JPH06291432A - Mullite ceramic substrate and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a mullite ceramic substrate having excellent adhesion to metallized particles but no warpage at all by specifying the content ratio between the mullite particles and a sintering agent as well as the composition of the latter. CONSTITUTION:A mullite ceramic substrate mainly comprising mullite is provided with an insulator containing Al2O3-SiO2-MgO base glass in 10-40wt.% while the glass composition comes within the range encircled by the four points of A, B, C, D in said glass composition figure. Within such a range, the weight% of Al2O3:SiO2:MgO is specified to be 40:58:2 at the point A, 42:43:15 at the point B, 60:23:17 at the point C and 58:38:4 at the point D. Through these procedures, the adhesion to the metallized particles can be enhanced while avoiding the warpage of the title mullite ceramic substrate by specifying the glass content as well as the composition ratio between Al2O3, SiO2 and MgO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mullite ceramic substrate and its manufacturing method. This mullite ceramic substrate can be suitably used for a high-density and highly reliable multilayer wiring substrate.

[0002]

2. Description of the Related Art A conventional ceramic wiring board is made of ceramics containing alumina as a main component, and has a plurality of plate-shaped insulating layers, and the main surface of each insulating layer is made of a refractory metal such as tungsten or molybdenum. And various formed wiring patterns.

Such a ceramic wiring board is manufactured by the following procedure. First, a through hole is formed in a green sheet containing ceramic powder such as alumina as a main component by punching, and a conductor paste is filled in the through hole. And
A conductive paste such as tungsten W is screen-printed in a predetermined pattern on the surface of the green sheet to form each wiring pattern. Next, stack these green sheets,
Glue under pressure. After that, the laminated body is fired at a high temperature of around 1500 ° C., and the surface thereof is sputtered with an active metal such as Ti, Cu, or Cr, or is plated with Ni or the like to form a ceramic multilayer wiring board. Thus, the conductor paste filled in the through holes becomes a conductor pillar and electrically connects the wirings of the respective layers.

By the way, in recent years, in order to increase the signal propagation speed and prevent connection failures and peeling of integrated circuit ICs, alumina ceramics are used as an insulating layer in a multilayer substrate of a high density IC package. A proposal has been made to use mullite ceramics instead of the above (Japanese Patent Laid-Open No. 61-230204).

That is, since the propagation delay time of an electric signal is proportional to the square root of the dielectric constant of the insulating layer surrounding the wiring conductor, mullite having a small relative dielectric constant is used as the main component of the insulating layer to achieve high speed signals. To do. When the integrated circuit IC is made of semiconductor silicon, the coefficient of thermal expansion of silicon is 3.4 × 10 ⁻⁶ / ° C., and thus mullite having a small thermal expansion difference is used as the main component of the insulating layer of the IC mounting portion. By doing so, the thermal stress of the IC connecting portion is reduced.

Incidentally, while the coefficient of thermal expansion of alumina ceramics is 7.5 × 10 ⁻⁶ / ° C. and the relative dielectric constant is about 9, the mullite substrate disclosed in the above-mentioned Japanese Patent Laid-Open No. 61-230204. It has a thermal expansion coefficient of 4.6 × 10 ⁻⁶ / ° C. and a relative dielectric constant of 5.7, which is an excellent material.

[0007]

Similar to the case of the alumina ceramic substrate, the mullite ceramic substrate is obtained by cofiring the conductor paste of the refractory metal and the ceramic powder, so that the mullite ceramic substrate adheres closely to the ceramic and is dense. In order to obtain a low resistance wiring pattern, it is necessary that the glass component functioning as a sintering aid in the ceramic substrate be sufficiently wet with the high melting point metal.

