by weight or more of an aliphatic monohydric alcohol; - 10% by weight or more of polyols and / or polyol derivatives, - 5% by weight or more of terpene alcohols;

[0012] and less than 0.5% by weight of water,

[0013] The ink composition relates to an ink composition in which the sum of the silver nanoparticles, the aliphatic monohydric alcohol, the polyol and polyol derivatives, the terpene alcohol, and the water constitutes at least 90% by weight of the ink composition.

[0014] The present invention also relates to the synthesis of the ink composition.

[0015] The present invention also relates to the use of the ink composition as an electromagnetic interference ("EMI") shield by spraying onto semiconductor chips, particularly epoxy molding compound ("EMC") chips.

[0016] The present invention also relates to a process for spraying the ink composition onto semiconductor chips, particularly epoxy molding compound ("EMC") chips, as an electromagnetic interference ("EMI") shield. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 shows the visual difference in the uniformity of the spray deposit on the EMC chip between spray formulations S-CS91544 (comparison - left) and S-CS91547 (invention - right).

[0018] [Figure 2] Figures 2 and 3 show the microscopic difference in the uniformity of the spray deposit on the EMC chip between spray formulations S-CS91544 (comparison - Figure 2) and S-CS91547 (invention - Figure 3).

[0019] [Figure 3] Figures 2 and 3 show the microscopic difference in the uniformity of the spray deposit on the EMC chip between spray formulations S-CS91544 (comparison - Figure 2) and S-CS91547 (invention - Figure 3). DETAILED DESCRIPTION OF THE INVENTION

[0020] The viscosity of the ink composition is an important property for EMI to improve sprayability and flowability, which must ensure a high level of uniformity and homogeneity of the electromagnetic wave shielding film on all shielding surfaces of the semiconductor chip. The viscosity of the ink according to the present invention measured at 20°C is generally between 5 and 100 mPa.s, for example between 7.5 and 50 mPa.s, for example between 9 and 25 mPa.s.

[0021] The Applicant has discovered that the ink compositions based on silver nanoparticles according to the invention, thanks to the combination of compounds claimed and their respective concentrations, make it possible to obtain inks with improved properties, in particular improved stability, good sprayability and also improved conductivity in a viscosity range particularly suitable for use in the field of non-contact spraying for EMI shielding. In particular, the ink formulations based on silver nanoparticles according to the invention have a series of improved properties, among which the following may be mentioned by way of example: - greater stability, e.g., greater stability over time than current inks, and / or - non-toxicity of the solvent and nanoparticles, and / or - Improved surface tension, and / or - preservation of the intrinsic properties of the nanoparticles after application by spraying, and / or - better annealing (homogeneity of the deposit after spraying), and / or - improved adhesion on the substrate, and / or - No bubbles / foaming after spraying, and / or - Generally, excellent conductivity is exhibited at annealing temperatures of 120°C to 220°C, with significant improvement at 150°C to 180°C.

[0022] The conductive nanoparticle-based ink according to the present invention can be advantageously sprayed onto all types of substrates. Examples that may be mentioned include paper, polymers and polymer derivatives, composites, organic materials, and / or inorganic materials. In particular, the claimed ink is particularly suitable for EMI shielding of integrated circuit ("IC") packaging, for example, epoxy molding compound ("EMC"). In fact, most of these packages are molded from epoxy plastics, which provide adequate protection for semiconductor devices and mechanical strength for supporting leads and handling the IC package. Examples of such plastics are cresol novolacs, siloxane polyimides, polyxylylenes, silicones, polyepoxides, and / or bisbenzocyclobutene materials.

[0023] In one embodiment of the present invention, a semiconductor package is provided that includes an electromagnetic wave shielding layer based on the claimed ink for protecting a semiconductor chip in the semiconductor package from external factors and for shielding electromagnetic waves.

[0024] As the market for electronic products expands, the demand for more functionality and smaller portable devices is rapidly increasing, and technology is therefore leading to smaller and lighter electronic components within electronic products. Here, in addition to the miniaturization of various electronic components, multiple individual semiconductor chips may be included within a single semiconductor package.

