JP2891375B2 - Ceramic substrate for high-speed electronic components and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate for a high-speed electronic component having a signal line capable of transmitting a high-frequency signal with a short propagation delay time and low noise.

[Prior Art] With recent miniaturization and high performance of electronic devices, signal lines capable of transmitting high-frequency signals with a short propagation delay time and low noise are densely mounted on ceramic substrates for mounting electronic components. Demand for ceramic substrates provided is increasing.

Recently, as a ceramic substrate having a signal line for transmitting a high-frequency signal, a ceramic having a low dielectric constant, a ceramic mainly containing mullite or silica, or a composite ceramic mainly containing alumina-borosilicate glass has recently been used. Ceramic substrates have been developed and used.
In other words, a conventionally used ceramic mainly composed of alumina has a dielectric constant of 9.4 at 1 MHz, whereas a ceramic mainly composed of mullite has a low dielectric constant of 7.3 at 1 MHz, for example.

The propagation delay time T _pd of a high-frequency signal transmitted through a signal line provided on a ceramic substrate is expressed by the following equation, where ε is the dielectric constant of the ceramic forming the substrate, and C is the light speed.

From this equation, it can be seen that if the ceramic substrate is formed from the above-mentioned ceramic having a low dielectric constant ε, the propagation delay time T _pd of the high-frequency signal transmitted through the signal line provided on the substrate can be reduced.

In recent years, the signal lines provided on a ceramic substrate have been increased in density, and as the frequency of signals transmitted through the signal lines has increased, the other signal has been transmitted to one signal line via a ceramic substrate which is a dielectric material. The crosstalk problem in which noise is mixed in from the line is becoming serious.

Therefore, recently, as described in Japanese Patent Application Laid-Open Nos. 1-227492 and 1-239995, a ceramic substrate in which the periphery of a signal line is surrounded by a film-like or lattice-like ground wall is used. Proposed. That is, according to this ceramic substrate, the signal line is formed in a coaxial structure or a pseudo-coaxial structure with the ground wall, and it is possible to prevent noise from being mixed into the signal line from another signal line.

Here, the coaxial structure refers to a structure in which the periphery of the signal line is surrounded by a film-like ground wall having no gap, and the pseudo coaxial structure refers to a lattice having a gap, a mesh shape, or a partial lattice shape surrounding the signal line. It refers to what is surrounded by a ground wall such as a film in another part.

[Problems to be Solved by the Invention] However, the above-mentioned ceramics having a low dielectric constant are inferior in mechanical strength as compared with a commonly used ceramic mainly composed of alumina or the like. That is, a ceramic containing alumina as a main component has a strength of 35 kg / mm ² , whereas a ceramic having a low dielectric constant such as mullite as a main component has a flexural strength of only ²⁰ to 30 kg / mm ² . Therefore, when the ceramic substrate is formed from the above-mentioned ceramic having a low dielectric constant, cracks are easily generated in the substrate, and there has been a problem that the reliability of the substrate is reduced.

The present invention has been made in view of such problems,
Equipped with a signal line that can transmit recent high-frequency signals with a short propagation delay time and without introducing noise.
It is an object of the present invention to provide a highly reliable ceramic substrate having high mechanical strength, and a method for manufacturing a ceramic substrate capable of easily and quickly forming the substrate without trouble.

[Means for Solving the Problems] For the purpose described above, the ceramic substrate of the present invention provides a signal having a coaxial structure or a pseudo coaxial structure in which a ceramic member is surrounded by a ground wall such as a film, a lattice, or a net. In a ceramic substrate having a line, a ceramic having high mechanical strength is used for an external ceramic member outside the ground wall, and a low dielectric constant ceramic is used for an internal ceramic member around a signal line inside the ground wall. And

Further, a method of manufacturing a ceramic substrate according to the present invention includes the following steps.

a. A step of applying a metallizing paste for forming a ground wall on a surface of a lower green sheet for forming an external ceramic member having high mechanical strength in a film shape, a lattice shape or a net shape, and drying.

b. A step of applying and drying a ceramic paste for forming an internal ceramic member having a low dielectric constant on the surface of the metallized paste for forming a ground wall dried in the step a).

c. A step of linearly applying a metallization paste for forming a signal line on the surface of the ceramic paste for forming the internal ceramic member dried in the step b, and drying.

d. A ceramic paste for forming an internal ceramic member having a low dielectric constant is applied to the surface of the ceramic paste for forming the internal ceramic member applied in the step b, including the surface of the metallized paste for forming the signal line dried in the step c. And drying.

e. The metallizing paste for forming the ground wall is applied to the surface of the metallizing paste for forming the ground wall, including the surface of the ceramic paste for forming the internal ceramic member, which has been dried in the step d, and the metallizing paste for forming the ground wall is formed into a film, lattice or net shape. Step of applying and drying.

f. An upper green sheet for forming an external ceramic member having high mechanical strength is stacked on the surface of the metallized paste for forming a ground wall dried in the step e, and
b, c, d, and heating the upper and lower green sheets sandwiching the metallized paste and the ceramic paste applied in the steps while pressing the inner and lower green sheets, and the upper and lower green sheets, the metallized paste,
A step of integrally firing the upper and lower green sheets, the ceramic paste, and the metallized paste while the ceramic pastes are in close contact with each other.

