JPH02221111A - Manufacture of pure silica powder - Google Patents

Abstract

PURPOSE: To obtain a high purity silica powder having coarse grain size distribution at a low cost by adopting specified conditions and using raw materials of industrial grade at the time of producing a silica powder by means of sol-gel processing.

CONSTITUTION: The pure silica powder is formed by the following processes (a) to (d), that is, (a) a process where a solution is prepared by mixing a fixed amount of hydrolyzable organometallic silicon material of industrial grade, an organic solvent of industrial grade capable of mixing with the above organometallic material, and acidified water of <pH 2 so that the ratio between the solvent and the organometallic silicon becomes about 0.1:1 to about 1:1 and the amount of the acidified water becomes about 520 to 720% of the stoichiometric amount; (b) a process where the above solution is heated to about 45 to 57°C to form a transparent gel; (c) a process where the above gel is dried at a temp. of about 110 to 150°C and the dried gel is crushed into powder; and (d) a process where the crushed powder is calcined and formed into the pure silica powder.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing pure silica, and more particularly to a method for utilizing raw materials of primarily industrial grade.

(Prior Art) In the electronics industry, 256K DRAM
As more and more megabit chips are being produced in large quantities, the need for purer silica powder becomes increasingly important.

In order to protect such chips from problems such as moisture, it is important to encapsulate them. As used herein, the term encapsulation refers to a package consisting of a microcircuit embedded in a material. Common examples of encapsulations include resin blocks, silica, urethanes, and the like. When the chips are very dense, as in the production of very large scale integrated circuits (VLSIs), the purity of the silicon powder used to form the material is very low.
It becomes important. Pure silica is needed to encapsulate these TPs and protect them from the environment. The relative purity of the powder is very important because impurities can change the electrical properties of the silica and create conductive paths. For example, carbon, iron, and other metal compounds in silica powder can create conductive paths that can cause short circuits within the encapsulated electronic components. Therefore, it is important to reduce the amount of carbon and iron in silica powder as much as possible in producing silica products for the electronics industry. Conventional electronic grade silica used for encapsulation typically contains about 200-300 pρ carbon. Furthermore, radiation from uranium and thorium isotopes that emit alpha radiation causes so-called soft errors.
These elements must be kept as low as possible as they can damage memory function.

Not only must the purity of the silica powder be controlled, but the particle size of the powder must also be controlled.

Powder is too fine (i.e. mostly less than 20 microns)
In this case, excessive amounts or resin must be used to form the anti-corrosion material.

To date, equal parts of distilled tetraethylorthosilicate (hereinafter sometimes referred to as TEO5), reagent grade ethanol and acidified distilled water have been gelled, dried, kneaded,
It is known that such pure silica powder can be formed by a sol-gel process by force calcining.

The raw materials must be distilled multiple times for purification and require extremely clean rooms to carry out the sol-gel process.

Although using the above ingredients results in a relatively pure silica powder, the cost of the raw materials used in this process is relatively high, the level of carbon found in the silica powder is relatively high, and , the substantial amount of particles in the 12S mesh residue is insufficient, resulting in relatively uneconomical results, resulting in an industrially unsatisfactory product as a whole. (Problem to be Solved by the Invention) Therefore, the present invention The objective is to produce a highly pure silica powder from relatively inexpensive stock raw materials, which contains substantially only low levels of carbon, iron, uranium and thorium, and which has the required coarse particle size distribution. The purpose of the present invention is to provide an industrially satisfactory powder.

Furthermore, it is an object of the present invention to produce microcircuits encapsulated with said ultrapure silica powder.

(Means for Solving the Problems) In the following example, TE01 is utilized as an organic source of silica. However, other hydrolyzable organometallic silicon sources can also be used, for example methyl silicate or 7MO5 (also called tetramethylorthosilicate, tetramethoxysilane or methyltrimethoxysilane).

TE01 reacts more slowly with water than 7MO3, so
Preferably, TE01 is used, which equilibrates as a silanol complex and is more stable over time than other silicon alkoxides in a partially hydrolyzed state.

Additionally, in the following examples, the alcohol solvent is exemplified with ethanol. However, it is understood that alcohols such as methanol, propatool, isopropanol, and butanol can also be used. Additionally, other organic solvents that are miscible with both TE01 and water may be suitably substituted for ethanol.

These include ketones and amides such as acetone, dioxane and dimethylformamide.

