JPH10194828A - Ceramic multilayered substrate fired at low temperature and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic multilayered substrate ensuring a high signal transmission speed and having >=20kgf/mm<2> bending strength and >=2kgf peeling strength by firing at a low temp. SOLUTION: This ceramic multilayered substrate consists of an inner ceramic insulator layer of a glass-ceramic material having a relative dielectric constant of <=4.5 obtd. by firing powdery starting material consisting of 30-69wt.% borosilicate glass, 5-55wt.% quartz, 5-55wt.% quartz glass, 1-5wt.% alumina and 25-65wt.%, in total, of quartz and quartz glass and outer ceramic insulator layers of a glass-ceramic material having >=25kgf/mm<2> bending strength and consisting of 60-40wt.% cordierite crystallized glass or anorthite crystallized glass and 40-60wt.% alumina.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature fired ceramic multilayer substrate mainly used as a substrate for mounting an electronic component in a ceramic package, the ceramic layer being composed of different ceramic materials for a surface layer and an inner layer, and its manufacture. And how to.

[0002]

2. Description of the Related Art In recent years, as a multi-layer substrate on which highly integrated LSIs and various electronic components are mounted, a ceramic multi-layer substrate using a ceramic material for an insulator layer has been demanded in order to satisfy requirements for miniaturization and high reliability. Has come to be used. The ceramic multilayer substrate is obtained by alternately laminating and integrating ceramic insulator layers and signal wiring layers, and can be manufactured by a green sheet multilayer laminating method or a thick film paste printing method, as is well known. Alumina has been mainly used as a ceramic material due to factors such as thermal conductivity, strength, electrical insulation, and price.

However, since alumina has a large relative dielectric constant of about 9, the signal transmission is slow and the signal delay time is long. The firing temperature of alumina is 1550 ℃
When the multilayer substrate is fired at once by the green sheet laminating method, W or W is added to the signal wiring layer of the multilayer substrate.
It is necessary to use a high melting point metal such as Mo. However, since these metals have high electric resistivity, signal transmission loss increases, and there is a limit to miniaturization of wiring patterns. These drawbacks of the alumina substrate have become a serious problem at present when the operating frequency of the LSI has increased significantly.

As a means for solving this problem, Ag, Ag-Pd, Cu, Au, which have a small relative dielectric constant and can be fired at a low temperature, can be used.
A multilayer substrate using a low-temperature-fired ceramic material has been developed, which can use a metal material having a low melting point and a low electric resistivity for the signal wiring layer.

[0005] A typical low-temperature fired ceramic material is a material also called a glass ceramic manufactured by mixing and firing glass powder that functions as an inorganic binder and inorganic powder that functions as an aggregate for maintaining strength. . Since the glass powder is softened during firing and a sintered body is obtained by combining the inorganic powder of the aggregate, the firing temperature may be slightly higher than the softening point of the glass, and generally,
1100 ° C or less.

Both glass and aggregate (inorganic powder) have a wide variety of types and composition ranges, and there are countless combinations thereof. Since the characteristics of the obtained ceramic substrate change due to the combination of the two and the reaction during firing, it is very difficult to find the best combination of components and firing conditions that can stably achieve the desired characteristics. is there.

For example, in order to lower the relative dielectric constant of a ceramic substrate fired at a low temperature, it is effective to use silicon oxide (SiO ₂ ) having a low relative dielectric constant as an aggregate. It has already been proposed.

As an example, Japanese Patent Publication No. 4-12639 discloses that the aggregate is made of at least two kinds of silicon oxides selected from quartz glass, quartz, cristobalite and tridymite, and the glass is preferably barium borosilicate or borosilicate. Made of magnesium silicate glass, the relative dielectric constant is
Glass ceramic materials of 4.0 to 6.0 are disclosed. By mixing two or more types of silicon oxides having different coefficients of thermal expansion, the coefficient of thermal expansion of the substrate can be controlled.

Japanese Patent Application Laid-Open No. 3-141153 discloses a glass-ceramic material having a low dielectric constant which can be fired at a low temperature of 1000 ° C. or less by adding silicate and / or quartz glass as an aggregate to borosilicate glass. .

However, as the relative permittivity of the glass ceramic material decreases, the mechanical strength tends to decrease at the same time. Therefore, a multilayer board manufactured from this material
It does not have sufficient strength for handling and mounting electronic components.For example, if an external force is applied to the electronic components mounted on the board, the board will break not the connection part but the reliability of the external connection. Inferior. As a result, their use has been very limited.

To improve this problem, Japanese Patent Publication No. 4-51078 discloses a high-strength glass-ceramic material having a tensile strength of 4 kgf / mm ² or more and a relative dielectric constant of 6.
A multilayer substrate made of a glass ceramic material having a low dielectric constant of 0 or less (specifically, about 5.2 to 5.5) has been proposed.

