Glass substrate for high frequency device, and circuit board substrate for high frequency device

Abstract

To provide a glass substrate for a high frequency device capable of reducing a dielectric loss of a high frequency signal and providing a practical electrical device.SOLUTION: A glass substrate 2 contains alkali metal oxide in a range of 0.001 to 5% by molar percentage based on oxide, and has a molar ratio represented by Na2O / (Na2O+K2O) in the alkali metal oxide in a range of 0.01 to 0.99, contains Al2O3 and B2O3 in a range of 1 to 40% as a total content, and has a molar ratio represented by Al2O3 / (Al2O3+B2O3) in a range of 0 to 0.45, and mainly contains SiO2. Surface roughness of at least one main surface of the glass substrate 2 is 1.5 nm or less as a value of arithmetic average roughness Ra, and a dielectric loss tangent at 35 GHz is 0.007 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a glass substrate for a high frequency device and a circuit board for a high frequency device. [Background technology]

[0002] In electronic devices such as communication devices like mobile phones, smartphones, personal digital assistants, and Wi-Fi devices, as well as surface acoustic wave (SAW) devices, radar components, and antenna components, signal frequencies are becoming higher in order to increase communication capacity and speed. Insulating substrates such as resin substrates, ceramic substrates, and glass substrates are generally used for circuit boards used in such high-frequency electronic devices. Insulating substrates used in high-frequency devices are required to reduce transmission loss due to dielectric loss, conductor loss, etc., in order to ensure characteristics such as the quality and strength of high-frequency signals.

[0003] Of these insulating substrates, resin substrates have low rigidity due to their characteristics. Therefore, resin substrates are difficult to use when rigidity (strength) is required for semiconductor package products. Ceramic substrates have the drawback of being difficult to smooth, which can lead to large conductor losses due to the conductors formed on the substrate surface. On the other hand, glass substrates have high rigidity, making it easy to make packages smaller and thinner, and they also have excellent surface smoothness, and the substrate itself can easily be made larger. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-077769 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-244271 Summary of the Invention [Problem to be solved by the invention]

[0005] However, while conventional alkali-free glass substrates are effective in reducing dielectric loss and the resulting transmission loss up to about 20 GHz, they have limitations in reducing dielectric loss beyond that, for example, in frequencies above 30 GHz. Therefore, circuit boards using conventional alkali-free glass substrates have difficulty maintaining characteristics such as the quality and strength of high-frequency signals above 30 GHz. On the other hand, while quartz glass substrates can maintain low dielectric loss even in frequencies above 30 GHz, their low thermal expansion coefficients result in excessive differences in the thermal expansion coefficients of other components when constructing electronic devices. This reduces the practical utility of electronic devices.

[0006] An object of the present invention is to provide a glass substrate for a high-frequency device that can reduce the dielectric loss of a high-frequency signal and can provide a practical electronic device, and a circuit board for a high-frequency device that uses the same and can reduce the transmission loss of a high-frequency signal. [Means for solving the problem]

[0007] A glass substrate for high-frequency devices according to a first embodiment of the present invention is a glass substrate containing SiO2 as its main component, which contains, in terms of molar percentage based on oxide, alkali metal oxides in a range of 0.001 to 5%, of which the molar ratio expressed as Na2O / (Na2O + K2O) is in a range of 0.01 to 0.99, and which contains Al2O3 and B2O3 in a total content of 1 to 40%, of which the molar ratio expressed as Al2O3 / (Al2O3 + B2O3) is in a range of 0 to 0.45, and which has a surface roughness of at least one main surface of the glass substrate of 1.5 nm or less as an arithmetic mean roughness Ra, and a dielectric loss tangent at 35 GHz of 0.007 or less.

[0008] A glass substrate for high-frequency devices according to a second embodiment of the present invention is a glass substrate containing SiO2 as a main component, which contains alkali metal oxides in a range of 0.001 to 5% by mole percentage based on oxide, and in which the molar ratio of the alkali metal oxides expressed as Na2O / (Na2O + KO) is in a range of 0.01 to 0.99, and which contains alkaline earth metal oxides in a total content of 0.1 to 13%, and at least one main surface of the glass substrate has a surface roughness of 1.5 nm or less as an arithmetic mean roughness Ra, and a dielectric loss tangent at 35 GHz of 0.007 or less.

[0009] A circuit board for a high-frequency device according to a third aspect of the present invention comprises a glass substrate according to the first or second aspect of the present invention and a wiring layer formed on the main surface of the glass substrate, and has a transmission loss of 1 dB / cm or less at 35 GHz. [Effects of the Invention]

[0010] The glass substrate for a high-frequency device of the present invention can reduce the dielectric loss of a high-frequency signal. A circuit board using such a glass substrate can reduce the transmission loss of a high-frequency signal, and can provide a high-frequency device such as a practical electronic device. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view showing the configuration of a circuit board according to the embodiment. [Figure 2] FIG. 10 is a diagram showing the relationship between the signal frequency and the transmission loss of the circuit boards according to Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described. In the following description, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. The content of each component in the glass substrate is expressed as a mole percentage (mol%) based on the oxide, unless otherwise specified. In this specification, "high frequency" refers to 10 GHz or higher, preferably greater than 30 GHz, and more preferably greater than 35 GHz.

[0013] FIG. 1 shows a circuit board for a high-frequency device according to an embodiment of the present invention. The circuit board 1 shown in FIG. 1 includes an insulating glass substrate 2, a first wiring layer 3 formed on a first main surface 2a of the glass substrate 2, and a second wiring layer 4 formed on a second main surface 2b of the glass substrate 2. The first and second wiring layers 3 and 4 form a microstrip line as an example of a transmission line. The first wiring layer 3 constitutes a signal line, and the second wiring layer 4 constitutes a ground line. However, the structure of the first and second wiring layers 3 and 4 is not limited to this, and the wiring layers may be formed on only one main surface of the glass substrate 2.

