JP3521954B2 - Manufacturing method of aluminum nitride green sheet - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing aluminum nitride green sheets. [0002] In recent years, high-power modules such as high-power and high-efficiency inverters have been changing along with the high performance of industrial equipment such as robots and motors, and the heat generated from semiconductor elements has also been increasing. . In order to efficiently dissipate this heat, an aluminum nitride substrate having high thermal conductivity has recently been used. Conventionally, an aluminum nitride substrate has been manufactured by sintering an aluminum nitride green sheet formed by a doctor blade method. The doctor blade method consists of applying a slurry on a film of PET or the like and drying the formed sheet. However, the solvent often expands in the green sheet and voids are generated. These voids become voids in the aluminum nitride sintered body as they are, which is a major cause of deteriorating strength and thermal resistance and impairing reliability. In particular,
The problem of voids was serious because aluminum nitride has a higher adsorptive power to the solvent than alumina. The inventors of the present invention have conducted various studies to solve the above problems, and have found that controlling the initial drying speed of the green sheet according to the specific surface area of the aluminum nitride powder can significantly reduce the generation of voids. They have found and completed the present invention. [0005] That is, the present invention provides:
In a method in which aluminum nitride powder is slurried with a solvent and then sheeted with a doctor blade and then dried,
When the amount of solvent required to make the aluminum nitride powder into a slurry is V parts by weight , the ratio of the aluminum nitride powder is
When the surface area is less than 4 m ² / g, the evaporation up to 0.7 V is dried at a rate of 0.01 V to 0.015 V / min.
And the specific surface area of the aluminum nitride powder is 4 m ² / g or less.
When it is above, evaporation up to 0.6 V is performed from 0.01 V to
A method for producing an aluminum nitride green sheet , comprising drying at a rate of 0.015 V / min . Hereinafter, the present invention will be described in more detail. A slurry for forming an aluminum nitride green sheet by the doctor blade method is usually 1 to 8 parts of a sintering aid and 100 parts (parts by weight) of an aluminum nitride powder, and an organic binder. 3 to 15
Parts, plasticizer 1 to 10 parts, dispersant 0.3 to 3 parts, solvent 10
It is prepared by blending ボ ー ル 100 parts and mixing with a ball mill. As the sintering aid, oxides and carbonates of alkaline earth metals, alumina, oxides of rare earth elements and the like are used, and yttria is most suitable. Organic binders such as polyvinyl butyral, polyvinyl alcohol, acrylic polymers, etc., plasticizers such as dibutyl phthalate, dioctyl phthalate, etc. Organic solvents such as alcohols such as isopropanol, ketones, aromatics, paraffins and chlorines are used. The slurry has a viscosity of 1000 in a vacuum defoamer.
After being adjusted to about 0 to 30,000 cps, it is coated on a film of PET or the like by a doctor blade, formed into a sheet, and then dried. The main thing that evaporates in the drying step is a solvent. When observing the existence form of the solvent in the slurry in detail, a certain amount of the solvent acts as a solvent for the slurry, but the rest is present in a state of being supported in the aggregated particles of the aluminum nitride powder. The solvent that has participated in this solvent action evaporates immediately and jumps out of the system, but the one carried in the agglomerated particles of aluminum nitride powder evaporates immediately even when the temperature in the system rises and approaches the boiling point Without any changes. Therefore, if the temperature is rapidly increased shortly after the application and the amount of the solvent is still large, the solvent as the solvent will evaporate rapidly. There is no problem if such a solvent exists on the sheet surface, but if it exists inside the sheet, it evaporates and expands in the sheet before flying off the system, and that part becomes a void. If the situation worsens, the part is broken and cracked. If the solvent almost disappears as the solvent and the solvent carried in the aggregated particles of the aluminum nitride powder becomes dominant, the temperature does not evaporate immediately at a low temperature, so that the temperature needs to be considerably increased. The ratio between the solvent as the solvent and the solvent carried in the aggregated particles of the aluminum nitride powder is closely related to the specific surface area of the aluminum nitride powder rather than the type of the solvent. The ratio changes when the BET specific surface area of the aluminum nitride powder is 4 m ² / g, depending on the cohesion state and surface tension of the aluminum nitride powder in the slurry, and when the specific surface area is smaller than 4 m ² / g, the solvent is reduced. Is about 70% by weight, and when it is 4 m ² / g or more, about 60% by weight. In order to dry the green sheet so as not to cause voids, the specific surface area of the aluminum nitride powder used is 4 m ² / g when the amount of the solvent required for slurrying is V parts by weight. 0.7V if less than
Until the solvent in the slurry is reduced to 0.3 V, the drying speed is 0.01 V to 0.015 V / min, and the specific surface area of the aluminum nitride powder is 4 m ² / g.
