JP2006028213A - Functional electroconductive coating, electronic circuit using the same and its formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-temperature-curing electroconductive coating which shows high adhesion to a resin substrate or copper foil, shows good electroconductivity and is solderable, and to provide an inexpensive, environmentally friendly functional electroconductive coating which enables simplification of a circuit manufacturing step and does not produce any waste liquid by etching, an electronic circuit using the same and its formation method. <P>SOLUTION: The functional electroconductive coating contains a metal powder, a binder, an unsaturated fatty acid and an organic solvent, wherein the metal powder is an Ag-coated Ni powder and an Ag powder, wherein the Ag content in the Ag-coated Ni powder is 5-20 wt.%. The compounding ratio of the Ag-coated Ni powder and the Ag powder is preferably (100-50):(0-50) by weight. The binder contains a thermosetting resin, the unsaturated fatty acid is oleic acid, and the organic solvent is butyl carbitol. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a functional conductive paint having electrical conductivity that can be soldered, an electronic circuit using the same, and a method of forming the same.

  Conventionally, conductive paint containing metal powder in the resin is used in various fields such as bonding of electronic components and wiring, jumper wires using printed wiring boards, and terminal lead wires for printed resistors, etc. Currently being actively researched. Among them, as a resin binder type low-temperature curing conductive paint, a resin powder containing metal powder such as silver, copper, or nickel is used as a printed wiring or a conductive adhesive for an electronic circuit.

  However, these conductive paints contain about 20% resin by weight, so the volume ratio is overwhelmingly high, and any of the commercially available conductive paints cannot be soldered. there were. Moreover, although the electrically conductive paint which can be soldered as disclosed in Patent Documents 1 and 2 has been proposed, it does not have sufficient performance.

On the other hand, since most recent electronic circuit elements and ICs have been surface-mounted, a copper foil printed board that can be soldered is generally used for joining the circuit board and the electronic elements or ICs.
Japanese Patent Laid-Open No. 7-14429 JP 2002-212492 A

  However, a copper foil printed circuit board that requires an etching process or the like has a complicated manufacturing process, which has been a cause of increased costs for electronic devices. That is, the current copper foil etching process requires a process of (resist coating → photosensitive process → etching process → resist film peeling process → waste liquid process), and has a large number of manufacturing processes. In addition, the waste liquid generated by the etching process requires a processing cost and generates an environmental load.

  The present invention has been made in view of the above prior art, and provides a low-temperature curable conductive paint that has high adhesion to a resin substrate and copper foil, good conductivity, and can be soldered. Another object of the present invention is to provide a functional conductive paint that simplifies the circuit manufacturing process, eliminates waste liquid due to etching, is inexpensive and has a low environmental load, an electronic circuit using the same, and a method for manufacturing the same.

  As a result of earnest research to solve the above problems, the present inventors have mixed Ag powder Ni powder alone as metal powder, or mixed metal powder, binder, and organic solvent to produce a conductive paint, or A conductive paint mixed with a paint as a mixture of Ag-coated Ni powder and Ag powder and baked and cured at a low temperature of about 150 to 170 ° C. exhibits excellent conductivity and good solder wettability. The present inventors have found that the bondability is excellent and have completed the present invention.

  That is, the present invention is a functional conductive paint that contains a metal powder, a resin binder, and an unsaturated fatty acid in an organic solvent and can be soldered. The metal powder is an Ag-coated Ni powder and an Ag powder, and a mixing ratio of the Ag-coated Ni powder and the Ag powder is Ag-coated Ni powder = 100 to 50: Ag powder = 0 to 50 in weight ratio. Moreover, Ag content of the said Ag coat Ni powder is 5 to 20 weight%. The functional conductive paint according to claim 2 or 3.

  The unsaturated conductive fatty acid is oleic acid, and the organic solvent is butyl carbitol. Furthermore, the binder contains a thermosetting resin. This thermosetting resin is a polyfunctional epoxy resin and / or a phenol resin.

  The present invention is also an electronic circuit obtained by applying or printing a functional conductive paint containing a metal powder, a binder, an unsaturated fatty acid and an organic solvent in a desired pattern on an insulating substrate and baking.

  Furthermore, the present invention applies a functional conductive paint containing a metal powder, a binder, an unsaturated fatty acid and an organic solvent and capable of soldering to a desired pattern on an insulating substrate and firing at a temperature of 150 to 200 ° C. This is a method of forming an electronic circuit.

  According to the present invention, in electronic circuit manufacturing including printed wiring using an insulating substrate such as a resin substrate, electronic bonding such as chip components and circuit components can be soldered to printed wiring. Can be manufactured.

