Curable inkjet composition for manufacturing printed circuit boards

Abstract

A curable inkjet composition for a printed circuit board, comprising (a) one or more thermal crosslinking agents selected from the group consisting of an unblocked isocyanate, a blocked isocyanate, and a triazine compound, and (b) at least two photopolymerizable compounds, wherein at least one photopolymerizable compound has a chemical structure represented by the general formula (I) [Chemical Formula 1] TIFF2025524829000011.tif50161In the formula, R1, R2, R3, and R4 are each independently hydrogen or a substituted or unsubstituted C1-C 10 alkyl group, and a curable inkjet composition characterized by the above.

Description

Technical Field

[0001] The present invention relates to a curable composition for use as an inkjet composition in the manufacture of electronic devices. The present invention also relates to a cured product of the composition.

Background Art

[0002] Printed circuit boards (PCBs) have conventionally been manufactured by a large-scale process including multi-step photolithography and etching processes, and thus generate a large amount of waste. There is a growing interest in the digitization of the PCB manufacturing workflow for the purpose of reducing the number of process steps, manufacturing costs, and waste.

[0003] Inkjet printing is a digital manufacturing technique suitable for a plurality of PCB manufacturing processes, such as the application of an etching resist and a solder mask, or the printing of a legend.

[0004] A PCB solder mask, i.e., a solder resist, acts as an insulator between copper wirings and prevents the formation of solder bridges. Moreover, it plays an important role in protecting the substrate from oxidation triggered by external influences such as weather conditions, temperature changes, and humidity. If mechanical defects occur in the solder mask due to exposure to such external conditions, the protection and insulation functions of the solder mask are negatively affected. Therefore, the main purpose of manufacturing an effective solder mask is to provide good resistance to the conditions to which the solder mask is exposed.

[0005] When manufacturing a PCB solder mask via inkjet, an important essential requirement is that the solder mask must be able to withstand the operating conditions during typical finishing processes (pH and temperature) where severe and diverse conditions are used, such as during electroless nickel immersion gold (ENIG) plating (ENIG plating resistance).

[0006] Patent Document 1 (Agfa-Gevaert) discloses a radiation-curable inkjet ink for preparing a solder mask, which ink contains a polymerizable compound, a phenolic resin, and a thermal crosslinking agent. The combination of these compounds ensures good adhesion and good ENIG plating resistance.

[0007] Patent Document 2 (Taiyo Ink Manufacturing) discloses an inkjet ink for solder mask printing, which ink contains a (meth)acrylate monomer having a thermosetting functional group. Patent Document 3 (Electra Polymers) discloses an inkjet ink for solder mask printing, which ink contains a reactive monomer, an oligomer of a prepolymer having at least one epoxy or oxetane functional group, a free radical polymerizable compound, a thermal crosslinking agent, and a radical initiator.

[0008] Patent Document 4 (Taiyo Ink Manufacturing) discloses an inkjet ink for solder mask printing, which ink contains a photopolymerizable monomer having a cyclic skeleton and a shrinkage rate of less than 10%, which brings about an improvement in heat resistance before ENIG plating.

[0009] Finally, it is beneficial for the inkjet ink to have good LED sensitivity. An ink with good LED sensitivity is desirable because improved curing efficiency results in better image quality and line sharpness. It is often the case that good LED sensitivity is also an indicator of good mechanical properties of the cured ink, such as hardness and strength. Therefore, there is a need for an inkjet ink that combines good LED sensitivity and good ENIG plating resistance for use in the PCB manufacturing process.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

[0011] An object of the present invention is to provide an inkjet composition having good electroless nickel immersion gold (ENIG) plating resistance for use in the PCB manufacturing process. The object of the present invention is achieved by a curable composition as defined in claim 1. A further object of the invention is to provide an inkjet composition having both good ENIG plating resistance and good LED sensitivity for use in the PCB manufacturing process.

[0012] A further object of the present invention will become apparent from the description hereinafter. [Modes for Carrying Out the Invention]

[0013] Definitions The term "monofunctional" means that, for example, in the case of a monofunctional polymerizable compound, the polymerizable compound has one polymerizable group.

[0014] The term "bifunctional" means that, for example, in the case of a bifunctional polymerizable compound, the polymerizable compound has two polymerizable groups.

[0015] The term "polyfunctional" means that, for example, in the case of a polyfunctional polymerizable compound, the polymerizable compound has more than two polymerizable groups.

[0016] The term "alkyl" means all possible deformed forms for alkyl groups with each number of carbon atoms, that is, methyl, ethyl, for those with 3 carbon atoms, n-propyl and isopropyl, for those with 4 carbon atoms, n-butyl, isobutyl, and tert-butyl, for those with 5 carbon atoms, n-pentyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, and 2-methylbutyl, etc.

[0017] Unless otherwise specified, the substituted or unsubstituted alkyl group is preferably a C1-C6-alkyl group.

[0018] Unless otherwise specified, the substituted or unsubstituted alkenyl group is preferably a C2-C6-alkenyl group.

[0019] Unless otherwise specified, the substituted or unsubstituted alkynyl group is preferably a C2-C6-alkynyl group.

[0020] Unless otherwise specified, the substituted or unsubstituted aralkyl group is preferably a phenyl or naphthyl group having one, two, three, or more C1-C6-alkyl groups.

[0021] Unless otherwise specified, the substituted or unsubstituted aralkyl group is preferably a C7-C 20 -alkyl group having a phenyl group or a naphthyl group.

[0022] Unless otherwise specified, the substituted or unsubstituted aryl group is preferably a phenyl group or a naphthyl group.

[0023] Unless otherwise specified, the substituted or unsubstituted heteroaryl group is preferably a five-membered or six-membered ring substituted with one, two, or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms, or combinations thereof.

[0024] The term "substituted" means, for example, in the case of a substituted alkyl group, that the alkyl group can be substituted with atoms different from those (i.e., carbon and hydrogen) normally present in such a group. For example, a substituted alkyl group can have a halogen atom or a thiol group. An unsubstituted alkyl group has only carbon atoms and hydrogen atoms.

[0025] Unless otherwise specified, substituted alkyl groups, substituted alkenyl groups, substituted alkynyl groups, substituted aralkyl groups, substituted alkaryl groups, substituted aryls, and substituted heteroaryl groups are preferably substituted with one or more components selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl, esters, amides, amines, ethers, thioethers, ketones, aldehydes, sulfoxides, sulfones, sulfonic acid esters, sulfonamides, -Cl, -Br, -I, -OH, -SH, -CN, and -NO2.

