Chung, Byung-joo (625-3 Yodang-ri, Yanggam-Myeon 445-931 Hwaseong-city, Kyungki-do, KR)
Kim, Bong-gi (625-3 Yodang-ri, Yanggam-Myeon 445-931 Hwaseong-city, Kyungki-do, KR)
Yoo, Young-gil (625-3 Yodang-ri, Yanggam-Myeon 445-931 Hwaseong-city, Kyungki-do, KR)
Park, Chan-seok (625-3 Yodang-ri, Yanggam-Myeon 445-931 Hwaseong-city, kyungki-do, KR)
Chung, Byung-joo (625-3 Yodang-ri, Yanggam-Myeon 445-931 Hwaseong-city, Kyungki-do, KR)
Kim, Bong-gi (625-3 Yodang-ri, Yanggam-Myeon 445-931 Hwaseong-city, Kyungki-do, KR)
Yoo, Young-gil (625-3 Yodang-ri, Yanggam-Myeon 445-931 Hwaseong-city, Kyungki-do, KR)
| 1. | An Ag paste composition for microelectrode formation, comprising: a) 60 to 80 wt% of Ag powders; b) 1 to 10 wt% of an inorganic binder; c) 0.001 to 1 wt% of a stabilizer; and d) 15 to 35 wt% of a negative photoresist composition that disperses conductive micropowders and is soluble in an alkaline. |
| 2. | The Ag paste composition of claim 1, wherein the Ag powders have an average particle size of 0.5 to 3 um. |
| 3. | The Ag paste composition of claim 1, wherein the inorganic binder is one or more selected from the group consisting of lead borosilicate frit, bismuth borosilicate frit, BOSiOMO, and B 0SiOM'0 where M is a divalent 2 3 2 2 3 2 2 metal ion and M'is a monovalent metal ion. |
| 4. | The Ag paste composition of claim 3, wherein the inorganic binder has a glass transition temperature of 360 to 500 °C and a glass softening temperature of 400 to 550 °C. |
| 5. | The Ag paste composition of claim 1, wherein the stabilizer is one or more selected from the group consisting of benzotriazole, ascorbic acid, phosphoric acid, phosphorous acid, and a salt thereof. |
| 6. | The Ag paste composition of claim 1, wherein the negative photoresist composition comprises: a) 30 to 70 wt% of a photoresist acrylate copolymer represented by Formula 1 below: Formula 1 wherein R1 is hydrogen, phenyl group, benzyl group, phenyl group substituted with nitro group, phenyl group substituted with halogen, benzyl group substituted with nitro group, alkyl group of C1 to C10, or alkyl group of C1 to C10 substituted with hydroxyl group; R2 is ethylhexyl group, isobutyl group, tert butyl group, octyl group, 3methoxybutyl group, or methoxypropyleneglycol group; R is hydrogen or methyl group; R is hydrogen or methyl group; n is an 3 4 1 integer of 8 to 40; n2 is 1 or 2, or Formula 2 below: Formula 2 wherein R is hydrogen or carboxyl group; R6 is phenyl group, carboxyl group,<BR> 5 6 orOCOCH group; R is hydrogen orCH COOH group; R, R, n, and n are 37 2 241 2 as defined above; b) 10 to 40 wt% of a photopolymerizable monomer; c) 0.5 to 10 wt% of a photopolymerization initiator; d) 0.1 to 10 wt% of an antifoaming agent; and e) 0.1 to 10 wt% of a leveling agent. |
| 7. | The Ag paste composition of claim 6, wherein the photopolymerization initiator is one or more selected from the group consisting of 2, 4bistrichloromethyl6pmethoxystyrylstriazine, 2pmethoxystyryl4, 6bistrichloromethylstriazine, 2,4trichloromethyl6triazine, 2, 4trichloromethyl4methylnaphthyl6triazine, benzophenone, p (diethylamino) benzophenone, 2, 2dichloro4phenoxyacetophenone, 2, 2'diethoxyacetophenone, 2, 2'dibutoxyacetophenone, 2hydroxy2methylpropiophenone, p tbutyltrichloroacetophenone, ptbutyldichloroacetophenone, 4,4'ethylaminobenzophenone, thioxantone, 2chlorothioxantone, 2methylthioxantone, 24sobutylthioxantone, 2dodecylthioxantone, 2, 4dimethylthioxantone, and 2, 4diehtylthioxantone2, 2'bis2chlorophenyl4,5, 4', 5'tetraphenyl2'1, 2'biimi dazole. |
| 8. | The Ag paste composition of claim 6, wherein the photopolymerizable monomer is one or more selected from the group consisting of 1,4butanediolediacrylate, 1,3butyleneglycoldiacrylate, ethyleneglycoldiacrylate, diethylenegly coldiacrylate, triethyleneglycoldiacrylate, polyethyleneglycoldiacrylate, dipen taerythritolkisacrylate, dipentaerythritolhydroxypentacrylate, glyceroldiacrylate, trimethylolpropanetrimethacrylate, pentaerythritoltrimethacrylate, pentaerythri toldimethacrylate, sorbitoltrimethacrylate, bisphenol A diacrylate derivative, trimethylolpropanetriacrylate, and dipentaerythritolpolyacrylate. |
| 9. | The Ag paste composition of claim 6, wherein the leveling agent is one or more selected from the group consisting of anionic copolymers and aralkyl modified polymethylalkylsiloxanes, and the antifoaming agent is one or more selected from the group consisting of polyester modified polymethylalkylsiloxanes, polysiloxanes, nonsilicon based polymer compounds, modified urea solutions, polyester modified dimethylpolysiloxanes, and polyester modified dimethylpolysiloxane copolymers. |