[0025] Although not a preferred embodiment of the present invention, the semiconductor package may further include an insulating layer between the semiconductor chip and the shielding layer, the insulating layer including a thixotropic or hot-melt material. The thixotropic material may include at least one of composite fine silica, bentonite, surface-treated calcium carbonate microparticles, hydrogenated castor oil, metal soap, aluminum stearate, polyamide wax, polyethylene oxide, and linseed polymerized oil. The hot-melt material may include at least one of polyurethane, polyurea, polyvinyl chloride, polystyrene, acrylonitrile butadiene styrene, polyamide, acrylic, and polybutylene terephthalate. The thixotropic or hot-melt material may be cured by ultraviolet curing or thermal curing.

[0026] In one embodiment of the present invention, the semiconductor chip package to be shielded is a three-dimensional object having a top and side surface that can be advantageously treated with the claimed ink. Because this three-dimensional object may be made of layers of different materials, it is important that the shield provide adequate adhesion and uniformity of the sprayed layer on all surfaces to be shielded. Such materials include the epoxy-based compounds cited above, as well as illustrative examples such as copper, polyimide (e.g., Kapton), silicon, silicon-based compounds, silica, and the like.

[0027] The present invention also relates to a process for spraying our claimed ink composition onto at least two different materials of a semiconductor chip package as an electromagnetic interference ("EMI") shield, the package essentially comprising an epoxy molding compound ("EMC") with copper, polyimide (e.g., Kapton), silicon, silicon-based compounds, or silica.

[0028] Our claimed silver nanoparticle-based ink can be advantageously spray-coated onto electronic components to protect them from electromagnetic interference. This technology allows for the formation of efficient EMI shielding directly on chips through one-step spraying, preferably before the components are picked and placed on electronic flexible circuit boards. Using a very thin layer of sprayed ink, high shielding efficiency can be achieved, allowing for a reduction in the weight and size of the final electronic device. Conventional techniques for such shielding include adding a metal housing directly to the chip requiring shielding, which has several drawbacks, requires a large process line, and has a significant environmental impact. It also increases the weight of the system and takes up space on the printed circuit board ("PCB"). Another existing solution is metallization by physical vapor deposition (PVD). While this method is lighter for the final device, it is a complex process and requires a large investment in the production line.

[0029] On the other hand, our claimed solution is compatible with high-volume industrial production equipment (e.g., ultrasonic spray coating). Our claimed ink has been optimized and fine-tuned to exhibit strong adhesion on EMI, copper, PCB, and Si wafers, creating a uniform, ultrathin shielding layer on the top and sidewalls of the external package. The ink exhibits better electrical performance, allowing for better EMI shielding on top of the chip compared to copper foil. Furthermore, our claimed coating solution is resistant enough to pass electronic post-processing standards such as solvent wash baths and durability / reliability tests under environmental conditions. Our claimed solution is environmentally friendly, as it uses non-toxic and non-carcinogenic, mutagenic, and reproductively toxic (CMR) solvents in its formulation. Furthermore, less investment is required to adapt existing production lines.

[0030] Silver nanoparticles The silver nanoparticles constitute at least 25 wt% of the ink composition according to the present invention. In particular, the silver nanoparticle content in the ink composition according to the present invention is at least 30 wt%, for example at least 35 wt%, and preferably less than 60 wt%, for example less than 50 wt% (weight of silver nanoparticles divided by weight of ink composition).

[0031] According to a variant of one embodiment of the present invention, the object of the present invention is in particular achieved when compound "a" consists of silver nanoparticles having a size between 1 and 250 nm, the nanoparticle size being defined as the average diameter of the silver-containing particles, excluding stabilizers, as determined, for example, by transmission electron microscopy.

[0032] According to a variant of this embodiment of the present invention, the silver nanoparticles are spheroidal and / or spherical. In the present invention and in the following claims, the term "spheroidal" means that the shape resembles that of a sphere, but is not perfectly round ("quasi-spherical"), e.g., elliptical. The shape of the nanoparticles is generally determined by photographs taken under a microscope. Thus, according to a variant of this embodiment of the present invention, the nanoparticles have a diameter between 1 and 250 nm.

