JPS6252170A - Method of burning mullite sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for firing a mullite sintered body.

[Background of the invention]

In recent years, ceramic wiring boards have become popular in electronic computers due to their ability to be miniaturized and highly reliable.

It is used as a substrate for mounting IC chips and small electronic components in communication equipment, home appliances, etc. A mullite ceramic wiring board whose main component is mullite is one example, and the manufacturing method is similar to that of a general alumina ceramic wiring board, and is manufactured by the following steps.

That is, after producing a raw ceramic sheet (green sheet) in which raw material powder is bonded with an organic resin, a wiring pattern is formed on this green sheet by drilling holes and using conductive paste, and multilayer wiring is created by printing multilayers and laminating. ,
It is made by firing.

However, it is difficult to produce a mullite wiring board with high dimensional accuracy for the following reasons. it is,
The firing process involves placing a raw mullite substrate on top of plywood. Firing is carried out by placing a raw mullite substrate on a plywood board, and the plywood is made of alumina-based or mullite-based ceramics that can withstand the temperature and atmosphere during firing, or molybdenum, tungsten, or the like. When a mullite substrate is placed on a base plate made of these materials and fired, a phenomenon occurs in which the mullite substrate sticks to the plywood. If it sticks in this way, the board may crack or become impossible to peel off, or even if it does come off, part of the board may be missing, or a part of the plywood may adhere to the mullite board as a foreign object. Incidentally, even if the substrate is not chipped or foreign matter is not attached to the substrate, the dimensional accuracy of the mullite substrate after firing is significantly deteriorated.

Therefore, in order to avoid such adhesion between the mullite substrate and plywood, spherical particles (10 to 100 μm in diameter) of alumina or mullite are applied to the plywood as a bedding powder, and the mullite substrate is placed on top of this bedding powder. A method of firing is generally used. This method eliminates adhesion between the mullite substrate and the plywood, but new adhesion between the mullite substrate and the bedding powder occurs. The adhered bedding powder can be removed by applying external force, but it is difficult to remove it completely, and part of the substrate may be missing when the bedding powder is removed.

As described above, with the conventional firing method, it is not possible to obtain a mullite substrate with high dimensional accuracy that is free from defects such as chipping.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a mullite wiring board with no defects and high dimensional accuracy.

[Summary of the invention]

An outline of the present invention will be described below. The key is to use plywood, which does not stick to the mullite wiring board, and fire it.

The materials for mullite wiring boards are mullite composition powder, sintering aid, and metal/metallic powder for wiring. Among these, those that cause adhesion are formed by the reaction between the sintering aid and mullite composition powder. It is a glass component. As a result of examining the degree of adhesion between this glass component and various high-temperature heat-resistant materials, it was found that zirconia (Zr02)-based materials were the best. The degree of adhesion is also related to the surface roughness of the plywood surface on which the mullite wiring board is placed, and the surface roughness is 10 to 60.
A range of 0 μm is suitable. If it is less than 10 μm, slight adhesion will occur, and if it is still more than 500 μm, small irregularities will occur on the substrate or minute scratches will occur during firing shrinkage.

[Embodiments of the invention]

An embodiment of the present invention will be described below.

Example 1 First, a method for manufacturing a raw mullite wiring board as an object to be fired,
That is, the production of a green sheet and the printing of wiring patterns on this green sheet will be described.

As the ceramic powder, mullite powder was used, and the total composition was Ae2os 56wt%, SAO-
Particle size of z43wt%, My01wt% 5μ+n
100 parts of the following powder, 6 parts of butyral resin as a binder, 2.5 parts of a plasticizer for resin, and trichlorethyl as a solvent.

Add 5 parts of ethylene, perchlorethylene, and alcohol, and perform wet mixing continuously for 24 hours in a ball mill using an alumina lining and alumina balls. Subsequently, o and i parts of a silicone-based antifoaming agent were added, and the mixture was mixed for 1 hour to form a slurry-like mixture.

Next, the slurry-like mixture is taken out from the ball mill and stirred under reduced pressure to remove some air from the slurry.The viscosity of the homogeneous slurry thus made is adjusted to 5,000 to 10,000 centimeters. The mixture was coated onto a carrier film using a Dr. Plaid type casting device and dried to produce a 0.3-thick green sheet.

Next, a method for producing a conductive tungsten paste for forming a wiring pattern will be described.

