Curable inkjet composition for manufacturing printed circuit boards

Abstract

A curable inkjet composition for a printed circuit board, comprising more than one polymerizable compound and one or more thermal crosslinking agents, wherein at least one polymerizable compound is a methacrylate.

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 legends.

[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 protective and insulating 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, the first essential requirement is that the cured ink has good adhesion to various substrates such as copper and FR-4.

[0006] The adhesion to various substrates can be improved by adding an adhesion promoter, as disclosed in Patent Document 1 and Patent Document 2 (Avecia). Patent Document 3 (Agfa-Gevaert / Electra Polymers) discloses a combination of an adhesion promoter and a compound having at least two phenolic groups. However, the presence of the adhesion promoter may deteriorate the stability of the inkjet ink.

[0007] The second essential condition is that the solder mask must be able to withstand the severe conditions in typical finishing processes, such as soldering and ENIG plating (solder resistance and ENIG plating resistance). Especially in the ENIG plating process, various severe conditions (pH and temperature) are used, so this process is very demanding regarding the essential conditions for the adhesion of inkjet inks.

[0008] Patent Document 4 (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. By combining these compounds, good adhesion and good ENIG plating resistance are ensured.

[0009] Patent Document 5 (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 6 (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.

[0010] However, even if it has good adhesion and ENIG plating resistance, there is still a possibility that cracks may occur in the solder mask as a result of thermal stress during soldering of electronic components on the PCB or due to temperature changes during the product life of the PCB. Therefore, the printed and cured solder mask must withstand multiple thermal stress tests such as immersion in a solder bath and IR reflow. Such stress tests are particularly relevant when performed after the ENIG plating process.

[0011] Patent Document 7 (Taiyo Ink Manufacturing) discloses an inkjet ink for solder mask printing, which 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.

[0012] However, there is still a need for an inkjet ink that has good ENIG plating resistance and sufficient ink stability for use in the PCB manufacturing process, and also has good resistance to thermal stress tests before and after ENIG plating.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

[0014] An object of the present invention is to provide a curable composition for solder mask printing in a printed circuit board (PCB) manufacturing process, which has good stability, good resistance to an ENIG plating process, and good heat resistance before and after the ENIG plating process.

[0015] The object of the present invention is achieved by a curable composition as defined in claim 1.

[0016] A further object of the present invention will become apparent from the description hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Definitions The term "monofunctional" means, for example, in the case of a monofunctional polymerizable compound, that the polymerizable compound has one polymerizable group.

[0018] The term "bifunctional" means, for example, in the case of a bifunctional polymerizable compound, that the polymerizable compound has two polymerizable groups.

[0019] The term "polyfunctional" or "multifunctional" means, for example, in the case of a polyfunctional polymerizable compound, that the polymerizable compound has more than two polymerizable groups.

[0020] The term "alkyl" means all possible deformed forms for alkyl groups having each number of carbon atoms, that is, methyl, ethyl, for those having 3 carbon atoms, n-propyl and isopropyl, for those having 4 carbon atoms, n-butyl, isobutyl, and tert-butyl, for those having 5 carbon atoms, n-pentyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, and 2-methylbutyl, and the like.

[0021] Unless otherwise specified, the substituted or unsubstituted alkyl group is preferably a C1-C6-alkyl group.

[0022] Unless otherwise specified, the substituted or unsubstituted alkenyl group is preferably a C2-C6-alkenyl group.

[0023] Unless otherwise specified, the substituted or unsubstituted alkynyl group is preferably a C2-C6-alkynyl group.

[0024] 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.

[0025] 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.

[0026] Unless otherwise specified, the substituted or unsubstituted aryl group is preferably a phenyl group or a naphthyl group.

[0027] 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.

[0028] The term "substituted" means that, for example, in the case of a substituted alkyl group, the alkyl group can be substituted with atoms different from those normally present in such a group (i.e., carbon and hydrogen). 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.

[0029] Unless otherwise specified, the substituted alkyl group, substituted alkenyl group, substituted alkynyl group, substituted aralkyl group, substituted alkaryl group, substituted aryl, and substituted heteroaryl group are preferably substituted by one or more components selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl, ester, amide, amine, ether, thioether, ketone, aldehyde, sulfoxide, sulfone, sulfonic acid ester, sulfonamide, -Cl, -Br, -I, -OH, -SH, -CN, and -NO2.

[0030] Unless otherwise specified, an alkyl, cycloalkyl, or aryl into which a heteroatom is inserted means that the heteroatom is present in the carbon chain of the group, for example, -C-O-C-C- or -C-S-C-C-. Curable inkjet composition

[0031] The curable composition according to the present invention is as follows - More than one polymerizable compound, at least one of which has a vinyl group, and the vinyl group is selected from the group consisting of a vinyl ether group, an N-vinylamide group, and an N-vinylcarbamate group. - One or more thermal crosslinking agents, which are selected from the group consisting of an unblocked isocyanate, a blocked isocyanate, and a triazine compound. At least one polymerizable compound is a methacrylate.

[0032] 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.