[0033] According to a variant of one embodiment of the present invention, the silver nanoparticles, if they do not have a defined morphology, are in the form of beads (1 to 250 nm), rods (L<200 to 300 nm), wires (hundreds of nanometers or even a few microns), cubes, platelets or crystals.

[0034] According to certain embodiments of the present invention, the silver nanoparticles are previously synthesized by physical or chemical synthesis. Any physical or chemical synthesis can be used in the context of the present invention. In one particular embodiment according to the present invention, the silver nanoparticles are obtained by chemical synthesis using organic or inorganic silver salts as silver precursors. Non-limiting examples that may be mentioned include silver acetate, silver nitrate, silver carbonate, silver phosphate, silver trifluoride, silver chloride, and silver perchlorate, either alone or in mixtures. According to one variant of the present invention, the precursor is silver acetate.

[0035] Therefore, the nanoparticles preferably used in the present invention, regardless of the synthesis method (physical or chemical), are characterized by a D50 value of preferably between 1 and 250 nm. They are also preferably characterized by a monodisperse (homogeneous) distribution without agglomerates. D50 values ​​of 10 to 150 nm for spheroidal silver nanoparticles can also be used advantageously.

[0036] Aliphatic monohydric alcohol The aliphatic monohydric alcohol constitutes at least 15% by weight of the ink composition according to the present invention. In particular, the content of the aliphatic monohydric alcohol in the ink composition according to the present invention is at least 20% by weight, for example at least 25% by weight, and preferably less than 40% by weight, for example less than 30% by weight (weight of the aliphatic monohydric alcohol divided by the weight of the ink composition).

[0037] The aliphatic monohydric alcohol is preferably selected from the group consisting of ethanol, propanol, butanol, pentanol, and hexanol, and isomers thereof (e.g., isopropanol, n-butanol, tert-butanol), and / or mixtures of two or more of said aliphatic monohydric alcohols. Isopropanol is particularly suitable for EMI shielding spray applications of the ink.

[0038] Polyol and / or polyol derivative The polyol and polyol derivatives constitute at least 10% by weight of the ink composition according to the present invention. In particular, the content of polyol and polyol derivatives in the ink composition according to the present invention is at least 15% by weight, for example at least 19% by weight. Preferably, the content is less than 35% by weight, for example less than 27% by weight (weight of polyol and polyol derivatives divided by weight of the ink composition).

[0039] The polyols and / or polyol derivatives are preferably characterized by a boiling point of less than 260° C. Examples that may be mentioned include glycols (e.g., ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 2,3-butylene glycol, pentamethylene glycol, hexylene glycol, etc.) and / or glycol ethers (e.g., glycol mono- or diethers, among which examples that may be mentioned are ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol phenyl ether, propylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether, diethylene glycol butyl ether, propylene ... Examples of suitable solvents include ethanol methyl ether, propylene glycol butyl ether, propylene glycol propyl ether, dipropylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, glyme, diethylene glycol diethyl ether, dibutylene glycol diethyl ether, diglyme, ethyl diglyme, and butyl diglyme, and / or glycol ether acetates (e.g., 2-butoxyethyl acetate, diethylene glycol monoethyl ether acetate, diethylene glycol butyl ether acetate, and propylene glycol methyl ether acetate), and / or mixtures of two or more of the aforementioned solvents. Dipropylene glycol monomethyl ether, also known as Dowanol DPM, 2-(2-butoxyethoxy)ethan-1-ol, also known as Butyl Carbitol, and propylene glycol methyl ether acetate, also known by the abbreviation PGMEA, are particularly suitable solvents for formulations according to the present invention. In a preferred embodiment according to the present invention, the ink contains a mixture of these three solvents.

[0040] terpene alcohol The terpene alcohol constitutes at least 5% by weight of the ink composition according to the present invention. In particular, the content of the terpene alcohol in the ink composition according to the present invention is at least 6% by weight, for example at least 8% by weight, and preferably less than 18% by weight, for example less than 15% by weight (weight of the terpene alcohol divided by the weight of the ink composition).