In the method for manufacturing a ceramic substrate according to the present invention, b, c, d,
e) heating the metallized paste or / and ceramic paste applied before that together with the lower green sheet while pressing the metallized paste and / or ceramic paste from above over a protective metal film with a smooth metal plate before at least one step of e. ,
The metallizing paste and / or the ceramic paste may be buried inside the lower green sheet, or an organic solvent may be applied to the surface of the upper green sheet to soften the surface of the upper green sheet before the step f. It is preferred.

Further, in the method of manufacturing a ceramic substrate according to the present invention, the upper and lower green sheets for forming the external ceramic member use ceramic green sheets containing alumina as a main component, and mullite is mainly used for the ceramic paste for forming the internal ceramic member. Use a ceramic paste as a component, and use a metallized paste containing tungsten or molybdenum as a main component for the metallization paste for forming signal lines and ground walls, or use mullite for the upper and lower green sheets for forming external ceramic members. A ceramic green sheet as a component is used, a ceramic paste containing silica as a main component is used as a ceramic paste for forming an internal ceramic member, and tungsten or a metal is used as a metallization paste for forming a signal line and a ground wall. Use metallized paste containing butene as the main component, or use ceramic green sheets containing aluminum nitride as the main component for the upper and lower green sheets for forming the external ceramic member, and use boron nitride for the ceramic paste for forming the internal ceramic member. Use a metal paste containing tungsten or molybdenum as the main metallization paste for forming signal lines and ground walls, or use alumina paste for upper and lower green sheets for forming external ceramic members. Using a composite ceramic green sheet mainly composed of borosilicate glass, using a composite ceramic paste mainly composed of silica-borosilicate glass as a ceramic paste for forming an internal ceramic member, and forming a signal line and It is preferred and the use of metallized paste on camera rise paste lands wall forming gold, as a main component silver or copper.

[Operation] In the ceramic substrate having the above-described configuration, a low dielectric constant ceramic such as a ceramic mainly composed of mullite or silica or a silica-borosilicate glass is used for the internal ceramic member surrounding the signal line inside the ground wall. A composite ceramic as a main component is used. Therefore, the propagation delay time T _pd of the high-frequency signal transmitted through the signal line surrounded by the low dielectric constant internal ceramic member is suppressed to be short, and the high-frequency signal is transmitted quickly through the signal line.
This is because, in a signal line having a coaxial structure or a pseudo coaxial structure, an electric field generated around the line is confined inside the ground wall, and the propagation delay time T _pd of a signal transmitted through the signal line is _equal to the (1). This is because, as shown in the equation, the length is reduced in proportion to the square root of the dielectric constant ε of the internal ceramic member inside the ground wall.

In addition, an external ceramic member covering the periphery of the internal ceramic member via a ground wall is made of a ceramic having high mechanical strength, such as alumina, mullite, aluminum nitride, or the like as a main component, or alumina-borosilicate or the like as a main component. Composite ceramic is used. Therefore, the external ceramic member with high mechanical strength
By compensating for the mechanical strength of the low dielectric constant internal ceramic member having low mechanical strength around the signal line, the mechanical strength of the ceramic substrate is increased.

In the method for manufacturing a ceramic substrate according to the present invention comprising the above steps, the metallized paste for forming a ground wall is formed on the surface of the lower green sheet through the ceramic paste for forming an internal ceramic member around the metallized paste for forming a signal line. When forming a signal line forming body having a coaxial structure or a pseudo coaxial structure surrounded by, a ceramic paste for forming an internal ceramic member is simultaneously applied to both sides of a linear metallizing paste for forming a signal line and an upper surface thereof at a time. Or the metallizing paste for forming the ground wall on the surface of the metallizing paste for forming the ground wall on the surface of the lower green sheet applied in step a including the surface of the applied ceramic paste at the same time in the form of a film, lattice or net at a time. Or applied. Therefore, a signal line forming body formed by applying the ceramic paste and the metallizing paste on the surface of the lower green sheet can be formed easily and quickly.

In the method of manufacturing a ceramic substrate according to the present invention, the metallized paste and / or the ceramic paste applied before the step f may be buried inside the lower green sheet, or the surface of the upper green sheet may be softened before the step f. In the manufacturing method, when the upper and lower green sheets are heated while being pressed inward in the step f, the metallized paste or / and ceramic paste sandwiched between the upper and lower green sheets are crushed. The metallized paste and / or ceramic paste sandwiched between the upper and lower green sheets can be securely adhered to the buried state without breaking its shape. Then, when they are integrally fired, delamination (peeling) between them can be properly prevented.

In the method of manufacturing a ceramic substrate according to the present invention, the upper and lower green sheets, the ceramic paste, and the metallized paste each include a ceramic green sheet mainly containing alumina, a ceramic paste mainly containing mullite, tungsten, or molybdenum. In the manufacturing method using the above-listed combinations such as metallized pastes as components, the green sheets of these combinations, ceramic paste, when forming a ceramic substrate by integrally firing the metallized paste, The thermal stress based on the difference in thermal expansion coefficient when sintering causes cracks in the substrate, and the interaction between them causes the external ceramic member, the internal ceramic member, and the signal line to contain foreign substances from other members. Forgive and invade Or lowering the mechanical strength of the outer ceramic member, or increase the dielectric constant of the inner ceramic member, without and increasing the conductor resistance of the signal line to form a ceramic substrate of the present invention.

