JPS6140811A - Hydrated silica for melting and manufacture of melted silica by using it - Google Patents

Abstract

PURPOSE:To obtain the hydrated silica for melting suitable as raw materials in case of manufacturing the melted silica which has specified physical properties and is used a resin filler for sealing the semiconductor elements. CONSTITUTION:The hydrated silica for melting which has (i) <=10ppb content of alpha-radiator (expressed in terms of U and Th), (ii) <=10ppm content of Na plus Cl respectively and (iii) 0.5-10wt% water content is formed from an aq. alkali silicate soln. The melted silica obtained by subjecting the above-mentioned hydrated silica to the flame-melting treatment has less contents of impurities and also is excellent in melt fluidity and suitable as a filler used as the resin composition for sealing of semiconductors.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a raw material for high purity spherical fused silica and a method for producing fused spherical silica glass using the same.

More specifically, the present invention relates to a method for producing high-purity hydrated silica and anhydrous silica that can be used as intermediate raw materials that require high purity and high functionality, such as fillers for semiconductor resin filling, abrasive materials, substrates, and package materials.

Conventional technology A large amount of inorganic filler is used in the resin encapsulation of semiconductors, but this mainly uses crushed natural quartz, a certain type of crystalline silica, and fused silica, which is made by melting it at high temperatures such as in an oxyhydrogen flame. It is being

Recently, especially with the increasing integration of semiconductors, quality characteristics requirements for encapsulants have become even stricter. For example, regarding silica fillers, (1) higher filler filling, (2) lower alpha emitters (e.g., uranium, thorium) and (3) reduction of ionic impurities. In order to cope with these problems, using silica obtained by conventional crushing and/or melting of natural quartz as a filler has problems with purity, securing the quantity of resources, and economic efficiency, and also requires a stable state. It has become necessary to use a new synthetic silica. In response to this, halogenated silicon and organic silicon hydrolysis have been proposed, and recently silicic acids such as alkali silicates have been proposed. The reaction between salt and mineral acid is determined by hydrogen ion concentration/,
A method was proposed for producing quartz glass powder by precipitating hydrated silicic acid at below j, followed by washing, drying and firing (
Problems to be Solved by the Invention The present inventors first precipitated silica gel from a silica sol based on ion exchange using an aqueous alkali silicate solution as a silica source, or precipitated silica gel from a silica sol based on ion exchange, or reacted with a mineral acid. We have developed a method for producing silica with an extremely low α-emitter content by treating the silica gel produced in the above with acid, or a method for producing spherical silica by melting it.

When manufacturing spherical silica glass powder by melting the above-mentioned silica gel as a raw material, it was found that there were problems with the charging and foaming properties of the raw silica, especially when expanding the production scale. Looking at the charging properties of the raw material silica, problems occur with the fluidity within the raw material supply pipe of the melting equipment, making smooth supply impossible, and depending on the water content of the silica, foaming may occur during melting. There are problems such as the inability to obtain spherical silica glass with the desired performance.

The manufacturing method of quartz glass powder found in the above-mentioned JP-A-Sq-Otl, J- issue does not clearly mention the removal of thorium, and since the quartz glass is based on a firing method, the above-mentioned "recognition of the title" is not clear. do not have.

The inventors of the present invention conducted intensive research in view of the problem of slanting, and surprisingly completed the present invention based on the knowledge that the moisture content of the raw material is an extremely important factor.〇Problem Means and effect for solving the problem, namely, the present invention provides α-
The radiator has a purity of U + Th / Oppb or less, Na, α each / Oppm or less, and a water content of O
, S to IO as a molten raw material. □
Another object of the present invention is to produce molten glass using the above-mentioned raw materials.

The hydrated silica gel powder according to the present invention is mainly used as a raw material for melting, but due to its high purity, predetermined particle size and water content, it has fluidity and can be used for other purposes, such as as a ceramic material or its raw material.

As for the purity of hydrated silica gel, α-radiator is U + Th / Oppb or less, Na and α are each / Oppm
Preferably, ■ and Th are indispensable as fillers for resin encapsulation of semiconductors.
Highly integrated LSI with high purity of ppb or less,
It is needed as a filler for VLSI sealing in order to eliminate malfunctions caused by soft errors when used.