[0041] The terpene alcohols are preferably selected from menthol, nerol, cineol, lavandulol, myrcenol, terpineol (α-, β-, γ-terpineol and / or terpinen-4-ol; preferably α-terpineol), isoborneol, citronellol, linalool, borneol, geraniol and / or mixtures of two or more of said alcohols. Mixtures of α-terpineol and γ-terpineol have proven particularly suitable for the formulations according to the invention.

[0042] water Water comprises less than 0.5% by weight (weight of water divided by weight of ink composition) of the ink composition according to the present invention.

[0043] According to one embodiment of the present invention, the ink does not incorporate water into its composition. However, since some of the ink components can tolerate trace amounts of water as a function of their purity, it is understood that the total of these corresponding trace amounts of water is tolerated in the claimed ink. Therefore, the water content in the final ink generally depends essentially on the water content of the solvent used in its preparation. According to a specific embodiment of the present invention, the water content in the ink composition is less than 0.25% by weight, for example, less than 0.1% by weight, or even zero.

[0044] According to a preferred embodiment of the present invention, no water is added during the formulation of the claimed ink composition, except for trace amounts of water that may be present in the compounds of the ink formulation / preparation.

[0045] Adhesion promoter According to a variant of one embodiment of the present invention, the ink composition also contains at least one adhesion promoter, preferably at a concentration of more than 0.1% by weight, preferably more than 0.25% by weight, for example more than 0.5% by weight of the ink composition. The concentration of the adhesion promoter divided by the weight of the ink composition is preferably less than 2.5% by weight. Examples of adhesion promoters include vinylpyrrolidone / vinyl acetate copolymers, acrylic polymers, silanes, siloxanes, and / or polysiloxanes, the purpose of which is to improve resistance to various types of mechanical stress, for example, adhesion to a variety of substrates. A linear random copolymer of N-vinyl-2-pyrrolidone and vinyl acetate in a 30:70 to 70:30 (monomer ratio VP / VA), for example, a linear random copolymer of N-vinyl-2-pyrrolidone and vinyl acetate in a 60:40 ratio, is a preferred adhesion promoter. According to one preferred embodiment of the present invention, the ink composition contains at least 0.7% by weight of vinylpyrrolidone / vinyl acetate copolymer.

[0046] Specific examples of the preparation of inks according to the present invention are set forth below for illustrative purposes.

[0047] Any adhesion promoter is preferably dissolved in one of the solvents in the first step. Then, silver nanoparticles are added to this mixture along with the remaining solvent, and stirring is continued for 3 hours. Then, ultrasonic treatment is carried out for 15 minutes, and then finishing is carried out using a filtration process on a glass microfiber filter with a cutoff of 1 μm.

[0048] A further advantage of the ink according to the present invention lies in the fact that its preparation can be carried out under non-limiting pressure and / or temperature conditions, for example, under pressure and / or temperature conditions close to or identical to normal or ambient conditions. It is preferable for these pressure and / or temperature conditions to remain below 40% of normal or ambient pressure and / or temperature conditions. For example, the applicant has found that it is preferable to maintain the pressure and / or temperature conditions during the preparation of the ink at oscillation values ​​of up to 30%, preferably 15%, around the values ​​of normal or ambient conditions. Therefore, controlling these pressure and / or temperature conditions can be advantageously included in the ink preparation device to meet these conditions. This advantage associated with the preparation of ink under non-limiting conditions is also clearly reflected by the ease of use of the ink.

[0049] According to one embodiment of the present invention, the ink composition comprises at least: - 25% by weight or more of silver nanoparticles; - 15% by weight or more of an aliphatic monohydric alcohol; - 10% by weight or more of polyols and / or polyol derivatives, - 5% by weight or more of terpene alcohols; - 0.5% by weight or more of vinylpyrrolidone / vinyl acetate copolymer;

[0050] and less than 0.5% by weight of water,

[0051] The sum of all above-defined compounds constitutes at least 95% by weight of the ink composition. According to a particular variant of the invention, the sum of all above-defined compounds preferably constitutes at least 97.5%, at least 98%, at least 99% or even 100% by weight of the final ink.