Example Next, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a preferred embodiment of the ceramic substrate of the present invention, and specifically shows a side sectional view thereof. Hereinafter, the embodiment in this figure will be described.

In the figure, reference numeral 10 denotes an external ceramic member forming a ceramic substrate main body. As the external ceramic member 10, a ceramic having high mechanical strength, mainly composed of alumina, mullite or aluminum nitride, or a composite ceramic mainly composed of alumina-borosilicate glass or the like is used.

Reference numeral 20 denotes a signal line provided inside the external ceramic member 10 for transmitting a high-frequency signal. For this signal line 20, metallization mainly containing tungsten or molybdenum having a high conductor resistance or metalization mainly containing gold, silver or copper having a low conductor resistance is used.

An internal ceramic member 30 surrounds the signal line 20 inside the external ceramic member 10 without any gap. As the internal ceramic member 30, a ceramic having a low dielectric constant and mainly containing mullite, silica, boron nitride, silicon nitride, or the like, or a composite ceramic mainly containing silica-borosilicate glass or the like is used.

Reference numeral 40 denotes a film-like, lattice-like, or net-like ground wall that covers the periphery of the internal ceramic member 30 surrounding the signal line 20. For the ground wall 40, metallization mainly containing tungsten or molybdenum, or metallization mainly containing gold, silver or copper is used.

The ceramic substrate shown in FIG. 1 is configured as described above, and according to this ceramic substrate, its signal line
20 is surrounded by an internal ceramic member 30 made of the ceramic having a low dielectric constant, and the surrounding of the internal ceramic member 30 is covered by a ground wall 40 made of metallization, so that a high-frequency signal propagates through the signal line 20 in a propagation delay time. The signal is transmitted short and quickly, and noise is not mixed into the signal line 20 from another signal line. In addition, since the periphery of the internal ceramic member 30 made of the ceramic having low mechanical strength and low dielectric constant around the signal line 20 is covered with the external ceramic member 10 made of ceramic having high mechanical strength in a reinforcing manner, the ceramic substrate Mechanical strength is increased.

In the illustrated embodiment, the periphery of the signal line 20 is cylindrically covered by the ground wall 40 via the internal ceramic member 30, but the periphery of the signal line 20 is covered by the ground wall via the internal ceramic member 30. 40 may cover the shape of a square tube, an elliptical tube, or the like. Even in such a case, a ceramic substrate having the same operation as the above-described embodiment can be formed.

2 to 7 show a preferred embodiment of the method for manufacturing a ceramic substrate according to the present invention, and more specifically show explanatory views of the manufacturing process. Hereinafter, the embodiment in this figure will be described.

a. A lower green sheet 100 for forming an external ceramic member having high mechanical strength is prepared. This lower green sheet 1
For 00, a ceramic green sheet mainly composed of alumina or mullite for forming a ceramic having high mechanical strength or a composite ceramic green sheet mainly composed of alumina-borosilicate glass or the like is used. And
As shown in FIG. 2, a metallizing paste 400 for forming a ground wall is applied to the surface of the lower green sheet 100 in the form of a film, a lattice, or a mesh (in the figure, the film is formed), and the metallization is applied. The organic solvent or the like inside the paste 400 is scattered in the outside air by heating or the like, and dried. As the metallization paste 400, a metallization paste containing tungsten, molybdenum, gold, silver, or copper as a main component is used.

b. Next, as shown in FIG. 3, a ceramic paste 300 for forming an internal ceramic member having a low dielectric constant is applied in a strip shape on the surface of the dried metallized paste 400, and By heating the ceramic paste 300 or the like, the organic solvent or the like inside the ceramic paste 300 is scattered in the outside air and dried. As the ceramic paste 300, a ceramic paste mainly containing mullite or silica for forming a ceramic having a low dielectric constant, or a composite ceramic paste mainly containing silica-borosilicate glass or the like is used.

c. Next, as shown in FIG. 4, a metallization paste 200 for forming a signal line is applied linearly to the center of the surface of the dried belt-like ceramic paste 300 in a vertical direction, and the metallization paste is applied. The organic solvent or the like inside the 200 is scattered in the outside air by heating or the like and dried. The metallizing paste 200 includes a metallizing paste 7 mainly containing tungsten or molybdenum for forming a metallized metal having a high conductor resistance, a metal for forming a metallized metal having a low conductor resistance, similar to those used in the step a, A metallized paste containing silver or copper as a main component is used.

d. Next, as shown in FIG. 5, on the surface of the band-shaped ceramic paste 300 applied in the step b including the surface of the metallized paste 200 applied in the step c, a ceramic for forming a low dielectric constant internal ceramic member is formed. The paste 300 is applied, and the organic solvent and the like inside the ceramic paste 300 are scattered in the outside air by heating or the like, and dried. As the ceramic paste 300, the same ceramic paste as that used in the step b for forming a ceramic having a low dielectric constant is used.

In steps b, c and d, the ceramic paste
3 and 4 and 5
Band-like or linear slits on the surface as shown by the broken lines in the figure
Using a screen 50 having 52 holes, it is preferable to apply it in a band or a line by a screen printing technique.

e. Next, as shown in FIG. 6, the metallized paste 400 for forming the ground wall was widely applied to the surface of the metallized paste 400 applied in the step a, including the surface of the ceramic paste 300 applied in the step d. The metallized paste 400 is applied in a lattice shape or a net shape (in the drawing, a film shape) or the like, and the organic solvent or the like in the metallized paste 400 is scattered in the outside air and dried. As the metallization paste 400, the same metallization paste as that used in the step a is used.

