JP7737076B2 - Glass ceramic dielectric material, sintered body, method for producing sintered body, and high frequency circuit component - Google Patents

Description

The present invention relates to a glass ceramic dielectric material, which is a precursor to a sintered body having a low dielectric tangent and high mechanical strength advantageous for signal processing in the high frequency range of 20 GHz or higher, as well as to a sintered body and a high-frequency circuit component.

Alumina ceramic is widely used as a wiring board and circuit component. However, due to its high dielectric constant of 10, alumina ceramic has the disadvantage of slow signal processing speed. Another disadvantage is that tungsten, which has a high melting point, must be used as the conductor material, resulting in high conductor loss.

To overcome this drawback, glass-ceramic dielectric materials made from glass powder and ceramic powder have been developed, and sintered bodies of these materials are used as dielectric layers. For example, sintered bodies of glass-ceramic dielectric materials made from glass powder that precipitates diopside as the primary crystal have a relative dielectric constant of 7.3 to 7.8 at 0.1 GHz, lower than that of alumina ceramic materials. Furthermore, because they can be fired at temperatures below 1000°C, they can be co-fired with low-melting-point metal materials such as Ag and Cu, which have low conductor loss, and have the advantage of being able to be used as inner-layer conductors (see Patent Document 1).

Japanese Patent Application Publication No. 10-120436

In recent years, the frequency bands used in mobile communication devices, such as 5G, and local network communication fields, such as Wi-Fi, have been increasing to 20 GHz and above, and there is a strong demand for ceramic dielectric materials with even lower dielectric loss tangents in such high-frequency ranges.

The transmission loss of electromagnetic waves in electronic circuits is proportional to the product of the square root of the dielectric constant of the circuit board, the dielectric loss tangent, and the frequency of the electromagnetic wave. The glass-ceramic dielectric material disclosed in the above patent document exhibits high dielectric properties at 10.1 GHz, but its dielectric loss tangent is not sufficiently low in the high-frequency range of 20 GHz and above, resulting in the problem of large transmission loss.

Another problem was that the bending strength was low at approximately 200 MPa, making it insufficient for use as a high-frequency circuit board.

The object of the present invention is to provide a glass ceramic dielectric material, which is a precursor to a sintered body having a low dielectric tangent and high bending strength in the high frequency range of 20 GHz or higher, as well as a sintered body and a high-frequency circuit component.

The laminated glass-ceramic dielectric material of the present invention has a laminated structure in which at least an outer layer, an inner layer and another outer layer are laminated in this order, the outer layers each being made of alumina and having a thickness of 0.1 to 5 μm, and the inner layer contains a crystallizable glass powder containing, in mass %, 50 to 60% SiO ₂ , 20 to 30% CaO, and 15 to 21% MgO as a glass composition.

In the present invention, "crystallizable glass powder" refers to amorphous glass powder that has the property of precipitating crystals from the glass matrix when heat-treated. "Heat treatment" refers to heat treatment at 800 to 1000°C for 10 minutes or more.

In the laminated glass-ceramic dielectric material of the present invention, the inner layer is preferably a green sheet compression-bonded body or a printed laminate.

In the laminated glass-ceramic dielectric material of the present invention, the inner layer preferably contains substantially no ceramic powder. "Substantially no ceramic powder" means that the content of ceramic powder in the inner layer is less than 0.1% by mass.

The laminated glass-ceramic dielectric material of the present invention preferably includes a metal conductor in the inner layer.

In the laminated glass-ceramic dielectric material of the present invention, the metal conductor is preferably silver or a silver alloy.

The sintered body of the present invention is a sintered body obtained by sintering the laminated glass-ceramic dielectric material, and preferably has diopside-based crystals precipitated as the main crystals from the glass matrix of the inner layer. Note that "diopside-based crystals" refers to diopside crystals (diopside, CaMg( _Si2O6 )) and _diopside solid solution crystals.

The sintered body of the present invention has a laminated structure in which at least an outer layer, an inner layer and another outer layer are laminated in this order, the outer layers each being made of alumina and having a thickness of 0.1 to 5 μm, and the inner layer contains, in mass %, 50 to 60% SiO ₂ , 20 to 30% CaO and 15 to 21% MgO, and is characterized in that diopside-based crystals are precipitated in the inner layer.

The sintered body of the present invention preferably has a three-point bending strength of 250 MPa or more. Note that "three-point bending strength" refers to a value evaluated based on JIS R1601.