[0026] Curable inkjet composition The curable composition according to the present invention includes one or more heat crosslinking agents selected from unblocked isocyanates, blocked isocyanates, and triazine compounds, and at least two photopolymerizable compounds as described below.

[0027] The composition is preferably a radiation curable composition. Although any type of radiation can be applied, suitable types of radiation are UV light and UV-LED light. Therefore, the curable composition according to the present invention is preferably a UV curable composition.

[0028] In a preferred embodiment, the composition according to the present invention includes a mixture of a UV curable compound and a heat crosslinking agent. Therefore, the curable composition according to the present invention is preferably also a heat curable composition. Although any type of heat source can be used in the heat curing process, preferably, the heat curing is carried out in an oven.

[0029] The two curing processes of heat and UV can occur simultaneously or sequentially. This so-called dual-cure principle results in the formation of an interpenetrating polymer network, and the inventors believe that this is the reason why mechanical properties superior to those of individually cured polymer networks are observed.

[0030] The curable composition according to the present invention is preferably applied as an inkjet ink.

[0031] For reliable industrial inkjet printing, the viscosity of the curable inkjet ink is preferably 20 mPa·s or less at 45°C, more preferably 1 to 18 mPa·s at 45°C, and most preferably 5 to 15 mPa·s at 45°C, all of which are at a shear rate of 1000 s -1 therein.

[0032] A suitable jet injection temperature is 10 to 70°C, more preferably 20 to 55°C, and most preferably 25 to 50°C.

[0033] For good image quality and adhesion, the surface tension of the curable inkjet ink is preferably in the range of 18 to 70 mN / m at 25°C, more preferably in the range of 20 to 40 mN / m at 25°C.

[0034] Photopolymerizable compound The curable inkjet composition according to the present invention contains at least one photopolymerizable compound having a chemical structure represented by General Formula I.

Chemical formula

[0035] Preferably, R1, R2, R3, and R4 are, independently of one another, hydrogen or a substituted or unsubstituted C1-C 10 alkyl group selected therefrom.

[0036] Suitable compounds are disclosed in WO 2015 / 022228 (BASF) and US 4831153 (DOW CHEMICAL).

[0037] The cyclic compound according to general formula I is often referred to as oxazolidinone. A particularly preferred oxazolidinone is N-vinyl-5-methyl-2-oxazolidinone of general formula II, which is also referred to as vinylmethyl oxazolidinone, or VMOX. [Chemical formula]

[0038] By including a compound according to general formula I or II, the LED sensitivity of the cured ink layer is improved. The amount of the compound according to general formula I or II is preferably 1 to 40% by weight, more preferably 2.5 to 30% by weight, and most preferably 5 to 20% by weight based on the total weight of the curable inkjet composition. Moreover, the compound according to general formula I or II has a lower viscosity compared to other N-vinyl compounds, which makes these compounds particularly suitable for inkjet printing.

[0039] The curable composition according to the present invention may also contain other photopolymerizable compounds.

[0040] The photopolymerizable compound is preferably a free radical polymerizable compound. The free radical polymerizable compound can be a monomer, an oligomer, and / or a prepolymer. Such monomers, oligomers, and / or prepolymers can have different degrees of functionality, that is, the amount of free radical polymerizable groups can be different. Mixtures containing combinations of monofunctional, difunctional, trifunctional, and higher functional monomers, oligomers, and / or prepolymers can be used. The viscosity of the curable inkjet ink can be adjusted by changing the ratio of monomer to oligomer.

[0041] The photopolymerizable compound can also have functional groups such as thiol, hydroxyl, amine, sulfonic acid, phosphoric acid, and carboxylic acid. Examples of hydroxyl functional group-introduced polymerizable compounds are those listed in paragraphs

[0028] to

[0029] of US2015 / 0090482A.

[0042] Suitable photopolymerizable compounds are those listed in paragraphs

[0106] to

[0115] of EP-A 1911814.

[0043] Particularly preferred monofunctional photopolymerizable compounds are selected from the group consisting of 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, isobornyl acrylate, 2-phenoxyethyl acrylate, and acryloylmorpholine.

[0044] The curable inkjet composition preferably contains one or more polyfunctional photopolymerizable compounds.

[0045] Suitable polyfunctional photopolymerizable compounds are selected from the group consisting of polyethylene glycol diacrylate, hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, polyester acrylate oligomer, and polyether acrylate oligomer.

[0046] The curable inkjet composition can further contain a photopolymerizable compound having a vinyl group, and the vinyl group is selected from the group consisting of a vinyl ether group and an N-vinylamide group.

[0047] Preferable examples of the photopolymerizable compound having a vinyl ether group or an N-vinylamide group are those listed in paragraphs

[0047] to

[0056] of EP-A 3686251.

[0048] Particularly preferable vinyl ether-containing photopolymerizable compound is 2-(2-vinyloxyethoxy)ethyl acrylate because it is advantageous in providing a good balance between the curability and viscosity of the curable inkjet composition. The amount of 2-(2-vinyloxyethoxy)ethyl acrylate is preferably at least 5% by weight, more preferably at least 7.5% by weight, and most preferably at least 10% by weight based on the total weight of the curable inkjet composition.

[0049] Particularly preferable vinylamide-containing photopolymerizable compounds are N-vinyl-2-pyrrolidone and N-vinylcaprolactam because they combine a high Tg, good ink curability, and good adhesion of the cured ink layer to the recording medium.

[0050] Any of the above photopolymerizable compounds can be used in combination.

[0051] Thermal crosslinking agent The curable composition of the present invention contains one or more thermal crosslinking agents selected from the group consisting of an unblocked isocyanate, a blocked isocyanate, and a triazine compound. The presence of the thermal crosslinking agent may improve the adhesion of the coating film obtained after soldering or ENIG plating.

[0052] The thermal crosslinking agent can be monofunctional, difunctional, or polyfunctional.

[0053] The inkjet composition can contain a mixture of different thermal crosslinking agents.

[0054] Typical thermal crosslinking agents are oxirane, oxetane, melamine formaldehyde resin, urea formaldehyde resin, benzoguanamine formaldehyde resin, cyclic carbonate compounds, carbodiimide, isocyanate, blocked isocyanate, triazine compounds, and combinations thereof.

[0055] A suitable thermal crosslinking agent is an isocyanate compound. The isocyanate compound is preferably used in combination with a compound having an active hydrogen functional group, and examples of the compound having an active hydrogen functional group include, but are not limited to, alcohol, thiol, amine, water, or combinations thereof. Atmospheric moisture can also cause isocyanate crosslinking. When atmospheric moisture reacts with the isocyanate, it may not always be necessary to prepare an ink by combining an isocyanate compound and a compound having an active hydrogen functional group.