[0012]

When the low dielectric constant material of the inner layer for signal transmission has a relative dielectric constant of 5 to 6 as disclosed in Japanese Patent Publication No. 4-51078, the transmission characteristics are insufficient. In order to achieve the same or better performance as organic materials such as epoxy resin and polyimide, the relative permittivity is 4.
Must be 5 or less. In order to reduce the relative dielectric constant to 4.5 or less, it is conceivable to use silicon oxide having a low relative dielectric constant as an aggregate, as disclosed in Japanese Patent Publication No. 4-12639 and Japanese Patent Application Laid-Open No. 3-141153. However, when silicon oxide was used as the aggregate, the following problems were found.

The silicon oxide mineral generally has a low-temperature type crystalline phase.
(α) and the high-temperature type crystal phase (β).
When β or vice versa transition occurs, rapid volume expansion or contraction occurs. This transition temperature is about 117 for tridymite.
° C, cristobalite is relatively low at about 230 ° C. Solder is generally used for mounting electronic components on ceramic substrates, but recently the reflow method has become widespread, so the entire substrate is heated to the melting temperature of the solder, and in some cases it may exceed 300 ° C. Exposed to extremely high temperatures. In this case, if the ceramic material of the substrate contains tridymite or cristobalite, the above phase transition causes rapid volume expansion and contraction, and micro cracks may occur on the substrate, which greatly reduces the reliability of the substrate. I do.

On the other hand, the above-mentioned transition temperature of quartz is as high as about 573 ° C., and phase transition does not occur by heating applied when mounting electronic components. Quartz glass is amorphous and does not change at a temperature of about 300 ° C. Therefore, when silicon oxide is used as the aggregate having a low relative dielectric constant, quartz or quartz glass is preferable, and cristobalite or tridymite is inappropriate.

Based on this finding, when a glass-ceramic material containing quartz and quartz glass as an aggregate was prepared, it was recognized that an undesired crystal phase of cristobalite might be formed in the sintered body. Although the cause has not been elucidated, it is considered that the aggregate was formed by the reaction of the aggregate with the glass during firing. Japanese Patent Application Laid-Open No. 3-141153 discloses that a raw material comprising borosilicate glass, quartz and quartz glass is
It is described that crystallization of cristobalite does not occur even when calcined at 00 ° C. or lower, but this is considered to be due to a special factor such as a small amount of aggregate.

A low-temperature fired ceramic substrate having silicon oxide as an aggregate and having a low relative dielectric constant has a bending strength of 10 kgf / m 2.
m ² for the lower back and forth as shown in Japanese Patent Kokoku 4-51078, it is effective to strengthen by arranging a high strength material in the surface layer. However, there are countless combinations of glass ceramic materials for the surface layer and the inner layer.Moreover, for example, the thermal expansion coefficients of the surface layer and the inner layer are brought close to each other so that warpage does not occur during batch firing. In addition, new requirements such as sufficient close contact and integration are added, so that selection of each material becomes more difficult.

As described above, noble metals such as Ag, Au and Ag alloys and Cu are used as signal wiring layer materials of the low-temperature fired ceramic multilayer substrate, but they are inexpensive in terms of cost.
It is advantageous to use Cu. Cu also has the advantage that it does not easily react with the substrate and facilitates diffusion control. However, unlike noble metals, Cu is easily oxidized when heated in an oxidizing atmosphere such as air, so it is not possible to form Cu wiring by co-firing with a substrate in air in the green sheet multilayer stacking method There is a point.

An object of the present invention is to provide a ceramic multilayer substrate using different ceramic materials for the surface layer and the inner layer, by selecting materials that are optimal for the surface layer and the inner layer and that are compatible with each other, so that the effective relative dielectric constant of the entire substrate is selected. Rate is
4.5 or less and low (hence, faster signal transmission speed), sufficient strength required for the multi-layer substrate (20 kgf / mm ² or higher) and peel strength (2 kgf or more, the insulator layers, in particular surface insulating layer and the inner insulating It is an object of the present invention to provide a ceramic multi-layer substrate having (peeling strength between body layers).

Another object of the present invention is to provide the above-mentioned performance,
It is another object of the present invention to provide a ceramic multilayer substrate capable of forming a low-resistance Cu wiring by simultaneous firing by a green sheet multilayer lamination method even when the signal wiring layer is Cu, and a method for manufacturing the same.

[0020]

SUMMARY OF THE INVENTION The object of the present invention is generally to provide a ceramic multilayer substrate in which ceramic insulator layers and signal wiring layers are alternately laminated and integrated, wherein the surface insulator layer has a flexural strength. consists 25 kgf / mm ² or more ceramic materials, the inner layer of the insulating layer contains no cristobalite,
This is realized by a ceramic multilayer substrate, which is made of a ceramic material having a relative dielectric constant of 4.5 or less.

Here, the bending strength is a value obtained by a three-point bending test method. Further, "not containing cristobalite" means that a cristobalite phase is not detected when examined by X-ray diffraction.

The ceramic multilayer substrate of the present invention has an effective relative dielectric constant of the substrate of 4.5 or less, a bending strength of 20 kgf / mm ² or more,
It can meet the target characteristics of a peel strength of 2 kgf or more, has a high signal transmission speed, and has sufficient strength desired in terms of handling and mounting.

