JPH06336563A - Conductive coating material - Google Patents

Abstract

PURPOSE:To obtain a conductive coating material which is used for through-hole continuity and is superior to a silver-based conductive coating material in migration resistance and contains neither additive nor a large amount of copper ions unlike a copper-based conductive coating material. CONSTITUTION:100 pts.wt. silver-plated copper powder having a silver plating surface layer is mixed with 15-40 pts.wt. resol-modified thermosetting resin to give a conductive coating material, wherein the peak width delta2theta in the X-ray powder diffraction pattern by using Cu Kalpha radiation on the 111 surface of silver in the silver plating layer of the silver-plated copper powder is at most 0.5, and the silver-plated copper powder has a mean particle diameter of 1-20mum and a silver plating weight of 3-30wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paint, and more particularly to a conductive paint which is excellent in humidity resistance, oxidation resistance and migration resistance and is suitable for through-hole conduction in double-sided or multilayer printed circuit boards.

[0002]

2. Description of the Related Art In the process of manufacturing double-sided and multi-layer printed circuit boards, a so-called plating method has been conventionally used in which plating is applied to the inner peripheral surface of a through hole when conducting electrical connection between the layers through the through hole. There is. In the through-hole conduction by the plating method, the conduction resistance between the layers can be reduced, but on the other hand, steps such as coating and peeling of a resist material accompanying the plating are required, and the entire substrate needs to be immersed in the plating solution.

Recently, the mounting density of components on a substrate has become higher, and the diameter of through holes has been reduced accordingly. In addition, since the substrate tends to be multi-layered, the through hole has a smaller diameter and a higher aspect ratio.
As a result, it is becoming difficult to achieve through-hole conduction by the plating method.

On the other hand, along with the plating method, a through-hole conduction method using a conductive paint has been developed. It has been used especially for double-sided boards. With the increase in the diameter and aspect ratio of the through-hole, this conductive paint is used. Through-hole conduction has been attracting attention as an alternative to the plating method. As the conductive paint, a paint containing silver powder as a conductive filler is mainly used.

[0005]

By the way, a conductive paint containing silver powder as a filler is an excellent material having high conductivity and oxidation resistance. However, silver is caused by moisture existing in the periphery. This migration may cause a short circuit in the circuit due to a drawback of a unique migration phenomenon, so-called migration. Therefore, when this conductive paint is used for through-hole conduction, there are restrictions such as widening the through-holes at the circuit design stage.

On the other hand, through-hole conduction by a conductive paint containing copper or copper-based composite powder having excellent migration resistance as a conductive filler is disclosed in, for example, Japanese Patent Publication No. 62-62.
It is proposed in Japanese Patent Publication No. 7642. However, when using a copper-based conductive filler, it is necessary to add several kinds of additives in the conductive coating in order to obtain conductivity comparable to that of the conductive coating using silver as the conductive filler.
In many cases, since the conductive filler contains a considerable amount of copper ions, these additives and copper ions may adversely affect the substrate material. Therefore, the practical use of the conductive paint using the copper-based conductive filler has been limited to a part, and the conductive paint using silver as the conductive filler has not been replaced.

As described above, when the conductive paint is used for through-hole conduction, the silver-based and copper-based conductive paints have their respective drawbacks. The present invention has improved these drawbacks, and is a conductive coating that combines the advantages of silver-based and copper-based, that is, it has excellent migration resistance as compared to silver-based coatings, and has a large amount of additives and copper-based additives. Its purpose is to obtain a conductive paint containing no copper ions.

[0008]

The present inventors have examined the application of silver-plated copper powder to a conductive filler in order to achieve the above object. As a result, it is clear that it is better to use, as the silver-plated copper powder, a powder X-ray diffraction peak width Δ2θ of 0.5 or less due to copper Kα rays on the silver 111 surface in the silver-plated film, which has good crystallinity. It became This is because if Δ2θ is larger than 0.5, the oxidation resistance is lowered, and as a result, it is necessary to add an additive in order to prevent deterioration due to oxidation, as in the case of using copper powder as the conductive filler. Because there is.

The grain size of the silver-plated copper powder used in the present invention is 1 to 20 μm, preferably 10 μm or less. This is because if the particle size is less than 1 μm, the cost required to form the copper powder increases, the silver content required to obtain the same characteristics increases, and the cost required for plating itself increases, while the particle size increases. This is because if the diameter exceeds 20 μm, it becomes too large as a conductive filler, which adversely affects the physical properties of the conductive coating material and limits its use.

Further, the shape of the silver-plated copper powder used in the present invention is not particularly limited, but it is preferably spherical powder, granular powder or flat powder which is easily plated with silver. The amount of silver plating varies depending on the particle size and shape, but is 3 to 30 weight percent, more preferably 5 to 2
Within the range of 5 weight percent. This is because when the amount of silver plating is too small, it becomes difficult to prevent deterioration without additives, and when the amount of silver plating is too large, cost increases and migration resistance is high. This is because the

In the present invention, it is most preferable to use the above-mentioned silver-plated copper powder as the conductive filler, but it is not necessary that the total amount is this silver-plated copper powder, and even conventional silver-plated copper powder having poor crystallinity is used. It may well be a mixture thereof, or may be a mixture of small amounts of silver powder, copper powder and palladium powder added and mixed.