Similarly, although the examples illustrate hydrochloric acid, other acids can be used to catalyze the reaction between TE01 and water. Preferably, hydrochloric acid is used since it can be easily removed from the silica powder by simple heating.

Referring to FIG. 2, a microcircuit or integrated circuit chip 30 is shown. Here, package base 34
An integrated circuit 32 is housed therein and connected to an external lead wire 36 through an internal conductor wire 38. The entire unit, except for the outer portion of the external leads 36, is encapsulated with pure silica 40 of the present invention. The particular circuits 32, base ports, leads 3G, and conductors 38 may be those commonly used in integrated circuit chips.

Chip 3G is manufactured by an industrially known method, and then
Encapsulation is performed by any known technique utilizing conventionally used silica. In addition to integrated circuit chips, the pure silica of the present invention can be used in other types of encapsulation applications commonly encapsulated with silica.

The values shown in Table r below are a representative analysis of electronic grade silica as a conventionally used sealant and the pure silica of the present invention.

Table ■ Carbon! 00-300 20-40 Radioactive material p
pb The invention will be further described in connection with the following examples, which are included for illustrative purposes only.

Examples Example I TE01 was distilled at 173° C. using a liquid cooled evaporator tube and the silicate was collected. A 0.1 molar hydrochloric acid solution prepared from reagent grade ethanol, distilled TEO5, and distilled water was mixed for approximately 5 minutes until a clear liquid formed. Sol-
It has been found that the gel solution should be kept acidic. high p) (in solution (preliminary test results), low p
) yielded significantly less silica gel than the 1 solution. The pH of the solution is preferably maintained below 2.0. The amount of acidified water used in this method is a stoichiometric amount of 720-N.

It was also decided that it should be %. The solution was placed in a dry volume at 73° C. for 4 hours. Gelation occurred during this time. Drying was continued at 110°C for an additional 14 hours. The dried gel was then ground with multiple solid plastic balls in a plastic jar for 48 hours. The resulting powder was passed through a +50 mesh sieve using a polyester sieve. The passed powder was then calcined in a silica sheath for 3 hours at 1000°C. The heating rate used was 17℃
/ It was time.

Although the silica powder made in Example 1 was satisfactory with the purity of most standards, the level of carbon was excessive and it was too fine. Additionally, the process required distillation and the use of reagent grade raw materials, making the process too expensive to use for industrially producing silica powder. Therefore, there is a need to improve both the method and the raw materials to eliminate the above-mentioned drawbacks.

An initial attempt to reduce raw material costs was to replace distilled TEO3 with technical grade TEOS. The TEOS trademarks tested were: DyhsilA, commercially available from K. Fries Company; Pure 5ilboad and Caadeused 5, commercially available from Stauffer Chemical Company.
ilboad; Condensed Ethyl commercially available from Union Carbide Company
It was 5ilicate. TEOS of each supplier,
Mixed with reagent grade alcohol and 0.1 molar hydrochloric acid solution. The gelation method described above was used to produce /Lica powder. Chemical analysis of silica powder reveals industrial grade Dy++5
sil A or Union Carbide Conden
It was concluded that either sed Etbyl SilicgLe could be used in place of distilled TEO5.

A similar analysis was performed to determine whether technical grade ethanol could be substituted for reagent grade ethanol. Solvent No. 3 obtained from US Industrial Chemical Company was mixed with 0.1 molar hydrochloric acid solution, distilled TEO5 and industrial grade Dyn1sil.
CoodCnsed of A and Union Carbide Co.
Both Ejhyl 5ilicate and Ejhyl 5ilicate were used.

Chemical analysis of the silica powder prepared from the above mixture using the sol-gel method revealed that the technical grade alcohol was found to have a technical grade D
It has become clear that it can be used in combination with ynasil A.

A similar analysis was conducted to determine whether acidified water prepared with tap water could be substituted for acidified water prepared with distilled water. Distilled TEOS and technical grade τEO5
and both technical grade alcohol and reagent grade alcohol were prepared with acidified water prepared with distilled water and tap water; Acidified water was used to prepare silica powder. Analysis of the silica powder thus produced concludes that distilled water must be used.

The method was modified to eliminate two remaining problems, namely the relatively high level of carbon content in the compacted silica powder and the very fine particle size of the powder. I tried. As mentioned above, the sol-gel method is
It involves mixing the raw materials until they form a clear liquid. Then solution 3, for 24 hours until gelation occurs.
Place in a dry base at 75°C. At high temperature, for example 110℃,
Furthermore, dry for 24 hours! ! control The dried gel is then crushed and sieved. The sieved powder is then crushed.

