JP7017362B2 - Spherical crystalline silica particles and their manufacturing method - Google Patents

Description

The present invention relates to spherical crystalline silica particles and a method for producing the same, particularly spherical tridymite crystal particles and a method for producing the same.

Silica particles are used as fillers for resins, and are used, for example, as fillers for encapsulants for semiconductor devices. If the shape of the silica particles is angular, the fluidity, dispersibility, and filling property in the resin will deteriorate. In order to improve these, spherical silica particles are widely used.

Generally, a thermal spraying method is used as a method for producing spherical silica. In thermal spraying, the particles are melted by passing them through a high temperature region such as a flame, and the shape of the particles becomes spherical due to surface tension. The melt-spheroidized particles are collected by airflow so that the particles do not fuse with each other, but the particles after thermal spraying are rapidly cooled. Since silica is rapidly cooled from the molten state, it contains almost no crystals, has an amorphous structure, and becomes glass-like particles generally called quartz glass.

Since spherical silica is amorphous, its thermal expansion rate and thermal conductivity are low. These physical properties are considered to be substantially the same as the thermal expansion rate of quartz glass having an amorphous structure without a crystal structure, the thermal expansion rate is 0.5 ppm / K, and the thermal conductivity. Is 1.4 W / mK.

Since spherical silica particles generally used as a sealing material are amorphous, they have a low thermal expansion rate, and therefore have an effect of lowering the thermal expansion rate of a mixture (resin composition) when mixed with a resin. As a result, the thermal expansion rate of the resin composition can be brought close to that of the semiconductor device, and when the resin composition is used as a sealing material, deformation that occurs during heating and cooling such as the curing process of the resin can be suppressed. .. However, since semiconductors are becoming thinner and smaller, it is necessary to control the thermal expansion rate more precisely than before in order to suppress deformation.
For example, in order to obtain a resin composition having higher strength with a sealing material or the like, it is necessary to increase the amount of silica particles mixed with the resin, but the amorphous silica particles mixed with the resin When the amount is increased, the thermal expansion rate of the resin composition becomes lower. For this reason, the thermal expansion rate becomes too low as compared with the semiconductor chips and substrates, and there arises a problem that deformation occurs during heating and cooling processes such as the curing process of the resin.

In order to suppress deformation due to the difference in thermal expansion coefficient between the semiconductor component and the resin composition, it is necessary to precisely control the thermal expansion coefficient of the resin composition. As a method of controlling the thermal expansion rate of the resin composition, a method of mixing low thermal expansion amorphous silica particles and high thermal expansion particles and adjusting the thermal expansion rate to a desired value by changing the mixing ratio thereof. Is useful. Crystalline ceramic particles can be used as the high thermal expansion particles used by mixing with amorphous silica particles, but a higher effect can be obtained by using crystalline silica particles such as cristobalite and tridimite. be able to. This is higher than other materials because cristobalite and tridimite undergo a phase transition near the curing treatment temperature of the encapsulant and the heat treatment temperature of the solder reflow, and the thermal expansion caused by the phase transition is large. It is considered possible to obtain the effect. On the other hand, quartz, which is crystalline silica, has a larger thermal expansion coefficient than amorphous silica, but the temperature at which large thermal expansion due to the phase transition occurs is 573 ° C, which is considerably higher than the process temperature of semiconductors. Compared to tridymite, it has less effect of suppressing deformation of semiconductor parts and the like.

As a means for obtaining crystalline silica particles, after surface-treating amorphous silica with an organic metal compound containing a metal selected from aluminum, magnesium and titanium in Patent Document 1, or a sol or slurry of the organic metal compound. , A method of heat-treating at 1,000 to 1,600 ° C. to crystallize is disclosed.
Further, Patent Document 2 discloses a technique for producing fine crystalline silica by treating a filtration residue obtained when producing water glass from silica sand and sodium carbonate with an alkali and an acid and neutralizing the mixture. There is.
Further, Patent Document 3 discloses a method of mixing silica sand, silica stone, molten silica and the like with an alkali metal and an alkaline earth metal product and firing them.
Further, as a means for obtaining spherical crystalline silica particles, in Patent Document 4 and Patent Document 5, the dispersed phase liquid in which the silica sol is dispersed is formed into a continuous phase liquid incompatible with the dispersed phase liquid, and pores are formed. An emulsion is prepared by injecting the liquid through the emulsion, the dispersed phase is separated from the emulsion to form a cake, and the cake obtained by the separation is selected from the group consisting of Ca, Y, La and Eu. Disclosed is a technique for holding and firing in a temperature range of 800 ° C. or higher and 130 ° C. or lower in the coexistence of a crystallization agent containing one or more of these elements.

