JP2001014943A - Circuit drawing conductive paste and circuit printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve conductivity which is high even with low resistivity provided from high temperature sintering type paste with even slender circuit line width, by specifying the maximum diameter of a spherical silver powder, the maximum length of a flake-like silver powder, molecular weight of an ammonia resol based resin as a low-temperature hardening resin, and a boiling point of a high-boiling point organic solvent, and mixing respective specific amount of them and a plasticizer. SOLUTION: The diameter of a spherical silver powder and the maximum length of a flake-like silver powder are less than a half of the minimum drawn line width, a low temperature hardening resin is an ammonia resol based resin and a high molecular type resin with 10,000 or higher molecular weight, a solvent is a high boiling point solvent having 150 deg.C or higher normal pressure boiling point that is inert to an ammonia resol based resin, and a plasticizer is an alkoxy group containing denaturation silicone oligomer based plasticizer which is solvable in the solvent. The low- temperature hardening resin of 4-17 pts.wt. and 2-10 pts.wt. plasticizer are mixed with respect to 100 pts.wt. metal silver powder, and 10-40 pts.wt. solvent is mixed with total 100 pts.wt. of metal silver powder, low-temperature hardening resin, and plasticizer. This can be used for drawing a line narrower than 50 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste for drawing a circuit, and more particularly to a conductive paste used for forming a conductive circuit on a printed circuit board or a glass substrate. And a conductive paste such as a low-temperature curable silver paste. More specifically, when a screen printing method is used for forming a drawing of a conductor circuit, an extremely thin circuit, for example, a line & space of 50 μm & 50 μm is required.
The present invention relates to a conductive paste which enables a circuit drawing of less than m and exhibits a good conductivity in which the volume specific resistivity does not exceed several tens ^-5 Ω · cm, and a circuit drawing method using the same.

[0002]

2. Description of the Related Art When drawing wiring conductors of an electronic circuit on a substrate that can withstand high-temperature processing, a circuit pattern is printed by screen printing or the like using a high-temperature sintering-type conductive paste and fired at a high temperature. Thus, a method of sintering between conductive metal powders contained in a conductive paste is often used. In the high-temperature sintering-type conductive paste, a paste obtained by dispersing a conductive metal powder and an inorganic binder in an organic vehicle is fired at a high temperature to burn out the organic vehicle, so that extremely good intermetallic conduction is achieved. . On the other hand, when forming a circuit on a substrate that does not withstand or is not suitable for high-temperature processing, instead of using a high-temperature sintering-type conductive paste, a resin that cures at a relatively low temperature (epoxy resin, phenol resin, etc.) A thermosetting conductive paste in which a conductive metal powder is dispersed is used. In the case of thermosetting conductive paste, by curing the resin, the conductive metal powders come into contact with each other and conduct, but in general, the volume resistivity tends to be higher than that of the sintered conductive paste. There is. In particular, as the circuit line width becomes narrower, the volume specific resistivity tends to increase, and in the case of a conventional thermosetting conductive paste, for example, when applied to a fine line circuit having a line & space of less than 50 μm & 50 μm, The situation where the desired low resistance could not be satisfied also occurred to some extent.

In addition, an organic binder (low-temperature curing resin)
When an epoxy resin is selected, a low molecular weight compound is used as a curing agent or the like, so that there is a drawback that bleeding easily occurs in a drawn pattern due to these low molecular weight components.
In particular, when drawing a narrow pitch line in which the line & space is less than 50 μm & 50 μm, bleeding occurs.
It is also a constraint on the lower pitch limit. On the other hand, when a phenol resin is used as the organic binder, the conductivity becomes better as compared with the epoxy resin, but the circuit line width is 50 μm.
When the thickness of the thin line was lower than the above, the low resistance had some difficulty in comparison with the paste of the firing type. In addition, when a phenol resin is used, a considerable amount of solvent is contained in the conductive paste. Therefore, when applied to ordinary screen printing, the pattern spreads due to the fluidity of the solvent, and the circuit line width is 50 μm. When drawing a sharp line shape, such as a thin line below, it was a big constraint.

In recent years, there has been an increasing demand and necessity to form a sharp line-shaped circuit such as a thin line having a circuit line width of less than 50 μm on a substrate that cannot withstand high-temperature processing. In particular,
By circuit printing using conductive paste, which is rich in mass production, the conductivity is as low as that of baking type paste, and in addition, it draws sharp line shapes such as thin lines with circuit line width less than 50 μm. Development of a low-temperature-curable conductive paste exhibiting a configuration and characteristics different from those of the conventional conductive paste is awaited. Furthermore, line & space is 50μm &
There is also a long-awaited need for the development of a method that uses screen printing for drawing extremely sharp line shapes, such as narrow pitch line fine lines of less than 50 μm.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and an object of the present invention is to use it for drawing extremely sharp line shapes such as lines having a narrow pitch of less than 50 μm and 50 μm. In addition, a new structure that can achieve conductivity comparable to the low resistivity obtained with the conventional high-temperature sintering paste, even with a fine line having a circuit line width of less than 50 μm. -To provide a low-temperature curable conductive paste having a composition.
Still another object of the present invention is to provide a circuit printing method by screen printing using the low-temperature curable conductive paste having the above-mentioned novel constitution and composition.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems. As a result, when silver powder is used as the conductive metal powder, an ammonia resole resin is used as a low-temperature curable resin. By adopting a polymer type having a molecular weight of 10,000 or more, a circuit line width of 50 or more can be obtained.
Even with a fine line smaller than μm, it is possible to achieve conductivity comparable to the low resistivity obtained with the conventional high-temperature sintering paste, and, by screen printing, the narrow pitch as described above. It has been found that even when a line is drawn, the occurrence of bleeding can be suppressed. In addition, using a low-temperature curable conductive paste of a novel configuration and composition using the above-mentioned ammonia resole resin, when screen-printing a circuit,
The usual procedure, that is, spread the conductive paste evenly on the screen in advance, after the step called ink coating, instead of transferring the drawing pattern with a squeegee, omit the previous ink coating step, If a procedure of so-called double squeegee printing is used, in which the conductive paste is spread on the screen while simultaneously transferring the drawing pattern using two squeegees forming a pair, even sharper line-shaped drawing is possible. I found that.
The present invention has been completed based on the above findings.

