JPH0466809B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to fused spherical silica using an alkali silicate as a silica source and a method for producing the same, and particularly relates to a high-purity fused spherical silica suitable for use as a filler in synthetic resin compositions for IC sealants. This invention relates to silica and its manufacturing method. [Prior Art] Generally, the requirements that silica should have as a filler in a synthetic resin composition for an IC encapsulant are as follows. The shape and particle size distribution of silica particles are appropriate, and the synthetic resin composition blended with them has good fluidity when molded, making it suitable for blending at a high ratio, and eliminating the problem of burr generation during molding. No problems such as IC electrode disconnection or poor sealing due to increased internal stress of the molded product. The purity of silica is high, and the content of alpha-ray radioactive elements such as uranium and thorium is extremely low.
Soft errors due to alpha rays should not occur even if the degree of IC integration improves. In addition, the content of water-soluble components such as Na and C and corrosive components is low, so problems such as deterioration of the electrical properties of the sealant and corrosion of IC electrode materials do not occur. The raw materials are easy to obtain, the price as a silica filler is relatively low, the quality is reproducible, and stable supply is possible. Conventionally, silica fillers used in synthetic resin compositions for IC encapsulants are made of crystalline silica such as quartz, silica stone, or ingots made by heating and melting crystalline silica or various synthetic silicas. It is mainly used after being crushed to a fine particle size. However, since the particle surfaces of these crushed silicas are irregularly fractured surfaces, they are accompanied by drawbacks.
For example, in highly integrated LSIs such as 256KDRAM and 1MDRAM, the wiring pattern is less than 5μm, and because the wiring is extremely thin, it is easy to break due to heat shrinkage during molding. Since the calorific value increases, in order to release this, it is necessary to increase the amount of silica packed, but this has the disadvantage that fluidity tends to decrease due to the particle shape, making it unsuitable for high-rate blending. Recently, in order to improve these drawbacks of pulverized silica, silica obtained by instantaneously heating and melting pulverized silica into spheroidized silica has come to be used. Conventionally, crushed natural silica such as crystal or silica stone has been mainly used as the starting material for spherical silica, but as the degree of integration of ICs and LSIs has increased, radioactive substances such as uranium and thorium in the encapsulant have increased. The problem of elemental soft errors has become more important, and there is increasing interest in higher purity raw materials with less uranium and thorium. However, it has become increasingly difficult to obtain highly purified natural products, and attempts have been made to use various synthetic silicas. A typical example is high-purity synthetic silica, which uses high-purity raw materials such as ethyl silicate and silicon tetrachloride as a silica source. The drawback is that special considerations are required for processing. Other examples of synthetic silica include: relatively inexpensive;
Moreover, many methods for producing high-purity silica using alkali silicate as a silica source, which is expected to be stably supplied, have been proposed, and the present inventors have already proposed several methods for producing synthetic silica for IC encapsulant fillers. Patent applications have been filed (Japanese Patent Application Laid-open No. 180991/1983, 40811/1982). All of these fused synthetic silica spherical products are characterized by reacting an alkali silicate with an acid in an acidic region to precipitate silica gel, and are then produced by acid treatment, drying, and melting treatment. It is. [Problems to be solved by the invention] The greatest feature of fused spherical silica is that when used as a filler in a synthetic resin composition for IC encapsulant,
It has particularly good fluidity during molding, making it possible to mix at a higher ratio, making it possible to apply it to encapsulants for highly integrated ICs that require higher thermal conductivity and dimensional stability. It's about doing. For many conventional spherical silicas, the relationship between their physical properties and fluidity is relatively simple. However, in the case of high-purity synthetic silica obtained by a wet reaction between an alkali silicate and an acid, the structure of the silica before molten spheroidization The situation is markedly different from that of conventional fused spherical silica, perhaps because of the difference in
A new problem arises in that sufficient fluidity cannot be obtained simply by adjusting the shape, particle size distribution, etc. The purpose of the present invention is to solve this problem. [Means for Solving the Problems] The present inventors have developed a synthetic resin composition for IC encapsulant, which is a molten spheroid of high-purity synthetic silica obtained by a wet reaction between an alkali silicate and an acid. As a result of various experimental studies to realize fused spherical silica as a filler for products, which has good fluidity during molding, is suitable for high-rate compounding, and does not cause problems such as burrs, and its manufacturing method, In such a molten spheroidized synthetic silica, in order to ensure the fluidity of the synthetic resin composition, regardless of its particle shape and particle size distribution,
