JPH10190177A - Printed circuit board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the conductivity of via holes in printed circuit boards formed of conductive paste. SOLUTION: A printed circuit board has circuits formed by printing and curing thermosetting conductive paste containing conductive powder and thermosetting resin as major constituents. When the paste is cured by heating, pressure is applied, so that the volume fraction of the conductive powder in the cured material is increased and thus the conductivity of the cured material can be significantly improved. Via holes can be easily formed by employing a conductive paste with the volume fraction of conductive powder of 65% or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a printed circuit board using a conductive paste and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a technique for forming a circuit using a thermosetting conductive paste and manufacturing a printed circuit board has been well known. In particular, the conductive powder is Ag _X Cu _(1-X)
(Where 0.01 ≦ X ≦ 0.4, where X represents the atomic ratio), and when a powder having a portion where the Ag concentration on the powder surface is higher than the average Ag concentration is used, the conductivity and the ion It is known that a circuit having excellent migration properties can be obtained.

[0003]

However, the circuit formed by using the conductive paste has several tenths of conductivity compared to a circuit formed by patterning a copper foil by etching or the like. There is a problem that it is not suitable for use in a power supply line through which a large amount of current flows. When conducting via holes with a conductive paste, it is advantageous to completely fill the via holes in terms of conductivity. However, pastes using conventionally known conductive powders have high viscosity and poor fluidity. Because of its sufficient size, it was difficult to fill without introducing air bubbles.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, by applying pressure during curing of the conductive paste, the ratio of metal powder in the cured film is increased, and the conductivity is greatly increased. The inventors have found that they have improved, and have reached the present invention.
Further, the present inventors have found that by using a conductive powder having a specific shape, the viscosity of the conductive paste can be remarkably reduced, and it has become possible to fill a via hole.

That is, the gist of the present invention is to provide a printed circuit board including a circuit formed by printing and curing a conductive paste containing conductive powder and a thermosetting resin as main components. A printed circuit board characterized in that the volume fraction of the conductive powder in the conductive paste is 65% or more, and the method for producing the conductive powder comprises a conductive powder and a thermosetting resin as main components. In a method for manufacturing a printed circuit board including a circuit formed by printing and curing a conductive paste on a substrate, by applying heat and pressure in a curing step of the conductive paste, the conductivity in the cured conductive paste is increased. A method for manufacturing a printed circuit board, characterized in that the volume fraction of powder is 65% or more.

In addition, a conductive paste containing spherical conductive powder and thermosetting resin as main components, having a viscosity of 50 poise to 2000 poise and a solvent content of 0.5% or less is filled in a via hole. A printed circuit board filled and cured, wherein the volume fraction of the conductive powder in the cured conductive paste is 65% or more.

[0007] The via hole referred to in the present invention includes a through hole for establishing conduction between both surfaces of the substrate, or an inner via hole having one closed. For example, as a through hole, a copper-clad laminate or an insulating resin such as epoxy, a substrate drilled with a drill or laser, or after forming a circuit pattern on the substrate, after laminating or applying the insulating resin,
There is a substrate or the like perforated by photolithography or laser. The inner wall of the through hole is plated with a conductor such as copper,
Or it may be coated. The portion formed by the paste may be only the circuit portion, only the via hole portion, or a substrate on which the circuit and the via hole coexist.
(See FIGS. 1 and 2) Examples of commonly used base materials include rigid base materials such as a paper base-phenol substrate, a glass base-epoxy substrate, a composite substrate made of an inorganic powder and a polymer compound, and a metal core substrate. Examples include a substrate, a PET film, an aramid film, and a polyimide film. A circuit using a conductive paste can be formed on the base material. In addition, a circuit using a conductive paste can be formed on a base material obtained by patterning a copper foil by a known method such as an etching method or a plating method using a copper-clad laminate substrate using the above base material. As a method of patterning a copper foil, for example, in an etching method, a dry film resist for etching is laminated on the copper foil, ultraviolet light is exposed on the dry film through a negative mask film, and the uncured portion is removed by development to remove the resist. Get the pattern. Furthermore, by removing the exposed copper foil using a spray-type etching device, and finally stripping the cured resist with a predetermined stripper,
Obtain a circuit layer of copper foil. The substrate may be a single-sided substrate, a double-sided substrate, or a multilayer substrate. The insulating substrate on which the circuit layer is formed may have any surface as long as it is insulative, and is not particularly limited as long as it can be printed, whether the surface is flat or curved. The uniform metal layer forming the circuit is not limited as long as it is a metal having better conductivity than the conductive paste, and copper, silver, gold, nickel, iron, aluminum, a solder alloy or the like can be used. Further, a different kind of metal may be laminated on a predetermined metal layer by plating or the like.

