JPS627642B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a conductive method for through holes that is highly reliable, does not cause pollution, and can be achieved easily and inexpensively. In printed wiring boards, various methods have been put into practical use as conductive methods for through-hole portions. For example, the so-called copper through-hole plating method and the solder through-hole plating method are representative, but these methods require a plating step. The plating process is complicated because it not only requires a long time for plating, but also requires strict control of the plating bath. Furthermore, if the inner wall of the through-hole to be plated is not sufficiently leveled, there is a drawback that reliability is lacking. Furthermore, if the waste liquid from the smelt is not treated strictly, it may cause pollution. Another method for conducting electricity in the through-hole portion is to apply or fill it with a so-called conductive paste. Pastes using noble metals such as silver have been put into practical use as conductive pastes, but these noble metal pastes are expensive, and in the case of silver pastes, problems occur when the silver paste comes into contact with copper foil when baked. There are many cases where That is, the surface of the copper foil is oxidized to a very small extent, thereby producing cuprous oxide and forming a semiconductor. Therefore, it is often seen that a serious defect occurs in that when a minute current is passed, the electrical characteristics become directional. Furthermore, if current is continued to be applied under high humidity, there is a risk that so-called silver migration will occur and the conductive circuit will be short-circuited, and a method to solve this problem is strongly desired. The present inventor has improved the above-mentioned drawbacks of the conductive method for through-hole portions, and has achieved the present invention as a result of extensive research into a highly reliable, simple, and inexpensive method for conducting conduction for through-hole portions. That is, the present invention provides (a) metallic copper powder or copper composite powder, (b) a copper compound, (c) a reducing agent having a 1.4 or 1.2-dihydroxybenzene ring (hereinafter simply referred to as dihydroxybenzene ring), and (d) a through-hole characterized in that a conductive paste containing a resin or further containing (e) a chelate-forming substance in addition to (a) to (d) is applied or filled into the through-hole portion and then cured. This is the conduction method of the part. In the present invention, in the case of (e) a conductive paste that does not contain a chelate-forming substance, the mechanism is unknown, but
The storability of the conductive paste is somewhat poor, and as the storage time progresses, the surface of the conductive paste that comes into contact with the air hardens, degrading its quality and eventually rendering it unusable (hereinafter referred to as a phenomenon). There is a tendency for this to occur (abbreviated as skin burr phenomenon). If the composition of the present invention is to be used in a practical application that requires a long shelf life, this scalding phenomenon is inconvenient as it must be used immediately after preparation, so we are actively investigating ways to solve this problem. As a result, we found that (e) the addition of a chelate-forming substance can prevent the parenchymal epithelial burr phenomenon without causing any other problems, although the mechanism is also unclear. The shape of the metallic copper powder or copper composite powder used in the present invention is not particularly limited, and may be flaky, dendritic, spherical, irregularly shaped, etc., and the particle size is usually preferably 100μ or less, but in some cases Depending on the situation, 100μ to 1mm can also be used. In addition, pulverized metallic copper (including foil-shaped ones), reduced copper powder obtained by reduction of cupric oxide or cuprous oxide, copper powder made by rapid solidification of molten copper, electric Analysis of copper powder and these methods 2-3
Copper powder etc. obtained by combining types can be used. The copper composite powder used in the present invention refers to a metal powder in which metal particles are composed of copper and one or more other metals, particularly noble metals such as silver, platinum, palladium, mercury, and gold. There are metal powders whose surfaces are plated with the above noble metals, alloy powders of copper and the above noble metals, and the like. The alloy in this case is an alloy in a broad sense, and refers to a state in which one metal particle is simply composed of copper and other metals. For example, copper and other metals may be mixed and melted to create an atomically dissolved solid solution, or a eutectic state that is simply a mixture of component metals, or an intermetallic compound formed between component metals. There is a condition. It also includes metal powders obtained by mixing component metal powders and mechanically forcibly joining them using a vibration mill, ball mill, stamp mill, etc. It also contains metals other than copper and the above-mentioned precious metals, such as nickel, zinc, tin, lead, iron, aluminum, manganese, tungsten, titanium, silicon, magnesium, chromium, cadmium, cobalt, molybdenum, antimony, and vanadium. Good too. The content of copper in the copper composite powder is preferably 50% by weight or more, particularly preferably 70% by weight or more, mainly for economic reasons. Note that the metallic copper powder or copper composite powder may be an ordinary commercially available copper powder in which cuprous oxide or cupric oxide, which are examples of copper compounds described later, are present as a film on the surface, or , those that do not exist, those that have been subjected to, for example, antioxidant treatment, and those that have been treated with, for example, stearic acid to prevent agglomeration, can also be used. Of course, metallic copper powders having different shapes and particle sizes may also be mixed and used. In addition, in this application, resin has the following meaning. That is, it is a material that has already become a polymer before it is finally cured, or a material that becomes a polymer substance through a reaction during curing, and when the conductive paste of the present invention is cured, it becomes conductive. It means a substance that produces a hardened product with a high temperature. In addition to (a), the conductive paste in the present invention includes (b) and (c).