[0056] The isocyanate compound can be an aliphatic, alicyclic, or aromatic isocyanate. When the isocyanate compound is a polyfunctional isocyanate, this isocyanate compound can have a combination of aliphatic, alicyclic, or aromatic isocyanate functional groups.

[0057] Examples of aliphatic isocyanates include, but are not limited to, 1,6 - hexamethylene diisocyanate (HDI or HMDI), isophorone diisocyanate (IPDI), 1,3 - (isocyanatomethyl) cyclohexane (hydrogenated XDI), lysine diisocyanate (LDI), 2,2,4 - trimethylhexamethylene diisocyanate (TMDI), and dimeryl diisocyanate (DDI).

[0058] Examples of alicyclic isocyanates include, but are not limited to, isophorone diisocyanate (IPDI), methylcyclohexane 2,4-(2,6)-diisocyanate (hydrogenated TDI), and 4,4'-methylenebis(cyclohexyl isocyanate) (hydrogenated MDI).

[0059] Examples of aromatic isocyanates include, but are not limited to, toluene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), 4,4'-diphenylmethane diisocyanate (MDI), and xylylene diisocyanate (XDI).

[0060] Also by way of example, adducts (e.g., trimethylolpropane adducts), uretdiones, biurets, and isocyanurates of the isocyanates listed above are included.

[0061] The isocyanate compound can be either blocked or unblocked, but is preferably blocked.

[0062] Blocked isocyanates can be obtained by reacting the isocyanate with an appropriate blocking agent. Such a blocking agent is, for example, a protecting group that is cleaved at elevated temperature during a thermosetting process. The blocking agent can be selected such that it will be cleaved at a particular temperature, the so-called deblocking temperature. The use of blocked isocyanates typically improves the storage stability of inkjet inks.

[0063] Examples of blocking agents include alcohols such as ethanol, n-propanol, isopropanol, t-butanol, and isobutanol; phenols such as phenol, chlorophenol, cresol, xylenol, and p-nitrophenol; alkylphenols such as p-t-butylphenol, p-sec-butylphenol, p-sec-amylphenol, p-octylphenol, and p-nonylphenol; basic nitrogen-containing compounds such as 3-hydroxypyridine, S-hydroxyquinoline, and 8-hydroxyquinazoline; active methylene compounds such as diethyl malonate, ethyl acetoacetate, and acetylacetone; acid amides such as acetamide, acrylamide, and acetanilide; acid imides such as succinimide and maleimide; imidazoles such as 2-ethylimidazole and 2-ethyl-4-methylimidazole; pyrazoles such as pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole; lactams such as 2-pyrrolidone and ε-caprolactam; oximes of ketones or aldehydes such as acetoxime, methyl ethyl ketoxime, cyclohexanone oxime, and acetaldoxime; ethyleneimine; and bisulfites.

[0064] Hindered secondary amines can be used as blocking agents for toxicological reasons. Suitable hindered secondary amines are selected from the group consisting of ethyl-tert-butylamine, diisopropylamine, 2,6-dimethylpiperidine, ethyl isopropylamine, di-tert-butylamine, and diisobutylamine.

[0065] Suitable blocked isocyanate compounds are blocked HDI oligomers or blocked IPDI oligomers. Such oligomers can be, for example, trimethylolpropane adducts, biurets, or isocyanurates.

[0066] Particularly preferred blocked isocyanate compounds are Trixene Bl 7960 (supplier Lanxess), which is HDI biuret blocked with 3,5-dimethylpyrazole, and Trixene BI 7982 (supplier Lanxess), which is HDI trimer blocked with 3,5-dimethylpyrazole.

[0067] Other preferred thermal crosslinking agents are triazine compounds having a triazine skeleton. The triazine moiety is thought to contribute to the mechanical properties and heat resistance of the cured film. Any triazine compound having thermal crosslinking properties can be used.

[0068] Preferred triazine compounds have a chemical structure according to General Formula III,

Chemical formula

[0069] Preferred triazine compounds according to General Formula III and methods for their preparation are disclosed in US5084541 (American Cyanamid Company).

[0070] Preferred triazine compounds according to General Formula III are commercially available from Allnex under the name Cymel® NF 2000A and from BASF under the name Larotact® 150.

[0071] The inkjet ink according to the present invention preferably contains a blocked isocyanate compound or a triazine compound represented by the general formula III.

[0072] More preferably, the inkjet ink contains both a blocked isocyanate and a triazine compound represented by the general formula III.

[0073] The total amount of the thermal crosslinking agent is preferably 0.5 to a maximum of 20% by weight, more preferably 1 to 15% by weight, and most preferably 2 to 12% by weight, all based on the total weight of the inkjet ink.

[0074] The amount of the blocked isocyanate compound is preferably 0.1 to 12.5% by weight, more preferably 0.5 to 10% by weight, and most preferably 1 to 8% by weight, all based on the total weight of the inkjet ink.

[0075] The amount of the triazine compound is preferably 0.1 to 5% by weight, more preferably 0.5 to 4% by weight, and most preferably 1 to 3% by weight, all based on the total weight of the inkjet ink.

[0076] It has been observed that the presence of the thermal crosslinking agent improves various solder resist properties, such as heat resistance, hardness, resistance to soldering heat, chemical resistance, electrical insulation properties, and resistance to electroless plating and immersion plating.

[0077] Phenolic resin The curable composition according to the present invention can contain one or more phenolic resins.

[0078] The phenolic resin is preferably a polymer having a functional group introduced with a phenol group, and the polymer is selected from polyacrylate, polymethacrylate, or polystyrene.

[0079] Suitable phenolic resins are poly(4-hydroxystyrene) and its derivatives.

[0080] Particularly preferred phenolic resins are disclosed in US20060099531 (DuPont Electronic Polymers L.P.), and in particular, phenolic resins having structures I, II, III, and IV are disclosed in paragraph 0018.

[0081] The amount of the phenolic resin is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, and most preferably 2.5 to 10% by weight, all based on the total weight of the inkjet ink.

[0082] Photoinitiator The curable inkjet composition preferably contains a photoinitiator, and the photoinitiator is preferably a free radical photoinitiator.

[0083] A free radical photoinitiator is a compound that, upon exposure to actinic radiation, forms free radicals to initiate the polymerization of monomers and oligomers. A Norrish type I initiator is an initiator that cleaves after excitation to immediately yield initiating radicals. A Norrish type II initiator is a photoinitiator that is activated by actinic radiation to form free radicals by abstracting hydrogen from a second compound, and this second compound becomes the actual initiating free radical. This second compound is called a polymerization co-agent or co-initiator. Both type I and type II photoinitiators can be used in the present invention, either alone or in combination.

