JP2501492B2 - Ceramic substrate and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate used as a wiring substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art As the density of electronic parts has increased, ceramic wiring boards which have been formed by a printing method or the like have been required to have finer wiring and multilayer boards. That is, conventionally, Ag--Pd, Au, Cu,
Wiring has been formed by printing a metal powder paste such as Mo or W by a screen printing method and firing it. These printed wirings are usually formed on an alumina-fired multi-layer substrate which is obtained by alternately providing an alumina green sheet obtained by adding 3 to 10% by weight of a sintering aid to alumina powder and an internal wiring, and then firing. With this method, the line width that can be manufactured with a stable yield is limited to about 100 μm. Therefore, the thin film method is used to achieve the fine wiring of about 25 to 70 μm required for miniaturization in recent years. However, when the fine wiring is formed on the ceramics fired multilayer substrate by the thin film method, the surface of the substrate is State was a very important issue.

That is, the case of forming wiring on the surface of a conventional alumina fired multilayer substrate by the thin film method will be described as an example with reference to FIGS.
FIG. 5 (a) shows a sectional state when alumina 1 having a particle diameter of about 2 to 5 μm and 3 to 20% by weight of sintering aid 2 are mixed. FIG. 5B shows a state after firing. The sintering aid 2 exists at the grain boundaries of the alumina 1, but the particle size of the alumina 1 is 10 to 50 due to the growth of the alumina 1 due to the effect of the sintering aid.
It grows up to μm, the surface roughness increases and the surface roughness increases. Pores 3 are also formed on the surface of the fired body along with the grain growth of alumina 1, and the diameter and depth thereof reach 5 to 30 μm. In addition, internal pores 4 are also formed inside the ceramics. FIG. 5C shows a cross-sectional state when the thin film 5 is formed. As described above, when the thin film 5 is formed on the substrate shown in FIG. 5B by the thin film method, the thin film 5 cannot be deposited on the pores 3, so that the pores 6 are also formed in the thin film layer, which forms the wiring. It will cause later disconnection. Further, FIG. 5 (d)
As shown in FIG. 4, it is possible to polish to the position of the broken line 7 before forming the thin film. However, even in this case, the internal pores 4 are exposed on the surface and even if the thin film 5 is formed by the thin film method as in the above example. It leads to disconnection of wiring.

As described above, when the wiring is to be formed on the surface of the alumina fired multilayer substrate by the thin film method,
The surface condition of the substrate becomes a very important issue. In order to solve the problem, conventionally, (1) an alumina substrate in which the pores and the surface roughness of the substrate surface are made as low as possible by firing with a composition of 1% by weight or less of a sintering aid, (2) 3 ~ 2
There is known an alumina substrate in which the surface of an alumina substrate containing 0% by weight of a sintering aid is glazed with glass to seal pores and flatten the surface roughness.

[0005]

However, the substrate having the composition of 1% by weight or less of the firing aid as in the above-mentioned method (1) gives the surface state of the alumina-fired multilayer substrate suitable for the thin film method. However, since the amount of the sintering aid is small and the adhesion between the green sheets does not proceed well during firing, it cannot be obtained as a multilayer substrate, which is practically impossible. Further, when the pores are sealed with glass as in the method (2) described above, it is possible to obtain a substrate which is less expensive than the method described above, but such a substrate is heat-treated in a reducing heating atmosphere. Then, the glass component is reduced, the glaze layer is reduced, and there is a problem that discoloration or deterioration of the glaze layer occurs. Therefore, there is also a problem that such a substrate cannot be used when there is a process such as brazing performed in a reducing heating atmosphere after forming a thin film pattern.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a ceramic substrate for providing a surface layer on the surface of an alumina-fired multilayer substrate which has no surface pores and has a good surface roughness, and a method for producing the same.

[0007]

The ceramic substrate of the present invention is provided with an alumina fired multilayer substrate having a conductive via exposed portion on the surface, and a portion provided on the surface of this alumina fired multilayer substrate other than the exposed conductive via portion. A composite structure comprising an alumina surface layer having an average particle size smaller than that of the alumina fired multilayer substrate and a surface layer consisting of a metal pad provided on the exposed portion of the conductive via on the surface of the alumina fired multilayer substrate. It is a feature.