[0008] The conductive paste used in the present invention is not particularly limited as long as it can form a pattern by screen printing or the like and can form a conductive resin layer having conductivity after curing. Can be used.
For example, examples of the conductive powder include carbon powder, nickel powder, silver powder, copper powder, silver-plated copper powder, and silver-copper alloy powder.
Particularly, copper or a metal powder containing a large amount of copper is preferable because it has high conductivity and good ion migration resistance. In particular, the following silver-copper alloy powders are more preferable because of their high oxidation resistance and good ion migration.

The average composition of the silver-copper alloy powder used in the present invention is represented by Ag _X Cu _1-X (where 0.01 ≦ X ≦ 0.4, where X represents an atomic ratio). If it is less than 0.01, sufficient oxidation resistance cannot be obtained, and if it exceeds 0.4, the ion migration resistance is insufficient. Further 0.01
A copper alloy produced by an inert gas atomization method in the range of ≦ X ≦ 0.4, wherein the silver concentration on the powder surface is higher than the average silver concentration. The silver concentration at and near the surface of the powder can be determined by XPS (X-ray photoelectron spectroscopy). The average silver concentration can be measured by dissolving the sample in concentrated nitric acid and using ICP (high frequency inductively coupled plasma emission spectrometer). Although the copper alloy powder of the present invention has a high silver concentration on the surface of the powder, the silver concentration on the surface of the powder is 1.4 or more of the average silver concentration in order to more suitably exhibit properties such as oxidation resistance. It is preferred that

[0010] The resin composition of the conductive paste used in the present invention is not particularly limited as long as conductivity can be obtained. Generally, various molecular weight resole type phenolic resin, novolak type phenolic resin, bisphenol type epoxy resin, novolak type epoxy resin,
And a liquid epoxy compound having various glycidyl groups,
For example, hydrogenated bisphenol A diglycidyl ether,
Neopentyl glycol diglycidyl ether, N, N
Examples include a combination of diglycidyl toluidine and various epoxy curing agents. In particular, resol type phenol resins are preferable because of their excellent conductivity. Examples of other resins include acrylic resins, polyester resins, polyurethane resins, polyamide resins, polyimide resins, polyether resins, and bismaleimide-triazine resins. A diluting solvent may be used to adjust the viscosity as needed.

When the conductive paste is filled in a via hole, the amount of the solvent is 0.5% by weight or less and 5% by weight.
0 poise or more and 2000 poise or less is preferable, and 5 poise is more preferable.
It is preferably from 0 poise to 800 poise. This viscosity was measured with an E-type rotational viscometer at 25 ° C. and 10 rpm. If it is less than 50 poise, it flows out of the via hole, and if it exceeds 2000 poise, the fluidity is small and it is difficult to fill the via hole.

In the present invention, the most practical and easy method for forming a circuit of the conductive paste is a screen printing method.
There is no particular limitation as long as a predetermined pattern is formed, such as a method using a dispenser. As a method of filling the via holes, there are a screen printing method and a method of imprinting. As the screen printing method used in the present invention, a known method can be used. Generally, a printing mask is laminated on a substrate, and a wiring circuit is formed on the substrate using a screen printer. The printing mask to be used is not particularly limited.
Typical are stainless steel, silk,
Examples include a general screen plate obtained by applying an emulsion to a screen mesh made of a material such as polyester to form an image, and a metal mask plate formed by etching a stainless steel plate.

After printing the conductive paste, the paste is dried and pre-cured by heating at a predetermined temperature to remove volatile components in the paste and to suppress flow during pressurization. Examples of the heating furnace include a batch-type oven and a continuous-type conveyor furnace. The pressure hardening device used in the present invention is not particularly limited as long as it can heat the substrate surface while applying a predetermined pressure. For example, a heating press, particularly a vacuum heating press, is preferable. Other examples include calender rolls that can be heated. The higher the pressure at the time of pressurization, the higher the volume ratio of the metal powder in the cured film and the higher the conductivity. The pressure can be selected so as to obtain a desired volume fraction and conductivity. At the time of pressurizing, it is preferable to pressurize a film having releasability such as a Teflon film on the substrate surface.