[0014] The first and second wiring layers 3 and 4 are layers formed of a conductor, and their thickness is usually about 0.1 to 50 μm. The conductor forming the first and second wiring layers 3 and 4 is not particularly limited, and examples thereof include metals such as copper, gold, silver, aluminum, titanium, chromium, molybdenum, tungsten, platinum, and nickel, as well as alloys and metal compounds containing at least one of these metals. The structure of the first and second wiring layers 3 and 4 is not limited to a single-layer structure, and may also be a multi-layer structure, such as a laminate structure of a titanium layer and a copper layer. The method for forming the first and second wiring layers 3 and 4 is not particularly limited, and various known forming methods can be used, such as printing using a conductor paste, dipping, plating, vapor deposition, and sputtering.

[0015] The glass substrate 2 is made of a glass substrate for high-frequency devices according to an embodiment of the present invention and has a dielectric loss tangent (tanδ) of 0.007 or less at 35 GHz. The relative dielectric constant of the glass substrate 2 at 35 GHz is preferably 10 or less. By setting the dielectric loss tangent of the glass substrate 2 at 35 GHz to 0.007 or less, it is possible to reduce dielectric loss in high-frequency regions exceeding 30 GHz. By setting the relative dielectric constant of the glass substrate 2 at 35 GHz to 10 or less, it is also possible to reduce dielectric loss in high-frequency regions. The dielectric loss tangent of the glass substrate 2 at 35 GHz is more preferably 0.005 or less, and even more preferably 0.003 or less. The relative dielectric constant of the glass substrate 2 is more preferably 7 or less, further preferably 6 or less, and particularly preferably 5 or less.

[0016] Furthermore, the surface roughness of the main surfaces 2a and 2b of the glass substrate 2 on which the first and second wiring layers 3 and 4 are formed is set to 1.5 nm or less as the arithmetic mean roughness Ra. By setting the arithmetic mean roughness Ra of the main surfaces 2a and 2b of the glass substrate 2 on which the first and second wiring layers 3 and 4 are formed to 1.5 nm or less, the skin resistance of the first and second wiring layers 3 and 4 can be reduced, thereby reducing conductor loss, even when a skin effect occurs in the first and second wiring layers 3 and 4 in the high-frequency range exceeding 30 GHz. The arithmetic mean roughness Ra of the main surfaces 2a and 2b of the glass substrate 2 is more preferably 1.0 nm or less, and even more preferably 0.5 nm or less. The main surfaces of the glass substrate 2 refer to the surfaces on which wiring layers are formed. When a wiring layer is formed on one of the main surfaces, it is sufficient that the arithmetic mean roughness Ra of that one main surface satisfies the requirement of 1.5 nm or less. In this specification, the surface roughness Ra refers to a value obtained in accordance with JIS B0601 (2001).

[0017] The surface roughness of the main surfaces 2a and 2b of the glass substrate 2 can be achieved by subjecting the surface of the glass substrate 2 to a polishing treatment, if necessary. Examples of polishing methods for the surface of the glass substrate 2 include mechanical polishing using an abrasive primarily composed of cerium oxide or colloidal silica and a polishing pad; chemical mechanical polishing using a polishing slurry containing an abrasive, an acidic solution, or an alkaline solution as a dispersion medium, and a polishing pad; and chemical polishing using an acidic solution or an alkaline solution as an etching solution. These polishing methods are applied depending on the surface roughness of the glass plate from which the glass substrate 2 is made. For example, preliminary polishing and finish polishing may be combined. Furthermore, the edges of the glass substrate 2 are preferably chamfered to prevent breakage, cracks, or chipping of the glass substrate 2 due to the edges during processing. The chamfering may be any of C-chamfering, R-chamfering, and light chamfering.

[0018] By using such a glass substrate 2, the transmission loss of the circuit board 1 at 35 GHz can be reduced, specifically to 1 dB / cm or less. Therefore, the characteristics such as the quality and strength of high-frequency signals, particularly high-frequency signals above 30 GHz, and even high-frequency signals at 35 GHz or higher, are maintained, making it possible to provide a glass substrate 2 and circuit board 1 suitable for high-frequency devices that handle such high-frequency signals. In other words, the characteristics and quality of high-frequency devices that handle such high-frequency signals can be improved. The transmission loss of the circuit board 1 at 35 GHz is more preferably 0.5 dB / cm or less.

[0019] A glass substrate 2 having the dielectric properties such as the dielectric loss tangent described above can be realized by satisfying the following conditions (1) and (2), (1) and (3), or (1), (2), and (3) in a glass substrate containing SiO2 as the main network-forming substance. Here, the glass substrate 2 is formed by melting and hardening a raw material composition. The method for manufacturing the glass substrate 2 is not particularly limited, but a method in which molten glass is formed into a predetermined thickness by the float method, slowly cooled, and then cut into the desired shape to obtain a sheet glass can be applied.

[0020] Here, glass in this specification is, by definition, amorphous and refers to a solid that exhibits glass transition. It does not include crystallized glass, which is a mixture of glass and crystal, or sintered glass containing a crystalline filler. Whether a material is solely amorphous can be confirmed, for example, by performing X-ray diffraction measurement and finding that no clear diffraction peaks are observed.

[0021] In addition, in this specification, "SiO2 as the main component" means that the content of SiO2 is the largest in terms of the proportion of components in mole percent based on oxides.

[0022] Condition (1): The glass substrate 2 contains alkali metal oxides in a total content ranging from 0.001 to 5%, and the molar ratio of the alkali metal oxides expressed as Na2O / (Na2O+K2O) ranges from 0.01 to 0.99.

