JPH08311304A - Copper-based electroconductive composition - Google Patents

Abstract

PURPOSE: To obtain a copper-based electroconductive composition exhibiting excellent solderability as well as high electroconductivity at high temperature and/or over a long period in the solder mounting procedure and having high bonding strength. CONSTITUTION: This copper-based electroconductive composition contains metallic powder and a binder as main components. In the above composition, 100 pts.wt. of silver-clad copper-nickel powder is used as the metallic powder and 6-18 pts.wt. of a resol phenolic resin containing dimethyl ether bond is used as the binder. The content of nickel in the copper-nickel alloy to be clad with silver is 2.5-15wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer-type copper conductive composition used for electronic circuits and the like, and particularly to a resol-type phenol which uses silver-coated copper-nickel powder as a metal powder and satisfies specific conditions as a binder. The present invention relates to a copper conductive composition that simultaneously imparts high conductivity and good solderability in a wide range by using a resin.

[0002]

2. Description of the Related Art Generally, a polymer-type copper conductive composition used for electronic circuits or the like is required to have good solderability in order to facilitate soldering of lead wires and the like. In these conventional copper conductive compositions, it is indispensable to add an antioxidant of metal powder (copper) and a soldering accelerator, and although the solderability is good, it does not have sufficient conductivity. It was a difficult thing to do. Therefore, in order to solve the above-mentioned problems of the conventional copper conductive composition, the present applicants have previously used silver-coated copper as a metal powder and a specific binder as a binder, which is disclosed in Japanese Patent Laid-Open No.
The invention described in Japanese Patent No. 77547 was proposed, and a copper conductive composition which does not require addition of an antioxidant and a soldering accelerator and has good solderability was proposed. The invention described in this publication is composed of a silver-coated copper powder and a resol-type phenolic resin, and since a small amount of silver is coated on the surface of spherical or granular copper powder, oxidation does not occur even when highly filled in the cured film. To be prevented. Further, since the dimethyl ether bond is contained in an amount of 5% or more, the solubility with respect to the rosin flux is improved, and the soldering becomes good.

[0003]

However, the copper conductive composition as described in the above publication has a soldering property at a soldering temperature of 230 ° C., a dipping time of up to 5 seconds and a relatively short dipping time. Although good, there was a problem that solderability deteriorated when the temperature became higher, the immersion time became longer, or both of these conditions overlap.

The present invention solves the above-mentioned conventional problems,
An object of the present invention is to provide a copper conductive composition which is excellent in solderability even when the temperature is high, the dipping time is long, or both conditions are overlapped, and which can take a wide temperature range during solder mounting.

[0005]

The copper conductive composition of the present invention solves the conventional problems by using a silver-coated copper-nickel alloy instead of the silver-coated copper powder in the invention described in the above publication. It is a thing. Here, the silver-coated copper-nickel alloy in the present invention has a nickel content of 2.5 to 1
It shall be 5% by weight. Also silver coated copper-nickel alloy powder 1
The binder is 6 to 18 parts by weight with respect to 00 parts by weight. The binder may be the same as the invention described in the above publication.

[0006]

[Operation] Since silver-coated copper-nickel alloy powder is used as the metal powder in the present invention, it has the following effects. That is, with the conventional silver-coated copper powder, the solder temperature is 23
When heat is applied at 0 ° C. or higher for 5 seconds or longer, the silver-coated copper powder has weak adhesion to the binder and the powder falls off. FIG. 2 shows the state. From Fig. 2, the solder bath temperature is 2
It can be seen that when the temperature exceeds 30 ° C., the solder coverage decreases when the immersion time is 10 seconds and 20 seconds. On the other hand, in the present invention, the silver-coated copper-nickel alloy powder is used, and as shown in FIG. 1, the solder coverage does not decrease even when the solder bath temperature is 260 ° C. and the immersion is performed for a long time of 10 seconds or more. I understand. This is because the copper-nickel alloy powder used in the present invention has a strong adhesive force between the nickel portion and the binder and is unlikely to fall off. Here, the relationship between the nickel content in the silver-coated copper-nickel alloy powder and the solder coverage is shown in FIG. As can be seen from FIG. 3, if the nickel content in the silver-nickel alloy is not more than 2.5%, it has the same fallout prevention effect as the simple silver-coated copper powder, and conversely if the nickel content exceeds 15%. Although it has a fall-off prevention effect, it deteriorates solderability and conductivity. When the nickel content is in the range of 2.5 to 15%, the conductivity is less deteriorated, the powder is prevented from falling off, and a large amount of silver-coated copper is present, so that the solderability is secured.