Other characteristics of such hydrous silica gel include water content of o, 5
-10 weight range, which is an important characteristic in the present invention, as well as purity.

This transportation is because the chargeability and foamability of the particles are extremely closely related to the moisture content, and within the above moisture content range, powder transportation becomes easy and good fused silica can be obtained, so both of these problems are solved. In other words, if the water content is less than o, r weight ratio, there is no foaming problem, but the charging property is significant, and it is difficult to stably supply the material into the burner during melting. Moreover, if it exceeds 10% by weight, not only the fluidity is similarly poor but also foaming occurs when melting.
Good quality spherical silica glass cannot be obtained effectively.

For this reason, it is essential that the water content of the hydrated silica gel is within the above range, and is particularly preferably within the range of /-j% by weight, although this is related to the particle size of the fused silica product.

At the above water content, troubles due to the electrostatic properties of the particles can be practically avoided, but if necessary, a small amount of a known antistatic agent such as an Oda-class ammonium salt can be added to more effectively prevent the particles from becoming electrostatically charged. You can also do that.

It goes without saying that the antistatic agent added in this case is preferably a compound that completely volatilizes during melting.

In addition, in the present invention, the moisture content refers to a sample of 100
It is expressed as a value calculated from the heating loss after heating and baking at ℃ for 1 hour. Furthermore, the hydrated silica gel according to the present invention has a particle size of molten silica glass particles due to the effect of fluidity during melting and the particle size of fused silica glass particles. In order to obtain a predetermined range, if necessary, the range is from S to λooμm, preferably from 10 to 100μm.
It is desirable that the distribution is more than gos between the folding screens.

When looking at particles of hydrated silica gel, all missing particles are fine particles of 7991 m or less, but the particle size in the present invention refers to the apparent secondary particles that are aggregated primary particles, and this particle size distribution can be determined using a Coulter counter. As long as the hydrated silica gel according to the present invention has the above-mentioned characteristics, there is no need to particularly limit the treatment means used to produce it from an aqueous alkali silicate solution.

As a preparation method, for example, an aqueous alkali silicate solution is added to mineral acid and reacted to produce silica gel, then the recovered gel is treated with acid again to substantially remove harmful impurities at this stage, and after washing, it is heated to a predetermined water content. Dry to achieve the desired particle size and particle size.

Another method is to obtain a silica sol by converting a dilute aqueous alkali silicate solution into a 4-ion exchange resin, converting it into silica gel using a coagulant, subjecting it to acid treatment if necessary, and drying it in the same manner as described above.

In addition, when drying and adjusting the moisture content, for example, (1) determine the drying conditions of the raw silica gel by understanding the relationship between the silica particle size and the allowable moisture content (2) dry the raw material silica gel in advance at a temperature above aOO℃. Appropriate methods include exposing the material to the air or controlling its humidity by other methods (3) Spray-drying the silica gel slurry, but among these, method (1) is difficult due to workability and other aspects. preferable. Further, in order to narrow the particle size distribution, method (3) is preferable.

Note that an antistatic agent can be added at a desired stage if necessary, but for example, an antistatic agent can be added to (3).
It is effective to add it to the slurry in the following cases. Next, a method for producing spherical silica glass powder by melting the hydrated silica gel powder according to the present invention will be described.

The melting operation of silica powder can be carried out using, for example, oxygen-hydrogen flame, oxygen-
The hydrated silica gel particles are melted and spheroidized by continuously supplying the hydrated silica gel particles to a predetermined flame area such as an acetylene flame, an oxygen-propane flame, or a plasma flame. This is a long-known technique for melting inorganic powders.