In the case above, the evaporation rate up to 0.6 V, that is, the drying rate until the solvent in the slurry is reduced to 0.4 V is set to 0.1.
It is performed at a voltage of 01 V to 0.015 V / min. Regardless of the specific surface area, if the drying rate is less than 0.01 V / min, the productivity is reduced, and if it exceeds 0.015 V, the effect of suppressing the generation of voids is reduced. Such adjustment of the drying speed can be performed by adjusting the temperature of the drying zone, and adjusting the temperature and the amount of air when hot air is blown. The aluminum nitride green sheet produced according to the present invention is degreased and fired to form an aluminum nitride sintered body. The degreasing condition is usually set to a temperature of 900 ° C. or less in nitrogen and / or air, especially in an atmosphere containing air.
Performed at 0 ° C. or lower. The firing is performed at a temperature of about 1800 to 2000 ° C. in a non-oxidizing atmosphere such as nitrogen or argon. The present invention will be specifically described below with reference to examples and comparative examples. Examples 1 to 3 Comparative Examples 1 to 2 Two types of aluminum nitride powders 100 having different specific surface areas
Parts, yttria 4 parts, polyvinyl butyral 6
Parts, butyl phthalate 3 parts, glycerin triolate 1
Parts and 60 parts of xylene (V = 60) were mixed in a nylon pot for 24 hours. The obtained slurry was spread on a PET film into a sheet having a width of 30 cm by doctor blading, and dried under the conditions of drying profiles 1 to 3 shown in Table 1. The drying speed was adjusted by adjusting the temperature of the drying zone while constantly measuring the amount of decrease in the weight of the green sheet as a decrease due to evaporation of the solvent. The obtained green sheet is 30 cm × 30
cm, solidified with liquid nitrogen, and then fractured. Observe a 0.3 mm × 0.3 mm cross section with a scanning electron microscope (SEM), and determine the number of voids of 15 to 30 μm and more than 30 μm. 5 sections were counted. Such a measurement was performed for four other sheets (total of five sheets). Table 2 shows the average value of the results. Comparative Example 4 A green sheet was produced in the same manner as in Example 1 except that the sheet spread on the PET film by doctor blading was dried for 60 minutes in a drier kept at a temperature of 100 ° C. Was measured. This example is a typical example of the conventional method. [Table 1] [Table 2] According to the present invention, an aluminum nitride green sheet having a small number of voids can be manufactured.

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Claims (1)

(57) [Claims 1] In a method of slurrying aluminum nitride powder with a solvent, sheeting it with a doctor blade, and drying, the amount of solvent required for slurrying the aluminum nitride powder is determined. V parts by weight, aluminum nitride
When the specific surface area of the lithium powder is less than 4 m ² / g
Is, 0.01V~0.015V the evaporation of up to 0.7V /
Minutes, the aluminum nitride powder has a specific surface area of
When it is 4 m ² / g or more, evaporation up to 0.6 V
A method for producing an aluminum nitride green sheet , comprising drying at a rate of 0.01 V to 0.015 V / min .