JPH0274514A - Production of high-purity silica - Google Patents

Abstract

PURPOSE:To economically obtain high-purity silica with hardly any impurity content, such as Na, K, Cl ions, etc., including U in a simple process using an inexpensive commercially available raw material by washing a silica gel with an acid while treating the silica gel with ultrasonic waves and then washing the resultant silica gel with water. CONSTITUTION:A commercially available gel is washed with an acid, such as sulfuric or nitric acid. In the process, the silica gel is simultaneously subjected to ultrasonic treatment and then washed with water. Ionic impurities, such as Na, K and Cl, including U in pores of the silica gel are liberated from the silica gel and the pores thereof are extended. Thereby, the impurities are extracted, passed into the outside of the silica gel system and effectively removed even by treatment at ordinary temperature. The raw material is inexpensive and readily available and the respective steps of the above-mentioned washing with the acid and water are simply operated with a few steps according to the above-mentioned method. Thereby, high-purity silica can be surely produced at a low cost.

Description

[Detailed Description of the Invention] The present invention has an extremely low content of impurities such as uranium, Na, and CQ ions, and is suitable as a filler for electronic component encapsulating materials. The present invention relates to a method for producing high-purity silica.

In recent years, silica has been increasingly used as a filler for encapsulating electronic components such as LSIs and VLSIs, but in this case, silica contains trace amounts of uranium, etc. Even if there is, there is a problem that the alpha rays emitted from this will cause operational errors in the device. For this reason, the silica used as a filler for electronic component sealants is required to be of high purity.

In particular, the uranium content is 0.5 ppb or less, and the Na
, the content of impurities such as CQ ions is 2 pp, respectively.
It is desirable that it be less than m.

Conventionally, a method for producing high-purity silica involves producing silica gel from an alkali silicate and an acid, treating the silica gel with acid, and washing with water (JP-A-59-54632 and JP-A-60-42217).

No. 60-204613, No. 62-3011, No. 62
-83313) is known.

However, in the above-mentioned high purification method, even if the silica gel shape, acid concentration, treatment temperature, stirring intensity, etc. during acid treatment are adjusted, there is a limit to the ability to remove impurities from the silica.
! It has been difficult to obtain silica of extremely high purity sufficient to solve the problem of soft errors in child parts. Moreover,
The above method requires a large amount of time for spreading and washing with water after acid treatment.

Since the water content of the filter cake is high, it has the drawback that the thermal energy required for drying and heat treatment is enormous, which is also industrially disadvantageous.

In addition, as other methods for obtaining high purity silica, methods using gas phase reactions and methods using hydrolysis of silicate esters are also known (Japanese Patent Application Laid-open No. 8615/1986, 59
-13620, 60-90811, 60-90
No. 812, No. 6O-1809L1, No. 60-1910
16 No. 5 No. 60-204.614, No. 61-1414
No. 4, No. 61-17416, No. 61-40811,
No. 61-48421, No. 61-270209, No. 6
(No. 2-3012, No. 62-12608) However, these methods are economically disadvantageous because the production of high-purity silica is expensive.

Therefore, it has been desired to develop a method for producing silica that can advantageously obtain silica of higher purity industrially and economically.

The present invention was made in view of the above circumstances, and has a very low content of uranium, Na, Cα ions, etc.
An object of the present invention is to provide a method for producing high-purity silica, which can easily and efficiently produce high-purity silica suitable as a filler for electronic component sealing materials at low cost using inexpensive raw materials.

In order to achieve the above object, the inventor of the present invention has conducted extensive studies and found that although silica gel is inexpensive, it contains several tens of degrees of PPb of uranium derived from the raw material silica. As mentioned above, removing ionic impurities such as uranium, other Na, and Cα ions from this silica gel requires considerable effort. It has been discovered that uranium, Na, Cα ions, etc. can be effectively removed in a short time by acid washing while treating with ultrasonic waves.

In other words, when commercially available silica gel is used as a raw material, and when it is washed with acids such as sulfuric acid or nitric acid and treated with ultrasonic waves at the same time, the cavitation phenomenon caused by the ultrasonic waves causes fluctuations in pressure waves ranging from vacuum to several thousand atmospheres. uranium, Na, and K in the pores of silica gel.

Impurities such as CQ are liberated from the silica gel, and the silica gel pores are expanded, and these impurities are extracted and moved out of the silica gel system. The above-mentioned impurities, which could only be removed by transferring acid, can be effectively removed even by treatment at room temperature, and uranium and even Na can be effectively removed.

High purity silica with a very low content of K, Cα ions, etc. can be obtained, and the above impurities can be more reliably removed by ultrasonication, especially in the water washing step following the acid treatment. It was discovered that the raw materials for this method are cheap and easy to obtain, the operations of the acid washing and water washing steps are simple, the number of steps is small, and high-purity silica can be produced reliably and at low cost. This led to the invention.

The present invention will be explained in more detail below.

The method for producing high-purity silica of the present invention is to wash silica gel with acid while treating it with ultrasonic waves as described above, and then washing it with water. By acid cleaning, uranium, Na,
Since Cα ions etc. are effectively removed, uranium is reduced to 0.
Less than 5ρpb.

Furthermore, it is possible to produce silica with higher purity, in which Na, Cα ions are each 2 ppm or less.

Here, the silica gel used as a raw material is produced by a known manufacturing method 1, for example, a silicate ester hydrolysis method.

