Dual-curable electronic component impregnating composition

Abstract

The present invention relates to an electronic component impregnating composition comprising at least one polymerizable ethylenically unsaturated monomer, an initiator system comprising at least one photolabile initiator and at least one thermolabile initiator and a reactive thiol as well as the use and the application thereof. The composition comprises an at least trifunctional (meth)acrylate, a poly(oxyalkylene glycol) di(meth)acrylate and a linear or branched diurethane di(meth)acrylate. The thermolabile initiator has a 10-hour half life temperature of ≤ 50 °C.

Description

[0001] Dual-Curable electronic component impregnating composition

[0002] Technical field of the invention

[0003] The present invention relates to an electronic component impregnating composition comprising at least one polymerizable ethylenically unsaturated monomer, an initiator system comprising at least one photolabile initiator and at least one thermolabile initiator and a reactive thiol as well as the use and the application thereof.

[0004] Technical Background

[0005] In the electronics industry, the protection and reinforcement of electronic components are critical for ensuring their long-term functionality and reliability. Components such as printed circuit boards (PCBs), capacitors, connectors, sensors, and integrated circuits are frequently subjected to harsh operating environments that include exposure to moisture, chemicals, mechanical stress, and thermal cycling. To mitigate these risks, various impregnating compositions have been developed and applied to electronic components to provide a protective barrier.

[0006] Traditional impregnation techniques often involve the use of thermally cured resins. These methods, while effective in some cases, present several limitations. The thermal curing process typically requires elevated temperatures, which can induce thermal stress and potentially damage sensitive electronic components. Additionally, the longer curing times associated with thermal processes can hinder manufacturing efficiency and increase production costs.

[0007] Moreover, solvent-based impregnating compositions, which have been widely used, pose environmental and safety concerns due to the emission of volatile organic compounds (VOCs). The handling and disposal of such solvents require stringent regulatory compliance, adding complexity and cost to the manufacturing process.

[0008] Recent advancements have introduced photoinitiated polymerization as a promising alternative for electronic component impregnation. This technology leverages light-activated initiators to rapidly cure compositions at ambient or slightly elevated temperatures. Photoinitiated polymerization offers several advantages over traditional thermal curing methods, including faster curing times, lower energy consumption, and reduced thermal stress on the components.

[0009] However, the implementation of photoinitiated polymerization for electronic component impregnation is not without challenges. On assembled circuit boards, so-called shadow areas arise. In these shadow areas, such as around capacitors or connectors, coatings cannot be photochemically initiated. This leads to incomplete polymerization and, consequently, inadequate protection against moisture, corrosion, or oxidation. The development of suitable electronic component impregnating compositions that provide excellent adhesion, mechanical strength, and chemical resistance while maintaining rapid and uniform curing remains a significant technical hurdle.

[0010] US 4,591 ,522 describes a photocurable, liquid-at-ambient temperature, hydrolysis resistant and fire-retardant composition consisting of (1) the reaction product of (a) an aliphatic unsaturation containing chlorendate, and (b) a non-ester containing polythiol, said (a) and (b) being reacted non-stoichiometrically; (2) a member of the group consisting of either (a) or (b) in an amount up to that sufficient to react with the excess of the other in (1) and a liquid acrylate monomer or oligomer, and (3) at least one photoinitiator.

[0011] US 2023 / 015729 A1 provides a dual-curable hybrid adhesive composition including a photoinitiator, a thermal initiator, and a thiol group-containing compound, and more particularly, to an adhesive composition which may be cured through a single curing by ultraviolet (UV) light or heat, and where thermal curing proceeds concurrently with UV curing by a heat generated during the UV curing such that even a light shield portion which may not transmit UV light therethrough may be sufficiently cured.

[0012] CN 114874469 A discloses a method for rapidly preparing a flexibly-expandable dark-color fiber composite material based on a two-stage and photo-thermal synergistic technology and application of the method. The method comprises the following steps: step 1 , preparing a resin system; step 2, coating carbon fibers with the resin system prepared in the step 1 to completely infiltrate the carbon fibers, covering the carbon fibers with a PET film, and transferring the carbon fibers to a dark place at room temperature to carry out first-stage curing; and step 3, placing the room-temperature thermocuring intermediate product in the first stage at room temperature, and carrying out photo-thermal synergistic curing to obtain the flexibly expandable dark fiber composite material. According to the method, the deep-color fiber composite material is prepared through first-stage room-temperature thermocuring and second-stage photo-thermal synergistic curing, the problem of rapid curing of the deep-color fiber composite material with soft-rigid conversion can be solved, and a first-stage roomtemperature thermocuring product can be flexibly folded and unfolded; and the second-stage photo-thermal synergistic curing is used for widening the application prospect of photo-curing in the field of dark fiber composite materials.

[0013] CN 111334198 A relates to a UV double-component double-curing structural adhesive. The structural adhesive is characterized by comprising a component A and a component B, wherein the component A is a main agent part, the component B is a curing agent part, and the volume ratio of the component A to the component B in a double-component rubber tube is 1 :1 ; the component A comprises acrylic resin, bisphenol polyether polyol with an acrylic acid structure, epoxy resin and a polymerization inhibitor; and the component B comprises bisphenol polyether polymercaptan, a photoinitiator and a peroxide radical initiator. The structural adhesive has good strength and flexibility, has a good refractive index due to the sulfur element, realizes a good transparent optical effect, can control the pre-fixing time by using UV, can solve the problem of curing of a shadow part of the UV glue, and can be widely applied to the fields of structural bonding and gap filling. US 4,935,454 describes a dielectric composition capable of being polymerized for use in sealing electrical and electro-optical connectors and devices is disclosed. Said composition is comprised of a major proportion of vinyl ester resins, a minor proportion of polymerizable acrylic diluent monomers, and a polymerization activation system comprised of from about 0.25 percent to about 17 percent by weight of the resin. A process of the present invention includes applying a layer of said composition to desired areas or to desired locations such as apertures surrounding electrical terminals extending from a connector housing, and exposing said composition to actinic radiation which activates the polymerization activation system which causes the composition to polymerize to form a sealant material that exclused solder and solvents from the connector and its apertures.