Japanese Unexamined Patent Publication No. 2008-162849 Japanese Unexamined Patent Publication No. 6-247709 Japanese Unexamined Patent Publication No. 2001-3034 Japanese Unexamined Patent Publication No. 2005-231973 Japanese Unexamined Patent Publication No. 2012-102016

Semiconductor products are becoming thinner and finer, and in order to obtain a high-strength resin composition as a filler used for semiconductor encapsulants, a high filling rate can be obtained and fine gaps can be filled. Spherical particles are indispensable because a sealing material having high fluidity is required for this purpose. Further, in order to precisely control the thermal expansion rate of the encapsulant or the like, in addition to the conventional amorphous spherical silica particles having a small thermal expansion rate, crystalline spherical silica particles having a large thermal expansion rate are mixed. It is necessary to use it. Among crystalline spherical silicas, tridymite and cristobalite spherical particles, which undergo large thermal expansion at the semiconductor process temperature, are considered to be effective.
In tridymite, a two-step phase transition occurs, with a phase transition from α-tridymite to β1-tridymite at 117 ° C and a phase transition from β1-tridymite to β2-tridymite at 163 ° C. In addition, cristobalite undergoes a one-step phase transition from α-cristobalite to β-cristobalite at 200-275 ° C. Although these phase transitions are accompanied by thermal expansion, cristobalite undergoes rapid thermal expansion in a one-step phase transition, so that the interface with the resin is likely to be peeled off. On the other hand, in tridymite, thermal expansion occurs with the two-step phase transition, and the thermal expansion generated at each phase transition is smaller than that in the case of cristobalite, and occurs relatively slowly. For this reason, in the case of tridymite, problems associated with rapid thermal expansion such as peeling at the interface with the resin are unlikely to occur, and since thermal expansion occurs at a lower temperature than cristobalite, heating and cooling of the resin curing process and solder reflow process A greater effect can be obtained due to the suppression of deformation in the process. Therefore, tridymite spherical particles are considered to be particularly useful.

As a method for obtaining spherical crystalline silica, a method of heat-treating amorphous spherical silica at a high temperature to crystallize it is disclosed. However, when the heat treatment is performed at a high temperature, there is a problem that the silica particles are fused or sintered to be bonded to each other. Therefore, since the particles are obtained by crushing a mass of strongly bonded particles, only crushed (atypical) particles can be obtained. Further, a method of producing and calcining spherical particles in a liquid phase using silica sol or the like as a raw material has been disclosed, but there are problems that productivity is low and production cost is high.

