JPH0460053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing round-cornered silica fine powder particles, and in particular to a method for producing silica fine powder particles suitable as a filler for synthetic resin compositions for encapsulating semiconductor devices. Regarding manufacturing methods.

(Prior Art) (Problems to be Solved by the Invention) Semiconductor elements are encapsulated with ceramic packages or resin to protect them from the external environment. For these reasons, synthetic resin compositions containing inorganic fillers have become popular.

This synthetic resin composition is composed of a synthetic resin such as an epoxy resin and an inorganic filler such as silica, but these compositions have a small coefficient of thermal expansion, good thermal conductivity, low moisture permeability, and mechanical properties. In order to have excellent properties and low cost, it is necessary to incorporate this inorganic filler in as much amount as possible, as long as its moldability allows.

In particular, silica-based fillers are considered to be most suitable as inorganic fillers, and are used in most synthetic resin sealing fillers. There are two types of silica fillers: crystalline and amorphous. Crystal type silica is manufactured by crushing and refining highly pure natural white silica or crystal. This type has excellent thermal conductivity.

Amorphous silica includes fused silica, which is produced by melting crystalline silica at high temperatures, and dry and wet synthetic silica. Since this fused amorphous silica has excellent thermal expansion characteristics, it is used in large quantities industrially. However, as the integration of semiconductor devices progresses, there is a tendency to emphasize thermal conductivity, and the need for crystalline silica is also increasing.

The finely divided silica particles commonly used as fillers are obtained through a conventional crushing process, and the particles have corners as shown in the photographs in FIG. 2 or 4. If the particles have corners, their viscosity will increase when they are mixed with resin to seal a semiconductor element, which will cause a lot of wear on the mold, which will not only reduce workability, but also cause impurities to form due to wear on the mold. There are adverse effects such as contamination, and the amount of filler mixed cannot be increased, which limits the ability to improve performance.

Regarding amorphous type fused silica, attempts have been made to produce spherical silica. For example, Tokukai Akira
According to JP 58-145613 or JP 61-118131, crystalline fine powder silica is jetted out from a nozzle along with a gas flow, and particle dispersion, melting, cooling, etc. are controlled under appropriate conditions to form spherical non-silica particles. Create crystalline fine powder silica particles. However, this method has drawbacks such as high cost, particles melting into each other during the melting process, making it difficult to obtain a predetermined particle size distribution, and the strength of the resin composition decreasing due to the true spherical shape. It is limited to the intended use.

Furthermore, a method of spheroidizing particles using a mechanical method is also known. For example, spheroidization and adjustment of the required particle size distribution are performed using a fret mill such as a pan mill or an edge runner, but this method is applicable to particles of so-called medium or larger particles with a maximum particle size exceeding 500 microns. However, even if the above method is applied to fine silica powder with a maximum particle size of about 500 microns or less, the frictional resistance will be small because the fine particles will contain a large amount of air bubbles between the agglomerated particles, resulting in volume destruction due to compression. There is no abrasion. Therefore, it is not possible to obtain silica fine powder particles with rounded corners, which is the intended purpose.

Therefore, an example of manufacturing crystalline spherical silica is as follows:
Not proposed to date.

(Means for Solving the Problems) As a result of intensive study on a low-cost manufacturing method for silica fine powder particles having no corners, the present inventors have discovered that crystalline silica or amorphous silica fine powder particles are heated by a rotating roller from the outside. It was discovered that angular silica fine particles can be industrially advantageously rounded by rubbing the fine powder particles against each other in the presence of an aqueous medium while applying pressing force with a silica powder, etc., and this has led to the present invention. be.

The present inventors discovered that under a certain water pressure, the force of the waves causes the sand particles to rub against each other, causing the corners to be ground up.
Focusing on the formation process of singing sand, which has a shape close to a true spherical shape, we thought that by rubbing silica fine powder particles together, we could create rounded fine particles with rounded corners.As a result of our extensive research, we found that we could make silica fine powder particles from outside. It has been found that it is very effective to apply an appropriate pressing force and to add an aqueous medium to make this pressing force effectively reach the silica particles.