Regarding this point, the above-mentioned JP-A-61-2302
According to the 04 publication, the glass matrix component is Al
₂ O ₃ (4 to 30%)-SiO ₂ (60 to 95%)-Mg
By limiting the content to O (1 to 10%), it is possible to rapidly co-fire with the conductor metal tungsten or molybdenum metallized particles, and to maintain the low thermal expansion coefficient and low dielectric constant, which are the original characteristics of the mullite substrate. There is. However, since the mullite particles are hardly sintered particles, the mullite ceramic substrate obtained by liquid-phase sintering the mullite particles is easily affected by the characteristics of the glass component.

For example, one of the problems in actual production of substrates is fusion of the substrate and the setter during firing and warpage of the fired substrate. Yield can be greatly affected. JP-A-6
Even with the composition described in JP-A 1-230204, only the ratio of Al ₂ O ₃ and SiO _{2 in} the glass component has been investigated, and the amount of MgO added has not been thoroughly investigated. Defect occurs.

Therefore, when the mullite powder and the refractory metal are co-fired in this way to produce a wiring board, the wettability between the mullite particles and the glass and the wettability between the metallized particles and the glass are set to the optimum ranges. Moreover, the composition of the auxiliary glass that can exhibit excellent properties as a fired substrate has not been clarified. The object of the present invention is to solve such problems, and by specifying the content ratio of the mullite particles and the sintering aid and the composition of the sintering aid, there is no warp and excellent adhesion with the metallized particles. It is to provide a mullite substrate.

[0011]

A mullite ceramic substrate of the present invention comprises an insulator containing mullite as a main component and 10 to 40% by weight of Al ₂ O ₃ —SiO ₂ —MgO system glass, and has a glass composition. , Al ₂ O ₃ —SiO shown in FIG.
_2- MgO 3-component composition chart, points A, B, C and D
It is characterized by belonging to the range surrounded by (including on the boundary line).

[0012] Similarly, the manufacturing method is a method in which a sintering aid is added to and mixed with mullite powder, and the mixture is molded into a green sheet and fired, and the addition amount of the sintering aid is 10 to 40% by weight in the mixture. That is, the composition belongs to the range surrounded by the following points A, B, C and D (including the boundary line) of the Al ₂ O ₃ —SiO ₂ —MgO ₃ component composition diagram in terms of oxide. It is characterized by

Al ₂ O ₃ SiO ₂ MgO point A 40 58 2 point B 42 43 15 point C 60 23 17 point D 58 38 4 [unit: wt%]

The function of the present invention is to add the glass addition content and Al.
_The reason for limiting the composition ratio of ₂ O ₃ , SiO ₂ and MgO will be described in detail.

First, the reason why the glass addition content is limited to 10 to 40% will be described. Like the alumina substrate, the mullite substrate is co-fired with tungsten or molybdenum metal. Therefore, the ceramic is also fired at the temperature at which these metallizations sinter. This co-firing temperature is usually 1500 ° C to 1650 ° C.

When the glass component is more than 40%, the firing temperature becomes 1500 ° C. or less due to the presence of excess glass, which is not suitable for simultaneous firing with tungsten and molybdenum. In addition, a substrate that has been fired due to an excessive amount of glass will be dominated by the mechanical properties of the glass, resulting in weak strength. Conversely, the mullite content is 9
If it exceeds 0%, the firing temperature becomes high due to lack of glass, which is not practical. Therefore, the glass addition content is 1
It was set to 0 to 40%.

Next, the reason why the composition of the sintering aid is limited to a range surrounded by four points including points A, B, C and D in the three-component composition diagram (FIG. 1) will be described in detail. Since the mullite particles themselves are difficult to sinter, they are treated as Al ₂ O ₃ -SiO _2.
Liquid phase sintering is performed with a _2- MgO-based three-component sintering additive, but the problem in this case is mullite particles at the firing temperature of the substrate and metallized particles such as tungsten and molybdenum, and molten glass. It is wettable with. Factors that influence the wettability are the glass melting start temperature and the glass viscosity at the substrate baking temperature.