| 10. | The Ag paste composition of claim 1, which has a viscosity of 3,000 to 60,000 cP. |
| 11. | A microelectrode formed using the Ag paste composition of any one of claims 1 through 10. |
Background Art [2] Recently, as display devices with large size, high density, high precision, and high reliability are increasing in demand, developments on various patterning techniques have been made. Also, studies on compositions for microelectrodes compatible with these patterning techniques have been actively performed.
[3] Plasma display panels (hereinafter, referred to as'PDPs') have advantages over liquid crystal panels such as fast response speed and large size, and thus, have been currently used in various areas. Electrodes for PDPs had been conventionally fabricated by patterning of an electrode material using a screen printing method.
However, the conventional screen printing method requires great skill, and during screen printing, a paste may flow on a substrate due to low viscosity. Also, due to low precision by a screen, it is difficult to accomplish a high precision, large screen pattern required in PDPs. In addition, the conventional screen printing method has dis- advantages in that short circuit or disconnection may be caused by the screen during printing and the sintering temperature is as high as 1, 000 °C or more.
[4] Recently, a photolithography using a photosensitive resin composition for high precision electrode circuits compatible with a large area was developed. The pho- tolithography is a method forming a desired pattern by printing a photosensitive resin composition, in which conductive micro-powders are dispersed, to form a uniform thick film, and exposing the thick film thus formed to light using a desired shaped mask, followed by development with an alkaline developer.
[5] The miscibility between the photosensitive resin composition and the conductive micro-powders, adhesion of the photosensitive resin composition to a glass substrate during developing, and heat resistance of the photosensitive resin composition during sintering are very important factors that must be considered in formation of high precision electrode circuits. Also, high viscosity of 3,000 cP or more is required to allow a shear stress for uniform dispersion of the conductive micro-powders, which are inorganic materials, in the organic photosensitive resin composition. It is also required that the photosensitive resin composition is stable against external forces such as static electricity on the surfaces of the conductive micro-powders to maintain a uniform dispersion state, has a low crystallinity of a polymer resin, and has good adhesion with a glass surface and good thermal decomposition property.
Disclosure of Invention Technical Problem [6] Conventional photosensitive conductive pastes are sintered at 800 °C or more. In this case, since a sodium carbonate glass is generally used, conventional photosensitive conductive pastes are not suitable in fabrication of PDPs in which a sintering temperature must be maintained at 600 °C or less. Also, in a case where conventional photosensitive conductive pastes are sintered at 600 °C or less, there arise problems in that a sintered residue may be generated and conductivity may be deteriorated.
[7] With respect to conductive powders dispersed in a photosensitive resin composition, gold (Au) and copper (Cu) powders that had been conventionally widely used are treated with a separate organic solvent for developing after exposure to light, which may cause environmental pollution. Also, there are problems in that Au and Cu powders are expensive and have a high sintering temperature.
[8] In addition, with respect to a commercially available photosensitive resin composition which is a conductive paste with low viscosity of 500 to 1,500 cP that uses Ag powders of plate shape, the Ag powders exhibit poor dispersion characteristics due to their plate shapes. Even when spherical Ag powders are used, there arises a problem in that due to a large average particle size of several um to several tens um, micro pattern formation becomes difficult.
Technical Solution [9] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a high viscosity Ag paste composition for microelectrode formation. The Ag paste composition can be applied in a sintering process of 600 °C or less. Also, due to high viscosity, the Ag paste composition is suitable for formation of a precise microelectrode that cannot be formed by a con- ventional screen printing method, and has good printing property. In addition, because a surfactant and an organic solvent are not separately used, the Ag paste composition can be prepared simply and economically, and is environmental friendly.