and (d) or further includes (e), but four or five distinct types corresponding to (a), (b), (c), (d), and (e). It is not always necessary to use a substance; for example, commercially available metallic copper powder or copper composite powder with a copper oxide film on the surface that serves as both (a) and (b) may be used, or (c ) and (d) by using a substance that also serves as some of (a), (b), (c), (d), and (e), such as using a resin that has a dihydroxybenzene ring part that also serves as 4. It is also possible to achieve the objective simply by mixing three or two types of substances. Hereinafter, various substances used in the conductive paste of the present invention will be explained using representative examples. (1) Copper compounds having only the properties specified in (b) Cuprous chloride, cuprous oxide, cupric oxide, copper acetate, copper salicylate, copper stearate. (2) Substances having only the properties of (c) with a dihydroxybenzene ring: Hydroquinone, catechol, 2-methyl-
Hydroquinone, vinylhydroquinone, tertiarybutylhydroquinone, chlorohydroquinone, phenylhydroquinone, and other substances with the following structures.

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[Formula] A substance that produces a reducing agent having a dihydroxybenzene ring as described above by further heating or adding other substances, such as adduct of catechol, hydroquinone, etc. and phenyl isocyanate, 2-methylhydroquinone 2
A substance such as an adduct of 1 mole of tolylene diisocyanate and 1 mole of tolylene diisocyanate. (3) Resins, i.e. substances that have only properties as (d): urea formaldehyde resin, melamine
Formaldehyde resin, phenol-formaldehyde resin, unsaturated polyester resin, thermosetting saturated polyester resin, polycarbonate resin, polyphenylene oxide resin, polyphenylene sulfide resin, fatty acid alkyd resin, polyamide resin, polyimide resin, epoxy acrylate resin , aryl resin (such as diallyl phthalate resin), epoxy resin, urethane resin, polyoxymethylene resin, spiroacetal resin, silicone resin, xylene resin, ketone resin, polysulfide rubber, acrylic resin, styrene resin, olefin resin, vinyl alkano resin ate resin, butadiene rubber,
Isobutylene rubber, ethylene-propylene rubber, chloroprene rubber, epichlorohydrin rubber, cellulose resin, rosin resin, fluorine resin, phosphonitrile chloride resin,
Ethyl silicate polymer. (4) a copper compound having a dihydroxybenzene ring,
That is, a substance that serves both (b) and (c); a copper salt of the substance in item (2) above; copper salt. (5) Resin-like copper compounds, i.e. substances that serve as both (b) and (d) Copper salts of saturated or unsaturated polyester resins, copper salts of vinyl chloride-vinyl acetate-maleic acid copolymers, sulfoethyl methacrylate-ethyl acrylate Copper salt, copper salt of rosin resin. (6) Resin having dihydroxybenzene ring, i.e.
