Coatings that make electronic components waterproof

Abstract

Provided is a waterproof coating composition for circuit boards, comprising: at least one passivating agent, preferably comprising molecules comprising thiofunctional groups (ideally thiol groups), azole moieties or azoles, and combinations thereof; at least one binder component comprising an organic or inorganic film-forming polymer, and / or one or more polymer precursors polymerizable on the surface of a substrate; and optionally one or more additives. Also provided are methods of preparing and using the coating composition and the coated circuit boards.

Description

Technical Field

[0001] The present disclosure generally relates to so-called "water-repellent" coating compositions that increase the water resistance of coated substrates by depositing thin and ultrathin coatings; the coating compositions are used to coat electronic components, particularly circuit boards. The coating compositions comprise at least one passivating agent for passivating metal components of circuit boards, and one or more film-forming polymers and / or polymer precursors that deposit a passivating polymer coating that forms a water-repellent layer. The present disclosure also relates to methods for preparing such coating compositions, methods for depositing the passivating polymer coating on substrates, and electronic components, particularly circuit boards, coated with the passivating polymer coating, preferably an ultrathin water-repellent layer. Background Art

[0002] This section provides background information that is not necessarily prior art to the inventive concepts related to the present invention.

[0003] Many substrate surfaces benefit from various types of coatings, including functional layers, such as those that improve corrosion resistance and / or form a water-repellent coating. Water-repellent conformal coatings are particularly suitable for electronic components such as printed circuit boards (PCBs), a fundamental building block of electronic systems such as tablets and mobile phones.

[0004] Printed circuit boards use conductive traces adhered or otherwise attached to a non-conductive substrate to mechanically support and electrically connect the electronic components on the board. The conductive traces are typically metallic traces of copper, aluminum, or other conductive metal elements. Achieving moisture-resistant printed circuit boards (PCBs) that remain functional in a range of service environments, particularly in the handheld electronics market, has become increasingly important. Attempts to protect electronic products often utilize some form of conformal coating across the entire printed circuit board. Conformal coating materials are typically polymeric films that conform to the contours of the printed circuit board to provide barrier protection for the components on the board. To provide barrier protection, conformal coatings are typically approximately 50-250 μm (micrometers) thick after drying, which translates to a dry coating thickness of approximately 1 mil to 10 mils. The added mass of the coating increases device weight, which manufacturers seek to minimize, particularly in handheld devices. Such polymer coating thicknesses also tend to hinder heat dissipation, which is also undesirable. Some conformal coating compositions also have the disadvantage of containing volatile solvents that evaporate to form the final coating. As used herein, volatile organic compounds refer to any carbon compound other than CO, CO2, carbonic acid, metal carbides or carbonates, and ammonium carbonate that participates in atmospheric photochemical reactions, except those designated by the EPA as having insignificant photochemical reactivity (see EPA.gov).

[0005] Thin protective coatings have been applied using vacuum processes such as chemical vapor deposition (CVD), in which a volatile precursor chemically reacts to form solid and volatile products, which are then deposited on a substrate. However, vacuum processes build up coating thickness slowly, a disadvantage for the rapidly evolving electronics industry. Vacuum processes also have the economic disadvantage of requiring specialized chambers and the environmental disadvantage of using volatile precursors.

[0006] Therefore, there is a need for a coating composition that can rapidly deposit a water-resistant coating and a deposition method that passivates corrosion-prone metal traces, thereby providing lightweight and cost-effective protection for electronic components and that does not require a vacuum during application. Such a coating composition would preferably be suitable for use in electronic products, particularly printed circuit boards. Summary of the Invention

[0007] Applicants have developed coating compositions and methods of applying them that, among other benefits that will be apparent from reading the following description, provide improved water resistance at reduced thicknesses compared to conformal coatings and avoid the slow application process and complex equipment associated with CVD and other vacuum deposition methods. Coating compositions, coating methods, and coated substrates are provided that overcome one or more of the aforementioned disadvantages.

[0008] In one aspect (Aspect 1) of the present disclosure, a circuit board waterproof coating composition is provided, comprising, consisting essentially of, or consisting of:

[0009] (A) at least one dissolved and / or dispersed passivating agent; (B) at least one dissolved and / or dispersed adhesive component comprising an organic or inorganic film-forming polymer; and / or one or more polymer precursors polymerizable on the surface of a substrate; wherein the film-forming polymer and / or one or more polymer precursors 1) react with (A), or 2) do not react with (A); and optionally (C) one or more dissolved and / or dispersed additives selected from waxes, adhesion promoters, flow modifiers, wetting agents, rheology modifiers, stabilizers, catalysts, photoinitiators, biocides and biostats; (D) at least one solvent or solvent system comprising an organic solvent.

[0010] In a similar aspect (Aspect 2), a circuit board waterproof coating composition is provided, comprising, consisting essentially of, or consisting of:

[0011] (A) at least one dissolved and / or dispersed passivating agent, which preferably contains molecules containing thiofunctional groups, preferably thiol groups; azolic moieties; or azoles, and combinations thereof; (B) a dissolved and / or dispersed adhesive component comprising one or more of the following types of adhesives: 1) an organic or inorganic film-forming polymer that is unreactive with (A.); 2) an organic or inorganic film-forming polymer that is capable of reacting with (A.); 3) one or more polymer precursors, such as monomers, oligomers and / or prepolymers, that are polymerizable on the substrate surface and unreactive with (A.); 4) one or more polymer precursors, such as monomers, oligomers and / or prepolymers, that are polymerizable on the substrate surface and capable of reacting with (A.); (C) optionally, one or more dissolved and / or dispersed additives selected from waxes, adhesion promoters, leveling agents, flow modifiers, wetting agents, rheology modifiers, stabilizers, catalysts, pigments, photoinitiators, biocides and biostatics; and (D) optionally, at least one organic solvent.

[0012] Aspect 3: A circuit board waterproof coating composition according to Aspect 1 or 2, wherein the passivator (A) is different from the adhesive component (B); (A) is present in an amount of about 0.5 to about 60 weight %; (B) is present in an amount of about 1 weight % to about 97 weight %; (C) is present in an amount of about 1-80 weight %; and the remainder to 100 weight % is (D) at least one organic solvent, all based on the total weight of the coating composition.

[0013] Aspect 4: The circuit board waterproof coating composition according to any one of aspects 1 to 3, wherein at least a portion of the passivating agent (A) comprises a thiol group; an azole moiety; or an azole; and further comprises a secondary functional group.

[0014] Aspect 5: The circuit board waterproof coating composition according to any one of Aspects 1 to 4, wherein at least a portion of the binder component (B) is grafted to at least some molecules of the passivating agent (A).

[0015] Aspect 6: The circuit board waterproof coating composition according to any one of Aspects 1 to 4, wherein the organic or inorganic film-forming polymer (B) comprises a polymer or copolymer of an olefin monomer and a vinyl ester, preferably a block copolymer, most preferably an ethylene vinyl acetate copolymer.

[0016] Aspect 7: The circuit board waterproof coating composition of any one of Aspects 1 to 4, wherein the one or more polymer precursors comprise UV-curable monomers, oligomers and / or prepolymers.

[0017] Aspect 8: The circuit board waterproof coating composition according to any one of Aspects 1 to 7, wherein (A) comprises a molecule having a thiol functional group and an azole moiety.

[0018] Aspect 9: The circuit board waterproof coating composition according to any one of Aspects 1 to 8, wherein (A) comprises a mercaptosilane oligomer.

[0019] Aspect 10: The circuit board waterproof coating composition according to any one of Aspects 1 to 9, wherein (C) comprises a wax having a melting point of about 50 to 100°C.

[0020] Aspect 11: The circuit board waterproof coating composition of any one of Aspects 1-10, wherein the one or more polymer precursors contain an olefin monomer, and the olefin monomer includes at least one of (meth)acrylate monomers, vinyl monomers, styrenes, acrylonitriles and mixtures thereof.

[0021] Another aspect of the present disclosure (Aspect 12) is provided, which includes a method for waterproofing a circuit board, consisting essentially of a method for waterproofing a circuit board, or consisting of a method for waterproofing a circuit board, the method comprising the steps of: a) applying a coating composition according to any of the preceding aspects to a substrate surface, optionally including one or more conductive traces fixed thereon, preferably, the substrate being an electronic component, more preferably a circuit board, and most preferably a printed circuit board; b) drying the coating composition on the substrate surface; c) optionally UV curing the coating composition on the substrate surface; during any of steps a)-c), reacting the available reactive functional groups of the binder component (B) and the passivating agent (A) with the coating composition components and optionally with the conductive traces, preferably metal traces, thereby depositing a water-insoluble passivating polymer film on the substrate surface. A related aspect (Aspect 13) provides a passivating polymer film deposited on a circuit board according to the method of Aspect 12, wherein the film is removable from the circuit board by peeling. Another related aspect (Aspect 14) provides an electronic component, preferably a circuit board, coated according to Aspect 12, wherein the electronic component exhibits no current leakage during immersion in distilled water for 30 minutes with an applied power of 3 volts, preferably 10 volts, more preferably 20 volts, and most preferably 30 volts.

[0022] Another aspect of the present disclosure (Aspect 15) includes a method for waterproofing a circuit board, consisting essentially of a method for waterproofing a circuit board, or consisting of a method for waterproofing a circuit board, the method comprising, consisting essentially of, or consisting of the following steps: (a) providing a liquid coating composition comprising: (A) a passivating agent; (B1) an organic or inorganic film-forming polymer; and / or (B2) one or more polymer precursors polymerizable on the surface of a substrate; and optionally: (C) an additive; (b) applying the coating composition to the exposed surface of the circuit board and maintaining the composition in a liquid state, thereby allowing (A) to react and adsorb to the metal portion of the surface; (c) solidifying the composition, for example, removing the solvent from the layer, and optionally curing the composition to form an ultra-thin film having a thickness sufficient to waterproof the surface. Depending on the thickness required to meet the waterproofing test that is easily performed by a technician, cost, and weight constraints (i.e., seeking to minimize these parameters), the final coating can have a thickness in the range of about 0.2 to 1.6 μm, 0.6 to 15 μm, or the like.

[0023] Another aspect of the present disclosure (Aspect 16) is provided, comprising, consisting essentially of, or consisting of a printed circuit board comprising an adherent passivating polymer coating applied to a surface of the printed circuit board and conductive traces affixed thereto, the polymer coating comprising: a cured adhesive matrix comprising one or more organic or inorganic film-forming polymers, optionally crosslinked; a reaction product of one or more polymer precursors; a reaction product of a film-forming polymer with one or more polymer precursors; a passivating agent comprising a thiol functional group, preferably a thiol group; an azole moiety; an azole and combinations thereof; and / or a reaction product of a passivating agent with the conductive traces and / or at least a portion of component a); and optionally particles of a wax insoluble in the cured adhesive matrix and dispersed therein. In a related aspect (Aspect 17), is the substrate of Aspect 16, wherein the adherent polymer coating comprises a polymer made from olefin monomers comprising at least one of (meth)acrylate monomers, vinyl monomers, styrenes, acrylonitriles, and mixtures thereof.

[0024] Another aspect of the present disclosure (Aspect 18) consists of, consists essentially of, or consists of a passivating polymer film deposited according to the method of Aspect 12 on a substrate surface that is a tape, backing, or other support to form a removable film for later transfer to an end-use article, for example, as an applied preformed film in the form of a tape or by lamination to an end-use article such as a printed circuit board.

[0025] Another aspect of the present disclosure (Aspect 19) comprising, consisting essentially of, or consisting of a polymeric waterproof coating of any of the preceding aspects can be prepared using an olefin monomer that is completely soluble or at least partially soluble in a solvent and / or reactive diluent. In one embodiment, the present disclosure provides a coated substrate comprising at least one conductive metal trace on a non-conductive substrate, the metal trace and the non-conductive substrate having deposited thereon an adherent waterproof polymer coating, the adherent waterproof polymer coating being the reaction product of the coating composition described above, the metal trace being passivated by the coating.

[0026] In one embodiment of the present invention, the coating is applied to conductive traces on a printed circuit board. In one embodiment, the passivating agent may comprise a molecule containing a thiol functional group; an azole moiety; or an azole, and combinations thereof. In one embodiment, the adhesive component may comprise:

[0027] About 0.5-45 wt. % of an adhesive component selected from polyesters, or copolymers of olefins and vinyl esters, preferably block copolymers, most preferably ethylene vinyl acetate copolymers, based on the total weight of the composition, or

[0028] About 20-98 wt. % of an adhesive component, based on the total weight of the composition, comprising organic molecules having ethylenically unsaturated bonds and optionally UV curable.

[0029] In one embodiment, optional additives (C.) may be present and comprise: about 2-80 wt. % of one or more additives selected from waxes, adhesion promoters, flow modifiers, wetting agents, rheology modifiers, stabilizers, catalysts, photoinitiators, biocides, biostatic agents and other additives useful for passivation or polymer coatings, based on the total weight of the composition.