[0014] CN 111929989 A discloses a photosensitive resin composition, a preparation method thereof, a photosensitive organic carrier and yellow light slurry. The photosensitive resin composition comprises an acidic monomer, a high-oxygen-content monomer, a skeleton monomer, a photocuring monomer and a thermal initiator. According to the technical scheme, the photosensitive resin composition which is well matched with inorganic precious metal powder, high in resolution ratio and good in adhesive force can be obtained.

[0015] CN 117467228 A belongs to the technical field of liquid crystal elastomers, and discloses a multi-responsive liquid crystal elastomer composite film as well as a preparation method and application thereof. The multi-responsive liquid crystal elastomer composite film comprises a liquid crystal elastomer and a functional medium combined on the surface of the liquid crystal elastomer, the functional medium comprises acrylate group functionalized conductive carbon and metal silver compounded on the surface of the acrylate group functionalized conductive carbon. According to the multi-responsiveness liquid crystal elastomer composite film, when the liquid crystal elastomer is heated and passes through a phase change point, a liquid crystal network can be converted from parallel orientation to isotropic orientation, and shrinkage deformation of the liquid crystal elastomer is macroscopically caused; and the functional medium transfers heat to the liquid crystal elastomer matrix by virtue of excellent photo-thermal performance and electric heating performance, and induces the composite film to deform, so that the composite film has an excellent stimulation response characteristic. Detailed description

[0016] The present invention relates to an electronic component impregnating composition comprising at least one polymerizable ethylenically unsaturated monomer, an initiator system comprising at least one photolabile initiator and at least one thermolabile initiator and a reactive thiol. The composition comprises an at least trifunctional (meth)acrylate, a poly(oxyalkylene glycol) di(meth)acrylate and a linear or branched diurethane di(meth)acrylate and the thermolabile initiator has a 10-hour half life temperature of < 50 °C.

[0017] The inventors have found that such a composition can at least partially cure in shadow areas of an article which are not accessible by UV radiation. This is even possible for very thin films of the composition, such as having a thickness of 50 pm or less. Such thin films would otherwise present considerable challenges in sustaining a shadow polymerization because of the rapid dissipation of the heat formed by the polymerization reaction. A sufficient degree of shadow polymerization improves processing and handling steps and reduces the time needed to fully cure the impregnated electronic component by a subseqent thermal step.

[0018] An electronic component impregnating composition is a material used to impregnate electronic components, such as coils, circuit boards, transformers, capacitors, connectors and other devices. An electronic component impregnating composition is mainly used to enhance the performance, reliability, and / or longevity of electronic components. The electronic component impregnating composition typically penetrates and encapsulates the electronic components, providing protection against environmental factors, mechanical stresses, and electrical failures.

[0019] The electronic component impregnating composition of the present invention comprises at least one polymerizable ethylenically unsaturated monomer. A polymerizable ethylenically unsaturated monomer is a type of molecule that contains one or more carbon-carbon double bonds (C=C) and can undergo polymerization, preferably by radical polymerization. The at least trifunctional (meth)acrylate serves to form a for polymer network formation and to increase the reaction heat of the polymer formation. It can be obtained from the reaction of triols, tetraols, pentaols, hexaols and the like with acrylic acid or methacrylic acid. Preferred are trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, dimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, di pentaerythritol penta(metha)crylate, dipentaerythritol hexa(metha)crylate or a mixture of at least two of the aforementioned compounds.

[0020] The poly(oxyalkylene glycol) di(meth)acrylate imparts flexibility to the polymer as brittle films are not desired in electronic component applications. It is preferably a poly(oxyethylene glycol) (meth)acrylate. It is also preferred that the poly(oxyalkylene glycol) di(meth)acrylate has > 5 to < 20 oxyalkylene groups. Particularly preferred are poly(oxyethylene) glycol diacrylates which are obtainable from the reation of the corresponding polyether diols with acrylic acid.

[0021] The linear or branched diurethane di(meth)acrylate also serves to impart flexibility to the polymer. Furthermore, such a component increases the viscosity of the composition. This is desired as it reduces the heat disspation during polymer formation. A low heat dissipation is beneficial for sustaining a thermal polymerization pathway. The diurethane di(meth)acrylate is prefereably the reaction product of an aliphatic a,w-diisocyanate (such as 1 ,5-pentamethylene diisocyanate, 1 ,6-hexamethylene diisocyanate or 2,2,4-trimethyl-1 ,6-hexamethylene diisocyanate) or with hydroxyalkyl(meth)acrylates (such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate or hydroxypropyl methacrylate).

[0022] The acrylates may be present in the composition according to the following weight percentages, based on the total weight of the composition. It is understood that the weight percentages add up to 100 weight-% or less. At least trifunctional (meth)acrylate: > 10 weight- % to < 50 weight-%, preferably > 25 weight-% to < 35 weight-%. Poly(oxyalkylene glycol) di(meth)acrylate: > 5 weight-% to < 30 weight-%, preferably > 10 weight-% to < 20 weight-%. linear or branched diurethane di(meth)acrylate: > 25 weight-% to < 75 weight-%, preferably > 45 weight-% to < 55 weight-%. The electronic component impregnating composition of the present invention further comprises an initiator system. An initiator system is a combination of substances that start the polymerization process. The initiator system of the present invention comprises at least one photolabile initiator and at least one thermolabile initiator. Preferably, the initiator system comprises at least one photolabile radical initiator and at least one thermolabile radical initiator.

