JP7472653B2 - Composite powder, granular powder, tablet, sintered sheet and sintered body - Google Patents

Description

The present invention relates to composite powders, granular powders, tablets, sintered sheets, and sintered bodies that have low dielectric constants and dielectric tangents in the high frequency range of 2 GHz or more. In particular, the present invention relates to composite powders, granular powders, tablets, sintered sheets, and sintered bodies that are suitable for coaxial lines in the high frequency circuit field, millimeter wave radar transmission and reception modules, high frequency electronic circuit modules, etc.

Dielectric materials containing insulating glass have traditionally been used to protect and insulate the wiring of electrical signal circuits. These dielectric materials can be fired at temperatures below 1000°C, making them advantageous in that they can be fired simultaneously with low-melting-point metals such as Ag and Cu, which have low conductor loss, and can be used as inner-layer conductors.

The frequency of electrical signals has increased with the development of wireless communication technology, and in recent years communication frequencies of 2 GHz or higher have been used. The next generation of communication technology, known as 5G, is expected to use even higher frequencies, and electromagnetic waves of 25 to 40 GHz will be used. Furthermore, millimeter wave radars for preventing automobile collisions use electromagnetic waves with frequencies of 75 to 80 GHz. Dielectric materials used in these communications have the advantage of having a low dielectric constant (ε) and low dielectric tangent (tan δ); for example, Patent Document 1 discloses a dielectric material with a dielectric constant of 3.15 to 3.74 and a dielectric tangent of 0.00317 to 0.0171.

JP 2019-108263 A

However, the dielectric material described in Patent Document 1 does not have sufficiently low dielectric properties in the high frequency range, which causes a problem of slowing down the speed of signal processing.

The object of the present invention is to provide a composite powder, granular powder, tablet, sheet sintered body, and sintered body that can be sintered at a temperature of 1000°C or less and have low dielectric properties in the high frequency range.

As a result of various experiments, the inventors have found that when an alkaline earth carbonate powder is added to a glass powder made of an alkali borosilicate glass and then the glass powder is fired at a temperature equal to or higher than the softening point, carbon dioxide generated from the alkaline earth carbonate is trapped in the glass to form bubbles. They have also found that the bubbles can significantly reduce the relative dielectric constant while maintaining a low dielectric tangent, and propose this invention. That is, the composite powder of the present invention is a composite powder containing at least a glass powder and an alkaline earth carbonate powder, wherein the glass powder contains, in mass %, as a glass composition, 60 to 85% SiO ₂ , 15 to 40% B ₂ O ₃ , and 0.1 to 5.0% R ₂ O (Li ₂ O + Na ₂ O + K ₂ O), the alkaline earth carbonate powder is one or more selected from the group consisting of MgCO ₃ , CaCO ₃ , SrCO ₃ , and BaCO ₃ , and the alkaline earth carbonate powder is contained in an amount of 0.01 to 3.0 parts by mass per 100 parts by mass of the glass powder.

The granular powder of the present invention is a granular powder containing at least the above-mentioned composite powder and a binder resin, and it is preferable that the composite powder content is 80 to 99 mass % and the binder resin content is 1 to 20 mass %.

The tablet of the present invention is a tablet obtained by sintering granular powder, and it is preferable that the granular powder is the granular powder described above.

The sheet sintered body of the present invention is a sheet sintered body obtained by sintering a composite powder into a sheet shape, and it is preferable that the composite powder is the composite powder described above.

The sintered body of the present invention is characterized in that it contains at least glass containing, by mass%, 60-85% SiO ₂ , 15-40% B ₂ O ₃ , and 0.1-5.0% R ₂ O (Li ₂ O + Na ₂ O + K ₂ O) as a glass composition, and has a porosity of 5-40%. Here, the "porosity" is a value calculated from (1-(apparent specific gravity/true specific gravity)) x 100 (%). The apparent specific gravity can be calculated by measuring the specific gravity of the sintered body and the true specific gravity can be calculated by measuring the specific gravity of glass not containing pores by the Archimedes method.