[0030] As used in this specification and claims, the following terms have the meanings as defined herein. The term "ultrathin" as used herein is based on the IPC-CC-830 definition, which states that ultrathin (UT) conformal coatings are characterized by having a thickness of 12.5 microns (0.49 mils) or less and can be organic, inorganic, or a combination of organic and inorganic components. "Bath" is understood in the coating art to refer to a composition in a container into which an article to be treated can be immersed or partially immersed so that the article or a portion thereof comes into contact with the composition in the container. For example, a coating bath is understood to refer to a coating composition in a container typically used in a method of applying a coating composition. As used herein, a "stage" refers to a period of time or step in a method, for example, a cleaning stage, a rinsing stage, a coating stage, and can also refer to a bath used to perform the step. For example, a rinsing stage can refer to a rinsing bath used in a rinsing step in a method. The term "solvent" refers to a liquid used as a medium to at least partially dissolve a solute (e.g., a component of a coating composition or concentrate according to the present disclosure) and can include water, organic molecules, inorganic molecules, and mixtures thereof, unless otherwise defined in this specification. "Solvent system" or "solvent mixture" will be understood to include two or more solvents. The term "soluble" with respect to any component means that the component acts as a "solute" that dissolves in the solvent or solvent system or reaction mixture or coating composition to form a solution that does not form a separate phase, whether liquid or solid, such as a precipitate visible to the human eye. As used herein, the term "olefin monomer" refers to a monomer having at least one carbon-carbon double bond (C=C) in its structure, which is also referred to as an ethylenically unsaturated bond. Olefin monomers may include (meth)acrylate monomers, vinyl monomers, and other polymerizable monomers having a C=C structure. As used herein, the term "(meth)acrylate monomer" includes acrylic acid, methacrylic acid, and esters thereof, which may be substituted or unsubstituted. As used herein, vinyl monomers include monomers having a vinyl functional group -CH=CH2 in its structure. As used herein, "fixed to a substrate" refers to adhering, depositing, laminating, printing, etching, pressing, embossing, or otherwise attaching to a substrate. "Passivation" and its grammatical variations will be understood by those skilled in the art to mean a reduction in the chemical reactivity of a surface (e.g., a metal surface) by contacting the metal surface with one or more compositions to chemically react, coordinately complex, or otherwise separate the metal surface, thereby forming a more passive surface with less tendency to corrode. In the present disclosure, a "waterproof coating" is defined as a coating that adheres to a surface and forms a barrier that resists corrosive damage to the circuit board associated with immersion in water or other aqueous electrolytes when powered. The water-proof coating can desirably resist and / or prevent the penetration of oxygen and / or aqueous fluids to the coated surface. Certain water-proof coatings disclosed herein also passivate some or all of the metal surfaces, particularly traces, on a printed circuit board.One measure of water repellent coating performance is the ability to prevent or reduce damage to assembled printed circuit boards caused by exposure to water or aqueous liquids due to immersion, condensation, or humidity while energized (meaning when voltage is applied to the printed circuit board). Damage associated with such exposure of inadequately protected circuit boards includes electrochemical migration phenomena such as dendritic growth and the formation of conductive anodic filaments, as well as corrosive degradation of conductive traces and conductive connections to electronic components.

[0031] For a variety of reasons, it is preferred that the coating compositions and concentrates disclosed herein be substantially free of many ingredients used in prior art compositions that serve similar purposes. Specifically, for each of the preferred minimized ingredients listed below, it is increasingly preferred, independently in the order given, that at least some embodiments of the coating compositions or concentrates according to the present invention contain no more than 1.0%, 0.5%, 0.35%, 0.10%, 0.08%, 0.04%, 0.02%, 0.01%, 0.001% or 0.0002% of each of the following ingredients, more preferably, the amounts stated are in grams per liter, more preferably in ppm: copper, silver, gold, oxidizing agents such as peroxides and peroxyacids, permanganates, perchlorates, chlorates, chlorites, hypochlorites, perborates, hexavalent chromium, sulfuric acid and sulfates, nitric acid and nitrate ions; as well as fluorine, formaldehyde, formamide, hydroxylamine, cyanide, cyanate; rare earth metals; boron, for example, borax, borates; strontium; and / or free halide ions, for example, fluoride, chloride, bromide or iodide. Moreover, for each of the preferred minimized ingredients listed below, independently in the order presented, it is increasingly preferred that at least some embodiments of the deposited compositions according to the present invention contain no more than 1.0%, 0.5%, 0.35%, 0.10%, 0.08%, 0.04%, 0.02%, 0.01%, 0.001% or 0.0002% of each of the foregoing ingredients and additional unreacted monomer or solvent, more preferably, the values ​​being reported in parts per thousand (ppt).

[0032] The simple term "metal" or "metallic" will be understood by those skilled in the art to refer to a material, whether it is an article or a surface, composed of atoms of a metal element (e.g., aluminum), the metal element being present in an amount of at least (in the order of increasing preference given) 55 atomic percent, 65 atomic percent, 75 atomic percent, 85 atomic percent, or 95 atomic percent, e.g., the simple term "aluminum" includes pure aluminum and alloys thereof containing at least (in the order of increasing preference given) 55 atomic percent, 65 atomic percent, 75 atomic percent, 85 atomic percent, or 95 atomic percent of aluminum atoms. Bare metal surface is understood to refer to a metal surface in the absence of a coating, as opposed to oxides of the metal derived from the metal surface by aging in air and / or water.

[0033] Except in the operating examples, or where otherwise indicated, all numbers used herein expressing amounts of ingredients, reaction conditions, or defining parameters of ingredients are to be understood as modified in all instances by the term "about". Throughout this specification, unless expressly stated to the contrary: percentages, "parts of..." and ratio values ​​are by weight or mass; description of a group or class of materials as suitable or preferred for a given purpose in connection with the present invention implies that mixtures of any two or more members of that group or class are likewise suitable or preferred; description of an ingredient in chemical terms refers to that ingredient upon addition to any combination specified in the description or to that ingredient produced in situ within the composition by a chemical reaction between one or more newly added ingredients and one or more ingredients already present in the composition at the time the other ingredients are added; specification of an ingredient in ionic form additionally implies the presence of sufficient counterions to produce a desired effect on the composition as a whole. electronically neutral and produces electronic neutrality towards any substance added to the composition; any counterions implicitly specified are preferably, to the extent possible, selected from other ingredients explicitly specified in ionic form; otherwise, such counterions may be freely selected except to avoid counterions that would adversely affect the purposes of the invention; unless otherwise indicated, molecular weights (MW) are weight average molecular weights; the word "mole" means "gram mole", and the word itself and all its grammatical variations may be applied to any chemical species defined by all types and numbers of atoms present therein, whether or not the species is ionic, neutral, unstable, hypothetical, or actually a stable neutral species having well-defined molecules.

[0034] This section provides an overall overview of the disclosure and is not a comprehensive disclosure of its full scope or all features, aspects and targets. These features and advantages and other features and advantages of the present invention will become more apparent to those skilled in the art based on the detailed description of the preferred embodiments. The following description is accompanied by the accompanying drawings of specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a graph showing the results of current leakage tests run on printed circuit boards coated according to the present invention and printed circuit boards coated with a comparative commercial coating.

[0036] Figure 2 This is a confocal image at 10 times magnification using polarized light of a printed circuit board coated at a thickness of 12 microns according to Example 11F. DETAILED DESCRIPTION

[0037] The present disclosure provides a circuit board coating composition, preferably a liquid, comprising:

[0038] (A.) at least one passivating agent, which preferably comprises a molecule comprising a thiofunctional group, preferably a thiol group; an azole moiety; or an azole, and combinations thereof;

[0039] (B.) A binder component, which may include one or more of the following types of binders:

[0040] 1) an organic or inorganic film-forming material that does not react with (A.), such as a polymer;

[0041] 2) an organic or inorganic film-forming material capable of reacting with (A.), such as a polymer;

[0042] 3) one or more polymer precursors, such as monomers, oligomers, and / or prepolymers, that are polymerizable on the substrate surface and unreactive with (A.);

[0043] 4) one or more polymer precursors, such as monomers, oligomers, and / or prepolymers, that are polymerizable at the substrate surface and capable of reacting with (A.); and

[0044] (C.) Optionally, one or more additives such as waxes, adhesion promoters, flow modifiers, rheology modifiers, stabilizers, catalysts, photoinitiators, biocides, biostats.

[0045] The at least one passivating agent (A) comprises one or more compositions capable of reacting, coordinating, or otherwise modifying at least one metal present in the electrical component, thereby creating a less reactive surface for the metal component of the printed circuit board, such that the surface of the metal component exhibits less corrosion, particularly when in contact with water, salt water, or the like. Ideally, the at least one passivating agent (A) comprises a molecule comprising a thiol functional group (preferably a thiol), an azole moiety, or an azole, and combinations thereof. Preferred passivating agents include thiol-functional compounds and compounds containing azole moieties.

[0046] The thiofunctional group can be a thioester, thioether, thiol and its derivatives, such as thiolates and disulfides, for example, thiolsulfinates, thiolsulfonates and sulfonic acids, as well as other organic molecules containing a thiol group that is capable of reacting with, coordinating with, or otherwise modifying at least one metal used as a trace or electrical part on a printed circuit board and is suitable for incorporation into the polymer coating according to the present disclosure.

[0047] In one embodiment, the thiofunctional material is a thioether. The thioether can be monofunctional or polyfunctional. Ideally, the number of thioether functional groups per molecule is at least 1 and can be as high as 10. Optionally, thioether functional groups greater than 10 per molecule can be used, provided that the additional functional groups do not interfere with the purpose of the present invention. The thioether can also include other functional groups. Non-limiting examples include dimethyl sulfide, methionine, 2,2-thiodiacetic acid, 3,3-thiodipropionic acid, thioanisole, and S-acetylmercaptosuccinic anhydride. The thioether can also be part of a ring or aromatic system. Non-limiting examples include thiophene, 2-thiophenecarboxylic acid, tetrathiafulvalene, 2-thiophenecarboxaldehyde, 3-thiophenecarboxaldehyde, thiazolidine, 4-thiazolidinecarboxylic acid, xylazine, and phenothiazine.

[0048] The thiol-functional compound suitable for use as the at least one passivating agent (A) may have a single thiol functional group or multiple thiol functional groups. Ideally, the number of thiol functional groups per molecule is at least 1 and may be as high as 10, although greater than 10 thiol functional groups per molecule may be used, provided that the additional functional groups do not interfere with the objectives of the present invention. Non-limiting examples of useful types of thiol-functional compounds include alkylene glycol thiols, alkyl thiols, and esters of mercaptocarboxylic acids.

[0049] The alkylene glycol dithiol may ideally correspond to Formula I:

[0050] HS-[-(CH2) a O-] b -(CH2) c SH Formula I

[0051] wherein "a" and "c" are independently 2 to 4; and "b" is 1 to 6.

[0052] Desirably, the alkylene glycol dithiol may be ethylene glycol dithiol, propylene glycol dithiol, ethylene glycol / propylene glycol dithiol, and mixtures thereof.

[0053] Typically, the esters of mercaptocarboxylic acids are preferably based on C1-C22 mercaptocarboxylic acids, ideally C1-C18, and more ideally C2-C12. Preferred esters of mercaptocarboxylic acids include esters of mercaptopropionic acid with polyfunctional alcohols, esters of mercaptoacetic acid with polyfunctional alcohols, and combinations thereof. Ideally, the polyfunctional alcohols may include alkyl and aryl alcohols having more than one OH functional group. Suitable alcohols include alkylene and polyalkylene glycols, such as diethylene glycol, dipropylene glycol, glycerol, trimethylolpropane, pentaerythritol, and dipentaerythritol.

[0054] Non-limiting examples of thiol functional compounds useful in the present invention include 2,2'-oxydi-1-ethanethiol; 1,8-dimercapto-3,6-dioxaoctane; tetrakis(ethylene glycol)dithiol; ethylene glycol dimercaptoacetate (GDMA), ethylene glycol dimercaptopropionate (GDMP), trimethylolpropane mercaptopropionate (TMPMP), pentaerythritol tetrakis 3-mercaptopropionate (PETMP), pentaerythritol tetrakis 2-mercaptoacetate (PETMA), dithiothiophene; Pentaerythritol tetrakis 3-mercaptopropionate (DiPETMP), dipentaerythritol tetrakis-2-mercaptoacetate (DiPETMA), dipentaerythritol hexa-3-mercaptopropionate, dipentaerythritol hexa-3-mercaptoacetate, and trithiol-functional compounds based on ethoxylated trimethylolpropane, such as ethoxylated trimethylolpropane tris-3-mercaptopropionate, the degree of ethoxylation ideally being 5 to 12 moles of ethoxylation per thiol group, one such product being ETTMP 1300 is commercially available. Other examples of thiol functional compounds include thiol functionalized silane oligomers, including alkoxysilane oligomers having one or more thiol functional groups, for example mercaptoethoxysilane oligomers such as T-Cure; thiol-functionalized polycaprolactones, for example polycaprolactone tetrakis (3-mercaptopropionate), such as PCL4MP 1350, and thioesters of trishydroxyethyl isocyanurate, such as Tempic.

[0055] In other embodiments, the thiol-functional compound may have secondary functional groups including, but not limited to, ethylenically unsaturated bonds, azole groups, silanol groups, or hydroxyl groups.

[0056] Suitable thiol-functional compounds that also contain one or more silicon atoms include mercaptoalkoxysilanes of the general formula II:

[0057]

[0058] in:

[0059] - the substituents R are identical or different and are: C1-C8 alkyl (preferably CH3); alkenyl (preferably C2-C12 alkenyl); aryl (preferably C6-C10 aryl); aralkyl (preferably C7-C16 aralkyl); or a group OR';

[0060] - the substituents R' are the same or different and are: C1-C24 (preferably C1-C4 or C12-C18) branched or unbranched monovalent alkyl or alkenyl; aryl (preferably C6-C10 aryl) or aralkyl (preferably C7-C16 aralkyl);

[0061] -R" is a branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic / aromatic divalent C1-C30 hydrocarbon group, which is optionally substituted with NH2 or NHR'; and

[0062] -x is 1-3.