In the present invention, a resol type phenol resin having a dimethylene ether bond is used as the binder. The details may be the same as those in the invention described in the above publication. That is, the binder is a resol-type phenol resin obtained by the addition condensation reaction of phenols and formaldehyde, and has a dimethylene ether bond (-CH ₂ -O-CH _2- ) in its skeletal structure, Bonding Dimethyl ether bond in formaldehyde 5
% Or more, the charged molar ratio of formaldehyde and phenols (formaldehyde / phenol) is in the range of 1.0 to 3.0, and in the area ratio of the pattern by the GPC method, the polystyrene equivalent molecular weight A
It is assumed that the components are 20 to 60%, the B component is 40 to 70%, and the C component is 0 to 30%.

Specific examples of the phenols used as the raw material of the resol type phenol resin used in the present invention include:
Examples thereof include phenol, cresol, xylenol, ethylphenol, trimethylphenol, propylphenol, butylphenol, octylphenol, dihydroxybenzene, naphthols and bisphenols. These phenols can be used alone or as a mixture.

For those having a dimethylene ether bond in the resin skeleton structure, the following structures as formaldehyde bound to phenols (hereinafter, bound formaldehyde), methylol (-CH ₂ OH), methylene ((-CH ₂ -),
Dimethylene ether _{(-CH 2 -O-CH 2 -} ), alkyl ether
When (-CH ₂ -OR), hemiacetal (-(CH ₂ O) nH) and the like are set to 100, the content of dimethylene ether bond is 5% or more. When the dimethylene ether bond is contained at 5% or more, the solubility in the rosin-based flux is improved, the solderability is improved, and the flexibility and adhesion are also improved.
On the other hand, when the dimethylene ether bond is less than 5%, the solubility with respect to the rosin-based flux becomes poor, and the solderability, flexibility, and adhesion are poor. Further, even if the content of the dimethylene ether bond is too large, it is necessary to be concerned that a curing failure may occur due to a decrease in the amount of functional groups involved in crosslinking during curing. Therefore, the more preferable content of the dimethylene ether bond is 15 to 45%.

Regarding the molar ratio of formaldehyde and phenols charged (formaldehyde / phenols),
When the charged molar ratio exceeds 3.0, strength reduction and curing failure occur due to lower molecular weight, and when it falls below 1.0, the crosslink density decreases and the content of dimethylene ether bonds decreases. A more preferable molar ratio is 1.0 to 2.5 for a resin having a dimethylene ether bond.

Further, regarding the molecular weight of the resol type phenolic resin, when it is classified into A component, B component and C component in the GPC pattern, the content of dimethylene ether bond increases in the A component having a low molecular weight. Therefore, if the component A in the resin is 20% or more, the contents of dimethylene ether bond and alkyl ether bond increase, and the solderability becomes good. On the contrary, the medium molecular weight B component and the high molecular weight C component have a small content of dimethylene ether bond, and when the content of the B component in the resin exceeds 70%, or the content of the C component exceeds 30%. And the solderability is poor. However, the molecular weight affects not only the solderability but also the conductivity, adhesion, etc. of the conductive paste, and it is necessary to study the molecular weight distribution taking these factors into consideration. That is, if the content of A component having a low molecular weight in the resin exceeds 60%, strength deterioration, poor curing, poor adhesion, etc. occur, so that the B component of medium molecular weight, and further the C component of high molecular weight, Inclusion is desirable. Therefore, the molecular weight distributions in which solderability, conductivity, adhesion and the like are totally excellent are 20 to 60% for the A component, 40 to 70% for the B component, and 0 to 30% for the C component.