[0084] Suitable photoinitiators are disclosed in CRIVELLO, J.V., et al. Photoinitiators for Free Radical, Cationic and Anionic Photopolymerization. 2nd edition. Edited by BRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998. p.276-293.

[0085] Specific examples of free radical photoinitiators include, but are not limited to, the following compounds or combinations thereof: benzophenone and substituted benzophenones; 1-hydroxycyclohexyl phenyl ketone; thioxanthone, such as isopropyl thioxanthone; 2-hydroxy-2-methyl-1-phenylpropan-1-one; 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1-one; benzyl dimethyl ketal; 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one; 2,2-dimethoxy-1,2-diphenylethane-1-one or 5,7-diiodo-3-butoxy-6-fluorone.

[0086] A preferred photoinitiator is the thioxanthone compound Darocur ITX, which is an isomer mixture of 2- and 4-isopropyl thioxanthone.

[0087] Another preferred photoinitiator is an acylphosphine oxide compound. The acylphosphine oxide compound can be selected from the group consisting of monoacylphosphine oxides and diacylphosphine oxides. Preferred acylphosphine oxide photoinitiators are diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, and 2,4,6-trimethoxybenzoyl-diphenylphosphine oxide.

[0088] Other preferred photoinitiators are α-hydroxy-ketone type I photoinitiators, such as oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinylphenyl]propanone], etc., which is available from IGM Resins as Esacure® KIP IT.

[0089] The preferred amount of the photoinitiator is from 0.2 to a maximum of 20% by weight, more preferably from 0.5 to a maximum of 10% by weight, most preferably from 1 to a maximum of 8% by weight, and particularly preferably from 1.5 to a maximum of 6% by weight, all based on the total weight of the curable inkjet composition.

[0090] For the purpose of further improving the photosensitivity, the curable inkjet composition can additionally contain a co-initiator. Suitable examples of co-initiators can be classified into three groups: (1) Tertiary aliphatic amines such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine, and N-methylmorpholine; (2) Aromatic amines such as amyl para-dimethyl-aminobenzoate, 2-n-butoxyethyl 4-(dimethylamino)benzoate, 2-(dimethylamino)-ethyl benzoate, ethyl 4-(dimethylamino)benzoate, and 2-ethylhexyl 4-(dimethylamino)benzoate; and (3) (Meth)acrylated amines such as dialkylaminoalkyl (meth)acrylates (e.g., diethylaminoethyl acrylate) or N-morpholinoalkyl-(meth)acrylates (e.g., N-morpholinoethyl acrylate).

[0091] A preferred co-initiator is aminobenzoate.

[0092] A preferred low molecular weight aminobenzoate is Genocure® EPD from RAHN.

[0093] Particularly preferred aminobenzoate co-initiators are selected from the group consisting of polymerizable, oligomeric aminobenzoate co-initiators and polymeric aminobenzoate co-initiators.

[0094] Polymerizable co-initiators are disclosed in EP-A 2033949 (Agfa Graphics N.V.).

[0095] In a more preferred embodiment, the aminobenzoate co-initiator is an oligomeric aminobenzoate derivative.

[0096] Particularly preferred aminobenzoates are polyether derivatives of aminobenzoates, and the polyether is selected from the group consisting of poly(ethylene oxide), poly(propylene oxide), their copolymers, and poly(tetrahydrofuran), ethoxylated or propoxylated neopentyl glycol, ethoxylated or propoxylated trimethylpropane, and ethoxylated or propoxylated pentaerythritol.

[0097] Suitable oligomeric aminobenzoates are disclosed in W01996 / 33157 (Lambson Fine Chemicals Ltd.) and WO2011 / 030089 (Sun Chemicals B.V.). Typical examples of polyethylene glycol bis p-dimethylaminobenzoate are OMNIPOL ASA (supplier IGM Resins) and Speedcure 7040 (supplier Lambson Fine Chemicals).

[0098] Other oligomeric co-initiators or polymeric co-initiators include, for example, ESACURE A198 (a polyfunctional amine manufactured by IGM) and SARTOMER® CN3755 (an acrylated amine co-initiator manufactured by ARKEMA).

[0099] Inhibitor The curable inkjet composition can contain at least one inhibitor to improve the thermal stability of the ink.

[0100] Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphorous antioxidants, hydroquinone monomethyl ether commonly used in (meth)acrylate monomers, and hydroquinone, and t-butyl-catechol, pyrogallol, 2,6-di-tert·butyl-4-methylphenol (=BHT) can also be used.

[0101] Suitable commercially available inhibitors include, for example, Sumilizer™ GA-80, Sumilizer™ GM, and Sumilizer™ GS (manufactured by Sumitomo Chemical Co., Ltd.); Genorad™ 16, Genorad™ 18, and Genorad™ 20 (manufactured by Rahn AG); Irgastab™ UV10 and Irgastab™ UV22, Tinuvin™ 460 and CGS20 (manufactured by Ciba Specialty Chemicals); Floorstab™ UV series (range) (UV-1, UV-2, UV-5, and UV-8) (manufactured by Kromachem Ltd), Additol™ S series (range) (S100, S110, S120, and S130) (manufactured by Cytec Surface Specialties).

[0102] If such polymerization inhibitors are added in excess, it may slow down the curing rate, so it is preferable to specify the amount that can prevent polymerization before blending. The amount of the polymerization inhibitor is preferably less than 5% by weight, more preferably less than 3% by weight, of the total amount of the curable inkjet composition.

[0103] Adhesion promoter The curable inkjet composition can include an adhesion promoter to further optimize the adhesion of the cured composition to various surfaces, particularly copper surfaces.

[0104] Any adhesion promoter can be used, for example, those disclosed in WO2004 / 026977 and WO2004 / 105 (both AVECIA); WO2017 / 009097 and WO2020 / 104302 (both Agfa-Gevaert); and WO2018 / 087059, WO2018087052, WO2018087056, and WO2018087055 (all Agfa-Gevaert / Electra Polymers).

[0105] The curable inkjet composition can contain one kind of adhesion promoter, or can also contain a combination of two kinds, three kinds, or more kinds of adhesion promoters.

[0106] The total amount of the adhesion promoter is preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight, and most preferably 1 to 10% by weight, all based on the total weight of the inkjet composition.