[0063] When x=1, R" is preferably -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2-, -CH(CH3)-, -CH2CH(CH3)-, -CH(CH3)CH2-, -C(CH3)2-, -CH(C2H5)-, -CH2CH2CH(CH3)-, -CH2CH(CH3)CH2-, or

[0064] When x=2, R″ is preferably CH, —CH—CH2, —CH2—CH, C—CH3, —CH—CH2—CH2, —CH—CH—CH3 or —CH2—CH—CH2.

[0065] Preferred (mercapto)alkoxysilanes of formula II include:

[0066] 3-Mercaptopropyl (trimethoxysilane); 3-Mercaptopropyl (triethoxysilane); 3-Mercaptopropyl (diethoxymethoxysilane); 3-Mercaptopropyl (tripropoxysilane); 3-Mercaptopropyl (dipropoxymethoxysilane); 3-Mercaptopropyl (tridodecyloxysilane); 3-Mercaptopropyl (tritetradecyloxysilane); 3-Mercaptopropyl (trihexadecyloxysilane); 3-Mercaptopropyl (trioctadecyloxysilane); 3-Mercaptopropyl (didodecyloxy)tetradecyloxysilane; 3-Mercaptopropyl (dodecyloxy)tetradecyloxy (hexadecyloxy) silane; (dimethoxymethylsilane); 3-Mercaptopropyl (methoxydimethylsilane) ); 3-mercaptopropyl (diethoxymethylsilane); 3-mercaptopropyl (ethoxydimethylsilane); 3-mercaptopropyl (dipropoxymethylsilane); 3-mercaptopropyl (propoxydimethylsilane); 3-mercaptopropyl (diisopropoxymethylsilane); 3-mercaptopropyl (isopropoxydimethylsilane); 3-mercaptopropyl (dibutoxymethylsilane); 3-mercaptopropyl (butoxydimethylsilane); 3-mercaptopropyl (diisobutoxymethylsilane); 3-mercaptopropyl (isobutoxydimethylsilane); 3-mercaptopropyl (di-dodecyloxymethylsilane); 3-mercaptopropyl (dodecyloxydimethylsilane); 3-mercaptopropyl (di-tetradecyloxymethylsilane); silane); 3-mercaptopropyl (tetradecyloxydimethylsilane); 2-mercaptoethyl (trimethoxysilane); 2-mercaptoethyl (triethoxysilane); 2-mercaptoethyl (diethoxymethoxysilane); 2-mercaptoethyl (tripropoxysilane); 2-mercaptoethyl (dipropoxymethoxysilane); 2-mercaptoethyl (tridodecyloxysilane); 2-mercaptoethyl (tritetradecyloxysilane); 2-mercaptoethyl (trihexadecyloxysilane); 2-mercaptoethyl (trioctadecyloxysilane); 2-mercaptoethyl (didodecyloxy)tetradecyloxysilane; 2-mercaptoethyl (dodecyloxy)tetradecyloxy (hexadecyloxy) silane; 2- Mercaptoethyl (dimethoxymethylsilane); 2-mercaptoethyl (methoxydimethylsilane); 2-mercaptoethyl (diethoxymethylsilane); 1-mercaptoethyl (ethoxydimethylsilane); 1-mercaptomethyl (trimethoxysilane); 1-mercaptomethyl (triethoxysilane); 1-mercaptomethyl (diethoxymethoxysilane); 1-mercaptomethyl (dipropoxymethoxysilane); 1-mercaptomethyl (tripropoxysilane); 1-mercaptomethyl (trimethoxysilane); 1-mercaptomethyl (dimethoxymethylsilane); 1-mercaptomethyl (methoxydimethylsilane); 1-mercaptomethyl (diethoxymethylsilane); 1-mercaptomethyl (ethoxydimethylsilane);

[0067] 1,3-Bismercaptopropyl(trimethoxysilane); 1,3-Bismercaptopropyl(triethoxysilane);

[0068] 1,3-Bismercaptopropyl (tripropoxysilane); 1,3-Bismercaptopropyl (tridodecyloxysilane);

[0069] 1,3-Bismercaptopropyl (tri-tetradecyloxysilane); 1,3-Bismercaptopropyl (tri-hexadecyloxysilane);

[0070] 2,3-dimercaptopropyl(trimethoxysilane); 2,3-dimercaptopropyl(triethoxysilane);

[0071] 2,3-dimercaptopropyl(tripropoxysilane); 2,3-dimercaptopropyl(tridodecyloxysilane);

[0072] 2,3-dimercaptopropyl (tri-tetradecyloxysilane); 2,3-dimercaptopropyl (tri-hexadecyloxysilane); 3-mercaptobutyl (trimethoxysilane); 3-mercaptobutyl (triethoxysilane); 3-mercaptobutyl (diethoxymethoxysilane); 3-mercaptobutyl (tripropoxysilane); 3-mercaptobutyl (dipropoxymethoxysilane); 3-mercaptobutyl (dimethoxymethylsilane); 3-mercaptobutyl (dimethoxymethylsilane); ethoxymethylsilane); 3-mercaptobutyl (dimethylmethoxysilane); 3-mercaptobutyl (dimethylethoxysilane); 3-mercaptobutyl (tri-dodecyloxysilane); 3-mercaptobutyl (tri-tetradecyloxysilane); 3-mercaptobutyl (tri-hexadecyloxysilane); 3-mercaptobutyl (di-dodecyloxy) tetradecyloxysilane; or 3-mercaptobutyl (dodecyloxy) tetradecyloxy (hexadecyloxy) silane. These compounds and other compounds of formula I may be used alone or as a mixture of the compounds.

[0073] Representative, non-limiting examples of preferred coating compositions include passivating agents having a second functional group in / on the molecule:

[0074] Thiol-functionalized polyacrylate oligomers and prepolymers with reactive unsaturated bonds, such as thiol-functionalized urethane acrylates, polyester acrylates, amino acrylates, and epoxy acrylates. Preferred examples include Ebecryl ultraviolet (UV) and electron beam (EB) energy curable prepolymers, such as mercapto-modified polyester acrylate resins;

[0075] Mercaptobenzotriazoles, which have a thiol functionality on the triazole ring fused to benzene;

[0076] Thiol-functional silanes as described above, in particular 3-mercaptopropyltrimethoxysilane; and thiol-bearing silanol precursors that produce thiol-functional silanes upon hydrolysis, such as, by way of non-limiting example, Dow Corning Z-6062, Momentive A-189, Evonik MTMO, HENGDA-M2133, SHinEtsu KBM-803, Wacker GF70, and Coatosil Tcure, a silane oligomer of about 600-700 g / mol;

[0077] Thio-functional silanes, such as 2-(3-trimethoxysilylpropylthio)thiophene;

[0078] Thiols having polar functional groups in the molecule, such as ether moieties, hydroxyl functional groups, or acid functional groups. Non-limiting examples include dithiothreitol, poly(ethylene glycol) methyl ether thiol, poly(ethylene glycol) 2-mercaptoethyl ether acetic acid, and

[0079] • Silanes bearing an azole moiety, such as N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole.

[0080] Other preferred materials for use as at least one passivating agent (A) are compounds or azole compounds having an azole moiety. Suitable azole functional compounds for use as at least one passivating agent (A) may have a single azole moiety or multiple azole moieties, i.e., a single azole ring or multiple azole rings. Ideally, the number of azole moieties per molecule is at least 1 and may be as high as 10, and optionally azole moieties greater than 10 per molecule may be used, provided that the additional functional groups do not interfere with the purposes of the present invention. Non-limiting examples of available types of azole ring functional compounds include single or thiol-modified triazoles, imidazoles, triazines, tetrazoles, and Azoles.

[0081] Non-limiting examples include substituted and unsubstituted benzotriazoles, tolyltriazole, mercaptobenzotriazole, including alkyl-substituted benzothiazoles, such as tolylbenzotriazole.

[0082] Triazole chemicals, such as tolyltriazole (TTA), benzotriazole (BZT), and mercaptobenzotriazole (MBT), are preferred as at least one passivating agent (A) for copper-containing traces. Triazole compounds are believed to passivate copper by forming a protective cuprous oxide (Cu2O) film on the metal surface.

[0083] Suitable thiol-modified azoles include 2-mercaptobenzo azole; benzothiazole, mercaptobenzotriazole; mercaptobenzothiazole; 2,5-dimercapto-1,3,4-thiadiazole; 2-amino-5-ethylthio-1,3,4-thiadiazole (AETD); 2-amino-5-ethyl-1,3,4-thiadiazole; 5-(phenyl)-4H-1,2,4-triazole-3-thiophene; 5-mercapto-1-methyl-tetrazole; 5-mercapto (sodium salt)-1-methyl-tetrazole; 5-mercapto-1-acetic acid (sodium salt) -tetrazole; 5-mercapto-1-phenyl-tetrazole (5Mc-1Ph-T); 5-phenyl-tetrazole (5Ph-T); 5-phenyl-tetrazole; 5-mercapto-1-phenyl-tetrazole (5Mc-1Ph-T); 5-aminotetrazole (5NH2-T); 5-(4'-dimethylaminobenzylidene)-2,4-dioxotetrahydro-1,3-thiazole; 2-mercaptobenzothiazole; 2-(octadecylthio)benzothiazole and combinations thereof.

[0084] Other suitable azoles include:

[0085] 1,2,4-Triazole and derivatives: 3-amino-1,2,4-triazole; 4-amino-1,2,4-triazole; 4-amino-4H-1,2,4-triazole-3-thiol; 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol; 4-amino-5-ethyl-4H-1,2,4-triazole-3-thiol; 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole; bis-(4-amino-5-mercapto-1,2,4-triazol-3-yl)-butane;

[0086] Imidazole and derivatives: 2-mercapto-1-methylimidazole; 4-methyl-1-(p-tolyl)-imidazole; 4-methyl-1-phenylimidazole; 4-methyl-1-(o-tolyl)-imidazole; benzimidazole; 2-mercaptobenzimidazole; 2-thiobenzylbenzimidazole; 2-thiomethylbenzimidazole; 5-methoxy-2-(octadecylthio)benzimidazole;

[0087] Thiadiazole; and derivatives: 2,5-dimercapto-1,3,4-thiadiazole; 5-phenyl-1,3,4-thiadiazole-2-thiol; 2-(5-mercapto-1,3,4-thiadiazole-2-yl)-phenol; potassium 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione; 5-phenyl-2-amino-1,3,4-thiadiazole, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole azole, 5-(4-nitrophenyl)-2-amino-1,3,4-thiadiazole; 5-methyl-[1,3,4]thiadiazole-2-ylsulfonyl)-acetic acid; (4-dimethylamino-benzylidene)-hydrazide; 2-amino-5-(4-pyridyl)-1,3,4-thiadiazole; 1,2-dihydro-3-(octadecylthio)benzotriazine; 2,4,6-trimercapto-1,3,5-triazine (TMTA).

[0088] Also suitable are benzotriazole derivatives, for example N-[benzotriazol-1-yl-(phenyl)-methylene]-N-phenyl-hydrazine; N-[benzotriazol-1-yl-(4-methoxy-phenyl)-methylene]-N-phenyl-hydrazine; N-(2-thiazolyl)-1H-benzotriazole-1-carbothioamide; N-(furan-2-ylmethyl)-1H-benzotriazole-1-carbothioamide; N-benzyl-1H-benzotriazole-1-carbothioamide; 1-(2-thienylcarbonyl)-benzotriazole and 1-(2-pyrrolecarbonyl)-benzotriazole. Derivatives of benzotriazole, i.e. 5-pentyl-BTA; 5-chloro-BTA, N-[benzotriazol-1-yl-(phenyl)-methylene]-N-phenyl-hydrazine; N-[benzotriazol-1-yl-(4-methoxy-phenyl)-methylene]-N-phenyl-hydrazine, N-(2-thiazolyl)-1H-benzotriazole-1-carbosulfamide, N-(furan-2-ylmethyl)-1H-benzotriazole-1-carbosulfamide; N-benzyl-1H-benzotriazole-1-carbosulfamide, 1-(2-thienylcarbonyl)-benzotriazole; 1-(2-pyrrolecarbonyl)-benzotriazole are also suitable as at least one passivating agent (A).

[0089] In a preferred embodiment, the coating provides a waterproof function to the coated circuit boards in electronic devices (such as handheld phones), meaning increased water resistance. The passivator can be a solid or a liquid. In some embodiments, the passivator is preferably a liquid at ambient temperature, typically about 2°C to 100°C, preferably 10°C to 32°C. In some embodiments, the passivator can chemically react with the film-forming polymer of the coating composition. Alternatively, in other embodiments, the passivator does not react with the film-forming polymer of the coating composition, so that the passivator is dispersed in the polymer matrix of the coating and can advantageously be mobile within the applied and dried coating. The mobility of the passivator enables interaction with damaged traces, for example, providing self-repairing repassivation of the metal after corrosion or physical damage has begun, for example, due to the creation of new component connections.

[0090] The binder component (B.) may comprise one or more of the following types of binders:

[0091] B1) an organic or inorganic film-forming polymer that does not react with (A.);

[0092] B2) an organic or inorganic film-forming polymer capable of reacting with (A.);

[0093] B3) one or more polymer precursors, such as monomers, oligomers and / or prepolymers, that are polymerizable on the substrate surface and unreactive with (A.);

[0094] B4) One or more polymer precursors, such as monomers, oligomers and / or prepolymers, that are polymerizable on the substrate surface and capable of reacting with (A.).

[0095] In some embodiments, the coating composition is deposited onto an end-use article, such as an electronic component to be coated, or the coating composition may be formed into a removable film on a tape, removable backing, or the like for subsequent transfer to an end-use article, such as in the form of a preformed film.