Here, the molecular weight of the resol type phenolic resin in the present invention means that the standard polystyrene is used for GPC.
It is the value obtained by the method. The GPC chromatograph is measured, for example, by connecting one Tosoh column G300Hxl and two Tosoh columns G2000Hxl in series to a Tosoh Corp. HLC-8020 chromatograph, and using 0.8 ml of tetrahydrofuran as a carrier solvent. Flowing at a flow rate of / min. In the chromatograph, a differential refractometer was used as a detector. And the molecular weight is standard polystyrene manufactured by Tosoh Corporation.
(Weight average molecular weight 7.91 × 10 ⁵ , 3.54 × 10 ⁵ , 9.89 × 10 ⁴ , 4.
30 x 10 ⁴ , 1.01 x 10 ⁴ , 6.4 x 10 ³ , 2.8 x 10 ³ , 9.5 x 10 ² ,
A calibration curve was prepared by a cubic regression method using 5.3 × 10 ² (9 points in total) and a styrene monomer, and the molecular weight was determined from the calibration curve.

The binder may be a single kind or a blend of two or more kinds. In particular, in the latter case, even if it does not satisfy the requirements of the present invention by itself, as long as it satisfies the requirements as a blend, this case is included in the scope of the present invention. These binders are added in an amount of 6 to 18 parts by weight with respect to 100 parts by weight of the silver-coated copper-nickel alloy powder. When the amount of the binder is less than 6 parts by weight, the conductivity, the strength of the cured film and the adhesion to the substrate are reduced. On the other hand, when the amount of the binder is more than 18 parts by weight, the solderability and the conductivity are poor.

In the present invention, the silver-coated copper-nickel alloy powder and the binder are the main components, but it is a matter of course that the present invention may further contain a dispersant and a solvent. It goes without saying that a foaming agent, a leveling agent, a thixotropic agent, etc. may be added as appropriate.

An organic titanate compound can be preferably used as the dispersant in the present invention. This is an organic compound in which a hydrophilic group and a lipophilic group are bonded to the central element titanium, and is called a titanate coupling agent, and is classified into the following four types by different hydrophilic groups. That is, a monoalkoxy type (one having an isopropoxy group), a chelate type (one having a residue of oxyacetic acid), a chelate type (one having a residue of ethylene glycol), and a coordinate type (tetraalkyl titanate to phosphorous acid) To which an ester is added), the most effective of which is the monoalkoxy type. This organic titanate compound is coordinated or adsorbed on the surface of the silver-coated copper-nickel alloy powder to improve the dispersibility in the binder during kneading. In particular, when the copper-nickel alloy powder filling rate is high as in the present invention, the above improvement becomes remarkable. In order to obtain a cured film with good solderability, it is needless to say that a large number of silver-coated copper-nickel alloy powders are present on the surface of the cured film, but further, they may be evenly distributed. Equally important. Therefore, if a cured film is formed using a paste having improved dispersibility during kneading by blending an organic titanate compound, good solderability can be obtained. These dispersants are 100 parts by weight of silver-coated copper-nickel alloy powder,
Add in an amount of 0.05 to 1 part by weight. If the amount of the dispersant is less than 0.05 part by weight, the conductivity and the solderability will be poor, and if it exceeds 1 part by weight, the adhesion to the substrate will be reduced.