Brief Description of the Drawings [10] FIG. 1 is a scanning electron microphotograph (SEM) after developing a 50 um pattern formed of a Ag paste composition according to the present invention; [11] FIG. 2 is a fractured surface SEM after developing a 50 um pattern formed of a Ag paste composition according to the present invention; [12] FIG. 3 is a SEM after sintering a 50 um pattern formed of a Ag paste composition according to the present invention; and [13] FIG. 4 is a fractured surface SEM after sintering a 50 um pattern formed of a Ag paste composition according to the present invention.
Best Mode for Carrying Out the Invention [14] According to an aspect of the present invention, there is provided a high viscosity Ag paste composition for microelectrode formation, including: [15] a) 60 to 80 wt% of Ag powders; [16] b) 1 to 10 wt% of an inorganic binder; [17] c) 0.001 to 1 wt% of a stabilizer; and [18] d) 15 to 35 wt% of a negative photoresist composition that disperses conductive micro-powders and is soluble in an alkaline.
[19] In the Ag paste composition for microelectrode formation, the negative photoresist composition includes: [20] a) 30 to 70 wt% of a photoresist acrylate copolymer represented by Formula 1 below: [21] Formula 1 [22] [23] wherein R is hydrogen, phenyl group, benzyl group, phenyl group substituted with nitro group, phenyl group substituted with halogen, benzyl group substituted with nitro group, alkyl group of to C, or alkyl group of to substituted with hydroxyl group; R is ethylhexyl group, isobutyl group, tert-butyl group, octyl group, 3-methoxybutyl group, or methoxypropyleneglycol group; R is hydrogen or methyl 3 group; R is hydrogen or methyl group; n is an integer of 8 to 40; n is 1 or 2, or 4 12 Formula 2 below: [24] Formula 2 [25] [26] wherein R5 is hydrogen or carboxyl group; R6 is phenyl group, carboxyl group, or - OCOCH group; R is hydrogen or -CH COOH group; R, R, n, and n are as defined 37 2 241 2 above; [27] b) 10 to 40 wt% of a photopolymerizable monomer; [28] c) 0.5 to 10 wt% of a photopolymerization initiator; [29] d) 0.1 to 10 wt% of an anti-foaming agent; and [30] e) 0.1 to 10 wt% of a leveling agent.
[31] According to another aspect of the present invention, there is provided a micro- electrode formed using the Ag paste composition.
[32] Hereinafter, the Ag paste composition of the present invention will be described in more detail.
[33] The present invention provides a high viscosity Ag paste composition for micro- electrode formation, which includes: a) 60 to 80 wt% of Ag powders; b) 1 to 10 wt% of an inorganic binder; c) 0.001 to 1 wt% of a stabilizer; and d) 15 to 35 wt% of a negative photoresist composition that disperses conductive micro-powders and is soluble in an alkaline.
[34] The conductive micro-powders as used herein are Ag powders. The Ag powders are used in the Ag paste composition in an amount of 60 to 80 wt%, preferably 65 to 75 wt%.
[35] If the content of the Ag powders is less than 60 wt%, the density of the Ag powders decreases, thereby increasing surface porosity after pattern formation and sintering. As a result, electric resistance increases and short circuit may be caused. Also, due to low viscosity, the Ag paste composition may flow on a glass substrate during printing.
[36] On the other hand, if the content of the Ag powders exceeds 80 wt%, due to ex- cessively high viscosity, there may arise a printing problem in that printing on a glass substrate is impossible or the glass substrate is not separated from a screen mask. Also, low smoothness after printing may cause a localized thickness difference and a mesh mark of a screen mask. In addition, as the density of the Ag powders increases,'under cut'phenomenon may worsen.
[37] There are no limitations on the shapes of the Ag powders used. However, with respect to dispersion characteristics, spherical Ag powders are preferred. The average particle size of the Ag powders is preferably in a range of 0.3 to 3 um, more preferably 0.5 to 2 um, most preferably 0.6 to 1. 3 um [38] The purity of the Ag powders is preferably 96% or more, more preferably 98% or more. This is because as the purity of the Ag powders decreases, due to impurities, electric resistance may be increased after sintering.
[39] The Ag paste composition of the present invention includes the inorganic binder to sinter and adhere the conductive powders on a glass substrate. The inorganic binder is used in an amount of 1 to 10 wt%, preferably 2 to 6 wt%, based on the total weight of the Ag paste composition.
