Curable inkjet composition for manufacturing a printed circuit board

Abstract

(a) At least one thermosetting agent selected from the group consisting of non-blocked isocyanates, blocked isocyanates, and triazine compounds, (b) A polymerizable compound containing a vinyl group selected from the group consisting of vinyl ether groups, N-vinylamide groups, and N-vinylcarbamate groups, (c) A monofunctional (meth)acryloyl-containing compound, and a homopolymer of the monofunctional (meth)acryloyl-containing compound having a Tg of less than 0 °C, characterized by a curable inkjet composition for printed circuit boards.

Description

[Technical Field]

[0001] Technical Field The present invention relates to curable compositions for use as ink-jet compositions in the manufacture of electronic devices. The present invention also relates to cured products of the compositions. [Background technology]

[0002] Printed circuit boards (PCBs) are traditionally manufactured in an extensive process involving multiple photolithography and etching steps, which generates a lot of waste. There is growing interest in digitizing the PCB manufacturing workflow to reduce process steps, production costs, and waste volume.

[0003] Inkjet printing is the preferred digital manufacturing technology for several PCB production steps, such as applying etch resist and solder mask or printing legends.

[0004] PCB solder mask or solder resist acts as an insulator between copper traces and prevents the formation of solder bridges. Furthermore, PCB solder mask or solder resist plays an important role in protecting the board from oxidation caused by external influences such as weather conditions, temperature fluctuations, and humidity. Mechanical defects in the solder mask due to exposure to these external conditions can negatively impact the protective and insulating functions of the solder mask. Therefore, the primary objective for producing an effective solder mask is to provide good resistance to the conditions to which it will be exposed.

[0005] For the production of PCB solder mask via inkjet, the first requirement is that the cured ink has good adhesion on various substrates (such as copper and FR-4).

[0006] Adhesion to various substrates can be improved by adding adhesion promoters 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 containing at least two phenol groups. However, the presence of an adhesion promoter can lead to insufficient stability of the inkjet ink.

[0007] The second requirement is that the solder mask must be able to withstand the severe conditions during typical finishing processes such as soldering (solder resistance) and ENIG plating (ENIG plating resistance). In particular, the ENIG plating process, which uses severe and fluctuating conditions (pH and temperature), has very strict requirements regarding the adhesion requirements of the inkjet ink.

[0008] Patent Document 4 (Agfa-Gevaert) discloses a radiation-curable inkjet ink for preparing a solder mask, which contains a polymerizable compound, a phenol resin, and a thermal crosslinking agent. The combination of these compounds ensures good adhesion and good ENIG plating resistance.

[0009] Patent Document 5 (Taiyo Ink Manufacturing) discloses an inkjet ink for solder mask printing containing a (meth)acrylate monomer containing a thermosetting functional group. Patent Document 6 (Electra Polymers) discloses an inkjet ink for solder mask printing containing a reactive monomer, an oligomer of a prepolymer containing at least one epoxy or oxetane functional group, a polymerizable free radical compound, a thermal crosslinking agent, and a radical initiator.

[0010] However, although it has good adhesion and ENIG plating resistance, cracks may still exist in the solder mask as a result of thermal stress generated during soldering of electronic components onto the PCB or due to thermal fluctuations during the use of the PCB. Therefore, the printed and cured solder mask needs to withstand several thermal stress tests such as immersion in a solder bath and IR reflow. Such stress tests are particularly important when carried out especially after the ENIG plating process.

[0011] Patent Document 7 (Taiyo Ink Manufacturing) discloses an inkjet ink for solder mask printing containing a photopolymerizable monomer having a cyclic skeleton. Since the shrinkage rate of this photopolymerizable monomer is less than 10%, it improves the heat resistance before ENIG plating.

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

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 the manufacture of printed circuit boards (PCBs) that has good stability, good resistance to the ENIG plating process, and good heat resistance.

[0015] The object of the present invention is achieved by the curable composition according to claim 1.

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

DETAILED DESCRIPTION OF THE INVENTION

[0017] definition The term "monofunctional" (e.g., as in a monofunctional polymerizable compound) means that the polymerizable compound contains one polymerizable group.

[0018] The term "bifunctional" (e.g., as in a bifunctional polymerizable compound) means that the polymerizable compound contains two polymerizable groups.

[0019] The term "polyfunctional" or "multifunctional" (e.g., as in a polyfunctional polymerizable compound) means that the polymerizable compound contains three or more polymerizable groups.

[0020] The term "alkyl" means all possible variants for each number of carbon atoms in the alkyl group, i.e., methyl, ethyl, for three carbon atoms, n-propyl and isopropyl, for four carbon atoms, n-butyl, isobutyl, and tertiary-butyl, for five carbon atoms, n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl, and 2-methyl-butyl (and so on).

[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 group or a naphthyl group containing 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 containing 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 5-membered or 6-membered ring substituted by one, two, or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms, or combinations thereof.

[0028] The term "substituted" (e.g., in a substituted alkyl group) means that the alkyl group can be substituted by atoms other than those normally present in such a group (i.e., carbon and hydrogen). For example, a substituted alkyl group can contain a halogen atom or a thiol group. An unsubstituted alkyl group contains only carbon atoms and hydrogen atoms.

[0029] 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 by one or more components selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tertiary-butyl, esters, amides, amines, ethers, thioethers, ketones, aldehydes, sulfoxides, sulfones, sulfonic acid esters, sulfonamides, -Cl, -Br, -I, -OH, -SH, -CN, and -NO2.

[0030] Unless otherwise specified, an alkyl, cycloalkyl, or aryl interrupted by a heteroatom means that a heteroatom is present in the carbon chain of the group (e.g., -C-O-C-C- or -C-S-C-C-).

[0031] Curable inkjet composition The curable composition according to the present invention includes one or more thermal crosslinking agents selected from the group consisting of non-blocked isocyanates, blocked isocyanates, and triazine compounds, a polymerizable compound containing a vinyl group selected from the group consisting of vinyl ethers, N-vinylamides, or N-vinyl carbamates, and a monofunctional (meth)acryloyl-containing compound described below.

[0032] The curable inkjet composition may further include other polymerizable compounds.