According to Patent Document 1, amorphous silica is surface-treated with an organometallic compound containing a metal selected from aluminum, magnesium and titanium, or a sol or slurry of the organometallic compound, and then heated at 1,000 to 1,600 ° C. A method of processing and crystallizing is disclosed. However, with this method, only cristobalite can be precipitated as the crystalline phase, and crystalline silica containing tridymite cannot be obtained.
Patent Document 2 proposes a method for producing fine crystalline silica by sequentially treating a filtration residue obtained when producing water glass from silica sand and sodium carbonate with an alkali and an acid and neutralizing the mixture. ing. In this method, α-quartz, cristobalite and tridymite have been identified by X-ray diffraction, but their ratios have not been specified, and it is considered that silica particles containing a large amount of tridymite cannot be produced. In addition, this method uses a filtration residue obtained together with a filtration aid such as diatomaceous soil when filtering a glassy substance (cullet) obtained by dissolving and solidifying a mixture of silicon and sodium carbonate in water. The precipitates produced by the dissolution of the above form fine amorphous or scaly solids, and spherical particles cannot be obtained by this method.
Patent Document 3 proposes a method of mixing silica sand, silica stone, molten silica and the like with an alkali metal and an alkaline earth metal and firing them. In this method, molten quartz powder is mixed with sodium carbonate and fired at 1200 ° C. for 4 hours to obtain a tridimite crystal phase ratio of 100%. The fired product is crushed and crushed and fired. Is passed through a 400 mesh sieve to obtain an abrasive. From this, the processed product after firing is in a solid state that requires pulverization, and this technique is for obtaining particles used for an abrasive, and obtains a product having high polishing characteristics, that is, an angular shape. The purpose is to crush the fired product obtained by firing to obtain an abrasive. Therefore, it is not possible to obtain spherical particles with a high content of tridymite by this technique.

In Patent Documents 4 and 5, a silica sol dispersion liquid is passed through pores to form a spherical emulsion, and then the dispersed phase is separated into a cake, which is crystallized containing one or more of Ca, Y, La and Eu. We propose a method to obtain crystalline silica by heat treatment in the coexistence of an agent. In this method, since the steps of separating and drying the emulsion are added, the productivity is low, and since an expensive silica sol is used as a raw material, the production cost is also high. Further, the crystalline silica obtained by this method has a crystalline phase of α-quartz and cristobalite, and spherical particles having an α-quartz ratio of 24-67% and a cristobalite ratio of 76 to 33% can be obtained. However, it is not possible to obtain spherical particles containing tridymite.

As described above, the conventionally disclosed technique has not been able to obtain crystalline spherical silica particles containing a large amount of tridymite crystals. Since tridymite has a high thermal expansion rate and expands relatively slowly during a phase transition, if spherical silica particles containing a large amount of tridymite crystals can be obtained, they are mixed with a resin together with amorphous silica particles and sealed. When used as a stopping material, the effect of suppressing deformation of semiconductors in a semiconductor manufacturing process such as a sealing process or a reflow process can be obtained. Further, since tridymite is a crystal and has a higher thermal conductivity than amorphous silica, it can be expected to have an effect of efficiently dissipating heat generated by a semiconductor chip.

The present invention contains a large amount of tridymite crystals having a high thermal expansion rate, has a spherical shape in order to have high fluidity, high dispersibility, and high filling property, and is applicable to the semiconductor field as spherical crystalline silica particles. And its manufacturing method.

As a result of diligent studies to solve the above problems, the inventor stated, "By adding a predetermined ratio of Na compound to the raw material, the crystal phase is 90% by mass or more of the whole, and the tridimite crystal is the whole. It was found that "spherical crystalline silica particles having an amount of 50% by mass or more of the above" can be produced, whereby the productivity is higher than before, the production cost is lower, and a large amount of tridimite having a high thermal expansion rate is contained. It has been found that spherical crystalline silica particles having high rate, high fluidity, high dispersibility, and high filling property and applicable to the semiconductor field can be realized. This led to the invention.

The gist of the present invention is as follows.
[1]
Spherical crystalline silica particles, characterized in that the crystal phase is 90% by mass or more of the whole and the tridymite crystal is 50% by mass or more of the whole.
[2]
The spherical crystalline silica particles according to [1], which contains 1 to 10% by mass of Na in terms of oxide with respect to the entire particles.
[3]
The spherical crystalline silica particles according to [2], wherein the Al content is 50 to 1000 ppm in terms of Al2O3 with respect to the entire particles.
[4]
The spherical crystalline silica particle according to any one of [1] to [3], wherein the average particle size (D50) is 1 to 100 μm.
[5]
The spherical crystalline silica particle according to any one of [1] to [4], which has an average circularity of 0.85 or more.
[6]
The amorphous spherical silica particles are mixed with 1 to 10% by mass of the Na compound in terms of oxide with respect to the total of the weight of the amorphous spherical silica particles and the weight of the Na compound in terms of oxide.
The mixed spherical silica particles are heat-treated at 800 to 1200 ° C.
Including the step of cooling the heat-treated spherical silica particles,
A method for producing spherical crystalline silica particles, wherein the cooled spherical silica particles have a crystal phase of 90% by mass or more, and tridimite crystals are 50% by mass or more of the whole.
[7]
The method for producing spherical crystalline silica particles according to [6], wherein the content of Al of the amorphous spherical silica particles mixed with the Na compound is 50 to 1000 ppm in terms of Al2O3.
[8]
The spherical crystalline silica particles according to any one of [6] to [7], which are produced so that the average particle size (D50) of the spherical crystalline silica particles is 1 to 100 μm. How to make.
[9]
The spherical crystalline silica particles according to any one of [6] to [8], which are produced so that the average circularity of the spherical crystalline silica particles is 0.85 or more. Method.