[40] If the content of the inorganic binder is less than 1 wt%, the adhesion between a glass substrate and an electrode after sintering decreases, thereby causing electrode separation. On the other hand, if the content of the inorganic binder exceeds 10 wt%, the electric resistance of the electrode after sintering may increase or a short circuit may be caused.
[41] Preferably, the inorganic binder is one or more selected from the group consisting of lead borosilicate frit, bismuth borosilicate frit, B 0-SiO-MO, and B 0-SiO- 2 3 2 2 3 2 M'O where M is a divalent metal ion and M'is a monovalent metal ion.
2 [42] The particle shape of the inorganic binder may be spherical but is not limited thereto. The average particle size of the inorganic binder is preferably in a range of 0.3 to 3 um, more preferably 0.5 to 2 um, most preferably 0.6 to 1. 3 um [43] Preferably, the inorganic binder has a glass transition temperature (Tg) of 360 to 500 °C, and a glass softening temperature (Ts) of 400 to 550 °C.
[44] If the glass transition temperature and the glass softening temperature are re- spectively less than 360 °C and 400 °C, the sintering of the inorganic binder is initiated in a state wherein an organic material is incompletely decomposed. Therefore, an organic material may be present in a pattern, thereby lowering the performance of the pattern.
[45] On the other hand, if the glass transition temperature and the glass softening temperature respectively exceed 500 °C and 550 °C, the sintering of the inorganic binder may not be completed. Therefore, the adhesion between a microelectrode and a glass substrate may decrease, pattern characteristics may worsen, and pattern detachment may occur.
[46] It is preferable to store the inorganic binder in a place free of moisture. This is because moisture adsorbed in the inorganic binder may promote gelation of the paste composition. In this regard, it is preferable to dry the inorganic binder at a temperature of 80 to 350 °C in order for a foreign substance not to be attached to the surface of the inorganic binder. If the inorganic binder is stored at a temperature of more than 350 °C which is above transition temperature, the inorganic binder is out of powder phase, and thus, may not be used in the Ag paste composition.
[47] The Ag paste composition of the present invention includes the stabilizer to prevent the gelation of the paste composition, maintain storage stability, and control a de- velopment rate. The stabilizer is used in an amount of 0.001 to 1 wt%, preferably 0.005 to 1 wt%, most preferably 0.01 to 0.6 wt%, based on the total weight of the Ag paste composition.
[48] If the content of the stabilizer is less than 0.001 wt%, gelation of the paste easily occurs. On the other hand, if it exceeds 1 wt%, the viscosity of the composition may decrease or pattern formation may not occur.
[49] An antioxidant generally used, for example, benzotriazole, ascorbic acid, phosphoric acid, phosphorous acid, or a salt thereof may be used as the stabilizer but are not limited thereto.
[50] The Ag paste composition of the present invention includes the negative photoresist composition that facilitates dispersion of the conductive micro-powders such as Ag powders due to high viscosity and can be developed at high speed in an alkaline developer. The negative photoresist composition is used in an amount of 15 to 35 wt%, preferably 20 to 35 wt%, and most preferably 25 to 35 wt%, based on the total weight of the Ag paste composition.
[51] If the content of the negative photoresist composition exceeds 35 wt%, pores may be present in an electrode during electrode formation. As a result, electrode resistance increases, thereby causing short circuit during circuit driving. On the other hand, if it is less than 15 wt%, it is difficult to obtain a desired electrode pattern.
[52] Preferably, the negative photoresist composition includes: [53] a) 30 to 70 wt% of a photoresist acrylate copolymer represented by Formula 1 below: [54] Formula 1 [55] [56] wherein is hydrogen, phenyl group, benzyl group, phenyl group substituted with nitro group, phenyl group substituted with halogen, benzyl group substituted with nitro group, alkyl group of C to C, or alkyl group of C to C substituted with hydroxyl group; R is ethylhexyl group, isobutyl group, tert-butyl group, octyl group, 2 3-methoxybutyl group, or methoxypropyleneglycol group; R is hydrogen or methyl group; R is hydrogen or methyl group; n is an integer of 8 to 40; n is 1 or 2, or 4 1 2 Formula 2 below: [57] Formula 2 [58] [59] wherein R is hydrogen or carboxyl group; R is phenyl group, carboxyl group, or- OCOCH group ; R is hydrogen or-CH COOH group; R, R, n, and n are as defined 37 2 241 2 above; [60] b) 10 to 40 wt% of a photopolymerizable monomer; [61] c) 0.5 to 10 wt% of a photopolymerization initiator; [62] d) 0.1 to 10 wt% of an anti-foaming agent; and [63] e) 0.1 to 10 wt% of a leveling agent.