[0033] The polymerizable compound is preferably a polymerizable free radical compound. The polymerizable free radical compound can be a monomer, an oligomer, and / or a prepolymer. Such monomers, oligomers, and / or prepolymers can have different degrees of functionality, i.e., they can have different amounts of polymerizable free radical groups. Mixtures containing combinations of monomers, oligomers, and / or prepolymers having monofunctionality, difunctionality, trifunctionality, and higher functionality can be used. The viscosity of the curable inkjet ink can be adjusted by varying the ratio of the monomer to the oligomer.

[0034] The polymerizable compound can also include functional groups such as thiol, hydroxyl, amine, sulfonic acid, phosphoric acid, and carboxylic acid. Examples of polymerizable hydroxyl-functionalized compounds are those described in paragraphs

[0028] -

[0029] of US2015 / 0090482A.

[0035] Preferred polymerizable compounds are those described in paragraphs

[0106] -

[0115] of EP - A1911814.

[0036] Particularly preferred polymerizable compounds are selected from the group consisting of 2 - phenoxyethyl acrylate, acryloylmorpholine, and polyethylene glycol diacrylate.

[0037] The composition is preferably a radiation - curable composition. Any type of radiation can be applied, but the preferred 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.

[0038] In a preferred embodiment, the composition according to the present invention comprises a mixture of a UV - curable compound and a thermal cross - linker. Therefore, the curable composition according to the present invention is preferably also a thermosetting composition. Any type of heat source can be used for the thermosetting step, but preferably, the thermosetting is carried out in an oven.

[0039] The two curing processes, heat and UV, can be carried out simultaneously or sequentially. As a result of this so-called dual curing principle, an interpenetrating polymer network is formed, which the inventors believe is the reason for the excellent mechanical properties observed compared to polymer networks that cure alone.

[0040] The curable composition according to the invention is preferably applied as an inkjet ink.

[0041] 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 4 to 14 mPa·s at 45 °C (all at a shear rate of 1000 s -1 ).

[0042] The preferred jetting temperature is 10 to 70 °C, more preferably 20 to 55 °C, and most preferably 25 to 50 °C.

[0043] 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.

[0044] Thermal Crosslinking Agent The curable composition of the present invention contains one or more heat crosslinking agents selected from the group consisting of non-blocked isocyanates, blocked isocyanates, and triazine compounds. The presence of the heat crosslinking agent can improve the adhesion of the resulting coating film after soldering or ENIG plating.

[0045] The heat crosslinking agent can be monofunctional, difunctional, or polyfunctional.

[0046] The inkjet composition can contain a mixture of different heat crosslinking agents.

[0047] Typical thermal crosslinking agents include oxirane, oxetane, melamine-formaldehyde resin, urea-formaldehyde resin, benzoguanamine-formaldehyde resin, cyclic carbonate compounds, carbodiimide, isocyanate, blocked isocyanate, and combinations thereof.

[0048] A preferred thermal crosslinking agent is an isocyanate compound. The isocyanate compound is preferably used in combination with a compound containing active hydrogen functionality, including, but not limited to, alcohol, thiol, amine, water, or combinations thereof. Moisture in the air can also cause isocyanate crosslinking. When moisture in the air reacts with the isocyanate, it may not be necessary to prepare an ink integrating the isocyanate compound with a compound containing active hydrogen functionality.

[0049] The isocyanate compound can be an aliphatic isocyanate, an alicyclic isocyanate, or an aromatic isocyanate. When the isocyanate compound is a polyfunctional isocyanate, the isocyanate compound can include a combination of aliphatic isocyanate functionality, alicyclic isocyanate functionality, or aromatic isocyanate functionality.

[0050] 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).

[0051] 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).

[0052] Examples of aromatic isocyanates include, but are not limited to, toluene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), 4,4'-diphenyl-methane diisocyanate (MDI), and xylylene diisocyanate (XDI).

[0053] Examples also include adducts of the above isocyanates (e.g., trimethylolpropane adducts), uretdione, biuret, and isocyanurate.

[0054] The isocyanate compound can be in a blocked or unblocked form, and preferably can be in a blocked form.

[0055] Blocked isocyanates can be obtained by reacting an isocyanate with a selected blocking agent. Such a blocking agent is, for example, a protecting group that is cleaved and removed when the temperature increases during a thermosetting process. The blocking agent can be selected such that it is cleaved and removed at a specific temperature (so-called deblocking temperature). The use of blocked isocyanates typically improves the storage stability of inkjet inks.

[0056] 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, 8-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 8-caprolactam), oximes of ketones or aldehydes (such as acetoxime, methyl ethyl ketone oxime, cyclohexanone oxime, and acetaldoxime), ethyleneimine, and bisulfite.

[0057] Due to toxicity reasons, hindered secondary amines can be used as blocking agents. Preferred hindered secondary amines are selected from the group consisting of ethyl-tert-butylamine, diisopropylamine, 2,6-dimethyl-piperidine, ethyl-isopropylamine, di-tert-butylamine, and diisobutylamine.

[0058] Preferred blocked isocyanate compounds are blocked HDI oligomers or blocked IPDI oligomers. Such oligomers can be, for example, trimethylolpropane adducts, biurets, or isocyanurates. IPDI oligomers and HDI oligomers are aliphatic polyfunctional blocked isocyanates having some flexibility or mobility in their structure, and this flexibility or mobility can contribute to good adhesion during the ENIG plating process.

[0059] Particularly preferred blocked isocyanate compounds are Trixene Bl 7960 (HDI biuret blocked with 3,5-dimethylpyrazole) and Trixene BI7982 (HDI trimer blocked with 3,5-dimethylpyrazole), which are commercially available from Lanxess.

[0060] In the present invention, heat crosslinking agents having a triazine skeleton are particularly preferred. The triazine moiety is considered to contribute to the mechanical properties and heat resistance of the cured film. Any triazine compound having heat crosslinking properties can be used.

[0061] Preferred triazine compounds have the general formula I [Chemical formula] and have a chemical structure according to wherein X represents N, O, S, P, or C, R1, R2, and R3 each independently represent a substituted or unsubstituted alkyl group, X preferably represents O or C, and most preferably represents O. Preferably, R1, R2, and R3 each independently represent a substituted or unsubstituted C1-C8 alkyl group. More preferably, R1, R2, and R3 each independently represent a group selected from the group consisting of methyl, ethyl, n-propyl, i-propyl, butyl, n-octyl, and 2-ethylhexyl.