[0107] However, it has been observed that the inkjet composition according to the present invention may have sufficient adhesiveness even in the absence of an adhesion promoter, even after soldering, gold plating, or ENIG plating. Since the presence of an adhesion promoter may cause deterioration of the stability of the inkjet ink, the curable inkjet composition according to the present invention preferably does not contain an adhesion promoter.

[0108] Flame retardant The curable inkjet composition preferably contains a flame retardant.

[0109] Suitable flame retardants include inorganic flame retardants such as alumina trihydrate and boehmite; organic phosphorus compounds such as organic phosphates (e.g., triphenyl phosphate (TPP), resorcinol bis(diphenyl phosphate) (RDP), bisphenol A diphenyl phosphate (BADP), and tricresyl phosphate (TCP)); organic phosphonates (e.g., dimethyl methylphosphonate (DMMP)); and organic phosphinates (e.g., aluminum dimethylphosphinate).

[0110] Suitable flame retardants are disclosed in WO2019 / 121098.

[0111] Colorant The curable inkjet composition can contain at least one colorant if it is possible for the inkjet ink to be substantially colorless. For example, when the inkjet ink is used as an etching resist, the colorant makes a temporary mask clearly visible to the manufacturer of the conductive pattern and enables visual inspection of the quality. When the inkjet ink is used for applying a solder mask, this typically contains a colorant. A suitable color for the solder mask is green, but other colors such as black or red can also be used.

[0112] The colorant can be a pigment or a dye.

[0113] The coloring pigment can be selected from those disclosed in HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley - VCH, 2004.ISBN 3527305769. Suitable pigments are disclosed in paragraphs

[0128] to

[0138] of WO2008 / 074548.

[0114] The pigment particles in the inkjet ink must be small enough to be able to flow freely through the inkjet printing device, particularly at the ejection nozzles. It is also desirable to use small particles to maximize the coloring power and slow down precipitation. Most preferably, the average pigment particle size is 150 nm or less. The average particle size of the pigment particles is preferably determined based on the principle of dynamic light scattering using a Brookhaven Instruments Particle Sizer BI90plus.

[0115] Generally, dyes exhibit higher lightfastness than pigments but do not cause any problems with jet injectability. It has been found that anthraquinone dyes exhibit only fine lightfastness under normal UV curing conditions used in UV curable inkjet printing. In a preferred embodiment, the colorant of the curable inkjet ink is an anthraquinone dye, such as Macrolex (trademark) Blue 3R (CASRN 325781-98-4) (manufactured by LANXESS), etc.

[0116] Other suitable dyes include crystal violet and copper phthalocyanine dyes.

[0117] It is possible to combine different colorants to obtain a desired color presentation or to improve dispersion stability. A combination of a blue colorant and a yellow colorant is a suitable combination of colorants for obtaining a green solder mask. In a particularly preferred embodiment, a combination of yellow pigment No. 150 and blue pigment No. 15:4 is used.

[0118] In a preferred embodiment, the colorant is present in an amount of 0.5 to 6.0% by weight, more preferably 0.75 to 2.5% by weight, based on the total weight of the curable inkjet ink.

[0119] Polymeric dispersant When the colorant in the curable inkjet ink is a pigment, the curable inkjet ink preferably contains a dispersant, more preferably a polymeric dispersant, to disperse the pigment.

[0120] Suitable polymeric dispersants are copolymers of two monomers, but it is also possible to include three, four, five, or even more monomers. The properties of the polymeric dispersant depend on both the nature of the monomers and their distribution in the polymer. The polymeric dispersant preferably has the following polymer composition: · Statistically polymerized monomers (for example, monomers A and B polymerize to form ABBAABAB); · Monomers with overlapping interactions (for example, monomers A and B polymerize to form ABABABAB); · Monomers with gradient (gradually decreasing) polymerization (for example, monomers A and B polymerize to form AAABAABBABBB); · Block copolymers (for example, monomers A and B polymerize to form AAAAABBBBBB), in this case, the block length of each block (2, 3, 4, 5, or more) is important for the dispersing ability of the polymeric dispersant; · Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to the backbone); and · Mixed forms of these polymers, for example, block-gradient copolymers, etc.

[0121] Suitable polymeric dispersants are listed in the "Dispersants" chapter of EP-A 1911814, more specifically in

[0064] -

[0070] and

[0074] -

[0077] .

[0122] Examples of commercially available polymeric dispersants are as follows: · DISPERBYKTM dispersants, sold by BYK CHEMIE GMBH; · SOLSPERSETM dispersants, sold by NOVEON; · TEGOTM DISPERSTM dispersants, manufactured by EVONIK; · EDAPLANTM dispersants, manufactured by MUeNZING CHEMIE; · ETHACRYLTM dispersants, manufactured by LYONDELL; · GANEXTM dispersants, manufactured by ISP; · DISPEXTM and EFKATM dispersants, manufactured by CIBA SPECIALTY CHEMICALS INC; · DISPONERTM dispersants, manufactured by DEUCHEM; and · JONCRYLTM dispersants, manufactured by JOHNSON POLYMER.

[0123] Surfactants The curable inkjet composition can contain at least one surfactant, which can act as a wetting agent, a dispersant, or an emulsifier.

[0124] The surfactant can be anionic, cationic, nonionic, or zwitterionic.

[0125] Suitable surfactants include fluorinated surfactants, fatty acid salts, ester salts of higher alcohols, alkylbenzene sulfonate salts, sulfosuccinic acid ester salts of higher alcohols, and phosphate ester salts of higher alcohols (e.g., sodium dodecylbenzene sulfonate and sodium dioctyl sulfosuccinate), ethylene oxide adducts of higher alcohols, ethylene oxide adducts of alkylphenols, ethylene oxide adducts of polyhydric alcohol fatty acid esters, and acetylene glycols and their ethylene oxide adducts (e.g., polyoxyethylene nonylphenyl ether, and SURFYNOL (trademark) 104, 104H, 440, 465, and TG (supplied by AIR PRODUCTS & CHEMICALS INC.).

[0126] Preferred surfactants are selected from fluorinated surfactants (e.g., fluorinated hydrocarbons, etc.) and silicone surfactants. The silicone surfactant is preferably a siloxane and can be alkoxylated, polyether-modified, polyether-modified hydroxy-functional group-introduced, amine-modified, epoxy-modified, and other modifications, or combinations thereof. A preferred siloxane is a polymer type, e.g., polydimethylsiloxane.

[0127] Suitable commercially available silicone surfactants include BYK (trademark) 333, BYK (trademark) 347, and BYK (trademark) UV3510 manufactured by BYK Chemie.

[0128] In a preferred embodiment, the surfactant is a polymerizable compound.