Further, in the method for manufacturing a ceramic substrate of the present invention, an alumina fired multilayer substrate having a conductive via exposed portion on its surface is prepared, the surface is polished, and then the conductive via exposed portion on the surface of this alumina fired multilayer substrate is exposed. , A metal pad is formed by printing and firing a metal paste, and a high-purity and easy-sinterability having an average particle size smaller than the average particle size of this alumina-fired multilayer substrate is formed on the surface of the alumina-fired multilayer substrate having the metal pad. The feature is that a high-purity easy-sinterable alumina layer is formed by applying an alumina paste and baking it, and then the high-purity easy-sintering alumina layer on the metal pad is polished to expose the metal pad on the substrate surface. It is what

[0009]

In the above-mentioned structure of the ceramic substrate of the present invention, most of the ceramic substrate is composed of a normal alumina fired multilayer substrate, and only the surface is made of finer alumina layers and metal pads than the alumina fired multilayer substrate. Since the surface layer is composed of the above, it is possible to obtain an inexpensive ceramic substrate having no pores and having a good surface roughness. Therefore, if a thin film is formed by the thin film method using the ceramic substrate of the present invention, the thin film can be formed on a multilayer substrate having a surface state with low surface roughness and few pore defects. However, it does not affect the adhesion strength of the thin film.

In the structure of the method for manufacturing a ceramics substrate described above, first, a metal pad is provided on the surface of an alumina-fired multilayer substrate having a normal conductive via exposed portion,
Next, since the paste of high-purity easy-sinterable alumina smaller than the average particle size of this alumina fired multilayer substrate is applied and fired, it can be fired at a low temperature and a low amount of sintering aid, and the composite structure of the present invention can be used. It is possible to obtain a ceramic substrate made of. Here, the high-purity easily sinterable alumina refers to, as an example of preferable properties, an alumina powder having a purity of 99.99% or more, an average particle diameter of alumina of 0.2 μm or less, and a sintering temperature of 1350 ° C. or less. .

The coating thickness of the high-purity easily sinterable alumina paste is preferably 3 to 30 μm after sintering. If the thickness is less than 3 μm, the sintering aid and the high-purity easily sinterable alumina in the fired multilayer substrate may be melted during firing, and a good surface condition may not be obtained, and the thickness exceeds 30 μm. In addition, the contraction of the high-purity easily sinterable alumina during sintering becomes significant, and cracks may occur after sintering. More preferable thickness is 5 to 1
It is 5 μm. Further, it is preferable to use an alumina-fired multilayer substrate containing 3 to 20% by weight of a sintering aid. If the amount of the sintering aid is less than 3% by weight, the high-purity easily sinterable alumina paste and the fired multilayer substrate are preferably used. In some cases, the adhesion to the surface is insufficient, and when the sintering aid exceeds 20% by weight, the sintering aid in the fired multi-layer substrate will be This is because the high-purity and easily-sinterable alumina permeates and promotes grain growth, so that good surface roughness and a pore-free surface state may not be obtained in some cases. A more preferable amount of the sintering aid is 5 to 15% by weight.

The high-purity and easily-sinterable alumina has an average particle diameter of 0.2 μm or less and a firing temperature of 1200 to 13
A temperature range of 00 ° C. is preferable because the number of pores on the surface of the substrate after firing can be further reduced, as will be understood from Examples described later. Further, it is preferable to use alumina as a material to be applied and fired on the surface of the alumina-fired multilayer substrate, because it is a material that can stably exist even during heat treatment in a reducing atmosphere. As a result, it is possible to prevent problems such as glass deterioration due to heat treatment in a reducing atmosphere such as that of a conventional glaze substrate.

[0013]

1 (a) to 1 (d) are views for explaining each step in the method for manufacturing a ceramic substrate of the present invention. First, as shown in FIG. 1A, an alumina fired multilayer substrate 20 having an inner layer wiring 18 inside and a conductive via exposed portion 19a of a conductive via 19 on the surface is prepared by a normal method. Next, after polishing the surface of the obtained alumina-fired multilayer substrate 20, as shown in FIG. 1B, the conductive via exposed portion 1 on the surface of the alumina-fired multilayer substrate 20 is exposed.
The metal pad 21 is formed by printing a metal paste on 9a and baking it at a temperature of about 1300 ° C. Next, as shown in FIG. 1C, a predetermined high-purity and easily-sinterable alumina paste is applied onto the alumina fired substrate 9 forming the surface of the alumina fired multilayer substrate 20 having the metal pads 21, preferably. By firing at a temperature of 1200 to 1300 ° C., the high-purity easily-sinterable alumina layer 10 is formed. Finally, as shown in FIG. 1D, the metal pad 21
The ceramic substrate having the composite structure of the present invention can be obtained by polishing the upper high-purity easy-sinterable alumina layer 10 to expose the metal pad 21 on the substrate surface.