[0033] In a preferred embodiment, the composition according to the invention comprises a mixture of a UV-curable compound and a thermal crosslinking agent. Thus, the curable composition according to the invention is preferably also a thermosetting composition. Although any kind of heat source can be used in the thermosetting process, preferably, the thermosetting is carried out in an oven.

[0034] 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.

[0035] The curable composition according to the invention is preferably applied as an inkjet ink.

[0036] 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 in.

[0037] A suitable jet injection temperature is 10 to 70°C, more preferably 20 to 55°C, and most preferably 25 to 50°C.

[0038] For good image quality and adhesion, the surface tension of the curable inkjet ink is preferably 18 to 70 mN / m at 25°C, more preferably 20 to 40 mN / m at 25°C.

[0039] Polymerizable compound The curable inkjet composition according to the invention contains more than one kind of polymerizable compound, and at least one of these polymerizable compounds has a vinyl group, and this vinyl group is selected from the group consisting of a vinyl ether group, an N-vinylamide group, and an N-vinylcarbamate group.

[0040] The polymerizable 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 polymerizable 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 polymerizable compounds are those listed in paragraphs

[0106] to

[0115] of EP-A 1911814.

[0043] Particularly suitable polymerizable compounds are selected from the group consisting of 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, isobornyl acrylate, hexanediol diacrylate, trimethylolpropane triacrylate, polyethylene glycol diacrylate, 2-phenoxyethyl acrylate, and acryloylmorpholine.

[0044] At least one polymerizable compound of the curable inkjet composition has a vinyl group, and this vinyl group is selected from the group consisting of a vinyl ether group, an N-vinylamide group, and an N-vinylcarbamate group.

[0045] Preferable examples of the polymerizable compound having a vinyl ether group or an N-vinylamide group are those listed in paragraphs

[0047] to

[0056] of EP-A 3686251.

[0046] Particularly preferable vinyl ether-containing polymerizable compounds are advantageous in providing a good balance between the curability and viscosity of the curable inkjet composition, and thus are 2-(2-vinyloxyethoxy)ethyl acrylate. In particular, this is suitable when it is used in an amount of 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.

[0047] Particularly preferable vinylamide-containing polymerizable 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.

[0048] The polymerizable compound having an N-vinylcarbamate group is preferably a cyclic compound represented by the general formula I.

Chemical formula

[0049] Preferably, R1, R2, R3, and R4 each independently represent hydrogen or a substituted or unsubstituted C1-C 10 alkyl group.

[0050] Suitable compounds are disclosed in WO 2015 / 022228 (BASF) and US 4831153 (DOW CHEMICAL).

[0051] Cyclic compounds according to general formula I are often referred to as oxazolidinones. A particularly suitable oxazolidinone is N-vinyl-5-methyl-2-oxazolidinone, which is also referred to as vinylmethyl oxazolidinone, or VMOX. By including VMOX, the hardness of the cured ink layer is improved, especially when VMOX is used in an amount of 1 to 50% by weight, preferably 2.5 to 40% by weight, most preferably 5 to 30% by weight based on the total weight of the curable inkjet composition. Moreover, VMOX has a lower viscosity compared to other N-vinyl compounds, which makes VMOX particularly suitable for inkjet printing.

[0052] Polymerizable compounds having vinyl ether, N-vinylamide, or N-vinylcarbamate can be used alone or in combination of one or more polymerizable compounds having vinyl ether, N-vinylamide, or N-vinylcarbamate.

[0053] The curable composition according to the present invention can contain at least one methacrylate, i.e., any methacrylic acid ester. The methacrylate can be a monofunctional, difunctional, or polyfunctional methacrylate. The methacrylate compound can also have other functional groups, and examples of such functional groups include, but are not limited to, hydroxyl, thiol, amine, sulfonic acid, phosphoric acid, and carboxylic acid. Mixtures of methacrylates can also be used.

