JPH11111051A - Conductive paste for printing and printed circuit board using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a conductive circuit having an excellent print characteristic and excellent electric conductivity by including a thermosetting resin to generate reduction gas at hardening sliver powder having specific tap density and the average particle size and a solvent at a specific rate. SOLUTION: A phenol resin or a melamine resin to generate formaldehyde to prevent oxidation of silver powder at heating/hardening, is desirably used as a thermosetting resin of a binder. Since tap density of the sliver powder included by 600 to 1000 pts.wt. to 100 pts.wt. of the thermosetting resin is not less than 3.0 g/cm<3> and the average particle size is 3 to 15 μm, increase in contact resistance between silver particles is prevented, and volume specific resistance is improved. When the silver powder having the averave particle size of 0.1 to 3 μm is mixed at a prescribed rate, filling density increases. When a conductive circuit is printed in a pattern on an insulating substrate by conductive paste constituted by adding 100 to 500 pts.wt. of a solvent, a pinhole is eliminated, and an excellent line characteristic can also be provided.

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 printing and a printed circuit board using the same.

[0002]

2. Description of the Related Art Printed circuit boards are used in various electronic devices such as word processors, personal computers, copying machines, and facsimile machines. In general, for the production of these printed boards, a manufacturing method is adopted in which a resist is pattern-printed on a copper foil adhered to the board and a conductive circuit (circuit pattern) is formed by etching. The printed circuit board manufactured by such a manufacturing method has a volume resistivity of copper itself of 1.72 ×.
It has very good conductivity close to 10 ⁻⁶ Ω · cm.

However, the above-mentioned manufacturing method requires a step of removing most of the area other than the circuit pattern by etching, which raises the problem of increased material cost and environmental pollution due to copper waste liquid. Therefore, a new method of manufacturing a printed circuit board that patterns only a predetermined portion is desired. Japanese Patent No. 2,616,526 discloses a print in which a paste is prepared by dispersing copper powder in a phenol resin and a polyimide resin, and the paste is printed on a substrate by a printing method, and then heated and cured to form a conductive circuit. A method for manufacturing a substrate is disclosed.

[0004] In the manufacturing method disclosed in the above publication, unlike the conventional manufacturing method, there is no need to worry about waste liquid contamination due to the etching process, and only a required amount of copper powder is required. Is planned.

[0005]

However, a printed circuit board made of the above-mentioned conductive paste cannot provide a conductive material having a volume resistivity of 10 ⁻⁵ Ω · cm or less, and has not yet been put to practical use. It is. The following can be considered as the reason. Generally, a phenol resin, a polyimide resin, an epoxy resin, a polyester resin, or the like having good adhesiveness and solvent resistance are frequently used as the resin. However, the conductive paste obtained by mixing the copper powder with these resins is oxidized on the surface of the copper powder during heating and curing to form copper oxide having a high insulating property, so that the conductivity is reduced.

In particular, when the above-mentioned paste is produced, if the thickness of the conductive circuit is large, the inside is not oxidized and thus has relatively good conductivity, but if the thickness is small, the conductivity rapidly decreases. A problem occurs, and a printed circuit board having a constant volume resistivity cannot be manufactured. Further, the conductivity of the printed circuit board is not only determined by the volume resistivity of the metal material itself used, but also largely depends on the contact resistance between the metal powders in the conductive circuit. For example, even if the resin is filled with metal particles at a high density, if the contact resistance between the metal powders is large, the conductivity of the entire printed circuit board becomes low.

On the other hand, in order to manufacture a printed board from the conductive paste, as described above, usually, a step of pattern-printing the conductive paste on the insulating substrate using a printing method such as screen printing or intaglio offset printing. Is adopted. Therefore, it is necessary that the conductive paste used in the above process has excellent printing characteristics such as no generation of pinholes during printing and good line linearity.