That is, the conductive paste for circuit drawing according to the present invention has a minimum line width to be drawn as a conductive metal powder.
Metal silver powder obtained by mixing spherical silver powder having a diameter of 1/2 or less and flake silver powder having a maximum length of 1/2 or less of the minimum line width to be drawn, and an ammonia resol-based resin as a low-temperature curing type resin. A high molecular weight resin having a molecular weight of 10,000 or more, an inert solvent for the ammonia resole resin as a solvent, and a high boiling point organic solvent having a boiling point at normal pressure of 150 ° C. or higher, a plasticizer, An alkoxy group-containing modified silicone oligomer-based plasticizer that can be dissolved in the solvent, and, if necessary, an anti-settling agent (thixo agent)
And 4 to 17 parts by weight of the low-temperature curable resin, 2 to 10 parts by weight of the plasticizer, and 100 parts by weight of the metallic silver powder, and the metallic silver powder, the low-temperature curable resin, and the plasticizer. The solvent is used in an amount of 10 to 4 based on 100 parts by weight in total.
A conductive paste mixed at a ratio of 0 parts by weight.

The metallic silver powder is a mixture of spherical silver powder and flake silver powder in a weight ratio of spherical silver powder: flake silver powder = 1: 9.
It is preferable to use a mixture in a range of ８8: 2, generally in a range of spherical silver powder: flake silver powder = 1: 9 to 5: 5. In particular, when the minimum line width to be drawn is set to be a fine line smaller than 50 μm, the metallic silver powder is composed of spherical silver powder and flake silver powder in a weight ratio of spherical silver powder: flake silver powder =
It is more preferable to use a mixture in the range of 2: 8 to 4: 6.

Further, the circuit printing method using the conductive paste for circuit drawing according to the present invention has a mask opening for a circuit pattern to be drawn and printed, and the screen grid size is 1 / the minimum line width to be drawn. 4 or less, using a masked screen, when printing a circuit on the substrate, using the conductive paste for drawing a circuit of the present invention, a step of pre-ink coating the conductive paste on the screen Not provided, instead, a pair of two squeegees is used, and by sliding the squeegee, at least the screen portion provided with the mask opening is brought into contact with the printed surface of the substrate and the screen, and the circuit pattern is formed. Is printed by a circuit printing method.

[0010] More specifically, a circuit printing method is characterized in that the two squeegees forming the set slide on each other so that the sliding directions of the squeegees are opposite to each other, thereby printing a circuit pattern. . The sliding by the two squeegees in this group is a sliding similar to the so-called double squeegee printing used in metal mask printing.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The essential components of a conductive metal powder, a low-temperature curable resin, a solvent, and a plasticizer which constitute the conductive paste for circuit drawing according to the present invention will be described in more detail.

In the conductive paste of the present invention, as the conductive metal powder, a spherical silver powder having a diameter of not more than 1/2 of the minimum line width to be drawn and a maximum of not more than 1/2 of the minimum line width to be drawn are used. Metal silver powder mixed with long flake silver powder is used. In the first place, the conductive paste of the present invention,
Since the configuration is determined on the assumption that circuit printing is performed by applying screen printing, the particle size of the metallic silver powder to be used is determined according to the grid size of the screen.

Generally, the grid size of the screen is determined based on the minimum line width in the circuit pattern to be drawn.
Is to be determined. Specifically, the screen size of the screen is desirably selected at most not more than the minimum line width, and preferably, not more than 1/2 of the minimum line width. If the gauze size is larger than the minimum line width, looking at the portion having the minimum line width in the pattern opening to be printed, there may be places where the gauze wire material exists and places where it does not exist in the pattern opening. become. In that case, there is a difference in the removability of the paste between the two, and the dispersion occurs. It should be noted that there are few screens currently available on the market that have a gauze size smaller than about 30 μm. If the desired opening diameter is not obtained, for example,
When using a screen with a gauze size of about 30 μm to draw a pattern with a line width less than the minimum line width of 50 μm,
By devising the angle (bias) of the gauze, even at the minimum line width of the pattern opening, variation due to the removability of the paste can be suppressed.

[0014] In consideration of the minimum line width of the pattern opening to be drawn as described above, the screen size of the screen is selected to be the optimum screen size, and the particle size of the metallic silver powder to be used is determined by the screen size. Select significantly finer than the gauze size. Desirably, the maximum value of the diameter of the spherical silver powder is selected to be equal to or less than 1/2 of the screen size of the screen. When the maximum particle size of the spherical silver powder is selected to this size, the silver particles can easily pass through the gauze of the screen, thereby preventing the occurrence of a bridging phenomenon in which a plurality of silver powders stay in a bridging state between the gauze.