[0054] Although not limiting, suitable methacrylates include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, ethylhexyl methacrylate, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 4-hydroxybutyl methacrylate, hydroxypentyl methacrylate, hydroxyhexyl methacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,8-octanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, 1,11-undecanediol dimethacrylate, 1,12-dodecanediol dimethacrylate, triethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, 2-(2-vinyloxyethoxy)ethyl methacrylate, isoamyl methacrylate, stearyl methacrylate, lauryl methacrylate, octyl methacrylate, decyl methacrylate, isoamylstyl methacrylate, isostearyl methacrylate, 2-ethylhexyl methacrylate, methacryloyl morpholine, 2-ethylhexyl-diglycol methacrylate, 2-methacryloyloxyethyl hexahydrophthalic acid, butoxyethyl methacrylate, ethoxydiethylene glycol methacrylate, methoxydiethylene glycol methacrylate, methoxypolyethylene glycol methacrylate, methoxypropylene glycol methacrylate, phenoxyethyl methacrylate, tetrahydrofurfuryl methacrylate, isobornyl methacrylate, 3,3,5 - Trimethylcyclohexyl methacrylate, 2 - hydroxy - 3 - phenoxypropyl methacrylate, vinyl ether methacrylate, 2 - methacryloyloxyethyl succinic acid, 2 - methacryloyloxyethyl phthalic acid, 2 - methacryloyloxyethyl - 2 - hydroxyethyl - phthalic acid, lactone - modified soft methacrylate, t - butylcyclohexyl methacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, tripropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 1,4 - butanediol dimethacrylate, neopentyl glycol dimethacrylate, dimethylol - tricyclodecane dimethacrylate, bisphenol A EO (ethylene oxide) adduct dimethacrylate, bisphenol A PO (propylene oxide) adduct dimethacrylate, hydroxypivalate neopentyl glycol dimethacrylate, propoxylated neopentyl glycol dimethacrylate, alkoxylated dimethylol tricyclodecane dimethacrylate and polytetramethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, EO - modified trimethylolpropane trimethacrylate, tri(propylene glycol) trimethacrylate, caprolactone - modified trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol ethoxytetramethacrylate, dipentaerythritol hexamethacrylate, ditrimethylolpropane tetramethacrylate, glycerin propoxytri - methacrylate, and caprolactam - modified dipentaerythritol hexamethacrylate are available.,

[0055] Particularly preferred methacrylates are 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, isobornyl methacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane trimethacrylate, 2-(2'-vinyloxyethoxy)ethyl methacrylate, and polyethylene glycol dimethacrylate.

[0056] It has been found that the cured layer formed by the curable inkjet composition containing a certain amount of methacrylate compound exhibits better heat resistance. This is attributed to the fact that the curing rate of the composition decreases, and as a result, the shrinkage of the cured layer decreases and the adhesion improves. To obtain this effect, the amount of the methacrylate compound in the curable inkjet composition is preferably more than 1% by weight, more preferably more than 2.5% by weight, and most preferably more than 5% by weight based on the total weight of the curable inkjet composition.

[0057] However, if the amount of methacrylate is too large, the curing of the cured solder mask becomes inefficient and may reduce the heat resistance of the cured layer.

[0058] Therefore, the amount of the methacrylate compound in the curable inkjet composition is preferably 15% by weight or less, more preferably 12.5% by weight or less, and most preferably 10% by weight or less.

[0059] Thermal crosslinking agent The curable composition of the present invention contains one or more thermal crosslinking agents selected from the group consisting of unblocked isocyanates, blocked isocyanates, and triazine compounds. The presence of the thermal crosslinking agent may improve the adhesion of the obtained coating film after soldering or ENIG plating.

[0060] The thermal crosslinking agent can be monofunctional, bifunctional, or polyfunctional.

[0061] The inkjet composition can include a mixture of different thermal crosslinking agents.

[0062] Suitable thermal crosslinking agents are oxirane, oxetane, melamine formaldehyde resin, urea formaldehyde resin, benzoguanamine formaldehyde resin, cyclic carbonate compounds, carbodiimide, isocyanate, blocked isocyanate, and combinations thereof.

[0063] 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. 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.

[0064] The isocyanate compound can be an aliphatic, cycloaliphatic, or aromatic isocyanate. When the isocyanate compound is a polyfunctional isocyanate, this isocyanate compound can have a combination of aliphatic, cycloaliphatic, or aromatic isocyanate functional groups.

[0065] 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).

[0066] 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).

[0067] 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).

[0068] Also by way of example, adducts (e.g., trimethylolpropane adducts), uretdiones, biurets, and isocyanurates of the isocyanates listed above are included.

[0069] The isocyanate compound can be either blocked or unblocked, but is preferably blocked.

[0070] 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. By using blocked isocyanates, typically the storage stability of the inkjet ink is improved.

[0071] 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.

[0072] 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, ethylisopropylamine, di-tert-butylamine, and diisobutylamine.

[0073] Suitable blocked isocyanate compounds are blocked HDI oligomers or blocked IPDI oligomers. Such oligomers can be, for example, trimethylolpropane adducts, biurets, or isocyanurates.

[0074] 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.

[0075] Thermosetting agents having a triazine skeleton are particularly preferred in the present invention. The triazine moiety is thought to contribute to the mechanical properties and heat resistance of the cured film. Any triazine compound having thermosetting properties can be used.

[0076] Preferred triazine compounds have a chemical structure according to general formula II,

Chemical formula

[0077] Preferred triazine compounds according to general formula II and methods for their preparation are disclosed in US5084541 (American Cyanamid Company).

[0078] Preferred triazine compounds according to general formula II are commercially available from Allnex under the name Cymel® NF 2000A and from BASF under the name Larotact® 150.

[0079] The inkjet ink according to the present invention preferably contains a blocked isocyanate compound or a triazine compound represented by General Formula II.

[0080] More preferably, the inkjet ink contains both a blocked isocyanate and a triazine compound represented by General Formula II.

[0081] The total amount of the heat crosslinking agent is preferably 0.5 to 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.

[0082] The amount of the blocked isocyanate compound is preferably 0.1 to 12.5% by weight, more preferably 2.5 to 10% by weight, and most preferably 5 to 8% by weight, all based on the total weight of the inkjet ink.