Accordingly, an object of the present invention is to provide a conductive paste for printing which solves the above-mentioned problems and has excellent printing characteristics and can form a conductive circuit having good conductivity. It is. Another object of the present invention is to provide a printed circuit board on which a conductive circuit is formed using the conductive paste.

[0009]

In order to solve the above-mentioned problems, a conductive paste for printing according to the present invention comprises 100 parts by weight of a thermosetting resin which generates a reducing gas upon curing, and a tap density of 3 parts. and a .0g / cm ³ or more and an average particle size is characterized in that containing the silver powder 600-1000 parts by weight of 3 to 15 [mu] m, and a solvent 100 to 500 parts by weight.

That is, according to the present invention, the oxidation resistance is good.
Using silver powder and reducing gas as binder
By using a thermosetting resin that generates heat,
Oxidation of silver powder is prevented during curing, and the body of silver itself
Product specific resistance (1.62 × 10 ^-6Ω ・ cm)
can do. As the reducing gas, at the time of curing
Use thermosetting resin that generates formaldehyde
Is preferred.

As the thermosetting resin, it is preferable to use a phenol resin or a melamine resin. In addition, in the present invention, the use of silver powder having a tap density of 3.0 g / cm ³ or more and an average particle diameter of 3 to 15 μm prevents an increase in contact resistance between the silver powders. It has good volume resistivity.

Particularly, as the silver powder, a silver powder (A) having an average particle diameter of 3 to 15 μm and a silver powder (A) having an average particle diameter of 0.1 to 15 μm are used.
A: B = 100: 1 by weight ratio with 3 μm silver powder (B)
By using a silver powder mixed in a ratio of １００100: 50, the packing density of the silver powder is increased, and a better volume resistivity is obtained. Further, in the present invention, 600 to 1000 parts by weight of the silver powder and 100 to 500 parts by weight of the solvent are added to 100 parts by weight of the thermosetting resin, so that the conductive property is obtained by using a printing method such as concave plate offset printing. When printing a conductive circuit on an insulating substrate using the paste, it is possible to print a pattern having no pinholes and excellent line linearity.

Therefore, by printing a circuit pattern on an insulating substrate using the conductive paste of the present invention and then heating and curing the printed circuit board, the printed circuit board on which the conductive circuit is formed has a good printed shape and a good volume resistivity. Have.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. The conductive paste is obtained by blending a specific thermosetting resin, silver powder, and a solvent in predetermined amounts, and kneading and dispersing the mixture using a three-roll or the like. In order to improve the dispersibility of the silver powder, it may be sufficiently mixed in advance with a planetary mixer or the like before kneading with three rolls.

As the specific thermosetting resin, a resin that generates a reducing gas (ammonia, hydrogen halide, formaldehyde, etc.) upon thermosetting, preferably a thermosetting resin that generates formaldehyde, is used. preferable. Examples of the thermosetting resin that generates formaldehyde include a phenol resin (especially a resole type phenol resin having many methylol groups) and an amino resin (especially melamine resin).

As the melamine resin, for example, part or all of the amino group is a group: —N (CH ₂ OH) CH ₂ O
As shown by R (wherein, R represents an alkyl group such as a methyl group or a butyl group), a melamine resin that is methylolated is exemplified. More specifically, examples of the resol-type phenol resin include Regeitop PL2211 and PL4348 of Gunei Chemical Industry Co., Ltd.
Examples of the melamine resin include Cymel 370, a Mitsui Cyanamid Co., Ltd.

In the present invention, the average particle diameter is 3 to 15 μm.
m, preferably 4 to 8 μm, and a silver powder having a tap density of 3.0 g / cm ³ or more, preferably 4.0 g / cm ³ or more. Tap density is 3.0g /
When the particle size is smaller than cm ³ , the space between the silver powders becomes large, so that the contact points between the silver powders become small and the contact resistance becomes large.

