JPH0127003B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 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, it 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 resin encapsulation of semiconductors, abrasive materials, substrates, and package materials. . Conventional technology A large amount of inorganic filler is used in resin encapsulation of semiconductors, and this mainly uses crystalline silica, which is a crushed product of natural quartz, and fused silica, which is melted at high temperatures such as in an oxyhydrogen flame. ing. Recently, especially with the increasing integration of semiconductors, the requirements for quality characteristics of encapsulants have become even stricter. and (3) reduction of ionic impurities. In order to cope with these problems, using conventional silica obtained by crushing and/or melting natural quartz as a filler has problems with purity, securing the quantity of resources, and economic efficiency, and is not necessarily in a stable state. However, it has become necessary to use a new synthetic silica. In response to this, hydrolysis of silicon halides and organic silicones has been proposed, and recently, silicates such as alkali silicates are reacted with mineral acids to precipitate hydrated silicic acid at a hydrogen ion concentration of 1.5 or less.
Next, a method of manufacturing quartz glass powder by washing, drying and firing was proposed (Japanese Patent Application Laid-Open No. 59-54632).
issue). 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 acid-treated the silica gel produced by reaction with a mineral acid. We developed a method for producing silica with an extremely low content of α-emitters, and a method for producing spherical silica by melting it. It has been found that when producing spherical silica glass powder by melting the above-mentioned silica gel as a raw material, there are problems with the chargeability and foamability of the raw silica, especially when expanding the production scale. In other words, when looking at the chargeability of silica as a molten raw material, troubles occur in the fluidity within the raw material supply pipe of the melting device, making it impossible to supply it smoothly, and depending on the water content of silica, foaming occurs during melting. However, there are problems such as the inability to obtain spherical silica glass having the performance that should be achieved. The method for producing quartz glass powder disclosed in JP-A-59-54632 does not clearly address the removal of thorium, and since the quartz glass is based on a firing method, the above-mentioned problem is not recognized. In view of the above-mentioned problems, the present inventors conducted extensive research and surprisingly completed the present invention based on the knowledge that the water content in the raw material is an extremely important factor. Means and Effects for Solving the Problems That is, the present invention provides a solution in which the α-emitter of silica obtained from an aqueous alkali silicate solution is U+Th.
One object of the present invention is to provide, as a molten raw material, a hydrous silica gel powder having a purity of 10 ppb or less, 10 ppm or less of Na and Cl, and a water content in the range of 1 to 10% by weight. Another object of the present invention is to produce fused silica glass using the above 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 also 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+
Less than 10ppb as Th, 10ppm each of Na and Cl
The following is essential for a filler for resin encapsulation of semiconductors. Particularly preferably, U and Th have a high purity of 1 ppb or less, respectively, from the viewpoint of eliminating malfunctions due to soft errors when used as a sealing filler for highly integrated LSIs and VLSIs. Another characteristic of such hydrous silica gel is that the water content must be in the range of 1 to 10% by weight, which is an important characteristic in the present invention as well as purity. The reason for this is that the chargeability and foamability of particles are extremely closely related to the water content, and within the above water content range, powder transportation becomes easy and good fused silica can be obtained, so both of these problems are solved. The problem is that it can actually be solved. That is, if the water content is less than 1% by weight, there is no problem with foaming properties, but the charging property is significant, making it difficult to stably feed the material into the burner during melting.
If it exceeds 10% by weight, not only the fluidity is similarly poor but also foaming occurs during melting, making it impossible to effectively obtain high quality spherical silica glass. 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 approximately 1 to 7% 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, it is possible to more effectively suppress the particles by adding a small amount of a known antistatic agent such as a quaternary ammonium salt. It can also prevent static electricity. It goes without saying that the antistatic agent added in this case is preferably a compound that completely volatilizes during melting. In the present invention, the moisture content is expressed as a value calculated from the loss on heating after firing a sample at 600° C. for 1 hour. Furthermore, the hydrated silica gel according to the present invention may be used in order to improve the flow characteristics during melting and to keep the particle size of the fused silica glass particles within a predetermined range.
~200μm range, preferably 50% between 10-100μm
It is desirable that the distribution is as follows. In addition, when looking at particles of hydrated silica gel, all primary particles are fine particles of 100 mμ or less, but in the present invention, the particle size refers to the apparent secondary particles that are aggregated primary particles, and this particle size distribution is measured with a Coulter counter. It is expressed as a value. Next, 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 for producing 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 pouring a dilute aqueous alkali silicate solution through an ion exchange resin, then converting it into silica gel with 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 for the raw silica gel by understanding the relationship between silica particle size and allowable moisture content (2) dry it in advance at 200°C or higher and expose it to the air or adjust the humidity by other methods (3) Spray drying the silica gel slurry is an appropriate method, but among these, method (1) is preferable from the viewpoint of workability and other aspects. 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 it is effective to add, for example, a quaternary ammonium salt to the slurry in case (3). Next, a method for manufacturing spherical silica glass powder by melting the hydrated silica gel powder according to the present invention will be described. The silica powder melting operation is carried out by continuously supplying the hydrated silica gel particles to a predetermined flame portion such as an oxygen-hydrogen flame, an oxygen-acetylene flame, an oxygen-propane flame, or a plasma flame. This flame melting operation itself is a long-known technique for melting inorganic powders. Therefore, in order to flame-melt and mold hydrated silica gel particles as a raw material to obtain spherical or elliptical fused silica having an average particle diameter of 1 to 100 μm, an appropriate amount of flame is required. That is, when fuel gas is used, the flame temperature must be at least 3000°C or higher, the flame length must be 30cm or more, and the flame length must be at least 2000°C. The configuration of the burner that can be used for this purpose is oxygen-fuel gas system.
Preferably, oxygen is injected from inside the burner and fuel gas is injected from a number of holes on the outside, and the hydrated silica gel particles are injected together with the oxygen gas. In the case of plasma arc, the temperature of the arc part is significantly higher than that in the oxygen-fuel gas system, so it can be processed without problems as long as the amount of powder injected is not 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 or elliptical particles with extremely good fluidity. The fused silica particles thus obtained are collected by a cyclone, a bag filter, etc. after being cooled by a gas stream, if necessary, or by wet collection using water, etc., to obtain the high-purity silica glass product according to the present invention. be able to. As described above, the method of the present invention enables industrially advantageous mass supply of high-purity fused silica particles as a filler for sealants that require high performance, rather than wet silica using an aqueous alkali silicate solution as a starting material. It is possible to do so. Examples The present invention will be described below with reference to Examples and Comparative Examples. Examples 1 to 4 and Comparative Examples 1 to 3 A commercially available No. 3 sodium silicate aqueous solution (containing 28.6% by weight of SiO ₂ , 9.4% by weight of Na ₂ O, 100 ppb of U per SiO ₂ and 240 ppb of Th per SiO ₂ ) was diluted with water. _SiO2 4% by weight
A diluted sodium silicate aqueous solution was prepared. A cation exchange resin (Amberlite) that is regenerated with sulfuric acid
IR-120B (manufactured by Organo) according to a conventional method to obtain an aqueous silica sol solution with a pH of 2.2. Ammonium nitrate 10.5% by weight aqueous solution 30 at room temperature
While stirring, add ammonia to the above silica sol aqueous solution to make the pH 10.5.
was added over 3 hours to cause coagulation and precipitation to obtain precipitated silica gel. Next, this was washed by filtration and displacement, and then redispersed in ion-exchanged water to a SiO ₂ concentration of 10% by weight, and nitric acid was added to it at 2M/2%.
1 of the mixture and stirred at 95°C for 3 hours. This is filtered, washed with water, and purified to a moisture content of 78.
A cake of % by weight purified silica gel was obtained. Disperse this purified silica gel cake in water.
After forming a 15% by weight silica gel suspension, it was 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 per SiO ₂
Na: 0.8 ppm, Cl: not detected, U: 0.4 ppb or less, and Th: 1 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 hydrous silica gel was melted at a flow rate of 1.2 Nm ³ /hr, an oxygen flow rate of 5.6 Nm ³ /hr, and a feed rate of hydrated silica gel particles of 1 kg/hr. The conditions and observation results at this time are as follows:
Listed in the table.