[0083] 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.

[0084] When both the triazine compound and the isocyanate compound are present in the inkjet ink, preferably, the amount of the blocked isocyanate compound is more than the amount of the triazine compound. The ratio of the amount of the triazine compound to the amount of the isocyanate compound is preferably 0.05 to 0.95, more preferably 0.15 to 0.7.

[0085] It has been observed that the presence of the heat 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.

[0086] Photoinitiator The curable inkjet composition preferably contains a photoinitiator, and the photoinitiator is preferably a free radical photoinitiator.

[0087] A free radical photopolymerization initiator 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 upon excitation to immediately yield initiating radicals. A Norrish type II initiator is a photopolymerization initiator 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 photopolymerization initiators can be used in the present invention, either alone or in combination.

[0088] Suitable photopolymerization initiators 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.

[0089] Specific examples of free radical photopolymerization initiators 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, etc.; 2-hydroxy-2-methyl-1-phenylpropan-1-one; 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1-one; benzyldimethyl 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.

[0090] A suitable photoinitiator is a thioxanthone compound, for example, Darocur ITX which is an isomer mixture of 2- and 4-isopropylthioxanthone.

[0091] Another suitable photoinitiator is an acylphosphine oxide compound. The acylphosphine oxide compound can be selected from the group consisting of monoacylphosphine oxides and diacylphosphine oxides. Suitable 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.

[0092] Other suitable photoinitiators are α-hydroxy-ketone type I photoinitiators, such as oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone], etc., which is available from IGM Resins as Esacure® KIP IT.

[0093] The suitable amount of the photoinitiator is 0.2 to 20% by weight, more preferably 0.5 to 10% by weight, most preferably 1 to 8% by weight, and particularly preferably 1.5 to 6% by weight, all based on the total weight of the curable inkjet composition.

[0094] For the purpose of further improving the photosensitivity, the curable inkjet composition can additionally contain a co-initiator. Suitable examples of the co-initiator can be classified into three groups: (1) Tertiary aliphatic amines, such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine, and N-methylmorpholine, etc.; (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, etc.; and (3) (Meth) acrylated amines, such as dialkylaminoalkyl (meth) acrylates (e.g., diethyl - aminoethyl acrylate) or N - morpholinoalkyl - (meth) acrylates (e.g., N - morpholinoethyl acrylate), etc.

[0095] A preferred co - initiator is aminobenzoate.

[0096] A preferred low - molecular - weight aminobenzoate is Genocure® EPD manufactured by RAHN.

[0097] Particularly preferred aminobenzoate co - initiators are selected from the group consisting of polymerizable, oligomeric aminobenzoate co - initiators and polymeric aminobenzoate co - initiators.

[0098] The polymerizable co - initiator is disclosed in EP - A 2033949 (Agfa Graphics N.V.).

[0099] In a more preferred embodiment, the aminobenzoate co - initiator is an oligomeric aminobenzoate derivative.

[0100] Particularly preferred aminobenzoates are polyether derivatives of aminobenzoates, and this 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.

[0101] Suitable oligomeric aminobenzoates are disclosed in WO1996 / 33157 (Lambson Fine Chemicals Ltd.) and WO2011 / 030089 (Sun Chemicals B.V.). Typical examples of polyethylene glycol bis p-dimethylaminobenzoate are OMNIPOL ASA (supplied by IGM Resins) and Speedcure 7040 (supplied by Lambson Fine Chemicals).

[0102] Other oligomeric co-initiators or polymeric co-initiators include, for example, ESACURE A198 (a multifunctional amine manufactured by IGM) and SARTOMER® CN3755 (an acrylated amine co-initiator manufactured by ARKEMA).

[0103] Inhibitor The curable inkjet composition can contain at least one inhibitor to improve the thermal stability of the ink.

[0104] 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.

[0105] 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).

[0106] Adding such polymerization inhibitors in excess 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.

[0107] 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.

[0108] 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).

[0109] The curable inkjet composition can contain one kind of adhesion promoter, or can also contain a combination of two kinds, three kinds, or more different adhesion promoters if possible.

[0110] 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.

[0111] 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. The amount of the adhesion promoter is preferably less than 2.5% by weight, more preferably less than 1% by weight, and most preferably less than 0.5% by weight based on the total weight of the composition.

[0112] Flame retardant The curable inkjet composition preferably contains a flame retardant.

[0113] 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).

[0114] Suitable flame retardants are disclosed in WO2019 / 121098.

[0115] Colorant The curable inkjet composition can contain at least one colorant if it is possible to be a substantially colorless inkjet ink. 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.

[0116] The colorant can be a pigment or a dye, but is preferably a pigment.

[0117] The colored 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.

[0118] The pigment particles in the inkjet ink must be small enough to be able to flow freely as the ink passes through the inkjet printing device, especially at the discharge 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.

[0119] 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™ Blue 3R (CASRN 325781-98-4) (manufactured by LANXESS), etc.