Therefore, appropriate flame conditions are required to flame-melt and mold hydrated silica gel particles as a raw material into spherical or elliptical fused silica with an average particle diameter of /-/DOμ. That is, when using fuel gas, the flame temperature should be at least 3000°C or higher, and the flame length should be 30°C or higher at 2000°C or higher.
Requires CIIL or higher. When the burner structure that can be used for this purpose is an oxygen-fuel gas system, it is preferable that oxygen is injected from inside the burner, fuel gas is injected from a number of holes on the outside, and the hydrated silica gel particles are ejected along with the oxygen gas. In the case of plasma arc, the temperature of the arc part is oxygen -
Since it is significantly higher than that of fuel gas systems, it can be processed without problems unless the amount of powder injected is excessive. Although the silica thus obtained is in contact for only a short time in the high-temperature part, it becomes substantially molten glass-like transparent spherical to elliptical particles with extremely good fluidity.

The fused silica particles obtained in this manner are collected by a cyclone, a Veg filter, etc. after being cooled by a gas stream, if necessary, or by wet collection using water, etc., to obtain the 10000-purity silica glass product according to the present invention. As described above, by the method of the present invention, it is possible to industrially produce high-purity fused silica particles as a filler for sealants that require higher performance than wet silica using an aqueous alkali silicate solution as a starting material. Advantageously, large quantities can be supplied.

EXAMPLES The present invention will be explained below with reference to Examples and Comparative Examples.

Example/-1 and Comparative Examples 1 to 3 Commercially available No. 3 sodium silicate aqueous solution (Sin, -g, 6% by weight
, Na, 09.4 for weight, S10. Hit U/θθpp
b.

A diluted sodium silicate aqueous solution containing 4I% by weight was prepared by diluting Sin (containing 'rha*0 ppb) with water.

This was treated with a cation exchange resin (Amberlite R-/IOB, manufactured by Organo Co., Ltd.) which had been regenerated with sulfuric acid according to a conventional method to obtain an aqueous silica sol solution with a pH of 2.

While stirring the ammonium nitrate 70.3 weight aqueous solution 301 at room temperature, ammonia was added to the silica sol aqueous solution to pH 10! Rot of alkali silica sol solution adjusted to r was added over 3 hours and coagulated and precipitated to obtain precipitated jiF-like silica gel. Next, this was filtered and washed by substitution, and then added to 810% ion-exchanged water. The mixture was redispersed to a concentration of 70% by weight, and nitric acid was added thereto at a concentration of λM/l, followed by stirring at 9°C for 3 hours. This was purified by filtration and washing with water to obtain a cake of purified silica gel with a water content of 1% by weight.

This purified silica gel cake was dispersed in water to form a silica gel suspension of IS% by weight, and then spray-dried using a production minor type spray dryer manufactured by Ashizawa Iro Co., Ltd. under various conditions to obtain various hydrated silica gel powders. .

The purity of this powder was measured and found that it contained SiO, fisNa.
: 0-ppm % α: α: Small detection: θ J ppb or less and Th: / ppb or less.

Next, flame melting experiments were conducted using various hydrated silica gel powders as raw materials, and the workability and foamability of the molten glass were observed.

That is, the flame melting device has an oxygen nozzle in the center from which oxygen and dehydrated silica are ejected, and a ring-shaped fuel gas nozzle surrounding the oxygen nozzle on the outside, from which fuel gas is ejected. A gas burner was used which was equipped with an oxygen jet hole and a fuel gas hole on the outside. Propane gas was used as the fuel gas, and the hydrated silica gel was melted at a flow rate of −1 m for 7 hours, an oxygen flow rate of z, bxm of 7 hours, and a supply rate of hydrated silica gel particles of 1 kli/hour.The conditions at this time and the observation results are listed in the table below.

In the above table, mi, I&Ls and N115 are respectively Comparative Example 1) Hydrous silica gel melt-treated products of Comparative Example Ko and Comparative Example 3, Nll Ko, Nada, Sui 6 and Ugly 7 are Examples/ and Implementation, respectively. These are hydrous silica melt-treated products of Example A, Example 3, and Example D.

Note) Observation of charging properties: Observe the fluidity in the silica supply device (pitot tube) during flame melting and the adhesion to the silica supply tube (made of rubber, some glass) to the burner, and the supply is stable and is the best. The product was evaluated on a three-grade scale of ◎, then ○ and ×; Observation of foaming property: The fused silica glass powder was observed with a scanning electron microscope, and the best one with no foaming was evaluated on a three-grade scale of ◎, then ○ and ×.

