JPH03229489A - Manufacture of ceramic base having through hole - Google Patents

Abstract

PURPOSE:To manufacture a ceramic base having a through hole enabling reduction of an electric resistance to the utmost by a method wherein paste made up of at least one kind of conductive particles selected from specific metal elements, a dispersive solvent for solating them and a dispersing agent selected from an anionic dispersing agent and a nonionic dispersing agent is filled up in a hole opened beforehand for forming the through hole in a green sheet and is baked. CONSTITUTION:For conductive particles, at least one kind of particles selected from tungsten, molybdenum, tantalum, niobium, etc., are used. As for a dispersive solvent, alpha-ternineol, butyral, glycol, etc., can be mentioned and these are used solely or as a mixture of two kinds or more of them. As to a dispersing agent, an anionic dispersing agent, e.g. aliphatic amine salt, aromatic amine salt, heterocyclic amine salt, alkylamine, a polyalkylene polyamine derivative or the like, or a nonionic dispersing agent of an ester type, an ester ether type, an ether type, a nitrogen-containing type or the like, is used solely or as a mixture of two kinds or more of these agents. Minute pores of a green sheet 1 are impregnated, in vacuum, with the alpha-terpineol, for instance and the paste is printed by a roller. Thereafter excessive paste extruded from the rear of the green sheet is removed by scraping and paste 3 is filled up in a through hole 2 of the green sheet 1. After the green sheet 1 thus prepared is dried preliminarily, it is dried by blowing nitrogen thereon and then the surface of the green sheet 1 is removed by a thickness (h) by grinding.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a ceramic substrate having through holes used in ceramic multilayer wiring boards and the like.

[Prior art and problems to be solved by the invention] Conventionally,
A predetermined amount of a dispersion solvent such as α-terpineol and a chicken agent are added to conductive particles such as tungsten into the through-hole forming holes of the green sheet that have been opened in advance, and the mixture is kneaded using a three-roll mixer or the like. After filling the thixotropic paste, the dispersion solvent in the paste was removed by drying, and the conductive particles were fixed in the through holes. Ceramic substrates have been manufactured by appropriately laminating and firing such green sheets.

However, the viscosity of the above paste is 3 to 5 million cps.
This is extremely high, and especially when the diameter of the through hole is as small as 0.1 mm or less, there is a problem that the paste cannot be filled into the through hole. On the other hand, if the content of the dispersion solvent is increased in order to improve the filling properties of the paste, the paste will shrink to some extent as the dispersion solvent is removed after filling the paste. Even if the thickness of the board is reduced by grinding the surface of the board and performing post-processing, the conductive particles will not be able to completely fill the through-holes, increasing the electrical resistance of the conductor circuits inside the through-holes. This caused some inconvenience.

Therefore, in order to minimize the drying shrinkage rate of the paste and reduce the electrical resistance of the conductor circuit in the through-hole, attempts have been made to make the paste lower in viscosity and higher in concentration by controlling the average particle size of the conductive particles. However, no method has been found that is satisfactory, including the ability to fill through-holes.

The present invention was made in view of the above circumstances, and its purpose is to easily fill the through-hole forming hole with paste, and to provide a through-hole with a small diameter (although the inside thereof is sufficiently filled with conductive particles). Another object of the present invention is to provide a method for manufacturing a ceramic substrate having through-holes that can minimize electrical resistance.

[Means and effects for solving the problems] In order to solve the above problems, the present invention provides tungsten (W), molybdenum (Mo), tantalum ( at least one kind of conductive particles selected from Ta), niobium (Nb),
Filled with a paste consisting of at least one dispersion solvent selected from α-terpineol, butyral, and glycol, and at least one dispersant selected from anionic dispersants and nonionic dispersants, and fired. By doing this, a ceramic substrate having through holes is manufactured.

According to this, the above paste has a viscosity of 1.5 million to 3 million cps as measured by a B-type viscometer, and a density of 8.5 to 9.2 g/
cn? It is prepared with much lower viscosity and higher concentration than conventional products. Therefore, the through holes of the green sheet are sufficiently filled with conductive particles, and the electrical resistance is kept as low as possible. Further, since the above paste has excellent filling properties into through holes, it can be smoothly and reliably filled into through holes having an inner diameter of 0.1 mm or less.

To explain the present invention in more detail, the conductive particles include tungsten, molybdenum, tantalum, niobium, etc., and at least one selected from these is used. The average particle size of this conductive particle is
A range of 1 to 10 μm is preferable. If the average particle diameter is less than 1 μm, the particle surface area per unit weight increases, and a larger amount of dispersion solvent is required to make these fine particles slippery, making it impossible to achieve a high concentration of the paste. On the other hand, if the average particle size exceeds 104 m, the ability to fill the through hole will be poor and the number of contacts between conductive particles will be reduced.
There is a risk of increasing the electrical resistance of the conductor circuit in the through hole.