[0096] First Adhesive Type:

[0097] The binder component (B) of the coating composition may comprise an organic or inorganic film-forming polymer that does not react with the passivating agent. The film-forming polymer produces a physical, continuous, and flexible film upon drying and may be thermoplastic or thermosetting. In some embodiments, these film-forming polymers may have an elongation value greater than 100%.

[0098] Suitable examples of film-forming polymers include polyesters; polyurethanes; polyolefins; olefin copolymers; (meth)acrylate copolymers that are unreactive with the passivating agent in the coating composition, and combinations thereof.

[0099] In a preferred embodiment, a suitable type of olefin copolymer, i.e., one made from olefin monomers, can be an ethylene-vinyl acetate copolymer (so-called EVA resin). Ideally, the weight ratio of ethylene to vinyl acetate monomers, including the EVA copolymer, can be in the range of 95:5 to 50:50, with the preferred ratio of ethylene to vinyl acetate monomers being in the range of 60:40 to 80:20. This ratio can be ideally selected to provide compatibility between the EVA copolymer and the other components of the coating composition, thereby controlling the solubility of the EVA copolymer in the formulated coating. The ratio of ethylene to vinyl acetate monomers can also be selected such that, upon drying and / or curing of the coating composition, a composite coating is formed in which the passivating agent is present as a dispersed second phase within the polymer matrix of the dried coating.

[0100] The (meth)acrylate copolymers of suitable types used as film-forming polymers that do not react with the passivating agent can be the reaction product of a (meth)acrylate monomer and other ethylenically unsaturated optional comonomers. The ethylenically unsaturated monomers and comonomers can be copolymerized to form the (meth)acrylate copolymers by polymerization methods well known in the art. The resulting copolymers can comprise the reaction products of a variety of monomers, such as methacrylic acid monomers, methacrylate monomers, acrylic acid monomers, acrylate monomers, styrene monomers, α-methylstyrene monomers, acrylonitrile monomers, methacrylonitrile monomers, hydroxyl-functional methacrylate monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and isobornyl (meth)acrylate. Particularly preferred (meth)acrylates include C1-C22 straight and branched alkyl esters. Preferred (meth)acrylate copolymers can be prepared from the above monomers by free radical reaction polymerization of alkyl esters comprising acrylic acid and methacrylic acid in the presence of a free radical generator. Generally speaking, (meth)acrylate monomers having an alkyl chain length of 2 to 18 carbons are preferred, with alkyl chain lengths of 4 to 8 carbons being particularly preferred.

[0101] Other film-forming polymers that do not react with passivating agents include polyesters, which are typically the reaction products of carboxylic acid and alcohol precursors; and polyurethanes, which are typically made of polyisocyanates and alcohol precursors. Non-limiting representative examples of polyesters include homopolymers and copolymers of ε-caprolactone. Non-limiting representative examples of polyurethanes include the reaction products of aliphatic polyisocyanates and hydroxylate functional reactants (such as polyether alcohols and aliphatic alcohols, which ideally have 2 or more moles of hydroxyl groups per molecule). Particularly preferred polyisocyanates include those based on hexamethylene diisocyanate. Typically, in the case of requiring hydrophobicity and flexible polymers, aliphatic precursors without ring structures are preferred.

[0102] Second adhesive type:

[0103] The binder component (B) of the coating composition may comprise an organic or inorganic film-forming polymer capable of reacting with the passivating agent. In some embodiments, it may be advantageous for the binder (thermosetting or thermoplastic) used to have functional groups that react with the passivating agent. A preferred type of functional group is that which reacts with thiols. Non-limiting examples of thiol-reactive functional groups include epoxy, isocyanate, carboxylic acid, and olefin (C=C) bonds.

[0104] Similar to the first binder type, the backbone of the film-forming polymer can be polyester; polyurethane; polyolefin; olefin copolymer; (meth)acrylate copolymer and combinations thereof, but the functional moiety different from that of the first binder type enables the second binder type to react with the passivating agent in the coating composition. Non-limiting examples of binders having one or more of these groups that react with the passivating agent include isocyanate-terminated polyurethanes; polyesters and (meth)acrylate copolymers containing ester bonds, carboxyl-terminated polyesters, ethylene acrylic acid copolymers, polyolefins containing unsaturated bonds, such as polybutadiene and copolymers of polybutadiene, such as copolymers of acrylonitrile and butadiene.

[0105] Third Adhesive Type:

[0106] Polymer precursors, building blocks for generating polymers to form coatings on substrates, can be used as adhesives in the present invention. Therefore, the adhesive component (B.) of the coating composition can include one or more polymer precursors, such as monomers, oligomers, and / or prepolymers, that are polymerizable on the substrate surface and do not react with the passivating agent. In some embodiments, it is preferred to perform a large amount of polymerization to form a cured coating after the coating composition is applied to the substrate, i.e., the PCB. Some polymerization after the coating composition is applied to the substrate may occur before the curing step (e.g., ultraviolet or thermal energy exposure). UV curing of one or more polymer precursors (e.g., monomers, oligomers, and / or prepolymers) is preferred. Any curing mechanism that is compatible with the components of the coating composition and produces a solid, adhered coating after curing can be used.

[0107] UV curable coatings are well known in the art and may comprise (meth)acrylate monomers, i.e., acrylate and methacrylate monomers, and similar oligomers having a functionality of 1 to 10 or more ethylenically unsaturated bonds per molecule. UV curable materials offer many advantages well known in the art, such as they can be rapidly cured and applied without solvents.

[0108] The UV-curable film-forming polymer precursor may comprise a mixture of monomers, oligomers and / or polymer precursors with ethylenically unsaturated bonds and a photoinitiator. The adhesive polymer precursor may have one or more ethylenically unsaturated groups. Examples of suitable (meth)acrylate monomers (i.e., acrylate and methacrylate monomers having polymerizable double bonds that can be used to form UV-curable and thermosetting polymer adhesives) include, but are not limited to: alkyl acrylates; alkyl methacrylates; hydroxyalkyl acrylates; hydroxyalkyl methacrylates; substituted alkyl acrylates or alkyl methacrylates, such as 2-ethylhexyl acrylate or 2-ethylhexyl methacrylate; and other acrylates and methacrylates, such as isobornyl acrylate; and mixtures thereof.

[0109] Other suitable examples of (meth)acrylate monomers having more than one double bond (i.e., acrylate and methacrylate monomers) include, but are not limited to, polyacrylate and polymethacrylate functional monomers such as: ethylene glycol diacrylate; propylene glycol diacrylate; diethylene glycol diacrylate; dipropylene glycol diacrylate; triethylene glycol diacrylate; tripropylene glycol diacrylate; tetraethylene glycol diacrylate; tetrapropylene glycol diacrylate; polyethylene glycol diacrylate; polypropylene glycol diacrylate; ethoxylated bisphenol A diacrylate; bisphenol A diglycidyl ether diacrylate; resorcinol diglycidyl ether diacrylate; 1,3-propylene glycol diacrylate; 1,4-butanediol diacrylate; 1,5-pentanediol diacrylate; 1,6-hexanediol diacrylate; neopentyl glycol diacrylate; cyclohexanedimethanol diacrylate; ethylene glycol diacrylate; bisphenol A diglycidyl ether ... Oxylated neopentyl glycol diacrylate; propoxylated neopentyl glycol diacrylate; ethoxylated cyclohexanedimethanol diacrylate; propoxylated cyclohexanedimethanol diacrylate; epoxy polyacrylate; aromatic polyurethane polyacrylate; aliphatic polyurethane polyacrylate; polyester polyacrylate; trimethylolpropane tri(meth)acrylate; glycerol tri(meth)acrylate; ethoxylated trimethylolpropane tri(meth)acrylate; propoxylated trimethylolpropane tri(meth)acrylate; trimethylolethane tri(meth)acrylate; tris(2-hydroxyethyl)isocyanurate triacrylate; ethoxylated glycerol tri(meth)acrylate; propoxylated glycerol tri(meth)acrylate; pentaerythritol tri(meth)acrylate; melamine triacrylate; epoxy novolac triacrylate; aliphatic epoxy triacrylate; and mixtures thereof. Preferred tetraacrylates that are also suitable, alone or in combination with the above monomers, include, but are not limited to, di-trimethylolpropane tetra(meth)acrylate; pentaerythritol tetra(meth)acrylate; ethoxylated pentaerythritol tetra(meth)acrylate; propoxylated pentaerythritol tetra(meth)acrylate; dipentaerythritol tetra(meth)acrylate; ethoxylated dipentaerythritol tetra(meth)acrylate; propoxylated dipentaerythritol tetra(meth)acrylate; divinylbenzene; divinyl succinate, diallyl phthalate; triallyl phosphate; triallyl isocyanurate; tris(2-acryloylethyl)isocyanurate; aromatic polyurethane tetra(meth)acrylate; aliphatic polyurethane tetra(meth)acrylate; polyester tetra(meth)acrylate; melamine tetra(meth)acrylate; epoxy novolac tetra(meth)acrylate; and mixtures thereof. Suitable higher functional acrylates include, but are not limited to, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol octa(meth)acrylate, and mixtures thereof. These monomers can be used to form UV-curable polymeric binders and thermosetting polymeric binders.

[0110] The coating composition can be a one-pot material, or if desired can be applied in two or more parts that react together on the substrate to form the coating. Preferred embodiments include UV-curable coating compositions wherein the passivating agent (A.) employed is substantially non-reactive with the other components of the UV-curable coating composition before, during, or after application and curing.

[0111] Fourth adhesive type:

[0112] Another type of adhesive that can be used for adhesive component (B.) can be an adhesive that is contained in one or more polymer precursors that can be polymerized on the substrate surface and can react with a passivating agent, such as monomers, oligomers and / or prepolymers. In some embodiments, preferably after the coating composition is applied to the substrate (e.g., PCB), a large amount of polymerization of the coating composition is carried out and the passivating agent is reacted with the functional groups in the coating composition. For example, monomers, oligomers and / or prepolymers may also include functional groups that react with the passivating agent. Non-limiting examples include adhesives that are polymerizable by UV energy, and the functional groups present therein are reactive to at least one of thiofunctional groups (preferably thiol functional groups), azole moieties or azoles. Typically, UV-curable polymer precursors have ethylenically unsaturated bonds that can directly react with the thiol functional groups in the passivating agent. In a preferred embodiment, the passivating agent comprises a polythiol that can react with the ethylenically unsaturated bonds in one or more polymer precursors, such as monomers, oligomers and / or prepolymers, present in the adhesive (B.). During the curing of the UV-curable coating comprising a polythiol, bound thiol functional groups can be formed within the cured coating by reaction with polymerizable monomers, oligomers and / or prepolymers. Non-limiting examples of thiol-reactive functional groups that may be present on the polymer precursor include epoxy, isocyanate, olefinic (C=C) bonds, and carboxylic acids.

[0113] In another embodiment, the passivating agent comprises a secondary functional group other than and in addition to the thiofunctional group; an azole moiety; or an azole. In this embodiment, one or more polymer precursors, such as monomers, oligomers and / or prepolymers, that are polymerizable on the surface of the substrate can react with the secondary functional group. This most often occurs when using the UV-curable polymer precursors disclosed herein, which have ethylenically unsaturated bonds that are reactive with the various secondary functional groups of the passivating agent. A non-limiting example of a passivating agent having a secondary functional group is vinylimidazole, which has an azole moiety and a secondary functional group in the form of a vinyl group. The UV-curable polymer precursor comprises an ethylenically unsaturated bond that reacts with the vinyl functional group of the passivating agent when exposed to UV curing conditions. Other non-limiting examples of secondary functional groups that can react with the ethylenically unsaturated bonds of the UV-curable polymer precursor of the adhesive include silane functional groups, hydroxyl functional groups, and carboxyl functional groups. Non-limiting examples of materials having both thio- or thiol functional groups or azole moieties and different secondary functional groups include thio- and thiol functional silanes, silanes with azole moieties, thiol compounds with hydroxyl groups, and thiols with carboxyl groups. Non-limiting examples include 2-(3-trimethoxysilylpropylthio)thiophene, 3-mercaptopropyltrimethoxysilane, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole, 6-mercapto-1-hexanol, and mercaptopropionic acid, respectively. UV-curable coating compositions are well known in the art and are described elsewhere in the specification.

[0114] As disclosed herein, several types of binders can be used alone or in combination. The combination of a passivating agent and a binder provides metal passivation chemical support properties in thinner coatings. One aspect of the present invention provides a flexible coating generally based on a first binder type and optionally a second binder type. These polymeric binders provide a coating composition that is free of all fluorine-based chemicals suitable for thermal drying / curing and provides a low viscosity, allowing the use of a spray coating process. A primary polymer binder having an elongation at break exceeding 1000% (ASTM D1708 (19 mm dog bone @ 1.3 mm thickness) can be used. Coatings comprising the first and second binder types can also be applied as peelable films. The resulting flexible coatings after drying / curing provide reduced current leakage and visible corrosion compared to commercial benchmarks. Another aspect of the present invention provides tougher, less flexible coatings generally based on the third and fourth binder types. These polymer binders provide coating compositions that are free of all fluorine-based chemicals and can provide solvent-free formulations. The resulting coating compositions have low viscosity, allowing for the use of spray coating processes and dual curing (e.g., ambient and UV or thermal). The resulting tougher UV cured coatings provide very low current leakage and visible corrosion even after immersion in a saline electrolyte powered at a 20 V bias for 30 minutes.

