JPH0421564A - Alumina substrate, production of the same alumina substrate and wiring board using the same alumina substrate - Google Patents

Abstract

PURPOSE:To readily obtain a substrate, having a smooth surface and hardly causing grain growth of alumina and zirconia by burning a formed product of a mixture containing alumina powder, zirconia powder and stabilizer powder for the zirconia, an organic binder, etc., in a specific proportion. CONSTITUTION:With 60-90 pts.wt. alumina powder, are mixed 10-40 pts.wt. zirconia powder and stabilizer powder for the zirconia, an organic binder, a plasticizer and a solvent. The resultant mixture is then formed to provide a formed compact, which is then burned. Thereby, an alumina substrate containing 60-90 pts.wt. alumina having <=5mum average crystal grain diameter and 10-40 pts.wt. zirconia and stabilizer for the zirconia having >=80% tetragonal phase is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an alumina substrate, a method for manufacturing an #alumina substrate, and a wiring board using the alumina substrate.

(Prior Art) Alumina is often used as a substrate for wiring boards on which conductor circuits are formed by applying a glass component and metal conductor powder to the surface and baking or vapor depositing. The smoother the surface of the substrate for wiring boards, the better, so it is necessary to make the alumina crystals finer. However, the crystal size of alumina tends to change depending on manufacturing conditions such as firing temperature, so a great deal of effort is put into manufacturing substrates for wiring boards, including the raw materials and chemical composition. Normally, when manufacturing alumina substrates, 8i0. , MgO.

A total of 0.1 to 5% by weight of CaO, etc. is added, and an organic binder, a plasticizer, a dispersant, a solvent, etc. are added, mixed, defoamed, poured onto a film, and dried to form a green tape. A method of firing is used. As the degree of integration of circuits on wiring boards increases, the substrates used are required to be smoother and free from defects. To achieve this requirement, a trace amount of MgO is added to fine alumina powder with an average particle size of 0.1 μm or less.

The method used is to suppress grain growth by adding 5i02 or the like, sintering at the lowest possible temperature, and polishing as necessary. A substrate made of such fine-grained alumina is so small that traces of falling particles caused by processing such as polishing can be ignored, so it is considered desirable because there is no risk of disconnection or short circuit in minute circuits.

(Problem to be Solved by the Invention) However, it is difficult to tape-form such a fine-grained, high-purity alumina substrate because a large amount of organic binder and solvent are added to the raw material alumina powder, which requires the use of fine powder. ,
The process of removing the binder tends to cause foaming and cracking, and the temperature conditions for sintering and management must be adjusted for each raw material alumina to prevent further particle growth during sintering, making it extremely difficult to manufacture. , which is extremely expensive.

The present invention solves the above problems and provides an alumina substrate with excellent surface smoothness, mechanical strength and thermal shock resistance, an easy and inexpensive manufacturing method for the alumina substrate, and a wiring board using the alumina substrate. The purpose is to provide.

(Means for Solving Problem 1) As a result of searching for alumina substrates with excellent surface smoothness, the present inventors found that adding zirconia powder to alumina powder improved surface smoothness, even with simple polishing. It was discovered that defects such as falling particles were eliminated, and further studies were conducted on the addition rate of zirconia, the amount of zirconia stabilizer and the addition rate of the stabilizer, and the particle size of raw material powder such as alumina powder. In addition, the present invention has been achieved.

The present invention provides (1) an alumina substrate containing 60 to 90 parts by weight of alumina with an average crystal grain size of 5 μm or less and 10 to 40 parts by weight of zirconia with a tetragonal phase of 80 or more and a zirconia stabilizer; 2) 60 to 90 parts by weight of alumina powder,
Zirconia powder, 10 to 40 parts by weight of zirconia stabilizer powder, an organic binder, and a solvent are mixed, then molded and fired. The present invention further relates to a method for producing a nuclear alumina substrate in which the surface is polished after firing, and (3) a wiring board using the alumina substrate.