[0052] According to one embodiment of the present invention, the silver ink may also optionally comprise an antioxidant. Examples of antioxidants that may be mentioned include: - Ascorbic acid or vitamin C (E300), sodium ascorbate (E301), calcium ascorbate (E302), 5,6-diacetyl L-ascorbic acid (E303), 6-palmityl L-ascorbic acid (E304); - Citric acid (E330), sodium citrate (E331), potassium citrate (E332) and calcium citrate (E333); - Tartaric acid (E334), sodium tartrate (E335), potassium tartrate (E336) and potassium sodium tartrate (E337); - butylated hydroxyanisole (E320) and butylated hydroxytoluene (E321); - octyl gallate (E311) or dodecyl gallate (E312); - sodium lactate (E325), potassium lactate (E326) or calcium lactate (E327); - Lecithin (E322); - natural tocopherol (E306), synthetic alpha-tocopherol (E307), gamma-tocopherol (E308) and delta-tocopherol (E309), which together constitute vitamin E; - eugenol, thymol and / or cinnamaldehyde, - Also, mixtures of two or more of said antioxidants.

[0053] According to one embodiment of the present invention, the silver ink may also optionally contain a dispersant. For example, an organic dispersant containing at least one carbon atom. These organic dispersants may also contain one or more non-metallic heteroatoms, such as halogenated compounds, nitrogen, oxygen, sulfur, or silicon. Examples include thiols and their derivatives, amines and their derivatives (e.g., amino alcohols and amino alcohol ethers), carboxylic acids and their carboxylate derivatives, and / or mixtures thereof.

[0054] Although this does not constitute a preferred embodiment according to the present invention, the ink composition may also include a rheology modifier, such as a urea-type rheology modifier (e.g., modified urea, polyurea, and / or mixtures thereof) and / or a cellulose-type rheology modifier (e.g., alkylcellulose (e.g., ethylcellulose), nanocellulose, nitrocellulose, and / or mixtures thereof). If present, the total concentration of such rheology modifiers in the ink is preferably less than 5 wt.%, less than 1 wt.%, less than 0.1 wt.%, or even less than 0.01 wt.%.

[0055] Although this does not constitute a preferred embodiment according to the present invention, the ink composition can also tolerate the presence of additional compounds, among which solvents are mentioned by way of example, such as hydrocarbons; alkanes containing 5 to 20 carbon atoms, such as pentadecane (C5H12), hexane (C6H14), heptane (C7H16), octane (C8H18), nonane (C9H20), decane (C10H22), undecane (C11H24), dodecane (C12H26), tridecane (C13H28), tetradecane (C14H30), pentadecane (C15H32), cetane (C16H34), heptadecane (C17H36), octadecane (C18H38), nonadecane (C19H40), eicosane ( Alkanes, of which examples include cyclohexane (C20H42), cyclopentane (C5H10), cyclohexane (C6H12), methylcyclohexane (C7H14), cycloheptane (C7H14), cyclooctane (C8H16) (preferably when not used as compound "b"), cyclonona (C9H18), cyclodecane (C10H20); aromatic hydrocarbons containing 7 to 18 carbon atoms, of which examples include toluene, xylene, ethylbenzene, ethyltoluene; and mixtures thereof. If present, the total concentration of such solvents in the ink is preferably less than 5 wt.%, less than 1 wt.%, less than 0.1 wt.%, or even less than 0.01 wt.%.

[0056] According to one embodiment of the present invention, the ink may be advantageously used for spray coating, as described in more detail below.

[0057] Spray Coating With the growing demand for advanced computing systems and the increasing power of personal portable devices, front-end manufacturers need to reduce the physical footprint of chips while integrating more functionality. According to the present invention, ultrasonic spraying, which can sputter a wide variety of materials while producing a uniform coating layer on the substrate, is a preferred technique for coating the claimed ink layer. Ultrasonic spraying preferably uses a spray tip (or nozzle) vibrated by an ultrasonic transducer.

[0058] As an illustrative example, the spray head is preferably an integrated assembly consisting of an ultrasonic transducer with a spray tip, a liquid applicator, and an air inductor (adjustable air flow through the air inductor determines the velocity of the spray).