[0062] Preferred triazine compounds according to general formula I and methods for their preparation are disclosed in US5084541 (American Cyanamid Company).

[0063] Preferred triazine compounds according to general formula I are commercially available from Allnex under the name Cymel® NF2000A and from BASF under the name Larotact® 150.

[0064] The inkjet ink according to the present invention preferably contains a blocked isocyanate compound or a triazine compound represented by the general formula I.

[0065] More preferably, the inkjet ink contains both a blocked isocyanate and a triazine compound represented by the general formula I.

[0066] The total amount of the thermal crosslinking agent is preferably 0.5 to 20 wt%, more preferably 1 to 15 wt%, and most preferably 2 to 12 wt% (all based on the total weight of the inkjet ink).

[0067] The amount of the blocked isocyanate compound is preferably 0.1 to 12.5 wt%, more preferably 2.5 to 10 wt%, and most preferably 5 to 8 wt% (all based on the total weight of the inkjet ink).

[0068] The amount of the triazine compound is preferably 0.1 to 5 wt%, more preferably 0.5 to 4 wt%, and most preferably 1 to 3 wt% (all based on the total weight of the inkjet ink).

[0069] When both the triazine compound and the isocyanate compound are present in the inkjet ink, the amount of the blocked isocyanate compound is preferably larger compared to 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, and more preferably 0.15 to 0.7.

[0070] The presence of the thermal crosslinking agent has been found to improve various solder resist properties such as resistance to heat, hardness, resistance to soldering heat, resistance to chemicals, electrical insulation properties, and resistance to electroless plating and immersion plating.

[0071] Polymerizable compounds containing vinyl groups The curable composition according to the present invention comprises a polymerizable compound containing a vinyl group selected from the group consisting of vinyl ethers, N-vinyl amides, and N-vinyl carbamates.

[0072] Preferred examples of polymerizable compounds containing vinyl ether groups or N-vinylamide groups are those described in EP-A 3686251 in paragraphs

[0047] to

[0056] .

[0073] A particularly preferred polymerizable vinyl ether-containing compound is 2-(2-vinyloxyethoxy)ethyl acrylate because it is advantageous in achieving a good balance between curability and viscosity of the curable inkjet composition, especially when used in an amount of 5 wt %, preferably in an amount of at least 7.5 wt %, and most preferably in an amount of at least 10 wt %, based on the total weight of the curable inkjet composition.

[0074] Particularly preferred polymerizable vinylamide-containing compounds are N-vinyl-2-pyrrolidone and N-vinylcaprolactam because they combine a high Tg with good ink curing properties and good adhesion of the cured ink layer to the recording medium.

[0075] The polymerizable compound containing an N-vinyl carbamate group preferably has the general formula II [ka] is a cyclic compound represented by In the formula, R4, R5, R6, and R7 each independently represent hydrogen, alkyl, cycloalkyl, or aryl, and combinations thereof, any of which may be separated by a heteroatom. R4 through R7 may each represent the atoms necessary to form a 5- or 6-membered ring.

[0076] Preferably, R4, R5, R6, and R7 are each independently hydrogen or a substituted or unsubstituted C1-C 10 represents an alkyl group.

[0077] Preferred compounds are disclosed in WO2015 / 022228 (BASF) and US4831153 (DOW CHEMICAL).

[0078] Cyclic compounds according to general formula II are often referred to as oxazolidinones. A particularly preferred oxazolidinone is N-vinyl-5-methyl-2-oxazolidinone, which is also referred to as vinylmethyl oxazolidinone or VMOX. By including VMOX, in particular, when it is used in an amount of 1 to 50 wt%, preferably 2.5 to 40 wt%, most preferably 5 to 30 wt% based on the total weight of the curable inkjet composition, the hardness of the cured ink layer is improved. Furthermore, since VMOX has a low viscosity compared to other N-vinyl compounds, it is particularly suitable for inkjet printing.

[0079] Polymerizable compounds containing vinyl ether, N-vinylamide, or N-vinylcarbamate can be used alone or in combination of one or more of the polymerizable compounds containing vinyl ether, N-vinylamide, or N-vinylcarbamate.

[0080] Monofunctional (meth)acryloyl-containing compounds The curable inkjet composition according to the present invention contains a monofunctional (meth)acryloyl-containing compound, and the monofunctional (meth)acryloyl-containing compound is characterized in that the Tg of the homopolymer of the monofunctional (meth)acryloyl-containing compound is less than 0°C.

[0081] By adding a (meth)acryloyl-containing compound having both the properties of being monofunctional and having a glass transition point (i.e., Tg) of the homopolymer less than 0°C, a cured layer having improved mechanical properties due to an increase in flexibility and an improvement in adhesion while maintaining sufficient heat resistance can be obtained.

[0082] The Tg of a polymer can be measured in several ways, and the most typical one is differential scanning calorimetry (DSC). On the other hand, the glass transition points of commercially available monomers are well known, and such glass transition points can be investigated in the literature or, for example, using a resin comparison tool by Sartomer.

[0083] Preferred monofunctional (meth)acryloyl-containing compounds include, but are not limited to, 2-ethylhexyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,2-trifluoroethyl acrylate, 4-cyanobutyl acrylate, n-butyl acrylate, lauryl (meth)acrylate, ethyl acrylate, hexyl (meth)acrylate, isobutyl acrylate, isopropyl acrylate, n-nonyl acrylate, propyl acrylate, sec-butyl acrylate, tetrahydrofurfuryl acrylate, decyl (meth)acrylate, isododecyl (meth)acrylate, octyl (meth)acrylate, tetradecyl (meth)acrylate, stearyl (meth)acrylate, 2-ethoxyethyl acrylate, 2-methoxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl acrylate, caprolactone acrylate, tridecyl acrylate, isodecyl acrylate, phenol (EO)2 acrylate, nonylphenol (EO)4 acrylate, nonylphenol (EO)8 acrylate, nonylphenol (PO)2 acrylate, ethoxyethoxyethyl acrylate, polypropylene glycol monomethacrylate, methoxy PEG600 methacrylate.

