JPH0625031B2 - How to make powder sinter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a sintered body from powder, and in particular,
TECHNICAL FIELD The present invention relates to a method of mixing a powder, a flux (firing aid), a binder and a solvent to form a slurry, forming a green sheet from the slurry, and firing the green sheet to form a sintered body. .

[Problems to be Solved by Conventional Techniques and Inventions] The size and accuracy of alumina substrates are rapidly increasing.
This is because it is indispensable for automation of manufacturing thick film hybrid ICs and packages. In the conventional alumina substrate, the dimensional accuracy was about ± 0.8%, and the warpage was 0.2 mm / 25 mm or less. On the other hand, in the case of a large, high-precision alumina substrate (100 x 100 mm or more), the dimensional accuracy is ± 0.
3% or less and warpage of 0.1 mm / 25 mm or less are required. Generally, a ceramics sintered body, for example, an alumina substrate, has a raw material α-alumina and a flux (sintering aid).
And the organic resin (binder) as a binder
It is prepared by mixing a solvent and a solvent to form a slurry, forming a green sheet by a doctor blade method, and firing it. At this time, the green sheet usually causes a volume contraction of 40 to 50%, and accordingly, a warp occurs. The volume shrinkage is considered to be closely related to the powder filling rate of the green sheet, but in reality, a large fluctuation is seen.

It is an object of the present invention to provide a method for producing a sintered body from powder, which has a low shrinkage anisotropy and is less likely to be deformed, warped, or cracked.

[Structure of the Invention] [Means for Solving the Problems] The gist of the present invention is to form an oxide powder or a metal powder and fire the formed body to form a sintered body. The method for producing a sintered body according to the method is characterized in that, when the formed body is formed of the powder, a binder is contained in an amount corresponding to the volume of voids formed by the powder. In that case, it is preferable that the content of the binder is set to 18% by weight or more and the filling rate of the powder is controlled to 60% by volume or more.

Generally, in the production of a sintered body, a powder of a raw material is mixed with a flux (firing aid), a binder and a solvent to produce a slurry, and a green sheet is molded from the slurry and dried. Various green sheets can be obtained. It was considered that the shrinkage rate of the fired sheet obtained by firing this green sheet depends not only on the particle size of the raw material powder but also on the powder filling rate in the green sheet.

That is, the inventors considered the relationship (formula) between the firing shrinkage rate and the powder filling rate as follows.

Apparent specific gravity ρ ₃ is ρ ₃ = W ₃ / V ₁ ...... A where ρ ₃ is the apparent density of the powder, W ₃ is the powder weight in the green sheet, and V ₁ is the green sheet It is the volume.

The logical density ρ of the substrate is expressed by the following equation, where W is the weight of the substrate whose volume is V ₁ .

ρ = W / V ₁ ... B The powder filling rate is expressed by the following formula C from formulas A and B.

ρ ₃ / ρ = (W ₃ / V ₁ ) / (w / v ₁ ) = W ₃ / W …… C The firing linear shrinkage in the X, Y, Z directions of the green sheet is α _X , α _Y , α _Z Then, the sintered density ρ _r of the substrate is _expressed by the D equation.

(Ρ _f / ρ) = (ρ ₃ / ρ) / {(1-α _X ) × (1-α _Y ) × (1-α _Z )}
...... D Therefore, the powder filling rate (σ ₃ / ρ) is (ρ ₃ / ρ) = (ρ _f / ρ) / ((1-α _X ) × (1-α _Y ) × (1-α _Z )}
...... E Here, (ρ _f / ρ) is the relative ratio of the sintered density to the logical density. If the firing shrinkage of the green sheet is isotropic, α _X = α _Y = α _Z and the following is obtained. That is, Therefore, it is understood that the linear shrinkage ratio can be uniquely obtained if the powder filling rate and the relative density are determined.