Here, the effective relative dielectric constant of the substrate is a dielectric constant calculated from the relationship between the propagation time of an electric signal passing through the wiring in the substrate and the wiring length, and the bending strength and peel strength of the substrate are Means a value measured for a multilayer substrate obtained by laminating only a surface layer and an inner insulator layer and firing without interposing a signal wiring layer.

Both the surface layer and the inner layer can be composed of one or more insulator layers. That is, the surface insulator layer means not only the outermost insulator layer but also one or more insulator layers following the outermost insulator layer in some cases. In other words, on both surfaces of the substrate, one or more surface-side insulator layers including the outermost layer are made of the above high-strength ceramic material,
Alternatively, two or more insulator layers (usually, a plurality of layers) serve as an inner insulator layer, and the insulator layer is made of the above-described ceramic material having a low dielectric constant. Preferably, at least one surface of the inner insulating layer is in contact with the signal wiring layer, and the surface insulating layer is a layer whose both surfaces are not in contact with the signal wiring layer.

The inner ceramic insulator layer having a relative dielectric constant of 4.5 or less can be formed of a glass ceramic material composed of borosilicate glass, quartz, quartz glass and a small amount of alumina. On the other hand, the high-strength ceramic material of the surface layer can be formed from a glass-ceramic material comprising cordierite-based or anorthite-based crystallized glass and alumina.

More specifically, the low dielectric constant glass-ceramic material of the inner layer comprises borosilicate glass 30-69 wt%, quartz 5-55 wt%, quartz glass 5-55 wt%, and alumina 1-5 wt%, And the sum of quartz and quartz glass is 25
It is formed by firing a raw material powder of about 65 wt%.

The composition of the borosilicate glass used for the glass ceramic material is as follows: SiO ₂ : 60 to 75 wt%, B ₂ O ₃ : 15 to
Preferably, the content is 30 wt%, Al ₂ O ₃ : less than 5 wt%, alkali metal oxide: less than 5 wt% in total, and other impurities: less than 5 wt% in total.

On the other hand, the high-strength glass-ceramic material of the surface layer can be formed by firing raw material powder composed of cordierite crystallized glass or anorthite crystallized glass 60 to 40 wt% and alumina 40 to 60 wt%. .

According to the ceramic multilayer substrate of the present invention, a plurality of green sheets having at least a part of the green sheets having a conductive paste pattern on their surfaces are laminated according to a green sheet multilayer laminating method. It is manufactured by baking at ℃. Therefore, it is preferable that each of the ceramic materials of the surface layer and the inner layer is a glass ceramic material that can be fired at a low temperature.

In the ceramic multilayer substrate of the present invention, even if at least a part of the signal wiring layer is formed of Cu, the signal wiring layer is integrated with the insulator layer by batch firing by a green sheet multilayer lamination method to form a flat ceramic multilayer substrate. Can be.
In that case, a conductor paste containing Cu and / or a Cu compound as a main component is used, and firing is performed in a non-oxidizing gas atmosphere.

In a preferred embodiment in this case, the conductive paste contains at least one selected from Cu, Cu ₂ O and CuO as a main component, and before firing in a non-oxidizing atmosphere, At a temperature lower than the sintering temperature of the green sheet,
An organic substance is removed by a heat treatment in an oxidizing atmosphere, and a reduction treatment is performed in a reducing atmosphere.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the following description, all percentages related to the composition of the ceramic material are wt%.

In the ceramic multilayer substrate of the present invention, the ceramic material of the surface insulator layer is different from the ceramic material of the inner insulator layer. The inner layer is made of a low dielectric constant ceramic material having a relative dielectric constant of 4.5 or less. Since most of the wiring for signal transmission is formed inside the substrate, the signal transmission speed is strongly affected by the relative permittivity of the ceramic material inside the substrate. In other words, the relative dielectric constant of the surface ceramic insulator layer does not significantly affect the signal transmission speed, and may be somewhat higher. When the relative dielectric constant of the inner ceramic insulator layer is 4.5 or less, the effective relative dielectric constant of the entire multilayer substrate also becomes 4.5 or less, which can satisfy the signal transmission speed currently required for LSIs and the like. The effective relative permittivity of the inner insulating layer and the entire substrate is preferably 4.2 or less.

On the other hand, the surface insulating layer has a bending strength of 25 kgf / m
It is made of a high-strength ceramic material of m ² or more, preferably 27 kgf / mm ² or more. The bending strength of the board required for mounting and handling electronic components is 20 kgf / mm ² or more. In view of the strength reduction due to the use of low ceramic material strength to the inner layer, if the bending strength of the surface layer of the ceramic material is 25 kgf / mm ² or more, even without particularly increasing the surface insulating layer, the substrate A desired bending strength of 20 kgf / mm ² or more, preferably 23 kgf / mm ² or more can be secured as a whole. As a result, the reliability of the external connection of the substrate is increased, and the handling becomes easy. If the high-strength surface insulator layer is thickened, the strength of the entire substrate can be increased.However, it is preferable to excessively thicken the surface insulator layer that does not form the inner-layer signal wiring because the thickness of the substrate increases. Absent. The preferred thickness of the surface insulator layer is 0.1 to 1.0 mm.