[0084] Particularly preferred monofunctional (meth)acryloyl-containing compounds are ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, n-butyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0085] The amount of the monofunctional (meth)acryloyl-containing compound in the curable inkjet composition is preferably at least 1 wt%, more preferably at least 2.5 wt%, and most preferably at least 5 wt% based on the total weight of the curable inkjet composition.

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

[0087] A free radical photoinitiator is a compound that initiates the polymerization of monomers and oligomers by forming free radicals upon exposure to actinic radiation. A Norrish type I initiator is an initiator that cleaves after excitation to immediately give initiating radicals. A Norrish type II initiator is a photoinitiator that is activated by actinic radiation and forms free radicals by abstraction of hydrogen from a second compound, and this second compound becomes the actual initiating free radical. This second compound is called a polymerization synergist or co-initiator. Both type I photoinitiators and type II photoinitiators can be used in the present invention, either alone or in combination.

[0088] 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.

[0089] Specific examples of free radical photoinitiators include, but are not limited to, the following compounds or combinations thereof: benzophenone and substituted benzophenone; 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.

[0090] Preferred photoinitiators are thioxanthone compounds (such as Darocur ITX, which is a mixture of isomers of 2-isopropyl thioxanthone and 4-isopropyl thioxanthone).

[0091] Another preferred photoinitiator is an acylphosphine oxide compound. The acylphosphine oxide compound can be selected from the group consisting of mono-acylphosphine oxide and di-acylphosphine oxide. 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-dimethyl-benzoyl)-2,4,4-trimethylpentylphosphine oxide, and 2,4,6-trimethoxybenzoyl-diphenylphosphine oxide.

[0092] Other preferred photoinitiators are α-hydroxy-ketone type I photoinitiators, such as oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl-phenyl]propanone] available as Esacure® KIP IT supplied by IGM resins.

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

[0094] To further improve the photosensitivity, the curable inkjet composition may additionally contain a co-initiator. Suitable examples of the co-initiator can be classified into the following three groups: (1) Tertiary aliphatic amines (such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine, and N-methylmorpholine, etc.), (2) Aromatic amines (such as amylparadimethyl-aminobenzoate, 2-n-butoxyethyl-4-(dimethylamino)benzoate, 2-(dimethylamino)-ethylbenzoate, ethyl-4-(dimethyl-amino)benzoate, and 2-ethylhexyl-4-(dimethylamino)benzoate, etc.), and (3) (Meth)acrylated amines (such as dialkylaminoalkyl (meth)acrylate (e.g., diethyl-aminoethyl acrylate) or N-morpholinoalkyl-(meth)acrylate (e.g., N-morpholinoethyl-acrylate), etc.).

[0095] A preferred co-initiator is aminobenzoate.

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

[0097] Particularly preferred aminobenzoate co-initiators are selected from the group consisting of polymerizable oligomer aminobenzoate co-initiators and polymer aminobenzoate co-initiators.

[0098] The polymerizable co-initiator is disclosed in EP-A2033949 (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 the polyethers are 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] Preferred 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 commercially available from IGM Resins and Speedcure 7040 commercially available from Lambson Fine Chemicals.

[0102] Other oligomeric co-initiators or polymeric co-initiators are, for example, ESACURE A198, a polyfunctional amine supplied by IGM, and SARTOMER® CN3755, an acrylated amine co-initiator supplied by ARKEMA.

[0103] Inhibitor The curable inkjet composition may include at least one inhibitor for improving the thermal stability of the ink.

[0104] Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphorus antioxidants, hydroquinone monomethyl ether, which is commonly used in (meth)acrylate monomers, and hydroquinone. t-Butylcatechol, pyrogallol, 2,6-di-tert-butyl-4-methylphenol (=BHT) can also be used.

[0105] Suitable commercially available inhibitors are, for example, Sumilizer™ GA-80, Sumilizer™ GM, and Sumilizer™ GS (produced by Sumitomo Chemical Co., Ltd.); Genorad™ 16, Genorad™ 18, and Genorad™ 20 (supplied by Rahn AG); Irgastab™ UV10 and Irgastab™ UV22, Tinuvin™ 460, and CGS20 (supplied by Ciba Specialty Chemicals); Floorstab™ UV range (UV-1, UV-2, UV-5, and UV-8) (supplied by Kromachem Ltd), Additol™ S range (S100, S110, S120, and S130) (supplied by Cytec Surface Specialties).

[0106] Adding such polymerization inhibitors in excess may reduce the curing rate, so it is preferable to determine the amount that can prevent polymerization before mixing. The amount of the polymerization inhibitor is preferably less than 5 wt%, more preferably less than 3 wt%, based on the total amount of the curable inkjet composition.

[0107] Adhesion promoter The curable inkjet composition may contain 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 supplied by AVECIA), those disclosed in WO2017 / 009097 and WO2020 / 104302 (both supplied by Agfa-Gevaert), and those disclosed in WO2018 / 087059, WO2018087052, WO2018087056, and WO2018087055 (all supplied by Agfa-Gevaert / ElectraPolymers) can be used.

[0109] The curable inkjet composition may contain one adhesion promoter or a combination of two, three, or more different adhesion promoters.

[0110] The total amount of the adhesion promoter is preferably 0.1 to 20 wt%, more preferably 0.5 to 15 wt%, and most preferably 1 to 10 wt% (all based on the total weight of the inkjet composition).

[0111] On the other hand, it has been recognized that the inkjet composition according to the present invention can have sufficient adhesion even after soldering, gold plating, or ENIG plating without the presence of an adhesion promoter. Since the presence of an adhesion promoter can impair 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 wt%, more preferably less than 1 wt%, and most preferably less than 0.5 wt% based on the total weight of the composition.

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

[0113] Preferred flame retardants include inorganic flame retardants (such as alumina trihydrate and boehmite); organic phosphorus compounds (organophosphates (e.g., triphenyl phosphate (TPP), resorcinol bis(diphenyl phosphate) (RDP), bisphenol A diphenyl phosphate (BADP), and tricresyl phosphate (TCP)); organophosphonates (e.g., dimethyl methylphosphonate (DMMP)); and organophosphinates (e.g., aluminum dimethylphosphinate), etc.).