The sintering properties of a powder material depend on the powder properties of the material and the natural properties of the material. That is, in the powder characteristics, the particle size,
Depends on particle size distribution, shape, etc. Agglomeration of powder during the production of green sheets also has a significant effect. In addition, the sintering temperature and reactivity, which are the original properties of the material, are considered. Regarding the particle size and shape of the powder, we have already developed a method for creating spherical monodisperse spheres, and also for the aggregation of powder, in addition to creating monodisperse spheres, the disaggregation method was used to disaggregate the aggregates. . From this, it can be easily inferred that the sintering characteristics of the material can be controlled by controlling the particle size of the powder. Further, it is possible to increase the powder filling rate. If the raw material is a spherical material having the same diameter, the powder packing rate can always be the closest packing regardless of the size of the system.

The present invention makes use of such a sintering control technique to obtain a sintered body. As a means for this, a green sheet with a controlled powder filling rate is prepared.

That is, the powder filling rate of the ceramic green sheet actually varies, and in particular, the powder filling rate variation in the Z-axis direction is large. For example, in the molding method by the doctor blade method, the powder filling rate of each of the blade surface, the central portion and the film surface is highest in the central portion, and decreases in the order of the blade surface and the film surface. As described above, due to the difference in the powder filling rate, the firing shrinkage rate is different in each green sheet layer, so that warpage occurs and the dimensional accuracy also deteriorates.

In the powder sintering technology as described above, the powder is molded,
When the obtained molded body was fired to obtain a sintered body, its characteristics were evaluated and measured as follows.

[Evaluation Method] The powder filling rate of the molded body was calculated by the following procedure. The molded body was punched with a mold and its weight (W ₁ ) was measured. Further, the underwater weight (W ₂ ) of this sample was measured, and the volume (V ₁ ) of the sample was measured by V ₁
= (W ₁ −W ₁ ) × (water density) Then 800
The binder and the plasticizer were removed by firing at 1 ° C. for 1 hour, and the weight (W ₃ : sum of the weight of alumina and glass flux) was measured. The true densities of alumina and glass flux were measured by the Archimedes method. From the above, the volume of alumina and glass flux in the compact V ₂ = (0.96 × W ₃ ) /3.97 and V ₃
= 0.04 × W ₃ ) /2.68 was calculated, and the powder filling rate was calculated from the equation (1).

Powder filling rate = (V ₂ + V ₃ ) / V ₁ = [{(0.96 × W ₃ ) /3.97} + {(0.04 × W ₃ ) /2.68}] / V ₁ …… (1) The total content (w) of the binder and the plasticizer contained was calculated as follows. First, the weight of the compact (W ₁ ) and 80
The weight (W ₃ ) after firing at 0 ° C for 1 hour was measured, and the weight difference (W ₁
-W ₃ ).

The composition of the glass flux contained in the molded body was quantified by a fluorescent X-ray analysis method. For SiO ₂ , MgO, and CaO in the flux, a sample curve having a known composition ratio was prepared and a comparative curve was quantified.

The particle size distribution of alumina and glass flux is Micro Full Autosizer (manufactured by Seishin Enterprise Co., Ltd., model SKN-50).
It was measured in 0). The average particle size was 50% of the particle size distribution curve.

The specific surface area of alumina and glass flux is measured by BET specific surface area automatic measuring device (manufactured by Shimadzu Corporation, model 220).
It was measured in 0).

The firing shrinkage was calculated from the equation (2). The sample is 34.7.
The molded body was die-cut into a size of 3 × 42.26 mm.
L ₁ and L _{2 in the} equation (2) are average values of the lengths in the long side direction before and after firing of 10 measurement samples.

That is, firing shrinkage (%) = {(L ₁ −L ₂ / L ₁ } × 100 ... (2) Warp is the distance between the platens when the baked substrates are sandwiched between two platens ( t ₁ ) and the thickness (t ₂ ) of the fired substrate were measured, and (t ₁ -t ₂ ) was calculated and converted per unit length.The direction of warpage was in contact with the carrier film (mylar film) of the molded product. The surface (abbreviated as a film surface) that warped inward was defined as a positive warp, and the surface opposite to the film surface (abbreviated as a blade surface) was defined as a negative warp.