[0023] The initiator system may preferably comprise one photolabile initiator, preferably photolabile radical initiator, and one thermolabile initiator, preferably a thermolabile radical initiator. A photolabile initiator is a chemical compound that generates a reactive species, preferably a radical when exposed to light, preferably when exposed to UV light.

[0024] The photolabile initiator may be a photolabile phosphine compound, oxime ester, thioxanthone derivative, a triaryl sulfonium, benzoin derivatives or mixtures thereof. Preferably, the photolabile initiator is a phosphine compound or a benzoin derivative. Even more preferably, the photolabile initiator is bisacylphosphinoxide.

[0025] The electronic component impregnating composition may comprise the photolabile initiator in an amount of at least 0.1%, preferably at least 1 %, even more preferably at least 2% by weight of the total composition. The electronic component impregnating composition may comprise the photolabile initiator in an amount of equal to or less than 5%, preferably equal to or less than 4%, even more preferably equal to or less than 3% by weight of the total composition. The electronic component impregnating composition may comprise the photolabile initiator in an amount from 0.5% to 5%, preferably from 1 % to 4%, even more preferably from 2% to 3% by weight of the total composition.

[0026] A thermolabile initiator is a chemical compound that decomposes upon heating to generate a reactive species, preferably a radical. With respect to the thermolabile initiator, the 10-hour half life temperature is the temperature at which the concentration of azo groups decreases to 50% of its initial value after storage for 10 hours. This measurement is typically conducted in a toluene solution. Examples of such thermolabile initiators include isobutyryl peroxide (10-hour half life temperature: 33 °C), 2,4,4-trimethylpentyl peroxyneodecanoate (41 °C), a-cumyl peroxyneodecanoate (38 °C), t-butyl peroxyneodecanoate (47 °C), di-3-methoxybutyl peroxydicarbonate (43 °C), di-2-ethylhexyl peroxydicarbonate (44 °C), bis(4-t- butylcyclohexyl)peroxydicarbonate (44 °C) and diisopropyl peroxydicarbonate (45 °C). Preferably the 10-hour half life temperature is > 25 °C to < 45 °C. 2,2’-azobis(4-methoxy-2,4- dimethylvaleronitrile), commonly referred to as V70, is particularly preferred with a 10-hour half life temperature of 30 °C.

[0027] The electronic component impregnating composition may comprise the thermolabile initiator in an amount of at least 0.1 %, preferably at least 1%, even more preferably at least 2% by weight of the total composition. The electronic component impregnating composition may comprise the thermolabile initiator in an amount of equal to or less than 5%, preferably equal to or less than 4%, even more preferably equal to or less than 3% by weight of the total composition. The electronic component impregnating composition may comprise the thermolabile initiator in an amount of from 0.5% to 5%, preferably from 1% to 4%, even more preferably from 2% to 3% by weight of the total composition.

[0028] In one embodiment, the photolabile initiator is a phosphine oxide. An example of a phosphine oxide is 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO) or diphenyl phosphine oxide (DPO). A preferred type of phosphine oxides are bis(acyl)phospine oxides. Particularly preferred is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO).

[0029] The electronic component impregnating composition of the present invention further comprises a reactive thiol. A reactive thiol is understood as an organic compound that comprises at least one reactive thiol group. A multifunctional thiol is understood as an organic compound that comprises at least two reactive thiol groups. Thiols are known as mercaptans and are characterized by the presence of a sulfur-hydrogen bond. Preferably, the reactive thiol is a multifunctional thiol and comprises two, preferably three, or even more preferably four reactive thiol groups. The reactive thiol may comprise an alkyl, alkenyl, aryl, cycloalkyl, hetero alkyl, hetero alkenyl, hetero aryl, or hetero cycloalkyl group and mixtures thereof. Preferably the reactive thiol is decandithiol, trimethylolpropane tris(3-mercaptopropionate), pentaerythrit-tetrakis-(3-mercapto-butylate), pentaerythrit-tetrakis-(3-mercapto-propionate) or a mixture of at least two of the aforementioned compounds.

[0030] The electronic component impregnating composition may comprise the reactive thiol in an amount of at least 0.1%, preferably at least 1%, even more preferably at least 2% by weight of the total composition. The electronic component impregnating composition may comprise the reactive thiol in an amount of equal to or less than 25%, preferably equal to or less than 20%, even more preferably equal to or less than 15% by weight of the total composition. The electronic component impregnating composition may comprise the reactive thiol in an amount of from 0.1% to 25%, preferably from 1% to 10%, even more preferably from 2% to 15% by weight of the total composition of the reactive thiol.

[0031] In another embodiment the composition further comprises an ethylenically unsaturated monomer with an isocyanate functional group. Such NCO groups can provide an alternative pathway for shadow curing as they are able to react with ambient moisture under formation of urea groups. An example of such a compound is 2-isocyanatoethyl methacrylate.

