Spherical crystalline silica particles and method of producing same

Abstract

Spherical silica particles suitable for an application as a filler for semiconductor encapsulation use having an excellent dielectric property in the millimeter wave band, that is, spherical crystalline silica particles with contents of alkali metals and alkali earth methods kept low while having a high degree of crystallinity and high ratio of quartz, and a method of producing the same. That is, spherical crystalline silica particles having a degree of roundness of 0.80 or more, containing lithium in 0.02 mass% or more and less than 0.40 mass% by oxide conversion, containing calcium in 0.004 mass% or more and less than 1.0 mass% by oxide conversion, and containing phases of crystalline silica, in which spherical crystalline silica particles, the degree of crystallinity in the spherical crystalline silica particles is 40.0% or more and the ratio of quartz in the phases of crystalline silica is 80.0 mass% or more.

Description

Spherical crystalline silica particles and method for producing same

[0001] The present invention relates to spherical crystalline silica particles and a method for producing the same, and in particular to spherical crystalline silica particles having a high proportion of quartz and a method for producing the same.

[0002] The increasing amount of information accompanying advances in communication technology and the rapid expansion of millimeter-wave bands, such as those used in millimeter-wave radar, are driving frequencies toward higher frequencies. Circuit boards that transmit these high-frequency signals consist of electrodes that form the circuit pattern and a dielectric substrate. To minimize energy loss during the transmission of high-frequency signals, the dielectric material must have a small dielectric loss tangent (tan δ). To achieve low dielectric loss, the dielectric material must have low polarity and a low dipole moment.

[0003] Dielectric materials mainly include ceramic particles, resins, and composites of these. In particular, with the recent expansion of millimeter-wave band usage, ceramic particles and resins with even lower dielectric loss tangents (tan δ) are in demand. Resins have a relatively low relative dielectric constant (εr) and are suitable for high-frequency devices, but their dielectric loss tangents (tan δ) and thermal expansion coefficients are higher than those of ceramic particles. Therefore, composites of ceramic particles and resins for millimeter-wave bands are best suited to: (1) reducing the dielectric loss tangent (tan δ) of the ceramic particles themselves; and (2) highly filling the ceramic particles to reduce the amount of resin with a large dielectric loss tangent (tan δ).

[0004] Silica (SiO ２ ) particles have traditionally been used. If the shape of the silica particles is angular, their fluidity, dispersibility, and filling properties in the resin will be poor, and they will also cause wear on the manufacturing equipment. To improve these, spherical silica particles are widely used. It is believed that the closer the spherical silica particles are to being, the better their filling properties in the resin, fluidity, and mold wear resistance will be, and so particles with high roundness have been pursued. Furthermore, further improvements in filling properties by optimizing the particle size distribution have also been investigated.

[0005] Generally, thermal spraying is used to produce spherical silica. In thermal spraying, particles are melted by passing them through a high-temperature region such as a flame, and the particles become spherical due to surface tension. The melted and spherical particles are transported by airflow to prevent them from fusing together, and are then collected. After spraying, the particles are rapidly cooled. Because they are rapidly cooled from a molten state, the silica does not crystallize, but instead has an amorphous structure, becoming glass-like particles commonly known as quartz glass.

[0006] Because spherical silica particles produced by thermal spraying are amorphous, their thermal expansion coefficient and thermal conductivity are low. The thermal expansion coefficient of amorphous silica particles is 0.5 ppm / K, and their thermal conductivity is 1.4 W / mK. These physical properties are roughly equivalent to the thermal expansion coefficient of quartz glass, which has an amorphous structure and does not have a crystalline structure. Generally, the thermal expansion coefficient of silicon (Si), the main raw material of IC chips, is 3-5 ppm / K. The thermal expansion coefficient of the encapsulating resin used to encapsulate IC chips is significantly higher than that of silicon. Therefore, the difference in thermal expansion behavior between the two materials (Si and encapsulating resin) can cause warping of IC chips, hindering production. On the other hand, when spherical silica, which has a low thermal expansion coefficient, is heavily loaded into a resin with a high thermal expansion coefficient, the thermal expansion of the encapsulating material (composite of spherical silica and resin) itself can be reduced. By adjusting the encapsulating material's thermal expansion coefficient to a value close to that of silicon, deformation due to thermal expansion behavior during encapsulation of IC chips can be suppressed.

[0007] As described above, the properties required for silica particles for encapsulation include excellent filling properties, fluidity, mold abrasion resistance, etc., which allow them to be blended in large quantities into resins and maintain the performance of the composite, as well as excellent dielectric properties at high frequencies in the millimeter wave band. Because dielectric properties are physical property values ​​of the material, it has been difficult to reduce the dielectric loss tangent of amorphous silica particles.

[0008] Patent Document 1 describes a method for producing a porous powder whose main crystalline phase is quartz, which is characterized by adding 0.5 mass % or more of a Zn compound, calculated as ZnO, to silica gel having an average particle size of 0.1 to 20 μm, and heat-treating the mixture at 900 to 1100° C.

[0009] Patent Document 2 discloses a method for producing spherical crystalline silica particles, which comprises the steps of: mixing amorphous spherical silica particles with an alkali metal compound in an amount of 0.4 to 5% by weight, calculated as oxide, based on the total weight of the amorphous spherical silica particles and the alkali metal (calculated as oxide); or mixing an alkaline earth metal in an amount of 1 to 5% by weight, calculated as oxide, based on the total weight of the amorphous spherical silica particles and the alkaline earth metal (calculated as oxide); heat-treating the spherical silica particles at 800°C to 1300°C; and cooling the heat-treated spherical silica particles; wherein the cooled spherical silica particles have a crystalline phase of 90% by weight or more and quartz crystals account for 70% by weight or more of the total. However, if the amount of alkali metal added is less than 0.4% by weight or the amount of alkaline earth metal added is less than 1% by weight, the probability of quartz appearing is low.

[0010] In Non-Patent Document 1, an alkali metal oxide was systematically added to synthesized amorphous spherical silica, which was then molded into pellets, and heat-treated to study the effects of crystallization and phase transition caused by the additive. ２ In the case of O), it is shown that quartz can be obtained by adding 0.5 mass % or more and firing at 800° C. or higher.

[0011] Non-Patent Document 2 investigates the effect of cations on the crystallization and phase transition of silica materials, and shows that when 10% by mass of LiCl is added to synthesized amorphous silica and heat-treated at 800°C, quartz appears as the most dominant phase.