[0023] Condition (2): The glass substrate 2 contains Al2O3 and B2O3 in a total content ranging from 1 to 40%, and the molar ratio represented by Al2O3 / (Al2O3+B2O3) is in a range of 0 to 0.45.

[0024] Condition (3): The glass substrate 2 contains alkaline earth metal oxides in a total content ranging from 0.1 to 13%.

[0025] Regarding condition (1), by setting the alkali metal oxide content of the SiO2-based glass substrate 2 to 5% or less, the low dielectric loss of the glass substrate 2 can be improved. Furthermore, by setting the alkali metal oxide content to 0.001% or more, practical glass meltability and productivity of the glass substrate 2 can be achieved without the need for excessive raw material refinement, and the thermal expansion coefficient of the glass substrate 2 can be adjusted. Examples of alkali metal oxides contained in the glass substrate 2 include Li2O, Na2O, K2O, Rb2O, and Cs2O. Since Na2O and K2O are particularly important, the total content of Na2O and K2O is preferably in the range of 0.001 to 5%. The alkali metal oxide content is preferably 3% or less, more preferably 1% or less, even more preferably 0.2% or less, even more preferably 0.1% or less, and particularly preferably 0.05% or less. The content of alkali metal oxides is more preferably 0.002% or more, further preferably 0.003% or more, and particularly preferably 0.005% or more.

[0026] Furthermore, by allowing Na2O and K2O to coexist in a glassy material mainly composed of SiO2, in other words, by setting the molar ratio expressed as Na2O / (Na2O + K2O) in the range of 0.01 to 0.99, the migration of alkali components is suppressed, thereby improving the low dielectric loss properties of the glass substrate 2. The molar ratio expressed as Na2O / (Na2O + K2O) is more preferably 0.98 or less, even more preferably 0.95 or less, and particularly preferably 0.9 or less. The molar ratio expressed as Na2O / (Na2O + K2O) is more preferably 0.02 or more, even more preferably 0.05 or more, and particularly preferably 0.1 or more.

[0027] In addition to condition (1) specifying the amount and ratio of the alkali metal oxides, by satisfying condition (2) the amount and ratio of Al2O3 and B2O3, condition (3) the amount of alkaline earth metal oxides, or both conditions (2) and (3), the dielectric dissipation factor of glass substrate 2 at 35 GHz can be reduced to 0.007 or less. In condition (2), Al2O3 is not essential, but it is a component that is effective in improving weather resistance, suppressing phase separation of glass, and reducing the thermal expansion coefficient, and its content is preferably in the range of 0 to 15%. B2O3 is a component that is effective in improving the melting reactivity of glass and lowering the devitrification temperature, and its content is preferably in the range of 9 to 30%.

[0028] In condition (2), when the molar ratio represented by Al2O3 / (Al2O3+B2O3) is 0.45 or less, the low dielectric loss of the glass substrate 2 can be improved. The molar ratio represented by Al2O3 / (Al2O3+B2O3) may be 0. The molar ratio represented by Al2O3 / (Al2O3+B2O3) is more preferably 0.4 or less, and even more preferably 0.3 or less. The molar ratio represented by Al2O3 / (Al2O3+B2O3) is preferably 0.01 or more, and more preferably 0.05 or more.

[0029] When the total content of Al2O3 and B2O3 (including when the Al2O3 content is 0) is 1% or more, the meltability of the glass can be improved. The total content of Al2O3 and B2O3 is more preferably 3% or more, even more preferably 5% or more, and particularly preferably 7% or more. Furthermore, when the total content of Al2O3 and B2O3 (including when the Al2O3 content is 0) is 40% or less, the low dielectric loss of the glass substrate 2 can be improved while maintaining the meltability of the glass. The total content of Al2O3 and B2O3 is more preferably 37% or less, even more preferably 35% or less, and particularly preferably 33% or less.

[0030] If the Al2O3 content is 15% or less, the meltability of the glass can be improved. The Al2O3 content is more preferably 14% or less. The Al2O3 content is more preferably 0.5% or more. If the B2O3 content is 30% or less, the acid resistance and strain point can be improved. The B2O3 content is more preferably 28% or less, even more preferably 26% or less, particularly preferably 24% or less, and most preferably 23% or less. Furthermore, if the B2O3 content is 9% or more, the solubility can be improved. The B2O3 content is more preferably 13% or more, and even more preferably 16% or more.

[0031] In condition (3), examples of alkaline earth metal oxides include MgO, CaO, SrO, and BaO, all of which function as components that enhance the dissolution reactivity of glass. If the total content of such alkaline earth metal oxides is 13% or less, the low dielectric loss properties of the glass substrate 2 can be improved. The total content of alkaline earth metal oxides is more preferably 11% or less, even more preferably 10% or less, particularly preferably 8% or less, and most preferably 6% or less. Furthermore, if the total content of alkaline earth metal oxides is 0.1% or more, the dissolution properties of the glass can be maintained well. The total content of alkaline earth metal oxides is more preferably 3% or more, and even more preferably 5% or more.

[0032] Although MgO is not an essential component, it increases Young's modulus without increasing specific gravity. In other words, MgO is a component that can increase the specific modulus, thereby reducing deflection problems and improving fracture toughness and glass strength. MgO also improves solubility. Although MgO is not an essential component, the MgO content is preferably 0.1% or more, more preferably 1% or more, and even more preferably 3% or more. If the MgO content is 0.1% or more, the effect of adding MgO can be fully obtained and the thermal expansion coefficient can be prevented from becoming too low. The MgO content is preferably 13% or less, more preferably 11% or less, and even more preferably 9% or less. If the MgO content is 13% or less, the increase in devitrification temperature can be suppressed.