FIG. 2 is a sectional view showing in more detail the constitution of an example other than the metal pad in the surface state of the ceramic substrate of the present invention. In FIG. 2, the cross section of the surface of the ceramic substrate of the present invention has a composite structure of an alumina fired substrate 9 forming the surface of the alumina fired multilayer substrate 20 and a high-purity easily sinterable alumina layer 10 provided on the surface. Has become.
The alumina substrate 9, which has already been sintered and preferably contains 3 to 20% by weight of the sintering aid, is composed of alumina 1 having a particle size of about 10 to 50 μm and the sintering aid 2 existing at the grain boundary of alumina 1. And has pores 3 of about 5 to 30 μm. Further, preferably, the high-purity easy-sinterable alumina 8 having an average particle diameter of 0.2 μm or less is applied on an alumina substrate 9,
The high-purity and easily-sinterable alumina layer 10 is formed by firing. Since the high-purity and easily-sinterable alumina 8 has a small average particle size of 0.2 μm or less, it is easy to seal the pores 3 on the surface of the alumina substrate 9.

3 (a) to 3 (c) are views for explaining an example of the surface condition in the firing process of the ceramic substrate of the present invention. FIG. 3A shows that a high-purity easy-sinterable alumina layer 10 is formed by coating a paste made of high-purity easy-sinterable alumina 8 on an alumina firing substrate 9 containing 3 to 20% by weight of a sintering aid 2. The formed state is shown. Here, as the sintering aid 2, ordinary MgO, CaO, SiO2, TiO is used.
2, ZrO2, etc. are used. The paste made of high-purity easy-sinterable alumina 8 is prepared by mixing high-purity easy-sinterable alumina powder with an organic binder and an organic solvent, and the viscosity is adjusted to be suitable for the coating method. As a coating method, it is preferable to select a method such as printing, calendar roll, spray, electrostatic coating, dip, knife coater, etc., which has as smooth a smoothness as possible after coating.

Next, high-purity and easily-sinterable alumina 8 after coating
The paste consisting of is dried. If the surface condition after drying the paste is not good, the desired surface condition will not be obtained even after firing. Therefore, the surface finish condition can be improved by further polishing the paste surface after drying. Next, the paste after drying is preferably 1200 to 1300.
Bake at a temperature of ° C.

FIG. 3 (b) shows the state of the cross section at the time of firing. When firing at an appropriate temperature, the sintering aid 2 in the alumina substrate 9 constitutes the alumina layer 10 and is a high-purity easily sinterable alumina. Penetrate between 8 In an appropriate firing state as shown in FIG. 3B, the sintering aid 2 remains only in a state of permeating the alumina layer 10, and the high adhesion strength between the alumina layer 10 and the alumina firing substrate 9 is high. It is possible to achieve a good adhesion state having the following, and also to achieve a good smoothness having a low surface roughness of the surface of the alumina layer 10. In addition, when the firing temperature is not appropriate and becomes high, the sintering aid 2 that has penetrated into the alumina layer 10 reacts with the alumina 8 as shown in FIG. Be promoted. As a result, the alumina layer 10 has
Pore formation occurs, surface irregularities become large, and the smoothness of the substrate surface is lost. As described above, the firing temperature affects the degree of permeation of the sintering aid 2 into the alumina layer 10, and affects the surface condition.