[0012] JP 2002-20111 A International Publication No. 2018 / 186308

[0013] Journal of Ceramics Society of Japan 105 [5] 385-390 (1997) Bulletin of the Faculty of Science, Kagoshima University. Earth Science and Biology Vol. 24, pp. 1-22 (1991) High Pressure Research 28 (4) 641-650 (2008)

[0014] The present inventors sought to develop filler particles for semiconductor encapsulation that have excellent dielectric properties in the millimeter-wave band (30 GHz to 80 GHz) and to prepare resin composites for high-frequency device applications by incorporating these filler particles into resins. As a result, they discovered that a resin composite with a low dielectric loss tangent can be obtained by first heat-treating spherical fused (amorphous) silica to crystallize it. Specifically, they confirmed that the dielectric loss tangent of crystalline silica in the millimeter-wave band (30 GHz to 80 GHz) is significantly lower than that of the amorphous silica that has been widely used up to now. As a result, spherical crystalline silica particles exhibit excellent dielectric properties for high-frequency device applications. The crystalline silica obtained by heat treatment is quartz, cristobalite, or a mixture thereof. Because the physical properties of quartz and cristobalite differ, it is preferable for the crystalline silica to be a single phase when used as a filler.

[0015] Furthermore, when crystallized into cristobalite, the thermal expansion coefficient of cristobalite increases by more than three times compared to before heat treatment, and furthermore, the inflection point is near 250°C, causing various problems in use. In particular, when used as a filler for semiconductor encapsulation, delamination occurs at the interface between the element and the encapsulant due to a mismatch in thermal expansion behavior with the semiconductor element. For such applications, among crystalline silicas, quartz, whose inflection point of thermal expansion is outside the mounting temperature range, is suitable. Using quartz as a filler for semiconductor encapsulation can improve mounting reliability while achieving low dielectric loss and a moderate thermal expansion coefficient.

[0016] As a method for obtaining quartz by crystallizing spherical amorphous silica, Patent Document 1 discloses adding 0.5 mass % or more of a zinc compound in terms of oxide and heat-treating the mixture at 900 to 1100°C. However, as a result of a reproduction test conducted by the present inventors, crystallization did not proceed at heat treatment temperatures of 950°C or less, and amorphous silica remained. When heat treatment was performed at temperatures above 950°C, crystallization began to proceed, but even at 1100°C, the degree of crystallization remained at approximately 20%. Furthermore, the crystalline phase that emerged was primarily cristobalite, and it was not possible to obtain a single quartz phase with a high content.

[0017] Patent Document 2 discloses a method for producing spherical crystalline silica particles, which includes heat-treating spherical silica particles containing 1 to 5% by weight of alkaline earth metals (calculated as oxides) at 800 to 1300°C and cooling the heat-treated spherical silica particles, characterized in that the cooled spherical silica particles have a crystalline phase of 90% by weight or more and quartz crystals account for 70% by weight or more of the total. While calcium is used as the alkaline earth metal in the examples, a comparative example in which 0.5% by weight of calcium (calculated as oxides) was added and the particles were heat-treated at 1100°C yielded a low quartz content of less than 30%. Furthermore, to date, spherical crystalline silica with a high quartz content has not been obtained when calcium was added at less than 1% by weight (calculated as oxides).

[0018] Similarly, Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2 also disclose lithium as an element that promotes quartz crystallization. Patent Document 2 discloses mixing lithium at a ratio of 0.4 to 5 mass% in terms of lithium oxide and heat treating at 800°C to 1300°C. Non-Patent Document 1 discloses that quartz can be obtained by adding 0.5 mass% or more of lithium oxide to synthesized amorphous spherical silica and firing at 800°C or higher. Furthermore, Non-Patent Document 2 discloses that quartz appears as the predominant phase when 10 mass% of lithium chloride (LiCl) is added to synthesized amorphous silica and heat treating at 800°C.

[0019] However, alkaline earth metals such as calcium and alkali metals such as lithium are not desirable as additive elements to semiconductor encapsulation materials. From the viewpoint of maintaining normal operation of semiconductor elements and mounting reliability, it is necessary to reduce the amount of alkaline earth metals and alkali metal elements added.

[0020] Temperature, pressure, and impurity elements are well known factors that affect the crystallization of amorphous silica. Regarding the influence of pressure, for example, Non-Patent Document 3 describes that heat treatment at 300°C to 1200°C under 20,000 to 30,000 atmospheres results in crystallization into quartz. However, pressure devices at several tens of thousands of atmospheres have limited throughput, making industrial mass production difficult and undesirable. Although many reports of crystallization experiments using temperature and impurity elements as variable factors have been published, no spherical crystalline silica has been obtained in which the crystalline silica content is 40% or more and the quartz proportion in the crystalline silica is 80% by mass or more. From the perspective of maintaining normal operation of semiconductor devices and mounting reliability, there has been a need to obtain silica particles with a high crystallization rate and essentially a single quartz phase while reducing lithium and calcium, in oxide equivalent, to less than 0.40% by mass and less than 1.0% by mass, respectively.

[0021] An object of the present invention is to provide spherical silica particles that have excellent dielectric properties in the millimeter wave band and are suitable for use as a filler for semiconductor encapsulation materials, i.e., spherical crystalline silica particles that have a high crystallization rate and a high proportion of quartz while keeping the alkali metal and alkaline earth metal contents low, and a method for producing the same.

[0022] The present inventors conducted extensive research aimed at solving the above-mentioned problems. As a result, they successfully promoted quartz crystallization while reducing the respective lithium and calcium contents compared to conventional methods by heating a mixed raw material powder obtained by mixing a powder of amorphous silica particles having a circularity of 0.80 or more with both a calcium raw material containing 0.004 to less than 1.0 mass% of calcium, calculated as oxide, and a lithium raw material containing 0.02 to less than 0.40 mass% of lithium, calculated as oxide, at a heat treatment temperature of 850 to 1150°C. While not being bound by any particular theory, it is believed that the simultaneous addition of lithium metal and calcium metal to silica exerts a synergistic effect on quartz crystallization, promoting quartz crystallization despite the reduced amounts added compared to when each element is added alone. The crystalline silica particles obtained by heat treatment at 850 to 1150°C contain a crystalline silica phase, which is essentially a single quartz phase. The term "single phase" used herein refers to a crystalline silica phase in which the proportion of quartz is 80% by mass or more, preferably 85.0% by mass or more, and more preferably 90.0% by mass or more.