On the other hand, flake silver powder is usually
With respect to the maximum length, the shape of the cross section does not exceed 1/2, that is, the aspect ratio (maximum length in the longitudinal direction / thickness of the flake cross section) is 2 or more. If you select a size smaller than the screen size, you can easily pass through the screen size. In flake-like silver powder, although the bridging phenomenon is unlikely to occur due to its shape, the shape around the flake is often not smooth.
It has poor fluidity compared to spherical silver powder. With this in mind,
It is preferable that the size be selected to be 1/2 or less of the screen size of the screen so that there is no difference between the spherical silver powder used in combination and the screen transmittance.

Specifically, if the minimum line width of the circuit pattern to be drawn is 40 μm, the screen size of the screen is 40 μm or less, and accordingly, flake silver powder having a maximum length of 20 μm or less and a maximum diameter of 20 μm or less. Are mixed and used. Note that the above numerical values indicate the upper limit, and usually, silver powder having a size significantly smaller than the upper limit value is used. In addition, in the drawn circuit, the maximum length of the flake silver powder is 3/2 of the maximum diameter of the spherical silver powder so that the flake silver powder and the spherical silver powder can take the closest packing. It is more preferable to select the following.
In other words, when the maximum length of the flake silver powder is selected within the above range, the silver flakes are superposed on each other so as to fill the gaps between the spherical silver powders, so that good volume specific resistivity can be achieved. For example, when the minimum line width of a circuit pattern to be drawn is 40 μm, a screen having a grid size of 30 μm is used, and a flake silver powder having a maximum length of 15 μm or less, which is 1/2 of the grid size of 30 μm, and 15 μm
It is more preferable to use a mixture with a spherical silver powder having a maximum particle diameter of 10 μm or less, which corresponds to 2/3 of the above.

In the drawn circuit pattern, the mixing ratio of the spherical silver powder and the flake silver powder is selected so that they are uniformly distributed and in contact with each other. That is, the mixing ratio should be appropriately selected according to the average particle size of the flaky silver powder and the spherical silver powder.
The flake silver powder is mixed so as to be in the range of 1: 9 to 8: 2. In general, as the proportion of flake silver powder increases, the resulting volume resistivity tends to decrease,
The releasability of the conductive paste from the gauze of the screen is gradually inferior, and the uniformity of the thickness of the printed circuit pattern and the leveling are also deteriorated. On the other hand, as the ratio of the spherical silver powder is increased, the removability and leveling of the screen from the gauze are improved, but the obtained volume resistivity tends to be not sufficiently low. In consideration of this point, generally, in terms of weight ratio, spherical silver powder: flake silver powder =
It is preferable to mix them so as to be in the range of 1: 9 to 5: 5. When the circuit pattern is thinned, the mixing ratio should be in the range of spherical silver powder: flake silver powder = 2: 8 to 4: 6. It is more preferable to select. In other words, the resulting volume specific resistivity can be reduced while maintaining good screen removability and leveling, which are problems when the circuit pattern is thinned. The dispersibility of the silver powder used in the resin can be further improved by treating the surface with a fatty acid or the like. In particular, when silver powder having a fine particle size is used, the above surface treatment is an effective means.

In the present invention, a high-molecular-weight resin having a molecular weight of 10,000 or more is used as the low-temperature curing resin in the present invention. This ammonia resol-based resin is a polymer compound obtained by reacting formaldehyde as an auxiliary material with phenol or a phenol derivative as a main material under an ammonia catalyst. The above reaction is characterized by the fact that ammonia is used as a catalyst, and the main raw material for providing a phenol skeleton is phenolic carbonate (phenol), as well as various phenol derivatives such as cresol, xylenol, and t-butylphenol. Even when an alkylphenol such as phenylphenol, resorcinol, hydroquinone, or the like is used, an ammonia resol-based resin can be obtained. In general, when the molecular weight of the ammonia resole resin is significantly smaller than 10,000, that is, when the phenol skeleton is significantly less than 80, the fluidity becomes high, the familiarity with silver powder is poor, and the printing time is poor. Bleeding is also likely to occur. In view of this point, the present inventors have selected a high molecular weight resin which is an ammonia resol-based resin and has a molecular weight of 10,000 or more. Since the above-mentioned ammonia resole resin is a polymer type resin, it has a distribution in the degree of polymerization,
Although the molecular weight distribution is shown, the molecular weight of 10,000 or more means that the average of the molecular weight is 10,000 or more. On the other hand, if the molecular weight is too high, the fluidity required for the low-temperature curable resin of the conductive paste is insufficient, and blurring tends to occur when drawing. In addition, if the molecular weight is too high,
At the time of curing, flexibility may be lacking, and the high-boiling solvent contained in the conductive paste may remain in the film in an island shape or generate bubbles. In order to avoid these problems, the upper limit of the molecular weight is determined within a range showing flexible properties. In particular, when lowering the minimum line width of a circuit pattern to be drawn to about 40 μm using screen printing, the upper limit of the molecular weight does not exceed about 90,000,
Preferably, it is 50,000 or less.

As described above, the ammonia resole resin includes a different phenyl source, a different polymerization form,
Specifically, there are various polymers of a random polymerization type, a block polymerization type and the like. Among them, the following general formula (I):

[0020]

Embedded image (In the formula, n is an integer of about 80 or more, A is oxygen (—O—) or amine (—NH—) arbitrarily arranged, and at least 1 or more is selected from amine (—NH—). Is more preferable. This ammonia resole resin is flexible and has high adhesion to the substrate. In addition, familiarity with metal (silver powder) is also good. The curing temperature is 250 ° C. or less,
And it has excellent quick-curing properties. In particular, heat shrinkage is large, and accordingly, contact between conductive metal powders (silver powder) contained in the conductive paste can be made more reliable, which is effective in lowering the volume specific resistivity. These attributes are:
This is well suited to the purpose and characteristics of the conductive paste of the present invention.