[0120] Other preferred dyes include crystal violet and copper phthalocyanine dyes.

[0121] It is possible to combine different colorants to obtain a desired color rendering 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 Pigment Yellow 150 and Pigment Blue 15:4 is used.

[0122] In a preferred embodiment, the colorant is present in an amount of 0.5 to 6.0 wt%, more preferably 0.75 to 2.5 wt%, based on the total weight of the curable inkjet ink.

[0123] 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.

[0124] Suitable polymeric dispersants are copolymers of two monomers, but can also contain 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 (e.g., 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 dispersion ability of the polymer 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.

[0125] Suitable polymer dispersants are listed in the "Dispersants" chapter of EP-A 1911814, more specifically, in

[0064] to

[0070] and

[0074] to

[0077] .

[0126] Examples of commercially available polymer dispersants are as follows: · DISPERBYK (trademark) dispersants, provided by BYK CHEMIE GMBH; · SOLSPERSE (trademark) dispersants, provided by NOVEON; · TEGO (trademark) DISPERS (trademark) dispersants, manufactured by EVONIK; · EDAPLAN (trademark) dispersants, manufactured by MUeNZING CHEMIE; · ETHACRYL (trademark) dispersants, manufactured by LYONDELL; · GANEX (trademark) dispersants, manufactured by ISP; · DISPEX (trademark) and EFKA (trademark) dispersants, manufactured by CIBA SPECIALTY CHEMICALS INC; · DISPONER (trademark) dispersants, manufactured by DEUCHEM; and · JONCRYL (trademark) dispersants, manufactured by JOHNSON POLYMER.

[0127] Surfactants The curable inkjet composition can contain at least one surfactant, which can act as a wetting agent, a dispersant, or an emulsifier.

[0128] The surfactant can be anionic, cationic, nonionic, or zwitterionic.

[0129] Suitable surfactants include fluorinated surfactants, fatty acid salts, ester salts of higher alcohols, alkylbenzene sulfonate salts, sulfosuccinate 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.).

[0130] 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.

[0131] Preferred commercially available silicone surfactants include BYK (trademark) 333, BYK (trademark) 347, and BYK (trademark) UV3510 manufactured by BYK Chemie.

[0132] In a preferred embodiment, the surfactant is a polymerizable compound.

[0133] 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. A suitable commercially available acrylated surfactant is Ebecryl 1360 (manufactured by Allnex).

[0134] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether-modified (meth)acrylated polydimethylsiloxane or a polyester-modified (meth)acrylated polydimethylsiloxane.

[0135] Preferably, the surfactant is present in the curable inkjet composition in an amount of 0 to 3% by weight based on the total weight of the curable inkjet composition.

[0136] 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.

[0137] 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 the curable inkjet composition as described above onto a substrate.

[0138] According to a preferred embodiment, the electronic device is a printed circuit board (PCB).

[0139] In a particularly preferred embodiment, the method for manufacturing a PCB includes a step of coating a solder mask composition onto a substrate through an inkjet printing process, followed by a step of UV curing and a step of heat treatment.

[0140] The substrate is preferably a dielectric substrate having an electrically conductive pattern, which typically includes conductive pads electrically connected to each other using wiring.

[0141] 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.

[0142] 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.

[0143] The substrate preferably undergoes one or more pretreatment processes before coating with 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.

[0144] 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" involves printing a line adjacent to the copper wiring. This preliminary printing process ensures sufficient coverage of the Cu wiring. If there is no lamp printed adjacent to the copper wiring, the cured solder mask may be too thin at the edge (also called 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 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 which time the Cu wiring is covered, but the Cu pads remain open for soldering.

[0145] 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 on the substrate, a UV pin curing process can be used immediately after printing. This UV pin curing can improve the print quality.

[0146] The heat treatment is preferably applied to a curable inkjet composition that has been jet sprayed 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.

[0147] The heat treatment is typically carried out for 15 to 90 minutes.

[0148] The purposes of the heat treatment are twofold: to cure the thermosetting agents present in the curable composition and to further polymerize the potentially unreacted radiation curable compounds. In this way, a high-density interpenetrating polymer network can be created.

[0149] 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.

[0150] A third inkjet printing step can be used for legend printing.

[0151] Inkjet printing apparatus The curable inkjet composition can be jet sprayed 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).

[0152] An inkjet printing system suitable printing head 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 print head changes to create a void, and then ink fills there. When the voltage is removed again, the ceramic expands to its original shape and ink droplets are ejected from the print 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.

[0153] 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. For obtaining a high area throughput, bidirectional printing is preferred. Another suitable printing method is by a "single-pass printing process", which can be carried out by using a page-width inkjet printing head extending across 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

[0154] 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.

[0155] VEEA is 2-(vinyloxy)ethyl acrylate (supplier NIPPON SHOKUBAI, Japan).

[0156] PEA is 2-phenoxyethyl acrylate (as Sartomer(™) SR339, supplier ARKEMA).

[0157] ACMO is acryloyl morpholine (supplied by RAHN).