The aqueous medium used in the present invention may be any liquid that allows fine silica particles to interact with each other and easily transmits pressure from the outside to the powder, and liquid substances such as water, alcohols, and mineral oil can be advantageously used. but,
Due to the cost of the medium, ease of handling during operation, and ease of separation after operation, water alone or water with ethanol,
A medium in which an alcohol such as methanol is dissolved can be most advantageously used industrially.

When carrying out the present invention, equipment suitable for the method of the present invention is firstly a roller mill. A roller mill has a grinding bowl rotated by a rotor and at least two grinding rollers rotating on a rotating track inside the grinding bowl, and uses air pressure to press the rollers against the material to be ground. It is designed to be able to apply pressure such as hydraulic pressure. When carrying out the present invention using a roller mill, if only the fine powder is charged into the roller mill and rounded without adding an aqueous medium, the fine powder will escape from the roller and the efficiency will be low. Adding an appropriate amount of water or other medium allows the pressing force of the roller to be smoothly transmitted to the powder, allowing efficient cornering operations.

The present invention can be applied equally advantageously to crystalline and amorphous silica fine powder particles.

The maximum particle size of the fine silica powder used as a raw material in the present invention is usually about 500 microns or less, and when cutting fine powder of such size with a roller mill, the amount of aqueous medium to be added is 0.5 to 18% by weight, preferably 3 to 18% by weight
13% by weight is suitable. The amount added is 0.5% by weight
If the amount is less, the pressing force of the roller will not reach the fine silica powder sufficiently, and the powder will escape from the roller, so that the frictional force between the particles will not work and the effect will be degraded. Furthermore, if the amount of liquid added is greater than the amount of fine silica powder, the fine silica powder will become lump-like or slurry-like, making the cornering operation difficult.

The maximum particle size of the silica fine powder particles obtained by the method of the present invention is usually 300 microns or less, and the average particle size is usually 7 to 35 microns.

In addition, the pressure applied to the roller from the outside cannot be numerically limited because the method of pressure differs depending on the machine, but if the pressure is too strong, not only the corners will be removed, but the particles will be crushed in volume, and the pulverization will progress. Cornering is inhibited. In addition, if it is too weak, the efficiency of cornering will decrease, so it is better to decide appropriately depending on the equipment, raw materials, type (crystalline, amorphous), etc. Furthermore, it is also possible to send coarsely crushed products of several mm or less directly to this squaring process, and perform the squaring operation at the same time as crushing to a desired particle size.

An example of implementing the present invention will be explained using FIG. 1.

First, a high-purity silica ingot or a high-purity fused silica ingot is coarsely ground using a crusher such as a geocrusher. In this case, to prevent contamination, the crusher liner is preferably made of high-purity alumina or the like. It is then further coarsely pulverized using a roll crusher or the like. In this case as well, the rolls etc. may be made of high purity alumina or the like.

Silica is pulverized to several millimeters or less at a normal outlet, but this is usually further pulverized using a ball mill or the like to obtain fine silica powder with a maximum particle size of about 500 microns or less. The finely powdered silica thus obtained is sent to a squaring process using a roller mill or the like according to the present invention. When using a roller mill,
The parts of the rotating bowl, rollers, etc. that come into contact with the fine silica powder particles are made of ceramic or lined with polyurethane resin to prevent contamination due to abrasion. In some cases, coarsely crushed products such as roll crushers are sent directly to the rounding process.
By appropriately controlling the operating conditions, it is also possible to carry out the pulverization and cornering operations at the same time. The maximum particle size of the fine silica powder after the shaving operation is usually 300 microns or less, and it is sent to the drying process to be dried and made into a product.