[64] Preferably, the acrylate copolymer of Formula 1 has a viscosity of 10,000 to 20,000 cP, and a molecular weight of 15,000 to 50,000, more preferably, 25,000 to 30,000.
Also, with respect to a printing method, the acrylate copolymer has preferably a glass transition temperature of 100 °C or more. If the glass transition temperature is less than 100 °C, due to strong adhesion, printing related problems may be caused.
[65] Examples of a monomer that can be used in preparation of the acrylate copolymer include an unsaturated carboxylic acid, an aromatic monomer, a self-plasticizable monomer, and an acrylic monomer except the self-plasticizable monomer.
[66] The unsaturated carboxylic acid is used to render the composition soluble in an alkaline. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinyl acetic acid, and an anhydride thereof. Preferably, the unsaturated carboxylic acid is used in an amount of 20 to 50 wt%, based on the total weight of the acrylate copolymer. If the content of the un- saturated carboxylic acid exceeds 50 wt%, gelation easily occurs during poly- merization, adjustment of the degree of polymerization is difficult, and storage stability of the resin composition during exposure to light is deteriorated. On the other hand, if the content of the unsaturated carboxylic acid is less than 20 wt%, time required for developing increases.
[67] The aromatic monomer is used to provide adhesion with a glass surface during developing and stable pattern formation. Examples of the aromatic monomer include styrene, benzylmethacrylate, benzylacrylate, phenylacrylate, phenylmethacrylate, 2-or 4-nitrophenylacrylate, 2-or 4-nitrophenylmethacrylate, 2-or 4-nitrobenzylmethacrylate, 2-or 4-chlorophenylacrylate, and 2-or 4-chlorophenylmethacrylate. The aromatic monomer is preferably used in an amount of 15 to 45 wt%, more preferably 20 to 40 wt%, based on the total weight of the acrylate copolymer. If the content of the aromatic monomer exceeds 45 wt%, time required for developing increases. Also, due to increased heat resistance, a photo- sensitive resin is left during sintering, thereby decreasing intrinsic electrode charac- teristics. On the other hand, if the content of the aromatic monomer is less than 15 wt%, adhesion with a glass surface during developing decreases. As a result, pattern detachment easily occurs and pattern straightness is deteriorated, which make it difficult to obtain a stable pattern.
[68] In particular, the self-plasticizable monomer serves to adjust the degree of poly- merization and to decrease crystallinity. Examples of the self-plasticizable monomer include 2-ethylhexyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, octyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, and methoxypropy- leneglycol (meth) acrylate. The self-plasticizable monomer is preferably used in an amount of 3 to 15 wt%, more preferably 5 to 10 wt%, based on the total weight of the acrylate copolymer. If the content of the self-plasticizable monomer exceeds 15 wt%, pattern detachment during developing worsens and pattern straightness is deteriorated.
On the other hand, if the content of the self-plasticizable monomer is less than 3 wt%, the degree of polymerization increases, thereby causing gelation. Even when gelation does not occur, a formed pattern is easily damaged after developing.
[69] The acrylate monomer except the self-plasticizable acrylate monomer serves to adjust the glass transition temperature, the adhesion with a substrate, and the polarity of the acrylate copolymer. Examples of the acrylate monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxyoctyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, and n-butylacrylate. The acrylate monomer is preferably used in an amount of 10 to 30 wt%, based on the total weight of the acrylate copolymer, considering the glass transition temperature and heat resistance and hydrophilicity with a developer of the acrylate copolymer.
[70] The acrylate copolymer can be obtained by polymerization of the above-described four monomers in a solvent with polarity appropriate to prevent the gelation of the monomers. Preferable examples of the solvent include carbitolacetate, gammabuty- rolactone, diethyleneglycolbutylether, trimethylpentanediolmonoisobutyrate, and dipropyleneglycolmonoethylether.
[71] The acrylate copolymer resin of Formula 1 or 2 is used in an amount of 30 to 70 wt%. If the content of the acrylate copolymer is less than 30 wt%, pattern formation becomes difficult. If it exceeds 70 wt%, the dispersion characteristics of powders becomes poor.