According to the present invention, it contains a large amount of tridymite having a high thermal expansion rate, has a spherical shape due to high thermal conductivity, high fluidity, high dispersibility, and high filling property, and has spherical crystallinity that can be applied to the semiconductor field. Silica particles and a method for producing the same are provided.

The silica particles of the present invention contain 90% by mass or more of a crystal phase. Since the thermal conductivity of amorphous silica is as low as 1.4 W / mK, if amorphous silica is contained in an amount of more than 10% by mass, the thermal conductivity of the silica particles is lowered. Further, the crystal phase is 50% by mass or more of the whole particles containing amorphous tridymite crystals. Crystal phases other than tridymite crystals may include cristobalite and quartz. Both crystals have a higher thermal expansion rate than amorphous silica. If 90% by mass or more of the whole particles are crystal phases and 50% by mass or more of all the particles are tridymite crystals, the desired high thermal conductivity spherical silica particles can be obtained. Further, when the content of tridymite or quartz is more than 50% by mass, the sufficient effect of high thermal expansion due to the volume expansion accompanying the phase transition of tridymite from α tridymite → β1 tridymite → β2 tridymite cannot be obtained. Therefore, it is important to increase the content of tridymite crystals to 50% by mass or more and reduce the content of cristobalite, quartz and amorphous.
The crystalline phase and amorphous content and the tridymite, cristobalite and quartz contents can be quantitatively analyzed by X-ray diffraction. In the quantitative analysis by X-ray diffraction, it is possible to perform the quantitative analysis without using a standard sample by using an analysis method such as the Rietveld method.

The silica particles of the present invention may contain 1 to 10% by mass of a compound of Na in terms of oxide.
Without being bound by a specific theory, it is conceivable that Na invades the inside of the amorphous silica network structure during heat treatment and stabilizes the crystal structure. Tridymite has the lowest density among several types of silica crystals, because it has a large space inside the crystal structure. In the phase diagram of silica, tridymite is said to be produced at 867 to 1470 ° C., but it is difficult to obtain crystals of tridymite even if it is heat-treated and cooled in that temperature range. It is considered that this is because the tridymite crystal has a large void inside the crystal, so that the crystal structure is not stable and changes to other crystals such as cristobalite during the heat treatment or cooling process.
The voids in the tridymite crystal have a size of about 170 pm, and it is considered effective to introduce an element into the void portion as a method for stabilizing the structure having such a large void portion. Alkali metals and alkaline earth metals can be considered as elements that enter the network structure of amorphous silica. However, since the voids of tridymite crystals are large, it is desirable that the element that stabilizes the structure also has a large ionic radius. In particular, Na has a large ionic radius of 116 pm and is therefore very effective as an element for stabilizing the crystal structure of tridymite. Li, which is an alkali metal of the same family, has a small ionic radius and cannot sufficiently obtain the effect of stabilizing the crystal structure of tridimite. Further, K, Rb, Cs, and Fr, which are alkali metals of the same family, have too large an ionic radius, and the effect of stabilizing the crystal structure of tridymite cannot be sufficiently obtained.