[0115] Ideally, the passivator and film-forming binder are compatible and soluble in the solvent carrier and / or reactive diluent of the coating composition. In some embodiments, the passivator and film-forming binder can be selected so that phase separation occurs upon drying, whereby the passivator forms a second phase within the resulting composite coating. This second phase can exist as isolated globules or domains within the composite coating, or can appear as stratified layers within the coating, comprising at least a first layer having a higher passivator concentration and a second layer having a lower passivator concentration. It has been surprisingly discovered that selecting a weight ratio of passivator to film-forming binder of about 100:1 to 1:100 and a solubility of the passivator in the binder or reaction product of the binder or matrix of the as-deposited coating that meets the above-identified criteria enables the selection of a coating morphology that maintains two phases and adhesion upon drying.

[0116] In some embodiments, it may be desirable to select a concentration of the passivating agent that is greater than the solubility limit of the passivating agent in the adhesive so that upon drying a second phase of a passivating agent reservoir is provided in the dried coating. Without wishing to be bound by theory, it is believed that such a second phase may serve as a passivating agent reservoir within the coating so that the passivating agent may be used to contact corrosive or physical damage on the printed circuit board, for example corresponding to corrosion initiation. This feature may enable the coating to prevent or reduce the undesirable consequences of changes in the service environment. Examples of changes in the service environment include electronic devices, such as cell phones, which contain coated PCBs that are in contact with or immersed in water or aqueous solutions, particularly in the powered state. In the absence of the coating features described in this embodiment, degradation pathways (such as dendrite growth between traces and corrosive damage to the traces) would cause catastrophic damage to the device.

[0117] In some embodiments, a waterproof coating is applied to all conductive surfaces of the printed circuit board, including one or more connection surfaces. When the coated surfaces of the printed circuit board and the connector come into contact with sufficient force to deform or penetrate the coating, an electrical connection is established. This process of invasively establishing an electrical connection can be viewed as a change in the service environment and the uniform presence of the passivating agent within the continuous phase of the coating matrix and the uniform presence of the passivating agent stored in reservoirs or stratified layers within the coating, enabling the coating to respond by moving the passivating agent to the disturbed or damaged coating area, whereupon the passivating agent repassivates the disturbed or damaged coating / conductor interface. The present invention provides a coating composition and a dry coating that enable PCB subunits to be repeatedly connected, disconnected, and reconnected while maintaining waterproof properties.

[0118] The present invention can be used to coat selected surfaces of electronic components, such as circuit boards, particularly printed circuit boards (PCBs). A printed circuit board is a non-conductive material having conductive traces (also referred to as "wires," "tracks," or "conductors" on the board). Electronic components, such as integrated circuits (ICs), resistors, capacitors, inductors, and connectors, switches, and relays, are mounted on the board, and the traces connect the components to form a working circuit or assembly. Depending on the number of components and the interconnection density, the board can be single-sided (one signal layer on the top of the board), double-sided (two signal layers on the top and bottom of the board), or multi-layer (more than two layers). The components are interconnected to each other by traces on the surface of the PCB and are typically embedded between the layers of the board. When protection is inadequate, corrosion or breakage of the traces leads to conductivity failure along the trace path, and damage associated with electrochemical migration phenomena, such as dendritic growth and conductive anodic filament formation, can occur.

[0119] Metals suitable for use as metal surfaces for traces include copper, iron, zinc, nickel, tin, lead, cobalt, titanium, molybdenum, ruthenium, palladium, rhodium, and rhenium, mixtures thereof, alloys thereof, and mixtures of alloys thereof. Preferred metal articles for coating include conductive metal traces secured to substrates according to the present disclosure, which desirably may include copper, zinc, iron, tin, lead, mixtures thereof, alloys thereof, and mixtures of alloys thereof. Preferably, the metal is copper or a copper alloy. The metal traces may include, consist essentially of, or consist of copper, zinc, iron, mixtures thereof, alloys thereof, and mixtures of alloys thereof.

[0120] Carbon can be present as a layer on the metal surface of the PCB, thereby adding or replacing some or all of the metal elements. In one embodiment, conductive carbon (such as graphene, graphite, etc.) comprises at least a portion of the trace. In some embodiments, an ink containing conductive carbon is used as a second layer on the metal trace to replace the gold plating of the trace. Conductive carbon-containing inks known in the art are generally carbon pigments dispersed in a thermosetting polymer medium, such as carbon black and / or other carbons disclosed above. Examples of uses for carbon include: cross-connectors that allow for a less complex circuit board manufacturing process; contacts that may require wear resistance (sliding contacts); and as a low-cost alternative to gold plating (usually used in combination with copper). The coating compositions and methods according to the present disclosure can also be applied to carbon-containing portions of PCBs that provide similar benefits as metal traces.

[0121] In one embodiment, the substrate is a circuit board having metal traces fixed thereto, preferably a printed circuit board, which can be used in electronic products. Typically, the circuits on a printed circuit board are printed using copper traces, aluminum traces, or other suitable conductive metals.

[0122] Suitable solvents that can be used for the present disclosure are organic solvents, which can optionally include water, provided that they do not interfere with purpose of the present invention. Ideally, solvents provide a single-phase solution or a passivating agent and a tackifier that is easily dispersed. Preferred solvent types include ketones, aromatic hydrocarbons, aliphatic hydrocarbons, ethers, glycol ethers, glycol ether esters, esters, and alcohols. The non-limiting representative examples of available solvents include methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, toluene, xylene, pentane, hexane, heptane, the monoalkyl ethers of propylene glycol, the dialkyl ethers of propylene glycol, the monoalkyl ethers of ethylene glycol, the dialkyl ethers of ethylene glycol, the monoalkyl ether acetates of propylene glycol, the monoalkyl ether acetates of ethylene glycol, butanols, isopropyl alcohol, isobutanol, propyl acetate, butyl acetate, amyl acetate, isobutyl isobutyrate, butyl propionate, amyl propionate, etc.

[0123] If desired, the coating composition can be solvent-free. Thus, the range of solvent amounts is generally quite wide and tends to vary depending on the method of application and other components of the coating composition. Generally speaking, organic solvents may be absent or present only in ppm amounts for applications where it is desirable to minimize organic solvent use, or may comprise up to 95% by weight of the coating composition, such as for dipping applications.

[0124] In a preferred embodiment, the coating composition is applied to electronic components or strips, support or backing by spraying for being applied to the final use substrate later. The preferred concentration of the solvent changes with used adhesive and passivating agent in the coating composition, but usually changes between 40 to 90 weight % of the formula. In another embodiment, the coating is applied by dipping. In this case, the preferred scope can change between 75 weight % to 95 weight %. In another embodiment, the coating composition is applied to a removable backing substrate and is applied to circuit components as a laminated film or strips.

[0125] The amounts of non-solvent components are provided herein as the concentration of the relevant component in the formulation excluding solvent, which can be added in a manner known to those skilled in the art:

[0126] - The passivating agent may be present in the coating composition of the present invention (excluding solvent) in an amount of from about 0.5% to about 55% by weight of the formulation. Within this range, the ideal amount may be at least (in increasing order of preference) 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, and, at least for economic reasons, may not exceed (in increasing order of preference) 50%, 47%, 45%, 43%, 40%, 38%, 36%, 34%, 32%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%.

[0127] - Binders (film-forming polymers, polymer precursors, and combinations thereof) may be present in the coating compositions of the present invention (excluding solvent) in an amount from about 25% to about 99% by weight of the formulation. Within this range, the ideal amount can be at least (in order of increasing preference) 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 61%, 62%, 63%, 64%, 65%, 66% and, at least for economic reasons, can be no more than (in order of increasing preference) 97%, 95%, 92%, 90%, 88%, 85%, 83%, 80%, 78%, 76%, 74%, 72%, 70%, 68%.

[0128] - Optional additives may not be present in the coating composition. Alternatively, optional additives may be present in the coating composition of the present invention (excluding solvent) in an amount from about 0.01% to about 15% by weight of the formulation. Within this range, the ideal amount may be at least (in order of increasing preference) 0.02%, 0.04%, 0.05%, 0.07%, 0.09%, 0.1%, 0.2%, 0.4%, 0.5%, 0.7%, 0.9%, 1.0%, 1.2%, 1.5%, 1.7%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.7%, 4.0%, 4.2%, 4.5%, 4.7%, %, 5.0 wt %, 5.2 wt %, 5.5 wt %, 5.7 wt %, 6.0 wt %, 6.2 wt %, 6.4 wt %, 6.5 wt %, 6.7 wt %, 6.9 wt %, 7.0 wt %, and at least for economic reasons may not exceed (in order of increasing preference) 14 wt %, 13 wt %, 12 wt %, 11 wt %, 10 wt %, 9.75 wt %, 9.50 wt %, 9.25 wt %, 9.0 wt %, 8.7 wt %, 8.5 wt %, 8.3 wt %, 8.0 wt %, 7.7 wt %, 7.5 wt %, 7.2 wt %.

[0129] As mentioned above, the coating composition may not contain a solvent. Alternatively, the solvent may be present in the coating composition of the present invention in a total amount of about 0.01 wt % to about 95 wt %. Within this range, the ideal amount may be at least (in increasing order of preference) 0.1 wt %, 0.5 wt %, 1 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt %, 45 wt %, 50 wt %, and at least for economic reasons may not exceed (in increasing order of preference) 92 wt %, 90 wt %, 85 wt %, 80 wt %, 75 wt %, 70 wt %, 68 wt %, 65 wt %, 63 wt %, 60 wt %, 58 wt %, 55 wt %, 53 wt %.

[0130] For each of the above-identified components, amounts greater than those preferred may be used within the scope of the present invention so long as they do not interfere with the objectives of the present invention, such as causing instability in the coating composition.

[0131] Suitable olefin monomers useful in the present disclosure are desirably soluble in the coating composition and / or in the solvent present in the coating composition.The process according to the present disclosure can be performed with a single olefin monomer or a mixture of olefin monomers.

[0132] The total monomer concentration in a coating composition according to the present disclosure may be at least (in order of increasing preference) about 0.05%, 0.1%, 0.25%, 0.5%, 0.75%, 1.0%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, and, at least for economic reasons, may not exceed 7.0%, 8.0%, 9.0%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 75% by weight. Higher percentages of monomers may be used so long as the increased amounts do not interfere with obtaining the benefits of the present invention. In some embodiments, the total monomer concentration in a coating composition according to the present disclosure desirably may be from 0.1 to 50 weight percent, preferably from 5 to 15 weight percent, based on the total weight of the coating composition.

[0133] Optional components of the compositions and concentrates may be one or more additives such as waxes, adhesion promoters, flow modifiers, rheology modifiers, stabilizers, catalysts, photoinitiators, biocides and biostats.

[0134] Optional additives may be ideally selected based on preferred electronic or dielectric properties, as dictated by the conformal coating design for an end-use device such as a tablet, cell phone, or the like. For example, where the dielectric strength of the additive may be selected for the end-use device, a preferred wax additive may have a dielectric constant greater than 1, more preferably >2, and most preferably >4. Such additives may contain functional groups such as C=O, or -O- or -NH-, or aromatic rings to provide specific dielectric properties to the conformal coating. Wetting agents and flow modifiers may be used in the present invention to promote thickness uniformity of the coating composition applied to a substrate such as a printed circuit board. Preferred examples include polydimethylsiloxanes, polyether-modified polydimethylsiloxanes, and polydimethylsiloxanes with functional groups including amines, carboxyls, or phosphorus-based acid moieties.

[0135] The photoinitiator or combination of photoinitiators appropriately selected in the coating formulation absorbs the peak wavelength band of the radiation source (such as a mercury arc UV lamp) used to initiate polymerization, thereby resulting in curing on the coating surface as well as in the bulk. Those skilled in the art of energy-curable compositions (primarily for UV light, LED and visible light curable compositions) also know that combining a suitable photoinitiator or type of photoinitiator with a co-initiator, synergist or catalyst can significantly improve curing efficiency and performance. Preferably, the photoinitiator is present in the coating composition in an amount of 1 to 6 weight percent, preferably at least 1, 1.5, 2, 2.5 or 3 and not more than 6, 5.5, 5.0, 4.5, 4, 3.5 or 3, based on the total weight of the UV-curable material in the formulation.

[0136] Conventional free radical photoinitiators useful in the present invention are categorized according to their chemical groups and include, but are not limited to: (1) hydroxyacetophenones, (2) alkylaminoacetophenones, (3) benzil ketals and dialkoxyacetophenones, (4) benzoin ethers, (5) phosphine oxides, (6) acyl oxime esters, (7) photoacid generators, (8) photobase generators, (9) 2,2-bis(2-chlorophenyl)-4,4,5,5-tetraphenyl-1,2-biimidazole (BCIM) and HABI, (10) benzophenones, (11) organosulfur compounds such as thiols, (12) substituted benzophenones, (13) benzoylformates, (14) anthraquinones, (15) camphorquinones, (16) oxime esters, (17) anthracene proxy groups, and mixtures thereof. Specific examples of such photoinitiators include, but are not limited to, benzyldimethylamino-1-(4-morpholinophenyl)butanone-1; benzyldimethylketal; dimethoxyphenylacetophenone; α-hydroxybenzylphenyl ketone; 1-hydroxy-1-methylethylphenyl ketone; oligo-2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone; benzophenone; methyl o-benzoylbenzoate; methyl benzoylformate; 2,2-diethoxyacetophenone ; 2,2-di-sec-butoxyacetophenone; p-phenylbenzophenone; 2-isopropylthioxanthone; 2-methylanthraquinone; 2-ethylanthraquinone; 2-chloroanthraquinone; benzoanthraquinone; benzyl; benzoin; benzoin methyl ether; benzoin isopropyl ether; α-phenylbenzoin; thioxanthone; diethylthioxanthone; 1,5-acetylnaphthalene; 1-hydroxycyclohexylphenyl ketone; ethyl p-dimethylaminobenzoate; titanocene; dibenzylidene ketone; 1,2-diketone; coumarin ketone; and mixtures thereof.