Further, the ceramic multilayer substrate of the present invention comprises:
A target value of peel strength of 2 kgf or more, preferably 3 kgf or more can be secured. This is because the strength of the surface insulator layer is high, and at the same time, the adhesion between the insulator layers is high.

The insulator layer having a low dielectric constant of 4.5 or less as the inner layer is made of a raw material powder obtained by mixing borosilicate glass with two kinds of silicon oxide materials of quartz and quartz glass and an aggregate composed of a small amount of alumina. Can be formed by firing. Quartz glass can be relatively inexpensive (also known as fused quartz or fused silica) manufactured by a fusion method or higher purity and expensive manufactured by a gas phase method such as pyrolysis of silicon tetrachloride. There is. Either can be used, but fused quartz glass (ie, fused quartz) is sufficient.

The use of borosilicate glass having a low relative dielectric constant as the glass mainly composed of silicon oxide having a low relative dielectric constant, and having a low relative dielectric constant of 4.5 or less, can be fired at a low temperature. The ceramic material has high adhesion to the high strength insulator layer on the surface. The sintering temperature of the glass ceramic material can be controlled by the total amount of the aggregate added.

The combination of the two types of silica, silica and quartz glass, as the silicon oxide of the aggregate is that quartz has a thermal expansion coefficient of about 12
~ 15 × 10 ^-6 / ° C, quartz glass is very different from just under 1 × 10 ^-6 / ° C. Therefore, depending on the mixing ratio of these two types of materials, the coefficient of thermal expansion of the inner insulating layer is determined by the high strength of the surface layer. This is because it can be adjusted to be close to the coefficient of thermal expansion of the insulator layer. In addition to the above two types of silicon oxide,
The reason for adding a small amount of alumina is to prevent cristobalite from being generated by the reaction between the silicon oxide aggregate and the borosilicate glass during firing.

When the content of quartz is less than 5% or the content of quartz glass exceeds 55%, the thermal expansion coefficient of the material of the inner insulating layer becomes too small. Conversely, if the quartz content exceeds 55% or the quartz glass content is less than 5%, the coefficient of thermal expansion of the inner insulating layer becomes too high. Thereby, when firing together with the ceramic material of the surface layer, warpage is likely to occur, and external connection becomes unstable.

If the sum of the two is less than 25%, or if the amount of borosilicate glass is more than 69%, the material of the substrate becomes too soft and the wiring formed therein may be cut.
In addition, the firing temperature is too low, and it is difficult to fire the ceramic material at the same time as the surface layer. On the other hand, the sum of quartz and quartz glass exceeds 65%, or the amount of borosilicate glass is 30%.
If it is less than 10%, it will not be sufficiently densified at the time of firing, which may lead to deterioration of insulation resistance and the like.

If the amount of alumina is less than 1%, cristobalite is precipitated, and if it is more than 5%, the relative permittivity of the insulator layer becomes high, and it is difficult to satisfy the condition that the relative permittivity is 4.5 or less. This adversely affects the signal transmission characteristics. Instead of or as a part of alumina, an aluminum-containing inorganic material such as mullite or aluminum nitride can be used. In this case, the addition amount may be 1 to 5% in terms of alumina.

Preferably, the inner insulating layer comprises 38 to 55% of borosilicate glass, 20 to 50% of quartz, 10 to 30% of quartz glass and 2 to 4% of alumina, and the total of quartz and quartz glass is 30%. It is formed by sintering of raw material powder of up to 65% and has an average coefficient of thermal expansion from room temperature to 350 ° C of 4.5 to
8 × 10 ⁻⁶ / ° C.

Borosilicate glass has a softening point of 600 to 800.
The composition is not particularly limited as long as it is in the range of ° C. and the relative dielectric constant is low. Preferred borosilicate glasses are those which do not substantially contain alkaline earth metal oxides (MgO, CaO, BaO, etc.) (impurity amount or less). Borosilicate glass containing an alkaline earth metal oxide tends to have a high relative dielectric constant.

The preferred borosilicate glass composition is as described above. SiO ₂ constitutes the main structure of borosilicate glass together with B ₂ O ₃ , but when it exceeds 75%, the softening point of the glass tends to increase, and when it falls below 60%, the multi-component system increases. Due to the effect, the relative dielectric constant may increase,
Moisture resistance may deteriorate. When B ₂ O ₃ falls below 15%,
If the softening point of the glass is increased, and if it exceeds 30%, phase separation is likely to occur during the production of the glass, and not only will not be a uniform glass, but also the moisture resistance will be reduced.

A small amount of Al ₂ O ₃ added to borosilicate glass
Is effective in suppressing phase separation in the production of glass, suppressing crystallization during cooling, and the like. However, when the amount is 5% or more, the relative dielectric constant of glass increases. Also, alkali metal oxides
(Li ₂ O, Na ₂ O, K ₂ O) has the effect of lowering the softening point of the glass, but if the total amount exceeds 5%, the dielectric strength, dielectric loss tangent, etc. of the glass are degraded. Other impurities may be present in a range that does not degrade the properties of the glass, but if the total is 5% by weight or more, the effect on the properties of the glass becomes too large.