[0033] Among alkaline earth metals, CaO is the second most important component after MgO in increasing the specific modulus without excessively lowering the strain point. Similarly to MgO, CaO also improves solubility. Furthermore, compared to MgO, CaO is less likely to increase the devitrification temperature. While CaO is not an essential component, the CaO content is preferably 0.1% or more, more preferably 1% or more, and even more preferably 3% or more. When the CaO content is 0.1% or more, the effect of including CaO can be fully achieved. Furthermore, the CaO content is preferably 13% or less, more preferably 10% or less, and even more preferably 8% or less. When the CaO content is 13% or less, the average thermal expansion coefficient does not become too high, and the increase in the devitrification temperature is suppressed, thereby preventing devitrification during glass production.

[0034] SrO is a component that improves the meltability without increasing the devitrification temperature of the glass. Although SrO is not an essential component, the SrO content is preferably 0.1% or more, more preferably 0.5% or more, even more preferably 1.0% or more, even more preferably 1.5% or more, and particularly preferably 2% or more. When the SrO content is 0.1% or more, the effect of including SrO can be sufficiently obtained. Furthermore, the SrO content is preferably 13% or less, more preferably 10% or less, even more preferably 7% or less, and particularly preferably 5% or less. When the SrO content is 13% or less, the specific gravity is not made too high, and the average thermal expansion coefficient is also prevented from becoming too high.

[0035] Although BaO is not an essential component, it does not increase the devitrification temperature of the glass and improves its melting point. However, a large amount of BaO tends to increase the specific gravity, decrease the Young's modulus, increase the dielectric constant, and increase the average thermal expansion coefficient too much. Therefore, the BaO content is preferably 10% or less, more preferably 8% or less, more preferably 5% or less, and even more preferably 3% or less, and it is particularly preferable that the BaO content is substantially zero.

[0036] In this specification, "substantially not containing" means that BaO is not contained except as an inevitable impurity mixed in from raw materials, etc., that is, BaO is not intentionally contained. In the present invention, "substantially not containing BaO" means, for example, 0.3% or less.

[0037] As described above, by satisfying condition (2) or (3) in addition to condition (1), the dielectric loss tangent at 35 GHz of the glass substrate 2 can be set to 0.007 or less, thereby reducing the dielectric loss of the glass substrate 2. To further enhance the low dielectric loss properties of the glass substrate 2, it is more preferable that the glass substrate 2 satisfy all of conditions (1), (2), and (3).

[0038] Among the components constituting the glass substrate 2, the content of SiO2 as a network former, which is the main component, is preferably in the range of 40 to 75%. If the SiO2 content is 40% or more, the glass-forming ability and weather resistance can be improved, and devitrification can be suppressed. The SiO2 content is more preferably 45% or more, even more preferably 50% or more, and particularly preferably 55% or more. Furthermore, if the SiO2 content is 75% or less, the melting property of the glass can be improved. The SiO2 content is more preferably 74% or less, even more preferably 73% or less, and particularly preferably 72% or less.

[0039] In addition to the above-described components, the glass substrate 2 may contain optional components such as Fe2O3, TiO2, ZrO2, ZnO, Ta2O5, WO3, Y2O3, and La2O3. Fe2O3 is a component that controls the light absorption performance, such as infrared absorption and ultraviolet absorption performance, of the glass substrate 2. If necessary, the Fe content, calculated as Fe2O3, can be up to 0.012%. A Fe content of 0.012% or less can maintain the low dielectric loss and ultraviolet transmittance of the glass substrate 2. To improve ultraviolet transmittance, the Fe content is preferably 0.01% or less, and even more preferably 0.005% or less. Increasing the ultraviolet transmittance of the glass substrate 2 allows the use of ultraviolet-curable materials in processes such as lamination in the manufacturing process of high-frequency devices, thereby improving the manufacturability of high-frequency devices.

[0040] Furthermore, the glass substrate 2 can have an increased ultraviolet shielding ability by containing 0.05% or more Fe, calculated as Fe2O3, as needed. The Fe content is preferably 0.07% or more, and more preferably 0.1% or more. By increasing the ultraviolet shielding ability of the glass substrate 2, the glass substrate 2 can function as a protective material when a resin that deteriorates under ultraviolet light is used as a component.

[0041] To further improve the low dielectric loss of the glass substrate 2, the β-OH value of the glass substrate 2 is set to 0.05 to 0.6 mm -1 The β-OH value is a value used as an index of the water content of glass, and is determined by measuring the absorbance of a glass sample at a wavelength of 2.75 to 2.95 μm and dividing the maximum absorbance value βmax by the sample thickness (mm). The β-OH value of the glass composition is preferably in the range of 0.6 mm. -1 The low dielectric loss of the glass substrate 2 can be further improved by making the β-OH value of the glass substrate 2 0.5 mm or less. -1 Less than 0.4mm is preferable. -1 It is more preferable that the β-OH value of the glass substrate 2 is 0.05 mm or less. -1If the β-OH value is 0.1 mm or more, it is not necessary to dissolve the glass in an extremely dry atmosphere or to drastically reduce the amount of water in the raw material, and it is possible to improve the productivity of the glass and the bubble quality. -1 More than 0.2 mm is more preferable. -1 The above is even more preferable.

[0042] The glass substrate 2 has a thermal expansion coefficient suitable for electronic devices, depending on the content of alkali metal oxides and alkaline earth metal oxides. Specifically, the average thermal expansion coefficient at 50 to 350°C is in the range of 3 to 15 ppm / °C. A glass substrate 2 having such a thermal expansion coefficient can more appropriately adjust the difference in thermal expansion coefficient with other components when configuring a semiconductor package or the like as a high-frequency device. For example, when configuring a 2.5D or 3D (three-dimensional) mounting type glass through-wiring substrate (TGV substrate) for high-frequency applications, the difference in thermal expansion coefficient with other components such as semiconductor chips can be more appropriately adjusted.