In the steps a and e, the metallized paste 400
Is applied in a grid or mesh pattern, it is preferable to apply the screen by a screen printing technique using a screen (not shown) having a grid or mesh slit on the surface.

f. Thereafter, as shown in FIG. 7, an upper green sheet 100 for forming an external ceramic member having high mechanical strength is stacked on the surface of the metallized paste 400 applied in the step e. As the upper green sheet 100, the above-mentioned green sheet for forming a ceramic having high mechanical strength similar to that used in the step a is used. And a, b, c,
The upper and lower green sheets 100 sandwiching the metallized pastes 400 and 200 and the ceramic paste 300 applied in the steps d and e are heated while being pressed inside, and the upper and lower green sheets 100 for forming these external ceramic members are formed. The ceramic paste 300 for forming the internal ceramic member and the metallized pastes 200 and 400 for forming the signal line and the ground wall are brought into close contact with each other without any gap. In that case, just in case, the upper and lower green sheets 100, metallizing paste 400, 20
0. It is preferable that the ceramic paste 300 is heated for a predetermined time, and the organic components that hinder the sintering of the ceramic paste 300 are scattered from the inside into the outside air to be removed. Then, the upper and lower green sheets 100, the metallized pastes 400 and 200, and the ceramic paste 300 are integrally fired by, for example, being placed in a furnace.

In the above-mentioned steps a, b, c, d, e, and f, when the upper and lower green sheets 100 are made of ceramic green sheets mainly composed of alumina or the like sintered at a high temperature, the metallizing paste is adjusted accordingly. 400,
The upper and lower green sheets are made of metallized paste mainly composed of tungsten or molybdenum and ceramic paste mainly composed of mullite etc., which are sintered at high temperature to 200 and ceramic paste 300 respectively.
When a composite ceramic green sheet containing alumina-borosilicate glass or the like as a main component that is sintered at a low temperature to 100 is used, a metallizing paste 400, 200
It is necessary to use a metallized paste mainly composed of gold, silver or copper and a composite ceramic paste mainly composed of silica-borosilicate glass, etc., which are sintered at a low temperature to the ceramic paste 300 and the ceramic paste 300, respectively. This is because otherwise, the upper and lower green sheets 100, the metallized pastes 400, 200, and the ceramic paste 300 cannot be simultaneously and integrally fired at a high or low temperature.

Further, the thickness of the ceramic paste 300 applied in the steps b and d is equal to or greater than the thickness of the metallized paste 200 applied in the step c, and the width of the metallized paste 200 applied in the step c is applied in the steps b and d. It is preferable that the width is not more than 1/3 of the width of the ceramic paste 300. This is because, by doing so, when the upper and lower green sheets 100 are heated while being pressed inward in the step f, the metallized paste 20 sandwiched therebetween is heated.
The metallized paste 200 for forming the signal line leaks out of the ceramic paste 300 for forming the internal ceramic member, because the shape of the 0,400 or the ceramic paste 300 is broken.
This is because it is possible to accurately prevent the metallized paste 400 for forming the ground wall from being short-circuited.

In addition, the upper and lower green sheets 100 used in the steps a and f are not very dense, and the organic components are included by changing the inorganic component powder distribution, the inorganic / organic component ratio, and the kneading conditions thereof. It is preferable that the relative density of all the components with respect to the theoretical density be around 70 to 80%. This is because if the upper and lower green sheets 100 are too dense, as shown in FIG. 7, when the upper and lower green sheets 100 are heated while being pressed inward in the step f, they are sandwiched between them. Metallized paste 200,
If 400 or the ceramic paste 300 is crushed and its shape collapses, or if the metallized paste 400, 200 or the ceramic paste 300 sandwiched between the upper and lower green sheets 100 is buried tightly and closely adhered Instead, when the upper and lower green sheets 100, the metallized pastes 400, 200, and the ceramic paste 300 are integrally fired, a gap is formed between them and they cause delamination (peeling). is there.

In order to prevent such delamination, f
Before the process, before the b, c, d, e before the process, even before the metallizing paste 400,
200 and the ceramic paste 300 are heated from above with the lower green sheet 100 while pressing with a smooth metal plate (not shown) through a protective film (not shown) made of plastic, etc. Metallizing paste 40
0,200 or ceramic paste 300 with lower green sheet 10
0 Make sure it is buried inside, or before f process,
If the surface of the upper green sheet 100 is coated with an organic solvent such as a phthalic acid ester that dissolves the binder in the green sheet, and the surface of the upper green sheet 100 is softened, the upper and lower green sheets 10 are formed in step f.
0400,200 metallized paste sandwiched between them
And the ceramic paste 300 are firmly buried without gaps without losing their shape, and their upper and lower green sheets 100, metallized pastes 400, 2
When the ceramic pastes 300 are integrally fired, delamination between them can be properly prevented.