The Na content is preferably 1% by mass or more. When the Na content is less than 1% by mass, it is not sufficient to stabilize the crystal structure of tridymite, so that many other crystals are generated, and silica particles having a high tridymite content of interest can be obtained. Is difficult. The Na content is preferably 10% by mass or less. If the Na content is more than 10% by mass, the resin may be hindered from curing when mixed with the resin, or it may cause corrosion of metals such as wiring.

Alkali metals are also known to have the effect of lowering the melting point of silica, and are also used, for example, as a melting point lowering agent for silica glass. In particular, Na is used to lower the melting point of SiO2-based glass as used for soda glass. Therefore, when the content of the alkali metal is increased, the melting point of the silica particles is remarkably lowered, and the silica particles are easily bonded to each other by fusion or sintering in the heat treatment required for crystallization of the amorphous silica particles. .. As the bonding between the particles progresses, it becomes difficult to obtain spherical particles, so that the fluidity, dispersibility, and filling property become insufficient when used as a filler for a semiconductor encapsulant or the like.

Further, when Na is added to obtain tridymite particles, it is desirable to contain 50 to 1000 ppm of aluminum in terms of metallic aluminum. Although not bound by a specific theory, aluminum acts as a crystal nucleation agent during heat treatment, and when used in combination with an alkali metal, particularly Na, can obtain the effect of producing a large amount of tridimite crystals. Further, since crystallization is likely to occur by low-temperature heat treatment due to the inclusion of aluminum, tridimite particles can be obtained by heat treatment at a low temperature at which silica particles are unlikely to fuse or sinter. Aluminum is metallic aluminum. If it is less than 50 ppm in terms of conversion, the effect of promoting crystallization cannot be obtained. Further, when the amount of aluminum exceeds 1000 ppm in terms of metallic aluminum, cristobalite is likely to be produced, and the amount of tridymite crystals produced is reduced. Therefore, it is more desirable that aluminum is in the range of 50 to 1000 ppm in terms of metallic aluminum.

The silica particles of the present invention may have an average particle size (D50) of 1 to 100 μm. If the average particle size exceeds 100 μm, when used as a filler for semiconductor encapsulants, the particle size may become too coarse and cause gate clogging or mold wear, and the average particle size is less than 1 μm. Then, the particles may become too fine to be filled in a large amount. The average particle size here can be obtained, for example, by measuring the particle size distribution by a laser diffraction method or the like.
The average particle size referred to here is called the median diameter, and the particle size is measured by a method such as a laser diffraction method, and the particle size at which the cumulative frequency of the particle size is 50% is the average particle size (D50). And.

It is possible to adjust the particle size of the raw material amorphous spherical silica particles (particles before crystallization) to the above particle size range. This is because the average particle size of the silica particles of the present invention hardly changes before and after the heat treatment for crystallization. Since ordinary amorphous silica particles require a high temperature of 1300 ° C. or higher for crystallization, the particles may be softened and bonded by fusion or sintering, but the silica particles of the present invention are 800. It can be crystallized at a relatively low temperature of about 1200 ° C., and the bonding between particles can be relatively suppressed by fusion or sintering. In particular, bonding by fusion or sintering of particles is more likely to occur as the surface area ratio of the particles is larger, that is, the smaller the particle size. However, since the silica particles of the present invention become crystalline at a relatively low temperature (800 to 1200 ° C.), even if the average particle size is 1 μm, bonding by fusion or sintering is sufficiently suppressed. , Hard to aggregate. Therefore, the silica particles of the present invention can have high fluidity, dispersibility, and filling property when used as a filler for a semiconductor encapsulant or the like.

The silica particles of the present invention are spherical. The means for forming the sphere is not particularly limited, and means such as pulverization and polishing may be used. In particular, by crystallizing spherical amorphous silica particles, spherical crystalline silica particles can be obtained with high productivity and low cost. In this case, spherical amorphous silica particles produced by the thermal spraying method can be used. In the case of amorphous spherical silica particles by spraying, the particle size of the spherical silica particles obtained can be changed by the particle size of the silica powder used as the raw material for spraying. Therefore, by crystallizing this, spherical crystals having a desired particle size can be obtained. Quality silica particles can be obtained. When the spherical crystalline silica particles are used as a filler for a semiconductor encapsulant, they have high fluidity, dispersibility, and filling property, and can suppress wear of the encapsulant manufacturing equipment.