Regarding the relationship between the melting point and viscosity of the glass and the composition, the composition ratio of Al ₂ O ₃ and SiO ₂ will be described first. The reason is that the melting point is remarkably lowered only by adding a small amount of MgO to the two components of Al ₂ O ₃ and SiO ₂ . Therefore, tungsten or molybdenum metallized particles and Al
Wettability between ₂ 0 ₃ -SiO ₂ -MgO based glass greatly influenced by the MgO addition amount. Therefore, the amount ratio of Al ₂ O ₃ and SiO ₂ is considered on the assumption that the amount of MgO is appropriate.
Next, the content of MgO will be described in detail.

When the SiO ₂ content of the Al ₂ O ₃ --SiO ₂ --MgO system ternary glass is more than 60%, the melting temperature of the glass lowers and the viscosity of the glass at the firing temperature also lowers. This is good for the wettability between the mullite particles and the metallized particles and the glass, but the glass component in the mullite ceramic flows out during the firing of the substrate, resulting in fusion with the setter. Since a rapid shrinkage occurs, the substrate warps due to uneven shrinkage due to a slight temperature difference during the baking of the substrate. In particular, since the corners and edge portions of the substrate follow the temperature inside the furnace quickly, warpage is likely to occur.

On the contrary, the SiO ₂ content is reduced to reduce the Al ₂ O ₃ content.
When the content is more than 40%, the melting point of the glass is high, and the viscosity of the glass at the firing temperature is high, so that the wettability with mullite particles and metallized particles is slightly deteriorated, but the glass does not flow out during firing and the setter does not flow out. There is no fusion with. Further, since the substrate shrinks slowly, no warpage occurs. However, if the Al ₂ O ₃ content is too high, the melting temperature of the glass becomes too high, which is not suitable for liquid phase sintering. Further, since Al ₂ O ₃ itself has a high thermal expansion coefficient and a high relative dielectric constant, it is not preferable to add an excessive amount of alumina also from this point.

Next, the amount of MgO added in the glass composition will be described. First, the Al ₂ O ₃ —SiO ₂ component alone is not preferable because the melting point of glass is too high, and the viscosity of glass is high and the wettability with mullite particles and metallized particles is poor. Therefore, the addition of a small amount of MgO is indispensable. On the contrary, when the addition of MgO is increased, the melting point of the glass is lowered and the wettability is improved, but when the excess amount is added, the viscosity of the glass becomes too low and the glass melts out during the baking of the substrate to melt with the setter. Adhesion or warpage of the substrate occurs. In addition, excess MgO is added to spinel (MgO.
A large amount of MgO-based composite oxide such as Al ₂ O ₃ ) is produced. Since the thermal expansion coefficient of these complex oxides is greatly different from that of silicon chips, it is not preferable to generate a large amount in the mullite substrate. Further, generation of a large amount of these complex oxides causes a spot-like discoloration due to segregation of MgO on the substrate, which is not preferable in appearance.

For the above reasons, the glass composition is limited to the above range.

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 In this example, the productivity of the mullite ceramic substrate of the present invention is evaluated. Electrofused mullite 7 with an average particle size of 2.4 μm
50 g, 115 g of alumina having an average particle size of 1.7 μm, 115 g of silica having an average particle size of 2.4 μm, and 0.4 μm of an average particle size
20 of magnesium carbonate is converted to magnesium oxide
and g were mixed in a ball mill for 24 hours with toluene as the dispersion medium. Then, dibutyl phthalate and polyvinyl butyral were added as a binder for forming the green sheet, and the mixture was further mixed for 24 hours.

The resulting mixture was vacuum degassed and then formed into a green sheet having a thickness of 0.5 mm by the doctor blade method. The green sheets were laminated and pressure-bonded and cut into green bodies having a size of 100 × 100 × 2.0 ^t mm before firing. 2 this green body in the oxygen atmosphere beforehand
After removing organic components at 50 ° C., 1400 ° C. to 165 ° C. using a metal molybdenum plate as a setter in a reducing atmosphere.
Firing was performed by changing the firing temperature to 0 ° C. The firing temperature and firing specific gravity at that time and the relationship between firing temperature and shrinkage are shown in FIGS. 2 and 3.