  Furthermore, in the present invention, an electronic circuit can be manufactured stably and simply with printed wiring at a low temperature of 200 ° C. or less, preferably about 150 to 170 ° C., and the manufacturing process can be greatly simplified. it can. Therefore, compared with the case where a circuit is formed by simply etching a copper foil on a conventional resin substrate, the cost and yield can be significantly improved by simply replacing the functional conductive paint of the present invention. It greatly contributes to the field.

  In addition, since a thin natural oxide film is formed on the surface of the metal powder in the paint by moisture or oxygen in the air, stable electrical conduction may not be obtained. Since the paint also removes the oxide film from the unsaturated fatty acid, an electronic circuit having a very small resistance value can be formed.

  Hereinafter, the functional conductive paint of the present invention, an electronic circuit using the same, and a method for forming the same will be described. First, examples of the metal powder used in the functional conductive paint include Ag-coated Ni powder, Cu powder, Ag powder, Ni powder, and Al powder. Among these, from the viewpoint of solderability, Ag-coated Ni powder or a mixed powder of Ag-coated Ni powder and Ag powder is preferable.

  The Ag-coated Ni powder is obtained by coating Ag on the surface of a substantially spherical Ni powder by plating. Ag is a ratio of 5 to 20 wt.%, For example, about 15 wt.%, And the coating amount can be appropriately set. The particle diameter of the Ag-coated Ni powder is, for example, a powder having an average particle diameter of about 7 μm. Further, the Ag powder is irregular particles, but when the particle size is 10 μm or less, the solderability is lowered, so that the average particle size is preferably 10 μm or more.

  Further, the content of the metal powder is preferably 70 to 99 wt.%, More preferably 70 to 95 wt.%, In the entire functional conductive paint.

  Examples of the thermosetting resin contained in the binder used in the functional conductive paint include an epoxy resin, a melamine resin, a phenol resin, a polyimide resin, and a polycarbonate resin. Of these, polyfunctional epoxy resins and phenol resins are preferred from the viewpoint of coating film properties. Further, the content of the thermosetting resin is preferably 1 to 30 wt.%, More preferably 5 to 15 wt.%, In the entire coating material.

  Curing agents such as dicyandiamide and aliphatic polyamine are added to the binder. Of these, dicyandiamide is preferred. Further, the content of the curing agent is preferably 1 to 30 wt.%, More preferably 4 to 20 wt.% In the entire coating material.

  Further, a curing accelerator such as 3- (3,4-dichlorophenyl) -1,1-dimethylurea and tertiary amine is added to the binder, and among these, 3- (3,4-dichlorophenyl) -1 , 1-dimethylurea is preferred. Further, the content of the curing accelerator is preferably 1 to 10 wt.%, More preferably 1 to 7.0 wt.% In the entire coating material.

  The organic solvent used in the functional conductive paint of the present invention is not particularly limited as long as the thermosetting resin is uniformly dispersed in the paint, and examples thereof include butyl carbitol, methyl carbitol, and Solvesso 150. An organic solvent may be added to adjust the viscosity so that screen printing can be performed (about 200 to 500 poise). Of these organic solvents, butyl carbitol is preferable, and the content thereof is preferably 0.1 to 20 wt.%, More preferably 0.5 to 15 wt.% In the entire functional conductive paint.

  Furthermore, unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid may be dissolved in the functional conductive paint for the purpose of preventing oxidation of the metal powder surface and promoting the destruction of the resulting oxide film. Of these unsaturated fatty acids, oleic acid is preferable, and the content thereof is preferably 0.1 to 5.0 wt.%, More preferably 0.5 to 3.0 wt. .

  Next, an example of the manufacturing method of the printed wiring board using the functional conductive paint of this invention is shown. First, the functional conductive paint having the above composition is mixed by using a revolving mixer such as a hybrid mixer until the blended materials are uniformly dispersed, and then printed by screen printing or the like, spraying, brush coating, etc. A desired shape is formed by various coating methods. And after drying at the temperature of 30-80 degreeC, the circuit pattern and electrode pattern of an electronic circuit are formed by baking at the temperature of 200 degrees C or less, Preferably it is the temperature of 150-170 degreeC for 5 to 30 minutes. Can do.

  Thereby, the printed wiring electrode provided with high electroconductivity and favorable solderability can be formed in the electronic circuit pattern by a conductive paint.