[0023] The present invention provides the following spherical silica particles and a method for producing the same. (1) Spherical crystalline silica particles having a circularity of 0.80 or more, containing 0.02% by mass or more but less than 0.40% by mass of lithium, calculated as oxide, and 0.004% by mass or more but less than 1.0% by mass of calcium, calculated as oxide, and comprising a crystalline silica phase, wherein the proportion of the crystalline silica phase in the spherical crystalline silica particles is 40.0% or more, and the proportion of quartz in the crystalline silica phase is 80.0% or more by mass. (2) The spherical crystalline silica particles according to (1), wherein the proportion of the crystalline silica phase is 70.0% or more, and the proportion of quartz in the crystalline silica phase is 85.0% or more by mass. (3) Spherical crystalline silica particles according to (2) above, in which the proportion of the crystalline silica phase is 80.0% or more and the proportion of quartz in the crystalline silica phase is 90.0% by mass or more. (4) Spherical crystalline silica particles according to any one of (1) to (3) above, in which the average particle size (D50) is 3 to 100 μm. (5) A method for producing spherical crystalline silica particles according to any one of (1) to (4), comprising mixing spherical amorphous silica particles having a circularity of 0.80 or more with a calcium raw material and a lithium raw material to obtain a mixed raw material powder, and heat-treating the mixed raw material powder at 850°C to 1150°C. (6) A method for producing spherical crystalline silica particles according to any one of (1) to (4), comprising: heat-treating a mixed raw material powder obtained by mixing a lithium raw material with spherical amorphous silica particles having a circularity of 0.80 or more and containing a calcium component, at 850°C to 1150°C. (7) A method for producing spherical crystalline silica particles according to any one of (1) to (4), comprising: heat-treating a mixed raw material powder obtained by mixing a calcium raw material with spherical amorphous silica particles having a circularity of 0.80 or more and containing a lithium component, at 850°C to 1150°C. (8) A method for producing spherical crystalline silica particles according to any one of (1) to (4), comprising: heat-treating spherical amorphous silica particles having a circularity of 0.80 or more and containing a calcium component and a lithium component, at 850°C to 1150°C.(9) The method for producing spherical crystalline silica particles according to any one of (5) to (8), wherein the temperature of the heat treatment is 875°C to 1110°C.

[0024] According to the present invention, it is possible to provide spherical silica particles that have excellent dielectric properties in the millimeter wave band and are suitable for use as a filler for semiconductor encapsulation materials, i.e., spherical crystalline silica particles that have a high crystallization rate and a high proportion of quartz while keeping the alkali metal and alkaline earth metal contents low, and a method for producing the same.

[0025] FIG. 1 shows XRD patterns of amorphous silica before heat treatment and silica according to one embodiment of the present invention (after heat treatment).

[0026] The spherical crystalline silica according to one aspect of the present invention is spherical crystalline silica particles, the circularity of which is more than 0.80, the lithium content is 0.02% by mass or more and less than 0.40% by mass in terms of oxide, the calcium content is 0.004% by mass or more and less than 1.0% by mass in terms of oxide, and the proportion of this crystalline silica phase in this spherical crystalline silica particle is 40.0% or more, and the proportion of quartz in this crystalline silica phase is 80.0% by mass or more.Here, the crystalline silica phase of 40.0% or more refers to the proportion of the crystalline silica phase in spherical crystalline silica particle, and how to calculate this will be described later.

[0027] Silica (SiO ２ Examples of crystalline structures of silica include cristobalite and quartz. Silica with these crystalline structures has higher thermal conductivity than amorphous silica. Therefore, by replacing an appropriate amount of amorphous silica with crystalline silica in a semiconductor encapsulation filler, it is possible to improve the heat dissipation from IC chips. Furthermore, since crystalline silica has a low dielectric loss tangent in the millimeter wave band, the more amorphous silica is replaced with crystalline silica in the semiconductor encapsulation filler, the lower the dielectric loss tangent of the semiconductor encapsulation material.

[0028] [Method for producing spherical crystalline silica particles] The spherical crystalline silica particles of the present invention may be produced by mixing spherical amorphous silica with both a calcium source and a lithium source and heat-treating the mixture (also referred to as a mixed raw material). According to one embodiment, the spherical crystalline silica particles may be produced by mixing spherical amorphous silica particles containing a calcium component with a lithium source and heat-treating the resulting mixed raw material. Alternatively, the spherical crystalline silica particles may be produced by mixing spherical amorphous silica particles containing a lithium component with a calcium source and heat-treating the resulting mixed raw material. Alternatively, the spherical crystalline silica particles may be produced by heat-treating spherical amorphous silica particles containing a calcium component and a lithium component.

[0029] (Spherical amorphous silica particles) The amorphous spherical silica particles used as the raw material can be produced by a method such as a thermal spraying method. In the thermal spraying method, natural silica powder that has been pulverized to a desired particle size is passed through a flame, whereby the particles melt and become spherical due to surface tension. By such a thermal spraying method, spherical amorphous silica particles having a circularity of 0.80 or more can be produced. The composition of the spherical amorphous silica particles is not particularly limited as long as the main component is silica and the spherical crystalline silica particles finally obtained fall within the desired range. In one embodiment, the composition of the spherical amorphous silica particles is such that 98.0 mass % or more of silica (SiO ２ ) and may contain trace elements such as Ca, Li, Al, Na, Mg, Ba, and Zn. In one embodiment, the composition of the spherical amorphous silica particles may contain less than 0.5 mass% of Zn.

[0030] (Calcium Source) The calcium source is mixed with spherical amorphous silica particles and heat-treated. The composition and amount of the calcium source are not particularly limited and can be adjusted appropriately as long as the spherical crystalline silica particles obtained ultimately have a desired content. The calcium source may be calcium hydroxide or calcium oxide, which are stable in the atmosphere, or a natural mineral. The calcium source can be added in the form of a powder or an aqueous solution so as to be uniformly mixed with the spherical amorphous silica particles. At least a portion of the calcium source may be a trace element contained in the spherical amorphous silica particles. For example, if the spherical amorphous silica particles contain sufficient calcium so that the final spherical crystalline silica particles have the desired calcium content, the spherical amorphous silica particles may also serve as the calcium source. Furthermore, if the spherical amorphous silica particles contain calcium but not enough, a calcium source can be added so that the final spherical crystalline silica particles have the desired calcium content.

[0031] (Lithium Source) The lithium source is mixed with spherical amorphous silica particles and heat-treated. The composition and amount of the lithium source are not particularly limited as long as the final spherical crystalline silica particles have a desired content, and can be adjusted as appropriate. The lithium source may be added in any form, including oxide, carbonate, hydroxide, or nitrate. It can be added in the form of a powder or an aqueous solution so as to be uniformly mixed with the amorphous spherical silica particles. At least a portion of the lithium source may be a trace element contained in the spherical amorphous silica particles. For example, if the spherical amorphous silica particles contain sufficient lithium so that the final spherical crystalline silica particles have the desired lithium content, the spherical amorphous silica particles may also serve as the lithium source. If the spherical amorphous silica particles contain lithium but not enough, a calcium source can be added so that the final spherical crystalline silica particles have the desired lithium content.