From FIGS. 2 and 3, it is clear that the sintering starts from 1400 ° C. and shows a stable shrinkage ratio in a wide range of 1500 ° C. to 1600 ° C. This is very useful in production because when the substrate is fired at a temperature of 1500 ° C. to 1600 ° C., variations in the dimensions of the substrate after firing can be suppressed.

-Example 2 and Comparative Example-This example seeks a desirable range of the composition of the sintering aid. With the content of mullite particles being 75% by weight and the total addition amount of the sintering additive being 25% by weight, the content ratio of the components of the sintering additive was variously changed as shown in Table 1, and the other conditions were the same as in Example 1. A mullite ceramic substrate was manufactured. However,
The firing temperature was the temperature at which the composition having the composition was completely sintered, and was basically changed depending on the content of mullite particles. Substrate No. 1 to 9 are mullite ceramic substrates belonging to the scope of the present invention. 10 to 15 are comparative examples. The substrate No. 1 is shown in Example 1.

[0026]

[Table 1] The following evaluations were performed on the substrates having each of these compositions. [Evaluation of basic characteristics of sintered body] First, the thermal expansion coefficient of the sintered body,
The relative dielectric constant and the anti-deposition strength were measured. The anti-deposition strength is JI
It measured based on SR1601. Also, the warpage of the substrate,
The presence or absence of spot-like discoloration on the substrate and the presence or absence of fusion between the substrate and the setter were observed. The results are shown in Table 2.

[0027]

[Table 2] As seen in Table 2, the substrate No. 1-9 are
The coefficient of thermal expansion is 4.0 to 4.6 × 10 ⁻⁶ / ° C. (0 to 400
C) close to that of semiconductor silicon, with a relative dielectric constant of 6.1
It was as low as ˜6.8 and had a high anti-deposition strength of 220-250 MPa. In terms of productivity, the warp amount of the substrate was as small as 50 to 150 μm. Moreover, there is no spot-like discoloration on the substrate during firing, and the fusion with the setter is also no. It was not confirmed except that some fusion occurred in No. 5.

On the other hand, the substrate No. having the composition of the sintering aids at points E, F, and G was not. It was confirmed that Nos. 10 to 12 had a large amount of SiO ₂ and had a large warp of the substrate, and that the glass component was fused with the setter due to the appearance of stains. In that case, the amount of warp,
The degree of fusion was greater as the content of SiO ₂ was higher. Substrate No. having a composition in which the sintering aid is point I. In No. 13, the content of MgO was too large and the warp of the substrate was still large, and fusion with the setter and discoloration of the substrate due to the spotting of the glass component were confirmed. Substrate No. having the composition of point J. No. 14 is not suitable as a wiring board on which a silicon chip is mounted, because the Al ₂ O ₃ content is too large and the thermal expansion coefficient becomes too high.

[Evaluation of Compatibility with Metallized Metal] 0.5 mm thick green sheet obtained under the same conditions as in Example 1 except that the composition was as shown in Table 1.
Through holes of φ, 0.25 mmφ, and 0.12 mmφ were punched out at 500 holes for a total of 1500 holes, and a conductor paste was filled therein. This conductor paste was obtained by adding 1 part by weight of mullite powder having an average particle size of 1.7 μm, 2.8 parts by weight of ethyl cellulose and 6 parts by weight of butyl carbitol to 100 parts by weight of tungsten powder having an average particle size of 2.0 μm. is there. Six layers of the green sheets thus filled with the conductor paste were laminated so that the through holes of each layer were connected and fired at the temperature shown in Table 1.