The sintered body of the present invention preferably has a dielectric loss tangent of 0.0009 or less at a measurement temperature of 25°C and 28 GHz.

The sintered body of the present invention preferably has a relative dielectric constant of 8.0 or less at a measurement temperature of 25°C and 28 GHz.

The "dielectric loss tangent" and "relative permittivity" refer to values measured at a temperature of 25°C and a frequency of 28 GHz, based on the method for measuring microwave dielectric properties of fine ceramic substrates (JIS R1641).

The sintered body of the present invention preferably has a thermal expansion coefficient of 8 to 10 ppm/°C. Note that "thermal expansion coefficient" refers to a value measured using a thermomechanical analyzer in the temperature range of 30 to 380°C.

The method for producing a sintered body of the present invention preferably involves firing the above-mentioned laminated glass-ceramic dielectric material.

In the method for producing the sintered body of the present invention, firing is preferably carried out at a temperature of 1000°C or less.

The high-frequency circuit component of the present invention is a high-frequency circuit component having a dielectric layer, and it is preferable that the dielectric layer be the above-mentioned sintered body.

The laminated glass-ceramic dielectric material of the present invention can be fired at low temperatures of 1000°C or less, and low-melting-point metal materials such as silver, silver alloys, and copper can be used as inner layer conductors. Furthermore, it has a low dielectric dissipation factor in the high-frequency range of 20 GHz or more, and a high bending strength of 250 MPa or more. Therefore, the glass-ceramic dielectric material of the present invention is suitable as a high-frequency circuit component to be mounted on a resin motherboard.

The laminated glass-ceramic dielectric material of the present invention is a laminate in which an outer layer, an inner layer, and an outer layer are laminated in this order, with the inner layer containing a crystallizable glass powder and the outer layer being made of alumina.

First, let's explain the inner layer.

The glass powder constituting the inner layer preferably contains, in mass %, 50-60% _SiO2 , 20-30% CaO, and 15-21% MgO as a glass composition. The reasons for limiting the content range of each component as described above are explained below. In the explanation of the content range of each component, % refers to mass %.

_SiO2 is a constituent of diopside crystals and a component that serves as a network former for glass. The _SiO2 content is 50 to 60%, preferably 53 to 57%, and particularly preferably 54 to 56%. If the _SiO2 content is too low, vitrification becomes difficult. On the other hand, if the _SiO2 content is too high, the melting temperature tends to be high and diopside crystals become difficult to precipitate.

CaO is a component of diopside crystals and lowers the softening point of the crystallizable glass powder. The CaO content is 20-30%, preferably 23-29%, and especially 25-27%. If the CaO content is too low, the softening point will be too high. Furthermore, the degree of crystallization will decrease, making the dielectric loss tangent more likely to increase. On the other hand, if the CaO content is too high, vitrification will be difficult. Furthermore, the dielectric loss tangent will be more likely to increase.

MgO is a component of diopside crystals and lowers the softening point of the crystallizable glass powder. The MgO content is 15-21%, and preferably 17-20%. If the MgO content is too low, the softening point will be too high. Furthermore, the dielectric loss tangent will tend to be high. On the other hand, if the MgO content is too high, vitrification will be difficult. Furthermore, the degree of crystallization will decrease, making the dielectric loss tangent more likely to be high.

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

Note that alkali metal oxides (Li ₂ O, Na ₂ O, K ₂ O) are components that lower the firing temperature but increase the dielectric loss tangent. Therefore, the content of Li ₂ O + Na ₂ O + K ₂ O is less than 2%, and preferably less than 1%, less than 0.5%, and particularly less than 0.1%. Note that the content of Li ₂ O is preferably less than 0.5%, and particularly less than 0.1%. The content of Na ₂ O is preferably less than 0.5%, and particularly less than 0.1%. The content of K ₂ O is preferably less than 0.5%, and particularly less than 0.1%. Here, "Li ₂ O + Na ₂ O + K ₂ O" means the total amount of Li ₂ O, Na ₂ O, and K ₂ O.

The inner layer is preferably a green sheet laminate or a printed laminate.

Incorporating ceramic powder into the inner layer can improve the dielectric properties and/or strength, but it may also hinder the densification of the sintered body. Therefore, it is preferable that the inner layer of the present invention be substantially free of ceramic powder.

The laminated glass-ceramic dielectric material of the present invention can be fired at temperatures below 1000°C, allowing for the introduction of a metal conductor with a low melting point into the inner layer. The metal conductor is preferably silver or a silver alloy, which has low conductor loss.