The tap density in the present invention refers to the weight per volume after a certain amount of silver powder is put into a certain container while vibrating vertically. As this value is larger, the packing density is higher and the contact point between the silver powders is larger, so that good conductivity can be obtained. However, in the present invention, the silver powder having a tap density of 6.0 g / cm ³ or less is used. It is appropriate to use

When the average particle diameter of the silver powder is smaller than 3 μm, the silver powder is difficult to be uniformly dispersed, and the contact resistance increases. Conversely, if the average particle diameter of the silver powder is larger than 15 μm, the contact points between the silver powders become too small, and the contact resistance increases. Moreover, the average particle diameter of the silver powder is 15 μm.
If it is larger than m, clogging tends to occur in the mesh portion of the screen during screen printing.

The silver powder used in the present invention may have any shape such as a sphere or a scale, but it is necessary to increase the contact surface between the powders (reduce the contact resistance). In consideration of the above, it is preferable to use scaly ones rather than spherical ones. More specifically, examples of the silver powder include the following silver powders. Product name of Fukuda Metal Foil & Powder Co., Ltd. "Silcoat AgCA" (flaky, average particle size:
6.0 μm, tap density: 3.3 g / cm ³ ) “Silcoat AgCD” (scale, average particle size:
7.0 μm, tap density: 3.5 g / cm ³ ) “Silcoat AgCL” (flaky, average particle size:
8.0 μm, tap density: 3.7 g / cm ³ ) Trade name of Mitsui Mining & Smelting Co., Ltd. “3200HD” (spherical, average particle size: 4.2 μm,
Tap density: 4.4 g / cm ³ ) The amount of the silver powder used is 600 to 1000 parts by weight, preferably 650 to 90 parts by weight, per 100 parts by weight of the thermosetting resin.
0 parts by weight.

If the amount of the silver powder is less than 600 parts by weight, the volume resistivity of the circuit pattern portion on the printed circuit board becomes large due to insufficient contact points between the silver powders. On the other hand, if the addition amount of the silver powder is more than 1000 parts by weight,
Since the amount of the thermosetting resin used is too small relative to the total amount of the paste, the force for bonding the silver powders becomes small, and the volume resistivity of the circuit pattern portion on the printed circuit board increases.

This means that, for example, when a tester electrode is inserted into a silver powder in a fixed container and a voltage is applied, no current flows at all. However, a pressure is applied to the silver powder pressed into the silver powder to apply a voltage. And the fact that current flows. That is, the thermosetting resin has an effect of bonding silver powders at the time of curing.However, when the amount of the thermosetting resin used is small, the bonding between the silver powders is weakened, and the pressure is not applied. This is because it becomes closer to silver powder.

If the amount of the silver powder is more than 1000 parts by weight, the strength of the circuit pattern on the printed circuit board may be insufficient. Further, in the present invention, the silver powder (A) having an average particle diameter of 3 to 15 μm so as to satisfy the tap density, the average particle diameter, and the amount of the silver powder described above.
And silver powder (B) having an average particle diameter of 0.1 to 3 μm in a weight ratio of A: B = 100: 1 to 100: 50. The silver powder thus obtained has a higher packing density of the silver powder,
The conductivity of the circuit pattern portion on the printed board is improved.

The solvent to be used is appropriately selected depending on the printing method used for the conductive paste. For example, when the conductive paste is used for screen printing or concave plate offset printing, the boiling point is 150 ° C. or more. Those are preferred. If the boiling point of the solvent used does not satisfy the above range, the solvent may be easily dried during printing, and pinholes may be generated.

Specifically, alcohols such as hexanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, stearyl alcohol, seryl alcohol, cyclohexanol; ethylene glycol monobutyl ether (butyl cellosolve) And alkyl ethers such as ethylene glycol monophenyl ether, diethylene glycol, diethylene glycol monobutyl ether (butyl carbitol), cellosolve acetate, butyl cellosolve acetate, carbitol acetate, and butyl carbitol acetate. It is appropriately selected.