[0032] The electronic component impregnating composition may further comprise a polymerization inhibitor. A polymerization inhibitor refers to a chemical substance or compound added to a reaction mixture or formulation to retard, suppress, or prevent the undesired polymerization of monomers, oligomers, or reactive species. The polymerization inhibitor acts by scavenging or neutralizing free radicals, initiating species, or other reactive intermediates that propagate the polymerization reaction. The inhibitor may be added in varying amounts, typically in small concentrations, to control the polymerization kinetics and ensure process stability. Examples of polymerization inhibitors include but are not limited to, hydroquinone, benzoquinone, and butylhydroxytoluene. Preferably, butylhydroxytoluene can be used as a polymerization inhibitor. The electronic component impregnating composition may comprise the polymerization inhibitor in an amount of at least 10 ppm, preferably at least 250 ppm, even more preferably at least 400 ppm based on the total weight of the composition. The electronic component impregnating composition may comprise the polymerization inhibitor in an amount of equal to or less than 1000 ppm, preferably equal to or less than 750 ppm, even more preferably equal to or less than 500 ppm based on the total weight of the composition. The electronic component impregnating composition may comprise the polymerization inhibitor in an amount of from 100 to 1000, preferably from 250 to 750 ppm, even more preferably from 400 to 500 ppm, based on the total weight of the composition.

[0033] The electronic impregnating composition may further comprise at least one additive. An "additive" is to be understood as a substance that is incorporated into formulation or composition quantities to modify or enhance one or more properties of the base formulation / composition without fundamentally altering its primary chemical structure. Additives are used to impart specific functional attributes such as improving stability, performance, processing characteristics, or overall efficacy of the primary formulation / composition. The additive may be selected from the group consisting of stabilizers, fillers, adhesion promoters, plasticizers, flame retardants, conductive additives, antimicrobial agents, thixotropic agents, dyes and pigments, surfactants and defoamers or combinations thereof.

[0034] The electronic component impregnating composition may comprise at least one additive in an amount of at least 0.01%, preferably at least 0.5% even more preferably at least 1% based on the total weight of the composition. The electronic component impregnating composition may comprise at least one additive in an amount of equal to or less than 10%, preferably equal to or less than 5%, even more preferably equal to or less than 3% by weight of the total composition. The electronic component impregnating composition may comprise at least one additive in an amount from 0.01% and 10%, preferably from 0.5% to 5%, even more preferably from 1% to 3% based on the total weight of the composition.

[0035] The invention also relates to a process for the preparation of an electronic component impregnating product comprising the steps of:

[0036] (a) providing a mixture of an at least trifunctional (meth)acrylate, a poly(oxyalkylene glycol) di(meth)acrylate, a linear or branched diurethane di(meth)acrylate and an initiator system comprising at least one photolabile initiator and at least one thermolabile initiator having a 10-hour half life temperature of < 50 °C,

[0037] (b) adding a reactive thiol to the mixture of step (a)

[0038] (c) curing the mixture of step (b) by irradiation, preferably UV irradiation, and

[0039] (d) curing the mixture of step (c) at temperatures sufficient to activate the thermolabile initiator, preferably by heating.

[0040] All definitions and embodiments related to the electronic component impregnation composition apply mutatis mutandis for the process of the preparation of an electronic component impregnating product. An electronic impregnating product typically comprises a cured electronic component impregnating composition.

[0041] The composition may be homogenized before the at least one photolabile and / or the at least one thermolabile initiator is / are added to the composition. The composition may not be homogenized before the photolabile and / or the thermolabile initiator is / are added to the composition. As used herein, the term "homogenized" refers to a process in which a mixture or composition is subjected to mechanical or physical treatment to achieve a uniform and consistent distribution of its components at a microscopic or molecular level. This process ensures that the composition exhibits uniform properties throughout, without phase separation, clumping, or the presence of unevenly distributed particles. Homogenization may be achieved through various methods such as high-shear mixing, ultrasonic treatment, mechanical agitation, or other techniques suitable for the specific nature of the components involved. The goal of homogenization is to create a stable and consistent product with predictable and reproducible performance characteristics. The homogenization may be carried out at temperatures less than or equal to 20 °C, preferably less than or equal to 10 °C, even more preferably less than or equal to 0 °C. The homogenization may be carried out for at least 1 min preferably for at least 10 min, even more preferably for at least 15 min. The homogenization may be carried out for less than 60 min, preferably for less than 45 min, even more preferably for less than 30 min. The homogenization may be carried out for 5 min to 60 min, preferably for 10 min to 45 min, even more preferably for 15 to 30 min. The homogenization may be carried out at temperatures less than or equal to 20 °C for at least 1 min preferably for at least 10 min, even more preferably for at least 15 mins. The homogenization may be carried out at temperatures less than or equal to 10 °C for at least 1 min preferably for at least 10 min, even more preferably for at least 15 mins. The homogenization may be carried out at temperatures less than or equal to 0°C for at least 1 min preferably for at least 10 min, even more preferably for at least 15 mins. The homogenization may be carried out at temperatures less than or equal to 20 °C, preferably less than or equal to 10 °C, even more preferably less than or equal to 0 °C for 1 min to 60 min, preferably for 10 min to 45 min, even more preferably for 15 to 30 min.

[0042] The at least one polymerizable ethylenically unsaturated monomer and the initiator system comprising at least one photolabile initiator and at least one thermolabile initiator may be added at the same time or stepwise to the process. The at least one polymerizable monomer may be premixed with the at least one photolabile and / or thermolabile initiator before being added to the process. As used herein, the term "premixed" refers to a composition or formulation that has been blended or combined prior to a specific application or further processing. Premixing involves the thorough and uniform incorporation of multiple ingredients or components into a homogeneous mixture in advance, ensuring consistent and reliable performance in subsequent use. This pre-blending process is typically conducted under controlled conditions to achieve desired proportions and uniformity. Premixed compositions are often prepared to simplify or streamline the final application process, improve ease of handling, or ensure optimal performance characteristics of the final product.

[0043] Typically, the defined process can be carried out in the absence of solvents and / or dispersing agents.