[0059] The ultrasonic transducer vibrates at an ultrasonic frequency that may advantageously be comprised between 16 kHz and 180 kHz, for example comprised between 20 kHz and 100 kHz; for example comprised between 20 kHz and 60 kHz.

[0060] Silver ink is delivered to the spray nozzle on the ultrasonic transducer by a liquid applicator. The silver ink is stored in a container and supplied to the liquid applicator at a precisely controlled rate by a positive displacement pump. Ultrasonic vibrations from the spray tip break the liquid into small droplets and force them out of the tip as a spray. An air inductor is used to generate an airflow to shape and accelerate the ultrasonically generated spray. The spray coating parameters are, for example, pressure: 40-50 (PSI); head speed: 150-400 (mm / s); height Z = 40 mm; pitch = 10 mm; ink throughput: 0.1-3 mL / min; head tilt = 30°; nb layers: 1-4; nb directions: 1-4.

[0061] In one embodiment of the present invention, the spray nozzle is capable of coating a layer of sprayed material having a thickness comprised between 0.5 and 1.5 microns. For electromagnetic interference shielding in semiconductor chip applications, the thickness of the final ink layer (after curing at 150°C for 30 minutes) is preferably comprised between 1 and 5 microns, representing, for example, 1 to 5 passes of the spray nozzle device over the chip.

[0062] It will therefore be apparent to those skilled in the art that the present invention allows for embodiments in many other specific forms without departing from the field of application of the invention as claimed. The present embodiments are therefore to be considered as examples, but can be modified within the field defined by the appended claims.

[0063] The invention and its advantages will now be illustrated by the formulations summarized in the table below. The ink formulations were prepared according to the embodiments described herein above. The compounds used and their properties are given in the table.

[0064] The stability of the ink referred to in the present invention can be measured according to any suitable method. As an example, the measurement of the stability of the ink follows the standard procedure of Genes ink: during the stability test, the material is tested every month (under ambient conditions and storage between 4 and 5°C) for a total period of 6 to 12 months. All characterization methods are performed to verify the stability of the material, such as the viscosity of the ink, the solid content, and the conductivity of the coated sample.

[0065] S-CS91547 is a formulation according to the present invention, while S-CS91544 and S-CS11520 are formulations given for comparative purposes.

[0066] [Table 1]

[0067] Silver nanoparticles (Ag NPs) are spheroidal and have a D50 of 50 nm.

[0068] Butyl carbitol is 2-(2-butoxyethoxy)ethan-1-ol (diethylene glycol butyl ether).

[0069] Dowanol DPM is dipropylene glycol monomethyl ether.

[0070] PGMEA is propylene glycol methyl ether acetate.

[0071] TEGME is triethylene glycol monomethyl ether.

[0072] PVP-VA is a vinylpyrrolidone / vinyl acetate copolymer, specifically Ashland™ PVP / VA S-630 copolymer, a 60:40 linear random copolymer of N-vinyl-2-pyrrolidone and vinyl acetate produced by free radical polymerization.

[0073] [Table 2]

[0074] Spray coatings were fabricated on the same EMC chip as follows: Printer: Spray USI Prism 400; Pressure: 50 PSI; Head Speed: 300 mm / s; Height Z: 40 mm; Pitch: 10 mm; Ink Throughput: 0.8 mL / min; Head Tilt: 30 °C; Number of Layers: 4, 1 in each direction. During the spraying process, the EMC-sprayed samples were simultaneously dried on a hotplate at 60 °C for 5 min and then cured in a conventional oven at 150 °C for 30 min.