[0043] Furthermore, the glass substrate 2 preferably has a Young's modulus of 40 GPa or more. With a glass substrate 2 having such a Young's modulus, the amount of deflection when the glass substrate 2 is caused to flow during the manufacturing process (wafer process) of a high-frequency device can be kept to, for example, 1 mm or less, thereby preventing the occurrence of manufacturing defects in high-frequency devices. The Young's modulus of the glass substrate 2 is more preferably 50 GPa or more, and even more preferably 55 GPa or more. Furthermore, the porosity of the glass substrate 2 is preferably 0.1% or less. This can prevent the generation of noise when manufacturing a high-frequency device. The porosity of the glass substrate 2 is more preferably 0.01% or less, and even more preferably 0.001% or less.

[0044] The transmittance of the glass substrate 2 at a wavelength of 350 nm is preferably 50% or more. This allows the use of ultraviolet-curable materials in the lamination process and other steps in the manufacturing process of high-frequency devices, thereby improving the manufacturability of high-frequency devices. Furthermore, the transmittance of the glass substrate 2 at a wavelength of 350 nm is more preferably 70% or more in order to shorten the irradiation time of ultraviolet light on the ultraviolet-curable material in the device manufacturing process and reduce uneven curing of the ultraviolet-curable material in the thickness direction.

[0045] For the same reason, the transmittance of the glass substrate 2 at a wavelength of 300 nm is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. The transmittance of the glass substrate 2 at a wavelength of 250 nm is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more.

[0046] The transmittance of the glass substrate 2 at a wavelength of 350 nm is preferably 80% or less. This allows the glass substrate 2 to have an ultraviolet blocking ability and function as a protective material when a resin that deteriorates under ultraviolet light is used as a component. The transmittance of the glass substrate 2 at a wavelength of 350 nm is more preferably 60% or less, even more preferably 30% or less, and most preferably 10% or less.

[0047] For the same reason, the transmittance of the glass substrate 2 at a wavelength of 300 nm is preferably 80% or less, more preferably 60% or less, even more preferably 30% or less, and most preferably 10% or less. Also, the transmittance of the glass substrate 2 at a wavelength of 250 nm is preferably 60% or less, more preferably 30% or less, even more preferably 10% or less, and most preferably 5% or less.

[0048] The shape of the glass substrate 2 is not particularly limited, but the thickness thereof is preferably in the range of 0.05 to 1 mm, and the area of ​​one main surface of the glass substrate 2 is preferably 225 to 10,000 cm. 2It is preferable that the thickness of the glass substrate 2 is 0.5 mm or less. When the thickness of the glass substrate 2 is 1 mm or less, it is possible to make high-frequency devices thinner and more compact, and further improve production efficiency. In addition, it is possible to increase the ultraviolet transmittance, and it is possible to use an ultraviolet-curable material in the device manufacturing process to improve manufacturability. The thickness of the glass substrate 2 is more preferably 0.5 mm or less. Furthermore, if the thickness of the glass substrate 2 is 0.05 mm or more, it is possible to maintain the strength of the glass substrate 2 when it flows. Furthermore, it is possible to increase the ultraviolet shielding ability, and it is possible to protect resins that deteriorate under ultraviolet light. The thickness of the glass substrate 2 is more preferably 0.1 mm or more, and even more preferably more than 0.2 mm. Furthermore, according to the glass substrate 2 of the embodiment, it is possible to make the glass substrate 2 have an area of ​​10,000 cm with the above-mentioned thickness. 2 The glass substrate 2 has an area of ​​3600 cm. 2 The following is more preferred:

[0049] The devitrification temperature of the glass substrate 2 is preferably 1400°C or lower. If the devitrification temperature is 1400°C or lower, the temperature of the components in the molding equipment can be lowered when molding the glass, thereby extending the life of the components. The devitrification temperature is more preferably 1350°C or lower, even more preferably 1330°C or lower, and particularly preferably 1300°C or lower. The devitrification temperature of glass is determined by placing crushed glass particles in a platinum dish, heat-treating them for 17 hours in an electric furnace controlled at a constant temperature, and observing the sample after the heat treatment with an optical microscope between the maximum temperature at which crystals precipitate on the surface and inside of the glass and the minimum temperature at which crystals do not precipitate.

[0050] Next, a method for manufacturing a glass substrate of an embodiment will be described. When manufacturing a glass substrate of an embodiment, a melting process for heating glass raw materials to obtain molten glass, a fining process for removing bubbles from the molten glass, a forming process for forming the molten glass into a plate shape to obtain a glass ribbon, and an annealing process for annealing the glass ribbon to room temperature are performed. Alternatively, a method for manufacturing a glass substrate by forming the molten glass into a block shape, annealing it, cutting it, and polishing it may be used.

[0051] In the melting step, raw materials are prepared to have the desired composition of the glass substrate, and the raw materials are continuously charged into a melting furnace and heated preferably to about 1450°C to 1750°C to obtain molten glass.

[0052] Halides such as oxides, carbonates, nitrates, hydroxides, and chlorides can also be used as raw materials. If the molten glass comes into contact with platinum during the melting or fining process, minute platinum particles may dissolve into the molten glass and become contaminated as foreign matter in the resulting glass substrate. However, the use of a nitrate raw material has the effect of preventing the generation of platinum foreign matter.