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

[0115] coloring agent The curable inkjet composition can be a substantially colorless inkjet ink or can contain at least one colorant. For example, when the inkjet ink is used as an etch resist, the colorant enables the manufacturer of the conductive pattern to visually verify the quality by making the temporary coating clearly visible. When the inkjet ink is used for the application of a solder mask, the inkjet ink typically contains a colorant. A preferred 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.

[0117] The coloring pigment can be selected from those disclosed by 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] Pigment particles in the inkjet ink should be small enough to allow the ink to flow freely through the inkjet printing device, especially at the ejection nozzles. It is also desirable to use small particles to maximize color intensity and to delay sedimentation. Most preferably, the average pigment particle size is 150 nm or less. The average particle size of the pigment particles is preferably determined using a Brookhaven Instruments Particle Sizer BI90plus based on the principle of dynamic light scattering.

[0119] Generally, dyes fade more readily than pigments, but do not cause problems with ejection ability. It has been shown that the photo - fading that occurs with anthraquinone dyes is minimal under the normal UV - curing conditions used in UV - curable inkjet printing. In a preferred embodiment, the colorant in the curable inkjet ink is an anthraquinone dye such as Macrolex™ Blue 3R (CASRN 325781 - 98 - 4) supplied by LANXESS.

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

[0121] By combining different colorants, it is possible to obtain the desired color or to improve dispersion stability. A preferred combination of colorants for obtaining a green solder mask is a combination of a blue colorant and a yellow colorant. 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 - 6.0 wt%, more preferably 0.75 - 2.5 wt%, based on the total weight of the curable inkjet ink.

[0123] polymer dispersants When the colorant in the curable inkjet ink is a pigment, the curable inkjet ink preferably contains a dispersant, more preferably a polymer dispersant, to disperse the pigment.

[0124] Suitable polymer dispersants are copolymers of two monomers, but may contain three, four, five, or more monomers. The properties of the polymer dispersant depend on both the nature of the monomers and their distribution in the polymer. Copolymer dispersants preferably have the following polymer compositions. · Those in which the monomers are polymerized statistically (for example, ABBAABAB formed by the polymerization of monomers A and B), · Those in which the monomers are polymerized alternately (for example, ABABABAB formed by the polymerization of monomers A and B), · Those in which the monomers are polymerized in a gradient (tapered) manner (for example, AAABAABBABBB formed by the polymerization of monomers A and B), · Block copolymers (for example, AAAAABBBBBB formed by the polymerization of monomers A and B) (the respective block lengths (2, 3, 4, 5, or more) of the blocks are important for the dispersing ability of the polymer dispersant), · Graft copolymers (a graft copolymer consists of a polymer backbone to which polymer side chains are attached), and mixed forms of these polymers (for example, block gradient copolymers).

[0125] Suitable polymer dispersants are described in the section on "Dispersants" in EP - A1911814, more specifically, in

[0064] -

[0070] and

[0074] -

[0077] .

[0126] Commercially available examples of polymer dispersants are as follows. · DISPERBYK (trademark) dispersants available from BYK CHEMIE GMBH, · SOLSPERSE (trademark) dispersants available from NOVEON, ·TEGO® DISPERS® dispersant supplied by EVONIK, ·EDAPLAN® dispersant supplied by MUeNZING CHEMIE, ·ETHACRYL® dispersant supplied by LYONDELL, ·GANEX® dispersant supplied by ISP, ·DISPEX® dispersant and EFKA® dispersant supplied by CIBA SPECIALTY CHEMICALS INC, ·DISPONER® dispersant supplied by DEUCHEM, and ·JONCRYL® dispersant supplied by JOHNSON POLYMER.

[0127] Surfactant The curable inkjet composition may contain at least one surfactant, and such at least one surfactant may act as a wetting agent, a dispersant, or an emulsifier.

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

[0129] Suitable surfactants include fluorinated surfactants, fatty acid salts, ester salts of higher alcohols, alkylbenzene sulfonates, sulfosuccinate ester salts of higher alcohols and phosphate ester salts (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 esters, and acetylene glycols and their ethylene oxide adducts (e.g., polyoxyethylene nonylphenyl ether, and SURFYNOL® 104, 104H, 440, 465, and TG (available from AIR PRODUCTS & CHEMICALS INC.)).

[0130] Preferred surfactants are selected from fluorinated surfactants (such as fluorinated hydrocarbons) and silicone surfactants. The silicone surfactant is preferably a siloxane and may be alkoxylated, polyether-modified, polyether-modified hydroxy-functionalized, amine-modified, epoxy-modified, and other modifications, or combinations thereof. Preferred siloxanes are polymers (e.g., polydimethylsiloxane).

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

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

[0133] Preferred polymerizable silicone surfactants include (meth)acrylated silicone surfactants. Since acrylates are more reactive than methacrylates, most preferably, the (meth)acrylated silicone surfactant is an acrylated silicone surfactant. A preferred commercially available acrylated surfactant is Ebecryl 1360 supplied 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 wt% based on the total weight of the curable inkjet composition.

[0136] Preparation of Inkjet Composition The preparation of colored curable inkjet inks is well known to those skilled in the art. A preferred method of preparation is disclosed in paragraphs

[0076] to

[0085] of WO2011 / 069943.

[0137] Electronic device manufacturing method The method for manufacturing an electronic device according to the present invention includes at least one step, and the above curable inkjet composition is jetted onto a substrate and cured there.

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

[0139] In a specific preferred embodiment, the method for manufacturing a PCB includes a certain step, and the solder mask composition is applied onto a substrate via an inkjet printing step, and then a UV curing step and a heat treatment step are performed.

[0140] The substrate is preferably a dielectric substrate including a conductive pattern, and this dielectric substrate typically includes conductive pads electrically connected to each other using traces.

[0141] The dielectric substrate of the electronic device can be any non-conductive material. The substrate is typically a paper / resin composite or a resin / fiber glass composite, a ceramic substrate, a polyester, or a polyimide. FR-4 is an example of a material frequently used as a dielectric substrate.