[0129] Suitable polymerizable silicone surfactants include (meth) acrylated silicone surfactants. Most preferably, the (meth) acrylated silicone surfactant is an acrylated silicone surfactant. This is because acrylate is more reactive than methacrylate. Examples include BYK (trademark) 3566 (manufactured by BYK Chemie) and Ebecryl 1360 (manufactured by Allnex). A preferred commercially available acrylated surfactant is Ebecryl 1360 (manufactured by Allnex).

[0130] In a preferred embodiment, the (meth) acrylated silicone surfactant is a polyether-modified (meth) acrylated polydimethylsiloxane or a polyester-modified (meth) acrylated polydimethylsiloxane.

[0131] Preferably, the surfactant is present in an amount of 0 to 3% by weight based on the total weight of the curable inkjet composition in the curable inkjet composition.

[0132] Preparation of Inkjet Composition The preparation of colored curable inkjet ink is well known to those skilled in the art. Suitable preparation methods are disclosed in paragraphs

[0076] to

[0085] of WO2011 / 069943.

[0133] Method for Manufacturing Electronic Device The method for manufacturing an electronic device according to the present invention includes at least one step of jet-injecting and curing a curable inkjet composition as described above onto a substrate.

[0134] According to a preferred embodiment, the electronic device is a printed circuit board (PCB).

[0135] In a particularly preferred embodiment, the method for manufacturing a PCB includes a step of coating a solder mask composition on a substrate through an inkjet printing process, followed by a step of UV curing and a step of heat treatment.

[0136] The substrate is preferably a dielectric substrate having an electrically conductive pattern, which typically includes conductive pads electrically connected to each other using wiring.

[0137] The dielectric substrate of the electronic device can be any non-conductive material. The substrate is typically a paper / resin composite, a resin / fiberglass composite, a ceramic substrate, a polyester or a polyimide. FR-4 is an example of a material often used as a dielectric substrate.

[0138] The electrically conductive pattern is typically made of any metal or alloy conventionally used in the preparation of electronic devices, and such metals or alloys include, for example, gold, silver, palladium, nickel / gold, nickel, tin, tin / lead, aluminum, tin / aluminum, and copper. The electrically conductive pattern is preferably made of copper.

[0139] The substrate preferably undergoes one or more pretreatment processes before the application of the solder mask composition. Such processes can be mechanical or chemical, or a combination thereof. A suitable pretreatment process is chemical micro-etching, which typically provides micro-roughness to the substrate. To prevent ink from penetrating into the micro-pores and to improve the printing quality, it is possible to additionally apply a so-called anti-bleeding treatment to the micro-etched surface. This anti-bleeding treatment typically includes applying a coating layer to the substrate for the purpose of adjusting the surface energy of the substrate, as a result of which the contact angle becomes sharp and the penetration of ink into the micro-pores is minimized. The anti-bleeding treatment is preferably used when printing with a low-viscosity composition.

[0140] The process of inkjet printing a solder mask layer on a dielectric substrate having an electrically conductive pattern preferably includes one or more printing steps as listed below. · The printing of the so-called "lamp" includes printing a line next to the copper wiring. This preliminary printing process ensures sufficient coverage of the Cu wiring. If there is no lamp printed next to the copper wiring, the cured solder mask may be too thin at the edge (also referred to as the shoulder) of the copper wiring. The thickness of the printed lamp is related to the height of the plated Cu wiring. When the height of the plated Cu wiring is large, a thicker lamp ink thickness is required to provide sufficient coverage at the Cu edge. The lower the height of the plated Cu wiring, the lower the thickness of the lamp that can be used. The lamp preferably has a thickness of 0 to 80 μm, more preferably 10 to 60 μm, and most preferably 20 to 40 μm. · The printing of the so-called "dam" is usually performed to show the outline of the entire solder mask layer. Such dams are usually cured using higher curing energy to provide accurate features and lines. The thickness of the dam is preferably at least the same as the thickness of the entire solder mask layer. The thickness of the dam is more preferably greater than the thickness of the entire solder mask layer for the purpose of avoiding the possibility of the ink flowing towards the open pad. The dam preferably has a thickness of 5 to 75 μm, more preferably 10 to 60 μm, and most preferably 20 to 40 μm. · Finally, print within the outline of the dam over the entire substrate, at this time covering the Cu wiring while leaving the Cu pads open for soldering.

[0141] The curable inkjet composition can be cured by exposing the composition to actinic radiation, such as electron beam or ultraviolet (UV) irradiation. Preferably, the curable inkjet composition is cured by UV irradiation, more preferably by using UV LED curing. To fix the curable composition to the substrate, a UV pin curing process can be used immediately after printing. This UV pin curing can improve the printing quality.

[0142] The heat treatment is preferably applied to a curable inkjet composition that has been jet-printed and UV-cured. The heat treatment is preferably carried out at a temperature of 80 °C to 250 °C. The temperature is preferably 100 °C or higher, more preferably 120 °C or higher. To prevent charring of the solder mask, the temperature is preferably 200 °C or lower, more preferably 160 °C or lower.

[0143] The heat treatment is typically carried out for 15 to 90 minutes.

[0144] The purposes of the heat treatment are twofold: to cure the thermosetting agents present in the curable composition and, furthermore, to polymerize potentially unreacted radiation-curable compounds. In this way, a high-density interpenetrating polymer network can be created.

[0145] The method for manufacturing a PCB can include two, three, or more inkjet printing steps. For example, the manufacturing method can include two inkjet printing steps, in one inkjet printing step, an etching resist is provided on a metal surface, and in the other inkjet printing step, a solder mask is provided on a dielectric substrate having a conductive pattern.

[0146] A third inkjet printing step can be used for legend printing.

[0147] Inkjet printing apparatus The curable inkjet composition can be jet-printed by one or more printing heads that eject droplets in a controlled manner through nozzles onto a substrate that is moving relative to the printing head(s).

[0148] A printing head suitable for an inkjet printing system is a piezoelectric head. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied. By applying a voltage, the shape of the piezoelectric ceramic transducer in the printing head changes to create a void, and then ink fills the void. When the voltage is removed again, the ceramic expands back to its original shape and ink droplets are ejected from the printing head. However, the inkjet printing method according to the present invention is not limited to piezoelectric inkjet printing. Other inkjet printing heads can be used, including various types such as continuous types.