[0053] As the nitrate, strontium nitrate, barium nitrate, magnesium nitrate, calcium nitrate, etc. can be used. It is more preferable to use strontium nitrate. The particle size of the raw material can be appropriately selected from raw materials with a large particle size of several hundred microns so that no undissolved residue remains, to raw materials with a small particle size of about several microns so that no scattering occurs during raw material transportation and no aggregation occurs as secondary particles. Granules can also be used. The moisture content of the raw material can also be appropriately adjusted to prevent scattering of the raw material. The oxidation-reduction degree of β-OH and Fe (redox [Fe 2+ / (Fe 2+ +Fe 3+ )) can also be used by adjusting the dissolution conditions as appropriate.

[0054] The next fining step is a step of removing bubbles from the molten glass obtained in the melting step. The fining step may be performed by degassing under reduced pressure, or by heating to a temperature higher than the melting temperature of the raw materials. In the manufacturing process of the glass substrate according to the embodiment, SO3 or SnO2 may be used as a fining agent. The SO3 source is preferably a sulfate of at least one element selected from Al, Na, K, Mg, Ca, Sr, and Ba, more preferably an alkaline earth metal sulfate. Among these, CaSO4·2H2O, SrSO4, and BaSO4 are particularly preferred because of their remarkable bubble-enhancing effect.

[0055] The fining agent used in the reduced pressure degassing method is preferably a halogen such as Cl or F. The Cl source is preferably a chloride of at least one element selected from Al, Mg, Ca, Sr, and Ba, more preferably an alkaline earth metal chloride. Among these, SrCl2·6H2O and BaCl2·2H2O are particularly preferred due to their significant bubble-enhancing effect and low deliquescence. The F source is preferably a fluoride of at least one element selected from Al, Na, K, Mg, Ca, Sr, and Ba, more preferably an alkaline earth metal fluoride. Among these, CaF2 is more preferred due to its significant effect of increasing the solubility of the glass raw materials.

[0056] Tin compounds, such as SnO2, generate O2 gas in molten glass. In molten glass, SnO2 is reduced to SnO at temperatures of 1450°C or higher, generating O2 gas and promoting bubble growth. In the production of the glass substrate 2 of this embodiment, glass raw materials are heated to approximately 1450 to 1750°C for melting, which effectively increases the bubble size in the molten glass. When SnO2 is used as a clarifier, the tin compound in the raw materials is adjusted to contain 0.01% or more of the tin compound, calculated as SnO2, relative to the total amount of the matrix composition (100%). An SnO2 content of 0.01% or more provides a clarification effect during melting of the glass raw materials, and is preferably 0.05% or more, more preferably 0.10% or more. An SnO2 content of 0.3% or less suppresses coloration and devitrification of the glass. The content of tin compounds in the alkali-free glass is more preferably 0.25% or less, further preferably 0.2% or less, and particularly preferably 0.15% or less, calculated as SnO2, relative to 100% of the total amount of the matrix composition.

[0057] The next forming step is a step of forming the molten glass from which bubbles have been removed in the fining step into a sheet to obtain a glass ribbon. As the forming step, a known method for forming glass into a sheet can be applied, such as a float method in which molten glass is poured onto a molten metal such as tin to form a sheet to obtain a glass ribbon, an overflow downdraw method (fusion method) in which molten glass is made to flow downward from a trough-shaped member, or a slit downdraw method in which molten glass is made to flow down through a slit.

[0058] Next, the annealing step is a step of cooling the glass ribbon obtained in the forming step to room temperature under controlled cooling conditions. In the annealing step, the glass ribbon is cooled so that the average cooling rate from the annealing point to the temperature at which the viscosity reaches the strain point is R, and then the glass ribbon is annealed to room temperature under predetermined conditions. The annealed glass ribbon is cut to obtain a glass substrate.

[0059] If the cooling rate R in the slow cooling step is too high, distortion is likely to remain in the cooled glass. Furthermore, the equivalent cooling rate, which is a parameter that reflects the fictive temperature, becomes too high, resulting in failure to obtain low dielectric loss characteristics. Therefore, it is preferable to set R so that the equivalent cooling rate is 800°C / min or less. The equivalent cooling rate is more preferably 400°C / min or less, even more preferably 100°C / min or less, and particularly preferably 50°C / min or less. On the other hand, if the cooling rate is too low, the process time required becomes too long, resulting in low productivity. Therefore, it is preferable to set R to 0.1°C / min or more, more preferably 0.5°C / min or more, and even more preferably 1°C / min or more.

[0060] The definition and evaluation method of the equivalent cooling rate are as follows: Glass of the target composition is processed into a rectangular parallelepiped of 10 mm x 10 mm x 0.3 to 2.0 mm, and is held at strain point +170°C for 5 minutes in an infrared heating electric furnace, after which the glass is cooled to room temperature (25°C). At this time, multiple glass samples are produced at cooling rates ranging from 1°C / min to 1000°C / min.

[0061] Using a precision refractive index measuring device (e.g., Shimadzu Devices KPR2000), the refractive index n of multiple glass samples at the d line (wavelength 587.6 nm) was measured. d The V-block method or the minimum deviation method may be used for the measurement. d is plotted against the logarithm of the cooling rate, the n d Obtain a calibration curve.

[0062] Next, we compared the n of glasses with the same composition that were actually manufactured through processes such as melting, molding, and cooling. d is measured by the above-mentioned measurement method. d The corresponding cooling rate (referred to as an equivalent cooling rate in this embodiment) is determined from the calibration curve.

[0063] The present invention is not limited to the above-described embodiments. Modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. For example, when manufacturing the glass substrate of the present invention, glass may be formed into a plate shape by a press molding method in which molten glass is directly formed into a plate shape.