  Since the functional conductive paint of the present invention is excellent in solder adhesion with a printed wiring, a circuit for a surface mount electronic component can be easily manufactured on an insulating substrate by printing the conductive paint. In addition, because it contains unsaturated fatty acids, oxidation of the metal powder surface is prevented, conductivity and solder adhesion are not impaired, surface oxidation is prevented even after the formation of printed wiring, etc., and the function deteriorates over time Does not occur.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not restrict | limited to a following example. First, FIG. 1 shows a test print pattern. This pattern is a zigzag pattern for screen printing, and the line width is 2 mm. Further, the volume resistivity ρ is obtained from the following equation.
ρ = (Rx / 184) × d (Ω · cm)
Where Rx: resistance value between both ends of the zigzag pattern (Ω), d: film thickness of the sample pattern (cm)

In Example 1, a conductive paint having the following composition was prepared and tested.
Ag coated Ni powder (Ag coating amount 15 wt%) 93 parts by weight Oleic acid 1 part by weight Polyfunctional epoxy resin 6 parts by weight Butyl carbitol 3 parts by weight mixed with a hybrid mixer, glass epoxy with zigzag pattern shown in FIG. Screen printing was performed on the resin substrate, and the conductive path was formed by baking at 170 ° C. for 30 minutes.
The volume resistivity of this product was 3.2 × 10 ⁻⁴ Ω · cm.
Moreover, when this thing and copper lead wires were adhere | attached with lead-free solder and the peeling test was done, solder peeling strength was 0.28 kgf / mm < ² > and shear strength was 0.60 kgf / mm < ² >.

In Example 2, a conductive paint having the following composition was prepared and tested.
Ag coated Ni powder (Ag coating amount 15 wt%) 91 parts by weight Oleic acid 1 part by weight Phenolic resin 8 parts by weight Butyl carbitol 4 parts by weight mixed with a hybrid mixer, glass epoxy resin substrate with zigzag pattern shown in FIG. Screen-printed on top and fired at 170 ° C. for 30 minutes to form a conductive path.
The volume resistivity of this product was 2.5 × 10 ⁻⁴ Ω · cm.
Moreover, when this thing and copper lead wires were adhere | attached with the lead-free solder | pewter and the peeling test was done, solder peeling strength was 1.17Kgf / mm < ² > and shear strength was 2.17Kgf / mm < ² >.

In Example 3, a conductive paint having the following composition was prepared and tested.
Ag powder 93 parts by weight Oleic acid 1 part by weight Polyfunctional epoxy resin 6 parts by weight Butyl carbitol 1 part by weight was mixed with a hybrid mixer and screen printed on a glass epoxy resin substrate in a zigzag pattern shown in FIG. A conductive path was formed by baking at 30 ° C. for 30 minutes.
The volume resistivity of this product was 3.9 × 10 ⁻⁴ Ω · cm.
Moreover, although this thing and the copper lead wire were adhere | attached with the lead free solder, it was not able to adhere | attach.

In Example 4, a conductive paint having the following composition was prepared and tested.
Ag powder 91 parts by weight Oleic acid 1 part by weight Phenolic resin 8 parts by weight Butyl carbitol 2 parts by weight mixed with a hybrid mixer was screen printed on a glass epoxy resin substrate in a zigzag pattern shown in FIG. A conductive path was formed by baking for 30 minutes.
The volume resistivity of this product was 6.5 × 10 ⁻⁵ Ω · cm.
Moreover, although this thing and the copper lead wire were adhere | attached with the lead-free solder, there exists a tendency for solder to repel with progress of soldering time, and preparation of the sample which can be used for a peeling strength test and a shear strength test was not able to be performed. Therefore, together with Example 3, it was found that soldering was not possible when the metal powder was only Ag powder.

In Example 5, a conductive paint having the following composition was prepared and tested.
Ag-coated Ni powder (Ag coat amount 15 wt%) 46.5 parts by weight Ag powder 46.5 parts by weight Oleic acid 1 part by weight Polyfunctional epoxy resin 6 parts by weight Butyl carbitol 3 parts by weight Screen printing was performed on a glass epoxy resin substrate with a zigzag pattern shown in FIG. 1 and baked at 170 ° C. for 30 minutes to form a conductive path.
The volume resistivity of this product was 3.0 × 10 ⁻⁴ Ω · cm.
Moreover, when this thing and the copper lead wire were solder-bonded with lead-free solder and a peel test was performed, the solder peel strength was 0.49 Kgf / mm ² and the shear strength was 0.75 Kgf / mm ² . Therefore, it was found that soldering is possible even when an Ag-coated Ni powder and an Ag powder are used as the metal powder.