The sintered body of the present invention preferably contains 0.01 to 3.0 mass% of MgO+CaO+SrO+BaO in the glass composition of the glass. Here, "MgO+CaO+SrO+BaO" is the total amount of MgO, CaO, SrO, and BaO.

In the composite powder, granular powder, tablet, and sintered sheet of the present invention, carbon dioxide is generated from the alkaline earth carbonate during firing, generating bubbles in the glass. These bubbles can sufficiently reduce the dielectric properties in the high frequency range. Therefore, the composite powder, granular powder, tablet, and sintered sheet of the present invention are suitable for use as high frequency circuit components.

The composite powder of the present invention includes a composite powder containing at least a glass powder and an alkaline earth carbonate powder. The glass powder has a basic composition of borosilicate glass and contains 0.1 mass % or more of _R2O ( _Li2O + _Na2O + _K2O ), and therefore can be fired at a temperature of 1000°C or less. In alkali borosilicate glass, alkali metal oxides cause an increase in the relative dielectric constant and dielectric loss tangent, but by reducing the content to 5 mass % or less, the increase in the relative dielectric constant and dielectric loss tangent in the high frequency range can be suppressed to a level that does not cause practical problems.

It is desirable for the alkali borosilicate glass to be amorphous glass that does not precipitate crystals even when fired at temperatures below 1000°C. This is because amorphous glass has better softening and fluidity during firing than crystalline glass, and a dense sintered body can be obtained.

The glass powder according to the present invention contains, in mass %, 60 to 85% SiO ₂ , 15 to 40% B ₂ O ₃ , and 0.1 to 5.0% R ₂ O (Li ₂ O + Na ₂ O + K ₂ O) as a glass composition. The reasons for limiting the content of each component as above are as follows.

_SiO2 is a component that constitutes the glass network, and its content is 60 to 85%, preferably 70 to 83%. If _{the SiO2} content is too low, the dielectric tangent becomes too high. If the _SiO2 content is too high, the melting temperature becomes high and the solubility decreases.

B ₂ O ₃ is a component that adjusts the viscosity of glass, and its content is 15 to 40%, preferably 20 to 30%. If the content of B ₂ O ₃ is small, the viscosity of the glass increases and the solubility decreases. If the content of B ₂ O ₃ is large, the dielectric tangent increases.

Alkali metal oxides (Li ₂ O, Na ₂ O, K ₂ O) are components that increase melting property and also reduce the firing temperature, and their content is 0.1 to 5.0%, preferably 0.5 to 3.0%. If the amount of Li ₂ O + Na ₂ O + K ₂ O is large, the dielectric tangent becomes high and the loss of the transmission signal becomes large. On the other hand, if the amount of Li ₂ O + Na ₂ O + K ₂ O is small, the melting property decreases and low-temperature firing becomes difficult.

In addition to the above components, components such as Al ₂ O ₃ , MgO, and CaO may be added in amounts up to 3 mass % each within the range that does not impair the dielectric properties.

In the composite powder of the present invention, the alkaline earth carbonate powder is one or more selected from the group consisting of MgCO ₃ , CaCO ₃ , SrCO ₃ and BaCO _3. When these alkaline earth carbonate powders are added and fired at a temperature equal to or higher than the softening point of the glass powder, carbon dioxide is generated from the alkaline earth carbonate, forming bubbles in the glass. These bubbles can significantly reduce the relative dielectric constant while maintaining a low dielectric tangent.

In the composite powder of the present invention, the content of the alkaline earth carbonate powder is 0.01 to 3.0 parts by mass, preferably 0.05 to 2 parts by mass, per 100 parts by mass of the glass powder. If there is too much alkaline earth carbonate powder, the porosity in the sintered body becomes too large, resulting in a high dielectric tangent. If there is too little alkaline earth carbonate powder, it becomes difficult to reduce the dielectric constant.

The composite powder of the present invention may be composed of only glass powder and alkaline earth carbonate powder, but ceramic filler powder can also be added. The mixing ratio of ceramic filler powder is preferably 20 to 50 mass %, more preferably 20 to 45 mass %. The reason for limiting the ratio of ceramic filler powder in this way is that if there is too much ceramic filler powder, it becomes difficult to densify the sintered body, and if there is too little ceramic filler powder, the bending strength of the sintered body decreases.