They discovered that it is an essential element that the tap density as a powder is at least a certain value, and completed the present invention. That is, the present invention is a molten spheroidized synthetic silica produced by a wet reaction of an alkali silicate and an acid, which has a tap density as a powder of 1.36 g/cm ³ or more and a BET specific surface area of 0.2 to 3 m ² / It relates to fused spherical silica characterized by g. Furthermore, in the present invention, a wet reaction between an alkali silicate and an acid is always carried out in an acidic region to achieve a BET specific surface area of 300 m ² /
Process of producing porous synthetic silica with a weight of 50 g or more; heating the porous synthetic silica so that the BET specific surface area is 50
m ² /g or less; pulverizing the obtained sintered synthetic silica to an average particle size of 2 to 5 μm; and spraying and melting the pulverized material. It relates to a method for producing silica. [Function] The tap density (hereinafter referred to as
(written as TD) must be 1.36 g/cm ³ or more. TD is significant as a comprehensive physical property measure related to silica particle shape, particle size distribution, melting and aggregation status, surface condition, etc., and can be measured with good reproducibility using the measurement method below. There is a strong correlation between this TD and the physical properties of the epoxy resin composition filled with silica filler, especially the fluidity. Therefore, by measuring this parameter called TD, the fluidity as a filler for epoxy resin can be easily and appropriately evaluated. Therefore, it is necessary for the silica to have a TD of 1.36 g/cm ³ or more, preferably 1.39 to 1.39.
1.46 g/cm ³ is practical. Furthermore, the specific surface area of the fused spherical silica of the present invention is
It must be 0.2 to 3 m ² /g as measured by the BET method (hereinafter simply referred to as specific surface area). If the specific surface area is less than 0.2 m ² /g, troubles such as burrs will occur during molding as a filler for epoxy resin are likely to occur.On the other hand, if the specific surface area is less than 3 m ² /g
If it exceeds g, fluidity tends to be insufficient, and practicality is lost in both cases. Furthermore, the fused spherical silica according to the present invention is produced by thermal spraying and melting synthetic silica obtained through a wet reaction between an alkali silicate and an acid, and contains less than 1 ppb of radioactive elements such as uranium and thorium, and less than 1 ppb of Na.
Substantially spherical particles of high purity, less than 1 ppm, often with an average particle size of 2 to 50 μm
It is within the range of Such fused spherical silica can be produced by the following method. That is, the fused spherical silica of the present invention is produced by constantly performing a wet reaction between an alkali silicate and an acid in an acidic region.
Process of producing porous synthetic silica with a BET specific surface area of 300 m ² /g or more; heating porous synthetic silica
A process of firing until the BET specific surface area becomes 50 m ² /g or less; a process of pulverizing the obtained synthetic silica sintered product to an average particle size of 2 to 5 μm; and a process of thermal spraying and melting the pulverized product. It can be manufactured as As the alkali silicate used in the method of the present invention, a commercially available sodium silicate solution (water glass) with a molar ratio SiO ₂ /Na ₂ O of 1 to 4 can be used, but one with a relatively large molar ratio is preferable. It is economical because the amount of mineral acid required for the reaction is small.
The sodium silicate solution may be used after being appropriately diluted with water or an aqueous solution of a sodium salt of a mineral acid. On the other hand, examples of mineral acids used in the method of the present invention include hydrochloric acid, nitric acid, and sulfuric acid. Mineral acids can be used alone or as a mixed acid of two or more. Furthermore, the mineral acid can be used after being diluted as appropriate. In the method of the present invention, when producing high-purity silica using the above raw materials, other reaction aids such as a chelating agent and hydrogen peroxide may be appropriately present in the reaction system in order to remove impurities. The production process of porous synthetic silica with a specific surface area of 300 m ² /g or more is performed by adding the above-mentioned alkali silicate to mineral acid, or by adding an aqueous alkali silicate solution and mineral acid simultaneously into a reactor to form a precipitate. However, in any case, it is important to always maintain the reaction system in an acidic region, preferably at a pH of 1 or less. The deposited precipitate is subjected to appropriate treatments such as acid treatment, water washing, drying, and pulverization as necessary. Details of the method for producing porous synthetic silica with a specific surface area of 300 m ² /g or more and particularly high purity are described in, for example, Japanese Patent Application Laid-open No. 12608/1983 by the present inventors. As mentioned above, in the synthetic silica production process,
The reason for setting the specific surface area to 300 m ² /g or higher is that unless porous synthetic silica with a specific surface area value or higher is obtained in an acidic region, α-ray radioactive elements and other impure metal components cannot be removed during generation or cleaning. This is because high purity cannot be obtained. Next, the firing step is a step in which synthetic silica dried by a conventional method is dehydrated and fired by heating prior to thermal spray melting (in this case, it can be pulverized if necessary after drying). In the present invention, in this step, porous synthetic silica having a specific surface area of 300 m ² /g or more is added in an amount of 50 m ² /g.