[0044] The mixture obtained in step (a) can be homogenized before step (b). The homogenization after step (a) and before step (b) may be carried out at temperatures less than or equal to 20 °C, preferably less than or equal to 10 °C, even more preferably less than or equal to 0 °C. The homogenization after step (a) and before step (b) may be carried out for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization after step (a) and before step (b) may be carried out for less than 30 min, preferably for less than 15 min, even more preferably for less than 10 min. The homogenization after step (a) and before step (b) may be carried out for 1 min to 30 min, preferably for 3 min to 15 min, even more preferably for 5 to 10 min. The homogenization after step (a) and before step (b) may be carried out at temperatures less than or equal to 20 °C for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization after step (a) and before step (b) may be carried out at temperatures less than or equal to 10 °C for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization after step (a) and before step (b) may be carried out at temperatures less than or equal to 0°C for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization after step (a) and before step (b) may be carried out at temperatures less than or equal to 20 °C, preferably less than or equal to 10 °C, even more preferably less than or equal to 0 °C for 1 min to 30 min, preferably for 3 min to 15 min, even more preferably for 5 to 10 min.

[0045] The process of the present invention comprises the further step of adding a reactive thiol to the mixture of step a). The mixture of step (b) may be homogenized after the reactive thiol is added to the composition. The homogenization may be carried out at temperatures less than or equal to 20 °C, preferably less than or equal to 10 °C, even more preferably less than or equal to 0 °C. The homogenization may be carried out for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization may be carried out for less than 30 min, preferably for less than 15 min, even more preferably for less than 10 min. The homogenization may be carried out for 1 min to 30 min, preferably for 3 min to 15 min, even more preferably for 5 to 10 min. The homogenization may be carried out at temperatures less than or equal to 20 °C for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization may be carried out at temperatures less than or equal to 10 °C for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization may be carried out at temperatures less than or equal to 0°C for at least 1 min preferably for at least 3 min, even more preferably for at least 5 mins. The homogenization may be carried out at temperatures less than or equal to 20 °C, preferably less than or equal to 10 °C, even more preferably less than or equal to 0 °C for 1 min to 30 min, preferably for 3 min to 15 min, even more preferably for 5 to 10 min. The mixture of step (b) may be stored at temperatures of less than 5 °C, preferably of less -5 °C, even more preferably of less than -15 °C after the reactive thiol is added to the composition and, optionally, homogenized.

[0046] The mixture of step (b) may be applied to an electronic component after the reactive thiol is added to the composition.

[0047] The term “electronic component” refers to a discrete device or part used in electronic circuits, systems, or devices to perform specific functions related to electrical signal processing, transmission, or control. Electronic components may include but are not limited to, passive components, such as resistors, capacitors, inductors, and transformers, which modify or store electrical energy without amplification; active components, such as transistors, diodes, integrated circuits, and sensors, which control or amplify electrical signals; electromechanical components, such as relays, switches, connectors, and connectors, which combine electrical and mechanical functions; and other specialized components, such as antennas, filters, oscillators, and detectors, which serve specific purposes in electronic systems. Electronic components may be fabricated from various materials, such as semiconductors, conductors, insulators, or magnetic materials, and may be packaged individually or integrated into larger assemblies or modules to form complete electronic systems.

[0048] Preferably, the electronic component is selected from the group consisting of a circuit board, a capacitor and a connector.

[0049] The mixture of step (b) may raked up to an electronic component after the reactive thiol is added to the composition.

[0050] As used herein, the term "raked up" refers to the process of distributing or leveling a composition on a surface by employing a tool equipped with spaced prongs, teeth, or blades. This method involves drawing the tool across the surface of an electronic component, thereby achieving a uniform application of the composition. The "raked up" process is specifically designed to control and ensure a consistent layer thickness of the composition, which is critical for the performance and reliability of the electronic component. This technique enhances the uniformity, adhesion, and functional properties of the applied layer, contributing to the overall effectiveness of the composition in protecting or enhancing the electronic component.

[0051] The layer-thickness of the raked-up composition on the electronic component may be equal or less than 10000 pm, preferably equal or less than 5000 pm, even more preferably equal or less than 1000 pm, even more preferably equal or less than 500 pm, even more preferably equal or less than 100 pm. The layer-thickness of the raked-up composition on the electronic component may be at least 10 pm, preferably at least 20 pm, even more preferably at least 25 pm.

[0052] The process of the present invention comprises the further step of curing the mixture of step

[0053] (b) by irradiation, preferably by UV irradiation. Curing the mixture of step (b) by irradiation, preferably by UV irradiation may take place on an electronic component, preferably wherein the mixture of step (b) is raked up on the electronic component. The curing time of step (c) may be at least 10 sec, preferably at least 30 sec, and even more preferably at least 60 sec. The curing time of step (c) may be less than 600 sec, preferably less than 300 sec, even more preferably less than 180 sec. The curing time of step (c) may be from 15 sec to 600 sec, preferably from 30 sec to 300 sec, even more preferably from 60 sec to 180 sec.

[0054] The process of the present invention comprises the further step of curing the mixture of step

[0055] (c), preferably by heating. Curing the mixture of step curing the mixture of step (c), preferably by heating may take place on an electronic component, preferably wherein the mixture of step (c) is raked up on the electronic component. The curing time of step (d) may be at least 1 min, preferably at least 30 min, even more preferably at least 60 min. The curing time of step (d) may be less than 600 min, preferably less than 300 min, even more preferably less than 240 min. The curing time of step (d) may be from 1 min to 600 min, preferably from 30 min to 300 min, even more preferably from 60 min from 240 min. The curing step (d) can be carried out at a temperature of less than 200 °C, preferably less than 100 °C. The curing step (d) can be carried out at a temperature of at least 19 °C, preferably at least 70 °C. The curing step (d) can be carried out at a temperature ranging from 20 to 200 °C, preferably ranging from 70 to 100 The invention also relates to an electronic impregnating product obtained by the process according to the invention.