The preferred range of the heating temperature is 130 ° C. or higher and 2
20 ° C. or less. If the temperature is lower than 130 ° C., the curing is not sufficient. If the temperature exceeds 220 ° C., the conductivity is deteriorated due to decomposition of the resin and oxidation of the conductive powder. A preferred range of the pressurizing pressure is 5 kg / cm ² or more and 250 kg / cm ² or less. If it is less than 5 kg / cm ² , sufficient conductivity will not be exhibited, and if it exceeds 250 kg / cm ² , cracks and the like will occur, which is not preferable.

The time is determined by the temperature and pressure, but is preferably 5 minutes or more. The conductivity tends to improve as the volume fraction of the conductive powder in the cured film increases. In particular, if it exceeds 65%, the effect of improving the conductivity starts to increase, which is preferable.
The above is a further advantage because a great effect is recognized. On the other hand, depending on the resin system, the adhesive strength may decrease, so it is necessary to select an optimal region.

As a method of calculating the volume fraction of the conductive powder in the cured film, for example, the cross section of the cured film is imaged with an SEM photograph or the like, and the calculation is performed from the ratio of the sectional area of the cured film to the conductive powder. it can. After the circuit board shown in the present invention is formed, an overcoat layer may be formed on the surface circuit layer by using an insulating resin as necessary. As a method of forming the overcoat layer, a method of printing an ink made of an insulating resin in a predetermined pattern by a three-dimensional printing method and curing the ink is used. For example, a commercially available thermosetting solder resist ink or ultraviolet curing solder resist ink can be used. In addition, various thermosetting resin compositions, such as epoxy resin and phenolic resin, and various photocurable resins such as epoxy resin methacrylic acid-modified resin and the like and a combination of a corresponding curing agent, as required, And an inorganic filler or a diluting solvent.

After printing the insulating ink, the ink is cured in a batch-type or conveyor-type heating furnace in the case of a thermosetting type, and in a variety of general batch-type or conveyor-type ultraviolet exposure machines in the case of an ultraviolet-curing type. To cure. It is preferable that the thickness of the insulating layer is close to the thickness of the circuit layer, and even if one layer is effective, two or more layers may be stacked as necessary.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to examples and comparative examples. The conductive paste made of the copper alloy powder used here was prepared by the following method. (1) Copper alloy powder Copper alloy powder was obtained by the following method. Copper powder (purity 99.9%)
837 g and 63 g of silver powder (purity 99.9%) were mixed, put into a graphite crucible (with a boron nitride nozzle), melted by high frequency induction heating in an argon atmosphere, and heated to 1600 ° C. This melt was ejected from the nozzle under argon atmospheric pressure for 30 seconds. At the same time, 4.2 NTPm3 of argon gas in a cylinder (cylinder pressure 150 atm) was jetted from the surrounding nozzles over the melt. Observation of the obtained powder with a scanning electron microscope revealed that the powder was spherical (having an average particle size of 1).
9.6 μm). The silver concentration on the surface of this powder was determined by XPS
As a result of analysis by using, Ag / (Ag + Cu) (atomic ratio) was 0.147. The particles were dissolved in concentrated nitric acid and the average silver concentration was measured by ICP.
(Ag + Cu) (atomic ratio) X was 0.042. Therefore, the silver concentration on the powder surface was 3.5 times the average silver concentration. A part of the powder having a diameter of 10 μm or less in the obtained copper alloy powder was classified and used as a paste. (2) Preparation of conductive paste 1 100 parts by weight of the above-mentioned copper alloy powder, 14 parts by weight of resole type phenol resin and 10 parts by weight of butyl carbitol were added and kneaded with a three-roll mill for 30 minutes to form conductive paste 1. I got (3) Preparation of conductive paste 2 100 parts by weight of the above conductive alloy powder and 10 parts by weight of propylene glycol diglycidyl ether were added and kneaded with a three-roll mill for 30 minutes to obtain conductive paste 2. The viscosity was 500 poise. (E-type viscometer, 25 ° C, 1
(4 rpm) (4) Preparation of conductive paste 3 A conductive paste 3 was obtained in the same manner as (3) except that electrolytic copper powder (average diameter 5 μm, non-spherical shape) was used. Similarly, the viscosity was 3000 poise.