In addition, before the step f, as shown in FIG.
In the valley 402 of the metallized paste 400 applied in the process, the ceramic paste 300 or the metallized paste 400 (in the figure,
Ceramic paste) and apply the valley
402 is filled with a paste or, as shown in FIG. 10, a groove 102 is provided in a band shape on the surface of the upper green sheet 100 used in the step f, and the groove 102 is sandwiched between the upper and lower green sheets 100. Metallized paste 400,2
00 or ceramic paste 300,
In the process, the metallized paste 400, 200 and the ceramic paste 300 sandwiched between the upper and lower green sheets 100 are closely adhered to the state buried without gaps without breaking their shapes, and when they are integrally fired, A gap may be formed between them, so that they can be more appropriately prevented from causing delamination.

In addition, in order to prevent the delamination, the metallized pastes 400 and 200, and the shape of the ceramic paste 300 from being deformed, the pressure and the heating temperature applied to press the upper and lower green sheets 100 inward in the step f. Setting is important, and its pressure and heating temperature,
It is necessary to adjust according to the combination of the upper and lower green sheets 100, metallized pastes 400 and 200, and ceramic paste 300.

In the case where the metallizing paste 400 for forming the ground wall is applied in a grid or mesh shape in the steps a and e, the upper and lower green sheets for forming the external ceramic member are formed.
100 Metallizing paste 400 for ground wall formation on the surface
The ceramic paste 300 for forming the internal ceramic member is in direct contact with the metallized paste 400 for forming the ground wall, and the barrier effect of the metallized paste 400 for forming the ground wall is weakened. Paste 300, Metallized paste 40
When the ceramic paste 300 is fired integrally, an interaction or diffusion occurs between the upper and lower green sheets 100 and the ceramic paste 300, and the dielectric constant of the internal ceramic member 30 formed by sintering the ceramic paste 300 is reduced. There is a possibility that the mechanical strength of the external ceramic member 10 formed by sintering the upper and lower green sheets 100 may decrease or the mechanical strength of the external ceramic member 10 may decrease. Therefore, when the metallizing paste 400 for forming the ground wall is applied in a lattice or mesh shape as described above, when the upper and lower green sheets 100 and the ceramic paste 300 are integrally fired,
It is necessary to use a combination that does not cause the above-described interaction or diffusion.

Also, the upper and lower green sheets 100,
When the metallized pastes 400 and 200 and the ceramic paste 300 are integrally fired, the upper and lower green sheets 100 and metallized to prevent the substrate from cracking due to thermal stress based on the difference in coefficient of thermal expansion when they are sintered. To the pastes 400 and 200 and the ceramic paste 300, a sintering aid for adjusting the densification start time and shrinkage speed when sintering them may be appropriately added as necessary.

The method of manufacturing the ceramic substrate shown in FIGS. 1 to 7 comprises the above steps. By the above steps, a low dielectric constant internal ceramic member 30 is formed around the signal line 20 as shown in FIG. Through, and covered with a ground wall 40 such as a film, a lattice, or a net, and around the ground wall 40,
The ceramic substrate of the present invention, which is reinforced and covered with the external ceramic member 10, can be formed.

Hereinafter, preferred examples of ceramic substrates formed by the above-described manufacturing method and unsuitable comparative examples will be described.

Example 1 A green sheet mainly composed of alumina was used for upper and lower green sheets for forming an external ceramic member, a ceramic paste mainly composed of mullite was used for a ceramic paste for forming an internal ceramic member, and a signal line and a ground were used. A metallizing paste containing tungsten or molybdenum as a main component was used as a metallizing paste for forming a wall. Then, the upper and lower green sheets sandwiching the metallized paste and the ceramic paste were heated at about 60 ° C. for about 10 minutes while pressing the inside of the upper and lower green sheets at, for example, 200 kg / cm ² to bring them into close contact with each other. . Also, just in case, the upper and lower green sheets, ceramic paste, and metallized paste are heated in a humid nitrogen atmosphere at a temperature of 750 ° C. or less for about 5 hours to prevent sintering. The resulting organic components were scattered from the inside into the outside air and removed. Then, the upper and lower green sheets 100, metallized pastes 400 and 200, and ceramic paste 300 were integrally fired at a high temperature of 1500 to 1600 ° C. in a weak reducing atmosphere to form a ceramic substrate. Here, the reason why the ceramic substrate is fired in the weakly reducing atmosphere as described above is to prevent the metallized paste from causing an oxidation reaction during firing. Further, in order to match the sintering behavior of the upper and lower green sheets and the ceramic paste, that is, the sintering temperature thereof, an alumina ceramic green sheet having a purity of 92 to 96% is used for the upper and lower green sheets, and the ceramic paste has a purity of 92 to 96%. 95-99%
And a sintering aid was added to each of the upper and lower green sheets and the ceramic paste. Then, the periphery of the signal line is surrounded by an internal ceramic member made of a ceramic mainly composed of mullite having a low dielectric constant of 7.3 at 1 MHz, and the periphery of the internal ceramic member is grounded through a ground wall made of metallization. Flexural strength 35Kg / mm ²
As a result, a ceramic substrate having high mechanical strength and high heat radiation was obtained, which was reinforced and covered with an external ceramic member made of ceramic containing alumina as a main component and having a high thermal conductivity of 15 W / mK. The coefficient of thermal expansion of the ceramic mainly composed of mullite is 4.5 × 10 ⁻⁶ / ° C., and the coefficient of thermal expansion of the ceramic mainly composed of alumina is 7.2 × 10 ⁻⁶ / ° C.
When they are sintered, thermal stress works between them,
Since the volume ratio of the ceramic mainly composed of mullite to the entire ceramic substrate was small, its thermal stress was small, and no cracks occurred in the ceramic substrate during firing.