[0137] Typical free radical photoinitiators useful in the present invention are commercially available under trade names including: 184. 1173, Omnirad 102, Esacure KIP 150, Esacure KIP EM, 2959、Omnirad 669、 127. Micro-PICS, Esacure ONE, 907, Quadracure MMMP-3, 369, Omnipol910, Quadracure BDMD-3, 379, benzyl dimethyl ketal (BDK), 651(DMPA), diethoxyacetophenone (DEAP), 10. TPO, TPO-L, 819, BAPO, PDO, PAG (103, 203, 108, 121), oxe 01, oxe 02, Esacure1001M, Trigonal P1, 1000, tribromomethylphenylsulfone (BMPS), trichloromethyl-S-triazine, o-nitrobenzyl carbamate, Ciba PLA-1, 907, 1173, Ciba PLA-2, MBP, Esacure TZT, MBB, P36, Omnipol BP, Genopol BP-1, 7005, Goldcure 2700, Trigonal 12 (PBZ) (4-phenylbenzophenone), Goldcure 2300, BMS, Esacure 1001M (sulfonyl ketone), MBF and MBF, TX-A, 754 and 2-ethylanthraquinone.

[0138] Those skilled in the art of energy curable formulations may substitute cationic photopolymerizable monomers or oligomers for the free radical photopolymerizable components in the examples. Conventional cationic photoinitiators useful in this invention are categorized by chemical group and include, but are not limited to: (1) sulfonium salts; (2) iodonium salts; (3) ferrocenium salts; and mixtures thereof.

[0139] Typical commercial examples of cationic photoinitiators useful in this type of invention are available under trade names including: 250, 270, PAG 290, GSID 26-1, QL cure211, QL cure 212, SP 150, Sp 170, Omnicat 550, Imnicat555, Omnicat 650, Esacure1187, Irgacure MacroCat, Hycure 810, 1600, Sarcat CD 1012, Omnicat 440, Omnicat 445, 250, UV 9310, Rhodorsil 2047, 2076, 261, Omnicat 320, Omnicat 430, Omnicat 432, 937, 938, 976 and 992. Molecular or polymeric co-initiators, synergists, and catalysts useful in the present invention are categorized by chemical group and include, but are not limited to: (1) primary, secondary, and tertiary amines; (2) amides; (3) alpha amino acids; (4) thioxanthones; (5) thiols; and mixtures thereof. Specific examples useful in the present invention include, but are not limited to: 2-ethylhexyl-p-dimethylaminobenzoate; ethyl 4-(dimethylamino)benzoate; trimethylolpropane tris(3-mercaptopropionate); methyl dimethanolamine; poly(ethylene glycol) bis(p-dimethylaminobenzoate); polyethylene glycol-bis(β-(4(p-acetylphenyl)piperazine))propionate; and mixtures thereof.

[0140] Commercially available examples of coinitiators, synergists, and catalysts that can be used in the present invention include, but are not limited to: EHA, EPD, MEDA, DMB, EDB, Omnirad IADB, Omnipol ASA and Omnipol SZ, ITX (isopropylthioxanthone), Kayacure DETX (diethylthioxanthone), CTX (chlorothioxanthone), Kayacure RTX (dimethylthioxanthone), Kayacure DITX (diisopropylthioxanthone), CPTX (1-chloro-4-propoxythioxanthone), 7010, Omnipol TX, Genopol TX-1.

[0141] Adhesion promoters are found in the present invention to improve the adhesion of applied coatings to substrates such as printed circuit boards. Preferred examples generally have functional groups such as amines, thiols, carboxyls, and phosphorus-based acids to improve adhesion of the coating to metal traces or backing substrates.

[0142] In one embodiment, the coating composition is provided in the form of a concentrate comprising: a passivating agent, at least one binder component, and optionally a solvent sufficient to uniformly dissolve and / or disperse the passivating agent and binder component to provide a stable concentrate without separation into distinct liquid phases or formation of a solid precipitate visible to the human eye, such that the separate phases do not readily recombine after storage at 25°C for at least one month. The concentrate can be formulated for dilution with a solvent to form a working concentration or as a bath extender known in the art to replenish a previously formed bath. Alternatively, the coating composition can be provided as a ready-to-use solution.

[0143] The method of preparing the coating composition of the present disclosure comprises dissolving and / or dispersing the passivating agent and the binder component in at least one of a solvent or a reactive diluent. The coating composition components are stirred together in a vessel to form a bath, such as a bath from a single component, a separate combination of two or more components, or a concentrate of the coating composition.

[0144] This disclosure discloses a method for waterproofing a substrate, particularly a printed circuit board. The method is rapid and efficient, and can be adapted to various substrates and metal traces. In one embodiment, a method for forming a polymer film on a substrate, such as a method for waterproofing a circuit board, according to the present invention comprises:

[0145] a) applying a coating composition as described herein to a surface of a substrate comprising one or more conductive traces fixed thereto, preferably, the substrate is an electronic component, more preferably a circuit board, most preferably a printed circuit board;

[0146] b) drying the coating composition on the surface of the substrate;

[0147] c) optionally UV curing the coating composition on the substrate surface;

[0148] d) during any of steps a) to c), reacting the available reactive functional groups of the binder component (B) and the passivating agent (A) with the coating composition components and optionally with the conductive traces, preferably metal traces, thereby depositing a water-insoluble passivating polymer film on the substrate surface.

[0149] The coated substrate according to the present disclosure comprises at least one metal trace secured to the substrate and a passivating polymer coating on at least one surface of the metal trace. In one embodiment, the substrate is a non-conductive material and the metal trace is a conductive material, preferably a printed circuit board.

[0150] Depending on the adhesive selected and the environment of use, the thickness of the passivating polymer coating can be from about 0.2 to about 40 microns (in the case of a desired range), including from about 0.6 to 3.8 microns; such as 0.6 to less than 12 microns for ultra-thin coating applications; 8-15 microns or 11-25 microns for specific applications such as strippable coatings, or up to 40 microns or more, provided that the thickness does not affect the performance of the coating. Within this range, desirable coating thicknesses can be at least (in order of increasing preference) 0.2 microns, 0.3 microns, 0.4 microns, 0.5 microns, 0.6 microns, 0.7 microns, 0.9 microns, 1.0 microns, 1.2 microns, 1.5 microns, 1.7 microns, 2.0 microns, 2.2 microns, 2.4 microns, 2.5 microns, 2.7 microns, 3.0 microns, 3.2 microns, 3.5 microns, 3.7 microns, 3.8 microns, 4.0 microns, 4.2 microns, 4.5 microns, 4.7 microns, 5.0 microns, 5.2 microns, 5.5 microns, 5.7 microns, 6.0 microns, 7.1 microns, 7.2 microns, 7.5 microns, 7.7 microns, 8.0 microns, 8.2 microns, 8.5 microns, 8.7 microns, 8.8 microns, 9.0 microns, 9.1 microns, 9.2 microns, 9.5 microns, 9.6 microns, 9.7 microns, 10.0 ... In one embodiment, the thickness of the ultrathin coating is about 700 nm to about 1600 nm.

[0151] The coating formed according to the present disclosure is waterproof, meaning that it is waterproof when immersed in water or an aqueous electrolyte, such as saline or artificial sweat, for at least 30 minutes while under power. The coating also significantly reduces the formation of dendrites between adjacent metal traces on a substrate. Dendrite formation is a problem with existing systems and can cause circuit failure due to the formation of a short circuit between two traces via dendrites. When tested as described in the examples below, use of the presently disclosed method produced a coating that reduced, and preferably did not form, dendrites between the traces of a test circuit board. This is far lower than the large amount of dendrites that formed during this testing using conventional coating methods.

[0152] Prior to the coating step using the coating composition according to the present invention, at least a portion of the substrate to be coated (e.g., the metal surface of the metal traces) can be cleaned using any method known in the art for removing contaminants from metal surfaces, such as solvent cleaning, cleaning with a fluorine-based fluid, or plasma methods. The substrate surface can also be rinsed prior to coating with water alone or with a pre-rinsing solution containing one or more substances that can further improve the properties (e.g., adhesion, water resistance, etc.) of the polymer coating subsequently formed on the substrate surface (including, for example, the metal traces). A so-called pre-conditioning treatment can be used, but coating methods without a pre-conditioning step are also suitable.

[0153] In this specification, embodiments have been described in a manner that enables a clear and concise description to be written, but it is intended and will be understood that various combinations or splits of the embodiments may be made without departing from the present invention. For example, it will be appreciated that all preferred features described herein apply to all aspects of the invention described herein.

[0154] In some embodiments, the invention herein can be interpreted as excluding any element or method step that does not substantially affect the basic and novel characteristics of the composition, article or method. Additionally, in some embodiments, the invention can be interpreted as excluding any element or method step not specified herein.

[0155] Although the present invention is shown and described herein with reference to specific embodiments, the present invention is not intended to be limited to the details shown. In the experiments disclosed in this specification, the passivating agent selected was used in an exemplary manner to deposit a passivating polymer coating on a printed circuit board, thereby passivating the metal traces on the circuit board. It is only an example of an article that can benefit from the coating of the present invention. To be precise, various modifications can be made in detail within the scope and scope of the equivalents of the claims without departing from the present invention. Exemplary embodiments are provided so that this disclosure will be thorough and the scope of the present invention will be fully conveyed to those skilled in the art. Many specific details, such as examples of specific components, devices and methods, are set forth to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details do not need to be applied, and the exemplary embodiments can be embodied in many different forms and should not be construed as limiting the scope of the present disclosure. In some exemplary embodiments, well-known methods, well-known device structures and well-known technologies are not described in detail.

[0156] Example

[0157] Test substrate:

[0158] Unless otherwise specified herein, the test substrates are commercially available, PCB-B-25A test printed circuit boards (PCBs) approved by the IPC-Association Connecting Electronics Industries (formerly known as the Institute for Printed Circuits, also known as IPC). These test printed circuit boards comply with the IPC / Surface Mount Technology Association (SMTA) and meet the guidelines for testing solder masks (IPC-SM-804C) and conformal coatings (IPC-CC-830A). Each test printed circuit board is a 1.6 mm (0.062 inch) thick FR-4 grade glass reinforced epoxy laminate and is a simple print and etch with bare copper traces that do not form a complete circuit, i.e., no current flows through the PCB-B-25A in the absence of corrosion-induced conductive paths (i.e., short circuits). The grid of the PCB-B-25A used for testing is grid F.

[0159] UV curing parameters

[0160] Unless otherwise specified herein, test substrates coated with UV-curable coating compositions, whether by a single-step or multi-step coating process, were UV-cured using a conveyor equipped with H+ bulbs. The UV energy source provided sufficient curing energy to the substrate surface to cure the coating. Depending on the initiator used, a minimum of at least one of the following energy levels was provided, as known in the UV coating art:

[0161] The type of UV energy provided <![CDATA[mJ / cm 2 > UVA 807 UVB 758 UVC 250 UVV 775

[0162] Waterproof test:

[0163] The effectiveness of the coating in providing water resistance to the printed circuit boards of the examples was tested as follows: the coated test circuit boards were connected to a voltage source in the disconnected position, immersed in water or an electrolyte solution ("artificial sweat"), and then the voltage was applied for 30 minutes. Unless otherwise specified herein, saline electrolyte refers to artificial sweat; the composition of the artificial sweat is as follows:

[0164] 100ml DI

[0165] 5g NaCl

[0166] 5g Na2HPO4-12H20

[0167] 2ml 99% acetic acid.

[0168] Short Circuit Formation: A voltage between 3 and 30V is selected for this test and maintained constant during the test. If a complete circuit does not exist, no current flows. As corrosion-induced degradation of the conductive traces begins, the current reading increases from zero, creating a short circuit and allowing current to flow. During the 30-minute immersion period, an in-line ammeter is used to detect current leakage from the electrified printed circuit board by measuring the current flowing through the circuit during the test. The lower the observed current, the better. Readings are taken every 1 second for 30 minutes.

[0169] The reported average current (mA) is the average of the currents measured over the entire 30 minute experiment. The reported maximum current (mA) is the single highest current value observed during the 30 minute experiment.

[0170] Dendrite and Oxide Formation: Coating performance was also judged by the number of dendrites or bulk oxide formation visible between and on traces at 12x magnification after testing, with fewer dendrites and oxides indicating better performance. Dendrites and macroscopic oxide formation are indicative of corrosion. Separate rating scales were used for dendrite and oxide formation. For dendrites, the scale is represented by the letters A to D, with A indicating no dendrite formation and increasing to D, indicating widespread dendrite formation between every trace in the test area. Oxide formation is represented by numbers 0 to 4, with 0 indicating no oxide formation in the test area and increasing to 4, indicating widespread oxide formation on 100% of the traces in the test area.

[0171] Example 1

[0172] In this example, five different coating compositions were prepared with the components shown in Table 1-1 below.

[0173] Table 1-1

[0174] Components (g) 1A 1B 1C 1D Poly(ethylene-co-vinyl acetate) 40% VA 4.55 4.55 4.55 4.55 Toluene 35.45 35.45 Methyl isobutyl ketone 34.75 55.45 Mercaptosilane oligomer* 1.5 1.5 4.55 4.55 Xylene 5 5 Propylene glycol monomethyl ether acetate 5 5

[0175] *Mercaptoalkoxysilane oligomer

[0176] Coating compositions containing the ingredients and amounts listed in Table 1-1 were prepared using the following procedure. 40% VA EVA polymer was dissolved in the listed first solvent at 70°C with stirring. The second solvent was then added, followed by the indicated thiol. Stirring was continued until the coating composition was clear and free of visible solids.