Hereinafter, in order to determine the preferable ranges of various conditions, the average particle diameter of the high-purity easily sinterable alumina, the relationship between the firing temperature and the number of pores, the relationship between the firing temperature and the surface roughness, and the adhesion strength were actually measured. The result of the experiment will be described. Example 1 The following experiment was conducted in order to investigate the relationship between the average particle size and the firing temperature of high-purity easily sinterable alumina and the number of pores. First, according to a usual method, an alumina slurry is slip-cast by a doctor blade method to prepare a green sheet, and the green sheet is punched.
o, W conductors were printed, vias were filled with a conductor paste, green sheets were laminated, cut into a predetermined size and fired to obtain an alumina fired multilayer substrate. The amount of sintering aid in the raw material ceramics was 10% by weight. The surface roughness of the alumina-fired multilayer substrate after firing was 0.4 μm in terms of center line average surface roughness (indicated by Ra).

Next, 20 μm of a paste made of high-purity and easily-sinterable alumina was applied to the surface of the obtained alumina-fired multilayer substrate by a screen printing method. The high-purity easily sinterable alumina was compared by using two types of particles having an average particle size of 0.9 μm and 0.2 μm. The firing temperature is 11
00 ° C, 1200 ° C, 1300 ° C, 1400 ° C, 150
Five kinds of 0 ° C. were used, and firing was performed at each temperature to obtain a ceramic substrate. Then, the surface of the fired ceramics substrate was observed with a scanning electron microscope at a magnification of 500 times. At this time, the diameter of the pores found was measured, and the number of pores having a diameter of 5 μm or more was measured. The result is shown in FIG.
In FIG. 4, the number of pores is shown as the number of pores existing per square millimeter.

From the results of FIG. 4, 0.9 μm and 0.2 μm
Each of the two types of alumina having an average particle size of 1300
It can be seen that the number of pores is minimum around ℃. Also, it can be seen that the number of pores decreases as the average particle size decreases. Therefore, in order to reduce the number of pores, the average particle size should be 0.2 μm or less and the firing temperature should be 120 μm.
It can be seen that 0 to 1300 ° C. is preferable.

Example 2 The following experiment was conducted in order to investigate the relationship between the firing temperature and the number of pores of high-purity easily sinterable alumina. First, similarly to Example 1, an alumina slurry was slip-cast by a doctor blade method to prepare a green sheet, and multilayered with internal wiring, followed by firing at 1600 ° C. to obtain an alumina-fired multilayer substrate. The amount of sintering aid in the raw material ceramics was 10% by weight. The surface roughness of the fired alumina-fired multilayer substrate was 0.7 μm in terms of center line average surface roughness (denoted by Ra). Further, the obtained substrate was polished until the surface roughness Ra became 0.4 μm, and the pore number was measured in the same manner as in Example 1 for comparison.

Then, 20 μm of a paste made of high-purity and easily-sinterable alumina having an average particle diameter of 0.2 μm was applied to the surface of the alumina-fired multilayer substrate after polishing by a screen printing method. After coating, 1300 ℃, 1400 ℃, 1500 ℃
A ceramic substrate was obtained by firing at a temperature of. Then, the center line average surface roughness Ra of the obtained ceramic substrate was obtained, and the number of pores of 15 μm or more was measured and measured by the same method as in Example 1. The results are shown in Table 1.

[0023]

[Table 1]

From the results shown in Table 1, it was confirmed that by firing the high-purity easily sinterable alumina paste at 1300 ° C., the surface roughness was reduced and the pores of 15 μm or more were also significantly reduced.

Example 3 The following experiment was conducted to investigate the adhesion strength when a thin film was formed using the ceramic substrate of the present invention. First, a thin film was formed on a ceramic substrate obtained by firing the high-purity easily sinterable alumina paste produced in Example 2 at 1300 ° C., and the adhesion strength was examined. As a thin film, T
i: 500Å, Mo: 7000Å, Cu: 4 μm were formed on the substrate. Adhesion strength is 1.4 mm for the formed thin film
0.8mm patterned to a 1.4mm square
The diameter of the tin-plated copper wire was soldered, and the soldered copper wire was pulled vertically to determine the tensile strength. Also, for comparison, after patterning the thin film, hydrogen was added in a nitrogen atmosphere at 30%.
%, The adhesion strength of the substrate that was heat-treated at 750 ° C. for 10 minutes was also measured. The results are shown in Table 2.

[0026]

[Table 2]

From the results shown in Table 2, it was found that the ceramic substrate of the present invention did not undergo deterioration of the substrate surface even when subjected to heat treatment in a reducing atmosphere, and strong adhesion strength was obtained.