[0158] VMOX is N-vinyl-5-methyl-2-oxazolidinone (supplied by BASF).

[0159] EHMA is 2-ethylhexyl methacrylate.

[0160] TMCHMA is 3,3,5-trimethylcyclohexyl methacrylate (supplied by ARKEMA as Sartomer™ SR421A).

[0161] IBOA is isobornyl acrylate (supplied by IGM resins as Photomer 4012).

[0162] IBOMA is isobornyl methacrylate (supplied by ARKEMA as Sartomer™ SR423D).

[0163] HDDA is hexanediol diacrylate (supplied by ARKEMA as Sartomer™ SR238).

[0164] HDDMA is hexanediol dimethacrylate (supplied by ARKEMA as Sartomer™ SR239).

[0165] TMPTA is trimethylolpropane triacrylate (supplied by ARKEMA as Sartomer™ SR351).

[0166] TMPTMA is trimethylolpropane trimethacrylate (supplied by ARKEMA as Sartomer™ SR350).

[0167] VEEM is 2-(2’-vinyloxyethoxy)ethyl methacrylate (supplied by NIPPON SHOKUBAI).

[0168] PEGDA is polyethylene glycol diacrylate (supplied by ARKEMA as Sartomer™ SR259).

[0169] DAROCUR ITX is a mixture of isomers of 2- and 4-isopropylthioxanthone (manufactured by BASF).

[0170] BAPO is a bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide photoinitiator (supplied by BASF as Irgacure™ 819).

[0171] BISAPHOS is a flame retardant containing a mixture of aromatic polyphosphates (supplied by ADEKA).

[0172] Trixene BI 7960 is a DMP blocked isocyanate crosslinker (sold by LANXESS).

[0173] Cymel NF2000A is a triazine crosslinker (sold by ALLNEX).

[0174] Ebecryl 1360 is a silicone hexa-acrylate (supplied by ALLNEX).

[0175] WET is a 1% solution of Ebecryl 1360 in VEEA.

[0176] Cyan is the cyan pigment SUN FAST BLUE 15:4 (supplied by SUN CHEMICALS).

[0177] Yellow is the yellow pigment CROMOPHTAL YELLOW D 1085J (supplied by BASF).

[0178] INHIB is a mixture that forms a polymerization inhibitor having the composition shown in Table 1.

Table 1

[0179] Cupferron(trademark) AL is aluminum N-nitrosophenylhydroxylamine (manufactured by WAKO CHEMICALS LTD).

[0180] PRECIP 162 is a dispersant and was precipitated from Disperbyk 162. Disperbyk 162 is a dispersion (supplied by BYK (ALTANA)).

[0181] DISP is a VEEA solution containing 30% by weight of PRECIP 162 and 1% by weight of INHIB.

[0182] GD is a green dispersion prepared as follows: A thick green dispersion GD having the composition shown in Table 2 was prepared.

Table 2

[0183] 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 -1.

[0184] In the case of industrial inkjet printing, the viscosity at 45 °C and a shear rate of 1000 s -1 -1 is preferably less than 15 mPa·s. More preferably, the viscosity at 45 °C and a shear rate of 1000 s -1 -1 is 5.0 to 15 mPa·s.

[0185] [[ID=1X]] The viscosity was measured again after 7 days. An ink with a viscosity change of less than 20% is considered stable.

[0186] ENIG resistance An ENIG simulation experiment was conducted using the procedure as described below: - The substrate was immersed in a bath of acidic cleaner (Umicore Cleaner 865) at 40 °C for 4 minutes. Then, 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% Na2S2O8 and ±3.2 wt% H2SO4 (98%) at a temperature of 26 - 33 °C for 100 seconds. Then, the substrate was taken out and rinsed with DW, a 2.5 wt% aqueous H2SO4 solution, and DW, respectively. All rinsing was performed at RT for 90 seconds. - The substrate was immersed in a 2.5 wt% aqueous H2SO4 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. - 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% aqueous H2SO4 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. It should be noted that there seems to be an error in the original text where the unit of shear rate in and is incomplete. It should be "1000 s-1" as corrected in the translation. Also, in the translation of , it is assumed that the "-1" is part of the unit for shear rate. If there are other specific requirements or corrections needed, please adjust accordingly.·Finally, the substrate was immersed in a gold bath (Gobright TAM 55) at a temperature of approximately 80 °C for 12 minutes. Subsequently, the substrate was taken out and immersed in a DW rinsing bath at RT for 90 seconds.

[0187] After ENIG treatment, so-called blistering may occur, especially around the open pads. In such areas, the ENIG solution appears to penetrate the solder mask layer and lift it up. In addition to blistering, a so-called "halo effect" may also 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.

[0188] The occurrence of blisters was microscopically evaluated using a digital microscope Dino-LITE and scored with a value of 0 - 5 according to the observed blistering density: ·0: No blistering. ·1: Blistering density less than 5% of the ink layer. ·2: Blistering density between 5% and less than 15% of the ink layer. ·3: Blistering density between 15% and less than 35% of the ink layer. ·4: Blistering density between 35% and less than 65% of the ink layer. ·5: Blistering density more than 65% of the ink layer.