[Table] In the above table, No. 1, No. 4, and No. 6 are the hydrous silica gel melt-treated products of Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively, and No. 2, No. 3, No. 5, and No. 7 is the hydrous silica melt-treated product of Example 1, Example 2, Example 3, and Example 4, respectively. 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 〇 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 〇 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 ability, but as the silica particles become larger, the degree of foaming increases, and there is a certain degree of foaming. It was found that there is a correlation between particle size and allowable moisture content under melting conditions. Based on numerous experimental results, the water content is 10% by weight or less for an average particle size of 10 μm, 8% by weight or less for 20 μm, and 7% by weight or less for 30 μm. On the other hand, if the raw material hydrated silica gel is dehydrated to a moisture content of 1% or less by pre-calcining or increasing the temperature during spray drying and then fed to a flame melting burner, the powders may coagulate with each other and the powders may adhere to equipment. This causes clogging of the conduit, bridge formation 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 1 to 10% by weight.
It is concluded that preferably a range of 1 to 7% by weight is required. Examples 5 to 8 and Comparative Examples 4 to 6 Various hydrous silica gel powders were prepared by the methods shown in Table 2:

【table】

[Table] All hydrous silica gels have Na per _SiO2 :
1ppm or less, Cl: not detected, U: 0.4ppb or less, Th:
It was less than ppb. 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 melted.
1.8Nm ³ /hour, propane gas flow rate 1.8Nm ³ /hour,
Total oxygen flow rate 6.7Nm ³ /hour, silica addition amount 1.8Kg /
The melting process was carried out in the same manner as in Example 1, except that the flame melting process was performed under different conditions. Table 3 shows the characteristic values of the produced fused silica glass and the fluidity of the raw material hydrous silica gel powder. The bulk specific gravity was measured based on the pigment test method. :

[Table] The physical properties such as purity of this spherical fused silica were measured and the results were as follows. :

[Table] Measuring electrical conductivity.
Examples 9 to 12 and Comparative Examples 7 to 9 The flow rate of oxygen for silica supply was 1.8Nm ³ /hour, the hydrogen gas flow rate was 20Nm ³ /hour, the total oxygen flow rate was 8.5Nm ³ /hour, and the amount of silica added was 1.2Kg/hour. Raw material No.1
-7 were flame-melted in the same manner. Table 5 shows the flowability of the produced fused silica and silica powder. :

[Table] 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 can produce highly reliable quality high-purity silica under stable operability. It is of great industrial significance. 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 containing α-emitters of 10 ppb or less as U+Th, Na,
Cl content is 10 ppm or less and water content is 1 to 1.
Hydrated silica for melting, characterized in that it 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 fused hydrated silica according to any one of claims 1 to 4, which contains an antistatic agent. 6. When producing fused spherical silica by flame-melting silica powder, an aqueous alkali silicate solution is treated to contain α-emitters of 10 ppb or less as U+Th, Na, Cl
The content of each is 10 ppm or less, and the water content is 1 to 1.
A method for producing fused silica, characterized in that it uses hydrated silica gel powder in the range of 10% by weight.