On the other hand, as a result of various studies as the binder, the most preferable result in terms of conductivity and the like is obtained when a resole-modified thermosetting resin is used, and particularly when the amount is large, the conduction of each layer is excellent. all right. this is,
Since the resole-modified thermosetting resin has a methylene ether bond and a methylol group at the terminal, it is presumed that the oxide film on the end face of the inner layer copper foil can be reduced during curing.

Here, the addition amount of the resole-modified thermosetting resin is 5 to 50 parts by weight (preferably 15 to 40 parts) with respect to 100 parts by weight of the conductive filler.
Parts by weight). This is because when the amount of the resol-modified thermosetting resin added is less than 5 parts by weight of the conductive filler, the strength of the coating film is lowered and a good coating film cannot be obtained, while it exceeds 50 parts by weight of the conductive filler. In that case, the conductivity is drastically reduced and the required conductivity cannot be obtained.

Here, as the resole-modified thermosetting resin used in the present invention, a resole-type phenol and a cresol-modified resole-type phenol resin, and an epoxy resin or xylene resin in which a resole-type phenol or cresol is bonded to the terminal, One or more resins selected from resole-modified thermosetting resins such as amino resins, alkyd resins, polyurethane resins, polyester resins, acrylic resins, polyimide resins and melamine alkyd resins can be mentioned. Further, these resole-modified thermosetting resins may be combined with any resin such as novolac resin to form a binder, as long as the characteristics of the resole-modified thermosetting resin are not impaired.

Further, depending on the physical properties of the resin and the conductive composition, one of known solvents is used for the purpose of adjusting the viscosity.
It is also possible to use one kind or a mixture of several kinds of solvents. Examples of the solvent include aromatics such as toluene and xylene, ketones such as MEK and MIBK, esters such as ethyl acetate and butyl acetate, ethylene glycol, diethylene glycol, triethylene glycol diethers and monoethers, and acetic acid thereof. Ester, β-
Examples thereof include alcohols such as alkoxypropionic acid esters, ethanol, isopropanol, n-butyl alcohol and terpineol, amides such as n-methylpyrrolidone, DMF and dimethylacetamide, ethers and phenols.

[0016]

The silver-plated copper powder used in the present invention is, for example, 4
Even when exposed to an environment of 0 ± 2 ° C. and a humidity of 90 to 95% for 1344 hours (8 weeks), the characteristics hardly change, and it has excellent corrosion resistance. It is considered that this is related to the interface state between silver and copper. That is, since the silver-coated copper powder used in the present invention has no gap between the silver film and the copper powder, it is presumed that the oxidation of copper is prevented.

Further, a paste containing the same amount of resin as a binder and kneaded with silver and the silver-coated copper powder of the present invention was printed on a substrate having a hydrophilic surface at a gap of 0.5 mm and 40 ±. D at 2 ° C and humidity of 90-95%
When C10V is applied and the migration resistance is compared, the time until the short-circuit current due to migration in the silver-coated copper paste of the present invention is observed is about 30 times that in the case of silver. This shows that the silver-coated copper powder of the present invention has high migration resistance.

Then, by mixing the above silver-plated copper powder and a resole-modified thermosetting resin together with a solvent,
It is possible to obtain a conductive paint exhibiting conductivity equivalent to that of silver and having excellent migration resistance, which is suitable for through-hole conduction.
In this case, it is not necessary to add an additive or a chelating agent for preventing deterioration of the silver-plated copper powder due to oxidation. This is a great feature of the present invention. Further, the silver-plated copper powder and the silver powder can be mixed and used, and various additives can be further added.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Powder X-ray diffraction peak width Δ2 of copper Kα ray on silver 111 surface
When θ is 0.5 or less, a total of 10 g of granular copper powder coated with 10% by weight of silver and having an average particle size of 5 μ and 10 μ and a flat copper powder coated with 20% by weight and having a thickness of 1 μ and an average particle size of 10 μ is taken, Mixed in a paper tube. To this mixed powder, 5.1 g of a resol-modified alkylphenol resin solution having a solid content of 60% was added and sufficiently kneaded with a steel spatula, and then an alcohol solvent was added to form a paste.
Moreover, when the viscosity of the paste was measured at 25 ° C. using a B type viscometer, it was 150 Pa · s. To 10 g of this paste, 0.5 g of a ketone solvent was added to reduce the viscosity, and a conductive coating material was produced as a trial.