As the ceramic filler powder, it is preferable to use a ceramic filler powder having a relative dielectric constant of 9 or less and a dielectric loss tangent of 0.0010 or less in the high frequency range of 2 GHz or more. For example, one or more of α-quartz, α-cristobalite, β-tridymite, α-alumina, mullite, and cordierite can be used. In this way, the relative dielectric constant and dielectric loss tangent of the composite powder can be reduced in the high frequency range.

The granular powder of the present invention is a granule for producing a sintered body by press molding, and preferably contains 80 to 99% by mass of the composite powder described above and 1 to 20% by mass of binder resin. By adding binder resin and granulating, the filling property is improved, and a molded body that does not chip or crack even when press molded can be produced.

Granular powder can be produced by adding and mixing composite powder, resin binder, and solvent to obtain a mixture, and then drying the mixture with a drying device such as a spray dryer. The resin binder is preferably an acrylic resin, a butyral resin, or a polyether such as polyethylene glycol. The solvent is preferably ethanol, IPA, water, etc.

The tablet of the present invention is preferably produced by press-molding the above-mentioned granular powder, followed by pre-sintering at a temperature below the softening point of the glass powder. Press molding can be performed by uniaxial press molding, isostatic press molding, or the like. Pre-sintering at a temperature below the softening point of the glass powder allows the resin component to be removed while maintaining the strength of the molded body. Removing the binder resin allows the glass to be fired in a non-oxidizing atmosphere such as nitrogen without discoloring it.

The sheet sintered body of the present invention is a sheet sintered body obtained by sintering a composite powder into a sheet shape, and the composite powder is preferably the above-mentioned composite powder. The sheet sintered body of the present invention can be produced by the following method. A predetermined amount of a binder, a plasticizer, and a solvent are added to the composite powder to prepare a slurry. For example, polyvinyl butyral resin, methacrylic acid resin, etc. can be suitably used as the binder, for example, dibutyl phthalate, etc. can be suitably used as the plasticizer, and for example, toluene, methyl ethyl ketone, etc. can be suitably used as the solvent. The above-mentioned slurry is formed into a green sheet by a doctor blade method. Furthermore, this green sheet is dried, cut to a predetermined size, and via holes are formed by mechanical processing, and low-resistance metal materials that become, for example, silver conductors or electrodes are printed on the via holes and the green sheet surface. Then, a plurality of such green sheets are stacked and integrated by thermocompression. The obtained laminated green sheet is fired to obtain a sheet sintered body. The sheet sintered body produced in this way has conductors and electrodes inside and on the surface. The firing temperature is preferably 1000°C or less, and more preferably 800 to 950°C.

The sintered body of the present invention is characterized in that it contains at least a glass containing, by mass%, 60-85% SiO ₂ , 15-40% B ₂ O ₃ , and 0.1-5.0% R ₂ O (Li ₂ O + Na ₂ O + K ₂ O) as a glass composition, and has a porosity of 5-40%. Some of the technical features of the sintered body of the present invention have already been described, and detailed description will be omitted here.

In the sintered body of the present invention, the porosity is 5 to 40%, preferably 10 to 35%, and more preferably 15 to 30%. If the porosity is too high, the dielectric tangent of the sintered body will be high. On the other hand, if the porosity is low, it will be difficult to reduce the dielectric constant of the sintered body.

The sintered body of the present invention preferably contains 0.01 to 3.0 mass %, particularly 0.05 to 2 mass %, of MgO+CaO+SrO+BaO in the glass composition of the glass, and these alkaline earth metal oxides are preferably introduced by dissolving alkaline earth metal carbonate powder in the glass during firing. If the content of MgO+CaO+SrO+BaO is too high, the dielectric tangent of the sintered body tends to be high. On the other hand, if the content of MgO+CaO+SrO+BaO is too low, it becomes difficult to introduce the alkaline earth metal carbonate powder, making it difficult to reduce the dielectric constant of the sintered body.