Solvents include polyhydric alcohols such as butyl cellosolve, dibutyl cellosolve, methyl carbitol, ethyl carbitol, butyl carbitol, dibutyl carbitol, butyl cellosolve acetate, methyl carbitol acetate, ethyl carbitol acetate, butyl carbitol acetate. Derivatives are preferable, and trimethylhexanol may be used. Such a polyhydric alcohol derivative is a good solvent for the resol-type phenol resin, suppresses volatilization of the solvent at the time of printing, and has little residual in the film at the time of curing. These solvents are silver coated copper
2 to 15 parts by weight is added to 100 parts by weight of nickel alloy powder. If the amount of the solvent is less than 2 parts by weight, blurring occurs during screen printing, and if it exceeds 15 parts by weight, blurring occurs, and the conductivity and solderability are poor.

The composition prepared as described above is applied by screen printing or dipping in a conventional manner,
It is put into practical use by being heat-cured.

Examples will be shown below.

Example: 100 parts by weight of granular copper-nickel alloy powder (average particle size: 8 μm) coated with 2 wt% of silver, 10 parts by weight of a resol type phenol resin (manufactured by Gunei Chemical Co., Ltd.), an organic titanate compound (Preact TTS (manufactured by Ajinomoto Co.) )) 0.05 parts by weight and 3 parts by weight of the solvent (methyl carbitol) was added to 3 parts.
The composition of Examples 1 to 3 of the present invention and Comparative Examples 1 to 4 was prepared by kneading with the present roll mill, and these were printed on a paper phenol substrate (1.6 mm thickness) with a 200 mesh Tetron screen, and then air oven was used. It was cured by heating at 160 ° C. for 30 minutes. These were tested for solder wettability, specific resistance, adhesion strength and printability, and the results are also shown in Table 1.

Each test method is shown below. (1) Solder wettability Use a print pattern of 2 mm x 2 mm. Flux # 366
Apply (multi-core) and 150 on the hot plate.
After preheating at ℃ for 20 seconds, soak in eutectic solder bath at 230 ℃ for 3 seconds. The solder wettability on the raised pattern is determined as follows. ◯: Solder coating area 100% △: Solder coating area 80 to 99% ×: Solder coating area 79% or less (2) Use a printed pattern with a specific resistance of 1 mm × 200 mm. The electric resistance R (Ω) and the average film thickness t (μm) at both ends are measured, and the specific resistance ρ (Ω · cm) is calculated by using the following formula. (3) Use a printed pattern with an adhesion strength of 2 mm × 2 mm. Using the sample obtained in the solder wettability test as it is, a 0.8 mmφ tin-plated annealed copper wire is erected at the center of a 2 mm square, and soldered with a thread solder and a soldering iron. Next, a 90 degree pull test is performed with a tensile tester to measure the load F (kg) at break. The adhesion strength T (kg / mm ² ) is calculated using the following formula. T = F / 4

[0020]

[Table 1]

From the results shown in Table 1, the copper conductive composition according to the present invention has good solderability and good adhesion, whereas the comparative examples have poor solderability and almost no solder. Therefore, the adhesion test could not be performed.

[0022]

As described above, according to the present invention, the solder has high conductivity and high solderability at a high temperature during solder mounting for a long time or under any condition, and has a large adhesion strength. A copper conductive composition having is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a solder bath temperature and a solder coverage of silver-coated copper-nickel alloy powder in a copper conductive composition according to the present invention.

FIG. 2 is a relationship diagram between a solder bath temperature and a solder coverage of silver-coated copper powder in a copper conductive composition according to a conventional example.

FIG. 3 is a relationship diagram between a solder bath temperature of silver-coated copper-nickel alloy powder and a solder coverage rate.

Claims (2)

[Claims] 1. A copper conductive composition containing metal powder and a binder as main components, wherein 100 parts by weight of silver-coated copper-nickel powder is used as the metal powder, and 6 to 18 parts by weight of a resol-type phenol resin having a dimethyl ether bond is used as the binder. A copper conductive composition, characterized in that it contains a part. 2. The copper conductive composition according to claim 1, wherein the nickel content in the silver-coated copper-nickel alloy is 2.5 to 15% by weight.