[0056] The invention also relates to the use of an electronic impregnating composition for the impregnation of an electronic component.

[0057] All definitions and embodiments related to the electronic component impregnation composition, the process for the preparation of an electronic component impregnating product, the electronic impregnating product apply mutatis mutandis for the use of an electronic impregnating component for the impregnation of an electronic component.

[0058] The electronic impregnating composition may be used for its protective and performanceenhancing properties in electronic components. The electronic impregnating composition may be used to provide moisture protection, thermal management, mechanical strength, chemical resistance, electrical insulation, and / or improved adhesion for an electrical component. Preferably, the electronic impregnating composition may be used for insulation, preferably electrical insulation, of an electronic component.

[0059] Preferably, the electronic component is selected from the group consisting of a circuit board, a capacitor and a connector.

[0060] The invention also relates to a method for impregnating an electronic component with an electronic impregnating composition comprising the steps of:

[0061] (a) applying the electronic impregnating composition on an electronic component and

[0062] (b) curing the mixture of step (a) by irradiation, preferably UV irradiation, and curing the mixture of step (b), preferably by heating.

[0063] All definitions and embodiments related to the electronic component impregnation composition, the process for the preparation of an electronic component impregnating product, the electronic component impregnating product and to the use of an electronic impregnating component for the impregnation of an electronic component apply mutatis mutandis for the method for impregnating an electronic component with an electronic impregnating composition.

[0064] The method comprises the step of applying the electronic impregnating composition on an electronic component. The electronic impregnation composition may be applied to the electronic component by raking up the electronic impregnation composition on the electronic component. The layer-thickness of the raked-up composition on the electronic component may be less than 10000 pm, preferably less than 5000 pm, even more preferably less than 1000 pm, even more preferably less than 500 pm, even more preferably less than 100 pm.

[0065] The layer-thickness of the raked-up composition on the electronic component may be at least 10 pm, preferably at least 20 pm, even more preferably at least 25 pm. According to one embodiment, in step (a) the composition is applied at a film thickness of 50 pm or less. It is particularly preferred to apply the composition at a layer thickness of > 10 pm to < 50 pm and preferably > 10 pm to < 25 pm.

[0066] The invention also relates to an electronic component comprising an electronic impregnation product. All definitions and embodiments related to the electronic component impregnation composition, the process for the preparation of an electronic component impregnating product, the electronic component impregnating product, the use of an electronic impregnating component for the impregnation of an electronic component and the method for impregnating an electronic component with an electronic impregnating composition apply mutatis mutandis for the electronic component.

[0067] The following examples illustrate the invention without limiting its scope.

[0068] Examples

[0069] General Procedure: The polymerizable ethylenically unsaturated monomers and Sudan Blue II were weighed into a glass vial covered with aluminum foil a stirring bar and the glass vial was put into an ice bath. Then, the mixture was homogenized at 120 rpm for 15 min. The initiator system was added and the resulting mixture was homogenized for another 5 min at 150 rpm. The stirring barwas removed, and the reactive thiol was added. The resulting mixture was transferred to a circuit board via a syringe. The desired layer thicknesses are then applied by means of a film casting knife. Shadow areas are then simulated on the coated printed circuit boards using 3D-printed masks made of poly(lactic acid). The individual quadrants are irradiated using the LIV-LEB Spot P for 1 min. After complete UV irradiation, the printed circuit boards are transferred to a drying oven (Binder ED 23) for 1 h at 70 °C. To check the shadow areas, the tables were carefully removed from the printed circuit board using tweezers and the shadow area is inspected.

[0070] The areas that were coated with the polymerizable compositions were evaluated visually and haptically after irradiation and thermal treatment. In the examples, “liquid” denotes a failed polymerization, while the result of a partial polymerization is “sticky”. Here the film of the obtained composition has a higher viscosity than before irradiaton and thermal treatment. Further advanced, but not nearing completeness, degrees of polymerization lead to a pastelike consistency. Polymer areas are “tacky” if they are solid and display a surface tack. It will be appreciated that shadow areas where, at film thicknesses of 50 pm or below, the monomer composition was polymerized to a low degree or unpolymerized after irradiation but before thermal curing are associated with compositions that are not according to the invention.

[0071] The following starting materials were used:

[0072] Table 1 : Starting materials

[0073] Compound Code

[0074] Trimethylolpropane triacrylate TMPTA

[0075] Dipentaerythritol penta- / hexa-acrylate DPEPHA

[0076] Dimethylolpropane tetraacrylate DMPTA

[0077] Polyethylene glycol diacrylate Mn700 g / mol PEDGA

[0078] Dioxane glycol diacrylate DOGDA Diurethane diacrylate DUDA

[0079] Diurethane di methacrylate DUDMA

[0080] Urethane acrylate / methacrylate resin U-835 UAMAR

[0081] 2-lsocyanatoethyl methacrylate NCOMA

[0082] 2,2’-Azobis(4-methoxy-2,4-dimethylvaleronitrile) V70

[0083] Azobis(isobutyronitrile) AIBN

[0084] 2,2'-Azobis(2,4-dimethylvaleronitril) V65

[0085] Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide BAPO

[0086] Isopropylthioxanthone ITX

[0087] 4-(4-methyl-phenylthio)benzophenone BMS

[0088] Benzoin methyl ether BME

[0089] Pentaerythrityl-tetrakis-(3-mercapto-propionate) PETMP

[0090] Sudan blue II SB II

[0091] The structure of DOGDA, which is clearly not a poly(oxyalkylene glycol) di(meth)acrylate, is: The structure of UAMAR is: n-pentyl

[0092] In this structure, OR denotes an acrylate- or methacrylate-bearing moiety. Owing to its cyclohexyl substructre, LIAMAR is not regarded as a linear or branched diurethane di(meth)acrylate.