The silica particles of the present invention may have an average circularity of 0.85 or more, preferably 0.86 or more. The circularity can be measured by a commercially available flow-type particle image analyzer. Further, it can be obtained from a micrograph such as a scanning electron microscope (SEM) by using image analysis processing software as follows. Take a picture of a sample of silica particles and measure the area and perimeter of the silica particles (two-dimensional projection). Assuming that the silica particles are a perfect circle, calculate the circumference of the perfect circle with the measured area. The circularity is calculated by the formula of circularity = circumference / circumference length. A perfect circle is when the circularity is 1. That is, the closer the circularity is to 1, the closer to a perfect circle. The average circularity is calculated as the average value of the circularity measured for 100 or more particles. If the average circularity is less than 0.85, the fluidity, dispersibility, and filling property are not sufficient when used as a filler for a semiconductor encapsulant, and the wear of the encapsulant manufacturing equipment is accelerated. May be done.
The upper limit of the circularity may be 1.0, but it is practically difficult to actually make the circularity 1.0, and if it is to be realized, the manufacturing cost and the management cost will be high. The upper limit of the circularity may be 0.98, preferably 0.95, depending on the intended use.

The above average circularity can be achieved by adjusting the circularity of the amorphous spherical silica particles (particles before crystallization). If it is a thermal spraying means, the silica powder can be easily made into particles having a high circularity. The average circularity of the silica particles of the present invention hardly decreases before and after the heat treatment for crystallization. This is because the silica particles of the present invention are crystallized at a relatively low temperature (800 to 1200 ° C.), and the circularity hardly decreases in this temperature range. That is, when crystallizing ordinary amorphous silica particles, a high temperature of 1300 ° C. or higher is required, so that the particles may be bonded to each other by fusion or sintering, and when the particles are bonded to each other, the circularity is increased. descend. However, since the silica particles of the present invention become crystalline at a relatively low temperature (800 to 1200 ° C.), they are sufficiently suppressed from being bonded by fusion or sintering, so that the average circularity is hardly reduced. Therefore, the silica particles of the present invention can have high fluidity, dispersibility, and filling property when used as a filler for a semiconductor encapsulant or the like.

The manufacturing method of the present invention will be described in detail below. The spherical crystalline silica particles of the present invention can be produced by a method including the following steps. That is, the manufacturing method of the present invention is
Amorphous spherical silica particles are mixed with a compound of 1 to 10% by mass of Na in terms of oxide, and the mixture is mixed.
The mixed spherical silica particles are heat-treated at 800 to 1200 ° C.
The step of cooling the heat-treated spherical silica particles is included. The spherical crystalline silica particles produced by this method have a crystal phase of 90% by mass or more, and tridymite crystals are 50% by mass or more of the whole.
It is desirable that the spherical silica particles are placed in a container that does not react with silica particles such as alumina and heat-treated. The heat treatment is performed by heating to a predetermined temperature using, for example, an electric furnace, a gas furnace, or the like. It is desirable to perform cooling while controlling the cooling rate.

Amorphous spherical silica particles as a raw material can be produced by a method such as a thermal spraying method. For example, in the thermal spraying method, silica powder prepared by crushing to a desired particle size is passed through a flame to melt the particles, and the shape of the particles becomes spherical due to surface tension.