The cross-sections of the through-holes having the respective hole diameters after firing were subjected to elemental analysis with an electron probe microanalyzer, and Al ₂ O ₃ and S, which are glass components in the mullite sheet, were analyzed.
It was observed whether iO ₂ and MgO were uniformly diffused in tungsten. Further, the specific resistance of 30 through-hole portions was measured for each hole diameter, and the average value was calculated. The results are shown in Table 3.

Furthermore, the line width 1 after firing on the green sheet
The metallizing paste was printed so that the wiring had a thickness of 00 μm, and was baked at 1550 ° C. The metallizing paste used at this time was obtained by adding 4.0 parts by weight of ethyl cellulose and 6 parts by weight of butyl carbitol to 100 parts by weight of tungsten powder having an average particle size of 2.0 μm. At the time of printing, the viscosity of the paste was adjusted by adding butyl carbitol so that the viscosity became suitable for printing.

The metallized portion after firing, that is, the wiring portion was subjected to elemental analysis by an electron probe microanalyzer, and Al ₂ O ₃ and SiO ₂ which were glass components in the mullite sheet were analyzed.
It was observed whether MgO and MgO were uniformly dispersed in the conductor. The specific resistance was also measured. The results are shown in Table 3.

Further, 30 positions on the green sheet were subjected to metallization printing in a circular pattern so as to have a diameter of 1.4 mm after firing, followed by firing at the temperature shown in Table 1 and nickel plating on the metallization to form pin pads. Subsequently, 0.45 mmφ I / O pins made of Kovar were joined on each pad with silver-copper eutectic solder (72Ag-28Cu). Then I /
The O pin was pulled in the direction of 45 ° with respect to the pin pad, the bonding strength between the pin pad and the mullite ceramic, that is, the metallized adhesion strength was measured, and at the same time, the fracture mode was observed. The results are shown in Table 3.

[0034]

[Table 3] As shown in Table 3, the substrate N whose composition of the sintering aid is point K
o. In all the substrates except 15, the glass in the mullite ceramic was uniformly permeated between the tungsten particles in both the through hole portion and the wiring portion. In addition, even though the glass of the insulating material permeated in this manner, the specific resistance of those substrates was 14 to 18 μΩ in the through hole portion.
Cm, the wiring portion was as low as 14-18 μΩ · cm, and required conductivity was secured. It is considered that this is because the tungsten particles were densely sintered due to the presence of glass. Further, the metallized adhesion strength is 8 to 10 kgf
It was high enough to cause pin breakage under a tensile load of (n = 30).

On the other hand, when the composition of the sintering aid is Point K, the substrate No. No. 15 was satisfactory as the basic characteristic of mullite ceramic (see Table 2), but M
Since the gO content was too small, the glass component did not fully penetrate into the metallization, and the metallized particles were not completely sintered, resulting in a high resistance value and a metallized adhesion strength of 1 kgf or less ( It was so low that the pin pad was peeled off under a tensile load of n = 30). Therefore, it was not suitable as a wiring board.

Example 3 In this example, the desirable range of the addition amount of the sintering aid is determined. The mullite ceramic substrate was manufactured under the same conditions as in Example 1 except that the mullite particle content, the total addition amount of the sintering aid, and the component content ratio of the sintering aid were variously changed as shown in Table 4. However, the firing temperature was set to a temperature at which the composition having the composition was completely sintered, and was basically changed depending on the content of mullite particles. Substrate No. thus obtained 16 to 27 are mullite ceramic substrates that all belong to the scope of the present invention.

[0037]

[Table 4] The following evaluations were performed on the substrates having each of these compositions. [Evaluation of Basic Properties of Sintered Body] First, the thermal expansion coefficient, the relative dielectric constant and the segregation strength of the sintered body were measured under the same conditions as in Example 2. The results are shown in Table 5.