[0093] The 10-hour half life temperature of the thermolabile initiators were 30 °C (V70, in toluene), 51 °C (V65, in toluene) and 65 °C (Al BN, in toluene). Table 2: Compositions tested (in parts by weight).

[0094] Example 1 Example 2

[0095] TMPTA 11 5.5

[0096] PEGDA 5.3 2.65

[0097] DUDA 16.8 8.4

[0098] NCOMA - 16.55

[0099] V70 1 1

[0100] BAPO 1 1

[0101] PETMP 5 1

[0102] SB II 0.01 0.01

[0103] In both examples the irradiated areas displayed a slight tack. The shadow areas were sticky for all wet film thicknesses tested. The samples were tack-free after drying in the oven for 1 - 2 hours. Part of the samples were left at room temperature after UV-radiation, it took about 24 hours to get full cure of the shadow areas.

[0104] Comparative example with a commercial product: 0.025 wt.% Sudan Blue II was added to Bectron PT 4700N (ELANTAS Europe GmbH) and thoroughly mixed. The resulting mixture was transferred to a circuit board via a syringe. The desired layer thicknesses was applied by means of a film casting knife. Shadow areas are then simulated on the coated printed circuit boards using 3D-printed tables made of poly(lactic acid). The individual quadrants are irradiated using the UV-LEB Spot P for 1 min. After complete UV irradiation, the printed circuit boards are transferred to a drying oven. The samples was tack-free after > 2 hours drying at 70 °C. Part of the sample was left at room temperature after UV-radiation, it took about 2-3 days to get full cure of the shadow areas.

[0105] In the next set of experiments the effect of omitting acrylates from the compostions was tested.

[0106] Table 3: Benchmark according to the invention and comparative examples V1-V3 (in grams)

[0107] Benchmark V1 V2 V3

[0108] TMPTA 1.111 1.106 1.096

[0109] PEGDA 0.615 0.536 0.531

[0110] DUDA 1.677 1.676 1.679

[0111] V70 0,103 0.100 0.100 0.099

[0112] BAPO 0,101 0.100 0.099 0.099

[0113] PETMP 0.520 0.509 0.481 0.480

[0114] SB II 0.001 0.003 0.001 0.001

[0115] The composition of the benchmark corresponded to the foregoing example 1. Test results were the same after irradiation and thermal curing. Compositions V1-V3 were tested as laid out in the general procedure above with wet layer thicknesses of 250 pm, 100 pm, 50 pm and 25 pm. For V-1 it was observed that after the irradiation step the shadow areas for the 50 pm and 25 pm experiments were still liquid, indicating that insufficient or no polymerization had taken place. Thermal curing was effected for 1 hour at 70 °C. For V-2 and V-3 it was observed that after the irradiation step the shadow areas for all experiments were still liquid, indicating that insufficient or no polymerization had taken place. Thermal curing was effected for 1 hour at 70 °C.

[0116] DSC analysis was performed at a heating rate of 10 K / min for the first heating and 20 K / min for the second heating. Polymerization initiation temperatures (exothermic peak at first heating) were: benchmark: 43 °C, V1: 58 °C, V2: 51 °C and V3: 46 °C. Glass transition temperatures (second heating) were: benchmark: 35-40 °C, V1: 38 °C and V2: 17 °C. No meaningful glass transition temperature could be determined for V3. In the next set of experiments one component is varied with respect to the benchmark.

[0117] Comparative examples are designated “V” and examples according to the invention “E”.

[0118] Table 5: Further experiments (in grams)

[0119] V-4 V-5 E-6 E-7 V-8 V-9 V-10

[0120] TMPTA 1.103 1.104 1.105 1.104 1.099

[0121] DPEPHA - - 1.100

[0122] DMPTA - - - 1.101

[0123] PEGDA 0.546 0.544 0.543 0.526 - 0.532 0.545

[0124] DOGDA . . . . 0.533

[0125] DUDA - - 1.732 1.702 1.672 1.689 1.696

[0126] DUDMA 1.681 - - - - - -

[0127] UAMAR - 1.684 - - - - -

[0128] V70 0.100 0.100 0.102 0.103 0.100

[0129] AIBN > . . . . 0.099

[0130] V65 - - - - - - 0.104

[0131] BAPO 0.100 0.100 0.097 0.101 0.099 0.100 0.100

[0132] ITX - - - - - - -

[0133] BMS > . . . . . .

[0134] BME > . . . . . .

[0135] PETMP 0.500 0.529 0.493 0.493 0.492 0.512 0.572

[0136] SB II 0.001 0.001 0.001 0.001 0.001 0.001 0.002 The compositions were tested as laid out in the general procedure above with wet layer thicknesses of 250 pm, 100 pm, 50 pm and 25 pm. The results are given below. DSC analysis was performed at a heating rate of 10 K / min for the first heating and 20 K / min for the second heating. Polymerization initiation temperatures (exothermic peak at first heating) are designated Tj and glass transition temperatures (second heating) are designated Tg.