In Example 6, a conductive paint having the following composition was prepared and tested.
Ag coated Ni powder (Ag coating amount 15 wt%) 45.5 parts by weight Ag powder 45.5 parts by weight Oleic acid 1 part by weight Phenolic resin 8 parts by weight Butyl carbitol 4 parts by weight were mixed with a hybrid mixer as shown in FIG. A screen was printed on the glass epoxy resin substrate with the zigzag pattern shown in FIG.
The volume resistivity of this product was 2.0 × 10 ⁻⁴ Ω · cm.
Moreover, when this thing and the copper lead wire were solder-bonded with lead-free solder and a peel test was conducted, the solder peel strength was 0.91 kgf / mm ² and the shear strength was 2.05 kgf / mm ² . Therefore, it was found that soldering was possible even when using Ag-coated Ni powder and Ag powder as the metal powder, as in the above example.

In Example 7, a conductive paint having the following composition was prepared and tested.
Ni powder 93 parts by weight Oleic acid 1 part by weight Polyfunctional epoxy resin 6 parts by weight Butyl carbitol 3 parts by weight mixed with a hybrid mixer was screen printed on a glass epoxy resin substrate in a zigzag pattern shown in FIG. A conductive path was formed by baking at 30 ° C. for 30 minutes. The volume resistivity of this product was 1.1 × 10 ⁻³ Ω · cm.
Moreover, although this thing and the copper lead wire were adhere | attached with the lead free solder, it was not able to adhere | attach. Therefore, it was found that soldering was not possible when the metal powder was Ni powder alone.

In Example 8, a conductive paint having the following composition was prepared and tested.
Ag coated Ni powder (Ag coating amount 5 wt%) 93 parts by weight Oleic acid 1 part by weight Polyfunctional epoxy resin 6 parts by weight Butyl carbitol 3 parts by weight mixed with a hybrid mixer, glass epoxy with zigzag pattern shown in FIG. Screen printing was performed on the resin substrate, and the conductive path was formed by baking at 170 ° C. for 30 minutes.
The volume resistivity of this product was 3.4 × 10 ⁻⁴ Ω · cm.
Moreover, when this thing and copper lead wires were solder-bonded with lead-free solder and a peel test was performed, the solder peel strength was 0.16 Kgf / mm ² and the shear strength was 0.44 Kgf / mm ² . Therefore, it was found that the Ag content when Ag coated Ni powder is used as the metal powder can be soldered even at 5 wt%.

In Example 9, a conductive paint having the following composition was prepared and tested.
Ag coated Ni powder (Ag coating amount 20 wt%) 93 parts by weight Oleic acid 1 part by weight Polyfunctional epoxy resin 6 parts by weight Butyl carbitol 3 parts by weight mixed with a hybrid mixer in a zigzag pattern shown in FIG. Screen printing was performed on the resin substrate, and the conductive path was formed by baking at 170 ° C. for 30 minutes.
The volume resistivity of this product was 3.1 × 10 ⁻⁴ Ω · cm.
When this product and a copper lead wire were soldered with lead-free solder and a peel test was performed, the solder peel strength was 0.19 Kgf / mm ² and the shear strength was 0.48 Kgf / mm ² . Therefore, by comparing with Example 8, it was found that the solderability was not significantly different even if the Ag content when using the Ag-coated Ni powder was increased.

  The functional conductive paint of the present invention can be used for the connection part of electronic components that involve the manufacture of electronic circuits, the formation of electronic circuits, and other soldering.

It is a top view which shows the printing pattern of the Example which tested the functional conductive coating material of this invention.

Claims (10)

  A functional conductive paint containing a metal powder, a resin binder, and an unsaturated fatty acid in an organic solvent.   The functional conductive paint according to claim 1, wherein the metal powder is an Ag-coated Ni powder and an Ag powder.   3. The functional conductive paint according to claim 2, wherein a mixing ratio of the Ag-coated Ni powder and the Ag powder is Ag-coated Ni powder = 100-50: Ag powder = 0-50 in a weight ratio.   The functional conductive paint according to claim 2 or 3, wherein the Ag content of the Ag-coated Ni powder is 5 to 20% by weight.   The functional conductive paint according to claim 1, wherein the unsaturated fatty acid is oleic acid.   The functional conductive paint according to claim 1, wherein the organic solvent is butyl carbitol.   The functional conductive paint according to claim 1, wherein the resin binder contains a thermosetting resin.   The functional conductive paint according to claim 7, wherein the thermosetting resin is a polyfunctional epoxy resin and / or a phenol resin.   An electronic circuit in which a circuit pattern made of a functional conductive paint containing a metal powder, a resin binder, and an unsaturated fatty acid is formed on an insulating substrate. A method for forming an electronic circuit, in which a functional paint containing a metal powder, a resin binder, and an unsaturated fatty acid in an organic solvent is applied or printed in a desired pattern on an insulating substrate and baked at a temperature of 150 to 200 ° C.

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