The above-mentioned ammonia resole resin is usually used in an amount of 4 to 17 parts by weight based on 100 parts by weight of silver powder contained in the conductive paste. If the low-temperature curing type resin is used in an amount exceeding 17 parts by weight, the individual silver powder is covered with the resin, and the mutual contact of the silver powder is hindered. Therefore, the volume resistivity is high. Whether or not sufficient contact between the silver powders can be ensured also depends on the shape of the silver powder itself. That is, when arranged in a state where sufficient contact between the silver powders can be secured, it is most preferable that the resin is filled in the gaps between the silver powders and the volumetric shrinkage of the resin due to thermosetting makes the contacts between the silver powders more dense. . The upper limit of 17 parts by weight of the low-temperature curing resin to 100 parts by weight of silver powder is the low-temperature curing used when the gap between the silver powders is maximized in consideration of the silver powder shape and the mixing ratio of spherical silver powder and flake silver powder. This corresponds to the upper limit of the amount of mold resin used.

On the other hand, if the amount of the low-temperature curable resin used is less than 4 parts by weight, a dense binding between silver powders cannot be obtained, and the volume specific resistivity also becomes high. That is,
Even if the silver powders are arranged in a state where sufficient contact between them can be secured, the resin is present only in a part of the gap between the silver powders, and due to the shrinkage of the resin volume due to thermosetting, the contact between the silver powders is improved. The effect of densification cannot be obtained. The lower limit of 4 parts by weight corresponds to an amount indispensable for binding silver powders when the gap between the silver powders is minimized in consideration of the silver powder shape and the mixing ratio of the spherical silver powder and the flake silver powder. If the amount of the low-temperature curing resin is insufficient, some silver powder is not bound sufficiently, and when hardened after printing, it is easy for silver powder to fly (a phenomenon in which silver powder is free to be observed outside the circuit). . In addition, leveling during curing also tends to be poor.

As described above, the most appropriate amount of the low-temperature curable resin to be used is also related to the tap density of silver powder and depends on it, so that the mixing ratio of silver powder shape, spherical silver powder and flake silver powder is taken into consideration. It should be selected appropriately, for example,
When selecting the mixing ratio in the range of spherical silver powder: flake silver powder = 2: 8 to 4: 6, it is more preferable to select the mixing ratio in the range of 6 to 12 parts by weight.

The solvent supplements the fluidity of the low-temperature curable resin itself, and adjusts the viscosity of the conductive paste to an appropriate range when drawing a circuit by screen printing using the conductive paste. Therefore, it is added as a diluting solvent. Therefore, an inert solvent for the ammonia resole resin is used. When drawing a circuit by screen printing, it is preferable to use a solvent having a high boiling point so that clogging does not occur in a screen or the like due to evaporation of the solvent. Therefore, it is usual to use at least a high-boiling organic solvent having a boiling point of 150 ° C. or higher at normal pressure, and preferably a solvent having a boiling point of 200 ° C. or higher. For example, for the ammonia resole resin represented by the above general formula (I), methyl carbitol, ethyl carbitol, methyl carbitol acetate, ethyl carbitol acetate, butyl carbitol, butyl carbitol acetate, ethyl cellosolve It is preferable to use a solvent such as ethyl cellosolve acetate, butyl cellosolve, or butyl cellosolve acetate alone or as a mixed solvent. On the other hand, when the above-mentioned low-temperature curing type resin is thermally cured, the solvent is preferably evaporated (dried). That is,
A high-boiling solvent having a boiling point lower than the temperature at which the thermosetting treatment is performed and the curing temperature is selected. Therefore, when the curing temperature is low, a solvent having a relatively low boiling point is used. In order to make the circuit thickness after curing a desired value, the conductive paste layer to be drawn is drawn in consideration of the volume decrease due to the evaporation (drying) of the solvent and the heat shrinkage of the low-temperature curing resin itself. Adjust the thickness of the. Specifically, the thickness of the conductive paste layer to be drawn is adjusted according to the emulsion thickness of the mask used for screen printing. At the time of drawing, if the initial viscosity of the conductive paste is too low, the pattern spreads and bleeds, and if the initial viscosity is too high, the separation between the printed surface of the substrate and the screen (plate separation) becomes poor after drawing. Usually, it is preferable to dilute the conductive paste by adding a solvent so that the initial viscosity of the conductive paste is in the range of 30 to 120 Pa · s.

Therefore, considering both the volume decrease due to evaporation (drying) of the solvent and the initial viscosity of the conductive paste,
For example, in a conductive paste using 4 to 17 parts by weight of the low-temperature-curable resin and 2 to 10 parts by weight of the plasticizer with respect to 100 parts by weight of the metallic silver powder, the metallic silver powder, the low-temperature-curable resin, and It is preferable to mix the solvent at a ratio of 10 to 40 parts by weight with respect to the total of 100 parts by weight of the plasticizer. In general, as the minimum line width to be drawn becomes smaller, it is necessary to increase the initial viscosity of the conductive paste to suppress the spread and bleeding of the pattern. Therefore, when the minimum line width to be drawn becomes narrow, it is preferable to relatively reduce the addition ratio of the solvent to the low-temperature curing type resin. In addition, when a large decrease in viscosity is expected due to components other than the low-temperature curable resin, that is, a plasticizer or the like, a mode in which the amount of the solvent to be added is slightly lower than the above lower limit of 10 parts by weight is also substantial. Are included in the present invention. That is, when the component added for use such as the plasticizer substantially complements the role of the solvent, the amount of the solvent to be added can be relatively reduced in order to naturally obtain a suitable initial viscosity. .