[0149] The inkjet printing head usually reciprocates in a transverse direction across a moving ink-receiving surface (substrate). The inkjet printing head often does not print when returning. To obtain a high area throughput, bidirectional printing is preferred. Another suitable printing method is by a "single-pass printing process", which can be performed by using a page-width inkjet printing head that spans the entire width of the ink-receiving surface or a plurality of staggered inkjet printing heads. In the single-pass printing process, the inkjet printing head usually remains stationary while the ink-receiving surface is transported under the inkjet printing head.

Examples

[0150] Materials All materials used in the following examples were readily available from standard suppliers such as ALDRICH CHEMICAL Co. (Belgium) and ACROS (Belgium) unless otherwise specified. The water used was deionized water.

[0151] VMOX is N-vinyl-5-methyl-2-oxazolidinone (supplied by BASF).

[0152] DPGDA is dipropylene glycol diacrylate (sold by ARKEMA as Sartomer (trademark) SR508).

[0153] VEEA is ethyl 2-(vinyl ethoxy)acrylate (supplied by NIPPON SHOKUBAI, Japan).

[0154] PEGDA is polyethylene glycol diacrylate (supplied by ARKEMA as Sartomer™ SR259).

[0155] EHMA is 2-ethylhexyl methacrylate.

[0156] CTFA is cyclic trimethylolpropane formal acrylate (supplied by ARKEMA as Sartomer™ SR531).

[0157] DAROCUR ITX is a mixture of isomers of 2- and 4-isopropylthioxanthone (manufactured by BASF).

[0158] BAPO is a bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide photoinitiator (supplied by BASF as Irgacure™ 819).

[0159] BISAPHOS is a flame retardant containing a mixture of aromatic polyphosphates (supplied by ADEKA).

[0160] Cymel NF2000A is a triazine crosslinker (sold by ALLNEX).

[0161] Trixene BI7960 is a DMP blocked isocyanate crosslinker (sold by LANXESS).

[0162] Cyan is the cyan pigment SUN FAST BLUE 15:4 (supplied by SUN CHEMICALS).

[0163] Yellow is the yellow pigment CROMOPHTAL YELLOW D 1085J (supplied by BASF).

[0164] INHIB is a mixture that forms a polymerization inhibitor having the composition shown in Table 1.

Table 1

[0165] Cupferron(trademark) AL is aluminum N-nitrosophenylhydroxylamine (manufactured by WAKO CHEMICALS LTD).

[0166] PRECIP 162 is a dispersant and was precipitated from Disperbyk162. Disperbyk162 is a dispersion (supplied by BYK (ALTANA)).

[0167] DISP is a VEEA solution containing 30% by weight of PRECIP 162 and 1% by weight of INHIB.

[0168] GD is a green dispersion prepared as follows: A concentrated green dispersion GD having the composition shown in Table 2 was prepared.

Table 2

[0169] Evaluation method Viscosity The viscosity of the ink was measured using a HAAKE RotoVisco 1 at 45 °C and a shear rate of 1000 s -1 .

[0170] In the case of industrial inkjet printing, the viscosity at 45 °C and a shear rate of 1000 s -1 is preferably 5.0 to 15 mPa·s. More preferably, the viscosity at 45 °C and a shear rate of 1000 s -1 is less than 15 mPa·s.

[0171] LED sensitivity To evaluate the LED sensitivity of the ink, a PET substrate was coated with the inkjet ink using a bar coater and a Braive automatic film applicator. A coating with a thickness of 10 μm was obtained by the bar coater, and these were cured using a Fusion LED station (UV LED lamp 12 W). The coating was passed through the LED light using a belt. The belt was set to move at 50 m / min, and the LED light output was set to 4 W.

[0172] After coating and curing, the ink was evaluated using a Q-tip. The coating was wiped with the Q-tip and scored as follows: · 0: No wiping marks are visible on the coating · 1: Wiping marks are visible on the coating, but no ink adheres to the Q-tip · 2: Wiping marks are visible on the coating, and ink adheres to the Q-tip, but there is no damage to the coating · 3: Ink adheres to the Q-tip and there is minor damage to the coating · 4: Ink adheres to the Q-tip and there is major damage to the coating · 5: After wiping with the Q-tip, the ink is completely removed

[0173] ENIG resistance An ENIG simulation experiment was conducted using the procedure described below: · The substrate was immersed in a bath of acidic cleaner (Umicore Cleaner 865) at 40 °C for 4 minutes. Subsequently, the substrate was taken out and immersed in a rinsing bath of deionized water (DW) at room temperature (RT) for 90 seconds. · The substrate was immersed in a micro-etching bath of water containing 8.5 wt% Na2S208 and ±3.2 wt% H2SO4 (98%) at a temperature of 26 - 33 °C for 100 seconds. Subsequently, the substrate was taken out and rinsed in DW at RT for 90 seconds. · The substrate was immersed in a 2.5 wt% H2SO4 aqueous solution at RT for 30 seconds. Then, the substrate was taken out and rinsed in DW at RT for 90 seconds. The substrate was immersed in the same solution again for 60 seconds and then transferred to a palladium bath. · The substrate was immersed in a palladium activator bath (Accemulta MKN 4) at a temperature of approximately 30 °C for 90 seconds, followed by immersion in a 5 wt% H2SO4 aqueous solution at RT for 75 seconds. Then, the substrate was taken out and immersed in a rinsing bath of DW at RT for 90 seconds. · Then, the substrate was immersed in a nickel bath (Nimuden NPR4) at a temperature of approximately 85 °C for 35 minutes. Then, the substrate was taken out and immersed in a rinsing bath of DW at RT for 90 seconds. · Finally, the substrate was immersed in a gold bath (Gobright TAM 55) at a temperature of approximately 80 °C for 12 minutes. Then, the substrate was taken out and immersed in a rinsing bath of DW at RT for 90 seconds.

[0174] After ENIG treatment, so-called blistering may occur, especially around the open pads. In such areas, the ENIG solution seems to penetrate the solder mask layer and lift it up. In addition to blistering, a so-called "halo effect" may be observed as an area around the open pads with a different appearance. Both phenomena may create weak points in the adhesion of the solder mask to the substrate and may lead to delamination of the layer.

[0175] The occurrence of blisters and the halo effect was microscopically evaluated using a digital microscope Dino-LITE, and scored with a value of 0 - 5 according to the observed blistering density and halo width: · 0: No blistering and no halo. 1: Blistering density is less than 5% of the ink layer and / or halo width is less than 1 mm. ·2: Blistering density is 5-15% of the ink layer and / or halo width is 1mm-2mm. · 3: Blistering density is 15-35% of the ink layer and / or halo width is 2mm-3mm. ·4: Blistering density is 35-65% of the ink layer and / or halo width is 2mm-4mm. 5: Blistering density is greater than 65% of the ink layer and / or halo width is greater than 4mm.