Furthermore, upon firing, it is preferable that diopside-based crystals precipitate as the main crystals from the crystallizable glass powder contained in the inner layer. Precipitating diopside-based crystals in the inner layer makes it easier to reduce the relative dielectric constant and dielectric loss tangent.

The thickness of the inner layer is preferably 0.1 to 3.0 mm.

Next, we will explain the outer layer.

The outer layer is made of alumina. Alumina has high strength and a thermal expansion coefficient of 7 to 7.7 ppm/°C, similar to that of the highly expansive inner layer, making it suitable for increasing the mechanical strength of the glass-ceramic dielectric material of the present invention.

It is also preferable that the outer layer be formed on the surface of the inner layer with a thickness of 0.1 to 5 μm, and particularly 0.3 to 4 μm. If the outer layer is too thin, the mechanical strength is likely to decrease. On the other hand, if the outer layer is too thick, there is a risk of the outer layer peeling off.

Next, the characteristics of the sintered body of the present invention will be described below.

The three-point bending strength of the sintered body of the present invention is preferably 250 MPa or more, particularly 260 MPa or more. If the three-point bending strength is too low, cracks and other problems will easily occur in the sintered body. There is no particular lower limit to the three-point bending strength, but in reality it is 100 MPa or more.

The sintered body of the present invention preferably has a dielectric dissipation factor of 0.0009 or less, and particularly 0.0008 or less, at 25°C and 28 GHz. If the dielectric dissipation factor is too high, transmission signal loss is likely to increase. There is no particular lower limit for the dielectric dissipation factor, but in practice it is 0.0001 or more.

The sintered body of the present invention preferably has a relative dielectric constant of 8.0 or less, and particularly 7.5 or less, at 25°C and 28 GHz. If the relative dielectric constant is too high, the signal processing speed tends to slow down. There is no particular lower limit to the relative dielectric constant, but in reality it is 5.0 or more.

The thermal expansion coefficient of the sintered body of the present invention is preferably 8 to 10 ppm/°C, and particularly 8.5 to 9 ppm/°C. If the thermal expansion coefficient of the sintered body is too low, distortion is likely to occur due to differences in thermal expansion when subjected to a heat cycle after soldering to a resin motherboard. On the other hand, if the thermal expansion coefficient is too high, thermal shock resistance will decrease. The "thermal expansion coefficient" is measured using a thermomechanical analyzer in the temperature range of 30 to 380°C.

Furthermore, the method for producing the sintered body of the present invention is described below.

First, a slurry is prepared by adding predetermined amounts of binder, plasticizer, and solvent to the above-mentioned crystallizable glass powder. Suitable binders include polyvinyl butyral resin and methacrylic acid resin, suitable plasticizers include dibutyl phthalate, and suitable solvents include toluene and methyl ethyl ketone.

The above-mentioned slurry of crystallizable glass powder is then formed into a green sheet using the doctor blade method, dried, cut to the specified size, and mechanically processed to form via holes. A low-resistance metal material, such as a silver conductor or an electrode, is then printed into the via holes and on the surface of the green sheet. Several such green sheets are then stacked to obtain a laminated green sheet.

Furthermore, the above-mentioned laminated green sheet can be dip-coated with alumina slurry to form a uniform alumina layer, and then fired to obtain a sintered body. The alumina layer can also be formed by printing an alumina paste on the surface after firing the laminated green sheet, and then firing it again. The thickness of the alumina layer can also be changed by adjusting the viscosity of the paste.

The sintered body produced in this way can also have conductors or electrodes inside or on its surface. Furthermore, in order to use low-melting-point metal materials such as silver and copper, which have low conductor loss, it is desirable for the firing temperature to be 1000°C or less, and particularly 800 to 950°C.

The high-frequency circuit component of the present invention can be produced by forming a coil with wiring or by connecting a Si-based or GaAs-based semiconductor chip to the surface of the sintered body produced as described above.

The present invention will be described below based on examples, but the present invention is not limited to these examples.

Table 1 shows examples of the present invention (samples No. 1 to 4) and comparative examples (samples No. 5 and 6).

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. The mixture was then placed in a platinum crucible and melted at 1500-1580°C for 3 hours. The molten glass was then formed into a thin plate using water-cooled rollers. The resulting glass film was then coarsely crushed, and after adding alcohol, it was wet-pulverized in a ball mill. The glass was then classified to obtain a glass powder with an average particle size of 1.5-3 μm.