[0142] The conductive pattern is typically made from any metal or alloy conventionally used in the preparation of electronic devices (such as gold, silver, palladium, nickel / gold, nickel, tin, tin / lead, aluminum, tin / aluminum, and copper, etc.). The conductive pattern is preferably made from copper.

[0143] Before applying the solder mask composition, the substrate is preferably subjected to one or more pretreatment processes. Such processes can be mechanical, chemical, or a combination thereof. A preferred pretreatment process is chemical micro-etching, which typically results in fine irregularities on the substrate. By additionally applying a so-called anti-bleeding treatment to the micro-etched surface, bleeding of the ink into the pores can be prevented and the printing quality can be improved. This anti-bleeding treatment typically includes applying a coating layer on the substrate to adjust its surface energy and sharpen the contact angle to minimize bleeding of the ink into the pores. The anti-bleeding treatment is preferably used when printing a composition with a low viscosity.

[0144] The process of inkjet printing a solder mask layer on a dielectric substrate having a conductive pattern preferably includes one or more of the printing steps described below. · So-called "ramp" printing involves printing a line adjacent to the copper trace. This preparatory printing step ensures sufficient coverage of the Cu trace. If the ramp is not printed adjacent to the copper trace, the cured solder mask on the edge (also called the shoulder) of the copper trace may become too thin. The thickness of the printed ramp is related to the height of the Cu trace to be soldered. When the height of the Cu trace to be soldered is high, it is necessary to increase the height of the ramp ink thickness to ensure sufficient coverage on the Cu edge. When the height of the Cu trace to be soldered is low, the ramp thickness can be reduced. The ramp 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 carried out to show the outline of the entire solder mask layer. Such dams are usually cured with increased curing energy so as to obtain distinct features and lines. The thickness of the dam is preferably at least the same as that of the complete solder mask layer. The thickness of the dam is more preferably made higher than that of the complete solder mask layer in order to avoid the possibility of ink flowing into the open pads. 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, printing is carried out over the entire substrate within the outline of the dam to coat the Cu traces, while the Cu pads for soldering are left open.

[0145] The curable inkjet composition can be cured by exposing the composition to actinic radiation (such as electron beam or ultraviolet (UV) light, etc.). Preferably, the curable inkjet composition is cured by UV radiation, and more preferably, it is cured using UV LED curing. In order to fix the curable composition on the substrate, a UV pinning curing step can be used immediately after printing. This UV pinning curing can improve the printing quality.

[0146] Preferably, a heat treatment is applied to the jetted and UV-cured curable inkjet composition. The heat treatment is preferably carried out at a temperature of 80°C to 250°C. The temperature is preferably 100°C or higher, and more preferably 120°C or higher. In order to prevent charring of the solder mask, the temperature is preferably 200°C or lower, and more preferably 160°C or lower.

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

[0148] The heat treatment has two purposes: to cure the thermally crosslinking agent present in the curable composition and to further polymerize the radiation-curable compounds that may not have reacted. In this way, a high-density interpenetrating polymer network can be created.

[0149] The method of manufacturing a PCB may include two, three, or more inkjet printing steps. For example, the method may include two inkjet printing steps, where an etch resist is applied onto a metal surface in one inkjet printing step, and a solder mask is applied onto a dielectric substrate including a conductive pattern in another inkjet printing step.

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

[0151] Inkjet Printing Device The curable inkjet composition may be jetted by one or more print heads ejecting small droplets in a controlled manner through nozzles onto a substrate (which moves relative to the print head(s)).

[0152] A preferred print head for an inkjet printing system is a piezo type head. Piezo inkjet printing is based on the operation of a piezo ceramic transducer when a voltage is applied thereto. The application of the voltage creates a void by changing the shape of the piezo ceramic transducer of the print head, and then this void is filled with ink. When the voltage is removed again, the ceramic expands and returns to its original shape, ejecting droplets of ink from the print head. However, the inkjet printing method according to the present invention is not limited to piezo inkjet printing. Other inkjet print heads can also be used, and such inkjet print heads include various types (such as continuous types).

[0153] An inkjet printhead typically performs a reciprocating scan in the lateral direction across a moving ink-receiving surface (substrate). The inkjet printhead often does not perform printing during the return operation. Bidirectional printing is preferred to increase the area throughput. Another preferred printing method is by a "single-pass printing process", which can be implemented by using a page-width inkjet printhead or by using a plurality of inkjet printheads arranged alternately to cover the entire width of the ink-receiving surface. In the single-pass printing process, the inkjet printhead usually remains stationary while the ink-receiving surface is conveyed under the inkjet printhead.

Example

[0154] Materials All the 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 available from NIPPON SHOKUBAI of Japan.

[0156] PEA is 2-phenoxyethyl acrylate available from ARKEMA as Sartomer (trademark) SR339.

[0157] ACMO is acryloyl morpholine available from RAHN.

[0158] VMOX is N-vinyl-5-methyl-2-oxazolidinone available from BASF.

[0159] EHA is 2-ethylhexyl acrylate.

[0160] EHMA is 2-ethylhexyl methacrylate.

[0161] LA is lauryl acrylate available from Sartomer.

[0162] LMA is a mixture of 60 - 80% lauryl methacrylate and 40 - 20% myristyl methacrylate, available from ARKEMA as Sartomer™ SR313E.

[0163] SA is stearyl acrylate available from KYOEISHA CHEMICAL COMPANY LTD as Light Acrylate S - A.

[0164] SMA is stearyl methacrylate.

[0165] IBOA is isobornyl acrylate available from IGM resins as Photomer 4012.

[0166] PEGDA is polyethylene glycol diacrylate available from ARKEMA as Sartomer™ SR259.

[0167] DAROCUR ITX is a mixture of isomers of 2 - isopropylthioxanthone and 4 - isopropylthioxanthone supplied by BASF.

[0168] BAPO is a bis(2,4,6 - trimethylbenzoyl) - phenylphosphine oxide photoinitiator available from BASF as Irgacure™ 819.

[0169] BISAPHOS is a flame retardant containing a mixture of aromatic polyphosphates available from ADEKA.

[0170] Trixene BI7960 is a DMP block isocyanate crosslinker commercially available from LANXESS.

[0171] Cymel NF2000A is a triazine crosslinker commercially available from ALLNEX.