When firing a formed body or green sheet formed from a slurry, parameters such as the composition of the raw material powder, the flux composition ratio, and the particle size distribution of the oxide powder are used for the accuracy, warpage, and firing shrinkage of the produced sintered body. Although it is considered to have an influence, according to the present invention, the factor due to the fluctuation of the powder filling rate is the largest. That is, in the method for producing the powder sintered body, the variation of the powder filling rate in the raw material powder compact is about 60%.
It becomes smaller by controlling the capacity to be more than%. In the present invention, by further mixing the binder amount corresponding to the voids formed by the powder particles, the difference in the powder filling rate becomes almost zero, and the production method for obtaining a fired sheet with almost no warpage is found. Is.

Furthermore, as described above, it is more preferable to control the filling rate of the raw material powder to 60% by volume or more if possible.

The present inventors have conducted the following experiments and found out the gist of the present invention.

That is, first, it is considered that the warpage of the sintered substrate, which occurs when firing the molded body (green sheet), is influenced by the powder physical properties of the raw material powder (alumina, flux) and the characteristics of the molded body. The experiment was conducted.

First, two types of green sheets with different powder filling rates are
It was created by changing the specific surface area of the flux.

Green sheets with powder filling rates of 57% by volume and 61% by volume were fired at 1550 ° C. The shape of the warp in the X direction at that time is shown.

A green sheet having a powder filling rate of 61% by volume was prepared by using a glass flux having a specific surface area of 20 m ² / g.

Further, a green sheet having a powder filling rate of 57% by volume was manufactured using a glass flux having a specific surface area of 364 m ² / g. As a result, the warpage became larger toward the edge of the substrate. All of the warps occurred in the direction in which the film surface was rolled up. Moreover, when the blade surface was baked down, the amount was 1/2 or less of that when the blade surface was baked up.
A green sheet with a high powder filling rate, that is, a specific surface area,
In the case of using 20 m ² / g of glass flux,
The warpage was 0.03 mm / cm. It is considered that the warp of the substrate occurs due to the difference in firing shrinkage between the film surface of the green sheet and the blade surface.

In the preparation of the green sheet described above, when the solvent in the slurry evaporates, a void corresponding to the solvent is formed on the surface, and the binder solution moves along this void (capillary tube) due to the capillary phenomenon (chemical suction). As a result, when the binder amount is less than 39.55% by weight of all the voids, the binder content on the film surface becomes smaller than that on the blade surface, resulting in a difference in filling rate. As shown in the examples below, when the binder is 18% by weight or more, which corresponds to the void volume, the voids are filled with the binder, which can be prevented.

Further, although the present invention will be described by the doctor blade method in the present specification and examples, other methods such as a slurry casting method can be used. That is, if there is movement of the solvent (the above-mentioned chemical suction), the same variation of the filling rate occurs, and the same application is possible.

Next, the method for producing the powder sintered body of the present invention will be described with reference to specific examples, but the present invention is not limited to the description.

[Example 1] As an alumina powder, AL-45 manufactured by Showa Denko KK
R α-alumina (purity 99.5% by weight, average particle size 1.1
[mu] m) with 96% by weight, as a flux, Al ₂
O ₃ 6.1% by weight, SiO ₂ 61.9% by weight, MgO ₂
Using 4% by weight of glass flux having a composition of 8.6% by weight and CaO 3.4% by weight, the specific surface area of the raw material powder is 20%.
m ² / g. As a binder, polyvinyl butyral (manufactured by Sekisui Chemical Co., type BL-2) was used at an addition amount of 4, 6, 9, 12, 18 and 19% by weight with respect to the inorganic substance to prepare 6 types of compounded samples.

As the plasticizer, butylbenzyl phthalate (manufactured by Daihachi Chemical Co., Ltd.) was added in an amount of 3 parts by weight with respect to the inorganic substance. These compounds were mixed with a solvent in a ball mill, and then the mixture was collected in a ball mill pot and dispersed by a dispersion mixing method in which 60% by weight of trichlorethylene, 23% by weight of terrachlorethylene and n-butanol 17 were mixed. Mixed in wt% mixed solvent.