Example 2 A ceramic line mainly composed of mullite was used for upper and lower green sheets for forming an external ceramic member, and a ceramic paste mainly composed of silica was used for a ceramic paste for forming an internal ceramic member. A metallizing paste containing tungsten or molybdenum as a main component was used as the metallizing paste for forming the ground wall. Then, in the same manner as in the first embodiment, the upper and lower green sheets sandwiching the metallized paste and the ceramic paste are heated while being pressed inside, so that they are brought into close contact with each other. A 1500 ~
By firing at a high temperature of 1600 ° C., a ceramic substrate was formed. Since silica alone does not easily become dense during sintering, a sintering aid combining mullite, alumina and a IIIa compound of a rare earth element is added to a ceramic paste containing silica as a main component. did.
Then, a ceramic mainly composed of silica having a low dielectric constant of 3.5 at 1 MHz is used for the inner ceramic member, and its mechanical strength is extremely low alone. strength 20~30Kg / mm ²
As a result, a ceramic substrate having high mechanical strength and high heat dissipation was obtained using a ceramic containing mullite as a main component and having a high thermal conductivity of 7 W / mK.

Comparative Example 1 The upper and lower green sheets for forming the external ceramic member were formed of ceramic green sheets containing mullite as a main component, and the ceramic paste for forming the internal ceramic member was formed of ceramic paste containing forsterite as a main component. A metallizing paste containing tungsten or molybdenum as a main component was used as a metallizing paste for forming a ground wall. Then, in the same manner as in Examples 1 and 2, the upper and lower green sheets sandwiching the metallized paste and the ceramic paste are heated while being pressed inside, so that they are brought into close contact with each other. Then, they were integrally fired at a high temperature to form a ceramic substrate. Then, the ceramic having mullite as a main component has a thermal expansion coefficient of 4.5 × 10 ⁻⁶ / ° C., and the ceramic having forsterite as a main component has a thermal expansion coefficient of 10.5 × 10 ⁻⁶ / ° C., Because there is a large difference in the thermal expansion coefficient between the two, when the ceramic substrate is fired, the metallizing paste for forming the ground wall interposed between them slightly acts as a buffer barrier due to the thermal stress acting between them. A crack has occurred in the substrate. In addition, when the ceramic green sheet containing mullite as a main component and the ceramic paste containing forsterite as a main component are simultaneously fired at a high temperature of 1500 to 1600 ° C., a ground wall interposed therebetween is provided. Although the metallizing paste for forming slightly plays a role of a barrier, the boundary between the two is liquefied due to chemical interaction and mixes with each other, and the main component is forsterite which surrounds the periphery of the signal line. The dielectric constant of the internal ceramic member made of ceramic has increased.

Example 3 A ceramic green sheet containing aluminum nitride as a main component was used for upper and lower green sheets for forming an external ceramic member, and a ceramic paste containing hexagonal boron nitride as a main component was used as a ceramic paste for forming an internal ceramic member. A metallization paste containing tungsten or molybdenum as a main component was used as a metallization paste for forming a signal line and a ground wall. Then, the upper and lower green sheets sandwiching the metallized paste and the ceramic paste are heated while being pressed inside, so that they are brought into close contact with each other. The ceramic substrate was formed by firing integrally in a reducing atmosphere. In addition, when boron nitride is sintered, the densification does not proceed by itself. Therefore, the ceramic paste containing boron nitride as a main component includes aluminum nitride as a sintering aid,
Calcium carbonate, yttrium oxide, and other Group IIa and IIIa compounds of the periodic table were added. Then, the signal propagation delay time of the signal line is kept short by using an internal ceramic member made of a ceramic mainly composed of boron nitride having a low dielectric constant, which is difficult to use because of its low mechanical strength. A highly reliable ceramic substrate was obtained in which the mechanical strength of the substrate was increased by using an external ceramic member made of a ceramic containing aluminum nitride as a main component. In this case, a good ceramic substrate can be formed even when the substrate is fired at a temperature of 1800 to 1900 ° C. In such a case, a ceramic paste mainly containing boron nitride for forming an internal ceramic member is formed at the time of firing the substrate. And tungsten or molybdenum metallizing paste for forming a signal line interact with each other to generate tungsten boride, which significantly increases the conductor resistance of the signal line and causes the signal transmitted through the signal line to become less conductive. Since the conductor loss increases, the firing temperature of the substrate is preferably set to 1800 ° C. or lower.