Substances that serve both (c) and (d) Vinyl hydroquinone polymers and copolymer resins, hydroquinone-formaldehyde phenolic resins, hydroquinone-phenol-formaldehyde phenolic resins, catechol-formaldehyde phenolic resins,
1,4-dihydroxynaphthalene-formaldehyde resin. Furthermore, as in the case of (2) above, resins that generate dihydroxybenzene rings by heating or reaction with other substances, such as adducts of vinyl hydroquinone polymer and phenyl isocyanate, and J. Polymer Sci. , part A-1, 7 ,
A mixture of bislactone and diamine of hydroquinone-2,5-bis(ethyl-2'-carboxylic acid) published by N.NAKABAYASHI et al. in 1275-1278 (1969). (7) A resinous copper compound having a dihydroxybenzene ring, that is, a substance that also serves as (b), (c), and (d): a copper salt of a vinylhydroquinone-methacrylic acid copolymer, a copper salt of the resin described in item (6) above. Among the substances that serve as (c) and (c) of the present invention described above, substances that serve as both (c) and (d), and substances that serve as (b), (c), and (d) are preferable, and only (c) When using a substance that functions as (b) and (c), the change in conductivity may be a little large when the cured conductive resin is immersed in a solder bath, or the initial conductivity may be slightly inferior. This may result in performance deterioration. (8) Chelate-forming substances, that is, substances exhibiting properties as (e) Chelate-forming substances suitable for the present invention include:
The logarithm value of the stability constant Kma for divalent copper ions at 25° C. and ionic strength of 0.1 is 3 or more, preferably 5 or more. These substances include the following: 8-1 Aliphatic amines and their derivatives Ethylenediamine, N-(2-hydroxyethyl)ethylenediamine, trimethylenediamine, 1,2-diaminocyclohexane,
Triethylenetetramine, 2-aminomethylpyridine. 8-2 Aromatic polyamine Purine, adenine, 2-aminomethylpyridine, histamine. 8-3 β-diketone acetylacetone, trifluoroacetylacetone, 4,4,4-trifluoro-1-
Phenyl-1,3-butanedione, hexafluoroacetylacetone, benzoylacetone, dibenzoylmethane, 5,5-dimethyl-1,3-cyclohexanedione. 8-4 Phenolic compounds oxine, 2-methyloxine, oxine-5-sulfonic acid, dimethylglyoxime,
1-Nitroso-2-naphthol, 2-nitroso-1-naphthol, salicylaldehyde. 8-5 Others 2,2'-dipyridine, 1,10-phenanthroline. Of course, it is also possible to use substances that have the property (e) and other properties such as (b), (c), and (d). The ratio of copper compound used in the present invention is 0.1 as the copper content of the copper compound to metallic copper powder and copper composite powder.
-30% by weight, preferably 0.2-10% by weight. The proportion of the reducing agent having a dihydroxybenzene ring used in the present invention is preferably 80 equivalent % or more, particularly preferably 95 equivalent % or more, based on the amount sufficient to reduce all the copper in the copper compound. The proportion of the resin used in the present invention is 5 to 60% by weight, preferably 8 to 45% by weight based on the total nonvolatile content of the composition used in the present invention. The resin used in the present invention may be solid in itself, but it may be one that becomes substantially or apparently liquid upon curing by itself or in the presence of an organic solvent, water, plasticizer, etc. . The usage form of resin is solvent-based type dissolved in organic solvent,
Water-soluble type, water emulsion type, solvent emulsion type,
It may be either a 100% liquid resin type or a 100% solid resin type that becomes liquid at the temperature during curing, and is not particularly limited. The substrate used in the present invention is not particularly limited, and may include inorganic substrates such as ceramic, ceramic, glass, etc., so-called paper/phenol laminates, paper/epoxy laminates, glass fiber/epoxy laminates, etc. Thermoplastic resin or thermosetting resin mixed with fillers such as paper, glass fiber, silica, alumina, aluminum hydroxide, polyester film,
Typical examples include polyimide films and metal surfaces such as aluminum, iron, and stainless steel (including through-holes) coated with insulating properties, and these substrates are coated with copper foil or conductive paste. A circuit may be formed therebetween. The shape of the substrate described above is generally plate-like or thin-film-like, but there are no particular restrictions, and it may be formed into a certain three-dimensional shape. There are also no particular restrictions on the method of applying or filling conductive paste into the through-holes of the board, such as applying conductive paste to the tip of a thin metal rod and applying it to the through-holes (pin-up method), screen method, etc. Typical methods include a method of printing and filling a conductive paste into a through-hole portion by printing or the like (printing method), and a method of applying and filling using a certain type of spacer, spray, or inkjet. The point is that conductivity can be imparted between the front side and the back side of the substrate by applying or filling the conductive paste into the holes provided in the substrate. In the present invention, the conductive paste is applied or filled into the through-hole portion and then cured, but the temperature at this time is usually 250°C or less, preferably room temperature to 200°C,