[0172] Ebecryl 1360 is a silicone hexa-acrylate available from ALLNEX.

[0173] WET is a 1% solution of Ebecryl 1360 in VEEA.

[0174] Cyan is SUN FAST BLUE 15:4, a cyan pigment available from SUN CHEMICALS.

[0175] Yellow is CROMOPHTAL YELLOW D 1085J, a yellow pigment supplied by BASF.

[0176] INHIB is a mixture that forms a polymerization inhibitor having the composition set forth in Table 1. [Table 1]

[0177] Cupferron™ AL is an aluminum N-nitrosophenylhydroxylamine supplied by WAKO CHEMICALS LTD.

[0178] PRECIP 162 is a dispersant that is precipitated from Disperbyk 162, a dispersant solution available from BYK (ALTANA).

[0179] DISP is a solution of 30 wt% PRECIP162 and 1 wt% INHIB in VEEA.

[0180] GD is a green dispersion prepared as follows. A concentrated green dispersion GD was prepared having the composition shown in Table 2. [Table 2] GD was prepared as follows: 138 g of VEEA, 2 g of INHIB, 30 g of DISP, 30 g of Cyan, and 30 g of Yellow were mixed using a DISPERLUX (trademark) dispenser. Stirring was continued for 30 minutes. A container was connected to a NETZCH MiniZet mill filled with 900 g of 0.4 mm yttrium-stabilized zirconia beads (the "high wear-resistant zirconia grinding media" supplied by TOSOH Co.). The mixture was circulated through the mill for 120 minutes (retention time 45 minutes), and the rotational speed of the mill was set to approximately 10.4 m / s. Throughout the grinding procedure, the contents of the mill were cooled to keep the temperature below 60 °C. After grinding, the dispersion was discharged into a container.

[0181] Evaluation method viscosity The viscosity of the ink was measured using a HAAKE RotoVisco1 at a shear rate of 1000 s -1 at 45 °C.

[0182] For industrial inkjet printing, the viscosity at a shear rate of 1000 s -1 at 45 °C is preferably 5.0 to 15 mPa·s. More preferably, the viscosity at a shear rate of 1000 s -1 at 45 °C is less than 15 mPa·s.

[0183] The viscosity was measured again after 7 days. An ink with a viscosity change rate of less than 20% is considered stable.

[0184] ENIG resistance ENIG simulation was performed using the procedure described below. · The substrate was immersed in a bath of 40 °C pickling cleaning solution (Umicore cleaner 865) for 4 minutes. Then, the substrate was taken out and immersed in a rinsing bath of room temperature (RT) deionized water (DW) for 90 seconds. · The substrate was immersed in a micro-etching bath 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 in DW, a 2.5 wt% aqueous H2SO4 solution, and DW respectively (all performed at RT for 90 seconds). · The substrate was immersed in a 2.5 wt% aqueous H2SO4 solution at RT for 30 seconds, then taken out and rinsed in DW at RT for 90 seconds. Then, the substrate was immersed in the same solution again for 60 seconds. · The substrate was immersed in a palladium activator bath (Accemulta MKN4) at a temperature of about 30 °C for 90 seconds, then in a 5 wt% aqueous H2SO4 solution at RT for 75 seconds. Then, the substrate was taken out and immersed in a rinsing DW bath at RT for 90 seconds. · Next, the substrate was immersed in a nickel bath (Nimuden NPR4) at a temperature of about 85 °C for 35 minutes. Then, the substrate was taken out and immersed in a rinsing DW bath at RT for 90 seconds. · Finally, the substrate was immersed in a gold bath (Gobright TAM55) at a temperature of about 80 °C for 12 minutes. Then, the substrate was taken out and immersed in a rinsing DW bath at RT for 90 seconds.

[0185] After ENIG treatment, so-called blistering may occur, which may occur especially around open pads. In such areas, the ENIG solution seems to penetrate the solder mask layer and lift the solder mask layer. In addition to blistering, a so-called "halo effect" may be observed as a visually different area around the open pad. Both phenomena may create weak points in the adhesion of the solder mask to the substrate, and as a result, layer peeling may occur.

[0186] The occurrence of blisters was evaluated microscopically 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.

[0187] The occurrence of the halo phenomenon 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: The halo phenomenon is not visible. 1: The halo width is less than 1 mm. 2: The halo width is 1 mm - 2 mm. 3: The halo width is 2 mm - 3 mm. 4: The halo width is 3 mm - 4 mm. 5: The halo width is more than 4 mm.

[0188] 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: No peeling, adhesion is perfect. ·1: Only a very small part of the cured layer is detached, adhesion is almost perfect. ·2: A minor part of the cured layer is peeled off by the tape, adhesion is good. ·3: A part of the cured layer is peeled off by the tape, adhesion is poor. ·4: Most of the cured layer is peeled off by the tape, adhesion is poor. ·5: The cured layer is completely peeled off from the substrate by the tape, adhesion is non-existent.

[0189] Solder resistance The solder resistance of the inkjet ink was evaluated using a SPL600240 Digital Dynamic Solder Pot (available from L&M PRODUCTS) filled with a TSC puralloy SN100C solder alloy (available from SOLDER CONNECTION). The temperature of the solder was set at 290°C.

[0190] A Q-tip was used to apply SC7560A (a soldering accelerator supplied from SOLDER CONNECTION) onto the surface of the sample to clean the surface. The soldering accelerator was dried by holding the sample for 1 minute on each side above the solder pot. The remaining accelerator was wiped off with a soft tissue.

[0191] The sample was placed in the solder pot for 10 seconds. This was repeated 3 times in total, and then the sample was cooled for at least 10 minutes.

[0192] After cooling the printed samples at room temperature, the adhesion of the inkjet ink after the solder immersion test was evaluated. Then, they were evaluated by visually observing peeling / delamination. If no peeling / adhesion loss was observed, the sample was considered okay. If solder was observed on top of the printed layer, this was regarded as a clear sign of failure in the solder immersion test (the solder mask peeled off, enabling the solder to adhere to the copper underneath). Based on visual verification, the following scores were assigned to the printed samples after the solder immersion test. · 0: No peeling, no damage to the ink layer. · 1: Slight peeling of the ink layer. Less than 5% of the ink layer peeled off. · 2: 5 - 15% of the ink layer peeled off. · 3: 15 - 35% of the ink layer peeled off. · 4: 35 - 65% of the ink layer peeled off. · 5: More than 65% of the ink layer peeled off.