Note that observations based on this experiment and other experiments show that silica gel powder with a small secondary particle size has relatively little foaming property, but as the silica particles get larger, the degree of foaming increases, and foaming requires certain melting conditions. It was found that there is a correlation between particle size and allowable moisture content. Based on numerous experimental results, the average particle size is 10μ, the water content is 10% by weight or less, J(7μ is 3wt. or less, and 30μ is 3wt. If raw material hydrated silica gel is dehydrated to a moisture content of t% or less by raising the temperature and then fed to a flame melting burner, the powders will coagulate with each other and adhere to equipment, resulting in clogging of conduits and formation of bridges in the hopper. etc., and the powder cannot be supplied quantitatively.

From the above, the water content of hydrated silica gel varies depending on the correlation with the particle size and the purpose of use of the molten glass powder, but it is at least O, S to IO weight %, preferably 1 to 10% by weight.
It is concluded that a weight range of 7 is necessary.〇Examples 3 to t and Comparative Example II-A Various hydrated silica gel powders were prepared by the method shown in the table below: is table Preparation conditions for hydrated silica gel Further hydrated silica gel Both are 810. Shang Na:/
ppm or less, α: not detected, U: 0. 'lppb
Below, Th:/ppb or less.

The above various hydrated silica gel powders were melted using the same flame melting device as in Example 1, and the flow rate of oxygen for supplying silica was: /, l: Nm
``7 hours, propane gas flow rate to g Nm'' 7 hours, total oxygen flow rate A, tNm'' 7 hours, silica addition amount / , g
The melting process was carried out in the same manner as in Example except that the flame melting process was carried out under the waiting time condition of kg-/'. The characteristic values of the produced fused silica glass and the fluidity of the raw material hydrated silica gel powder are shown in Table f3. The bulk specific gravity was measured based on the pigment test method: Table 3 The physical properties such as purity of this spherical fused silica were measured, and the results were as follows: Table 4 Note Measuring method of electrical conductivity: A certain amount of the sample was added to high purity water to make a 10% by weight slurry.

The electrical conductivity at 15° C. is measured using the extracted water that has been boiled for t hours as a sample.

Example 9 - Saw and Comparative Examples 7 - 9 Flow rate of oxygen for supplying silica/, g Nm"7 hours, hydrogen gas flow rate θHmj/hour, total oxygen flow rate t, SN
m aging, silica addition amount 1. The above-mentioned raw material fish was flame-melted in the same manner at 1cg/hour. The fluidity of the produced fused silica and silica powder is shown in Table 5. Effects of the Invention According to the present invention, a material suitable as a filler for encapsulants such as epoxy resins used in highly integrated semiconductors has been stabilized. It is of great industrial significance as it can provide high purity silica of highly reliable quality with ease of operation.

In particular, in the past, when manufacturing fused silica glass powder, there were large variations in the raw material supply stage to the flame melting furnace, which caused trouble, but according to the present invention, this can be improved with good reproducibility, and the molten glass The quality will also be stable.

Claims (1)

[Scope of Claims] 1. Silica obtained from an aqueous alkali silicate solution, wherein α
- Emitter is 10 ppb or less as U+Th, Na, Cl
The content of each is 10 ppm or less and the water content is 0.5 to 0.5.
Hydrated silica for melting, characterized in that the content is 10% by weight. 2. The hydrated silica for melting according to claim 1, wherein the silica obtained from the aqueous alkali silicate solution is obtained via a silica sol produced by an ion exchange resin. 3. The hydrated silica for melting according to claim 1, wherein the silica obtained from an aqueous alkali silicate solution is silica produced by adding the solution to a mineral acid. 4. The hydrated silica for melting according to any one of claims 1 to 3, which has an average particle diameter of 200 μm or less. 5. The hydrated silica for melting according to any one of claims 1 to 4, which contains an antistatic agent. 6. In producing fused spherical silica by flame-melting silica powder, an aqueous alkali silicate solution is treated so that the α-emitter is 10 ppb or less as U+Th, the content of Na and Cl is 10 ppm or less, and the water content is A method for producing fused silica, characterized in that a hydrated silica gel powder in the range of 0.5 to 10% by weight is used.