[0177] The coating composition was then sprayed onto the printed circuit board using a pneumatic spray gun. The gun pressure and the number of sprays applied were adjusted to achieve a coating thickness between 8 and 15 microns. The board was then heat-cured at 90°C for 15 minutes, followed by a subsequent heat-curing at 120°C for 10 minutes.

[0178] These coated printed circuit boards were then subjected to the above described water resistance test at 3V, 12V and 30V bias in distilled water and at 20V bias in artificial sweat as also described in the water resistance test, and the results are reported in Tables 1-2 below.

[0179] For the coating compositions in Table 1-1, the effects of solvent and EVA to thiol ratio on corrosion were determined and are shown in Table 1-2.

[0180] Table 1-2

[0181] Example# Test conditions Average current (mA) Maximum current (mA) Dendrite Growth Rating Visible corrosion rating 1A 30V water 0.002 0.004 A 0 1B 30V water 0.001 0.003 C 0 1C 30V water 0.009 0.014 A 0 1D 30V water 0.001 0.002 B 0 1A 20V sweat 0.059 0.144 A 2 1B 20V sweat 0.001 0.004 A 0 1C 20V sweat 2.46 3.293 C 3 1D 20V sweat 0.001 0.002 B 0 1A 12V water 0.01 0.029 N / R N / R 1B 12V water 0.001 0.003 N / R N / R 1C 12V water 2.029 10.458 N / R N / R 1D 12V water 0.001 0.002 N / R N / R 1A 3V water N / R N / R N / R N / R 1B 3V water N / R N / R N / R N / R 1C 3V water 0.012 0.015 N / R N / R 1D 3V water 0.001 0.002 N / R N / R

[0182] N / R means Not Rated

[0183] The toluene / xylene solvent system performed worse than the MIBK / PMA system, with maximum effect at a 50:50 EVA to mercaptan ratio.

[0184] Example 2

[0185] Coating compositions containing the ingredients and amounts listed in Table 2-1 were prepared using the following procedure. The specified EVA polymer was dissolved in the listed first solvent at 70°C with stirring. The second solvent was then added, followed by the specified thiol. Stirring was continued until the coating composition was clear and free of visible solids.

[0186] The study also included a commercial UV curable polyurethane acrylate product deposited at its typical coating thickness of 50 microns and below its recommended use thickness of 12 microns as a comparative example.

[0187] Table 2-1

[0188] Components (g) 2A 2B 2C 2D 2E Poly(ethylene-co-vinyl acetate) 40% VA 6.48 6.65 5.9 Poly(ethylene-co-vinyl acetate) 25% VA 6.48 6.65 Toluene 37.92 29.95 Methyl isobutyl ketone 43.62 29.95 40.4 Pentaerythritol tetrakis(3-mercaptopropionate) 2.1 2.1 1 1 5.9 Xylene 14.2 14.6 Propylene glycol monomethyl ether acetate 14.2 14.6 13

[0189] A coating composition, different from the commercial product used in the comparative example, was then sprayed onto the printed circuit board using a pneumatic spray gun. The spray gun pressure and the number of sprays applied were adjusted to achieve a coating thickness between 8 and 15 microns. The circuit board was then heat-cured at 90°C for 15 minutes, followed by a heat-curing step at 120°C for 10 minutes. The commercial product was applied and cured to thicknesses of 12 and 50 microns.

[0190] These coated printed circuit boards were then subjected to the above-described waterproof test under distilled water at 3V, 12V, and 30V biases and under artificial sweat at 20V bias, as also described in the waterproof test, and the results are shown in Table 2-2 below.

[0191] Table 2-2

[0192] Example Test conditions Average current (mA) Maximum current (mA) Dendrite Growth Rating Visible corrosion rating 2A 30V water 0.072 0.144 A 0 2B 30V water 0.391 0.792 A 1 2C 30V water 0.205 0.83 N / R N / R 2D 30V water 0.001 0.002 A 0 2E 30V water 0.015 0.021 A 0 PC40 12u 30V water 64.453 116.59 C 1 PC40 50u 30V water 0.053 0.109 A 0 2A 20V sweat 0.53 2.338 A 2 2B 20V sweat 0.42 2.184 A 2 2C 20V sweat 0.388 1.705 A 2 2D 20V sweat 0.01 0.107 A 0 2E 20V sweat 0.08 0.112 A 0 PC40 12u 20V sweat 0.46 4.857 A 2 PC40 50u 20V sweat 0.002 0.014 A 0 2A 12V water 0.172 0.252 A 0 2B 12V water 0.446 1.128 A 1 2C 12V water 0.244 0.426 A 1 2D 12V water 0.001 0.002 A 0 2E 12V water 0.002 0.003 A 0 PC40 12u 12V water 6.107 17.1 C 2 PC40 50u 12V water 2.58 5.105 A 0 2A 3V water 0.001 0.002 A 0 2B 3V water 0.001 0.002 A 0 2C 3V water 0.001 0.002 A 0 2D 3V water 0.001 0.002 A 0 2E 3V water 0.003 0.004 A 0 PC40 12u 3V water 22.891 28.44 C 1 PC40 50u 3V water 0.704 1.183 A 0

[0193] For the coating compositions in Table 2-1, the effects of solvent and EVA to thiol ratio on corrosion were determined and are shown in Table 2-2. The results show that various variations of the present invention performed better at lower coating thicknesses of 8-15 microns than commercial products, which require higher coating thicknesses for good corrosion performance.

[0194] Figure 1 This graph shows the current leakage test results for test PCB substrates coated according to Example 1 (Formula 2D) and Comparative Example 1 (Formula PC40 12u), subjected to a water resistance test in water at 30V for 30 minutes. During this period, the amount of current leakage was measured in one-second increments, with less being better. Graph markers are provided at 50-second intervals. For the test PCB of Comparative Example 1, while the current leakage of Comparative Example 1 was less than 1 / 10,000 of 1 mA, the measured current leakage increased rapidly during the 30-minute test. Figure 1 This negligible level of current leakage is shown as a flat line near zero.

[0195] In the present invention variant, the 40% vinyl acetate EVA polymer performed best under the conditions found in the previous examples using MIBK / PMA solvent and a 50:50 EVA to thiol ratio. However, the 25% vinyl acetate EVA polymer performed best at the highest EVA thiol ratio and using other solvents, indicating that these conditions must be adjusted depending on the polymer selected.

[0196] Example 3

[0197] Coating compositions containing the ingredients and amounts listed in Table 3-1 were prepared using the following procedure. 40% VAEVA polymer was dissolved in the listed first solvent at 70°C with stirring. The second solvent was then added, followed by the specified thiol, triazole, or other additive. Stirring was continued until the coating composition was clear and free of visible solids.

[0198] Table 3-1

[0199] Components (g) 3A 3B 3C 3D 3E Poly(ethylene-co-vinyl acetate) 40% VA 5.9 5.9 5.9 5.9 5.9 Methyl isobutyl ketone 26.6 26.6 26.6 26.6 26.6 Propylene glycol monomethyl ether acetate 13 13 13 13 13 2-Mercaptobenzothiazole 5.9 Vitamin E 5.9 2,5-dimercapto-1,3,4-thiadiazole 5.9 Benzotriazole 5.9 Cobratech 937 (proprietary azole blend) 5.9

[0200] The coating composition was then sprayed onto the printed circuit board using a pneumatic spray gun. The gun pressure and the number of sprays applied were adjusted to achieve a coating thickness between 8 and 15 microns. The board was then heat-cured at 90°C for 15 minutes, followed by a subsequent heat-curing at 120°C for 10 minutes.

[0201] These coated printed circuit boards were then subjected to the above-described waterproof test under distilled water at a bias of 30 V and artificial sweat at a bias of 20 V, also described in the waterproof test, and the results are shown in Table 3-2 below.

[0202] Table 3-2

[0203] Example Test conditions Average current (mA) Maximum current (mA) Dendrite Growth Rating Visible corrosion rating 3A 30V water 0.772 2.597 D 0 3B 30V water 98.435 125.01 C 1 3C 30V water 6.538 15.774 C 1 3D 30V water 18.617 47.443 C 1 3E 30V water 0.087 0.243 A 1 3A 20V sweat 0.69 3.468 D 0 3B 20V sweat 11.896 20.076 B 4 3C 20V sweat 0.798 8.189 B 2 3D 20V sweat 1.438 5.316 B 2 3E 20V sweat 0.306 0.627 B 2

[0204] For the coating compositions in Table 3-1, the effect of changing the thiol to other small molecules was determined and is shown in Table 3-2. The vitamin E system performed very poorly, suggesting that the (thiol / triazole) may be more than just a reducing agent. Thiols and triazoles are effective.

[0205] Example 4

[0206] Coating compositions containing the ingredients and amounts listed in Table 4-1 were prepared using the following procedure. 40% VA EVA polymer was dissolved in the listed first solvent at 70°C with stirring. The second solvent was then added, followed by the indicated thiol. Stirring was continued until the coating composition was clear and free of visible solids. This study also included a comparative example of a commercial product with a typical coating thickness of 50 μm, as shown in Example 2.

[0207] Table 4-1

[0208] Components (g) 1B Poly(ethylene-co-vinyl acetate) 40% VA 4.55 Methyl isobutyl ketone 34.75 Mercaptosilane oligomer 1.5 Propylene glycol monomethyl ether acetate 5

[0209] The printed circuit boards used for testing had polyamide masking tape applied to a portion of the test area as a mask. The coating composition was then sprayed onto the printed circuit boards using a pneumatic spray gun. The spray gun pressure and the number of sprays applied were adjusted to achieve a coating thickness between 8 and 15 microns. The boards were then heat-cured at 90°C for 15 minutes, followed by 120°C for 10 minutes. The commercial product was applied and cured according to its recommended usage.

[0210] After curing, the mask was removed to simulate a repair, exposing uncoated test areas on the circuit boards. Formulation 1B of Example 1 was then applied to these exposed areas using the spray gun described above. This was applied to the exposed areas of all circuit boards, regardless of the original formulation used to coat the boards, and dried at 90°C for 15 minutes, followed by drying at 120°C for 10 minutes.

[0211] These printed circuit boards with the repair coating were then subjected to the above-described waterproof test, specifically on the repaired area, under distilled water at a bias of 30V and under artificial sweat at a bias of 20V, as also described in the waterproof test, and the results are shown in Table 4-2 below.

[0212] Table 4-2

[0213]

[0214] The effectiveness of the repair was determined for the repaired coated circuit boards and is shown in Table 4-2. The repaired areas demonstrated excellent performance in the 30V distilled water test. Both also provided protection in the 20V artificial sweat test, but this was not the same standard as the 30V distilled water test.

[0215] Example 5

[0216] Coating compositions containing the ingredients and amounts listed in Table 5-1 were prepared using the following procedure. 40% VAEVA polymer was dissolved in the first solvent listed at 70°C with stirring. The second solvent was then added, followed by the indicated thiol. Stirring was continued until the coating composition was clear and free of visible solids.

[0217] Table 5-1

[0218] 5A Poly(ethylene-co-vinyl acetate) 40% VA 5.9 Methyl isobutyl ketone 26.6 Pentaerythritol tetrakis(3-mercaptopropionate) 5.9 Propylene glycol monomethyl ether acetate 13

[0219] The printed circuit board was then dipped into the coating composition while held vertically. The board was allowed to dry at room temperature for 1 hour and then heat-cured at 90°C for 15 minutes and then at 120°C for 10 minutes. The coating thickness was determined to be 3.8 microns.

[0220] These coated printed circuit boards were then subjected to the above-described waterproofing test under distilled water at a bias of 30 V and under artificial sweat, also described in the waterproofing test, at a bias of 20 V. For the coating compositions in Table 5-1, the effects of dip coating were determined and are shown in Table 5-2.

[0221] Table 5-2

[0222] formula# Test conditions Average current (mA) Maximum current (mA) Dendrite Growth Rating Visible corrosion rating 5A 30V water 2.513 19.302 B 3 5A 20V sweat 10.78 125.79 A 3

[0223] This application proved protective, but not as protective as the spray application.

[0224] Example 6

[0225] Coating compositions containing the ingredients and amounts listed in Table 6-1 were prepared using the following procedure. 40% VA EVA polymer was dissolved in the listed first solvent at 70°C with stirring. The second solvent was then added, followed by the indicated thiol compound. Stirring was continued until the coating composition was clear and free of visible solids.

[0226] Table 6-1

[0227] 6A Poly(ethylene-co-vinyl acetate) 40% VA 5.9 Methyl isobutyl ketone 26.6 Propylene glycol monomethyl ether acetate 13 2-Thiophenecarboxylic acid 5.9

[0228] The coating composition was then sprayed onto the printed circuit board using a pneumatic spray gun. The gun pressure and the number of sprays applied were adjusted to achieve a coating thickness between 8 and 15 microns. The board was then heat-cured at 90°C for 15 minutes, followed by a subsequent heat-curing at 120°C for 10 minutes.

[0229] These coated printed circuit boards were then subjected to the above described water resistance test under distilled water at a bias of 30 V and under artificial sweat at a bias of 20 V, also described in the water resistance test.

[0230] For the coating compositions in Table 6-1, the effect of changing the thiol to other small molecules was determined and is shown in Table 6-2. Thiophene was found to be effective.