In an attempt to coarsen the particle size distribution of the Rica powder, the drying time of the gel was increased. As shown in Table 1 below, the slow drying method resulted in a coarse particle size distribution.

The gel, which was slowly dried, milled, and then passed through a 48 mesh sieve before firing, had a particle size distribution dominated by 325 residual particles after calcination.

Drying method table ■ Examination of drying conditions for sol-gel silica Slow Normally at 73℃ for 24 hours After transferring the gel to a tray at 73℃ for 24 hours 73 At 110℃ for 24 hours
℃ for 2 hours at a rate of 8℃/hour to 73℃ and 110℃. Hold at 110℃ for 24 hours. Albin (Alp
i++e) Sieve analysis % 150 mesh residual % 200 mesh residual % 325 mesh 7 residual 7.31 +7.15 34.75 1, O3 5,13 17,57 X-ray Sedigra 7 (Sedi (raph) particle proportion (
bar)) In order to increase the amount of fine grains, 7 325 menyu residual particles from the dimensions below,
The grinding time of dry-treated gels was reduced.

As expected, decreasing the milling time increased the amount of 325 mesh residue before the mill. However, when crushed, all of the 325 residue disintegrated into a fine powder.

Table■ Time: 1010g loading and crushing sieve analysis 20 nosh residual 23.5% 200 mesh residual 49.3 mesh 5% 23.6 6.7% 63.7 Full pin sieve analysis 200 mesh residual of 2QO passing through 0.04% 325 Mesh Residue 10.120.004% 10.72 O,OS 5.01 The dried and ground gel was then milled in several different ovens. The data shown in Table 1 shows that airflow through the powder bed during rolling is beneficial for reducing the carbon content of the silica powder. The air should be directed upwards through the powder, as there is believed to be intimate contact between the carbon impurities, and the air will burn off virtually all of the carbon, thus eliminating any remaining carbon impurities. bring about a decrease. Merely increasing ventilation by forcing the box inside the box with the lid removed was not sufficient.

200 mesh residue 325 mesh residue 0.04% O,tS% 0.01% 0.05
% 0.65% 0.21%2.9s 0.99 1.54 0.76 6.42 eyes! lime Edited by 9 Denshu Zheng Cao S ○ In an attempt to reduce the cost of producing silica powder from the sol-gel process described above, further tests were conducted. The test results are shown in Table V below. The first test shows that less solvent can be used in batch formulation. Mixtures C and D show that suitable silica powders can be formed without solvent, but a certain level of solvent can, on an industrial basis,
It is desirable to react E01 with acidified water. It was concluded that a volume ratio of ethanol TEO5 of Ll to 1:1 can be used satisfactorily.

Table 3 shows that various variations made during the process increase coarse particles in the powder. Samples O and P had the coarsest particle distribution as a result of the addition of fused silica, with 16 vt% and IQ vL%, respectively. Samples K and L, which dried longer than usual, resulted in a rougher final product, while samples 0 and P did not. sample! and J were fired at 101°C (II&'0 higher than normal). These samples showed a reduction in coarse grains, probably due to the higher heat treatment.

Further tests were conducted to produce a silica powder with very low levels of carbon. Additionally, additional tests were performed to increase the particle size of the finished powder.

Rule 1 indicates that an evaporation temperature higher than 45°C is required to produce a clear gel. Temperatures below 45°C result in an amber gel.

(Continued) (N) X-ray diffraction analysis of the powder detected 0.062% cristobalite, but no iron.

Table 1 above shows that a calcination process of about 38° C./hr to a peak temperature of 1221° C. with air flow during the cylinder stage results in a silica powder with very low carbon levels.

Table ■ Variable mixing of the power cylinder method: F mixing a small amount of alcohol, 1 ail A 3 Rifdol No., 3 solvent L 75 liters 0.1 mol 11 Cl solution 3 Rifdol grinding: Mix 30 molecules of TE01 and alcohol, then Acidification is done by adding water. Mix the batch continuously (gelling) for 12kr at 49°C. Dry the gel at 110°C and 24br.