[0064] Furthermore, when producing the glass substrate of the present invention, in addition to the production method using a refractory melting tank, a crucible made of platinum or an alloy containing platinum as a main component (hereinafter referred to as a platinum crucible) may be used as the melting tank or refining tank. When a platinum crucible is used, the melting step involves preparing raw materials so as to obtain the composition of the glass substrate to be obtained, and heating the platinum crucible containing the raw materials in an electric furnace, preferably to about 1450°C to 1700°C. A platinum stirrer is inserted and the mixture is stirred for 1 to 3 hours to obtain molten glass.

[0065] In the forming process of glass plate manufacturing using a platinum crucible, molten glass is poured onto, for example, a carbon plate or a mold and formed into a plate or block. The slow cooling process typically involves maintaining the glass at a temperature of about Tg + 50°C, then cooling it to near the strain point at a rate of about 1 to 10°C / min, and then cooling it to room temperature at a cooling rate that does not leave any residual strain. After cutting and polishing into a predetermined shape, a glass substrate is obtained. Alternatively, the glass substrate obtained by cutting may be heated to, for example, about Tg + 50°C, and then slowly cooled to room temperature at a predetermined cooling rate. This allows the equivalent cooling temperature of the glass to be adjusted.

[0066] The circuit board 1 using the glass substrate 2 of the embodiment described above is suitable for high-frequency devices that handle high-frequency signals, particularly high-frequency signals exceeding 30 GHz, and even high-frequency signals of 35 GHz or higher, and can reduce transmission loss of such high-frequency signals to improve their characteristics, such as quality and strength. The glass substrate 2 and circuit board 1 of the embodiment are suitable for high-frequency devices (electronic devices) such as semiconductor devices used in communication devices such as mobile phones, smartphones, personal digital assistants, and Wi-Fi devices, surface acoustic wave (SAW) devices, radar components such as radar transceivers, and antenna components such as liquid crystal antennas. [Example]

[0067] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Examples 1 to 3 and 7 to 25 are working examples, and Examples 4 to 6 are comparative examples.

[0068] [Examples 1-3, 7-25]

[0069] Glass substrates with the compositions shown in Tables 1 to 4, thickness of 0.125 mm, dimensions of 50 × 50 mm, and arithmetic mean roughness Ra of the main surface of 1.0 nm were prepared. The glass substrates were fabricated by a melting method using a platinum crucible. Raw materials such as silica sand were mixed to prepare a batch of 1 kg of glass. To 100% of the raw materials of the target composition, 0.1% to 1% of sulfate (calculated as SO3), 0.16% of F, and 1% of Cl were added, expressed as mass percentages based on oxides. The raw materials were placed in a platinum crucible and heated in an electric furnace at 1650°C for 3 hours to melt them and produce molten glass. A platinum stirrer was inserted into the platinum crucible and the mixture was stirred for 1 hour to homogenize the glass. The molten glass was poured onto a carbon plate and formed into a plate. The plate was then placed in an electric furnace at a temperature of about Tg + 50°C and held for 1 hour. The furnace was then cooled to Tg - 100°C at a rate of 1°C / min, and the glass was then allowed to cool to room temperature. The glass was then cut and polished to form a plate.

[0070] For the glass substrates of Examples 1 to 3 and 7 to 25, the average thermal expansion coefficient, β-OH value, Young's modulus, porosity, transmittance at a wavelength of 350 nm, density, specific modulus of elasticity, and devitrification temperature at 50 to 350°C are shown in Tables 5 to 8. Note that values ​​in parentheses in the tables were calculated. Tables 9 to 12 also show the dielectric loss tangent at 35 GHz, the relative dielectric constant at 35 GHz, wiring width, transmission loss at 35 GHz, and transmission loss at 110 GHz. As shown in FIG. 1 , a 0.125 mm thick copper wiring layer was formed on the first main surface of the glass substrate as a signal wiring, and a 0.125 mm thick solid copper layer was formed on the second main surface as a ground wiring. The circuit boards fabricated in this manner were subjected to the characteristic evaluation described below.

[0071] [Example 4]

[0072] A soda-lime glass substrate manufactured by the float process was prepared, having the composition shown in Table 1, a thickness of 0.125 mm, a shape of 50 × 50 mm, and an arithmetic mean roughness Ra of the main surfaces of 1.0 nm. The properties of the glass substrate of Example 4 are shown in Tables 5 and 9, similarly to Example 1. A copper wiring layer and a copper layer, each having a thickness of 0.125 mm, were formed on both main surfaces of the glass substrate, similarly to Example 1, and the glass substrate was subjected to the characteristic evaluation described below.

[0073] [Example 5]

[0074] An alkali-free glass substrate manufactured by the float process was prepared, having the composition shown in Table 1, a thickness of 0.125 mm, a shape of 50 × 50 mm, and an arithmetic mean roughness Ra of the main surfaces of 1.0 nm. The properties of the glass substrate of Example 5 are shown in Tables 5 and 9, similarly to Example 1. A copper wiring layer and a copper layer, each having a thickness of 0.125 mm, were formed on both main surfaces of the glass substrate, similarly to Example 1, and the glass substrate was subjected to the characteristic evaluation described below.

[0075] [Example 6]

[0076] A quartz glass substrate manufactured by vapor phase synthesis was prepared, having the composition shown in Table 1, a thickness of 0.125 mm, a shape of 50 × 50 mm, and an arithmetic mean roughness Ra of the main surface of 1.0 nm. In the compositions in Table 1, (0.0) indicates that the component content is less than 0.05%. The properties of the glass substrate of Example 6 are shown in Tables 5 and 9, similarly to Example 1. A copper wiring layer and a copper layer, each having a thickness of 0.125 mm, were formed on both main surfaces of the glass substrate, similarly to Example 1, and the glass substrate was subjected to the characteristic evaluation described below.