Comparative Example 2 A signal line using a ceramic green sheet containing aluminum nitride as a main component for upper and lower green sheets for forming an external ceramic member, and a ceramic paste containing mullite as a main component as a ceramic paste for forming an internal ceramic member. A metallizing paste containing tungsten or molybdenum as a main component was used as a metallizing paste for forming a ground wall. Then, the upper and lower green sheets sandwiching the metallized paste and the ceramic paste are heated while being pressed inside, so that they are brought into close contact with each other, and they are sintered with a ceramic mainly composed of mullite. A high temperature was applied in the same wet reducing atmosphere as in the case of firing to integrally fire and form a ceramic substrate. As a result, an external ceramic member made of a ceramic containing aluminum nitride as a main component caused an oxidation reaction in the wet reducing atmosphere, and a good ceramic substrate could not be obtained. Therefore, the upper and lower green sheets, ceramic paste, and metallized paste are then integrally fired at a high temperature in the same nitrogen neutral atmosphere as when sintering a ceramic mainly containing aluminum nitride, A ceramic substrate was formed. Then, due to the residual carbon present in the furnace and the like at the time of firing the substrate and the nitrogen in the nitrogen-neutral atmosphere, the internal ceramic member made of mullite-based ceramic is nitrided, and cracks are generated on its surface and inside. A good ceramic substrate can be obtained because the ceramic mainly composed of mullite diffuses into the external ceramic member made of ceramic mainly composed of aluminum nitride and blackens the external ceramic member. Did not. That is, a ceramic mainly composed of mullite and a ceramic mainly composed of aluminum nitride are:
Since their thermal expansion coefficients are almost the same as around 4.5 × 10 ⁻⁶ / ° C., respectively, it is considered to be a good combination as the ceramic substrate forming member of the present invention. There was found.

Example 4 Composite ceramic green sheets containing alumina-borosilicate glass as a main component were used for upper and lower green sheets for forming an external ceramic member, and silica-borosilicate glass was used as a main component for a ceramic paste for forming an internal ceramic member. A metallizing paste containing gold, silver or copper as a main component was used as a metallizing paste for forming signal lines and ground walls. Then, the upper and lower green sheets sandwiching the metallized paste and the ceramic paste are heated while being pressed inside, so that they are brought into close contact with each other, and the metallized paste is mainly composed of gold or silver. When metallizing paste is used, it is baked in air at a temperature of 850 to 1000 ° C in air, and in a neutral or reducing atmosphere, when using metallizing paste containing copper as the main component. hand,
A ceramic substrate was formed. Further, matching of the heat shrinkage behavior of the upper and lower green sheets, the ceramic paste, and the metallized paste during sintering was performed by controlling the particle size distribution of the powder components constituting them. Then, the composite ceramic containing alumina-borosilicate glass as the main component and the composite ceramic containing silica-borosilicate glass as the main component have the same matrix component, so that no interaction occurs between them. 1MHz that is difficult to use alone because of its low mechanical strength
The dielectric constant of the low dielectric constant of 3.9-silica-borosilicate glass as a main component using an internal ceramic member made of a composite ceramic, while suppressing the signal propagation delay time of the signal line, the bending strength is 20 ~ 25Kg A highly reliable ceramic substrate was obtained in which the mechanical strength of the substrate was increased by using an external ceramic member made of a composite ceramic mainly composed of alumina / borosilicate glass having a thickness of / mm ² . In addition, a ceramic substrate having a signal line made of metallization containing gold, silver or copper as a main component and having a low conductor resistance and capable of transmitting a high-frequency signal with little conductor loss was obtained.

The ceramic substrate of the present invention can be manufactured by a method other than the manufacturing method of the present invention. For example, as shown in FIG. 11 (a), a low dielectric constant internal ceramic member 30 having a signal line 20 at an axis, and a columnar internal ceramic member whose periphery is covered with a ground wall 40.
30 and an external ceramic member 10 having a high mechanical strength for forming a ceramic substrate main body as shown in FIG.
Is fitted into the insertion hole 12 provided in the external ceramic member 10 by press-fitting or using an adhesive, whereby the ceramic substrate of the present invention can be formed. In such cases,
The selection range of the combination of the ceramic paste for forming the internal ceramic member 30, the green sheet for forming the external ceramic member 10, and the metallized paste for forming the signal line 20 and the ground wall 40 is integrated with the ceramic substrate of the present invention. Compared to the above-described manufacturing method of firing, the green sheets, metallized pastes, and ceramic pastes can be further expanded without being limited to the interaction at the time of firing or the difference in their thermal expansion coefficients.

Further, the ceramic substrate of the present invention is disclosed in
It can also be formed by the method for manufacturing a substrate for electronic components described in Japanese Patent Application Laid-Open No. H10-209,878. That is, a ceramic paste for forming a ceramic having a low dielectric constant is used as a ceramic paste for forming an internal ceramic member inside the metallizing paste for forming the ground wall, and a ceramic paste for forming an external ceramic member outside the metallizing paste for forming the ground wall is used. A ceramic paste or a green sheet for forming a ceramic having high mechanical strength may be used as the ceramic paste or the green sheet. However, when this manufacturing method is used,
Compared to the method of manufacturing a ceramic substrate of the present invention, several layers of the paste are used to form a signal line forming body having a coaxial structure composed of the metallized paste and the ceramic paste on the surface of the green sheet forming the substrate body. In addition, the coating must be performed many times, and the coating operation requires a great deal of time and labor.

[Effects of the Invention] As described above, according to the ceramic substrate of the present invention, a signal line having a coaxial structure or a pseudo-coaxial structure capable of transmitting a high-frequency signal with a short propagation delay time _Tpd and without mixing noise is provided. A ceramic substrate comprising:
A highly reliable ceramic substrate having high mechanical strength can be provided.

According to the method for manufacturing a ceramic substrate of the present invention,
Conventionally widely used screen printing technology for applying metallizing paste or ceramic paste to the surface of a green sheet or the like, and technology for integrally firing the metallizing paste or ceramic paste together with the green sheet using the coaxial structure or the pseudo-structure of the present invention. A ceramic substrate having a signal line for transmitting a high-frequency signal having a coaxial structure can be easily and quickly formed without trouble.

