JPH01190407A - Method for manufacturing green sheet - Google Patents

Abstract

PURPOSE:To enable the prevention of cracking to be rendered in a short period process of time by the use of adhering of a solvent permeable film on the slurry thin film as a laminate film and then drying and separating. CONSTITUTION:Drying is performed in a state of adhering the laminate film consisting of a solvent permeable material on the slurry thin film. A porous organic film is suitable as a solvent permeable film. As performing in this manner, rapidly drying on the surface can be restrained, so that it becomes possible to prevent the occurrence of cracking and, even if a doctor blade method may be employed with respect to a thick ceramic substrate, the substrate can be made without any crack.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for producing a thick green sheet, the purpose is to form a green sheet with no cracks and good surface roughness, by forming a slurry by a doctor blade method and placing it on a carrier tape. In the process of making slurry 119 and drying this thin film and peeling it off to form a green sheet, a solvent-permeable film is pasted on the slurry thin film as a laminate tape, used, and dried to form a green sheet. Manufacture sheets.

[Industrial application field]

The present invention relates to a method for manufacturing a thick green sheet.

Due to the need to process large amounts of information at high speed, information processing technology has progressed significantly, and electronic circuit elements, including semiconductor elements that make up the main body of information processing equipment, are becoming smaller. In particular, the amount of heat generated per unit area of a substrate on which a semiconductor element is mounted is increasing.

For example, the amount of heat generated per unit chip of LSI has reached about 10W, so the package and heat sink in which it is mounted must be heat resistant and have high insulation resistance, and alumina (α-A j! Ceramics such as zOs) are often used.

Furthermore, for applications such as heat sinks that require high thermal conductivity, ceramic substrates made from ceramics with excellent thermal conductivity such as aluminum nitride (AItN) and silicon carbide (SiC) are being put into practical use.

There are various methods for manufacturing such ceramic molded products, such as the hot press method, but in order to form a flat and large substrate, a green sheet of the required size is made using the Dokuku blade method, which is then fired after drying. This method of making ceramics is suitable for mass production and is used for -a.

[Conventional technology]

Multilayer ceramic substrates using Narumina are used as substrates on which semiconductor integrated circuits such as LSI and VLSI are mounted.

The method for producing this single-layer green sheet is to add a plasticizer, a dispersant, and a solvent to alumina powder, knead it thoroughly using a ball mill to form a slurry, and then form the green sheet using a doctor blade method to form a green sheet with a thickness of about 300 μm. forming a sheet.

After drying and solidifying the surface, the via holes are punched and formed, and then a conductive paste such as tungsten (W) paste is screen printed to fill in the conductive patterns and via holes, and then a green sheet is formed. A multilayer ceramic substrate is produced by aligning and stacking the materials, applying pressure to integrate them, and firing them at a high temperature.

However, ceramic substrates are not necessarily as thin as this, and some are as thick as 1111 or more, such as heat sinks.

In this case, in the doctor blade method, a blade is placed with a gap of about 50 μm in thickness (for example, 300 μm) in between, and the carrier film is transferred to apply a slurry of the thickness of the gap from the slurry reservoir onto the carrier film. A green sheet is formed by peeling after drying.

In this process, the green sheet is kept at a relative humidity of 50%,
By drying at a temperature of about 25° C., the concentration gradient of the solvent in the thickness direction becomes significant, resulting in cracks on the surface.

In other words, cracks occur because the surface is dry even though the inside is wet, and the limit at which cracks do not occur using conventional methods is approximately 350 μm.

Therefore, in order to form a thick green sheet with a thickness of Igum or more, drying under reduced pressure in a solvent atmosphere was required, but since it was done in a closed container, the workability was poor (drying took a long time, and the manufacturing yield was There were problems such as poor performance.

[Problem to be solved by the invention]

As mentioned above, like the package material, the thickness is 1-
When forming thick ceramic substrates using the doctor blade method, cracks are likely to occur during the drying process of the green sheet, and to avoid this, it takes a long time to dry, and the manufacturing yield is low. .