[0077] The methods for measuring each physical property are shown below. (relative permittivity, dielectric loss tangent) Measurements were taken using a cavity resonator and a vector network analyzer according to the method specified in JIS R1641 (2007). The measurement frequency was 35 GHz, which is the resonant frequency of the air in the cavity resonator. (average thermal expansion coefficient) Measurements were made using a differential thermal dilatometer in accordance with the method specified in JIS R3102 (1995). The measurement temperature range was 50 to 350°C, and the unit was expressed as ppm / °C. (Young's modulus) Measurements were carried out on glass with a thickness of 0.5 to 10 mm using an ultrasonic pulse method in accordance with the method specified in JIS Z 2280. The unit of measurement was GPa. (transmittance) The transmittance of a mirror-polished glass of a given thickness was measured using a visible-ultraviolet spectrophotometer. The transmittance was expressed as external transmittance, including loss due to reflection. (Porosity) The bubbles contained in the glass substrate were observed under an optical microscope, and the number and diameter of the bubbles were determined, and the volume of the bubbles contained per unit volume was calculated. (β-OH) The determination was performed using the method described in the above embodiment. (Ra) The average roughness of the glass surface in a 10 μm square area was measured using an AFM according to the method specified in JIS B0601 (2001). (density) The density of a glass block of about 20 g containing no bubbles was measured by the Archimedes method. (devitrification temperature) Crushed glass particles were placed in a platinum dish and heat-treated for 17 hours in an electric furnace controlled at a constant temperature. After heat treatment, the sample was observed under an optical microscope to determine the average value of the maximum temperature at which crystals precipitated inside the glass and the minimum temperature at which crystals did not precipitate.

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] [Table 4]

[0082] [Table 5]

[0083] [Table 6]

[0084] [Table 7]

[0085] [Table 8]

[0086] (Example of transmission loss calculation) To confirm the influence of the dielectric properties of the glass substrate materials in Examples 1 to 6 on the transmission loss of high-frequency signals, we calculated the transmission loss of the transmission line using a simplified model. The analysis method used was the commercially available moment-method simulator Sonnet Lite® (manufactured by Sonnet Software, Inc.). The transmission line was a microstrip line (MSL). The analysis model was as follows: The copper wiring layer formed on one main surface of the glass substrate was specified to have a width (shown in Tables 9 to 12) that would result in a characteristic impedance of 50 Ω, and the S parameters (scattering parameter S21) from 1 GHz to 110 GHz were calculated. The surface roughness of the copper layer was set to be sufficiently smooth so that the skin effect was not a problem. The calculated S21 (transmission characteristics) is shown in Figure 2. The signal transmission loss values ​​at 35 GHz and 110 GHz are also shown in Tables 9 to 12.

[0087] [Table 9]

[0088] [Table 10]

[0089] [Table 11]

[0090] [Table 12]

[0091] As shown in Figure 2 and Tables 9 to 12, circuit boards using the glass substrates of Examples 1 to 3 and 7 to 25 have improved transmission characteristics in the high frequency range compared to circuit boards using the conventional soda-lime glass substrate of Example 4 and the conventional alkali-free glass substrate of Example 5, and can achieve low transmission loss characteristics in the high frequency range similar to those of the circuit board using the conventional quartz glass substrate of Example 6. The quartz glass substrate of Example 6 has a small thermal expansion coefficient of 0.7 ppm / °C, so when it is used to construct an electronic device, the difference in thermal expansion coefficient with other components becomes too large to provide a practical electronic device. Note that, as shown in Example 5, conventional alkali-free glass substrates, although alkali-free, contain approximately 0.05 to 0.1% of alkali components.

[0092] As an example of ultraviolet transmittance, the transmittance values ​​at wavelengths of 250, 300, and 350 nm were measured for the glass of Example 21 at thicknesses of 0.5 mm and 1.0 mm when the Fe2O3 content was varied. The measurement results are shown in Table 13. The transmittance was measured using a visible-ultraviolet spectrophotometer. This shows that the ultraviolet transmittance of the glass can be adjusted to a desired value by adjusting the glass thickness and Fe2O3 content.

[0093] [Table 13] [Industrial Applicability]

[0094] The glass substrate for high-frequency devices of the present invention has excellent dielectric loss properties for high-frequency signals. Furthermore, circuit boards using such glass substrates have excellent transmission loss properties for high-frequency signals. Such glass substrates and circuit boards are useful for high-frequency electronic devices in general that handle high-frequency signals exceeding 10 GHz, particularly high-frequency signals exceeding 30 GHz, and even high-frequency signals of 35 GHz or higher, such as glass substrates for communication equipment, frequency filter components such as SAW devices and FBARs, bandpass filters such as waveguides, SIW (Substrate Integrated Waveguide) components, radar components, and antenna components (particularly liquid crystal antennas that are considered optimal for satellite communications). [Explanation of symbols]

[0095] 1...circuit board, 2...glass substrate, 2a, 2b...main surfaces, 3, 4...wiring layers.

Claims

[Claim 1] The total content of alkali metal oxides is in the range of 0.001 to 5% in terms of mole percentage based on oxides, and among the alkali metal oxides, Na ２ O / (Na ２ O+K ２ O) is in the range of 0.01 to 0.99, and Al ２ O ３ and B ２ O ３ The total content of these is in the range of 1 to 40%, and Al ２ O ３ / (Al ２ O ３ +B ２ O ３ ) is in the range of 0 to 0.45, ２ A glass substrate mainly composed of A glass substrate for a high frequency device, wherein at least one main surface of the glass substrate has a surface roughness of 1.5 nm or less as an arithmetic mean roughness Ra value, and a dielectric loss tangent at 35 GHz of 0.007 or less.

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