The dispersion method for disintegrating agglomerates is the first step in which agglomerated particles are disintegrated into primary particles in a low-viscosity slurry, and the second step in which a binder and a plasticizer necessary for sheet formation are added and uniformly dispersed.
The step is to add the binder and the plasticizer in order to impart moldability and handleability to the green sheet. Next, a green sheet having a width of 500 mm and a thickness of 0.6 mm was formed from the slurry by a doctor blade method. Molding conditions are blade cap 1.8m
m, molding speed; 100 mm / min, and drying was performed under two conditions of normal temperature and heat drying.

First, the green sheet was punched into a size of 34.73 × 42.26 mm with a die to obtain a fired sample. The green sheet is fired by a fast heating furnace (Cantal Gadelius, RT-
2). At the time of firing, the temperature was first raised to 300 ° C. at a heating rate of 450 ° C./hour and kept for 1 hour. The binder contained in the green sheet in this step is 60-
70% removed. Next, the temperature was raised to 1200 ° C. at a temperature rising rate of 900 ° C./hour, and the residual binder was decomposed and removed by burning. After that, the temperature was raised to a predetermined temperature (1550 ° C.) at a temperature rising rate of 4.5 ° C./min, and the temperature was maintained for 1 hour for sintering. Cooling is performed in the furnace (cooling rate; 7 ° C /
Minutes).

The firing profile up to 1200 ° C. is for avoiding problems such as swelling, deformation, and firing cracks of the substrate that often occur when removing the binder.

The binder content was changed as described above, and the binder content on the film surface and the blade surface of the green sheet was measured, and the difference was plotted on the vertical axis and shown in the graph of FIG. From the graph of FIG. 1, the difference in the content of the binder between the film surface and the blade surface decreased as the binder content increased, and disappeared when the binder content reached 18% by weight.

Further, the packing ratio of the alumina powder on the film surface and the blade surface of the formed green sheet was measured by the above-described measuring method, and the measured value was plotted against the binder content as shown in FIG. Is. From these, the difference in the powder filling rate between the film surface and the blade surface decreased as the binder amount increased. Then, when the amount of the binder reaches an amount corresponding to the void volume formed when the powder particles are arranged in eight coordination, that is, 18% by weight, the powder surface and the blade surface have the same powder filling rate of green. Turned out to get a sheet.

[Example 2] The binder content was set to 18% by weight, and the powder filling rate was set to 60.
~ 61% by weight of the green sheet, changing the thickness,
Prepared as above, degreased and fired at 1550 ° C.
The results of the warpage are observed, and the relationship with the thickness of the sintered body is plotted in a graph in FIG.

As shown in FIG. 3, even with a green sheet of 0.4 mm or more, almost no warpage occurred.

On the other hand, a green sheet having a binder content of 6% by weight and a powder filling rate of 61% was similarly prepared, degreased and prepared at 1550 ° C. At this time, the warp is 0.
It was 03 mm / cm.

[Effects of the Invention] The method for producing a powder sintered body of the present invention has the following remarkable technical effects.

First, in the case of forming a powder raw material and firing the formed body, if only specific parameters are controlled, it is possible to provide a method for producing a powder sintered body without causing warpage. It was

Secondly, a method for producing oxide ceramics with a very low firing shrinkage rate was provided.

Thirdly, therefore, there is provided a method by which a highly accurate ceramics sintered body can be easily produced.

[Brief description of drawings]

FIG. 1 is a graph showing changes in the difference in binder content on both sides of the green sheet when the binder amount is changed in the firing method according to the present invention. FIG. 2 is a graph showing changes in the difference in powder filling rate on both sides of the green sheet when the amount of binder is changed in the firing method according to the present invention. FIG. 3 is a graph showing the warpage that occurs when the thickness of the green sheet is changed in the firing method according to the present invention.

Claims (1)

[Claims] 1. A method of forming an oxide powder or a metal powder and firing the formed body to form a sintered body, wherein the powder is formed into the formed body by a doctor blade method. At this time, the method for producing a sintered body is characterized in that the binder is contained in an amount corresponding to the volume of voids formed by the powder.