When a higher alcohol is used as a solvent, the drying and fluidity of the ink may be inferior. Therefore, butyl carbitol, butyl cellosolve, ethyl carbitol, butyl cellosolve acetate, which have better drying properties than these, are used. And butyl carbitol acetate may be used in combination. The amount of the solvent used is determined by the viscosity of the obtained paste, and is usually 100 to 500 parts by weight, preferably 100 to 500 parts by weight, based on 100 parts by weight of the thermosetting resin in consideration of the amount of the silver powder to be added. 300
It may be by weight.

When the amount of the solvent is less than the above range, even if the addition amount of the silver powder is a minimum of 600 parts by weight,
The viscosity becomes 1000P or more, and pinholes are frequently generated when printing on an insulating substrate. On the other hand, when the amount exceeds the above range, even if the amount of the silver powder used is 1000 parts by weight, the viscosity becomes 10 P or less, and the paste repels on the insulating substrate, so that a good printed shape cannot be achieved. .

The viscosity of the conductive paste of the present invention varies depending on the printing method used. For example, when the conductive paste is used in an intaglio offset printing method, the viscosity is usually 1000 to 10P, preferably 500 to 100P. When the viscosity is lower than the above range, the printed shape is deteriorated. on the other hand,
When the viscosity is higher than the above range, pinholes occur frequently.

Next, the printed circuit board of the present invention will be described. The printed circuit board is formed by a conventionally known printing method.
After printing the conductive paste on the insulating substrate, heating and
It is manufactured by forming a conductive circuit by curing.
Examples of the printing method include a conventionally known printing method such as a screen printing method, a waterless offset printing method, and an intaglio offset printing method. In particular, it is preferable to use an intaglio offset printing method.

That is, in the intaglio offset printing method,
Excellent in line linearity and uniformity of the thickness of the conductive circuit, etc.The thickness required for the conductive circuit can be adjusted by adjusting the depth of the intaglio recess according to the thickness of the conductive circuit pattern. Can be formed by one printing. The depth of the recess is adjusted depending on the desired thickness of the conductive circuit, but is usually 3 to 25 μm, and preferably 5 to 15 μm.

Examples of the insulating substrate include soft glass such as soda lime glass, hard glass such as ena glass, telex, and pyrex, as well as polycarbonate (PC) and polyether sulfone (PE).
S), a resin plate of polyarylate, polyimide or the like, a fiber reinforced resin plate of a glass fiber reinforced epoxy resin, a glass fiber reinforced phenol resin or the like can be used.

The printed circuit board of the present invention is usually prepared by printing a pattern of the above-mentioned conductive paste on an insulating substrate, and then forming the printed pattern.
２５０250 ° C. for 10 to 90 minutes, preferably 150 to 25
By heating and curing at 0 ° C. for 15 to 60 minutes, a conductive circuit having a thickness of 5 to 20 μm, preferably 10 to 20 μm is formed and manufactured. If the temperature at the time of curing is less than 150 ° C., it is difficult to cure, and if the temperature at the time of curing exceeds 250 ° C., the resin used tends to deteriorate.

[0033]

The present invention will be described below with reference to examples and comparative examples. Example 1 (Preparation of Printed Circuit Board) 100 parts by weight of resole type phenol resin “REGITOP PL4348” (described above), 800 parts by weight of silver powder “AgCL” (described above), and a solvent (n-butyl carbitol acetate, (Boiling point: 246.8 ° C) 20
0 parts by weight were blended, kneaded and dispersed by three rolls to prepare a paste.