[0032] (Mixing) The spherical amorphous silica particles are mixed with both a calcium source and a lithium source. The calcium source and / or lithium source may be contained in the spherical amorphous silica. The mixing method is not particularly limited as long as the raw materials are uniformly dispersed and mixed in the mixture. Mixing may be performed using a powder mixer. By mixing, the calcium source and lithium source contact at least a portion of the spherical amorphous silica, promoting crystallization of the spherical amorphous silica, particularly crystallization into quartz, in the subsequent heat treatment process. During mixing, the respective raw materials are blended and mixed so that the lithium content in the produced spherical crystalline silica particles is 0.02% by mass or more but less than 0.40% by mass, calculated as oxide, and the calcium content in the produced spherical crystalline silica particles is 0.004% by mass or more but less than 1.0% by mass, calculated as oxide. Since the entire amount of the blended lithium source and calcium source is not necessarily contained in the produced spherical crystalline silica particles, it is preferable to blend them taking into account the content ratio. The mixing is performed by bringing at least a portion of the spherical amorphous silica into contact with the calcium raw material and the lithium raw material, and does not promote pulverization of the spherical amorphous silica, so that the circularity of the spherical amorphous silica is hardly reduced before or after the mixing.

[0033] (Heat Treatment) The mixed raw material obtained by mixing spherical amorphous silica particles, a calcium source, and a lithium source is heat-treated at a temperature ranging from 850°C to 1150°C. The heat treatment atmosphere can be an oxidizing atmosphere such as air or an inert gas atmosphere such as nitrogen or argon. The atmospheric pressure is preferably atmospheric pressure, as heat treatment is performed industrially on a large scale. If the heat treatment temperature is lower than 850°C, crystallization does not proceed or proceeds extremely slowly. On the other hand, if the heat treatment temperature is higher than 1150°C, cristobalite crystallization proceeds competitively with quartz crystallization. As a result, it becomes impossible to obtain spherical crystalline silica particles that are essentially a single quartz phase. Here, "substantially a single phase" refers to a state in which the quartz phase accounts for 80% by mass or more of the crystalline silica phase contained in the spherical crystalline silica particles. Preferably, the heat treatment temperature is 875°C to 1110°C.

[0034] The heat treatment time can be adjusted as appropriate to obtain the desired crystallinity. When lithium and calcium elements are uniformly present in the spherical amorphous silica particles, the synergistic effect of the two elements promotes quartz crystallization of the spherical amorphous silica particles more than when a single element is present. In one embodiment of the present invention, lithium may be added as a lithium source (such as lithium carbonate) during mixing, or may be pre-contained in the spherical amorphous silica particles. Calcium may be supplied as a calcium source (such as calcium oxide) during mixing, or may be pre-contained in the spherical amorphous silica particles. It is believed that because lithium and calcium are uniformly present in the spherical amorphous silica particles due to diffusion during the heating process, the entire spherical amorphous silica particle crystallizes into quartz. Therefore, the longer the heat treatment time, the more lithium and calcium diffuse into the spherical amorphous silica particles, and the more crystallization progresses. Typically, in other words, when the temperature increase / decrease rate is greater than 60°C / hour, the progress of crystallization is essentially determined by the heat treatment temperature, i.e., the holding time at the maximum temperature, and therefore, crystallization can be controlled by adjusting the holding time at the maximum temperature. In this case, the heat treatment time may be adjusted within a range of approximately 1 hour to 48 hours, and may be 3 hours or more, or 6 hours or more, from the viewpoint of sufficiently promoting crystallization. Moreover, since excessive extension of the heat treatment time leads to saturation of the crystallinity, the heat treatment time may be 25 hours or less, 18 hours or less, or 12 hours or less, from the viewpoint of cost reduction. Furthermore, as the heat treatment temperature increases, the diffusion coefficient of lithium element within the spherical amorphous silica particles increases, thereby promoting quartz crystallization. However, above 1150°C, the cristobalite phase appears competitively, and the quartz is no longer a single phase, so there is an upper limit to the heat treatment temperature. Furthermore, the degree of diffusion varies depending on the type and amount of lithium and calcium raw materials added, so the appropriate heat treatment time and temperature may be appropriately selected accordingly. When heat treatment is carried out in an electric furnace, the rate of temperature rise and cooling do not have a significant effect on the appearance of spherical crystalline silica particles.

[0035] The circularity of the spherical crystalline silica of the present invention hardly decreases before and after heat treatment for crystallization. The spherical crystalline silica particles of the present invention are made crystalline at a relatively low temperature by heat treatment at 850°C to 1150°C, and the circularity hardly decreases within this temperature range. While amorphous silica particles may bond together by fusion or sintering at temperatures above 1100°C, the spherical crystalline silica particles of the present invention are made crystalline at 850°C to 1150°C (are no longer amorphous), and therefore bonding of particles together by fusion or sintering can be completely prevented.

[0036] [Spherical Crystalline Silica Particles] (Circularity) The spherical crystalline silica particles of the present invention have a circularity of 0.80 or more. If the circularity is less than 0.80, when used as silica particles in a resin composite composition for semiconductor encapsulation, the fluidity, dispersibility, and packing properties may be insufficient, and wear of the equipment used to manufacture the encapsulation material may be accelerated. The average circularity of the spherical amorphous silica particles obtained by thermal spraying may be 0.80 or more. Since the temperature in the heat treatment step for crystallization is 850 to 1150°C, the circularity of the silica particles before and after the heat treatment hardly changes. Furthermore, particles with a high average circularity can be easily obtained using the thermal spraying method. As a result, the method of the present invention can produce spherical crystalline silica particles with a desired high circularity. From the viewpoints of improving fluidity, dispersibility, and packing properties and reducing wear of equipment, a higher circularity is preferable, and it may be 0.85 or more, or even 0.90 or more. On the other hand, since it may be difficult to achieve a circularity of 1.0, i.e., a perfect circle, the upper limit of the circularity may be 0.99 or less, or 0.97 or less.

[0037] The circularity is calculated by dividing the perimeter of the circle equivalent to the photographed particle projected area by the perimeter of the photographed particle image, and the closer this value is to 1, the closer the particle is to a perfect sphere. The circularity of the present invention was determined by flow particle image analysis. In flow particle image analysis, spherical crystalline silica particles are flowed through a liquid, a still image of the particles is captured, and image analysis is performed based on the obtained particle image to determine the circularity of the spherical crystalline silica particles. The average of these multiple circularities is taken as the average circularity. When measuring the average circularity by flow particle image analysis, if the number of particles is too small, an accurate average value cannot be obtained. At least 100 particles are required, preferably 500 or more, and more preferably 1000 or more. In the present invention, approximately 100 particles were used using a flow particle image analyzer "FPIA-3000" (manufactured by Spectris). The circularity of spherical amorphous silica particles is also determined in the same manner.