[Brief description of the drawings]

FIG. 1 is a partial side sectional view of a ceramic substrate of the present invention, FIGS. 2 to 7 are explanatory views of a method of manufacturing a ceramic substrate of the present invention, and FIG. 8 is formed by a method of manufacturing a ceramic substrate of the present invention. 9 and 10 are explanatory views of a method for preventing delamination, respectively, and FIGS. 11 (a) and (b) are other manufacturing methods of the ceramic substrate of the present invention, respectively. FIG. 10: External ceramic member, 20: Signal line, 30: Internal ceramic member, 40: Ground wall, 50: Screen, 100: Upper or lower green sheet, 200: Metallized paste, 300: Ceramic Paste, 400 ... metallized paste.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-53492 (JP, A) JP-A-55-6807 (JP, A) JP-A-62-131596 (JP, A) JP-A-1- 227492 (JP, A) JP-A-2-12395 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05K 3/46 H01L 23/12

Claims (8)

(57) [Claims] 1. A ceramic substrate having a signal line having a coaxial structure or a pseudo coaxial structure in which a ceramic member is surrounded by a ground wall such as a film shape, a lattice shape, or a net shape, wherein an external ceramic member outside the ground wall is provided. A ceramic substrate for a high-speed electronic component, wherein a ceramic having high mechanical strength is used, and a low dielectric constant ceramic is used for an internal ceramic member around a signal line inside a ground wall. 2. A method for manufacturing a ceramic substrate for high-speed electronic components, comprising the following steps. a. A step of applying a metallizing paste for forming a ground wall on a surface of a lower green sheet for forming an external ceramic member having high mechanical strength in a film shape, a lattice shape or a net shape, and drying. b. A step of applying and drying a ceramic paste for forming an internal ceramic member having a low dielectric constant on the surface of the metallized paste for forming a ground wall dried in the step a). c. A step of linearly applying a metallization paste for forming a signal line on the surface of the ceramic paste for forming the internal ceramic member dried in the step b, and drying. d. A ceramic paste for forming an internal ceramic member having a low dielectric constant is applied to the surface of the ceramic paste for forming the internal ceramic member applied in the step b, including the surface of the metallized paste for forming the signal line dried in the step c. And drying. e. The metallizing paste for forming the ground wall is applied to the surface of the metallizing paste for forming the ground wall, including the surface of the ceramic paste for forming the internal ceramic member, which has been dried in the step d, and the metallizing paste for forming the ground wall is formed into a film, lattice or net shape. Step of applying and drying. f. An upper green sheet for forming an external ceramic member having high mechanical strength is stacked on the surface of the metallized paste for forming a ground wall dried in the step e, and
b, c, d, and heating the upper and lower green sheets sandwiching the metallized paste and the ceramic paste applied in the steps while pressing the inner and lower green sheets, and the upper and lower green sheets, the metallized paste,
A step of integrally firing the upper and lower green sheets, the ceramic paste, and the metallized paste while the ceramic pastes are in close contact with each other. 3. The method according to claim 1, wherein prior to or in addition to step f, b,
Before at least one or more steps of c, d, and e, the previously applied metallized paste or / and ceramic paste are applied from above, via a protective film,
3. The method for manufacturing a ceramic substrate for a high-speed electronic component according to claim 2, wherein the metallized paste and / or the ceramic paste are buried inside the lower green sheet by heating together with the lower green sheet while pressing with a smooth metal plate. 4. The method according to claim 2, wherein an organic solvent is applied to the surface of the upper green sheet before the step f to soften the surface of the upper green sheet. 5. An upper and lower green sheet for forming an external ceramic member using ceramic green sheets containing alumina as a main component, and a ceramic paste for forming an internal ceramic member using a ceramic paste containing mullite as a main component. 5. The method for manufacturing a ceramic substrate for a high-speed electronic component according to claim 2, wherein a metallizing paste containing tungsten or molybdenum as a main component is used as the metallizing paste for forming the line and the ground wall. 6. An upper and lower green sheet for forming an external ceramic member, wherein ceramic green sheets containing mullite as a main component are used, and a ceramic paste containing silica as a main component is used as a ceramic paste for forming an internal ceramic member. 5. The method for manufacturing a ceramic substrate for a high-speed electronic component according to claim 2, wherein a metallizing paste containing tungsten or molybdenum as a main component is used as the metallizing paste for forming the line and the ground wall. 7. A ceramic green sheet mainly containing aluminum nitride is used for upper and lower green sheets for forming an external ceramic member, and a ceramic paste mainly containing boron nitride is used for a ceramic paste for forming an internal ceramic member. 5. The method for manufacturing a ceramic substrate for high-speed electronic components according to claim 2, wherein a metallized paste containing tungsten or molybdenum as a main component is used as a metallized paste for forming signal lines and ground walls. 8. A composite ceramic green sheet mainly composed of alumina-borosilicate glass is used for upper and lower green sheets for forming an external ceramic member, and silica-borosilicate glass is mainly used for a ceramic paste for forming an internal ceramic member. 5. The ceramic substrate for a high-speed electronic component according to claim 2, wherein a composite ceramic paste as a component is used, and a metallized paste containing gold, silver or copper as a main component is used as a signal line and a metallizing paste for forming a ground wall. Manufacturing method.