Examples of the dispersion solvent include α-terpineol, butyral, glycol, etc., which may be used alone or in combination of two or more. The blending ratio of the dispersion solvent is as follows: conductive particles 1
00 parts by weight, a range of 2 to 10 parts by weight is suitable. If this blending ratio is less than 2 parts by weight, it will not be possible to uniformly disperse the conductive particles to obtain a sol-like paste, and if it exceeds 10 parts by weight, the content of the conductive particles in the paste will decrease, and after drying. Increases the electrical resistance of the conductor circuit in the through hole.

Examples of the dispersant include anionic dispersants such as aliphatic amine salts, aromatic amine salts, heterocyclic amine salts, alkyl amines, polyalkylene polyamine derivatives, ester type, ester ether type, ether type, and nitrogen-containing type. Examples include nonionic dispersants such as these, which can be used alone or in combination of two or more.

As a dispersant, a cationic dispersant having poor affinity with the conductive particles is not suitable, and if such a dispersant is used, it will actually worsen the dispersibility of the conductive particles. Also,
A material that can be dissolved in the above-mentioned dispersion solvent is used. By adding this dispersant, the viscosity of the paste as a whole is reduced.

Further, a chicken agent may be added to the paste as necessary. Examples of the chicken agent include castor oil, polycarboxylic acid alkylamine for oil-based products, and polyvinyl alcohol, polyethylene oxide, etc. for water-based products, and the addition of this chicken agent imparts thixotropic properties to the paste.

Due to this property, the paste becomes a sol when applied with a roller, etc., making it easy to fill into the through hole.
After filling, the paste gels and retains better in the through-hole.

The above-mentioned conductive particles, dispersion solvent, dispersant, etc. are uniformly mixed and kneaded using a three-roll mixer or the like.
The viscosity and density are adjusted within the ranges described above.

A ceramic substrate to which the present invention can be applied is a substrate formed by firing a clean sheet formed from a ceramic material such as aluminum nitride, alumina, silicon carbide, silicon nitride, or the like.

The green sheet is generally pre-impregnated with a solvent as described above prior to being filled with the paste. This is to prevent the dispersion solvent in the paste from being absorbed from the inner wall surface of the through-hole when filling the paste into the through-hole, reducing the fluidity of the paste within the through-hole and preventing uniform filling. This is to prevent this from happening. Filling of the paste into the through holes is done according to a conventional method such as roller printing, and excess paste protruding from the back side of the green sheet is scraped off. Thereafter, the substrate is dried, and the solvent with which the substrate was previously impregnated and the dispersion solvent in the paste are removed. In this drying process, when heat drying is performed to shorten the time, it is preferable to dry under an inert gas atmosphere in order to prevent an increase in electrical resistance due to oxidation of the conductive particles.

Once the conductive particles are fixed in the through holes in this manner, the clean sheets are laminated as appropriate and fired in accordance with a conventional method to form a ceramic substrate having through holes.

[Examples and Comparative Examples] Examples and comparative examples embodying the present invention will be described below with reference to the drawings.

(Example) 5000g of tungsten fine particles with an average particle size of 3.3μm
200 g of a mixed solvent containing 10% by weight of ethyl cellulose in α-terpineol, 25 g of castor oil,
A paste for filling was prepared by kneading a mixture containing 9.0 g of Og z monoethylamine at 23° C. for 1 hour using a three-roll mixer.

On the other hand, an aluminum nitride green root (thickness 2 mm) with many through holes (inner diameter 0.15 mm) was installed.
) in the micropores of α-terpineol at 25°C.
Vacuum impregnated for a long time, then put on a spinner for 5
The process was performed at 600 rpm for 15 seconds to blow away the α-terpineol filled in the through holes. Then, a metal mask was applied to the surface of this clean sheet to expose only one hole and its surrounding area, and the paste was roller printed on the metal mask under the following conditions to fill the paste.

-Roller printing conditions> Roller used: Teflon resin processing Printing pressure: 2.0 to 2.3 kg/c Roll feed speed: 6. Ocm/sec.

Atmosphere temperature: 23 to 25°C After the above roller printing, the excess paste extruded from the back side of the green sheet was scraped off, and the through holes 2 of the clean sheet 1 were filled with the paste 3.
See figure (a)]. Next, 50 pieces of this green sheet 1
After pre-drying with nitrogen blowing for 1 hour at °C,
When main drying was carried out by blowing nitrogen at 0° C. for 12 hours, the paste 3 shrank slightly and tungsten particles 4 were fixed in the through holes 2 [see FIG. 1(b)].