[0038] (Composition) The spherical crystalline silica particles of the present invention contain, based on the mass of the silica particles (100 mass%), lithium in an amount of 0.02 mass% or more and less than 0.40 mass% in terms of oxide, and calcium in an amount of 0.004 mass% or more and less than 1.0 mass% in terms of oxide. The preferred lower limit of lithium is 0.05 mass%, more preferably 0.10 mass%, and even more preferably 0.25 mass%. The preferred upper limit of lithium is less than 0.35 mass%, more preferably less than 0.30 mass%. The preferred lower limit of calcium is 0.20 mass%, more preferably 0.6 mass%. The preferred upper limit of calcium is 0.9 mass%, more preferably 0.8 mass%. The lithium and calcium contents can be measured, for example, by atomic absorption spectrometry or inductively coupled plasma mass spectrometry (ICP-MS). Specifically, the measurements were performed using an ICP-MS (Agilent "7700X") in accordance with JIS-K0133. An aqueous solution in which silica particles were completely dissolved with hydrofluoric acid was used as the sample. Here, the impurity element content in the silica particles was defined as the impurity element content in the silica solution. A calibration curve may be obtained using a base solution containing only reagents. By performing a specific heat treatment with a composition containing lithium and calcium within the above ranges, single-phase spherical crystalline silica particles with a high crystallization rate and a substantially high quartz content can be obtained. Through heat treatment at temperatures ranging from 850 to 1150°C for crystallization, lithium and calcium exist almost entirely in the form of oxides. Subsequently, they react with silica and are incorporated into the silica structure, resulting in almost no change in their content before and after heat treatment within the above temperature range. If the lithium and calcium content changes before and after heat treatment, the composition of the raw materials can be appropriately adjusted to achieve the desired lithium and calcium content in the final spherical crystalline silica particles, taking into account the degree of change.

[0039] (Crystalline Properties) The spherical crystalline silica particles of the present invention contain a crystalline silica phase, and the proportion of the crystalline silica phase in the spherical crystalline silica particles is 40.0% or more, and the proportion of quartz in the crystalline silica phase is 80.0% by mass or more. When the silica particles obtained by heat treatment are composed of amorphous and crystalline silica, the proportion of amorphous and crystalline silica (referring to the so-called "crystallinity" and sometimes referred to as such in this specification) and the type and proportion of crystalline silica can be determined by XRD. In XRD measurement, the proportion of the crystalline phase can be calculated from the sum of the integrated intensity of the crystalline peak (Ic) and the integrated intensity of the amorphous halo part (Ia) using the following formula. More specifically, the proportion of the crystalline silica phase contained in the spherical crystalline silica particles can be determined. X (crystalline phase proportion) = Ic / (Ic + Ia) × 100 (%). In the present invention, XRD measurements were performed in the range of 2Θ = 10° to 90°. The crystalline phase proportion was determined from the sum of the crystalline peak intensities appearing in the 2Θ measurement range and the integrated intensity of the halo portion due to the broad amorphous phase appearing around 2Θ = 22°. Furthermore, the type and proportion (mass%) of crystalline phases such as cristobalite and quartz can be determined by quantitative analysis using X-ray diffraction. In the present invention, quantitative analysis by X-ray diffraction was performed using the Rietveld method without using a standard sample. In the present invention, an X-ray diffractometer "D2 PHASER" (manufactured by Bruker) was used. Quantitative analysis of crystalline phases using the Rietveld method was performed using the crystal structure analysis software "TOPAS" (manufactured by Bruker).

[0040] The spherical crystalline silica particles of the present invention contain a crystalline silica phase, and the proportion of the crystalline silica phase in the spherical crystalline silica particles is 40.0% or more, i.e., the spherical crystalline silica particles have a high crystallinity of 40.0% or more, and a dielectric loss tangent that is significantly lower than that of amorphous silica, which is preferable. From the viewpoint of reducing the dielectric loss tangent, the higher the crystallinity, the more preferable it is, and it may be 70.0% or more, and more preferably 80.0% or more.

[0041] The spherical crystalline silica particles of the present invention contain a crystalline silica phase, and the proportion of quartz in the crystalline silica phase is high, 80.0 mass% or more, and is essentially a single quartz phase.Therefore, the properties of the spherical crystalline silica particles, such as the thermal expansion coefficient and thermal conductivity, are essentially determined by the properties of quartz, that is, they do not fluctuate, and are preferred when used as fillers, etc.From the above perspective, the higher the proportion of quartz, the better, and it may be 85.0 mass% or more, and more preferably 90.0 mass% or more.

[0042] (Average particle size) In one embodiment of the present invention, the average particle size (D50) of the spherical crystalline silica particles may be 3 to 100 μm. An average particle size of less than 3 μm is undesirable because the particles tend to aggregate more and fluidity is significantly reduced. An average particle size of more than 100 μm is undesirable because voids tend to remain between the particles, making it difficult to improve packing. An average particle size in the range of 10 to 80 μm is more preferable. The spherical amorphous silica particles before heat treatment show almost no change in particle size before and after heat treatment in the temperature range of 850 to 1150°C.

[0043] The average particle size (D50) was determined by measuring the median diameter D50 at 50% cumulative volume in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. The laser diffraction / scattering particle size distribution measurement method involves irradiating a dispersion containing spherical crystalline silica particles with laser light and determining the particle size distribution from the intensity distribution pattern of the diffracted / scattered light emitted from the dispersion. In the present invention, a laser diffraction / scattering particle size distribution measurement device "CILAS920" (manufactured by Cielus Corporation) was used. The average particle size of spherical amorphous silica particles can also be determined in a similar manner.

[0044] (Example of Use) According to the present invention, a composite composition of the finally obtained spherical crystalline silica particles and a resin, and further a resin composite obtained by curing the resin composite composition can be produced. The composition of the resin composite composition will be described below.

[0045] A slurry composition containing spherical crystalline silica particles and a resin can be used to obtain a resin composite composition such as a semiconductor encapsulant (particularly a solid encapsulant), an interlayer insulating film, etc. Furthermore, by curing these resin composite compositions, resin composites such as an encapsulant (cured product), a substrate for a semiconductor package, etc. can be obtained.

[0046] When producing the resin composite composition, for example, in addition to the spherical crystalline silica particles and the resin, a curing agent, a curing accelerator, a flame retardant, a silane coupling agent, etc. are blended as necessary, and the resulting mixture is composited by a known method such as kneading, etc. Then, the resulting mixture is molded into pellets, films, etc. depending on the intended use.