The present invention will be described below based on examples. Note that the present invention is not limited to the following examples. The following examples are merely illustrative.

Examples of the present invention (samples No. 1 to 14) and comparative examples (samples No. 15 and 16) are shown in Tables 1 and 2.

Each sample was prepared as follows. First, glass raw materials of various oxides were prepared and mixed uniformly to obtain the glass composition shown in the table, and then placed in a platinum crucible and melted at 1550-1650°C for 3-8 hours. The resulting molten glass was formed into a thin plate using a water-cooled roller. Next, the obtained glass film was roughly crushed, and then alcohol was added and wet-pulverized in a ball mill. The glass was classified to obtain a glass powder with an average particle size of 1-3 μm.

Next, the alkaline earth carbonate powder (average particle size 2-5 μm) shown in the table was added to the above glass powder and mixed to obtain a composite powder (dielectric material). Note that in the table, the amount of alkaline earth carbonate powder added is shown as a percentage relative to 100 parts by mass of glass powder.

Next, 5% by mass of polyethylene glycol as a binder in aqueous solution was added to the composite powder, which was then mixed homogeneously, dried, and classified to obtain a granular powder. The resulting granular powder was press molded in a mold and fired at the firing temperature shown in the table to obtain a sintered body having the composition shown in the table.

The sheet sintered body was produced as follows. A slurry was prepared by adding 15% by mass of polyvinyl butyral as a binder, 4% by mass of butyl benzyl phthalate as a plasticizer, and 30% by mass of toluene as a solvent to the composite powder. The slurry was then formed into a green sheet by the doctor blade method, dried, and cut to the specified dimensions, after which multiple sheets were stacked and integrated by thermocompression. The resulting laminated green sheet was then fired at the temperatures shown in the table to obtain a sheet sintered body.

The dielectric properties of each sample thus obtained were measured. The results are shown in the table. The relative dielectric constant and dielectric tangent of the glass were measured at a temperature of 25°C and a measurement frequency of 16 GHz by processing the sintered body into a cylinder with a diameter of 13 mm and a height of 6.5 mm, based on the double-short-ended dielectric resonator method (JIS R1627).

The porosity was measured by (1 - (apparent specific gravity/true specific gravity)) x 100 (%). Note that the apparent specific gravity is the specific gravity of the sintered body, and the true specific gravity is the specific gravity of the glass that does not contain pores, which was determined by the Archimedes method.

As is clear from the table, samples No. 1 to No. 14 had a relative dielectric constant of 2.0 to 3.8 and a dielectric loss tangent of 0.0017 to 0.0035. In contrast, sample No. 15 had a large amount of alkaline earth carbonate powder added, which resulted in excessive porosity in the sintered body, resulting in a dielectric loss tangent of 0.0055. Sample No. 16 had a small amount of alkaline earth carbonate powder added, resulting in a dielectric constant of 4.3.

Claims (3)

A composite powder including at least a glass powder and an alkaline earth carbonate powder,
The glass powder contains, as a glass composition, in mass %, 70 to 79.0 % SiO ₂ , 15 to 27.4 % B ₂ O ₃ , and 0.1 to 1.6% R ₂ O (Li ₂ O + Na ₂ O + K ₂ O),
The alkaline earth carbonate powder is one or more selected from the group consisting of MgCO ₃ , CaCO ₃ , SrCO ₃ and BaCO ₃ ;
A composite powder comprising 0.01 to 3.0 parts by mass of an alkaline earth carbonate powder relative to 100 parts by mass of a glass powder. A granular powder comprising at least the composite powder according to claim 1 and a binder resin,
A granular powder characterized in that the content of the composite powder is 80 to 99 mass % and the content of the binder resin is 1 to 20 mass %. The glass composition includes at least a glass containing, in mass %, 70 to 78.7 % SiO ₂ , 15 to 27.3 % B ₂ O ₃ , 0.1 to 1.6% R ₂ O (Li ₂ O + Na ₂ O + K ₂ O), and 0.05 to 3.0% MgO + CaO + SrO + BaO,
A sintered body having a porosity of 20 to 40%.