As tungsten powder, 0.5 μm powder and 3. αμ
39 parts of ethyl cellulose was added to the binder with 80 parts of a powder prepared by mixing M powder at a weight ratio of 3. Add 1 part of diethylene glycol to the mixture, knead for 6 hours using a milling machine, then mix with three rolls for 30 minutes with a gap of 30 μm, add butycarpitol to adjust the viscosity, and prepare a paste for printing.

A method for producing a raw mullite wiring board using the green sheet and printing paste produced by the above method will be described below.

The 0.3ml thick green sheet prepared above was
- Cut into corners, and if necessary, make a through hole with a diameter of 0.131 using a punching die with NG control. Subsequently, using the printing paste, a wiring pattern is formed in the through-holes and on the surface of the green sheet by a screen printing method. The top part of the pattern was a pattern for mounting an LSI chip, the inside was a pad pattern for power supply and wiring, and the bottom part was a pad pattern for an input/output bin stand. Next, 20 green sheets with wiring patterns formed thereon were stacked and integrated. Temperature 120 for integration
'0, the pressure cuff was set to 0. After integration, unnecessary parts around 5 are cut to produce a raw mullite wiring board with an outer diameter of 1 ounce square.

The next step is the firing step. First, the firing method according to the present invention will be described in conjunction with the conventional method.

The conventional firing method is as follows. 10 produced above
A 0W square raw mullite wiring board was placed on an alumina plywood board covered with spherical alumina particles with an average particle size of 50 μm, and the temperature was raised to a maximum temperature of 1650 at a heating rate of 200'O1 per hour in a mixed gas atmosphere of nitrogen, hydrogen, and water vapor. Firing was performed at 'O.

The electric furnace used was a box-type electric furnace with a molybdenum heating element.

Next, the firing method according to the present invention will be described. The plywood used was made of stabilized zirconia to which 8 mol of ittria was added. That is, the raw mullite wiring board was placed on the base plate and fired under the same conditions as in the conventional method.

In this way, the mullite wiring boards fired by the conventional method and the mullite wiring boards fired by the method of the present invention were inspected for dimensional accuracy, chipping, deposits, unevenness, and other flaws after the board was fired6. In the mullite wiring board according to the company, the bedding powder adheres, so an electric brush was used to remove the bedding powder, and the bedding powder that could not be removed with the electric brush was treated as foreign matter. Dimensional accuracy was measured using a coordinate measuring machine, and inspection for defects such as missing deposits and unevenness was performed using a microscope at a magnification of 50x. The results of dimensional accuracy and defect inspection are shown below.

Note that the surface roughness of the stabilized zirconia plywood to which 8 mol of yttria was added used in this example was 60 μm. The surface roughness of the base plate has a close relationship with the dimensioning accuracy and the number of defects, and results similar to those described above were obtained when the surface roughness was in the range of 10 to 600 μm. If the surface roughness is less than 10μm, some adhesion may be observed, and if the surface roughness is thicker than 300βm, scratches may occur due to firing shrinkage, unevenness may occur on the substrate, and dimensional accuracy may deteriorate. Deteriorate.

Example 2 In this example, a case will be described in which plywood coated with zirconia is used.

The plywood used was a board containing 85% alumina and 15% by weight of silica, the surface of which was coated with zirconia containing 6 mol of itria.

A mullite substrate was fired under the same conditions as in Example 1, and compared with the conventional method, the following results were obtained.

In this example, plywood with a surface roughness of 30 μm was used for firing, but for the same reason as mentioned above, the surface roughness was 10 μm.
~300 μm is suitable. Furthermore, in this example, an example was described in which plywood was coated with zirconia containing 6 mol of ittria, but the amount of ittria added was adjusted to match the coefficient of thermal expansion of the material of the plywood to be coated. . In other words, if the amount of ittria added is reduced, the coefficient of thermal expansion becomes smaller, but if the amount is less than 4 moles, the rise and fall of temperature during firing will cause small particles to form on the surface of the plywood. This is not desirable as it may cause scratches.

In this example, plywood with a coating layer of 50 μm thick was used, but similar results were obtained using a plywood with a coating layer of 100 μm. That is, the thickness of the coating layer is not particularly important as long as the five base plates are completely covered.

〔Effect of the invention〕

As described above, according to the present invention, a mullite wiring board with no defects and high dimensional accuracy can be obtained by simply using plywood made of zirconia material in the firing process of the mullite wiring board.

Claims (1)

[Claims] 1. Mullite sintering, which is characterized in that, in the firing process for producing a ceramic sintered body mainly composed of mullite, the object to be fired is fired on a plate made of zirconia and stabilized zirconia, or a heat-resistant plate coated with these. Method of firing the solid body.