[0137] Composition V-4: the irradiated areas had the same appearance as in the benchmark experiment. The shadow areas were liquid to slightly sticky. After thermal curing the shadow areas were solid (250 pm, 100 pm wet film thickness) or sticky (50 pm, 25 pm wet film thickness). Tj: 60 °C, Tg: 64 °C.

[0138] Composition V-5: the irradiated areas had the same appearance as in the benchmark experiment. The shadow areas were liquid to slightly sticky in the 50 pm and 25 pm wet film thickness experiments. Thermal curing did not improve the appearance of the shadow areas. T,: 58 °C, Tg: 11 °C.

[0139] Composition E-6: the irradiated areas displayed a slight tack. The shadow areas were sticky for all wet film thicknesses tested. Thermal curing solidified all areas. Tj: 48 °C, Tg: n.d.

[0140] Composition E-7: the irradiated areas displayed a slight tack. The shadow areas were sticky for all wet film thicknesses tested. Thermal curing solidified all areas. Tj: 53 °C, Tg: 52 °C.

[0141] Composition V-8: the irradiated areas had the same appearance as in the benchmark experiment. The shadow areas were liquid to slightly sticky. Thermal curing solidified all areas. The shadow area of the 25 pm wet film thickness experiment still had a light tack after thermal curing. Tj: 45 °C, Tg: 63 °C.

[0142] Composition V-9: the irradiated areas were solid with a light tack. The shadow areas were slightly sticky for the 250 pm wet film thickness experiment and liquid for all the other experiments. Thermal curing solidified all areas. : 69 °C, Tg: 35-40 °C.

[0143] Composition V-10: the irradiated areas were solid. The shadow areas were liquid to slightly sticky for the 100 pm, 50 pm and 25 pm wet film thickness experiments. Thermal curing solidified all areas. Tj: 54 °C, Tg: 35-40 °C.

Claims

Claims1. An electronic component impregnating composition comprising• at least one polymerizable ethylenically unsaturated monomer,• an initiator system comprising at least one photolabile initiator and at least one thermolabile initiator, and• a reactive thiol, characterized in that the composition comprises• an at least trifunctional (meth)acrylate,• a poly(oxyalkylene glycol) di(meth)acrylate and• a linear or branched diurethane di(meth)acrylate and wherein the thermolabile initiator has a 10-hour half life temperature of < 50 °C.

2. The electronic component impregnating composition according to claim 1 , wherein the thermolabile initiator is 2,2’-azobis(4-methoxy-2,4-dimethylvaleronitrile) and / or the photolabile initiator is a phosphine oxide, preferably phenylbis(2,4,6- trimethylbenzoyl)phosphine oxide.

3. The electronic component impregnating composition according to any of the previous claims, wherein the poly(oxyalkylene glycol) di(meth)acrylate has > 5 to < 20 oxyalkylene groups and preferably is a poly(oxyethylene glycol) diacrylate.

4. The electronic component impregnating composition according to any of the previous claims, further comprising an ethylenically unsaturated monomer with an isocyanate functional group.

5. The electronic component impregnating composition according to any of the previous claims, wherein the at least trifunctional (meth)acrylate is trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, dimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, di pentaerythritoltetra(meth)acrylate, dipentaerythritol penta(metha)crylate, dipentaerythritol hexa(metha)crylate or a mixture of at least two of the aforementioned compounds.

6. The electronic component impregnating composition according to any of the previous claims, wherein the linear or branched diurethane di(meth)acrylate is the reaction product of an aliphatic a, co-di isocyanate with hydroxyalkyl(meth)acrylates, preferably of 2,2,4-tri methyl- 1 ,6-hexamethylene diisocyanate with hydroxyethylacrylate.

7. The electronic component impregnating composition according to any of the previous claims, wherein the reactive thiol is decandithiol, trimethylolpropan tris(3- mercaptopropionate), pentaerythrit-tetrakis-(3-mercapto-butylate), pentaerythrit- tetrakis-(3-mercapto-propionate) or a mixture of at least two of the aforementioned compounds.

8. A process for the preparation of an electronic component impregnating product comprising(a) providing a mixture of an at least trifunctional (meth)acrylate, a poly(oxyalkylene glycol) di(meth)acrylate, a linear or branched diurethane di(meth)acrylate and an initiator system comprising at least one photolabile initiator and at least one thermolabile initiator having a 10-hour half life temperature of < 50 °C,(b) adding a reactive thiol to the mixture of step (a),(c) curing the mixture of step (b) by irradiation, preferably UV irradiation, and(d) curing the mixture of step (c) at temperatures sufficient to activate the thermolabile initiator, preferably by heating.

9. The process according to claim 8, wherein the curing time of step (c) is at least 1 min.

10. The process according to any of claims 8 to 9, wherein the curing time of step (d) is at least 5 min, preferably at least 30 min, even more preferably at least 60 min.

11. The process according to any of claim 8 to 10, wherein the curing of step (d) is carried out at a temperature ranging from 20 to 200 °C, preferably ranging from 50 to 120 °C, even more preferably ranging from 70 to 100 °C.

12. An electronic impregnating product obtained by the process of any of claims 8 to 11.

13. Use of an electronic component impregnating composition according to any of claims 1 to 7 for the impregnating of an electronic component, preferably for insulating an electronic component, more preferably for the impregnating of a circuit board, a capacitor or a connector, even more preferably for insulating a circuit board, a capacitor or a connector.

14. A method for impregnating an electronic component with an electronic impregnating composition according to any of claims 1 to 7 comprising the steps of(a) applying the electronic impregnating composition according to any of claims 1 to 7 on an electronic component, and(b) curing the electronic impregnating composition.

15. The method according claim 14, wherein in step (a) the composition is applied at a film thickness of 50 pm or less.

Images