Although any one obtained by various methods such as ion exchange method and decomposition method of silicate with acid can be used, silica gel obtained from an aqueous alkali silicate solution and an acid can be used particularly effectively. In addition, there are no restrictions on the shape, particle size, pore size, M pore volume, etc. of silica gel, and the adsorbent,
Various silica gels that are generally commercially available as catalyst carriers, such as JIS-A type broken frame-shaped granular silica gel and JIS-B type beaded silica gel, can be used, but it is particularly preferable to use silica xerogel. This makes it possible to omit the step of removing water from the hydrogel by filtration or the like.

The present invention uses the above-mentioned silica gel as a raw material, and produces high-purity silica gel by washing it with acid while treating it with ultrasonic waves and washing it with water. First, when washing the silica gel mentioned above with acid, hydrochloric acid is Mineral acids such as , nitric acid, and sulfuric acid are preferably used, with sulfuric acid and nitric acid being particularly preferred.

In this case, the acid concentration is not necessarily limited to 9%, but it is preferable to dilute the acid with pure water such as ion-exchanged water or distilled water and use the acid at a concentration of 1N or more. If the concentration is too low, it may not be possible to sufficiently remove impurities such as uranium, and if the 1 degree is too high, a large amount of water will be required for washing, and even if the concentration is high, the acid washing effect will not be proportional. , it may be uneconomical.

Therefore, in the present invention, ultrasonic treatment is performed in such acid cleaning, and in this case, the conditions for ultrasonic treatment are not particularly limited, but for example, an output of 10 W to 2 k
It is preferable to carry out the acid treatment in an ultrasonic bath with W and an oscillation frequency of 15 to 60 kHz.

Further, although acid washing may be carried out with heating, in the present invention, impurities can be sufficiently removed even if acid washing is carried out at room temperature, so it can be carried out at room temperature.

Note that the acid washing step can be carried out in two or more parts if necessary.

Further, the acid cleaning may be carried out in a batch manner or in a continuous manner, but the acid cleaning time is preferably 10 minutes to 3 hours.

The silica gel that has been acid-washed as described above is then subjected to a water-washing process in which the acid is removed using pure water such as ion-exchanged water or distilled water. In this case, the washing temperature can be increased, but room temperature is sufficient.

Note that a normal batch type or continuous type can be used for washing with water.

In this water washing step as well, it is preferable to carry out ultrasonic treatment in the same manner as in the above-mentioned acid washing because impurities and acids can be removed more effectively. The ultrasonic treatment conditions in this case can also be the same as the ultrasonic treatment conditions for the above-mentioned sequential cleaning.

Next, the silica gel washed with acid and water as described above is dried at a normal silica gel drying temperature, and if necessary, pulverized to adjust the particle size.

As explained above, according to the present invention, a filler for encapsulating materials for electronic components such as semiconductors can be made by a simple process of washing with acid using ultrasonic waves and then washing with water. It is possible to produce high-purity silica with an extremely low content of uranium, Na, CQ ions, etc. as desired. Furthermore, the manufacturing method of the present invention can use commercially available silica gel that is inexpensive and easily available as a raw material, can minimize the amount of acid used, and does not require any special chemicals, so it is highly economical. Moreover, since the process is simple and xerogel can be used as a raw material, the step of removing excess water from the hydrogel can be omitted, and high-purity silica can be continuously produced by automation.

Industrially advantageous.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1] 50 g of commercially available silica gel (JIS-A type crushed product) and 400 g of 6N nitric acid were placed in a flask equipped with a stirring device, and stirred at room temperature in an ultrasonic bath with an output of 100 W and an oscillation frequency of 27 kHz. . 2 hours later.

The acid was discarded and washed with ion-exchanged water until the pH reached 6.

[Example 2] Similar to Example 1, silica gel was acid-treated in an ultrasonic bath,
Furthermore, washing treatment with ion-exchanged water was performed in an ultrasonic bath.

[Example 3] Processing was carried out in the same manner as in Example 1 except that JIS-A type beads were used as the silica gel and 6N sulfuric acid was used instead of nitric acid.

[Example 4] The same process as in Example 1 was carried out except that JIS-B type beads were used as the silica gel.

[Comparative Example 1] Processing was carried out in the same manner as in Example 1 except that ultrasonic treatment was not performed in the acid treatment step.

[Comparative Example 2] Processing was carried out in the same manner as in Example 3 except that ultrasonic treatment was not performed in the acid treatment step.

[Comparative Example 3] Processing was carried out in the same manner as in Example 4 except that ultrasonic treatment was not performed in the acid treatment step.

The impurity content, electrical conductivity, and water content after washing were measured for the silica gels obtained in Examples 1 to 4 and Comparative Examples 1 to 3 above. For comparison, similar measurements were also performed on the commercially available silica gel used as the raw material on each side.

The results are shown in Table 1.

From the results in Table 1, it can be seen that when the raw material silica gel was washed with ultrasonic waves and washed with water (Examples 1 to 4), the amount of uranium and N
In a., it was confirmed that high-purity silica with a low content of impurities such as CQ ions and low electrical conductivity could be obtained in a relatively short time with simple operations. In particular, when ultrasonic treatment was applied during water washing in addition to acid treatment (Example 2), it was observed that the electrical conductivity of the obtained silica was significantly lowered and the ionic impurities were extremely reduced.

Applicant: Shin-Etsu Chemical Co., Ltd. Agent: Patent attorney Takashi Kojima Year Continued Maki 1j Positive Calligraphy (self-published) October 1988 190 1.Display of the incident 1986 Patent Application No. 222961 2. Name of the invention Manufacturing method of high purity silica 3. Person who makes corrections Relationship with the incident address full name

Claims (1)

[Claims] 1. After washing the silica gel with acid while treating it with ultrasound,
A method for producing high-purity silica, which is characterized by washing with water.