[72] In the negative photoresist composition, the photopolymerization initiator may be one or a mixture of triazines, benzophenones, acetophenones, imidazoles, and thioxantones. Examples of the photopolymerization initiator include 2, 4-bistrichloromethyl-6-p-methoxystyryl-s-triazine, 2-p-methoxystyryl-4, 6-bistrichloromethyl-s-triazine, 2,4-trichloromethyl-6-triazine, 2, 4-trichloromethyl-4-methylnaphthyl-6-triazine, benzophenone, p- (diethylamino) benzophenone, 2, 2-dichloro-4-phenoxyacetophenone, 2, 2'-diethoxyacetophenone, 2, 2'-dibutoxyacetophenone, 2-hydroxy-2-methylpropiophenone, p-t-butyltrichloroacetophenone, p- t-butyldichloroacetophenone, 4,4'-ethylaminobenzophenone, thioxantone, 2-chlorothioxantone, 2-methylthioxantone, 2isobutylthioxantone, 2-dodecylthioxantone, 2, 4-dimethylthioxantone, and 2, 4-diethylthioxantone-2, 2'-bis-2-chlorophenyl-4,5, 4', 5'-tetraphenyl-2'-1, 2'-biimidazole . The photopolymerization initiator is preferably used in an amount of 0.5 to 10 wt%, more preferably 2 to 4 wt%. If the content of the photopolymerization initiator exceeds 10 wt%, storage stability may be decreased, and due to high degree of curing, pattern detachment during developing may worsen. On the other hand, if it is less than 0.5 wt%, due to low sensitivity, normal pattern formation becomes difficult and pattern straightness worsens.
[73] In the negative photoresist composition, the photopolymerizable monomer may be one or a mixture of polyfunctional acrylate derivatives. Examples of the photopoly- merizable monomer include 1,4-butanediolediacrylate, 1,3-butyleneglycoldiacrylate, ethyleneglycoldiacrylate, diethyleneglycoldiacrylate, triethyleneglycoldiacrylate, polyethyleneglycoldiacrylate, dipentaerythritolkisacrylate, dipentaerythritolhydrox- ypentacrylate, glyceroldiacrylate, trimethylolpropanetrimethacrylate, pentaerythri- toltrimethacrylate, pentaerythritoldimethacrylate, sorbitoltrimethacrylate, bisphenol A diacrylate derivative, trimethylolpropanetriacrylate, and dipentaerythritolpolyacrylate.
The photopolymerizable monomer is preferably used in an amount of 10 to 40 wt%, more preferably 20 to 30 wt%. If the content of the photopolymerizable monomer exceeds 40 wt%, due to high degree of curing, pattern detachment during developing and pattern straightness become worsen. On the other hand, if it is less than 10 wt%, due to low sensitivity and low degree of curing, normal pattern formation becomes difficult and pattern straightness is deteriorated.
[74] Meanwhile, at the time of coating using a printing method, micro bubbles may be generated during mixing the Ag powders with other components. The micro bubbles present in a thick film due to high viscosity are transformed into pin-holes during sintering, thereby causing electrode disconnection. The anti-foaming agent of the negative photoresist composition serves to prevent such electrode disconnection. The leveling agent serves to mitigate the reduction of miscibility between the Ag powders and the photoresist composition due to the surface tension of the photoresist composition, and to reduce problems that may be caused by lack of film uniformity.
[75] Examples of the leveling agent include anionic copolymers and aralkyl modified polymethylalkylsiloxanes. Examples of the anti-foaming agent include polyester modified polymethylalkylsiloxanes, polysiloxanes, nonsilicon based polymer compounds, modified urea solutions, polyester modified dimethylpolysiloxanes, and polyester modified dimethylpolysiloxane copolymers.
[76] Preferably, each of the anti-foaming agent and the leveling agent is used in an amount of 0.1 to 10 wt%. Using of more than 10 wt% of the anti-foaming agent and the leveling agent may leave a residual film during developing. If the content of the anti-foaming agent and the leveling agent is less than 0.1 wt%, desired characteristics are not easily obtained.
[77] The Ag paste composition of the present invention is prepared by pre-mixing the Ag powders, the inorganic binder, the stabilizer, and the negative photoresist composition, as described above, using a planetary mixer, and uniformly dispersing the Ag powders, the inorganic binder, and the stabilizer in the photoresist composition using a mill such as 3-roll mill to form a paste phase. The Ag paste composition thus prepared has a viscosity of 3,000 to 60,000 cP and exhibits a pseudoplastic behavior.
These characteristics enable the use of the Ag paste composition as the composition for microelectrode formation, which requires low resistance against stress during printing, enhanced printing characteristics in spite of high viscosity, and high smoothness after printing.
[78] According to another aspect of the present invention, there is provided a micro- electrode formed using the Ag paste composition. The microelectrode is formed by a micro pattern formation step and a sintering step.
[79] In the micro pattern formation step, the Ag paste composition as prepared above is printed on the surface of a substrate using a screen printer that uses a screen mask such as SUS 325 mesh and SUS 400 mesh. The coated specimens are dried in a convection oven at a temperature of 80 to 120 °C for 10 to 40 minutes. The Ag paste coated film thus formed is exposed to a light source such as a mercury lamp with a complex wavelength of 365nm for pattern formation, followed by development using an ap- propriate alkaline developer such as Na CO solution, KOH, and TMA II at room 2 3 temperature to 50 °C.