[0075] The sheet resistance of the ink referred to in the present invention can be measured according to any suitable method. By way of example, it can advantageously be measured according to the following method on a cured EMC sprayed sample, corresponding to the measurements collated in the table: - Mechanical Standard: S302 Resistance Stand from Microworld - 4-point head reference SP4-40045TFY (4 equally spaced collinear probes) - Current source reference: Agilent U8001A - Multimeter reference: Agilent U3400 - Measurement temperature: room temperature - Tension / resistance conversion factor: 4.5324 - A DC current is applied to the outer probe of the measurement head, resulting in a voltage increase between the other two points on the head. The sheet resistance is then calculated according to this formula: -

number

[0076] The content of silver nanoparticles referred to in the present invention can be measured according to any suitable method. By way of example, it can be advantageously measured according to the following method, corresponding to the measurements collated in the table: - Thermogravimetric analysis - Machine: TGA Q50 from TA Instrument - Crucible: Alumina - Method: Lamp - Measurement range: Room temperature to 600°C - Temperature increase: 20℃ / min

[0077] The viscosity of the ink referred to in the present invention can be measured according to any suitable method. By way of example, it can be advantageously measured according to the following method: - Machine: TA Instrument AR-G2 Rheometer - Conditioning time: 40 seconds -1 1 minute preshear / 1 minute equilibration - Test type: shear stage - Stage: 40s -1 , 100s -1 , and 1000s -1 - Stage duration: 5 minutes - Mode: Linear - Measurement: Every 10 seconds - Temperature: 20℃ - Curve reprocessing method: Newton's method - Reprocessing area: whole curve

[0078] The surface tension referred to in the present invention can be measured according to any suitable method. By way of example, it can be advantageously measured according to the following hanging drop method:

[0079] The measurements are carried out using a DataPhysics OCA 15 plus device equipped with a camera. This device allows measuring surface tensions in the range given by the manufacturer from 0.01 to 2000 mN / m ± 0.05 mN / m. The method is the pendant drop method.

[0080] During the measurement of surface tension, a droplet of the solution to be analyzed is generated in air from a needle connected to a syringe. An automated system allows for the control of the depression of the syringe plunger. The shape of the droplet or series of droplets is then recorded by a camera. Software then calculates the surface tension from these images.

[0081] Surface tension γ(Nm -1 ) is given by the following equation (simplified Laplace-Young equation):

[0082] γ=Δρgd 2 / H

[0083] During the ceremony:

[0084] Δρ(kg.m-3 ): density difference between the droplet liquid and the surrounding phase

[0085] g (gravitational acceleration at the Earth's surface): 9.81ms -2

[0086] d(m): Equatorial diameter

[0087] H: Shape factor

[0088] 1 / H is a function of S=ds / de, where ds is the diameter measured at a distance de from the base of the droplet. - Mechanical: OCA 15 from DataPhysics - Method: - Pendant Drop (Left) - Measuring volume: 0.2μL - Flow rate: 0.5μL / s - 1.65mm needle - Input ink density: 1.1675 - Measurement: Ink volume: 1mL of ink / measurement count = 4

[0089] The adhesion test referred to in this invention can be measured according to any suitable method. As an example, it can be advantageously measured according to the following simplified version of the ASTM D3359 standard: Use a diamond-tip pen and a metal ruler to make parallel and perpendicular cuts to form a grid pattern. Hold the pen between 15° and 30° to the plate. Use enough force to reach the surface of the substrate when cutting. The ruler should be placed on the uncut part of the surface. The reference tape is 3M610 (12.7 mm; 4.7 N / cm). Cut the tape to a length of approximately 75 mm, place the center of the tape on the grid, and then spread it over the surface. Leave a free area to allow the tape to be easily removed. Press the tape firmly with your fingers to stick it all over. Wait 90±30 seconds (use a stopwatch). Quickly remove the tape without tearing by bringing the angle with the substrate closer to 180°. The results are noted according to the standard's scale of 0B to 5B, with 0B being 100% of the coating removed and 5B being 0% of the coating removed.

[0090] Generally, annealing temperatures between 120°C and 220°C show good conductivity, as reflected by sheet resistance measurements.

[0091] The ink composition according to one variant of the invention is characterized by a sheet resistance characteristic value of less than 350 mOhm / square at a thickness of 500 nm or less (annealing temperature 150° C.).

[0092] The thickness referred to in the present invention can be measured according to any suitable method. As an example, the measurement can be advantageously carried out with a 1D mechanical profilometer, model Alpha Step IQ (KLA Tencor). A metal clamp is used to draw a straight line through the location of the square resistance measurement. Measurement method: Measure using default settings (range: 20 μm, length: 500 μm, speed: 50 μm / s, frequency: 50 Hz, duration: 1 time, 2 deposits). Electrical resistivity (μΩ.cm) = R (μΩ / square) × thickness (cm).