Particularly preferably the temperature is from 50°C to 180°C. At this time, it is preferable that a reduction reaction of the copper compound to metallic copper occur, and if the reduction reaction occurs earlier or too late than the completion of curing of the conductive paste, the through-hole portion obtained by the method of the present invention may Affects conductivity durability. Therefore, in order to satisfy such conditions, a reducing agent having a dihydroxybenzene ring,
Metallic copper powder, copper compounds, resins, chelate-forming substances, etc. may be selected. In order to harden the conductive paste used in the present invention, the following method may be used depending on the type of resin (d) used in the conductive paste. In other words, if these resins are cured while evaporating volatile substances by drying, such as ordinary temperature drying resins (Latzker type), or if they have thermosetting properties, depending on the type, (1) heat treatment may be applied as appropriate. (2) In the case of resins that are cured by vinyl polymerization, such as unsaturated polyester resins and acrylate resins, such as azobisisobutyronitrile, di-t-butyl peroxide, benzoyl peroxide, etc. Using known polymerization initiators and electron beams,
For epoxy resin, triethylenetetramine,
Known curing agents such as polyamide polyamines, diaminodicyclohexylmethane, diaminodiphenylmethane, adipic acid dihydrazide, imidazole derivatives, dicyandiamide, boron trifluoride/ethylamine complexes, polymercapto compounds, polycarboxylic acids and their anhydrides, etc. In the case of phenolic resins, curing agents or curing accelerators such as hexamethylenetetramine, paraformaldehyde, p-toluenesulfonic acid, etc. are used, and in the case of oxidation-curing resins, lead naphthenate, cobalt octylate, etc. It may be hardened by known means, such as by using a known dryer such as, for example, or, in the case of thermoplastic material, by heating and then cooling. In short, the resin may be cured by any known means depending on the type and nature of the resin. In addition, in the present invention, the atmosphere when curing the conductive paste is an inert gas such as nitrogen or carbon dioxide,
Alternatively, it may be in any atmosphere such as in the air, and there is no particular restriction on the atmosphere. When curing the conductive paste in the method of the present invention, various known additives such as those listed below may be added in advance. For example, molecular weight regulators such as mercaptopropionic acid, carbon tetrabromide, stabilizers such as p-benzoquinone, phenothiazine, reactive diluents such as butyl glycidyl ether, phenyl glycidyl ether, dibutyl phthalate, tricresyl phosphate, etc. Noble metals belonging to group B and groups of the periodic table such as gold, silver, and palladium, and their compounds; inorganic bases such as lithium hydroxide and potassium hydroxide; dimethylbenzylamine, ethanolamine, and tris(N.N. - amino compounds such as (dimethylaminomethyl)phenol, N/N-dimethylaniline, acids such as acetic acid, oxalic acid, benzoic acid, PH regulators such as sodium orthophosphate, borax, potassium acetate, polyvinyl alcohol, polyvinylpyrrolidone. Viscosity modifiers such as potassium oleate,
Surfactants such as sodium dodecylbenzenesulfonate, polyoxyethylene lauryl ether, octadecylpyridinium chloride, solvents such as water, toluene, methyl ethyl ketone, ethylene glycol monoethyl ether, paraffin wax, carbon black, methyl ethyl ketoxime, lubricants, These include flame retardants, colorants, blowing agents, and thixotropic agents. The through-hole portion that maintains conductivity obtained by the present invention may be subjected to various known protection treatments as described below, if consideration is given to the application, usage environment, and enhancement of reliability. That is, such treatments include electrical or chemical plating with nickel, copper, etc., coating with epoxy resin, phenolic resin, rosin-based substances, polyethylene film, etc., surface treatment with imidazole-based processing agents, silicone-based processing agents, etc. There is. Examples will be described below, in which parts and % hereinafter mean parts by weight and % by weight, respectively, and concentrations described in the examples represent the proportion of the component in all components in % by weight. (A) Fabrication of through-hole board Using a double-sided copper-clad glass-epoxy resin laminate and Toshiba Tecolite MEL-W-44-16 (product of Tokyo Shibaura Electric Co., Ltd.), 20 holes with an inner diameter of 1 mm were drilled at 5 mm intervals. After that, the copper foil on the land part of the hole is about 1mm wide, and the copper foil on the straight part connecting the holes is about 1.5mm wide.