It is important to carry out the firing until the specific surface area is 30 m ² /g or less, preferably 30 m 2 /g or less. The reason for this is that high-density fused spherical silica particles with a TD of 1.36 g/cm ³ or more cannot be obtained even if possible conditions are selected in the subsequent thermal spray melting process. The reason for this is that air bubbles are trapped in the spherical fused silica that is mainly produced due to the instantaneous melting process of thermal spray melting, and the surface of the particles becomes rough due to welding of other particles, resulting in hollow or concave shapes. This results in particles with a concave so-called navel, and no improvement in density can be expected. Therefore, whether or not the particles are of this type can be confirmed using a microscope. The firing conditions for reducing the specific surface area to 50 m ² /g or less vary depending on the properties of the porous synthetic silica and the firing method, but since there is a close relationship between temperature and time, they must be set as a function of these. However, in many cases the firing temperature is at least 1000°C or higher, preferably 1100-1300°C
The firing time is in the range of 0.2 to 2 hours. If the firing temperature is less than 1000°C, the time required will be extremely long and it is not practical. The firing method may be batch firing using a crucible or sagger, firing in a vertical furnace, continuous firing in a rotary kiln, or the like, and there is no need to limit the type of equipment used. Since the calcined synthetic silica is partially sintered, it is necessary to carry out a pulverization process in order to smoothly charge the synthetic silica during the melting process or to obtain desired fused silica particles. In this pulverization process, the average particle size is
The particle size is adjusted to 50 μm, preferably in the range of 5 to 35 μm. The synthetic silica is then sent to a melting process,
This melting treatment may be carried out using known thermal spray melting equipment and operations such as oxygen-propane, oxygen-water flame spraying or plasma spraying. Thus, according to the method of the present invention, TD is
1.36 g/cm ³ or more, preferably 1.39 to 1.46 g/cm ³ ,
In addition, high-purity, high-density fused spherical silica having a specific surface area of 0.2 to 3 m ² /g can be produced, and such silica is extremely suitable as a filler for IC resin encapsulation. In the manufacturing method of the present invention, the specific surface area is 300 m ² /
The specific surface area of porous synthetic silica
The details of the mechanism by which high-density spherical silica with a TD of 1.36 g/cm ³ or more is produced by thermal spray melting after reducing the silica to 50 m ² /g or less are not necessarily clear, but it is likely that the individual silica particles are A phenomenon in which the pore size increases sufficiently and air and water vapor can easily diffuse and move from inside the particles during thermal spray melting, trapping air bubbles within the molten particles, and rupturing the molten particles to form a complex shape. It is thought that this causes the glass to exhibit a high specific gravity value close to the original specific gravity of silica glass (approximately 2.2) and increased slipperiness between particles, resulting in a high TD. [Example] Example 1 A nitric acid aqueous solution (HNO ₃ =
19.3% by weight) was taken, and 6g of oxalic acid (dihydrate: commercially available) and 17g of 35% by weight hydrogen peroxide (commercially available) were added and dissolved therein. In this nitric acid aqueous solution,
JIS No. 3 Sodium Silicate (Na ₂ O = 9.2% by weight, SiO ₂ =
28.5% by weight) was added over a period of about 30 minutes.