[80] In the sintering step, the above-formed micro pattern is sintered in an electric furnace at 500 to 600 °C for 10 to 60 minutes. During the sintering, to completely remove the negative photoresist composition, the micro pattern is maintained at a temperature of about 300 to 400 °C for 10 to 60 minutes. When the photoresist composition is incompletely removed, an organic material of the photoresist composition is present in the form of carbonate, thereby incompletely sintering the Ag powders. Also, an electric resistance is increased after sintering or the micro pattern becomes dielectric. Furthermore, micro crack may be generated in the micro pattern after sintering.
[81] Hereinafter, the present invention will be described more specifically by Examples.
However, the following Examples are provided only for illustrations and thus the present invention is not limited to or by them. Unless specified otherwise in Examples, a numerical value indicates wt%.
Mode for the Invention [82] Examples [83] Examples 1 through 4 [84] Preparation of photoresist acrylate copolymers of negative photoresist com- positions that disperse conductive micro-powders and are soluble in alkalines [85] The acrylate copolymers of Formula 1 were prepared through polymerization according to the compositions and contents presented in Table 1 below. Here, as a solvent used for the polymerization, 50 wt% of gammabutyrolactone (GBL) was used in Examples 1 through 3, and 50 wt% of dipropyleneglycolmonoethylether (DPGME) was used in Example 4.
[86] Table 1 [87] Section Example 1 Example 2 Example 3 Example 4 Benzylmethacry 35 30 41 41 late (mol%) Methacrylic 50 45 45 45 Acid 2-Hydroxyethyl 8 7 7 methacrylate (mol%) Ethylhexylmeth 7 7 7 7 acrylate (mol%) Methylmethacry-18 late (mol%) Molecular 30,000 28,000 28,000 35,000 Weight Viscosity (cP) 15,000 12,000 12,000 >20,000 [88] Examples 5 through 9 [89] Preparation of negative photoresist compositions that disperse conductive micro- powders and are soluble in alkalines [90] According to the compositions and contents presented in Table 2 below, photopoly- merizaton initiators, anti-foaming agents, and leveling agents were added to the acrylate copolymers of Examples 1 through 4 followed by stirring at room temperature for 2 hours. Then, photopolymerizable monomers were added thereto and stirred at room temperature for 4 hours to give negative photoresist compositions that disperse conductive micro-powders and are soluble in alkalines. The photoresist compositions thus obtained were filtered with a 400 mesh to remove impurities.
[91] Table 2 [92] Composition Example 5 Example Example Example Example 6 7 8 9 Acrylate Example 1 60. 1 51. 1 Copolyme Example 2 60. 1 r Example 3 68. 0 Example 4 71. 7 Photopolymerization 1.6 2.0 2.8 2.8 2.8 Initiator Photopolymerizable 14.3 28.1 30.8 40.9 30.8 Monomer Anti-Foaming Agent 3.7 0.1 4.0 3.1 4.0 Leveling Agent 2 0. 1 2.0 2.0 2.0 Stabilizer 0. 01 0. 2 0.1 0.2 Others 6.69 0.8 0. 1 0. 1 [93] Example 10 [94] Preparation of Ag paste composition [95] 65 wt% of Ag powders, 3 wt% of an inorganic binder, 0.05 wt% of a stabilizer, and 31.95 wt% of a negative photoresist composition that disperses conductive micro- powders and is soluble in an alkaline were mixed, pre-mixed using a planetary mixer, and uniformly dispersed using 3-roll mill to give a Ag paste composition.
[96] Examples 11 through 14 [97] Evaluation of characteristics of Ag paste compositions according to the content of Ag powders [98] Table 3 [99] Section Example 11 Example 12 Example 13 Example 14 Ag Powders 63 67 71 73 Inorganic 2.95 2.95 2.95 2.95 Binder Stabilizer 0.05 0.05 0.05 0.05 Photoresist 34 30 26 24 Composition Developing Good Good Good Good Property Pattern 50 50 50 50 Formation (, um) Thickness after 8 9 11 11 developing Thickness after 4 5 6 7 sintering Viscosity (cP) 10,000 13,000 14,000 20,000 [100] The average particle size of the Ag powders used was 1. 2 um Lead borosilicate frit was used as the inorganic binder and phosphorous acid was used as the stabilizer. The photoresist composition included 68% of an acrylic copolymer, 28. 1% of a photopoly- merizable monomer, 2% of a photopolymerization initiator, and 1.9% of other additives.