[0047] Furthermore, when the resin composite composition is cured to produce a resin composite, for example, the resin composite composition is heated to melt it, processed into a shape according to the intended use, and then heated to a temperature higher than that used for melting to completely cure it. In this case, a known method such as a transfer molding method can be used.

[0048] For example, when manufacturing semiconductor-related materials such as package substrates and interlayer insulating films, known resins can be used as the resin for the resin composite composition, but epoxy resins are preferred. The epoxy resin is not particularly limited, but examples include bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, naphthalene epoxy resins, and phenoxy epoxy resins. One of these resins can be used alone, or two or more resins with different molecular weights can be used in combination. Among these, epoxy resins having two or more epoxy groups per molecule are preferred from the viewpoints of curability, heat resistance, and the like. Specific examples include biphenyl-type epoxy resins, phenol novolac-type epoxy resins, orthocresol novolac-type epoxy resins, epoxidized novolac resins of phenols and aldehydes, glycidyl ethers of bisphenol A, bisphenol F, bisphenol S, etc., glycidyl ester acid epoxy resins obtained by reacting polybasic acids such as phthalic acid or dimer acid with epochlorohydrin, linear aliphatic epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, alkyl-modified polyfunctional epoxy resins, β-naphthol novolac-type epoxy resins, 1,6-dihydroxynaphthalene-type epoxy resins, 2,7-dihydroxynaphthalene-type epoxy resins, bishydroxybiphenyl-type epoxy resins, and epoxy resins into which halogens such as bromine have been introduced to impart flame retardancy. Among these epoxy resins having two or more epoxy groups per molecule, bisphenol A-type epoxy resins are particularly preferred.

[0049] In addition, resins other than epoxy resins can also be used in resin composite compositions for applications other than semiconductor encapsulation composite materials, such as prepregs for printed circuit boards and various engineering plastics. Specifically, in addition to epoxy resins, examples of suitable resins include silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyamides such as polyimides, polyamideimides, and polyetherimides; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins. As the curing agent used in the resin composite composition, any known curing agent for curing the resin may be used, but for example, a phenolic curing agent can also be used. As the phenol-based curing agent, phenol novolac resin, alkylphenol novolac resin, polyvinylphenols, etc. can be used alone or in combination of two or more kinds.

[0050] The amount of the phenolic curing agent blended is preferably such that the equivalent ratio to the epoxy resin (phenolic hydroxyl group equivalent / epoxy group equivalent) is 0.1 or more and less than 1.0, thereby eliminating any unreacted phenolic curing agent from remaining and improving moisture absorption and heat resistance.

[0051] The amount of the spherical crystalline silica particles of the present invention added to the resin composite composition is preferably large from the viewpoints of heat resistance and thermal expansion coefficient, but is usually 70% by mass to 95% by mass, preferably 80% by mass to 95% by mass, and more preferably 85% by mass to 95% by mass. This is because if the amount of silica powder added is too small, it is difficult to obtain effects such as improving the strength of the sealing material and suppressing thermal expansion, and conversely, if it is too large, segregation due to aggregation of the silica powder is likely to occur in the composite material regardless of the surface treatment of the silica powder, and the viscosity of the composite material will also become too high, making it difficult to use as a sealing material.

[0052] As for the silane coupling agent, any known coupling agent may be used, but those having an epoxy-based functional group are preferred.

[0053] The present invention will be described below through examples and comparative examples, but the present invention should not be construed as being limited to the following examples.

[0054] Examples 1 to 3: Amorphous silica particles containing calcium were prepared by a thermal spraying method. The spherical amorphous silica particles were mixed with lithium carbonate particles, then packed into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) using a SUPER-BURN electric furnace (manufactured by Motoyama Corporation). The amount of lithium carbonate mixed was 0.25 mass% in terms of oxide, relative to the total mass of the spherical amorphous silica and the mass of lithium in terms of oxide, and the amount of calcium contained in the amorphous silica particles was 0.004 mass% in terms of oxide. The temperature was increased at a rate of 300°C / hour to 900°C (Example 1), 1000°C (Example 2), and 1100°C (Example 3), and maintained at this temperature for 6 hours. The mixture was then cooled to room temperature at a rate of approximately 100°C / hour.

[0055] (Examples 4 to 6) Amorphous silica particles containing calcium were produced by a thermal spraying method. The calcium content of the amorphous silica particles was 0.0040 mass%. Lithium carbonate was mixed in an amount of 0.10 mass% (Example 4), 0.07 mass% (Example 5), or 0.05 mass% (Example 6) calculated as oxide, relative to the total mass of the spherical amorphous silica and the mass of lithium calculated as oxide. The temperature was increased at a rate of 300°C / hour to 930°C (Example 4), 1030°C (Example 5), or 1130°C (Example 6), and maintained at this temperature for 6 hours. The particles were then cooled to room temperature at a rate of 100°C / hour.

[0056] (Examples 7 to 9) Amorphous silica particles containing calcium were produced by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.25 mass% (in oxide equivalent) relative to the total mass of the spherical amorphous silica and the mass of lithium (in oxide equivalent), and the calcium contained in the amorphous silica particles was 0.24 mass% (in oxide equivalent). The temperature was increased at a rate of 300°C / hour to 900°C (Example 7), 1000°C (Example 8), and 1100°C (Example 9), and maintained at this temperature for 6 hours. Other than these, heat treatment was performed in the same manner as in Example 1.

[0057] (Examples 10 to 12) Amorphous silica particles containing calcium were produced by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.25 mass% (in oxide equivalent) relative to the total mass of spherical amorphous silica and lithium (in oxide equivalent), so that the calcium content of the amorphous silica particles was 0.66 mass% (in oxide equivalent). The temperature was then increased at a rate of 300°C / hour to 900°C (Example 10), 1000°C (Example 11), or 1100°C (Example 12), and maintained at this temperature for 6 hours. The particles were then cooled to room temperature at a rate of approximately 100°C / hour.

[0058] (Examples 13 and 14) Amorphous silica particles containing calcium were produced by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.05 mass% (in oxide equivalent) relative to the total mass of spherical amorphous silica and lithium (in oxide equivalent), so that the calcium content of the amorphous silica particles was 0.66 mass% (in oxide equivalent). The temperature was then increased to 925°C in Example 13 at a rate of 300°C / hour, and to 1080°C in Example 14. The same heat treatment as in Example 1 was then performed, except that the temperature was maintained for 6 hours in Example 13 and for 24 hours in Example 14.