[0189] The occurrence of the halo effect was microscopically evaluated using a digital microscope Dino-LITE and scored with a value of 0 - 5 according to the observed width of the halo: ·0: No visible halo effect. ·1: Halo width less than 1 mm. ·2: Halo width between 1 mm and 2 mm. ·3: Halo width between 2 mm and 3 mm. ·4: Halo width between 2 mm and 4 mm. ·5: Halo width more than 4 mm.

[0190] The adhesion after ENIG plating was evaluated by a cross - hatch adhesion test using Tesatape (trademark) 4104 PVC tape. The evaluation was carried out according to the criteria described below. The adhesion was evaluated for both Cu and FR - 4. ·0: Nothing is removed, perfect adhesion. ·1: Only a very small part of the cured layer is detached, almost perfect adhesion. ·2: A small part of the cured layer is removed by the tape, but good adhesion. ·3: A part of the cured layer is removed by the tape, poor adhesion. ·4: Most of the cured layer is removed by the tape, poor adhesion. ·5: The cured layer is completely removed from the substrate by the tape, not adhered.

[0191] Solder resistance The solder resistance of the inkjet ink was evaluated using an SPL600240 Digital Dynamic Solder Pot (supplied by L&M PRODUCTS). The SPL600240 Digital Dynamic Solder Pot was filled with a TSC puralloy SN100C solder alloy (supplied by SOLDER CONNECTION). The solder temperature was set at 290 °C.

[0192] Using a Q - tip, a solder flux SC7560A (manufactured by SOLDER CONNECTION) for soldering was applied to the surface of the sample and the surface was cleaned. The sample was placed on the solder pot on each side for 1 minute to dry the soldering flux. The remaining flux was wiped off with a soft tissue.

[0193] The sample was placed in the solder pot for 10 seconds. This was repeated a total of 3 times, and then the sample was cooled for at least 10 minutes.

[0194] After cooling the printed samples at room temperature, the adhesion of the inkjet ink after the solder dipping test was evaluated. Subsequently, the samples were evaluated by visual observation of delamination / layer separation. If no delamination / adhesion loss was observed, the sample passed. When solder was observed on the upper surface of the printed layer, this was a clear indication of failure in the solder dipping test (since the solder mask peeled off, it was possible for the solder to adhere to the copper directly below). The following scores were assigned to the printed samples after the solder dipping test based on visual inspection: ·0: No delamination, the ink layer is not damaged. ·1: Slight delamination of the ink layer. Less than 5% of the ink layer is delaminated. ·2: 5 - 15% of the ink layer is delaminated. ·3: 15 - 35% of the ink layer is delaminated. ·4: 35 - 65% of the ink layer is delaminated. ·5: More than 65% of the ink layer is delaminated.

[0195] The occurrence of blisters after the solder dipping test was microscopically evaluated using a digital microscope Dino - LITE, and scored with a value of 0 - 5 according to the observed blistering density: ·0: No blistering. ·1: Blistering density is less than 5% of the ink layer. ·2: Blistering density is less than 5 - 15% of the ink layer. ·3: Blistering density is less than 15 - 35% of the ink layer. ·4: Blistering density is less than 35 - 65% of the ink layer. ·5: Blistering density is more than 65% of the ink layer.

[0196] IR Reflow To prepare a 40μm coating on FR - 4 EM 825, a 20μm ink layer was coated and cured 4 times using a 12W UV LED lamp. Subsequently, a second 20μm layer was coated and cured in the same way. Finally, the 40μm coating was placed in an oven at 150°C for 1 hour.

[0197] IR reflow evaluation was performed using an eC-reflow-mate V4 reflow oven. The temperature inside the reflow oven was measured with three sensors. One was at the top, one at the bottom, and the remaining one was the central sensor that measured the temperature of the sample. A 40-μm coating was placed in the IR eC-reflow-mate V4 reflow oven and positioned on the central temperature sensor. The reflow cycle started by heating the oven to 260°C. When the sample temperature reached 260°C, the oven was maintained at that temperature for 10 seconds, and then the sample was cooled with open air. The duration of one cycle was 4 minutes and 30 seconds. The ink coating was subjected to up to six IR reflow cycles (C1 to C6).

[0198] After each cycle, the sample was visually evaluated by counting the number of cracks.

[0199] Examples 1 to 6 and Comparative Examples 1 to 5 Settable inkjet compositions of Examples 1 to 6 and comparative settable inkjet compositions of Comparative Examples 1 to 5 were prepared according to Table 3. The weight percentages are based on the total weight of the settable inkjet composition.

Table 3-1

Table 3-2

[0200] Using MicroCraft CPS2013D (print head Konica Minolta KM1024iS, UV LED 395, total lamp output 12W), inkjet ink was printed on 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. In the chemical etching process, the substrate was heated to 30°C and moved at a speed of 0.4 m / min while spraying the chemical etching agent CZ2001 (supplied by MEC) through a Spray Etch machine equipped with a Bungard Sprint 3000 conveyor. After the rinsing process with demineralized water, an additional process of spraying 1M HCL was performed, followed by another rinsing process with demineralized water and a drying process in an Air2000 dryer (supplied by Bungard). The substrate was printed within 24 hours after this pretreatment.