A precipitate of silica formed. During this time, the reaction tank was heated and maintained while stirring. Note that the nitric acid concentration in the reaction mother liquor at this time was 1.1N. The silica separated and recovered from this reaction-completed slurry was placed in an acid treatment tank equipped with a stirrer, and acid treated with a small amount of oxalic acid and nitric acid containing hydrogen peroxide. Next, silica was over-separated from this slurry, followed by washing with water and solid-liquid separation using conventional methods, and then the silica precipitate was collected and dried at 105°C for 2 hours to obtain a specific surface area of 478 m ² /g by the BET method. Porous silica was obtained. This porous silica was placed in a refractory crucible and heated to 1300
It was calcined at ℃ for 30 minutes to obtain calcined silica with a specific surface area of 11.3 m ² /g. This calcined silica is crushed to obtain an average particle size of
After adjusting the particle size to 19 μm, thermal spray melting treatment was performed using an oxygen-propane gas flame to obtain fused spherical silica. Impurity content of the obtained fused spherical silica,
TD, specific surface area, etc. are shown in Table 1 below. As is clear from Table 1, this fused spherical silica has extremely low impurity content and high purity, and also has high TD and specific gravity, making it suitable as a filler for synthetic resin compositions for IC sealants. It has purity and physical properties. In addition, when observed under a microscope, each particle had an almost perfect spherical shape, and no air bubbles or pores were observed. Example 2 A specific surface area of 421 m ² / prepared by wet reaction of sodium silicate and nitric acid in the same manner as in Example 1.
g of porous silica in a vertical electric furnace at 1100-1200℃
Baked for 30 minutes at each temperature. The calcined silica was subjected to particle size adjustment (average particle size) in the same manner as in Example 1.
25 μm) and then subjected to flame spray melting treatment to obtain fused spherical silica. The analytical values and physical property values of the obtained spherical silica are
Also listed in the table. In addition, when observed under a microscope, the silica particles had an almost perfect spherical shape, and no air bubbles or pores were observed. Example 3 The porous silica described in Example 1 was continuously fired at 1200°C in a rotary kiln (average firing time 20 minutes), and the fired silica was pulverized to adjust the particle size (average particle size 16 μm). Flame spray melting treatment was performed in the same manner to obtain fused spherical silica. The analytical values and physical property values of the obtained spherical silica are
Also listed in the table. In addition, when observed under a microscope, the silica particles had an almost perfect spherical shape, and no air bubbles or pores were observed. Comparative Example 1 Molten spherical silica was obtained in the same manner as in Example 1, except that porous silica was pulverized and adjusted to an average particle size of 17 μm and then thermally sprayed and melted without being calcined at 1200°C. The analytical values and physical property values of the obtained spherical silica are
Also listed in the table. From Table 1, the specific surface area is 50 without firing.
It is clear that if porous silica with a particle size far larger than m ² /g is directly thermally sprayed and melted, fused spherical silica with low specific gravity and TD can be obtained. When observed under a microscope, each particle was generally spherical, but air bubbles within the particles and pores on the surface of the particles were noticeable, and some particles were observed to be fused together. The fused spherical silica obtained in this way was thermally sprayed and melted again, but the specific gravity and TD showed almost the same values as the fused spherical silica before remelting, and microscopic observation still showed that air bubbles inside the particles and on the particle surface were observed. A hole was observed. Comparative Example 2 Fused silica was obtained under the same operation and conditions as in Example 1 except that the firing operation was performed at 900° C. for 4 hours. When this silica was examined under a microscope, it was found that there were a considerable number of concave particles mixed with spherical particles. In addition, other chemical analysis values and physical property values are also listed in Table 1.

【table】

[Table] TD measurement method Weigh 10g of the sample and transfer it to a 25ml graduated cylinder. Next, after dropping this graduated cylinder from a height of 5 cm 300 times at a rate of 74 times per minute,
Read the volume of the sample (Vcm ³ ) and calculate TD using the following formula.