The optimum value of the initial viscosity of the conductive paste is governed by the thixotropic property, tackiness, and yield value, which are also related to the mixing ratio and shape of the silver powder contained in the paste. In accordance with the purpose such as the thickness, the thickness is selected from the range of 30 to 120 Pa · s. At that time, the thixotropic index was measured at 10 rp measured by a rotational viscometer.
with viscosity during the viscosity and 60rpm during m, when the value of log ₁₀ (viscosity when the viscosity / 60rpm at _{10rpm) / log 10 (60/10)} , the thixotropic index is 0.5 to 0. 9 is preferable.

The plasticizer is added to the conductive paste of the present invention in order to eliminate the drawback of leaving a problem in leveling when the low-temperature curable resin is cured when the initial viscosity of the conductive paste is set high. It is. Especially when applying screen printing to print fine pitch circuits,
As described above, in order to prevent the pattern from spreading or bleeding, the initial viscosity and the thixotropic property of the conductive paste cannot be reduced. In that case, there is a strong tendency that the leveling at the time of curing deteriorates, sometimes due to the application of screen printing,
The effect is even more pronounced on fine lines. The present inventors have intensively studied a measure for improvement, and as a result, at the beginning of curing, the conductive paste is softened once, and then, if possible, a step of hardening, if desired, the desired leveling is performed at the time of softening. I came to that. During this cure,
It has been found that it is effective to add a plasticizer to induce temporary softening. When a suitable plasticizer was searched for the above-mentioned ammonia resol-based resin, it was found that the alkoxy group-containing modified silicone oligomer had a preferable result when the curing temperature was set to a range not exceeding 250 ° C. Further, when the alkoxy group-containing modified silicone oligomer is added, the tackiness of the conductive paste is also reduced, and a favorable effect is exhibited in screen printing for maintaining more stable printing.

In particular, when a high-temperature type ammonia resole resin represented by the general formula (I) is used as the low-temperature curing type resin, the following general formula (II) is used as a plasticizer.

[0029]

Embedded image (Wherein, p and q are integers of 0 or more and are not both 0), and the like. The oligomer itself can be produced by a known method, and can be prepared into a target copolymer or the like by subjecting raw materials phenyltrialkoxysilane and methylalkoxysilane to a condensation reaction.
In the general formula (II), the oligomer in which the total (p + q) of the numbers p and q of the structural units is 2 or 3 is compatible with the polymer type ammonia resole resin represented by the general formula (I). Is excellent. On the other hand, when (p + q) exceeds 5, the compatibility with the resin is poor, and the effect as a plasticizer cannot be achieved. The poor compatibility has a bad influence on the curing properties of the conductive paste. Further, the cleaning property of the conductive paste is also deteriorated. On the other hand, when (p + q) is 1 or 2, the smaller the molecular weight is, the higher the volatility is, so that it is not possible to obtain a desired result of adding a plasticizer during curing. Also, when the amount of addition is increased, during printing,
It can also be a factor causing bleeding. Therefore, it is more preferable that the sum (p + q) of the numbers p and q of the structural units be 2 to 4. Among them, a compound having (p + q) of 3 is a more preferable plasticizer. Some of such alkoxy group-containing modified silicone oligomers are commercially available. Examples of the compound having (p + q) of about 3 include, for example, KR213 (trade name) (Shin-Etsu Chemical Co., Ltd.)
Manufactured). The product name KR2
The thirteen commercially available products are a mixture containing, as a main component, the compound having the above (p + q) of 3, but also containing components having slightly different combinations of (p, q).

The plasticizer plays a role of inducing the above-mentioned temporary softening phenomenon when curing the low-temperature curing resin, and is added at a fixed ratio to the low-temperature curing resin. For example, when 4 to 17 parts by weight of the low-temperature curable resin is used with respect to 100 parts by weight of the metallic silver powder, the amount of the plasticizer to be added is preferably selected in the range of 2 to 10 parts by weight. In general, as the amount of the low-temperature-curable resin used relative to the metallic silver powder decreases, the problem of leveling tends to become apparent, and it is more preferable to increase the ratio of the plasticizer to the low-temperature-curable resin. When the amount of used is large, the problem of leveling becomes rare, and the addition ratio of the plasticizer to the low-temperature curable resin can be reduced.

The conductive paste for drawing a circuit of the present invention is obtained by uniformly mixing the essential components described above, the conductive metal powder, the low-temperature curing resin, the plasticizer and the solvent.
As a product, when stored, due to the specific gravity difference, etc., to suppress the conductive metal powder from settling, if necessary,
A commercially available anti-settling agent (thixo agent) is added. Or,
Commercially available dispersants can also be added. Further, various kinds of coupling agents can be added, if necessary, depending on the material of the substrate or the like on which drawing is performed.

The coupling agent is selected according to the material of the substrate or the like. However, those which have high reactivity with the low-temperature curing type resin and impair the preservability of the conductive paste are naturally excluded. You. That is, a coupling agent can be appropriately added within a range that does not deteriorate the pot life of the conductive paste due to the reaction with the low-temperature setting resin. The amount of the coupling agent to be added is determined in a weight ratio to the low-temperature setting resin of 1 to 10% in consideration of adhesion to a substrate or the like and conductivity of a drawn circuit. When a high-molecular-weight ammonia resole resin represented by the general formula (I) is used as the low-temperature curing resin, for example, a preferable coupling agent that satisfies the requirements of low volatility and low reactivity with the resin. Examples of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropyldimethoxysilane, β- (3,4-
Epoxycyclohexyl) ethyltrimethoxysilane,
γ-aminopropyltriethoxysilane, N-phenyl
-γ-aminopropyltrimethoxysilane and the like.