[0201] After printing, the samples were fired in an oven at 150°C for 1 hour.

[0202] Different printing protocols were used: Print 1 (P1): An image with a resolution of 1440 dpi in the X direction and 1440 dpi 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).

[0203] Print 2 (P2): Compared with Print 1, the image achieved a certain thickness through two prints and cures, and the applied UV energy corresponded to 100% of the total output of the 12W lamp. Then, final curing was performed as described for Print 1.

[0204] The ENIG resistance and IR reflow resistance of the ink were evaluated as described above. These results are shown in Table 4.

Table 4-1

[0205] From the above results, it is clear that the curable ink composition containing the polymerizable compound and the thermal crosslinking agent has good stability and good ENIG resistance. The addition of methacrylate improves the IR reflow resistance.

[0206] All the inks had perfect solder pot resistance after ENIG plating (not shown in the table).

[0207] Examples 7 to 11 and Comparative Example 6 Curable inkjet compositions of Examples 7 to 11 and a comparative curable inkjet composition of Comparative Example 6 were prepared according to Table 5. The weight percentages are based on the total weight of the curable inkjet composition. [Table 5]

[0208] The inkjet ink was printed in the same manner as in Examples 1 to 6.

[0209] After printing, the samples were baked in an oven at 150 °C for 1 hour.

[0210] The printing protocol used was as follows: An image with a resolution of 1440 dpi in the X direction and 1440 dpi in the Y direction was printed and cured. The UV energy applied corresponded to 10% of the total output of a 12 W lamp. Final curing was applied to further cure the printed solder mask layer (passed 4 times with the full energy of a 12 W lamp).

[0211] The ENIG resistance and solder resistance of the inks were evaluated as described above. These results are shown in Table 6. [Table 6]

[0212] From the above results, it is clear that a curable ink containing 2-ethylhexyl methacrylate at 2.5% by weight or less has good ENIG resistance and good solder resistance. When 2-ethylhexyl methacrylate is present at 10% by weight or more, although the ENIG resistance is good, the solder resistance is not so good.

Claims

1. A curable inkjet composition for a printed circuit board, comprising the following - More than one polymerizable compound, at least one of which has a vinyl group selected from the group consisting of a vinyl ether group, an N-vinylamide group, and an N-vinylcarbamate group, more than one polymerizable compound, and - One or more thermal crosslinking agents selected from the group consisting of an unblocked isocyanate, a blocked isocyanate, and a triazine compound, wherein at least one polymerizable compound is methacrylate, characterized in that the curable inkjet composition.

2. The curable inkjet composition according to claim 1, wherein at least one polymerizable compound is selected from 2-(2-vinyloxyethoxy)ethyl acrylate, N-vinylcaprolactam, N-vinyl-2-pyrrolidone, and N-vinyl-5-methyl-2-oxazolidinone.

3. The curable inkjet composition according to claim 1 or 2, wherein at least one thermal crosslinking agent is a blocked isocyanate.

4. The curable inkjet composition according to claim 3, wherein the blocked isocyanate is a blocked HDI or IPDI oligomer, and the oligomer is selected from the group consisting of biuret, trimethylolpropane adduct, and isocyanurate.

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

6. The triazine compound has a chemical structure represented by General Formula II 【Chemical 1】 wherein 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 5.

7. The curable inkjet composition according to any one of the preceding claims, wherein the amount of the methacrylate is at least 5% by weight based on the total weight of the inkjet composition.

8. The curable inkjet composition according to any one of the preceding claims, wherein the one or more polymerizable compounds are selected from the group consisting of 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, isobornyl acrylate, hexanediol diacrylate, trimethylolpropane triacrylate, polyethylene glycol diacrylate, 2-phenoxyethyl acrylate, and acryloylmorpholine.

9. The curable inkjet composition according to any one of the preceding claims, wherein the methacrylate is 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, isobornyl methacrylate, hexanediol dimethacrylate, trimethylolpropane trimethacrylate, 2-(2'-vinyloxyethoxy)ethyl methacrylate, or polyethylene glycol dimethacrylate.

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

11. A cured product obtained by coating and curing the curable inkjet composition as defined in any one of the preceding claims on a substrate.

12. A method for manufacturing a printed circuit board, including an inkjet printing process, wherein the curable inkjet composition as defined in any one of Claims 1 to 10 is jet-injected and cured on a substrate.

13. The method according to Claim 12, further including a heating process.

14. The method according to Claim 13, wherein the heating process is performed at a temperature of 80°C to 250°C.

15. The method according to any one of Claims 12 to 14, wherein the substrate is a dielectric substrate provided with a conductive circuit.

16. A PCB substrate provided with a solder mask, wherein the solder mask is obtained using the curable inkjet composition as defined in any one of Claims 1 to 10.

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