[0038]

[Table 5] As seen in Table 5, the substrate No. 16-27
Has a thermal expansion coefficient of 3.7 to 4.9 × 10 ⁻⁶ / ° C. (0 to 4
At 00 ° C), it is close to that of semiconductor silicon, has a low relative dielectric constant of 6.0 to 7.4, and has a segregation strength of 200 to 290MP.
It was as high as a. In terms of productivity, the warp amount of the substrate was as small as 40 to 60 μm. Moreover, there was no spot-like discoloration on the substrate during firing, and no fusion with the setter was confirmed.

[Evaluation of Compatibility with Metallized Metals] Green sheets were prepared, laminated and fired under the same conditions as in Example 2 except that the raw material composition and firing temperature were as shown in Table 4. The specific resistances of the through hole portion and the wiring portion were measured in the same manner as in Example 2, and the average value thereof was calculated, and the results are shown in Table 6. Further, the state of penetration of the glass component into the conductor and the metallized adhesion strength were measured in the same manner as in Example 2. The results are shown in Table 6.
Shown in.

[0040]

[Table 6] As can be seen from Table 6, even if the addition amount of the sintering aid varies within the range of the present invention, the glass in the mullite ceramic uniformly permeates into the tungsten particles in both the through hole portion and the wiring portion. Was. In addition, even though the glass of the insulating material has permeated in this way, the specific resistance of these substrates is as low as 14 to 20 μΩ · cm at the through hole portion and 13 to 20 μΩ · cm at the wiring portion, which is necessary. The conductivity was secured. Further, metallized adhesion strength is 8 to 10k
It was high enough to cause pin breakage under a tensile load of g · f (n = 30). Therefore, it was found that the addition amount of the sintering aid is preferably 10 to 40% by weight.

[0041]

The mullite ceramic substrate of the present invention exerts great effects as follows. (1) Since it is possible to co-sinter with a refractory metal, it is easy to form a multilayer wiring. (2) Since the coefficient of thermal expansion is close to that of silicon chips,
The reliability of the joint with the silicon chip is excellent. (3) Since the relative permittivity is low, the signal propagation speed is high. (4) Because of high bending strength, cracking and chipping are unlikely to occur during transportation. (5) Since there is little warpage of the substrate, fusion with the setter, and discoloration on the substrate, the productivity is excellent. (6) Since the specific resistance is low, the wiring can be miniaturized, which is suitable for high-density wiring. (7) Since the metallized adhesion strength is high, the reliability of the joint with the input / output terminal is excellent.

[Brief description of drawings]

FIG. 1 is an Al ₂ O ₃ —SiO ₂ —MgO ₃ component system composition diagram.

FIG. 2 is a graph showing the relationship between the firing temperature and the firing specific gravity of the mullite ceramic substrate of Example 1.

FIG. 3 is a graph showing the relationship between the firing temperature and the firing shrinkage of the mullite ceramic substrate of Example 1.

Claims (2)

[Claims] 1. An insulator comprising mullite as a main component and containing 10 to 40% by weight of Al ₂ O ₃ —SiO ₂ —MgO-based glass and having a glass composition of Al ₂ O ₃ —SiO ₂ —MgO.
A mullite ceramic substrate characterized by belonging to a range (including a boundary line) surrounded by the following points A, B, C and D in a three-component composition diagram. Al ₂ O ₃ SiO ₂ MgO point A 40 58 2 point B 42 43 15 point C 60 23 17 point D 58 38 4 [unit: wt%] 2. A method in which a sintering aid is added to and mixed with mullite powder, and the mixture is molded into a green sheet and fired, wherein the addition amount of the sintering aid is 10 to 40% by weight in the mixture. The composition is Al ₂ O ₃ -Si in terms of oxide.
A method for manufacturing a mullite ceramic substrate, characterized in that it belongs to a range surrounded by points A, B, C and D (including the boundary line) of the O ₂ —MgO 3 component composition diagram. Al ₂ O ₃ SiO ₂ MgO point A 40 58 2 point B 42 43 15 point C 60 23 17 point D 58 38 4 [unit: wt%]