A more preferred composition of the borosilicate glass is:
SiO ₂ : 65 to 74%, B ₂ O ₃ : 22 to 28%, Al ₂ O ₃ : less than 2%, alkali metal oxide: less than 3% in total, other impurities: less than 4% in total.

On the other hand, the high-strength ceramic material of the surface layer can be fired at a low temperature and have a bending strength of 25 kgf / mm ² or more. As a ceramic material satisfying such conditions, there is a glass ceramic material whose glass component is made of cordierite crystallized glass or anorthite crystallized glass and whose aggregate is made of alumina. Cordierite-crystallized glass or anorthite-crystallized glass is partially crystallized by interaction with alumina, so that higher strength is obtained than when a glass material such as borosilicate glass that does not crystallize is used. Can be However, the strength of this material depends on the blending amount of alumina, and if the amount of alumina is less than 40%, sufficient strength cannot be obtained. Also,
When the amount of alumina exceeds 60%, sintering becomes insufficient at low temperature firing, and the strength also decreases. A more preferred blending amount of alumina is 45 to 55%.

Preferably, the cordierite crystallized glass comprises: MgO: 10 to 20%, Al ₂ O ₃ : 10 to 20%, SiO ₂ : 40 to
_{55%, B 2 O 3:} 10~20%, R 2 O: 0.5~5% (R is an alkali metal), impurities: consists of 5% or less of the composition, anorthite glass-ceramics CaO: 10 to 55% , SiO ₂ : 45-70%, Al ₂ O
_{3: 0~30%, B 2 O} 3: 0~30%, impurities: consisting of 10% or less of the composition.

Since either cordierite crystallized glass or anorthite crystallized glass used for the surface layer is crystallized during firing, it is not necessary to crystallize the glass before firing. Therefore, the raw material powder used for forming the surface layer may be a vitrified amorphous powder having a composition within the above range.

The ceramic multilayer substrate of the present invention can be manufactured by a thick film printing method, but is preferably manufactured by a well-known green sheet multilayer method. As described above, different ceramic materials are used for the surface insulator layer and the inner insulator layer. For both the surface layer and the inner layer, two or more kinds of ceramic materials may be used, but usually one kind may be used for each.

For both the surface insulator layer and the inner insulator layer, a green sheet having an appropriate thickness is formed from the above-mentioned raw material powder by a known method such as a doctor blade method. For each green sheet cut to a suitable size, drill a via (through hole) and fill it with a conductive paste (a paste made by mixing a fine powder of a conductor or its precursor with a vehicle). Do. A conductor paste is printed on the green sheet for the inner insulator layer so as to form the signal wiring layer, and the conductor paste is also formed on the green sheet for the surface insulator layer so that the surface electrode is formed as necessary. Print.

Thereafter, according to a conventional method, a laminate is formed in which at least one green sheet for a surface insulating layer is disposed on both sides and usually a plurality of green sheets for an inner insulating layer are disposed inside. This laminate can be obtained, for example, by stacking a plurality of green sheets as described above and hot pressing at about 100 ° C. This laminate is fired at once (ie,
When the ceramic material is sintered by simultaneously firing the green sheet and the inner layer wiring), the ceramic multilayer of the present invention in which the signal wiring layer formed from the conductive paste and the insulator layer formed from the green sheet are integrated A substrate is obtained.

If the composition of each ceramic material is selected such that the thermal expansion coefficients of the surface insulator layer and the inner insulator layer are close to each other, warpage or distortion during firing hardly occurs. However, in some cases, firing may be performed while pressing the laminate in the thickness direction in order to eliminate warpage or the like. This pressing is performed by pressing the laminate in the thickness direction (Z direction) via a jig that does not fuse to the laminate during firing or that can be easily removed from the obtained substrate even if the fusion is performed. It can be done by doing.

The firing temperature is in the range of 800 to 1,050 ° C. The preferred firing temperature is 850-950 ° C. Both the surface and inner ceramic materials are sufficiently sintered at this temperature,
Partial crystallization of the surface ceramic material also occurs at this firing temperature. Thereby, as a metal of the signal wiring layer, a noble metal such as Ag, Au, Ag-Pd, or Ag-Pt having low resistance or a metal such as Cu can be applied, and signal transmission loss can be minimized. The firing atmosphere is a non-oxidizing atmosphere when the metal of the signal wiring layer is Cu, but it is not necessary to be non-oxidizing when the metal is a noble metal, and may be an air atmosphere.

When the signal wiring layer is made of Cu, the conductor paste used for forming this wiring layer may be one containing a powder of Cu metal and / or Cu compound as a main component. Cu
As the compound, copper oxide, that is, Cu ₂ O and / or Cu
Although O 2 is preferred, other Cu compounds such as sulfides and copper salts can be used. In particular, when the inner wiring signal layer is formed of Cu, it is preferable to perform the firing of the laminate as follows.