Further, the silica powder may be prepared so that the silica powder before thermal spraying contains 50 to 1000 ppm of aluminum in terms of oxide. Without being bound by a particular theory, aluminum may act as a crystal nucleating agent during heat treatment. Through the thermal spraying step (melting), aluminum is uniformly dispersed in the silica particles. Aluminum is considered to act as a crystal nucleation agent during the subsequent heat treatment process, and by being uniformly dispersed in the silica particles, crystal growth can be achieved evenly and at a lower temperature and in a shorter time than before. Will be done.
In addition, alumina obtained by oxidizing aluminum can be expected to have the effect of increasing the chemical durability (acid resistance, etc.) of the silica particles. If the aluminum content is less than 50 ppm, the crystallization promoting effect and the chemical durability improving effect may not be sufficient. On the other hand, aluminum or alumina facilitates the formation of cristobalite when crystallizing amorphous silica. Therefore, when the aluminum content exceeds 1000 ppm, cristobalite is preferentially produced, and tridymite is less likely to be produced.
The aluminum content can be measured, for example, by atomic absorption spectrometry, ICP mass spectrometry (ICP-MS).

The particles after thermal spraying may be quenched so that the molten spheroidized particles do not fuse with each other. In that case, since the spherical silica particles are rapidly cooled from the molten state, the spherical silica particles do not have a crystal structure but have an amorphous structure. Since the spherical silica particles are sprayed, they may be non-porous. The non-porous spherical silica particles are expected to be dense and have high thermal conductivity.

The spherical silica particles obtained by thermal spraying may have an average particle size (D50) of 1 to 100 μm. Since the maximum temperature of the subsequent heating and cooling steps for crystallization is about 1200 ° C., the particle size of the spherical silica particles hardly changes. Then, if it is a thermal spraying means, the particle size can be easily adjusted. Therefore, in the method of the present invention, spherical crystalline silica particles having a desired average particle size can be easily realized.

The spherical silica particles obtained by thermal spraying may have an average circularity of 0.85 or more. Since the maximum temperature of the subsequent heating and cooling steps for crystallization is about 1200 ° C., the circularity of the spherical silica particles hardly changes. Then, if it is a thermal spraying means, particles having a high average circularity can be easily obtained. Therefore, in the method of the present invention, the desired spherical crystalline silica particles having a high degree of circularity can be easily realized.

Amorphous spherical silica particles mixed with a compound of 1 to 10% by mass of Na in terms of oxide are heat-treated, and the heat-treated spherical silica particles are cooled to obtain spherical crystalline silica particles. ..

The Na compound mixed with the amorphous spherical silica particles is not particularly limited in the form when added, such as an oxide, a carbonic acid oxide, a hydroxide, and a glass oxide. As long as it is uniformly mixed with amorphous spherical silica particles, it can be added in the form of powder, aqueous solution or the like.

The heat treatment of the mixture of the amorphous spherical silica particles and the Na compound is performed under conditions suitable for crystallization and retention of the spheres, depending on the particle size of the amorphous spherical silica and the amount of the Na compound added. The heat treatment temperature can be selected, for example, in the range of 800 to 1200 ° C. Further, the holding time can also be carried out in the range of, for example, 1 to 48 hours. Further, the rate of temperature rise and cooling can be carried out in the range of, for example, 100 to 300 ° C./hour.

When the heat-treated crystalline silica particles are agglomerated, the agglomeration can be unwound by using a crushing method such as a jet mill, and spherical crystalline silica particles can be obtained.

The cooled spherical crystalline silica particles have a crystal phase of 90% by mass or more. In addition, it contains 50% by mass or more of tridymite crystals. The crystalline silica particles have a higher thermal expansion rate than amorphous silica. When silica particles are used as a filler for a semiconductor encapsulant or the like, crystalline silica having a high thermal expansion rate is useful in order to suppress deformation of the semiconductor chip or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not construed as being limited to the following examples.

Amorphous silica particles having an average particle size (D50) of 11.9 μm and containing 147 ppm of Al in terms of Al2O3 are mixed with sodium carbonate, heated to 800 to 1200 ° C. in the air, held for 1 to 48 hours, and then at room temperature. Cooled down to. The obtained silica particles are shown in Table 1.

The circularity was measured using a flow-type particle image analyzer "FPIA-3000" manufactured by Sysmex Corporation.