In the present invention, if the raw material alumina powder is less than 60 parts by weight and the zirconia powder and zirconia stabilizer powder exceeds 40 parts by weight, the thermal conductivity of the resulting alumina substrate will decrease or the coefficient of thermal expansion will increase. This makes it difficult to use. On the other hand, if the amount of alumina powder exceeds 90 parts by weight and the amount of zirconia powder and zirconia stabilizer powder is less than 10 parts by weight, Al lotus particles will easily grow and sintering will become difficult. deteriorates. The average crystal grain size of alumina in the alumina substrate needs to be 5 μm or less to obtain a smooth surface, and if it is 3 μm or less, the surface roughness is 0.15 μm Ra
The following is preferable. The alumina powder used to obtain a substrate with a smooth surface may be one used in the manufacture of ordinary alumina substrates, and an average particle size of 0.3 to 25 .mu.m is preferable because tape molding is facilitated.

If the particles are too small, foaming or cracking will occur during firing, and if the particles are too large, the surface of the substrate will become rough. More preferably 0.3~z
It is Oμm.

The zirconia crystal in the alumina substrate has a tetragonal phase of 8° or more. If it is less than 80 inches, it will easily deteriorate during use in wiring boards, etc., and its thermal shock resistance will be insufficient.

As a stabilizer for making the zirconia crystal into a tetragonal phase, oxides of rare earth elements, especially cerium oxide (CeO2
) is preferable, and the added amounts are zirconia (Zr02) and ZrO, and HfO which is inevitably mixed in.

3 to 20 mole based on the total amount is preferred. Even if CeO2 is added in the form of a powder, it is easily dissolved in ZrO2 during firing, so there is no need to pre-dissolve it in zirconia. CeO2 also provides thermal stability to the tetragonal ZrO, making it durable under hot and humid conditions during thick film paste baking, soldering, and use in equipment. If the amount of CeO added is small, the effect will be small even if oxides of other rare earth elements such as YxOs are added, and if it is too large, ZrO2 crystals will easily grow during firing and the surface smoothness after polishing will decrease. . When adding 3 to 10 moles, Y, 0. ,
sm,o,.

It is preferable to use it in combination with oxides of other rare earth elements such as Gd and 03. At 10 to 20 molty, the effect can be obtained by adding CeO alone. The average particle diameter of the ZrO □ powder and the zro, ① stabilizer powder is preferably 0.3 to 1.5 μm.

If the particles are too small, it will be difficult to form the tape, and if the particles are too large, it will be difficult to sinter and the surface roughness will increase. This ZrO2, a stabilizer, and the above-mentioned alumina (Autos
) refers to the diameter of the primary particles.

Ultrafine powder having a specific surface area of 10 m''/g or more is undesirable because it contains a large amount of secondary particles.

In the production of this alumina substrate, raw materials are mixed.

Molding and firing are performed by known methods. A tape molding method is preferable for molding.

The wiring board is obtained by wiring the alumina substrate by a known method.

(Example) Next, the present invention will be explained in detail.

Example 1 In a ball mill, A7203 powder [A/-16 manufactured by Showa Denko
O-8G-1 (average particle size 0.4 μm), Aj-4 manufactured by the same company
5-1 (average particle size 1.8 μm) or Sumitomo Chemical ALM-
44 (average particle size 3.0 μm)), ZrO, powder (No.
5pz) made by Kigensu Kogyo) with an average particle size of 1.1 μm or 0.5
Coo (manufactured by Nissan Kigenso Kagaku, purity 99.9cm) was ground to an average particle size of 0.5 μm.

Y, 0. Powder (manufactured by Mitsubishi Chemical Industries, purity 99.9%) was ground to an average particle size of 0.3 μm, and Gd2O3 powder (manufactured by Mitsubishi Chemical Industries, purity 99.99%) was ground to an average particle size of 0.3 μm.
The crushed material was weighed to the value shown in Table 1 before being added, and butyral resin (manufactured by Block Chemical Co., Ltd.) was added as an organic binder.
Dioctyl phthalate (reagent) as a plasticizer and butanol as a solvent were wet-mixed, and after vacuum defoaming, the mixture was poured onto a Mylar film and then dried with hot air to obtain a green tape.