First, heat treatment is performed in an oxidizing atmosphere to remove organic substances from the green sheet and the conductive paste (debinding). The heating temperature of this heat treatment may be lower than the sintering temperature of each green sheet, but is usually 400
It is preferably in the range of -700 ° C. The oxidizing atmosphere may be an oxygen-containing gas, for example, air. If this heating is performed, for example, in an inert gas atmosphere, organic substances and carbon remain in the fired multilayer substrate, which may lower the firing density of the substrate, lower the bending strength, and cause discoloration of the substrate. The heat treatment for removing the binder may be performed even when a conductor paste containing a powder of a noble metal such as Ag is used. The binder may be removed while the temperature is raised to the maximum.

By heating in this oxidizing atmosphere, when the conductor paste contains Cu metal, it is oxidized to copper oxide. Therefore, not only when the conductor paste contains a Cu compound from the beginning, but also when it contains metal Cu, after heating in an oxidizing atmosphere for debinding, heating in a reducing atmosphere is performed. And reduce the Cu compound to metallic Cu. The heating temperature for this reduction may be lower than the sintering temperature of each green sheet.
It is preferably within the range of ° C. As a reducing atmosphere, a mixed gas of hydrogen and an inert gas (eg, nitrogen) is generally used. Finally, firing is performed in a non-oxidizing atmosphere (ie, an inert gas atmosphere such as N ₂ or Ar or a reducing atmosphere) so as not to oxidize the reduced Cu.

[0058]

【Example】

(Example 1) Quartz 25 was used as a low dielectric constant ceramic material.
%, Fused quartz (quartz glass manufactured by the melting method) 25%,
2.5% alumina, balance borosilicate glass (SiO ₂ : 70
%, B ₂ O ₃ : 25%, Al ₂ O ₃ : 0.2%, K ₂ O: 0.9%, Li ₂ O: 0.
(7%) was used. In order to investigate the properties of this ceramic material, a green sheet prepared from the above raw material powder was used for 1.
It was laminated to a thickness of 2 mm and baked at 900 ° C. for 1 hour in the atmosphere to produce a glass ceramic substrate. The relative dielectric constant of this substrate is 4.1, and the average coefficient of thermal expansion from room temperature to 350 ° C is
The bending strength was 5.2 × 10 ⁻⁶ / ° C. and 10 kgf / mm ² . The crystal phase present on the substrate was identified by powder X-ray diffraction, but no cristobalite was present.
This ceramic material is hereinafter referred to as “low dielectric constant material”.

Similarly, 30-69% of borosilicate glass,
Quartz 5 to 55%, fused quartz 5 to 55%, alumina 1 to 5%, and the mixing ratio is changed within the range of 25 to 65% of the sum of quartz and fused quartz, and the firing temperature is set according to the composition. 800 ~
Various glass-ceramic substrates were prepared by changing the temperature within the range of 1050 ° C., but the relative dielectric constant was 4.5 or less (often 4.2 or less), and the average thermal expansion coefficient was 3 to 8 × 10
^-6 / ° C., but when the amount of quartz was 20% or more, it was in the range of 4.5 to 8 × 10 ^-6 / ° C. Flexural strength is 5
In the range of 1313 kgf / mm ² , cristobalite was not present on any of the fired substrates.

As a high-strength ceramic material, the following A
~ C high strength materials were selected. High-strength material A : Cordierite crystallized glass (MgO: 1
5.6%, Al ₂ O ₃ : 11.7%, SiO ₂ : 50.7%, B ₂ O ₃ : 18.0
%, R ₂ O: 4.0%) Glass ceramic material composed of 50% and alumina 50%. In the same manner as above, green sheets prepared from vitrified amorphous raw material powder were fired in air at 900 ° C. for 1 hour, and the characteristics were examined using a fired substrate sintered and crystallized. The strength is 30 kgf / mm ² , the relative dielectric constant is 8.0, and the average coefficient of thermal expansion from room temperature to 350 ° C is 6.0
× 10 ^-6 / ° C.

High strength material B : anorthite crystallized glass
_{(CaO: 27.3%, SiO 2} : 50%, Al 2 O 3: 13.6%, B 2 O 3: 9.1
%) A glass ceramic material consisting of 50% and 50% alumina. In the same manner as above, green sheets prepared from vitrified amorphous raw material powder were fired in air at 900 ° C. for 1 hour, and the characteristics were examined using a fired substrate sintered and crystallized. strength was 28 kgf / mm ^2, the dielectric constant 8.9,
The average coefficient of thermal expansion from room temperature to 350 ° C. was 5.7 × 10 ⁻⁶ / ° C.

High-strength material C : a glass ceramic material composed of 50% of borosilicate glass and 50% of alumina same as that used for the low dielectric constant material. In the same manner as above, the green sheet prepared from the raw material powder was fired in air at 900 ° C. for 1 hour, and the characteristics were examined using a fired substrate. The bending strength was 24 kgf / mm ² and the specific strength was 24 kgf / mm ^2. Dielectric constant 5.8, room temperature to 350 ° C
The average coefficient of thermal expansion was 5.3 × 10 ⁻⁶ / ° C. That is,
This high-strength material C is a material for comparison because the bending strength does not reach 25 kgf / mm ² .