Then, by polishing and removing the surface of the clean sheet l by a thickness h (200 μm in this example), a green sheet 1 in which the inside of the through hole 2 was completely filled with tungsten particles 4 was obtained [Fig. (c)].

The density and viscosity of the paste prepared in this example, the change in viscosity over time at the start and end of roller printing, the measurement results of the electrical resistance of the conductor circuit in the through-hole, and the standard deviation of the electrical resistance value between multiple through-holes. Table 1 shows the calculation results.
Shown below.

(Comparative example) 5000g of tungsten fine particles with an average particle size of 3.3μm
270g of a mixed solvent containing 10% by weight of ethyl cellulose in α-terpineol and 20.0g of castor oil.
g The blended mixture was heated to 23°C using a three-roll mixer.
The mixture was kneaded for 1 hour to prepare a paste for filling.

Using this paste 8, roller printing was applied to the same aluminum nitride green sheet 6 as in the previous example in the same manner as described above to fill the through hole 7 with the paste 8 [see Fig. 2(a) ]. Then, the tungsten particles 9 are dried in the same manner as described above to fix the tungsten particles 9 in the through holes 7 [see FIG. A conductor circuit was formed in the hole 7 [see FIG. 2(c)]. In addition, in this comparative example, since the amount of drying shrinkage of the paste was large, as shown in FIG. 2(C), a defective region 10 in which the tungsten particles 9 were not filled was observed in a part of the through hole 7. .

The results of the physical properties of the paste prepared in this comparative example are as follows:
The results are shown in Table 1 as in the previous example.

Table - Example Comparative Example (Prepared paste) Density (g/c) Viscosity (cps) Viscosity over time> At the start of printing (cps) At the end of printing (cps) (1 day later) 8.9 to 9.0 8. 3 ~8.7180~23
00,000 3-5,000,000 2,200,000 3,500,000 2,000,000 50 5,000,000 Electrical resistance inside the through hole (mΩ) 0 Standard deviation σ.

7-8 As can be seen from Table 1, the pastes of the Examples had a higher density than the pastes of the Comparative Examples, although the viscosity was much lower. Further, the paste of the comparative example thickens over time after one day, whereas the paste of the example does not thicken at all over time and is excellent in stability over time. By incorporating a dispersant into the paste in this way, it is possible to prepare an ideal paste that is low in viscosity, highly concentrated, and has excellent stability over time.

Furthermore, the electrical resistance of the conductor circuit formed in the through hole is generally lower in the example than in the comparative example. Further, from the value of the standard deviation between the example and the comparative example, the variation in electrical resistance between the through holes of the substrate of the example is smaller than that of the comparative example. This is considered to be because, as a result of using a low-viscosity, high-concentration paste in the example, tungsten particles were fixed in the through-hole at a higher density than in the comparative example.

[Effects of the Invention] As detailed above, according to the present invention, it is easy to fill the through-hole with paste, and even if the diameter of the through-hole is small, the inside of the through-hole can be sufficiently filled with conductive particles. This provides an excellent effect in that the electrical resistance can be made as small as possible.

[Brief explanation of drawings]

FIGS. 1(a) to (c) are a series of explanatory diagrams showing the procedure for forming a through-hole conductor circuit in an embodiment embodying the present invention, and FIGS. FIG. 3 is a series of explanatory diagrams showing a procedure for forming a through-hole conductor circuit. ■...Green sheet, 2...Through hole, 3.
... Paste, 4... Tungsten particles as conductive particles.

Claims (1)

[Scope of Claims] 1. At least one type of conductive particles selected from tungsten, molybdenum, tantalum, and niobium (4 )and,
Filled with a paste (3) consisting of at least one dispersion solvent selected from α-terpineol, butyral, and glycol, and at least one dispersant selected from anionic dispersants and nonionic dispersants. 1. A method for manufacturing a ceramic substrate having through-holes, the method comprising: firing a ceramic substrate using a method of manufacturing a ceramic substrate; 2 The paste (3) contains 2 to 10 parts by weight of a dispersion solvent and 0.1 to 2 parts by weight of a dispersant per 100 parts by weight of conductive particles.
．． 2. The method for manufacturing a ceramic substrate according to claim 1, wherein 0 parts by weight are blended. 3. The method of manufacturing a ceramic substrate according to claim 1, wherein the ceramic substrate is an aluminum nitride substrate.