This tape was fired at the temperature shown in Table 1 to form a 30x70x
1 (mm) alumina substrate was obtained, and the surface roughness at the temperature at which the density was maximized, the crystal size of Altos, and the tetragonal Zr
O, ratio 0 bending strength was measured.

This is shown in Table 1.

Comparative Example 1 The ZrO2 powder in Example IK was pulverized to an average particle size of 0.08 μm, and the Y2O3 in Example 1 was added to contain 3 molt and placed in a ball mill.
In the same manner as above, an organic binder, a plasticizer, and a solvent were added, and after wet mixing, tape molding was performed, but the tape could not be molded (Sample NQ9 in Table 1).

Comparative Example 2 and Comparative Example 3 A/, O, powder 9 with an average particle size of 0.4 μm in Example 1
9 parts by weight of Sin with an average particle size of 1.0 μm, and 1 part by weight of powder (silica sand manufactured by Kanto Chemical Industry) were placed in a ball mill, and an organic binder, a plasticizer, and a solvent were added in the same manner as in Example 1. When the tape was molded after wet mixing, many cracks occurred. A crack-free molded product was selected and fired under the firing conditions shown in Samples NQIO and 11 in Table 1 to obtain an alumina substrate with the same dimensions as the example, and the surface roughness of the substrate, AI!
20. The crystal size and bending strength of the sample were measured and shown in Table 1.

Table 1 shows that the alumina substrate of the present invention has a small surface roughness (
Good surface smoothness) 9 High bending strength. However, since Sample 1 was a combination of raw material powders all using fine powders, tape molding was difficult.

Example 2 The surface of the alumina substrate shown in Table 1 was polished with a No. 400 resin-bonded diamond grindstone, and the surface roughness (μmRa)
was measured. The results are shown in Table 2.

Table 2 Sample Nn7 in Table 1. ? ! 111. A steel paste is baked on the substrates of &7' and NQ 11' in Table 2, and a photosensitive film is applied and formed, exposed, and then etched to have a line width of 50.
A wiring board was obtained in which a fine pattern a of 150 μm was formed. A comparative test was conducted on the occurrence of disconnections and short circuits for 100 wiring boards each of these four types of wiring boards.
While there was only one short circuit, ! 4111 had 11 short circuits and 15 disconnections.

In NQII', there were 5 short circuits and 2 disconnections. Also.

A test was performed on each of 10 test pieces by placing this substrate in water at a temperature of 250°C to 10°C.

All items on floor 7 and NC 17' were normal, but on NQII and floor 11', 9 each were damaged.

(Effects of the Invention) According to the present invention, 1. A/
,0. This allows the use of powder, ZrO powder, and zirconia stabilizer powder with approximately the same particle size.

Tape molding is easy, even when the tape is fired, alumina and zirconia particles do not grow easily, and even simple surface polishing does not cause defects such as particles falling off, making it possible to easily and inexpensively obtain a substrate with a smooth surface. It will be done.

In addition, this board has a smooth surface and excellent mechanical strength and thermal shock resistance, so it can be used to form wiring boards with fine wiring, wiring boards for portable equipment or high-load equipment. It will be done.

Claims (1)

[Scope of Claims] 1. An alumina substrate containing 60 to 90 parts by weight of alumina having an average crystal grain size of 5 μm or less, zirconia having a tetragonal phase of 80% or more, and 10 to 40 parts by weight of a zirconia stabilizer. 2. 60 to 90 parts by weight of alumina powder, 10 to 40 parts by weight of zirconia powder and zirconia stabilizer powder, organic binder,
2. The method for producing an alumina substrate according to claim 1, further comprising mixing a plasticizer and a solvent, molding and firing. 3. 60 to 90 parts by weight of alumina powder, 10 to 40 parts by weight of zirconia powder and zirconia stabilizer powder, organic binder,
2. The method of manufacturing an alumina substrate according to claim 1, further comprising mixing a plasticizer and a solvent, and polishing the surface after molding and firing. 4. A wiring board using the alumina substrate according to claim 1.