Example 2 3 g of the silver-coated copper powder having an average particle size of 5 μ described in Example 1 and 7 g of flat silver powder having an average particle size of 5 μ were mixed in the same manner as in Example 1. To this mixed powder, 4.7 g of a resole-modified alkylphenol resin solution having a solid content of 60% was added and sufficiently kneaded with a spatula made of steel, and then an alcohol solvent was added to form a paste. Moreover, when the viscosity of the paste was measured at 25 ° C. using a B type viscometer, it was 150 Pa · s. To 10 g of this paste, 0.4 g of a ketone-based solvent was added to reduce the viscosity, and a conductive paint was produced as a trial.

Example 3 Powder X-ray analysis peak width Δ2θ of Kα line on silver 111 surface
So as to be 0.5 or less, the total amount of the flat copper powder having an average particle size of 5μ and 10μ each coated with 10% by weight of silver and the thickness of 1μ and the average particle size of 10μ coated with 20% by weight are added in total. Taken and mixed in a tube of parchment paper. To this mixed powder, 2 g of a resol-type phenol resin having a solid content of 60% (resin content of 1.2 g) and 0.6 g of a bisphenol A-type epoxy resin were added and sufficiently kneaded with a steel spatula, followed by acetic acid-2. -Butoxyethyl was added to make a paste. Further, 2-butoxyethyl acetate was added to reduce the viscosity, and a conductive coating material for through holes was prototyped.

Example 4 Powder X-ray analysis peak width Δ2θ of Kα ray on silver 111 surface
So as to be 0.5 or less, the total amount of the flat copper powder having an average particle size of 5μ and 10μ each coated with 10% by weight of silver and the thickness of 1μ and the average particle size of 10μ coated with 20% by weight are added in total. Taken and mixed in a tube of parchment paper. To this mixed powder, 7 g of a resol-type phenol resin having a solid content of 60% (resin content of 4.2 g) was added and sufficiently kneaded with a steel spatula, and then 2-butoxyethyl acetate was added to form a paste. did. Further, 2-butoxyethyl acetate was added to reduce the viscosity, and a conductive coating material for through holes was prototyped.

Further, a through-hole conduction experiment of each layer was conducted using a model multilayer (6 layers) substrate made of glass epoxy resin having a structure as shown in FIG. In FIG. 1, reference numerals 1, 2, 3 and 4 are glass epoxy resin plates each having a predetermined thickness, reference numeral 5 is a copper foil having a thickness of 35 μm, reference numeral 6 is a copper foil having a thickness of 18 μm, and reference numeral 7 is a diameter 1 It is a through hole of 0.4 mm.

The conductive paint is applied to the through holes 7 respectively.
After applying to the inner wall of the, dried at 100 ℃ for 10 minutes, 150 ℃
And cured for 30 minutes. As a comparative example, the same experiment was conducted using a commercially available conductive paint for through holes containing silver powder as a filler. Table 1 shows the conduction resistance value between each layer.

[0026]

As shown in Table 1, the conduction resistance value was particularly low and stable when the through-hole conduction was performed using the conductive coating material according to the present invention.

Next, the through-hole conductive paint used in Example 1 and a commercially available through-hole conductive paint containing silver as a filler were printed on the substrate shown below, and at 30 ° C. at 30 ° C.
After heat-curing for a minute, migration properties were compared under the following conditions. Substrate: Polyester film coated with gelatin film Conditions: 40 ° C ± 2 ° C, 90-95% RH Pattern gap 1 mm Voltage DC10V

Here, as a specific comparison of migration properties, the time (migration time) at which a current of 100 μA was observed in μsec unit was compared. The results are shown in Table 2.

[0030]

As shown in Table 2, it is clear that silver-plated copper powder is a material that is much less likely to cause migration than silver.

[0032]

As described above, according to the present invention, the same conductivity as silver and excellent migration resistance are exhibited, and it does not contain additives such as copper-based conductive paint and a large amount of copper ions. It is possible to obtain a conductive paint suitable for conducting through holes.

[Brief description of drawings]

FIG. 1 shows a structure of a model multilayer substrate used for a through hole conduction experiment of each layer in an example of the present invention.

[Explanation of symbols]

 1,2,3,4 Glass epoxy resin 5,6 Copper foil 7 Through hole

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H05K 3/40 E 7511-4E (72) Inventor Seiichiro Minami 5-1, Ogimachi, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Denko K.K.

Claims (3)

[Claims] 1. A binder containing 5 to 50 parts by weight of a resole-modified thermosetting resin is added to 100 parts by weight of a conductive filler containing silver-plated copper powder having a silver-plated layer on the surface. Conductive paint that does. 2. A powder X-ray diffraction peak width Δ2 due to copper Kα rays on the silver 111 surface in the silver plating layer of the silver-plated copper powder.
The conductive coating material according to claim 1, wherein θ is 0.5 or less. 3. The silver-plated copper powder has an average particle size of 1 to 20.
3. The conductive coating material according to claim 1, wherein the conductive coating material has a thickness of .mu.m and a silver plating amount of 3 to 30% by weight.