JPH0558714A - Ceramic substrate and production of the same - Google Patents

Abstract

PURPOSE:To enable low temp. sintering of a ceramic substrate composed of alumina ceramics without decreasing the thick film adhesive strength. CONSTITUTION:A ceramic raw material composed of 92-94wt.% Al2O3 as a main component, 4-6wt.% SiO2 and the balance CaO and MgO is formed into a specified form and sintered in a high speed at 1460-1550 deg.C max. sintering temp. The sintering time from the start of temp. rising to the end of decreasing of temp. is <=6 hours. The quantity of SiO2 in the surface part of the obtd. ceramic substrate is 10-20wt.% to the quantity of Al2O3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate for electronic parts used as a thick film, a resistor, a DBC substrate and the like.

[0002]

2. Description of the Related Art Conventionally, a ceramic substrate made of alumina ceramics containing Al ₂ O ₃ as a main component has been used.

In this method of manufacturing a ceramic substrate, first, 96% by weight of Al ₂ O _{3 as} a main component and 4% by weight in total of SiO ₂ , CaO and MgO as a sintering aid have a weight ratio of SiO ₂ : A ceramic raw material was prepared by adding and mixing so that CaO: MgO = 70: 5: 25, and the ceramic raw material was mixed in an organic solvent, and then formed into a green sheet having a predetermined thickness by a doctor blade method, and then formed into a predetermined shape. After punching with a mold, firing is performed in an oxidizing atmosphere at a maximum firing temperature of 1550 to 1650 ° C. for a firing time of about 30 hours from the start of temperature increase to the end of temperature reduction, and the obtained sintered body is vibrated barrel and blasted. It was supposed to do surface treatment such as buffing.

In addition, such a ceramic substrate needs to be fired at a high temperature of 1550 to 1600 ° C. during the manufacturing process, and the firing time cannot be shortened, resulting in a high cost. Therefore, it has been considered to perform low temperature firing by reducing Al ₂ O ₃ to about 93% by weight and increasing the sintering aid.

[0005]

However, in the above-mentioned ceramic substrate for low temperature firing, it is necessary to add a large amount of SiO ₂ as a sintering aid, and moreover, a large amount of SiO ₂ is deposited on the surface layer portion during firing, so that the ceramic is SiO on the substrate surface
_The amount of ₂ increases to 20 to 30% by weight relative to Al ₂ O ₃ ,
There is a problem that the adhesion strength of the thick film becomes low.

That is, there are three types of thick film pastes, one of which is called frit bond, which is a physical adhesion in which the paste enters into irregularities on the substrate surface. The other is called chemical bond, which is a chemical bond that diffuses into the glass phase of the ceramic grain boundary, and there was also a mixed bond that combined these. Of these three types, the chemical bond and the mixed bond are such that the adhesion strength depends on the amount of SiO _{2 on} the substrate surface, and if the amount of SiO ₂ is too large, the adhesion strength is rather reduced.

[0007]

Therefore, according to the present invention, 92 to 94% by weight of Al ₂ O _{3 as} a main component and SiO ₂ 4 to 6 are used.
After molding a ceramic raw material composed of wt% and the balance CaO, MgO and unavoidable impurities into a predetermined shape, at a maximum firing temperature of 1460 to 1550 ° C., a firing time from the start of temperature increase to the end of temperature reduction is 6 hours or less and high speed. By performing the firing, low temperature firing is possible, the precipitation of SiO _{2 on} the surface portion is suppressed, and the amount of SiO ₂ existing on the surface portion of the ceramic substrate becomes 10 to 20 wt% with respect to Al ₂ O _3. It is the one.

In the above composition, if the amount of Al ₂ O ₃ is more than 94% by weight, low temperature firing cannot be performed, and if the amount of Al ₂ O ₃ is less than 92% by weight, the characteristics of the ceramic substrate become inferior. .. Therefore, the main component Al ₂
The amount of O ₃ is preferably 92 to 94% by weight. Further, if the amount of SiO ₂ is less than 4% by weight, low temperature firing becomes difficult, while
If the amount is more than 5% by weight, crystals that adversely affect the ceramic substrate such as anorthite will be deposited. Therefore, the amount of SiO ₂ is 4 to 6% by weight, preferably 4.8 to 5.2%.