A method for preparing the conductive paste for circuit drawing according to the present invention will be described. The essential components described above, conductive metal powder, low-temperature curable resin, plasticizer and solvent, and other anti-settling agents (thixotropic agents) added as necessary.
A dispersing agent, a coupling agent, and a predetermined ratio thereof are blended and uniformly kneaded to prepare a conductive paste. As means for performing uniform kneading, for example, in addition to commonly used equipment and devices such as a planetary mixer and three rolls, in particular, a kneading machine that is capable of kneading in a closed system, which is a combination of rotation and revolution, or Stirring defoaming machine,
For example, a commercially available machine such as model name MS-SNB-2000: manufactured by Matsuo Sangyo Co., Ltd. can also be suitably used.

At the time of kneading, the viscosity of the conductive paste is measured using a commercially available rotational viscometer (for example, product name Malcom PC1TL VS-
Using 3), measure the viscosity at 10 rpm. Depending on the use of the product, the amount of the solvent added is increased or decreased, the viscosity is adjusted to a predetermined value, and after defoaming under vacuum, the mixture is left and aged at a low temperature, for example, 10 ° C. or lower for several days.

Next, a circuit printing method using the above-described conductive paste for circuit drawing according to the present invention will be described. A printing machine used for drawing printing is slightly changed or modified in order to apply double squeegee printing, unlike a normal screen printing machine. A normal screen printing machine is equipped with a scraper and a squeegee for printing in order to perform ink coating in advance. In double squeegee printing, since no ink coating is performed, a scraper is unnecessary, and a second squeegee is provided instead. For example, two squeegees are arranged in a “C” shape facing each other. FIG. 1 is a conceptual diagram showing the arrangement of a scraper and a squeegee of a normal screen printing machine and the arrangement of two squeegees of a screen printing machine for double squeegee printing. As shown in FIG. 1, the mask length is extended in the squeegee sliding direction to secure a necessary squeegee stroke for a second squeegee arranged in place of the scraper. With the extension of the mask length, the design and modification of the screen printing machine are appropriately performed, such as creating a corresponding mask holder and replacing it with a normal mask holder.

In normal screen printing, ink coating is performed so that the paste on the screen cross-section is dried and does not cause clogging. When drawing an ultra-fine pattern with a very narrow line width, the screen grid size used becomes finer, and a capillary phenomenon occurs at the narrow grid opening, and the ink-coated paste leaches toward the substrate (work) side. A phenomenon occurs.

With this leaching phenomenon, the paste leaching area on the work side spreads out of the mask pattern on the screen, and each time ink coating is performed and printing is repeated, the spread slightly increases. . Therefore, in normal screen printing in which ink coating is performed, stable printing cannot be continued when a super fine pattern is drawn.

In the circuit printing method of the present invention, since the ink coating is not performed, the leaching of the paste to the work side due to the above-mentioned capillary phenomenon is essentially eliminated. On the other hand, in order to prevent the paste on the screen gauze from drying and clogging, the squeegee that wipes the gauze neatly is used to substantially eliminate the residue of the paste on the gauze. . In addition, since the conductive paste itself uses a high-boiling solvent as a solvent, clogging due to drying is further reduced. In addition, the alkoxy group-containing modified silicone oligomer added as a plasticizer also has the effect of lowering the tackiness of the conductive paste, and increases the permeability of the paste to the slit openings, thereby avoiding the problem of clogging. is there.

When the above-described printing method is applied, in the screen printing using the conductive paste for circuit drawing of the present invention, even if the line and space are extremely fine circuit patterns of 40 μm / 40 μm, the space interval is not reduced. In addition, a circuit having a sufficiently low volume resistivity can be formed.

The circuit pattern drawn on the substrate or the like by the circuit printing method of the present invention is such that the low-temperature curable resin such as an ammonia resole resin is flexible, and is compatible with and adheres to a metal such as aluminum. Therefore, various IC elements are used for flip-on-chip type face-down mounting. For example, when mounting a liquid crystal driver IC or the like face down on a wiring circuit pattern drawn on a glass substrate, a fine pitch circuit drawn using the circuit printing method of the present invention can be used. Also, since it is excellent in mass productivity, it is advantageous for cost reduction.

Hereinafter, a specific example will be given to prepare the conductive paste for drawing a circuit of the present invention, and use the conductive paste to screen-print a minimum line width of 50 μm.
Advantages when applied to the drawing of a delicate circuit pattern less than m will be described in more detail.

[0042]

EXAMPLES (Examples of Preparation of Conductive Paste) An ammonia resol-based resin used for preparing the conductive paste for circuit drawing according to the present invention is represented by the general formula (I) and has various degrees of polymerization (molecular weight). And a composition having a composition ratio (n / m).
For comparison, conventional resol-based resins having various degrees of polymerization (molecular weight) were also synthesized.

The ammonia resol-based resin represented by the general formula (I) can be synthesized using ammonia as a catalyst by the following synthesis procedure. Raw materials such as phenol, formaldehyde aqueous solution, and aqueous ammonia as a catalyst are charged into a flask, mixed, and heated at 85 ° C. for several hours with stirring. Then, a condenser for distillation is attached to the flask, and water is distilled off at 50 ° C. under reduced pressure (50 to 60 mmHg). As the dehydration proceeds, the pressure is reduced to 30 mmHg and further heated to 75 ° C. In the dehydration step, a small amount of the mixture (resin) in the flask is sampled for occasional sampling, and the temperature at which the sample solidifies when cooled to room temperature is checked. The solidification point during cooling is used as a guide to determine the end of dehydration. Immediately after the dehydration, the reaction product (resin) in the flask is poured out onto a metal vat. The phenol / formaldehyde charge ratio of the raw materials, the heating time of the addition / polymerization reaction, and the like are adjusted so that the desired molecular weight and composition ratio (n / m) are obtained.