Next, 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 were added to the glass powder to prepare a slurry. The slurry was then formed into 150 μm green sheets using the doctor blade method, dried, and cut to the specified size. Four of these green sheets were then stacked and integrated by thermocompression bonding. The laminated green sheets were then dip-coated with an alumina slurry to form a uniform alumina layer on the surface, and fired at 900°C for 1 hour to obtain glass ceramic.

Each sample obtained in this manner was evaluated for firing temperature, whether or not it could be co-fired with silver, precipitated crystals, three-point bending strength, dielectric loss tangent, relative dielectric constant, and thermal expansion coefficient. The results are shown in Table 1.

The firing temperature indicates the lowest temperature at which ink is applied to sintered bodies fired at various temperatures and then wiped off, leaving no ink behind (i.e., the body is densely sintered).

To determine whether silver co-firing was possible, a silver conductor was printed on the green sheet before firing, and then the silver wiring was visually inspected for discoloration or breaks after co-firing.

The precipitated crystals were identified using a powder X-ray diffractometer (Rigaku Corporation RINT2100).

Three-point bending strength was evaluated in accordance with JIS R1601.

The dielectric loss tangent and relative permittivity were measured by molding the green sheet, sintering it at the firing temperature shown in the table, and then cutting it into a measurement sample measuring 25 mm x 50 mm x 0.1 mm, in accordance with the method for measuring microwave dielectric properties of fine ceramic substrates (JIS R1641), at a measurement temperature of 25°C and a frequency of 28 GHz.

The thermal expansion coefficient was measured using a thermomechanical analyzer in the temperature range of 30 to 380°C.

As is clear from Table 1, the three-point bending strength of Samples No. 1 to No. 4, which are examples, was high at 260 to 270 MPa because the alumina layer thickness was 0.5 to 3 μm. The dielectric loss tangent was also low at 0.0003 to 0.0007. On the other hand, Sample No. 5 did not vitrify because it had a low _SiO2 content of 49% and a high MgO content of 26%. Sample No. 6 had a low bending strength of 190 MPa because no alumina layer was formed on the glass surface.

Claims (14)

A laminated glass-ceramic dielectric material having a laminated structure in which at least an outer layer, an inner layer and another outer layer are laminated in this order, wherein the outer layers are each made of alumina and have a thickness of 0.1 to 5 μm, and the inner layer contains, as a glass composition, a crystallizable glass powder containing, in mass %, 50 to 60% of SiO ₂ , 20 to 30% of CaO, and 15 to 21% of MgO. The laminated glass-ceramic dielectric material according to claim 1, characterized in that the inner layer is a green sheet laminate or a printed laminate. The laminated glass-ceramic dielectric material according to claim 1 or 2, characterized in that the inner layer is substantially free of ceramic powder. The laminated glass-ceramic dielectric material according to any one of claims 1 to 3, characterized in that the inner layer contains a metal conductor. 5. The laminated glass-ceramic dielectric material of claim 4 , wherein the metallic conductor is silver or a silver alloy. A sintered body obtained by sintering the laminated glass-ceramic dielectric material according to any one of claims 1 to 5, characterized in that diopside-based crystals precipitate as the main crystals from the glass matrix of the inner layer. A laminated glass-ceramic sintered body having a laminated structure in which at least an outer layer, an inner layer and an outer layer are laminated in this order, wherein the outer layers are each made of alumina and have a thickness of 0.1 to 5 μm, and the inner layer contains, in mass %, 50 to 60% SiO ₂ , 20 to 30% CaO and 15 to 21% MgO, and in which diopside-based crystals are precipitated. The sintered body according to claim 6 or 7, characterized in that it has a three-point bending strength of 250 MPa or more. The sintered body according to any one of claims 6 to 8, characterized in that the dielectric loss tangent measured at a temperature of 25°C and a frequency of 28 GHz is 0.0009 or less. The sintered body according to any one of claims 6 to 9, characterized in that it has a relative dielectric constant of 8.0 or less at a measurement temperature of 25°C and a frequency of 28 GHz. A sintered body according to any one of claims 6 to 10, characterized in that the thermal expansion coefficient of the inner layer is 8 to 10 ppm/°C. A method for producing a sintered body, comprising firing the laminated glass-ceramic dielectric material described in any one of claims 1 to 5. The method for producing a sintered body according to claim 12, characterized in that the sintering is carried out at a temperature of 1000°C or less. A high-frequency circuit component having a dielectric layer, wherein the dielectric layer is a sintered body according to any one of claims 6 to 11.