As shown in FIG. 1, a required number of green sheets of a low dielectric constant material are stacked so as to have a thickness of 1.2 mm, and high strength green sheets A to A of the same composition are formed on both surfaces thereof.
Any one of C was laminated so as to have a thickness of 0.2 mm, and was pressed and integrated by a hot press method at 100 ° C. and 100 kgf / cm ² . The obtained laminate was fired in the air at 900 ° C. for 1 hour to produce a ceramic multilayer substrate.

Table 1 shows the measurement results of the bending strength and the peel strength of this ceramic multilayer substrate. As shown in Fig. 2, the peel strength was measured by forming a 2 mm square Cu pad on the surface of the multilayer board using a post-installed Cu conductor, soldering a 0.6 mm diameter tin-plated copper wire with low-temperature solder, This was done by a method commonly used for ceramic thick film circuit boards, which pulls the wire vertically upward and measures the force required to peel it off the Cu pad or the ceramic underneath.

[0065]

[Table 1]

From the above results, according to the present invention, if the bending strength of the surface insulating layer is 25 kgf / mm ² or more, even if the bending strength of the inner insulating layer is as low as 10 kgf / mm ² , The desired overall bending strength of 20 kgf / mm ² or more was ensured, and the peel strength was 2 kgf or more, demonstrating the effectiveness of the present invention in terms of mounting strength.

(Example 2) The same material combination as that of No. 1 in Example 1 (that is, the inner layer is made of a low dielectric constant material and the surface layer is made of a high-strength material A), and an Ag conductor is used as a signal wiring layer. A sample of a ceramic multilayer wiring board having a strip line structure shown in FIG. The conductor paste used contained Ag powder (average particle size of about 2 μm), the thickness of each of the surface and inner insulator layers was 0.4 mm for the surface layer and 2.0 mm for the inner layer. Same as Example 1, but in air
After heat-treating at 0 ° C. for 1 hour to remove the binder, the substrate was fired at 900 ° C. for 1 hour in the air to obtain a substrate.

For comparison, a ceramic multilayer wiring board having a similar structure was manufactured using the same high-strength material A as the surface layer also for the inner layer. The propagation time of the electric signal passing through the wiring of these wiring boards was measured, and the signal transmission speed and the effective relative permittivity were calculated from the relationship with the wiring length. Table 2 shows the results.

[0069]

[Table 2]

From the above results, in the multilayer substrate of the present invention in which the periphery of the wiring for transmitting a signal is made of a low dielectric constant material, even if the relative dielectric constant of the surface layer is high, the signal transmission speed through the wiring is high and the effective ratio is high. The dielectric constant became the same as the low dielectric constant material of the inner layer. That is, the same signal transmission speed as when the entire substrate is made of a low dielectric constant material is achieved, and it has been proved that it is possible to cope with an increase in the speed of an LSI device or the like.

Example 3 30 parts by weight of a vehicle was added to 100 parts by weight of a commercially available copper oxide (Cu ₂ O) powder (average particle size: about 8 μm) and mixed to prepare a Cu conductor paste. This was screen-printed in a predetermined pattern on the surface of the green sheet of the same low dielectric constant material and the surface of the green sheet of the high-strength material A as in Example 1.

Next, a green sheet of a low-dielectric constant material is stacked so as to have a thickness of 1.2 mm, and green sheets of the high-strength material A are stacked on both surfaces of the green sheet so as to have a thickness of 0.2 mm, respectively. And 100 kgf / cm ² under pressure. Thereafter, the respective heat treatments of debinding, reduction, and firing were performed under the conditions shown in Table 3 to produce a sample of a ceramic multilayer wiring board having the same strip line structure as shown in FIG. The wiring resistance of the substrate was measured by a four-terminal method, and the residual carbon was measured by a gas analysis method, and the appearances of the substrate and the wiring were visually inspected. These results are also shown in Table 3.

[0073]

[Table 3]

When the inner signal wiring layer is made of Cu, if the firing atmosphere is the air atmosphere, the reduction treatment is omitted, or the binder is removed in an inert gas atmosphere, the ceramic multilayer having the required characteristics is obtained. It turns out that a substrate cannot be obtained. For example, when the binder was removed in an inert gas atmosphere, a large amount of carbon remained in the substrate, and as a result, the substrate became gray, the wiring was discolored, and the resistance was increased. Even when the reduction treatment was not performed, the wiring exhibited a black color, partially peeled off, and the resistance could not be measured. When the firing was performed in the air, the wiring was blackened due to oxidation of the wiring, and the wiring was partially peeled off, and the resistance could not be measured.

From the results of Examples 1 to 3, according to the present invention,
It has been proved that an excellent ceramic multilayer substrate having both mounting strength and transmission characteristics can be provided regardless of whether the signal wiring layer is made of a noble metal such as Ag or Cu.