[0231] Table 6-2

[0232] Example Test conditions Average current (mA) Maximum current (mA) Dendrite Growth Rating Visible corrosion rating 6A 30V water 9.327 50.34 C 1 6A 20V sweat 0.694 2.103 A 2

[0233] Example 7: UV curable coating composition

[0234] Coating compositions containing the materials shown in Tables 7-1 and 7-2 and the specified amounts were prepared by the following procedure: Component 7A was prepared by combining the materials listed in Table 7-1 with mixing to obtain a clear solution.

[0235] Table 7-1: Component 7A

[0236] Material Weight (g) ethanol 98.0 Triethylenetetramine 2.0 total 100.0

[0237] Component 7B was prepared by combining the materials listed in Table 7B with simple mixing.

[0238] Table 7-2: Component 7B

[0239] Material Weight (g) Hexanediol diacrylate 12.0 50 wt% polyester resin / 50 wt% tripropylene glycol diacrylate (1:1 ratio) 2.0 50 wt% nanosilica / 50 wt% hexanediol diacrylate (1:1 ratio) 11.2 C24-26 branched saturated primary alcohol 0.4 Liquid Acrylated Dimethicone 0.09 Butyl acetate 4.8 Pentaerythritol tetrakis(3-mercaptopropionate) 3.2 total 33.7

[0240] Component 7A was used as a precoat over which component 7B, a UV-curable coating mixture, was applied. Component 7A was sprayed onto a test printed circuit board using an air pressure spray gun and subsequently dried at ambient temperature (about 25° C.) for 5 minutes to form an amine precoat that measured 0.6 g / m2 after drying.

[0241] Component 7B was then applied over the pre-coat and dried at ambient temperature for 10 minutes, after which the Component 7A / B coating was UV cured using a conveyor equipped with H+ bulbs as described above in the UV curing parameters. The total cured coating thickness of the combined layer was 25 microns.

[0242] Multiple sets of coated printed circuit boards were then subjected to the above-described waterproofing test, the first set under distilled water at 30 V and the second set under saline electrolyte at 20 V, and the results are shown in Table 7-3 below.

[0243] Table 7-3 Test results of Example 7

[0244]

[0245] ND: Not determined.

[0246] Example 8: UV-curable coating composition for forming an ultrathin coating

[0247] Coating Composition 8 containing the materials shown in Table 8-1 and the specified amounts was prepared by combining the materials under mixing to achieve a homogeneous mixture.

[0248] Table 8-1

[0249] Material Weight (g) 5% nitrile rubber solution in methyl isobutyl ketone 44.62 Mercaptoalkoxysilane oligomer 0.56 2-Hydroxy-2-methyl-1-phenyl-propan-1-one 0.14 Methyl isobutyl ketone 52.8 total 98.12

[0250] The coating composition of Example 8 was sprayed onto the printed circuit board using an air pressure spray gun and subsequently dried at 70° C. for 10 minutes, after which it was UV cured on a conveyor equipped with an H+ bulb at UV curing parameters according to the UV curing procedure described herein. After drying and curing, the applied coating thickness measured 900 nm.

[0251] The coated printed circuit boards were then subjected to the above-described waterproof test under distilled water at 3 V, and the results are shown in Table 8-2 below.

[0252] Table 8-2

[0253] formula# Test conditions Average current (mA) Dendrite Growth Rating Visible corrosion rating Example 8 3V water 1.35 B 0

[0254] Example 9: UV-curable coating composition for forming an ultrathin coating

[0255] Coating compositions 9A and 9B containing the materials shown in Table 9-1 and in the specified amounts were prepared by combining the materials under mixing to achieve a homogeneous mixture.

[0256] Table 9-1

[0257] Material weight (g) 9A 9B 3.5 wt% polyisobutylene diacrylate solution in toluene 18.0 18.0 Mercaptoalkoxysilane oligomer 0.42 0.42 Triethylamine 0.01 0.01 2-Hydroxy-2-methyl-1-phenyl-propan-1-one 0.03 — total 18.46 18.43

[0258] Coatings 9A and 9B were sprayed onto the printed circuit board using an air pressure spray gun, followed by drying at ambient temperature (approximately 25° C.) for 5 minutes, and then heat drying at 70° C. for 10 minutes. The dried coatings were then UV cured on a conveyor equipped with an H+ bulb according to the UV curing parameters described in the UV curing procedure. After drying and curing, the applied coating thicknesses were measured to be 704 nm and 1570 nm, respectively.

[0259] The coated printed circuit boards were then subjected to the water resistance test described in Table 9-2 below in water at an applied bias of 3 V.

[0260] Table 9-2

[0261] formula# Test conditions Average current (μA) Dendrite Growth Rating Visible corrosion rating Example 9A 3V water 610 microamperes A 0 Example 9B 3V water 6 microamperes A 0

[0262] Example 10 - Effect of Additives

[0263] Formulations using mercaptoalkoxysilane oligomers provide thiol functionality and silane secondary functionality on the same molecule. The thiol-bearing silanol precursors, upon hydrolysis, yield thiol-functional silanes, conveniently providing film-forming polymers useful as passivating agents and adhesive components. Prepare concentrates as shown in the table below.

[0264] Table 10-1

[0265]

[0266] *Mercaptoalkoxysilane oligomers in solvents used as passivators and adhesives.

[0267] The concentrate formulations were diluted with butyl acetate to obtain coating compositions having a sprayable consistency for use with an air pressure spray gun. Each coating composition was sprayed onto a printed circuit board and subsequently dried at ambient temperature (about 25° C.) for 5 minutes and then heated at 126° C. for 5 minutes.

[0268] The coated printed circuit boards were then subjected to the water resistance test described in Table 10-2 below in water at an applied bias of 3 V.

[0269] Table 10-2

[0270]

[0271] Example 11: Plug and Play Example

[0272] The following examples provide conformal coating compositions and coated PCBs with selected film hardnesses. Coating solutions containing the ingredients and amounts listed in Table 11-1 were prepared using the following procedure. The materials were dissolved in the solvents in the order listed. Low and high passivation level formulations were used to prepare adjustable adhesion examples. The formulations were applied using a conventional air pressure spray gun.

[0273] Adhesion test

[0274] Peel Adhesion: Adhesion is tested by first placing an adhesive masking layer on top of the coating and performing a 20V sweat test (see the next section for details). After the sweat test, the adhesive masking layer is removed. If the waterproof coating is completely removed by pulling the adhesive masking layer, the coating is considered peelable. Note whether the coating has good adhesion. Good adhesion: The masking agent does not remove the coating. Partial peeling: The masking agent removes part of the coating. Peelable: The entire coating may peel away from the PCB.

[0275] Crosshatch method: 1mm crosshatch is done on the copper and PCB. 100% of the coating remains on the PCB; Failure: 0% of the coating remains on the PCB

[0276] This removability facilitates PCB rework. As shown in the results in Table 11-2 below, the coatings exhibited good adhesion at low thiol levels (Examples 11D, 11F, and 11H) or partial removability at very high thiol levels (Examples 11A, 11B, 11C, 11E, and 11G). This contrast was achieved without adjustable adhesion.

[0277] The coating exhibits viscoelastic properties and passivating activity, both of which contribute to providing a waterproof connection to the conductive surface of a PCB when the coating is present at the interface between the individual connectors and the PCB. In some embodiments, the conductor pierces the conformal coating to establish an electrical connection to the PCB, which is a waterproof connection. In other embodiments, the conformal coating does not need to be pierced to establish an electrical connection to the PCB, which is a waterproof connection.

[0278] With improved coating hardness and passivation, the coating of the present disclosure is suitable for use as a plug-and-play waterproof electrical connection. The coating's insertion conductivity facilitates the addition of electronic components (e.g., microchips or other components) to a PCB by puncturing and / or simply inserting an empty connection point on the PCB with low force, while maintaining conductivity and waterproofing in the dry conformal coating.

[0279] Table 11-1. Plug and Play Test Composition

[0280]

[0281] 1 The passivating agent is pentaerythritol tetrakis (3-mercaptopropionate).

[0282] 2 The film-forming polymer is soluble in the coating composition and is a commercially available thermoplastic polyester polymer having a MP of about 100°C.

[0283] *Additive 1: Liquid hydroxylated polyester adhesion promoter different from the film-forming polyester.

[0284] **Additive 2: The reactive additive is a blocked isocyanate that reacts with mercaptans at drying temperatures.

[0285] ***Additive 3: A polycaprolactone waxy additive with a dielectric constant of 2.9, different from the film-forming polyester polymer, which is insoluble but uniformly dispersible in the coating composition.

[0286] ****Additive 4: Triol of polycaprolactone polymer waxy additive.

[0287] 3 The silicone flow additive is a polyether silicone polymer available from Evonik.

[0288] Plug and Play refers to the coating enabling a simple, low-force push to assemble electronic components into a device, which facilitates rapid manufacturing, rework, and service environment repair processes. This also provides for faster and lower-cost manufacturing of circuit boards and consumer electronics. Example microchips with I / O (input / output) pins that serve as piercing connections through the conformal coating are known in the art and are typically assembled on PCBs using pin-type metal connectors.

[0289] Plug and Play Test Results

[0290] Table 11-2

[0291]

[0292] *According to IPC-TM-650 Test Method Manual

[0293] The test results are shown in Table 11-2. These tests measured characteristics of the cured conformal coating, such as voltage resistance, adhesion and the force required to penetrate the cured layer sufficiently to establish an electrical connection to evaluate suitability for use as a plug-and-play coating, as well as corrosion resistance and the average and maximum current pass tests described herein.

[0294] A 12 micron thick coating of Example 11F comprising polycaprolactone (PCL) for increasing the dielectric breakdown strength of the coating was examined using a Zeiss LSM 800 confocal microscope using polarized light. Figure 2 This is a confocal image of a printed circuit board coated with Example 11F at a thickness of 12 microns, magnified 10x using polarized light. The polycaprolactone appears as bright spots in the coating, visible using polarized light from a confocal microscope. The polycaprolactone is distributed throughout the surface of the printed circuit board. The 12-micron-thick Example 11F exhibits 100% adhesion, a withstand voltage limit of 3000 volts, and excellent corrosion resistance and resistance to current flow. Dielectric strength is a fundamental property of plastic insulators, making them excellent for protecting devices from components subjected to high voltages.

[0295] Example 12

[0296] This study examined the effects of three flow improver additives and certain combinations thereof relative to each other. Coating solutions containing the ingredients and amounts listed in Table 12-1 were prepared using the following procedure. The specified polyester polymer was dissolved in the solvent at 70°C with stirring. The mercaptan was then added, followed by the remaining components. Stirring was continued until the coating solution was clear and free of visible solids.

[0297] Table 12-1

[0298]

[0299] The film-forming polymer is soluble in the coating composition and is a commercially available thermoplastic polyester polymer having a MP of about 100°C.

[0300] *1 Commercially available from Evonik Corporation and described by the manufacturer as a polyether siloxane copolymer.

[0301] *2Commercially available from BYK-Chemie GmbH and described by the manufacturer as a 12% solids polyether-modified polydimethylsiloxane in an organic solvent.

[0302] *3 Commercially available from BYK-Chemie GmbH and described by the manufacturer as a polyether-modified polydimethylsiloxane.

[0303] The coating solution was sprayed onto the printed circuit board using a pneumatic spray gun. The gun pressure and the number of sprays applied were adjusted to achieve a coating thickness between 8 and 15 microns. The board was then heat-cured at 90°C for 15 minutes, followed by a heat-curing at 120°C for 10 minutes.

[0304] These coated printed circuit boards were then subjected to the above described water resistance test under distilled water at 18V and 30V bias and under artificial sweat at 20V bias as also described in the water resistance test.

[0305] For the coating solutions in Table 12-1, the effects of flow modifiers and their combinations are shown in Table 12-2. Formulations 12B and 12D both have similar excellent performance and share a common flow modifier.

[0306] Table 12-2

[0307]

[0308] The foregoing disclosure has been described in accordance with relevant legal standards, and the description of the embodiments is provided for illustrative purposes and is therefore exemplary, rather than restrictive. It is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable where applicable and may be used in a selected embodiment even if not specifically shown or described. They may also be varied in many ways. Such variations should not be considered as departing from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

[0309] The terms used herein are for the purpose of describing specific exemplary embodiments only and are not intended to be limiting. As used herein, the singular forms "a", "an", and "the" may also be intended to include plural forms unless the context clearly indicates otherwise. The terms "comprises", "comprising", "including", and "having" are inclusive and therefore specify the presence of the features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof. Unless explicitly identified as an order of execution, the method steps, processes, and operations described herein should not be interpreted as having to be performed in the specific order discussed or illustrated. It should also be understood that additional or alternative steps may be adopted.

[0310] Variations and modifications to the disclosed embodiments may become apparent to those skilled in the art and do fall within the scope of the invention. Therefore, the scope of legal protection given to this invention can only be determined by studying the following claims.

Claims

1. A method for making a circuit board waterproof, comprising the following steps: a) preparing component 7A by combining 98.0 weight percent ethanol and 2.0 weight percent triethylenetetramine with mixing to obtain a clear solution; and b) Prepare Component 7B by combining the following materials with simple mixing: 35.62% by weight of hexanediol diacrylate, 5.94 wt% of 50 wt% polyester resin / 50 wt% tripropylene glycol diacrylate (1:1 ratio), 33.24 wt% of 50 wt% nanosilica / 50 wt% hexanediol diacrylate (1:1 ratio), 1.19 wt% of C24-26 branched saturated primary alcohol, 0.27 wt% liquid acrylated polydimethylsiloxane, 14.25% by weight of butyl acetate, and 9.50 wt% pentaerythritol tetrakis(3-mercaptopropionate); Component 7A is used as a pre-coat, onto which component 7B is applied, and the component 7A / B coating is then UV cured.

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