Further, because of the low temperature firing, Si
Although the amount of O _{2 is} increased, by performing high-speed firing for 6 hours or less from the start of temperature increase to the end of temperature decrease,
SiO ₂ deposition on the surface of the substrate is reduced, and SiO on the surface is reduced.
_The amount of ₂ can be 10 to 20% by weight with respect to Al ₂ O ₃ . Also, by firing at high speed in this way,
The average crystal grain diameter can be reduced to 2 μm or less and the maximum crystal grain diameter to 5 μm or less, so that the crystal grain diameter can be reduced and the adhesion strength to frit bond of physical adhesion can be increased. Note that such high-speed firing can be easily performed by using, for example, a roller hearth kiln. In addition, the firing time is required to be 15 minutes or more for a small product and 30 minutes or more for a normal product.

Further, in addition to Al ₂ O ₃ and SiO ₂ mentioned above, the ceramic substrate of the present invention contains C as a sintering aid.
In addition to aO and MgO, 0.1% by weight or less of impurities may be contained in the whole ceramic.

[0011]

EXAMPLES Examples of the present invention will be described below.

Experimental Example 1 93 wt% Al ₂ O _{3 and} 5 wt% Si as a sintering aid
After O ₂ and the rest CaO and MgO were added and mixed, an organic solvent was further mixed and molded into a green sheet by the doctor blade method, and then punched with a mold to obtain a plate-shaped molded body. This molded product is No. 1 in Table 1. The ceramic substrate of the present invention was obtained by high-speed firing with a roller hearth kiln under the conditions shown in 1 and 2. In addition, as comparative examples, the above-mentioned molded body was normally fired in a tunnel furnace (No. 3 in Table 1), and A
The conventional one having the amount of l ₂ O ₃ of 96% (No.
4) was prepared. In Table 1, the firing temperature is the maximum firing temperature, and the firing time is the time from the start of temperature increase to the end of temperature decrease.

With respect to these ceramic substrates, the average crystal grain size, the amount of SiO _{2 on} the surface portion (ratio to Al ₂ O ₃ ) and the adhesion strength of a thick film using chemical bonds were examined. The results are shown in Table 2. The amount of SiO _{2 on the} surface portion was determined from the amount ratio of Si element and Al element by quantitatively analyzing the elements present on the surface portion of the ceramic substrate by Auger electron spectroscopy.

[0014]

[Table 1]

[0015]

[Table 2]

From these results, No. Three
Since the amount of SiO ₂ added was large and baking was carried out for a long time of 30 hours, the amount of SiO ₂ on the surface was as large as 20% by weight or more, and the adhesion strength of the thick film was low. On the other hand, No. 1 according to the embodiment of the present invention. Nos. 1 and 2 are Nos. Although the composition is the same as that of No. 3, since the high-speed firing is performed for 2 to 6 hours, the surface Si
The amount of O ₂ is as small as 20% by weight or less, and the adhesion strength of a thick film using a chemical bond is No. It was about the same as the conventional example shown in FIG.

Therefore, in order to increase the adhesion strength of the thick film, high-speed firing for 6 hours or less is performed to make the SiO _{2 on the} surface portion.
It is understood that the amount should be 20% or less. However, as a result of various experiments, when the amount of SiO ₂ becomes 10% or less, Si
Since the amount of O ₂ is too small and the adhesion strength of the thick film is reduced, the amount of SiO _{2 on} the surface of the ceramic substrate eventually becomes Al ₂
Those having 10 to 20% by weight with respect to O ₃ were good.

Further, since the ceramic substrate of the present invention is subjected to high-speed firing, the average crystal grain size is as small as 5 μm or less,
Not only the bending strength is high, but also the adhesion strength of a thick film using a frit bond which is a physical bond can be increased as described later.