[0093] A comparison of spray coatings made with the above formulations provides a good example of the visualization of the benefits provided by the present invention. Specifically, a significant improvement in the uniformity of spray formulation S-CS91547 is observed compared to the uniformity of S-CS91544.

[0094] These visual observations are also confirmed by microscopic observation: the deposits are observed using a Dino-Lite Edge AM4000 digital microscope, which allows measurements in the range of x650 to x950 (1280 x 1024 pixels). The microscope has only one zoom, and the focal length should be adjusted to obtain a clear image. Microscopic images of the S-CS91544 deposit show larger droplets of ink that are not fully fused with larger open spaces between the droplets compared to the S-CS91547 deposit.

Claims

1. At least the following: 25% by weight or more of silver nanoparticles; 15% by weight or more of an aliphatic monohydric alcohol; 10% by weight or more of a polyol and / or a polyol derivative; 5% by weight or more of a terpene alcohol; and less than 0.5 wt. % water, An ink composition comprising: An ink composition, wherein the sum of the silver nanoparticles, the aliphatic monohydric alcohol, the polyol and polyol derivatives, the terpene alcohol, and the water comprises at least 90% by weight of the ink composition.

2. At least the following: 25% by weight or more of silver nanoparticles; 15% by weight or more of an aliphatic monohydric alcohol; 10% by weight or more of a polyol and / or a polyol derivative; 5% by weight or more of a terpene alcohol; 0.5% by weight or more of vinylpyrrolidone / vinyl acetate copolymer; and less than 0.5 wt. % water, An ink composition comprising: An ink composition, wherein the sum of the silver nanoparticles, the aliphatic monohydric alcohol, the polyol and polyol derivatives, the terpene alcohol, the vinylpyrrolidone / vinyl acetate copolymer, and the water comprises at least 95% by weight of the ink composition.

3. 3. The ink composition according to claim 1, wherein the viscosity of the ink measured at 20°C is between 5 and 100 mPa.s.

4. 4. The ink composition of claim 1, wherein the silver nanoparticles are spheroidal and have a D50 value between 10 and 150 nm.

5. The ink composition of claim 1 , wherein the aliphatic monohydric alcohol is isopropanol.

6. 6. An ink composition according to claim 1, wherein the polyol and / or polyol derivative comprises a mixture of one or more glycol ethers and one or more glycol ether acetates.

7. 7. The ink composition according to claim 1, wherein the polyol and / or polyol derivative comprises a mixture of dipropylene glycol monomethyl ether, 2-(2-butoxyethoxy)ethan-1-ol, and propylene glycol methyl ether acetate.

8. The ink composition of claim 1 , wherein the terpene alcohol is terpineol.

9. 3. The ink composition of claim 2, wherein the vinylpyrrolidone / vinyl acetate copolymer is a linear random copolymer of N-vinyl-2-pyrrolidone and vinyl acetate in a monomer ratio of 30:70 to 70:

30.

10. 10. An ink composition according to any one of claims 1 to 9, wherein the water content in the ink composition according to the invention is less than 0.25% by weight, such as less than 0.1% by weight, or even zero.

11. Use of the ink composition according to any one of claims 1 to 10 as an electromagnetic interference shield by spraying it onto a semiconductor chip.

12. Use of the ink composition of any one of claims 1 to 10 as an electromagnetic interference shield by spraying it onto epoxy molding compound chips.

13. 12. The use according to claim 11 as electromagnetic interference shielding by spraying semiconductor chips with an ultrasonic spray nozzle.

14. 11. Use of an ink composition according to any one of claims 1 to 10, wherein the ultrasonic transducer of the ultrasonic atomizing nozzle vibrates at an ultrasonic frequency comprised between 20 kHz and 60 kHz.

15. 11. Sprayed epoxy molding compound chips by using the ink according to any one of claims 1 to 10, after curing at 150°C for 30 minutes with a final ink layer thickness comprised between 1 and 5 microns.

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