On the other hand, a conventional resole resin (resin B) is synthesized by using an aqueous solution of phenol or formaldehyde as a raw material, and using sodium hydroxide (NaOH) instead of ammonia.
Can be used as a catalyst in a similar procedure.

Using the above resin, a conductive paste having the following composition was prepared. First, 10 parts by weight of an ammonia resole resin, 5 parts by weight of a modified silicone oligomer containing an alkoxy group as a plasticizer: KR-213 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.), 10 parts by weight of a thixo agent, and ethyl carbyl as a solvent 30 parts by weight of tall acetate is stirred and mixed for 2 minutes with a stirring and defoaming machine MS-SNB-2000 (manufactured by Matsuo Sangyo Co., Ltd.). The metallic silver powder has a particle size of 2.0 to 15 μm.
m, a spherical silver powder having an average particle size of 7 μm, and a particle size of 2.0 to 1
100 parts by weight of silver powder mixed with flaky silver powder having an average particle diameter of 7 μm and having a weight ratio of 5 μm (approximately 2 in aspect ratio) and spherical silver powder: flake silver powder = a: b. Silver powder is added to the resin mixture, and the mixture is stirred and mixed for 3 minutes by the stirring defoaming machine. The obtained paste is uniformly ground by a three-roll mill to obtain a conductive paste.

Similarly, a conventional resole resin (resin B)
, A conventional conductive paste was prepared by the same composition and kneading procedure.

As the ammonia resole resin, three kinds having an average molecular weight of 5,000, 15,000 and 100,000, and a mixing ratio of silver powder (spherical silver powder: flake silver powder)
With respect to the above, a: b was selected from three types of 2: 8, 4: 6, and 6: 4, and a total of nine types of conductive pastes were prepared. In addition, three types of conventional resol-based resins (resin B) having an average molecular weight of 5,000, 15,000, and 100,000,
With respect to the mixing ratio of the silver powder (spherical silver powder: flake silver powder), a: b was selected from three types of 2: 8, 4: 6, and 6: 4 to prepare a total of nine types of conductive pastes.

Using these conductive pastes, the pattern shown in FIG. 2 was printed by screen printing, and cured by heat to form a circuit pattern. In a circuit pattern having a line & space of 50 μm & 50 μm, drawing property,
In addition, the volume resistivity of the obtained circuit was evaluated. If there is bleeding during printing and the line width is uneven, or if the printing is blurred and the circuit thickness is not uniform, the volume specific resistivity cannot be properly evaluated. Alternatively, it was shown as "blurred" in the evaluation results. Table 1 shows a total of 9 samples using an ammonia resole resin.
Table 2 shows the evaluation results of the nine types of conductive pastes using the conventional resol-based resin (resin B).

[0049]

[Table 1]

[0050]

[Table 2]

The line & space shown in Table 1 is 50 μm.
& 50 μm circuit pattern, molecular weight 1500
In the case of three kinds of conductive pastes using an ammonia resol-based resin of 0, no bleeding or blurring occurs and the volume resistivity is 5 irrespective of the mixing ratio of the silver powder (spherical silver powder: flake silver powder). It is less than × 10 ⁻⁵ Ω · cm, and extremely good circuit printing is possible.

The three conductive pastes shown in Table 2 using a conventional resole resin (resin B) having a molecular weight of 15,000 may differ depending on the mixing ratio of the silver powder (spherical silver powder: flake silver powder). A good circuit is formed. However, comparing the results shown in Table 1 and Table 2, it is clear that the conductive paste of the present invention using the ammonia resole-based resin has both drawability and volume resistivity,
It is judged to be significantly superior to the conductive paste using the conventional resol-based resin (resin B). In a fine circuit having a line & space of 50 μm & 50 μm, bleeding and blurring are slightly generated. The degree of the bleeding and the haze is the same as that of the conventional resol-based resin (resin B). It was much lighter than the conductive paste.

(Exemplary Drawing of Fine Circuit Pattern) When this fine pattern was drawn, there was no bleeding or haze, and the lower limit at which circuit printing could be formed with good reproducibility was repeatedly examined. Using three kinds of conductive pastes using an ammonia resole resin having a molecular weight of 15000 and three kinds of conductive pastes using a conventional resole resin (resin B) having a molecular weight of 15,000, a line & line as shown in FIG. The lower limit for forming a space pattern with high reproducibility without blurring or blurring was re-evaluated. Table 3 shows the lower limit of the line & space pattern that can be formed with high reproducibility as a result of the evaluation.
Also in this comparison, the conductive paste using the ammonia resole resin is the same as the conventional resole resin (resin B).
It is determined that the patterning characteristics of a fine pattern are superior to those of a conductive paste using the same.