Further, in the above No. While etching the ceramic substrates 1 and 4, the amount of SiO ₂ from the surface portion to the depth direction was measured. The results are shown in Figure 1.
Since the present invention example (No. 1) has a SiO ₂ distribution similar to that of the conventional Al ₂ O ₃ 96 wt% (No. 4), the adhesion strength of a thick film using a chemical bond is high. It turns out that it is about the same. The etching speed is 0.84Å / sec, and the etching time is 1
In the range up to the minute (depth 50 Å), the amount of SiO ₂ was 10% by weight or more.

Experimental Example 2 Next, the above No. An experiment was conducted to examine the thick film adhesion strength under more severe conditions using the first and fourth ceramic substrates. As the thick film, a frit bond that is a physical bond, a chemical bond that is a chemical bond, or a mixed bond in which both are mixed is used. Then, after adhering these thick films, an aging test at a temperature of 85 ° C. and a humidity of 85%,
A temperature cycle test was performed in which the temperature cycle of 55 to 125 ° C. was repeated once per hour, and changes in adhesion strength were examined.

The results of the aging test are shown in FIG.
The result of the temperature cycle test is shown in FIG.
Each is shown in (C). First, as is clear from FIG. 2A and FIG. 3A, in the case of the frit bond which is a physical bond, the example of the present invention showed a higher adhesion strength. This is because the ceramic substrate of the present invention has a small average crystal grain size of 2 μm or less. In addition, FIG. 2 (B)
As can be seen from FIGS. 3 (C) and 3 (B) (C), the ceramic substrate of the present invention has a conventional Al ₂ O ₃ 96 wt% ceramic substrate even when a chemical bond such as a mix bond or a chemical bond is used. And the adhesion strength was about the same.

Thus, the ceramic substrate of the present invention is
Al ₂ O ₃ amount is 93%, but conventional Al ₂ O ₃ 96%
It can be seen that the thick film adhesion strength is equal to or higher than that of the ceramic substrate.

[0023]

As described above, according to the present invention, a ceramic raw material containing 92 to 94% by weight of Al ₂ O _{3 as} a main component, 4 to 6% by weight of SiO ₂ , and the balance CaO, MgO and inevitable impurities. After being formed into a predetermined shape, by performing high-speed firing at a maximum firing temperature of 1460 to 1550 ° C. for a firing time of 6 hours or less from the start of temperature rise to the end of temperature fall, the amount of SiO ₂ present in the surface portion is Al. It is possible to obtain a ceramic substrate having a content of 10 to 20% by weight with respect to ₂ O _3. This ceramic substrate has a high adhesion strength of a thick film and can be fired at a low temperature, so that the manufacturing cost can be reduced, and electronic parts It can be preferably used as a ceramic substrate for use.

[Brief description of drawings]

FIG. 1 is a graph showing the SiO ₂ amount distribution in the depth direction in ceramic substrates of Examples of the present invention and Comparative Examples.

2 (A) to (C) are graphs showing the thick film adhesion strength after an aging test in the ceramic substrates of Examples of the present invention and Comparative Examples.

3A to 3C are graphs showing the thick film adhesion strength after a temperature cycle test in the ceramic substrates of Examples of the present invention and Comparative Examples.

Claims (2)

[Claims] 1. Al ₂ O ₃ 92 to 94% by weight as a main component
And SiO ₂ 4 to 6% by weight and the balance CaO, MgO and unavoidable impurities, and Si existing on the substrate surface.
A ceramic substrate, wherein the amount of O ₂ is 10 to 20% by weight with respect to Al ₂ O ₃ . 2. Al ₂ O ₃ 92 to 94% by weight as a main component
And, a ceramic raw material composed of 4 to 6% by weight of SiO ₂ and the balance of CaO and MgO is formed into a predetermined shape, and the maximum firing temperature is 1460 to 1550 ° C., and the firing time from the start of temperature increase to the end of temperature decrease is 6 hours. A method of manufacturing a ceramic substrate, characterized by performing high-speed firing as follows.