The paste prepared above was overprinted on soda lime glass with a line width of 100 μm by intaglio offset printing while adjusting the thickness, and then heated at 250 ° C. for 20 minutes using a hot plate to be cured. A printed circuit board having a conductive circuit having a thickness of 40 μm later was manufactured. Examples 2 to 5 Two kinds of silver powder “AgCL” (supra) and “3010” (manufactured by Mitsui Mining & Smelting Co., Ltd., spherical shape, tap density: 1.1 g / cm ³ , average particle diameter: 0,1) shown in Table 1. A printed board was produced in the same manner as in Example 1, except that a silver powder mixed with 11 μm) and a solvent were used. The average particle diameter and tap density of the silver powder shown in Table 1 are values of the silver powder after mixing. Examples 6 to 10 Printed circuit boards were produced in the same manner as in Example 1 except that the silver powder and the solvent shown in Table 1 below were used. Example 11 A printed circuit board was produced in the same manner as in Example 1 except that the melamine resin “Cymel 370” (described above) was used instead of the resol-type phenol resin. Comparative Example 1 In the same manner as in Example 1, except that a polyester resin (a product obtained by adding a methylated melamine as a curing agent to a polycondensate of trimellitic acid and neopentyl glycol) instead of the resole type phenol resin was used. A printed circuit board was manufactured. Comparative Examples 2 to 6 A printed circuit board was produced in the same manner as in Example 1 except that the silver powder and the solvent shown in Table 2 below were used. Comparative Example 7 Two types of silver powder “AgCL” shown in Table 2 below (supra)
A printed circuit board was prepared in the same manner as in Example 1 except that a silver powder and a solvent mixed with “3010” (described above) and a solvent were used. The average particle diameter and tap density of the silver powder shown in Table 2 are values of the silver powder after mixing.

[0035]

[Table 1]

[0036]

[Table 2]

(Measurement of Volume Specific Resistance) With respect to the printed circuit boards prepared in the above Examples and Comparative Examples, the resistance was measured by a digital multimeter, and the volume specific resistance was calculated from the line width, the film thickness and the measured distance. (Evaluation of print shape and appearance) Also, the shape and appearance of the printed circuit pattern were
Observation was made visually or by a stereoscopic microscope, and the evaluation was made according to the following criteria.

(Line linearity) (Presence / absence of pinhole) ○ ・ ・ ・ Good line linearity ○ ・ ・ ・ No pinhole △ ・ ・ ・ Somewhat poor line linearity △ ・ ・ ・ Some pinhole ×× ・ ・ ・Inferior in line linearity ×: Very many pinholes The above results are shown in Table 3.

[0039]

[Table 3]

As is clear from Table 3, when the pastes of the examples were used, no pinholes were observed at the time of printing, and pattern printing having good line linearity was possible. In addition, any of the printed circuit boards manufactured using the pastes of the above embodiments has a volume resistivity of 10 ⁻⁵ Ω.
cm or less, and it was found to have very good conductivity.

On the other hand, when the conductive paste of the comparative example is used, there is a problem that the printed shape is damaged at the time of printing or the volume resistivity is large, so that a printed circuit board having both of them is required. Could not

[0042]

According to the present invention, when the conductive paste of the present invention is used,
When printing a conductive circuit by a printing method such as offset printing, there is no occurrence of pinholes, and it is possible to print a pattern having good line linearity, and it is possible to produce a printed circuit board having good conductivity. This has the effect.

Claims (5)

[Claims] 1. A thermosetting resin which generates a reducing gas during curing, 100 parts by weight, a silver powder having a tap density of not less than 3.0 g / cm ³ and an average particle diameter of 3 to 15 μm. A conductive paste for printing containing 1000 parts by weight and 100 to 500 parts by weight of a solvent. 2. The silver powder has an average particle diameter of 3 to 15 μm.
Of silver powder (A) and silver powder (B) having an average particle size of 0.1 to 3 μm in a weight ratio of A: B = 100: 1 to 10
The conductive paste for printing according to claim 1, which is produced by mixing at a ratio of 0:50. 3. The conductive paste for printing according to claim 1, wherein said reducing gas is formaldehyde. 4. The conductive paste for printing according to claim 1, wherein said thermosetting resin is a phenol resin or a melamine resin. 5. A printed circuit board, wherein a circuit pattern is printed on an insulating substrate using the conductive paste according to claim 1, and then heated and cured to form a conductive circuit.