For the crystallization rate, the integrated area of the amorphous peak and the crystalline peak was obtained by X-ray diffraction, and the ratio of the crystalline area was taken as the crystallization rate. That is, it was calculated as crystallization rate = integrated area of crystalline peak / (integrated area of amorphous peak + integrated area of crystalline peak). Similarly, the proportions of amorphous, Christovalite, quartz, tridimite and other crystals were calculated.
The raw material and the average particle size (D50) after the heat treatment were measured using a laser diffraction type particle size distribution measuring device (CILAS 920 manufactured by CILAS). The D50 is also called a median diameter, and is a particle size having a cumulative weight% of 50%.
The raw material and the impurity content after the heat treatment were measured by the atomic absorption method using the sample aqueous solution obtained by heat-decomposing the sample with an acid.

In the examples according to the present invention, the crystallization rate was 90% by mass or more of the whole, and crystalline spherical silica particles containing 50% by mass or more of tridymite were obtained.
Further, the particles of the examples according to the present invention had a circularity of 0.86 to 0.95, and crystalline silica particles having an average particle size (D50) of 12.6 to 15.7 μm were obtained.
On the other hand, in the sample heat-treated at 700 ° C. for 48 hours in Comparative Example 6, crystallization was insufficient and a large amount of amorphous material remained at 34.4%. Further, in the sample heat-treated at 1300 ° C. for 1 hour in Comparative Example 7, the particles were in a solidified state, and particles could not be obtained.

Amorphous silica particles having an average particle size (D50) of 31.8 to 93.2 μm and containing Al of 194 to 2013 ppm in terms of Al2O3 are mixed with sodium carbonate, heated to 1000 ° C. in the air, and held for 6 to 24 hours. After that, it was cooled to room temperature. Table 2 shows the results of evaluating the obtained silica particles in the same manner as in Example 1.
In the examples according to the present invention, amorphous was not confirmed, and crystalline spherical silica particles having a crystallization rate of 100% by mass and containing 50% by mass or more of tridymite were obtained.
Further, the particles of the examples according to the present invention had a circularity of 0.86 to 0.91, and crystalline silica particles having an average particle size (D50) of 35.4 to 98.2 μm were obtained.
On the other hand, when the amount of Na in Comparative Example 12 was smaller than that of the present invention, spherical crystalline particles were obtained, but only those having a tridymite content of 4.2% by mass were obtained. When the amount of Na in Comparative Example 13 was larger than that of the present invention, the content of tridymite was 57.8% by mass, but the particles were tightly bound and became agglomerates, so that the particles were spherical even when crushed. Could not be obtained. Further, when amorphous silica containing Al of Comparative Example 14 at 2013 ppm in terms of Al2O3 was used as a raw material, the crystalline silica particles had a lower tridymite content than that of the present invention.

Claims (6)

The crystal phase is 90% by mass or more of the whole, and the tridymite crystal is 50% by mass or more of the whole.
Containing 1 to 10% by mass of Na in terms of oxide with respect to the entire particle
The Al content is 50 to 1000 ppm in terms of Al ₂ O ₃ with respect to the entire particles.
Spherical crystalline silica particles characterized by. The spherical crystalline silica particles according to claim 1, wherein the average particle size (D50) is 1 to 100 μm. The spherical crystalline silica particles according to claim 1 or 2 , wherein the average circularity is 0.85 or more. The amorphous spherical silica particles are mixed with 1 to 10% by mass of the Na compound in terms of oxide with respect to the total of the weight of the amorphous spherical silica particles and the weight of the Na compound in terms of oxide.
The mixed spherical silica particles are heat-treated at 800 to 1200 ° C.
Including the step of cooling the heat-treated spherical silica particles,
The cooled spherical silica particles have a crystal phase of 90% by mass or more, and the tridymite crystals are 50% by mass or more of the whole.
A method for producing spherical crystalline silica particles _, characterized in that the Al content of the amorphous spherical silica particles mixed with the Na compound is 50 to 1000 ppm in terms of _Al2O3 . The method for producing spherical crystalline silica particles according to claim 4 , wherein the spherical crystalline silica particles are produced so that the average particle size (D50) is 1 to 100 μm. The method for producing spherical crystalline silica particles according to claim 4 or 5 , wherein the spherical crystalline silica particles are produced so that the average circularity is 0.85 or more.