[0028]

As is apparent from the above description, according to the present invention, a high-purity easily sinterable alumina having an average particle size smaller than the average particle diameter of the alumina fired multilayer substrate is provided on the alumina fired multilayer substrate having a metal pad. After the paste is applied and then fired, most of the ceramic substrate is composed of a normal alumina fired multilayer substrate, and only the surface is a surface composed of finer alumina layers and metal pad layers than the alumina fired multilayer substrate. Since it is a layer, it is possible to obtain an inexpensive ceramic substrate having no pores and a good surface roughness. Therefore, if a thin film is formed by the thin film method using the ceramic substrate of the present invention, the thin film can be formed on a multilayer substrate having a surface state with low surface roughness and few pore defects. However, it does not affect the adhesion strength of the thin film.

[Brief description of drawings]

1A is a diagram for explaining one step of a method for producing a ceramic substrate of the present invention, and FIG. 1B is a diagram for explaining another step of a method for producing a ceramic substrate of the present invention;
(C) is a figure for demonstrating the other process of the manufacturing method of the ceramic substrate of this invention, (d) is a figure for demonstrating the other process of the manufacturing method of the ceramic substrate of this invention.

FIG. 2 is a diagram showing a cross-sectional structure of a surface of an example of a ceramic substrate of the present invention.

FIG. 3 (a) is a diagram showing a cross-sectional structure of an example in which a high-purity and easily-sinterable alumina layer is formed on the surface of an alumina-fired multilayer substrate in the present invention, and FIG. 3 (b) is appropriate in the present invention. The figure which shows the state of the cross section when baking at temperature, (c) is a figure which shows the state of the cross section when baking at a temperature higher than a proper temperature in this invention.

FIG. 4 is a graph showing the relationship between the average particle diameter and the firing temperature of the high-purity easily sinterable alumina of the present invention and the number of pores.

5A is a diagram showing a cross-sectional state in which alumina and a sintering aid are mixed in a conventional manufacturing process, FIG. 5B is a diagram showing a cross-sectional condition after firing in the conventional manufacturing process, and FIG. FIG. 4A is a diagram showing a cross-sectional state when a thin film is formed in a conventional manufacturing process, and FIG. 7D is a diagram showing a cross-sectional state when a thin film forming surface is polished in a conventional manufacturing process.

[Explanation of symbols]

 8 High Purity Sinterable Alumina 9 Alumina Sintered Substrate 10 High Purity Sinterable Alumina Layer 20 Alumina Sintered Multilayer Substrate 21 Metal Pad

Claims (6)

(57) [Claims] 1. An alumina-fired multilayer substrate having a conductive via exposed portion on its surface, and an average particle diameter of the alumina-fired multilayer substrate provided on a portion other than the exposed conductive via exposed portion on the surface of the alumina-fired multilayer substrate. A ceramic substrate having a composite structure of an alumina surface layer having an average particle diameter and a surface layer composed of a metal pad provided on an exposed portion of a conductive via on the surface of this alumina fired multilayer substrate. 2. An alumina fired multilayer substrate having a conductive via exposed portion on the surface is prepared, the surface is polished, and a metal paste is printed and fired on the exposed conductive via portion on the surface of the alumina fired multilayer substrate. Forming a metal pad,
A high-purity, easily-sinterable alumina paste with a metal pad layer is coated with a high-purity, easily-sinterable alumina paste having an average particle size smaller than the average particle size of this alumina-fired, multilayer substrate. After forming the alumina layer,
A method of manufacturing a ceramic substrate, comprising polishing a high-purity and easily-sinterable alumina layer on a metal pad to expose the metal pad on the surface of the substrate. 3. The thickness of the alumina paste layer is 3 to 3
The method for producing a ceramic substrate according to claim 1, wherein the thickness is 0 μm. 4. The method for manufacturing a ceramic substrate according to claim 2, wherein the alumina-fired multilayer substrate contains a sintering aid in an amount of 3 to 20% by weight. 5. The method for producing a ceramic substrate according to claim 2, wherein the high-purity easily sinterable alumina has an average particle size of 0.2 μm or less. 6. The firing temperature is 1200 to 1300.
The method for producing a ceramic substrate according to claim 2, wherein the method is at a temperature of ° C.