[0059] (Examples 15 and 16) Amorphous silica particles containing calcium were produced by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.10% by mass (Example 15) or 0.02% by mass (Example 16) calculated as oxide relative to the total mass of spherical amorphous silica and lithium calculated as oxide, so that the calcium contained in the amorphous silica particles was 0.66% by mass calculated as oxide. The temperature was then increased to 925°C in Example 15 at a rate of 300°C / hour, and to 950°C in Example 16. Heat treatment was then performed in the same manner as in Example 1, except that the temperature was maintained for 6 hours.

[0060] (Examples 17 to 20) Amorphous silica particles were produced by a thermal spraying method. The spherical amorphous silica particles were mixed with calcium hydroxide particles and lithium carbonate particles, and then the mixture was packed into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) using a SUPER-BURN electric furnace (manufactured by Motoyama Corporation). The amount of calcium hydroxide mixed was 0.48 mass % in terms of oxide, and the amount of lithium carbonate mixed was 0.04 mass % (Example 17), 0.06 mass % (Example 18), 0.08 mass % (Example 19), and 0.10 mass % (Example 20) in terms of oxide, relative to the total mass of the spherical amorphous silica, the mass of calcium (calculated as oxide), and the mass of lithium (calculated as oxide). The temperature was increased to 925°C at a rate of 300°C / hour and maintained for 12 hours. The mixture was then cooled to room temperature at a rate of approximately 100°C / hour.

[0061] (Example 21, Example 22) Amorphous silica particles containing calcium and lithium were produced by a thermal spraying method. The spherical amorphous silica particles were packed into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) using an electric furnace SUPER-BURN (manufactured by Motoyama Corporation). The calcium content of the amorphous silica particles was 0.82 mass % in terms of oxide, and the lithium content was 0.08 mass % in terms of oxide. The temperature was increased at a rate of 300°C / hour to 950°C (Example 21) or 1050°C (Example 22), and maintained at this temperature for 24 hours. The particles were then cooled to room temperature at a rate of approximately 100°C / hour.

[0062] Lithium-containing amorphous silica particles were also prepared by a thermal spraying method. After mixing the spherical amorphous silica particles with calcium compound particles, the spherical amorphous silica particles were packed into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) at a temperature range of 850°C to 1150°C using an electric furnace SUPER-BURN (manufactured by Motoyama Co., Ltd.).

[0063] Comparative Example 1 Amorphous silica particles containing 0.004 mass % of calcium in terms of oxide were prepared by a thermal spraying method, and heat treatment was carried out in the same manner as in Example 1, except that the spherical amorphous silica particles were not mixed with lithium carbonate particles, and the temperature was then increased to 900°C at a rate of 300°C / hour and maintained at that temperature for 6 hours.

[0064] Comparative Example 2 Amorphous silica particles containing calcium were prepared by a thermal spraying method. The lithium carbonate particles were mixed in an amount of 0.25 mass % (calculated as oxide) based on the total mass of the spherical amorphous silica and the lithium (calculated as oxide), so that the calcium content of the amorphous silica particles was 0.004 mass % (calculated as oxide). The mixture was then heated to 1200°C at a rate of 300°C / hour and maintained at that temperature for 6 hours. The heat treatment was carried out in the same manner as in Example 1.

[0065] Comparative Examples 3 and 4: Amorphous silica particles containing calcium were prepared by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.25 mass % (calculated as oxide) relative to the total mass of spherical amorphous silica and lithium (calculated as oxide), so that the calcium content of the amorphous silica particles was 0.24 mass % (calculated as oxide). The samples were then heated at a rate of 300°C / hour to 1200°C (Comparative Example 3) or 800°C (Comparative Example 4), and held for 6 hours. The procedure was otherwise the same as in Example 1.

[0066] Comparative Example 5: Amorphous silica particles containing calcium were prepared by a thermal spraying method. The same heat treatment as in Example 1 was carried out except that lithium carbonate particles were mixed in an amount of 0.25% by mass (calculated as oxide) based on the total mass of spherical amorphous silica and lithium (calculated as oxide), so that the calcium content of the amorphous silica particles was 0.0014% by mass (calculated as oxide). The mixture was then heated to 900°C at a rate of 300°C / hour and maintained at that temperature for 6 hours.

[0067] Comparative Example 6 Amorphous silica particles containing calcium were prepared by a thermal spraying method. The same heat treatment as in Example 1 was carried out except that lithium carbonate particles were mixed in an amount of 0.01% by mass (calculated as oxide) based on the total mass of spherical amorphous silica and lithium (calculated as oxide), so that the calcium content of the amorphous silica particles was 0.66% by mass (calculated as oxide). The mixture was then heated to 925°C at a rate of 300°C / hour and maintained at that temperature for 6 hours.

[0068] Comparative Example 7 Amorphous silica particles containing 0.66% by mass of calcium in terms of metal were prepared by a thermal spraying method, and heat-treated in the same manner as in Example 1, except that the spherical amorphous silica particles were not mixed with lithium carbonate particles, and the temperature was then increased to 1100°C at a rate of 300°C / hour and maintained at that temperature for 6 hours.

[0069] The proportion of amorphous and crystalline silica in the silica particles obtained by heat treatment, as well as the type and proportion of crystalline silica, were determined by XRD. In the present invention, an X-ray diffractometer "D2 PHASER" (manufactured by Bruker) was used. Quantitative analysis of the crystalline phase by the Rietveld method was performed using the crystal structure analysis software "TOPAS" (manufactured by Bruker).

[0070] The circularity was determined by flow particle image analysis using a flow particle image analyzer "FPIA-3000" (manufactured by Spectris).

[0071] The content of impurity elements such as lithium and calcium in the spherical silica particles of the present invention was measured by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, the measurement was performed in accordance with JIS-K0133 using an ICP-MS (Agilent "7700X"). An aqueous solution in which silica particles were completely dissolved with hydrofluoric acid was used as the sample. Here, the content of impurity elements contained in the silica particles was taken as the content of impurity elements in the silica solution. A calibration curve was made using a base solution containing only reagents.

[0072] The average particle size (D50) of the spherical quartz particles was measured by a laser diffraction / scattering particle size distribution measurement method. In the present invention, a laser diffraction / scattering particle size distribution measurement device "CILAS920" (manufactured by Cirrus Corporation) was used.