[0193] The occurrence of blisters after the solder immersion test was evaluated microscopically using a digital microscope Dino-LITE and scored with a value from 0 to 5 according to the observed blistering density. · 0: No blistering. · 1: Blistering density less than 5% of the ink layer. · 2: Blistering density 5 - 15% less than the ink layer. · 3: Blistering density 15 - 35% less than 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.

[0194] IR reflow A 40 - μm coating was prepared on FR - 4 EM 825 by coating a 20 - μm ink layer and curing it 4 times using a 12 - W UV LED lamp. Subsequently, a second 20 - μm layer was applied and cured in the same way. Finally, the 40 - μm coating was placed in an oven at 150 °C for 1 hour.

[0195] The IR reflow evaluation was carried out using an eC - reflow - mate V4 reflow oven. The temperature inside the reflow oven was measured by three sensors. One at the top, one at the bottom, and finally the central sensor measured the temperature of the sample. A 40 - μm coating was placed in the IR eC - reflow - mate V4 reflow oven and positioned above the central temperature sensor. The reflow cycle was started by heating the oven to 260 °C. When the sample temperature reached 260 °C, the oven temperature was held for 10 seconds, and then the sample was cooled with outside air. The time for one cycle was set to 4 minutes and 30 seconds. The ink coating was subjected to a maximum of 6 IR reflow cycles (C1 - C6).

[0196] The evaluation of the sample was visually carried out by counting the number of cracks after each cycle.

[0197] Examples 1 - 6 and Comparative Examples 1 - 3 According to Table 3, curable inkjet compositions Ex - 1 to Ex - 6 and comparative curable inkjet compositions Comp - 1 to Comp - 3 were prepared. The weight percentages are based on the total weight of the curable inkjet composition. Table 3 also shows the glass transition temperature (Tg) of the homopolymer of the monofunctional (meth) acryloyl compound added.

Table 3 - 1

Table 3-2

[0198] Using Craftpix CPS (Printhead Konica Minolta KM1024iS, UV LED 395 lamp total output 12W), inkjet ink printing was performed on a copper-clad laminate (CCL) to obtain a solder mask layer with a final thickness of + / -22μm. The CCL contains a 35μm copper foil roughened by chemical etching. In this chemical etching step, while spraying the chemical etching solution CZ2001 (available from MEC) heated at 30°C, the copper foil was passed through a Bungard Sprint3000 conveyor-type spray etching apparatus at a speed of 0.4 m / min. After the rinsing step with deionized water, an additional spray step using 1M HCL was carried out, followed by another rinsing step with deionized water. The copper foil was dried in an Air2000 dryer (available from Bungard). Printing was performed on this copper substrate within 24 hours from this pretreatment.

[0199] After printing, the samples were baked in an oven at 150°C for 1 hour.

[0200] 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. UV energy corresponding to 10% of the total output of the 12W lamp was applied. Final curing was applied to further cure the printed solder mask layer (4 passes with the full energy of the 12W lamp).

[0201] Print-2 (P2) : As a comparison with Print 1, the image was printed and cured in 2 passes to achieve a certain thickness, and UV energy corresponding to 100% of the total output of the 12W lamp was applied. Then, final curing was performed as described for Print 1.

[0202] As described above, the ENIG resistance, solder resistance, and IR reflow resistance of the ink were tested. The results are shown in Table 4.

Table 4

[0203] It is clear from the above results that the curable ink containing the polymerizable compound and the thermal crosslinking agent has good stability and good ENIG resistance. By adding a polymerizable monofunctional compound having a Tg of less than 0°C, the IR reflow resistance is improved.

[0204] All the inks had complete solder resistance after ENIG plating, and there was no blistering or peeling.

Claims

1. (a) one or more thermosetting agents selected from the group consisting of non-blocked isocyanates, blocked isocyanates, and triazine compounds; (b) a polymerizable compound containing a vinyl group selected from the group consisting of a vinyl ether group, an N-vinylamide group, and an N-vinylcarbamate group; (c) a monofunctional (meth)acryloyl-containing compound; A curable inkjet composition for a printed circuit board, comprising: The curable inkjet composition, wherein a homopolymer of the monofunctional (meth)acryloyl-containing compound has a Tg of less than 0°C.

2. The curable inkjet composition according to claim 1, wherein the polymerizable compound containing a vinyl group is 2-(2-vinyloxyethoxy)ethyl acrylate, N-vinylcaprolactam, N-vinyl-2-pyrrolidone, or N-vinyl-5-methyl-2-oxazolidinone.

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

4. The curable inkjet composition according to claim 3, wherein the blocked isocyanate is a blocked HDI oligomer or a blocked IPDI oligomer.

5. The curable inkjet composition according to any one of claims 1 to 4, wherein the at least one thermosetting agent is a triazine compound.

6. The triazine compound has a chemical structure of general formula I 【Chemical 1】 and in the formula, X represents N, O, S, P, or C; R1, R2, and R3 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 monofunctional (meth)acryloyl-containing compound is at least 5 wt% based on the total weight of the inkjet composition.

8. The curable inkjet composition according to any one of the preceding claims, wherein the monofunctional (meth)acryloyl-containing compound is selected from the group consisting of ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, n-butyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

9. 1000 s －１ The curable inkjet composition according to any one of the preceding claims, having a shear rate and a viscosity of 5 to 15 mPa·s when measured at 45°C.

10. A cured product obtained by applying the curable inkjet composition according to any one of the preceding claims onto a substrate and curing it there.

11. A method for manufacturing a printed circuit board including an inkjet printing step, wherein the curable inkjet composition according to any one of Claims 1 to 9 is jetted onto a substrate and cured there.

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

13. The method according to Claim 12, wherein the heating step is carried out 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 an electrically conductive circuit.

15. A PCB substrate including a solder mask layer, wherein the solder mask layer is obtained by using the curable inkjet composition according to any one of Claims 1 to 9.

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