The remaining copper foil was etched using the usual method to produce a substrate with the pattern shown in FIG. (B) Conductive method for through-hole parts The conductive paste obtained for each experiment number in the following examples was applied to the through-hole parts of the board produced by the above method using a 0.7 mm drill bit as shown in Figure 2. After filling as shown
It was pre-dried at 80°C for 60 minutes. Next, the material was cured by heating at 150°C for 90 minutes to form a conductor in the through hole. (C) Performance evaluation (C-1) Conductivity The resistance at both ends of the board produced by the method (B) above was measured using a Wheatstone bridge (manufactured by Yokogawa Electric Corporation, Type-2755). Since the measured value corresponds to the value for 20 through holes, it was converted to the resistance value per through hole. (C-2) Moisture resistance test A substrate with conductive paste filled in the through-holes made by the method (B) above was heated at 50℃ and relative humidity.
It was placed in a 95% constant temperature and humidity chamber and taken out at regular intervals, and after being left at room temperature for 2 hours, the resistance value was measured using the method described in (C-1). (C-3) Solder heat resistance The board prepared by the method (B) above was immersed in a solder bath at 260℃ for 20 seconds, left at room temperature for 2 hours, and then the resistance value was determined according to the method (C-1). I took measurements. (C-4) Skin tension 100g of conductive paste obtained in each experiment number was
A ml polyethylene container was sealed and left at room temperature, and the presence or absence of a skin on the surface of the conductive paste was checked at regular intervals. Example 1 Using the conductive pastes obtained in Experiments 1 to 9 below and the substrate made by the method (A) above, the conductive paste was filled into the through-hole portions by the method (B) above. Next, performance evaluation was performed according to method (C) above. The results are summarized in Table 1. Experiment No. 1 (Comparative Example) (a) 110 parts of industrial copper powder (amorphous, average particle size 15μ, containing about 2.0% copper oxide), (b) Resin content after curing is 80%
resol type phenolic resin (ethylene glycol monomethyl ether solution of resin obtained by reacting formalin containing 1 mole of phenol and 2 moles of formaldehyde in the presence of an ammonia catalyst)23
(c) 20 parts of 2-hydroxy-3-phenoxypropyl phosphite, and (d) 4 parts of dimethylaminoethanol were mixed with a mixed solvent of diacetone alcohol and ethylene glycol monomethyl ether in a ratio of 1:1. In addition, a conductive paste with a viscosity of 80 poise was obtained. Experiment number 2 (a) 110 parts of the industrial copper powder used in experiment number 1, (b)
A hydroquinone-modified resol type phenolic resin (obtained by reacting formalin containing 2 moles of hydroquinone, 0.5 moles of phenol, and 6 moles of formaldehyde in the presence of an ammonia catalyst) with a resin content of 80% dissolved in ethylene glycol monomethyl ether was prepared at 42 (c) 0.2 parts of tris(N-N'-dimethylaminomethyl)phenol, and (d) 12 parts of ethyl acetoacetate by adding a 1:1 mixed solvent of diacetone alcohol and ethylene glycol monomethyl ether. A conductive paste with a viscosity of 80 poise was obtained. Experiment No. 3 4,4,4-trifluoro-1-phenyl-1,3-butanedione as (d) in Experiment No. 2
A conductive paste with a viscosity of 80 poise was obtained using the same recipe except that 12 parts were used. Experiment No. 4 In Experiment No. 2, industrial flake copper powder (average particle size 20μ, copper oxide content approximately 3.5%) was used as (a).