[0073] The spherical crystalline silica particles obtained in the examples according to the present invention all had a lithium content in the range of 0.02% by mass or more but less than 0.40% by mass, calculated as oxide, and contained a crystalline silica phase, with the proportion of the crystalline silica phase in the spherical crystalline silica particles being 40.0% or more, and the proportion of quartz in the crystalline silica phase being 80% by mass or more. The spherical crystalline silica particles in the examples according to the present invention had a circularity of 0.83 to 0.95. The average particle size of spherical amorphous silica particles containing 0.004% by mass of calcium, calculated as oxide, was 35.1 μm, whereas the average particle size of spherical crystalline silica particles of the present invention using this raw material was 35.2 μm to 35.6 μm. Furthermore, the average particle size of spherical amorphous silica particles containing 0.24% by mass of calcium was 33.8 μm, whereas the average particle size of spherical crystalline silica particles of the present invention using this raw material was 33.3 μm to 33.9 μm. Furthermore, spherical amorphous silica particles containing 0.66 mass% calcium, calculated as oxide, had an average particle size of 41.1 μm, whereas the spherical crystalline silica particles of the present invention using this raw material had an average particle size of 40.9 μm to 41.5 μm. Furthermore, when a mixed raw material powder obtained by mixing amorphous silica particles with a calcium raw material containing 0.48 mass% calcium, calculated as oxide, and a lithium raw material containing 0.04 to 0.10 mass% lithium, calculated as oxide, was heat-treated, the average particle size of the spherical amorphous silica particles was 32.3 μm, whereas the spherical crystalline silica particles of the present invention using this mixed raw material powder had an average particle size of 31.6 μm to 35.1 μm. Furthermore, spherical amorphous silica particles containing 0.82 mass% calcium and 0.08 mass% lithium, respectively, calculated as oxide, had an average particle size of 21.5 μm, whereas the spherical crystalline silica particles of the present invention using this raw material had an average particle size of 20.3 μm and 21.9 μm.

[0074] Comparing Examples 1 and 7 with Comparative Example 5, it can be seen that even though the lithium content is the same at 0.25% by mass, the proportion of the crystalline silica phase in the spherical crystalline silica particles exceeds 40.0% only when the calcium content exceeds 0.004% by mass in terms of oxide. This shows that the synergistic effect of the coexistence of calcium and lithium elements is manifested, promoting crystallization. Furthermore, looking at Comparative Example 1, even when calcium is contained at 0.004% by mass in terms of oxide, crystallization does not progress unless lithium is added. This shows that the coexistence of lithium and calcium is necessary.

[0075] Comparing Examples 4 to 6 and 13 to 16 with Comparative Example 6 and Comparative Example 7, it is clear that the lower limit of the amount of lithium added is 0.02 mass %.

[0076] Comparing Examples 1 to 3 with Comparative Example 2, and Examples 7 to 9 with Comparative Example 3, it can be seen that the cristobalite content increases as the heat treatment temperature increases, and at 1200°C, the proportion of quartz in the crystalline silica phase falls below 80 mass%. Furthermore, comparing Examples 7 to 9 with Comparative Example 4, it can be seen that crystallization does not progress at a heat treatment temperature of 800°C, and the proportion of the crystalline silica phase in the spherical crystalline silica particles is less than 40%. A preferred heat treatment temperature is 850°C to 1150°C. A more preferred temperature range is 875°C to 1100°C.

[0077] Comparing Example 12 with Comparative Example 7, even when calcium was present at 0.66% by mass or more in terms of oxide, the proportion of the crystalline silica phase in the spherical crystalline silica particles was 11.4%, less than 40.0%, without the addition of lithium. When the lithium content was 0.02% by mass or more in terms of oxide, the proportion of the crystalline silica phase in the spherical crystalline silica particles exceeded 40%, and the proportion of quartz in the crystalline silica phase exceeded 80% by mass. This high quartz crystallization rate was found to be due to the synergistic effect of the coexistence of calcium and lithium. Furthermore, even when the lithium and calcium contents were increased (0.02% by mass or more in terms of lithium oxide, 0.004% or more in terms of calcium oxide), there were no problems with the crystallinity and quartz content, and the proportion of the crystalline silica phase in the spherical crystalline silica particles was 40.0% or more, and the proportion of quartz in the crystalline silica phase exceeded 80% by mass.

[0078] The spherical crystalline silica particles used in the examples and comparative examples of the present invention had a zinc content of less than 1.0 ppm, calculated as metals, a total of alkali metals other than lithium (K and Na) of 24 to 36 ppm, a total of alkaline earth metals other than calcium (Mg + Ba) of 1.8 to 42 ppm, and aluminum metal of 90 to 4552 ppm. These metal impurities other than lithium and calcium may be contained in silica as long as they do not affect crystallization.

[0079]

[0080]

[0081]

[0082]

[0083] The spherical crystalline silica particles of the present invention can be used not only for semiconductor encapsulation but also for other purposes, such as prepregs for printed circuit boards and various engineering plastics.

Claims

1. Spherical crystalline silica particles having a circularity of 0.80 or more, containing lithium in an oxide equivalent of 0.02% by mass or more but less than 0.40% by mass, and calcium in an oxide equivalent of 0.004% by mass or more but less than 1.0% by mass, and comprising a crystalline silica phase, wherein the proportion of the crystalline silica phase in the spherical crystalline silica particles is 40.0% or more, and the proportion of quartz in the crystalline silica phase is 80.0% or more.

2. Spherical crystalline silica particles according to claim 1, wherein the proportion of the crystalline silica phase is 70.0% or more, and the proportion of quartz in the crystalline silica phase is 85.0% by mass or more.

3. Spherical crystalline silica particles according to claim 2, wherein the proportion of the crystalline silica phase is 80.0% or more, and the proportion of quartz in the crystalline silica phase is 90.0% by mass or more.

4. Spherical crystalline silica particles according to any one of claims 1 to 3, having an average particle size (D50) of 3 to 100 μm.

5. A method for producing spherical crystalline silica particles according to any one of claims 1 to 4, comprising heat-treating a mixed raw material powder obtained by mixing spherical amorphous silica particles having a circularity of 0.80 or more with a calcium raw material and a lithium raw material at 850°C to 1150°C.

6. A method for producing spherical crystalline silica particles according to any one of claims 1 to 4, comprising: mixing spherical amorphous silica particles having a circularity of 0.80 or more and containing a calcium component with a lithium raw material to obtain a mixed raw material powder, and heat-treating the mixed raw material powder at 850°C to 1150°C.

7. A method for producing spherical crystalline silica particles according to any one of claims 1 to 4, comprising mixing spherical amorphous silica particles having a circularity of 0.80 or more and containing a lithium component with a calcium raw material to obtain a mixed raw material powder, and heat-treating the mixed raw material powder at 850°C to 1150°C.

8. A method for producing spherical crystalline silica particles according to any one of claims 1 to 4, comprising heat-treating spherical amorphous silica particles having a circularity of 0.80 or more and containing calcium and lithium components at 850°C to 1150°C.

9. The method for producing spherical crystalline silica particles according to any one of claims 5 to 8, wherein the temperature of the heat treatment is 875°C to 1110°C.