[0054]

[Table 3]

In addition to the evaluation of the drawing characteristics of the fine pattern, the degree of leveling during thermosetting was also evaluated. At this time, since the addition amount of the plasticizer has an effect on the drawing characteristics and the leveling at the time of thermosetting, the composition of the composition in which only the addition amount of the plasticizer: KR-213 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) is changed. The same evaluation was performed for the conductive paste. Table 4 shows that the lines and spaces are 50 μm and 50 μm.
In the formation of fine circuit of m, the difference between maximum and minimum of circuit thickness, peekto botto is used as an index of leveling during thermosetting.
The result of measuring m is shown. As shown in Table 4, the molecular weight was 15
Of the conductive pastes using 2,000 ammonia resole-based resins, those containing no plasticizer (0 parts by weight) have insufficient leveling during thermosetting, resulting in extremely slight fading. On the other hand, when the plasticizer was added to 15 parts by weight, excessive softening occurred at the time of thermosetting, and apparently,
Some of the bleeding occurred, though slightly. It is understood that the difference in the permeability of the paste due to the gauze at the time of screen printing can be smoothed by leveling at the time of thermosetting by adding an appropriate amount of a plasticizer. If the amount of the plasticizer is too large, the fluidity of the conductive paste itself is increased, so that even if there is no bleeding at the time of printing, the softening in the leveling at the time of thermosetting excessively proceeds, and as a result, it is confirmed that bleeding may occur. Was.

[0056]

[Table 4]

[0057]

By using the conductive paste for drawing a circuit of the present invention, it is possible to draw a delicate circuit pattern having a minimum line width of less than 50 μm by screen printing using a thermosetting paste at a low temperature. In particular, even for a thin line having a minimum line width of less than 50 μm, the volume resistivity is as follows:
Even in a thermosetting paste at a low temperature, a value comparable to that obtained by a conventional sintered conductive paste can be obtained. This advantage can be suitably used for forming a circuit used for face-down mounting such as a liquid crystal driver IC on a glass substrate, which requires a high circuit resistance, and can increase the production efficiency. In addition, in the circuit printing method of the present invention, since ink coating is not performed, even when performing repetitive printing, pattern spreading and bleeding can be significantly reduced, and a delicate circuit pattern having a minimum line width of less than 50 μm can be formed. Printing can be performed with good reproducibility.

[Brief description of the drawings]

FIG. 1 shows an arrangement of a scraper and a squeegee used in a conventional screen printing method for performing ink coating (upper figure) and an arrangement of a double squeegee used in a circuit printing method of the present invention (lower figure). FIG.

FIG. 2 shows that the line and space used for evaluation of the drawing property are 50
It is a figure which shows fine circuit patterns, such as μm & 50 μm.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 1/00 H01B 1/00 J H05K 3/12 610 H05K 3/12 610B (72) Inventor Daisuke Ito Ibaraki 5-9-3 Tokodai, Tsukuba-shi, Pref. Harima Chemicals, Inc. Tsukuba Research Laboratory F-term (reference) 4J038 DA041 HA066 JC32 KA06 KA18 KA20 MA14 MA15 NA20 PB09 5E343 AA26 BB25 BB72 BB76 BB77 DD03 FF04 FF13 GG08 5G301 DA03 DA42 DD01

Claims (7)

[Claims] 1. The conductive metal powder, comprising: a spherical silver powder having a diameter of 1/2 or less of a minimum line width to be drawn; and a flake silver powder having a maximum length of 1/2 or less of the minimum line width to be drawn. , A low-temperature curable resin, an ammonia resole resin, a high molecular weight resin having a molecular weight of 10,000 or more, and a solvent, which is an inert solvent for the ammonia resole resin. High-boiling point organic solvent having a boiling point of 150 ° C. or more under pressure, an alkoxy group-containing modified silicone oligomer-based plasticizer soluble in the solvent as a plasticizer, and, if necessary, an anti-settling agent (thixo agent). 4 to 17 parts by weight of the low-temperature curable resin, 2 to 10 parts by weight of the plasticizer, and a total of 1 part of the metallic silver powder, the low-temperature curable resin, and the plasticizer, based on 100 parts by weight of the metallic silver powder A conductive paste for drawing a circuit, wherein the solvent is mixed at a ratio of 10 to 40 parts by weight with respect to 00 parts by weight. 2. The metal silver powder, wherein the weight ratio of the spherical silver powder and the flake silver powder is spherical silver powder: flake silver powder = 1: 9 to
2. The conductive paste for circuit drawing according to claim 1, wherein the conductive paste is mixed in a range of 8: 2. 3. The method according to claim 1, wherein the ammonia resole resin is represented by the following general formula (I): (In the formula, n is an integer of about 80 or more, A is oxygen (—O—) or amine (—NH—) arbitrarily arranged, and at least 1 or more is selected from amine (—NH—). The conductive paste for circuit drawing according to claim 1 or 2, wherein the resin is a high molecular weight resin having a molecular weight of 10,000 or more. 4. The alkoxy group-containing modified silicone oligomer-based plasticizer is represented by the following general formula (II): (Wherein, p and q are integers of 0 or more, and are not both 0), wherein the alkoxy group-containing modified silicone oligomer is represented by the formula: The conductive paste for circuit drawing according to the above. 5. The conductive paste has a viscosity of 30 to 1
The conductive paste for circuit drawing according to any one of claims 1 to 4, wherein the conductive paste is adjusted to a range of 20 Pa · s. 6. The method according to claim 1, further comprising, if necessary, adding a coupling agent in a weight ratio of 1 to 10% with respect to the low-temperature curing resin. Conductive paste for circuit drawing. 7. A method of printing a circuit on a substrate using a masked screen having a mask opening of a circuit pattern to be drawn and printed and having a screen grid size equal to or smaller than a minimum line width to be drawn. The conductive paste for circuit drawing according to any one of claims 1 to 6, wherein a step of ink coating the conductive paste on the screen in advance is not provided. Instead, two squeegees forming a set are provided. A circuit printing method, wherein a circuit pattern is printed by contacting at least a screen portion provided with the mask opening and a printing surface of the substrate with a screen by sliding the squeegee.