2.5hr Line analysis of crushed gel: 91.5% Power passing through 150 meshes Baking process: Temperature raised from room temperature 24°C to 9°C at 238°C, temperature increased from +49 to 649°C at 21°C, 39' Temperature increased from 649 to 12H'll! with e-br 122
Airflow during biscuiting held at lhr at 1°C, 5CFH: 30 (powder became a solid mass but white or weight loss during biscuit % 10.7 X-ray Sedigra 7 analysis (% of finer than the following values) )fioμm foi140μ
98 20 μm 70 1071 m 41 14 μ m 7 1 JIml Sob-micro
n) It has been found that the addition of fused silica dramatically increases the particle size of the compacted powder. Apparently, fused silica is a "seed" that promotes the formation of a silica network during evaporation.
Acts as. The addition of 1 ovt% fused silica
It was more effective in making the particles coarser than the addition of 6vt%.

Referring to FIG. 1, the method includes mixing a hydrolyzable silicon organometallic material, a technical grade organic solvent, and acidified water at 12 points to form a solution;
Heating the solution at a temperature of from about 75°C to form a clear gel, heating the gel at a temperature of from about 110°C to about 150°C to dry the gel, and grinding the dried gel at a position I8. and form a powder, and then crush the powder to form pure silica powder. During the mixing stage, fused silica can be added at 24 positions. Fused silica increases the particle size of the compacted silica powder. At position 22, air can be directed upwardly past the ground powder in the force cylinder stage.

While preferred embodiments of the invention have been described and illustrated, the invention is not intended to be limited thereto, but may alternative embodiments within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram C of the method of the invention, and FIG. 2 is a diagrammatic representation of an integrated circuit chip of the invention. In the figure, 30... Microminiature circuit, 32... Integrated circuit, 3
4...Package pace, 36...External lead wire,
38...Internal conductor and 4G...Silica. Engraving of the drawings (no changes to the contents) M-f Closed rotation, No. 76 Firewood department - Silica secret red 2 concave procedure correction book Ui 埒 June 1989 μ day Heisei 1 j'' 48: r application No. 30915 No. 2, Title of the invention: Process for producing pure silica powder 3. Relationship with the person making the amendment Patent applicant's address Name: Dresser Industries, Inc. 4, Agent address: 2 Otemachi, Chiyo ITI-ku, Tokyo Chome 2-1 Shin-Otemachi Building 206 Ward 5, date of amendment order 1999 5Jj 30 units 0 koku 80)

Claims (1)

[Claims] 1. A certain amount of a technical grade hydrolyzable organometallic silicon material, a technical grade organic solvent miscible with the organometallic material, and acidified water with a pH of less than 2; mixing the solvent to the organometallic silicon in a ratio of about 0.1:1 to about 1:1 and the acidified water in an amount of about 520 to 720% of the stoichiometric amount to form a solution; heating the solution to about 45°C to about 57°C to form a clear gel; drying the gel to about 110 to about 150°C; grinding the dried gel to form a powder; and grinding. A method for producing pure silica powder consisting of steps of calcining the powder to form pure silica powder. 2. The method of claim 1 further comprising the step of directing air upwardly through the ground powder during the calcination step. 3. The method of claim 2 further comprising the step of adding up to about 16 wt% fused silica during the mixing step. 4. The method of claim 1, wherein the calcination step is carried out at about 800 to 1300°C for about 10 minutes to about 5 hours. 5. The method of claim 1 further comprising the step of adding up to about 16 wt% fused silica during the mixing step. 6. Pure, consisting of an amount of technical grade hydrolyzable organometallic silicon material, an amount of technical grade organic solvent miscible with the organometallic silicon material, and an amount of acidified water with a pH below 2. a composition for forming a silica powder, wherein the volume ratio of the solvent to the organometallic material is from about 0.1:1 to about 1:1, and the amount of water is from about 520 to about 1:1; The composition is present in a stoichiometric amount of about 720%. 7. The composition of claim 6 further comprising up to 16 wt% of finely divided fused silica. 8. The composition according to claim 6, wherein the organometallic material is TEOS. 9. The composition according to claim 8, wherein the organic solvent is ethanol. 10. The composition according to claim 6, wherein the organic solvent is ethanol. 11. A method for protecting a microcircuit comprising the steps of: making a microcircuit; and encapsulating the microcircuit chip in a product formed by the method of claim 1, 2, 3, 4, or 5. 12. Microminiature circuit; and claim 1, 2, 3, 4, or 5.
An encapsulated microcircuit formed from the product of the described method and comprising an encapsulating sealer covering said circuit.