[0176] Comparative Examples 1-2 and Examples 1-5 Curable inkjet compositions Examples 1 to 5 and comparative curable inkjet compositions Comparative Examples 1 and 2 were prepared according to Table 3. Weight percentages are based on the total weight of the curable inkjet composition. [Table 3]

[0177] The LED sensitivity was evaluated as described above, and the results are further shown in Table 4.

[0178] Next, using a MicroCraft CPS2013D (print head Konica Minolta KM1024iS, UV LED 395, total lamp output 12W), inkjet ink was printed onto a checkerboard (copper-plated on FR4) substrate (manufactured by Eurocircuits) to obtain a solder mask layer with a final thickness of + / -22μm. The checkerboard had a 35μm copper layer, which was roughened by chemical etching. Before chemical etching, the checkerboard was immersed in an acidic cleaner bath (MEKLEEN MAC-5330RTU, a demineralized aqueous solution containing approximately 12 - 15% H2SO4 and approximately 4 - 6% H2O2, sold by MEC Europe) activated by blowing air for 30 seconds, and then rinsed with demineralized water. In the chemical etching process, the substrate was passed through a Spray Etch machine equipped with a Bungard Sprint 3000 conveyor, heated to 30°C, and moved at a speed of 0.4 m / min while spraying the chemical etchant CZ2001 (supplied by MEC). After the rinsing process with demineralized water, an additional process of spraying 1M HCl was carried out, followed by another rinsing process with demineralized water and a resist bleeding treatment process. In the resist bleeding treatment process, the substrate was immersed in a resist bleeding solution (demineralized water containing 25 v / v% CL-8320C, pH 7.5, sold by MEC Europe) for 30 seconds. Then, the substrate was rinsed again with demineralized water and finally dried with an Air 2000 dryer (supplied by Bungard). Printing was performed on the substrate within 24 hours after this pretreatment.

[0179] After printing, the samples were fired in an oven at 150°C for 1 hour.

[0180] Various printing protocols were used: Printing 1 (P1): An image with a resolution of 1440 dpi in the X direction and 1440 in the Y direction was printed and cured. The applied UV energy corresponded to 10% of the total output of the 12W lamp. Final curing was applied to further cure the printed solder mask layer (passed 4 times with the full energy of the 12W lamp).

[0181] Print 2 (P2): Compared to Print 1, the image was printed at the same resolution, except that the UV energy applied corresponded to 100% of the total output of the 12 W lamp. Final curing was then carried out as described for Print 1.

[0182] Print 3 (P3): Compared to prints 1 and 2, the image was printed twice to achieve some thickness. In the first print, an image with a resolution of 1440 dpi in the X direction and 1080 dpi in the y direction was printed and cured. The UV energy applied corresponded to 100% of the total output of the 12 W lamp. In the second print, an image with a resolution of 720 dpi in the X direction and 1080 dpi in the y direction was printed and cured. The UV energy applied corresponded to 0% of the total output of the 12 W lamp. The final cure was then carried out as described for print 1.

[0183] ENIG resistance was assessed as described above, and these results are also shown in Table 4. [Table 4]

[0184] It is clear from Table 4 that the inks containing VMOX (Examples 1 to 5) have better ENIG resistance than the ink not containing VMOX (Comparative Example 1).

[0185] Table 4 further shows that the presence of VMOX improves LED sensitivity while maintaining good ENIG resistance. Improved LED sensitivity combined with good ENIG resistance is observed for inks containing 5-30 wt% VMOX.

[0186] Comparative Example 2 has the same composition as Example 3, except that Comparative Example 2 contains CTFA instead of VMOX. Comparative Example 2 has good ENIG resistance, but the LED sensitivity is poor even after the third and fourth passes.

Claims

1. A curable inkjet composition for a printed circuit board, comprising the following (a) one or more thermal crosslinking agents selected from the group consisting of unblocked isocyanates, blocked isocyanates, and triazine compounds, and (b) at least two photopolymerizable compounds, wherein at least one photopolymerizable compound has a chemical structure represented by General Formula I 【Chemical 1】 In the formula, R1, R2, R3, and R4 are each independently hydrogen or a substituted or unsubstituted C １ -C １０ alkyl group, and at least two photopolymerizable compounds, characterized in that: The curable inkjet composition containing the same.

2. The curable inkjet composition according to Claim 1, wherein the amount of the photopolymerizable compound represented by General Formula I is 5 to 30% by weight based on the total weight of the inkjet composition.

3. The curable inkjet composition according to Claim 1 or 2, wherein the photopolymerizable compound represented by General Formula I is N-vinyl-5-methyl-2-oxazolidinone.

4. The curable inkjet composition according to any one of Claims 1 to 3, wherein at least one thermal crosslinking agent is a blocked isocyanate.

5. The curable inkjet composition according to Claim 4, wherein the blocked isocyanate is a blocked HDI oligomer, and the oligomer is selected from the group consisting of biuret, trimethylolpropane adduct, and isocyanurate.

6. The curable inkjet composition according to any one of the preceding claims, wherein at least one thermal crosslinking agent is a triazine compound.

7. The triazine compound has the general formula III 【Chemical 2】 In the formula X represents N, O, S, P, or C; R5, R6, and R7 each independently represent a substituted or unsubstituted alkyl group. The curable inkjet composition according to Claim 6, having the chemical structure represented by the formula.

8. The curable inkjet composition according to any one of the preceding claims, wherein at least one photopolymerizable compound is a polyfunctional polymerizable compound.

9. The polyfunctional photopolymerizable compound is selected from the group consisting of 2-(2'-vinyloxyethoxy)ethyl acrylate, polyethylene glycol diacrylate, hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, polyester acrylate oligomer, and polyether acrylate oligomer. The curable inkjet composition according to Claim 8.

10. At 45°C and a shear rate of 1000 s －１ The curable inkjet composition according to any one of the preceding claims, wherein the viscosity is 5 to 15 mPa·s as measured at －１ .

11. A method for manufacturing a printed circuit board including an inkjet printing process, wherein a curable inkjet composition as defined in any one of the preceding claims is jet-injected onto a substrate and cured.

12. The method according to claim 11, further including a heating step.

13. The method according to claim 12, wherein the heating step is performed at a temperature of 80°C to 250°C.

14. The method according to any one of claims 11 to 13, wherein the substrate is a dielectric substrate provided with a conductive circuit.

15. A PCB substrate provided with a solder mask, wherein the solder mask is obtained using the curable inkjet composition according to any one of claims 1 to 10.

Images