[101] Ag paste compositions were prepared in the same manner as in Example 10 except that the contents of the Ag powders were as defined in Examples 11 through 14 of Table 3. According to evaluation results of characteristics of the Ag paste com- positions depending on the content of the Ag powders, the Ag paste compositions exhibited good developing property and pseudoplastic viscosity property. Also, printing property and pattern thickness after sintering were good.
[102] Examples 15 through 18 [103] Evaluation of characteristics of Ag paste compositions according to the content of stabilizer [104] Table 4 [105] Section Example 15 Example 16 Example 17 Example 18 Ag powders 67 67 67 67 Inorganic 2.95 2.95 2.95 2.95 Binder Stabilizer 0 0. 05 0. 3 1 Photoresist 30 30 30 30 Composition Developing Good Good Good Normal Property Pattern 50 50 50 Formation Gelation Gelation None None None [106] The average particle size of the Ag powders used was 1. 2 um Lead borosilicate frit was used as the inorganic binder and phosphorous acid was used as the stabilizer. The photoresist composition included 68% of an acrylic copolymer, 28. 1% of a photopoly- merizable monomer, 2% of a photopolymerization initiator, and 1.9% of other additives.
[107] Evaluation results of characteristics of the Ag paste compositions depending on the content of a stabilizer showed that while little or no stabilizer adversely affects the storage stability of the compositions, excess stabilizer renders pattern formation difficult.
[108] Examples 19 through 22 [109] Evaluation of characteristics of As paste compositions according to the type of stabilizers [110] Table 5 [111] Section Example 19 Example 20 Example 21 Example 22 Ag powders 67 67 67 67 Inorganic Binder 2.95 2.95 2.95 2.95 Stabilizer Phosphorous 0. 05--- Acid Phosphoric 0. 05 Acid Ascorbic 0. 05 Acid Benzotriazol---0. 05 e Photoresist Composition 30 30 30 30 Developing Property Good Good Good Good Pattern Formation 50 50 50 50 Gelation None None None None [112] The average particle size of the Ag powders used was 1. 2 um Lead borosilicate frit was used as the inorganic binder and the antioxidants listed in Table 5 above were used as stabilizers. The photoresist composition included 68% of an acrylic copolymer, 28. 1 % of a photopolymerizable monomer, 2% of a photopolymerization initiator, and 1.9% of other additives.
[113] The Ag paste compositions exhibited good characteristics regardless of the type of stabilizers.
[114] Examples 23 through 26 [115] Evaluation of characteristics of As paste compositions according to change in the amount of exposure to light [116] Table 6 [117] Section Example 23 Example 24 Example 25 Example 26 Ag Powders 67 67 67 67 Inorganic Binder 2.95 2.95 2.95 2.95 Stabilizer 0.05 0.05 0.05 0.05 Photoresist Composition 30 30 30 30 Amount of 300 0 Exposure to 400 Light (mJ) 800 1000-O Developing Property Good Good Good Good Pattern Formation 50 50 50 50 [118] The average particle size of the Ag powders used was 1. 2 um Lead borosilicate frit was used as the inorganic binder and phosphorous acid was used as the stabilizer. The photoresist composition included 68% of an acrylic copolymer, 28. 1% of a photopoly- merizable monomer, 2% of a photopolymerization initiator, and 1.9% of other additives.
[119] The Ag paste compositions of the present invention exhibited good developing property and pattern formation regardless of differences in the amount of exposure to light.
[120] Example 27 [121] Formation of microelectrodes [122] The Ag paste compositions according to above Examples were printed on the surface of a glass substrate using a screen printer with a SUS 325 mesh screen mask.
The printed specimens were dried in a convection oven at 90 °C for 20 minutes. The Ag paste coated films thus formed were exposed to light emitted from exposure equipment provided with a mercury lamp so that pattern formation occurred at 365 nm wavelength, and developed using a NaCO3 developer at 30 °C. The developed micro patterns were sintered in an electric furnace as the following program: sintering initiation at room temperature, maintaining at 350 °C for 30 minutes to carbonate an organic material, and sintering at 550 °C for 30 minutes, to form microelectrodes.
Industrial Applicability [123] An Ag paste composition for microelectrode formation according to the present invention can be applied in a sintering process of less than 600 °C and thus is suitable for PDP fabrication. Also, because of high viscosity, the Ag paste composition is suitable for formation of precise microelectrodes that cannot be formed by con- ventional screen printing technology, and has good printing property. In addition, because a surfactant and an organic solvent are not separately used, the Ag paste composition can be prepared simply and economically, and is environmental friendly.