A conductive paste with a viscosity of 80 poise was obtained using the same recipe except that 20 parts and 90 parts of industrial electrolytic copper powder (average particle size 15μ, copper oxide content approximately 0.5%) were used. Experiment No. 5 A conductive paste having a viscosity of about 80 poise was obtained using the same recipe as in Experiment No. 4 except that 5 parts of 2,2'-dipyridyl and 7 parts of methyl acetoacetate were used as (d). Experiment No. 6 In Experiment No. 4, a modified resol type phenolic resin with a resin content of 80% (1.2 moles of methylhydroquinone, 3 moles of catechol, 0.5 moles of tert-butylphenol and 4 moles of formaldehyde was dissolved in ethylene glycol monomethyl ether as (b) in Experiment No. 4). A conductive paste with a viscosity of about 80 poise was obtained using the same recipe except that 42 parts of (obtained by reacting the formalin it contained) in the presence of an ammonia catalyst and 12 parts of acetylacetone were used as (d). Experiment No. 7 The viscosity was determined using the same recipe as in Experiment No. 6 except that 110 parts of copper-silver alloy (flake form, copper content 60%, average particle size 13μ) and 0.5 parts of cupric oxide were used as (a). A conductive paste of about 60 poise was obtained. Experiment No. 8 In Experiment No. 6, copper-silver composite powder (85
% electrolytic copper powder and 15% silver powder were mechanically forcibly joined using a vibration mill. A conductive paste with a viscosity of about 60 poise was obtained using the same recipe except that 110 parts of flake-like, average particle size 15 μm, copper oxide content 0.58% was used. Experiment No. 9 In Experiment No. 3, as (a), industrial electrolytic copper powder (average particle size 7μ, copper oxide content approximately 1.6%) 105
A conductive paste with a viscosity of about 70 poise was obtained using the same recipe except that 5 parts of flaky silver powder (average particle size: 3 μm) were used. Example 2 Experiment numbers 2 and 8 of Example 1 and experiment numbers below
Experiments were conducted using the conductive pastes obtained in steps 10 and 11 on a substrate made by method (A), method (B), and evaluation method (C). The results are summarized in Table 2. Experiment No. 10 (a) Industrial electrolytic copper powder used in Experiment No. 9
110 parts, (b) A resol type phenolic resin with a resin content of 80% dissolved in ethylene glycol monomethyl ether (formalin containing 1.5 moles of phenol, 0.5 moles of tert-butylphenol and 4 moles of formaldehyde is reacted in the presence of an ammonia catalyst. ), 18 parts of (c)methylhydroquinone, 7 parts of catechol, (ni)tris (N.
0.2 parts of N′-dimethylaminomethyl)phenol,
(e) A 1:1 mixed solvent of diacetone alcohol and ethylene glycol monomethyl ether was added to a composition consisting of 12 parts of ethyl acetoacetate to obtain a conductive paste with a viscosity of about 70 poise. Experiment number 11 (a) The copper-silver composite powder used in experiment number 8
110 parts, (b) Epicote #1001 (Yuka Ciel Epoxy Co., Ltd. product) 8 parts, Yuban 20SE (Mitsui Toatsu Chemical Co., Ltd. product) 13.3 parts, (c) Catechol 23
part, 2 parts of hydroquinone, (ni)tris (N・N'-
A 1:1 mixed solvent of diacetone alcohol and ethylene glycol monomethyl ether was added to a composition consisting of 0.2 parts of dimethylaminomethyl)phenol, 5 parts of (e)acetylacetone, and 10 parts of ethylene glycol monomethyl ether to form a conductive paste with a viscosity of about 60 poise. Obtained.

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【table】 [Brief explanation of the drawing]

FIG. 1 shows a through-hole board for testing used in an embodiment of the present invention, in which A is a plan view, B is a sectional view of the through-hole portion, and C is a bottom view. FIG. 2 is a sectional view showing a state in which the through-hole portion is filled with conductive paste. 1... Board, 2... Through hole, 3... Copper foil, 4... Conductive paste.

Claims (1)

[Claims] 1 (a) Metallic copper powder or copper composite powder, (b) Copper compound, (c)
A reducing agent having a 1,4 or 1,2-dihydroxybenzene ring, and (d) a resin, or the above (a)
A conductive method for a through-hole portion, which comprises applying or filling a conductive paste containing (e) a chelate-forming substance to the through-hole portion on a substrate in addition to (d) and then curing the paste.