When carrying out the present invention, it is advantageous that an ordinary roller mill or the like can be used as is or with only a slight modification such as making the part that comes into contact with the fine silica powder a ceramic material or lining it with a polyurethane resin. Running costs are also very low, as most of them are mechanical power costs such as rotation.

The method of the invention can be carried out either in batch or continuous operation.

In this specification, the average particle diameter is measured using a laser diffraction particle size distribution analyzer (CILAS, model 715).
Measured using

(Example) The present invention will be specifically explained below using Examples.

Example 1 500 g of silica having an average particle diameter of 23.2 microns, which had been pulverized in advance by a ball mill, was placed in a roller mill (MPV-0.5 type, manufactured by Matsumoto Cast Iron Works), and 60 ml of water was added at the same time. Roller pressing force
40Kg/cm (linear pressure), the clearance between the roller and the bottom plate is 3mm, and the rotation speed of the bottom plate is set to 42rpm.
As a result of the time treatment, the average particle diameter of the obtained treated product was 19.4 microns. Compare the electron micrograph with the raw material figure 2 (100 times) and see figure 3 (200 times).
As shown in Figure 2, the shape of the treated silica particles was considerably rounder than that of the raw material.

Example 2 500 g of crushed fused silica with an average particle size of 24.6 microns was pulverized by a ball mill in advance in a roller mill (MPV-0.5 type, manufactured by Matsumoto Cast Iron Works).
and 60 ml of water was added at the same time. The treatment was carried out for 1 hour at a roller pressing force of 20 kg/cm (linear pressure), a clearance between the roller and the bottom plate of 3 mm, and a rotation speed of the bottom plate of 42 rpm. The average particle diameter of the obtained treated product was 18.6 microns, and the electron micrographs were compared with the raw materials in Figure 4 (100x) and Figure 5 (250x).
As shown in Figure 2, the particle shape of the treated silica was considerably rounder than that of the raw silica.

Example 3 The same treatment as in Example 1 was carried out except that 60 ml of 50% ethanol aqueous solution was used instead of 60 ml of water. As shown in Figure 3, the photograph shows that the treated product was considerably rounder than the raw material.

(Effect of the invention) Conventionally, in the technical field of fine pulverization, it has been found that if the pulverized material contains 5% by weight or more of water, the pulverized material will adhere to the inside of the pulverizer.
It was believed that the buffering effect significantly reduced the grinding efficiency. However, in the present invention, it has been found that the buffering effect unexpectedly has a large effect on the spheroidization of fine powder particles. This seems to be because the presence of 0.5 to 18% by weight of the aqueous medium based on the fine powder particles has the effect of changing the fluffy packing structure of aggregated particles of the fine powder to the packing structure of primary particles.

By carrying out the present invention, it is possible to make angular and crushed silica rounded, whether it is crystalline silica or amorphous silica, and the silica obtained by the present invention can be used as a filler for resin sealing of semiconductor elements. When used as an agent, workability in the resin-sealed transfer molding process can be improved.

[Brief explanation of the drawing]

Figure 1 is a process diagram showing an embodiment of the present invention, Figure 2 is a process diagram showing an embodiment of the present invention.
The figure and FIG. 3 are electron micrographs showing the crystal structure of the crystalline silica of Example 1 before and after the treatment;
4 and 5 are electron micrographs showing the crystal structure of the fused silica before and after the treatment in Example 2. FIG.

Claims (1)

[Scope of Claims] 1. While applying a pressing force to crystalline silica or amorphous silica fine powder particles from the outside with a rotating roller, the fine powder particles are rubbed against each other in the presence of an aqueous medium without causing volume destruction, thereby forming an angular shape. A method for producing fine silica powder particles characterized by rounding the particles. 2. The method according to claim 1, wherein the aqueous medium is water or a mixture of water and alcohol. 3. The method according to claim 1, in which the operation of applying pressing force from the outside with a rotating roller is performed using a roller mill. 4 The maximum particle size of the obtained silica fine powder particles is
The method according to claim 1, wherein the particle size is 300 microns or less.