[0019]

EXAMPLE 1 A copper foil of a copper-clad laminated substrate was pattern-etched, and 1 cm × 1 cm so that a distance between electrodes was 5 cm.
2 square electrodes were formed. A 0.3 mm × 6 cm conductive paste 1 is overlapped with a part of the surface of the electrode portion.
The pattern was printed. After drying and pre-curing at 120 ° C for 20 minutes in a hot air oven, a Teflon film is layered on top,
The composition was cured at 170 ° C. for 20 minutes while pressing with a hot press.
The pressure on the substrate surface was adjusted to 10 kg / cm ² . Using this evaluation substrate, the volume resistivity of the line formed of the conductive paste was determined from the resistance value between the electrodes.
It was 0 ^-5 Ω · cm. From the SEM photograph of the cross section of the cured film, the volume fraction of the metal powder was determined from the ratio of the cross-sectional area of the metal powder to the cross section of the cured film, and the result was 75%.

[0020]

Example 2 The same procedure as in Example 1 was carried out except that the pressure was 40 kg / cm ² . Volume resistivity is 8 ×
It was 10 ⁻⁶ Ω · cm, and the volume fraction was 87%.

[0021]

Comparative Example 1 In the same manner as in Example 1, the copper foil of the copper-clad laminated substrate was subjected to pattern etching to form two square electrodes of 1 cm × 1 cm so that the distance between the electrodes was 5 cm. A conductive paste pattern of 0.3 mm × 6 cm was printed so as to cover the surface of the electrode portion. 2 in a hot blast stove at 120 ° C
After pre-drying for 0 minutes, it was cured at 170 ° C. for 20 minutes. Using this evaluation board, the volume resistivity of the line formed of the conductive paste was determined from the resistance between the electrodes,
It was 6 × 10 ⁻⁵ Ω · cm. The volume fraction of the metal powder was determined from the ratio of the cross-sectional area of the metal powder to the cross-section of the cured film from the SEM photograph of the cross-section of the cured film, and the result was 59%.

[0022]

Example 3 A through hole (via hole) having a diameter of 0.4 mm was made by drilling a glass epoxy base material having a thickness of 0.4 mm.
The conductive paste 2 was imprinted with a squeegee and heated and pressed in the same manner as in Example 1. Temperature is 170 ° C,
The pressure was 30 kg / cm ² and the time was 1 hour. When the resistance value at both ends was measured and converted into volume resistivity, 4 ×
It was 10 ⁻⁵ Ω · cm. The volume fraction of the metal powder determined from the SEM photograph of the cross section of the cured film was 70%.

[0023]

Comparative Example 2 The same procedure as in Example 3 was carried out except that the pressure was 1 kg / cm ² . Volume resistivity is 8 × 10 ^-4 Ω
Cm, and the volume fraction of the metal powder was 55%.

[0024]

Comparative Example 3 Example 3 was repeated except that the conductive paste 3 was used.
Was performed in the same manner as described above. The paste was not completely filled in the through holes. Also, the through hole was broken.

[0025]

According to the present invention, a thermosetting conductive paste having a circuit-pattern printed thereon is heat-cured while being pressurized, so that the resulting cured paste film has a higher metal powder volume fraction than in the past and has a higher conductivity. The performance is greatly improved. In addition, by using a specific conductive paste, it is possible to easily fill the via hole.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a via hole in a printed circuit board according to the present invention.

FIG. 2 is a diagram showing an example of a via hole in the printed circuit board of the present invention.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 circuit 3 insulating resin 4 via hole

Claims (5)

[Claims] 1. A printed circuit board including a circuit formed by printing and curing a conductive paste containing a conductive powder and a thermosetting resin as main components, the conductive powder in the cured conductive paste. Wherein the volume fraction of the printed circuit board is 65% or more. 2. The conductive powder is Ag _X Cu _(1-X) (where 0.01 ≦ X ≦ 0.4, and X represents an atomic ratio).
The printed circuit board according to claim 1, wherein the printed circuit board has a portion where the Ag concentration on the powder surface is higher than the average Ag concentration. 3. A method for manufacturing a printed circuit board including a circuit formed by printing and curing a conductive paste containing a conductive powder and a thermosetting resin as main components on a substrate, wherein the conductive paste is cured. A method for manufacturing a printed circuit board, wherein heating and pressurizing are performed in a process so that a volume fraction of conductive powder in a hardened conductive paste is 65% or more. 4. The conductive powder is Ag _X Cu _(1-X) (where 0.01 ≦ X ≦ 0.4, and X represents an atomic ratio).
4. The method for manufacturing a printed circuit board according to claim 3, wherein the powder surface has a portion where the Ag concentration is higher than the average Ag concentration. 5. A conductive paste containing a spherical conductive powder and a thermosetting resin as main components, having a viscosity of 50 poise to 2000 poise and a solvent content of 0.5% or less is filled in a via hole. 3. The printed circuit board according to claim 1, wherein the printed circuit board is filled and cured.