Calculate the value of TD (g/cm ³ ) = 10 (g)/V (cm ³ ) Reference Example 1 An epoxy resin composition having the following composition was prepared using the fused spherical silica obtained in Examples 1 to 3 and Comparative Examples 1 to 2 as a filler. It was prepared and its physical properties were evaluated. Fused spherical silica 70 parts by weight Orthocresol novolac type epoxy resin (Epicron N665: manufactured by Dainippon Ink) 20 parts by weight novolac type phenolic resin (Barcam)
TD2131: manufactured by Dainippon Ink) 10 parts by weight OP wax (manufactured by Hoechst Japan) 1 part by weight The above compositions were mixed and melt-kneaded for 5 minutes using a mixing roll heated to 80 to 90°C, and then formed into a sheet. This was cooled and ground to obtain a resin composition powder. Measurement of melt viscosity of the obtained resin composition powder (Shimadzu Flow Tester CFT-20, 130℃,
(10 Kg/cm ² , using a 1 mm x 10 mm nozzle) and the flow state of the melt from the nozzle was observed. The results are shown in Table 2. Furthermore, the relationship between the melt viscosity in Table 2 and TD is shown in FIG. From Figure 1, TD
It is clear that the higher the value, the lower the melt viscosity and the better the fluidity.

[Table] ○: The molten material discharged from the nozzle is deposited flatly and solidified into a Go stone shape.
×: The molten material coming out of the nozzle accumulates in a thin streak and solidifies.
do.
Reference Example 2 An epoxy resin composition having the following composition was prepared using the fused spherical silica obtained in Examples 1 to 3 and Comparative Examples 1 to 2 as a filler, and its physical properties were evaluated. Fused spherical silica 70 parts by weight Orthocresol novolak-type epoxy resin (Epicron N665: manufactured by Dainippon Ink) 18 parts by weight novolak-type phenolic resin (Barcam)
TD2131: Dainippon Ink) 9 parts by weight OP wax (mold release agent) 0.3 parts by weight Surface treatment agent 0.5 parts by weight Curing accelerator 0.4 parts by weight Antimony trioxide 1.5 parts by weight Pigment 0.3 parts by weight Among the above compositions, first, Fused spherical silica and antimony trioxide are mixed with a surface treatment agent, then the remaining materials are added and mixed further, and then 80~
The mixture was melt-kneaded for 10 minutes using a mixing roll heated to 90°C, and then formed into a sheet. This was cooled and pulverized to obtain a resin composition powder for semiconductor encapsulation. The length of burr (mm) and EMMI1 when the obtained resin composition powder was molded using a slit mold for thin burr determination with a clearance of 5 μm.
−66 (Epoxy Molding Material Institute:
Spiral flow was measured according to the Society of Plastic Industry). The measurement results are shown in Table 3. Furthermore, the relationship between the spiral flow value in Table 3 and TD is shown in FIG. From Figure 2, it is clear that the higher the TD, the greater the spiral flow value as an indicator of liquidity.

[Table] [Effects of the Invention] The first effect of the present invention is that it can be used at a high compounding rate, which is desired as an excellent resin encapsulant for semiconductor ICs, which will become more highly integrated in the future with the development of the electronic industry. It becomes possible to stably supply a high-density spherical filler that can be filled and is suitable for increasing thermal conductivity, reducing residual stress, improving moisture resistance, etc. at a relatively low cost. In addition, the second effect of the present invention is that a spherical filler having the above-mentioned excellent properties can be reliably obtained using relatively inexpensive alkali silicate and mineral acid as main raw materials, and it also generates harmful or difficult-to-process by-products. It is possible to provide an industrially advantageous manufacturing method.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between melt viscosity and TD, and FIG. 2 is a graph showing the relationship between spiral flow value and TD.

Claims (1)

[Scope of Claims] 1. A molten spheroidized synthetic silica produced by a wet reaction between an alkali silicate and an acid, which has a tap density as a powder of 1.36 g/cm ³ or more and a BET specific surface area of 0.2 to 3 m ² /g of fused spherical silica. 2. Fused spherical silica contains α such as uranium and thorium.
Content of radioactive elements is 1ppb or less, Na is 1ppm
The fused spherical silica according to claim 1, which has the following high purity. 3 A step of producing porous synthetic silica with a BET specific surface area of 300 m ² /g or more by carrying out a wet reaction between an alkali silicate and an acid always in an acidic region; heating the porous synthetic silica and producing a BET specific surface area of 50 m ² /g. Production of fused spherical silica characterized by comprising the following steps: firing until the synthetic silica has a particle diameter of 2 to 5 μm; pulverizing the resulting fired synthetic silica to an average particle size of 2 to 5 μm; and spraying and melting the pulverized product. Method.