[Means to solve J]

The above problem can be solved by forming a thin film of slurry on a carrier tape using the doctor blade method, and then peeling it off after drying to form a green sheet. This can be solved by attaching it to the surface, drying it, and then peeling it off to produce a green sheet.

[Effect]

When a thick green sheet is formed by the doctor blade method, cracks, warpage, etc. occur, but this depends on the evaporation state of the solvent.

That is, cracks occur because the surface dries faster than the inside, and warpage occurs because the drying conditions differ between the front and back surfaces.

Therefore, the inventors realized that it would be sufficient to coat the thin slurry film with a solvent-permeable film and dry it.

That is, drying may be performed with a laminate film made of a solvent-permeable material attached on top of the thin slurry film in the same manner as the carrier film.

In this way, drying will occur from the surface.
It is possible to suppress the rapid drying of the surface, thus making it possible to eliminate the occurrence of cracks.

In addition, as mentioned earlier, the warpage of the substrate is caused by the difference in drying conditions between the front and back sides, so if a solvent-permeable film is used as the carrier film, this occurrence can be suppressed to a considerable extent. can.

In general, solvent-permeable films include paper and porous film, with the latter being suitable.

The reason for this is that paper has an excellent ability to penetrate solvents, but it also penetrates binders and plasticizers that make up the slurry, changing the composition of the slurry surface, and also causing the paper to become greener when peeled off after drying. It is difficult to obtain a smooth surface condition because parts of the sheet stick to the paper and tend to peel off.

On the other hand, organic films are made of 66 nylon, etc.
Ultrafiltration membranes are commercially available films that have a fixed average pore size and do not allow molecules larger than a specified size to pass through.

Therefore, if drying is performed using an ultrafiltration membrane that allows only the solvent to pass through but not large molecular weight liquids such as binders and plasticizers, a green sheet with a smooth surface and no cracks can be obtained.

〔Example〕

Alumina (main constituent material)...100 parts by weight Magnesia (additive material)...0.25
〃Dibutyl phthalate (plasticizer)...8.0 parts by weight Polyvinyl butyral (binder)...4.0〃
Fish oil (dispersant)...1.7 Ethyl alcohol (solvent)...50 is well kneaded in a ball mill to form a slurry, and this is used as a carrier tape using Mylar with a thickness of 50 μm as before. Using the doctor blade method, the molding gap is 2M and the molding speed is 2M.
．． The slurry was molded at a speed of 5 m/min.

Then, we made slurry thin films with and without ultrafiltration membranes and Gio tape attached to the surface, and kept the relative humidity at 50%.
It was dried at a temperature of 25°C and peeled off to form a green sheet.

The ultrafiltration membrane used in this example had a molecular weight of approximately 1000.
There are micropores that do not allow anything greater than 0 to pass through.
It allows the solvent (ethyl alcohol in this case) to pass through, but not materials such as polyvinyl butyral (abbreviated as PVB) and dibutyl chloride (abbreviated as DnP), and is suitable for the purpose of the present invention of removing only the solvent.

The table shows the results.

Next, the crack-free and smooth green sheet thus formed is then fired in the air at a temperature of 1,600°C for 3 hours to produce a crack-free ceramic substrate with a good surface condition. did it.

〔Effect of the invention〕

Claims (2)

[Claims] (1) The main component is ceramic powder, a plasticizer, a dispersant, and a solvent are added, kneaded to make a slurry, and the slurry is molded using a doctor blade method to form a thin film of the slurry on a carrier tape. A method for producing a green sheet, characterized in that, in the step of forming a green sheet by peeling off after drying, a solvent-permeable film is used as a laminate tape and adhered to the slurry thin film, and then dried. (2) The method for producing a green sheet according to claim 1, characterized in that an ultrafiltration membrane is used as the solvent permeable film.