[0076]

According to the ceramic multilayer substrate of the present invention, the relative dielectric constant of the ceramic material of the inner layer around the wiring is 4.5.
Since the signal transmission speed is as low as below, it is possible to realize a signal transmission speed that can respond to the speeding up of LSIs, etc. ・ Since it can be fired at a low temperature of 800 to 1,050 ° C, Ag, Cu, Au with low electrical resistivity and therefore low signal transmission loss The signal wiring layer can be formed with such conductors. ・ By integrating a high-strength ceramic material on the surface layer, the bending strength of the entire board can be 20 kgf / mm ² or more, and the peel strength can be 2 kgf or more. Even if the wiring layer is made of Cu, the above effects can be obtained, so that the substrate has excellent electrical characteristics and mounting reliability.

Further, since the ceramic material of the inner layer can be adjusted so that the coefficient of thermal expansion is close to that of the ceramic material of the surface layer, a trouble at the time of firing is small, and a multi-layer substrate with less warping without pressing is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of one example of a ceramic multilayer substrate according to the present invention.

FIG. 2 is an explanatory diagram showing a test method of peel strength adopted in Examples.

FIG. 3 is an explanatory diagram showing a structure of a stripline multilayer substrate used for measuring a signal transmission time in an example.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H05K 3/46 H05K 3/46 H

Claims (12)

[Claims] 1. A ceramic multilayer substrate in which ceramic insulator layers and signal wiring layers are alternately laminated and integrated, wherein a surface insulator layer is made of a ceramic material having a bending strength of 25 kgf / mm ² or more, and an inner layer. Wherein the insulator layer does not contain cristobalite and is made of a ceramic material having a relative dielectric constant of 4.5 or less. 2. The ceramic multilayer substrate according to claim 1, wherein the substrate has an effective relative permittivity of 4.5 or less, a bending strength of 20 kgf / mm ² or more, and a peel strength of 2 kgf or more. 3. The ceramic multilayer substrate according to claim 1, wherein the signal wiring layer is made of a noble metal and / or copper. 4. The method according to claim 1, wherein the inner insulating layer is made of borosilicate glass.
From glass ceramic material obtained from raw material powder consisting of ~ 69wt%, quartz 5 ~ 55wt%, quartz glass 5 ~ 55wt%, and alumina 1 ~ 5wt%, and the total of quartz and quartz glass is 25 ~ 65wt% The ceramic multilayer substrate according to any one of claims 1 to 3, wherein 5. The borosilicate glass 38 according to claim 5, wherein the inner insulating layer is made of borosilicate glass.
From 55% by weight, from 20 to 50% by weight of quartz, from 10 to 30% by weight of quartz glass, and from 2 to 4% by weight of alumina, wherein the total of quartz and quartz glass is from 30 to 65% by weight. The average coefficient of thermal expansion in the range of ℃ is 4.5-8 × 10
The ceramic multilayer substrate according to claim 4, which is made of a glass ceramic material having a temperature of ^-6 / C. 6. The composition of the borosilicate glass is SiO ₂ : 60 to 60.
_{75wt%, B 2 O 3:} 15~30wt%, Al 2 O 3: less than 5 wt%, alkali metal oxides: less than total 5 wt%, other impurities: less than total 5 wt% claim 4 or 5, wherein the ceramic Multi-layer board. 7. A method according to claim 1, wherein the surface insulator layer comprises cordierite crystallized glass and / or anorthite crystallized glass.
The ceramic multilayer substrate according to any one of claims 1 to 6, wherein the ceramic multilayer substrate comprises 40 wt% to 40 wt% and 40 to 60 wt% alumina. 8. The composition of the cordierite crystallized glass is as follows:
_{MgO: 10~20wt%, Al 2 O} 3: 10~20wt%, SiO 2: 40~55wt
%, B ₂ O ₃ : 10 to 20 wt%, alkali metal oxide: 0.5 in total
~ 5 wt%, and the composition of the anorthite crystallized glass is
_{CaO: 10~55wt%, SiO 2:} 45~70wt%, Al 2 O 3: 0~30wt
_{%, B 2 O 3: 0~30wt} %, or less impurities 10 wt%, the ceramic multilayer substrate according to claim 7 wherein. 9. A method comprising laminating a plurality of green sheets having at least a part of the green sheets having a conductive paste pattern on the surface, and firing the laminate at 800 to 1,050 ° C. collectively. 9. The method for producing a ceramic multilayer substrate according to any one of the above items 8. 10. At least a part of the conductive paste is made of Cu
The method for producing a ceramic multilayer substrate according to claim 9, wherein the firing is performed in a non-oxidizing gas atmosphere, wherein the firing is performed in a non-oxidizing gas atmosphere. 11. The method according to claim 10, wherein the Cu compound is at least one selected from Cu ₂ O and CuO. 12. Before firing in a non-oxidizing atmosphere, organic substances are removed by heat treatment in an oxidizing atmosphere and reduction treatment in a reducing atmosphere at a temperature lower than the sintering temperature of each green sheet. 12. The method for producing a ceramic multilayer substrate according to claim 10 or 11.