Spherical crystalline silica particles and method for producing the same

Abstract

(Problem) To provide: spherical silica particles which are suitable for use as a filler for a semiconductor sealing material having excellent dielectric properties in the millimeter wave band, i.e., spherical crystalline silica particles which are reduced in the contents of an alkali metal and an alkaline earth metal to lower levels and have a high crystallization rate and a high quartz content; and a method for producing the spherical crystalline silica particles. (Solution) Provided are spherical crystalline silica particles each having a degree of circularity of 0.80 or more, containing lithium in an amount of 0.02% by mass or more and less than 0.40% by mass in terms of oxide content, also containing calcium in an amount of 0.004% by mass or more and less than 1.0% by mass in terms of oxide content, and also containing a crystalline silica phase, in which the content ratio of the crystalline silica phase in the spherical crystalline silica particles is 40.0% or more, and the content ratio of quarts in the crystalline silica phase is 80.0% by mass or more.

Description

Technical Field

[0001] The present invention relates to spherical crystalline silica particles and a method for producing the same, and more particularly to spherical crystalline silica particles having a high quartz ratio and a method for producing the same.

Background Art

[0002] With the increase in the amount of information accompanying the advancement of communication technology and the rapid expansion of the use of millimeter-wave bands such as millimeter-wave radars, the frequency is becoming higher. A circuit board for transmitting these high-frequency signals is composed of an electrode serving as a circuit pattern and a dielectric substrate. In order to suppress energy loss during the transmission of high-frequency signals, it is necessary that the dielectric tangent (tanδ) of the dielectric material be small. To achieve low dielectric loss, the dielectric material must have low polarity and a low dipole moment.

[0003] As dielectric materials, mainly ceramic particles, resins, and composites obtained by combining them are used. In particular, with the recent expansion of the use of millimeter-wave bands, ceramic particles and resins with an even lower dielectric tangent (tanδ) are required. Resins have a relatively small relative dielectric constant (εr) and are suitable for high-frequency devices, but their dielectric tangent (tanδ) and coefficient of thermal expansion are larger than those of ceramic particles. Therefore, for composites of ceramic particles and resins for millimeter-wave bands, (1) reducing the dielectric tangent (tanδ) of the ceramic particles themselves and (2) increasing the filling ratio of the ceramic particles and reducing the amount of resin showing a large dielectric tangent (tanδ) are suitable.

[0004] Silica (SiO 2 ) particles have been conventionally used as ceramic particles. When the shape of silica particles is angular, the fluidity, dispersibility, and fillability in the resin deteriorate, and the wear of the manufacturing equipment also progresses. To improve these, spherical silica particles are widely used. It is considered that the closer the spherical silica particles are to a perfect sphere, the better the fillability, fluidity, and mold wear resistance in the resin, and particles with a high roundness have been pursued. Furthermore, further improvement in fillability by optimizing the particle size distribution of the particles has also been studied.

[0005] Generally, the spraying method is used as a method for producing spherical silica. In spraying, particles are passed through a high-temperature region such as a flame, so that the particles melt, and the shape of the particles becomes spherical due to surface tension. The melted and spheroidized particles are recovered by being transported by an air current so that the particles do not fuse with each other, but the particles after spraying are rapidly cooled. Since it is rapidly cooled from the molten state, silica does not crystallize and has an amorphous structure, and generally becomes glassy particles called fused silica.

[0006] Since the spherical silica particles obtained by the spraying method 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 the thermal conductivity is 1.4 W / mK. These physical properties are generally equivalent to the thermal expansion coefficient of fused silica having an amorphous structure without a crystal structure. Generally, the thermal expansion coefficient of Si, which is the main raw material of an IC chip, is 3 to 5 ppm / K, and the thermal expansion coefficient of the encapsulating resin for encapsulating the IC chip is extremely large compared to Si. Therefore, warping occurs in the IC chip due to the difference in the thermal expansion behavior of both materials (Si and the encapsulating resin), which hinders production. On the other hand, when high-filling spherical silica with a small thermal expansion coefficient into a resin with a large thermal expansion coefficient, an effect of reducing the thermal expansion of the encapsulant (a composite of spherical silica and resin) itself can be obtained. By making the thermal expansion coefficient of the encapsulant close to that of Si, deformation caused by the thermal expansion behavior when encapsulating the IC chip can be suppressed.

[0007] As described above, the characteristics required for silica particles for an encapsulant include, in addition to fillability, fluidity, and mold wear resistance that can be compounded in a large amount in a resin to maintain the performance as a composite, excellent dielectric properties at high frequencies in the millimeter wave band. Since the dielectric property is a physical property value 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 having a main crystal phase composed of quartz, which is characterized in that a Zn compound is added to silica gel having an average particle size of 0.1 to 20 μm in an amount of 0.5% by mass or more in terms of ZnO, and this mixture is heat-treated at 900 to 1100°C.

[0009] In Patent Document 2, an alkali metal compound is mixed with amorphous spherical silica particles at a ratio of 0.4 to 5% by mass in terms of oxide based on the total mass of the amorphous spherical silica particles and the mass of the alkali metal converted to oxide, or an alkaline earth metal is mixed at a ratio of 1 to 5% by mass in terms of oxide based on the total mass of the amorphous spherical silica particles and the mass of the alkaline earth metal converted to oxide. The spherical silica particles thus obtained are heat-treated at 800°C to 1300°C and then cooled. The cooled spherical silica particles have a crystal phase of 90% by mass or more, and quartz crystals account for 70% by mass or more of the whole, and a method for producing spherical crystalline silica particles is disclosed. However, when the addition amount of the alkali metal is less than 0.4% by mass and the addition amount of the alkaline earth metal is less than 1% by mass, the appearance probability of quartz becomes low.

[0010] In Non-Patent Document 1, an alkali metal oxide was systematically added to synthesized amorphous spherical silica, formed into pellets, and then heat-treated to examine the effects of additives on crystallization and phase transition. According to this, when the additive is lithium oxide (Li 2 O), it is shown that quartz can be obtained when 0.5% by mass or more is added and the firing temperature is 800°C or higher.

[0011] In Non-Patent Document 2, the effects of cations on the crystallization and phase transition of silica substances were investigated. Among them, it is shown 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.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0013] [Non-Patent Document 1] Journal of Ceramics Society of Japan 105 [5] 385-390 (1997) [Non-Patent Document 2] Memoirs of the Faculty of Science, Kagoshima University. Geology and Biology, Vol. 24, pp. 1-22 (1991) [Non-Patent Document 3] High Pressure Research 28(4) 641-650 (2008) [Summary of the Invention] [Problems to be Solved by the Invention]

[0014] The inventors aimed to search for filler particles for semiconductor encapsulation having excellent dielectric properties in the millimeter wave band with a frequency of 30 GHz to 80 GHz and to produce a resin composite for high-frequency device applications by mixing them with a resin. As a result, it was found that in order to obtain a resin composite with a low dielectric tangent, first, it is effective to heat-treat spherical molten (amorphous) silica to crystallize it. That is, it was confirmed that the dielectric tangent of crystalline silica in the millimeter wave band (30 GHz to 80 GHz) is significantly lower than that of amorphous silica that has been widely used conventionally. As a result, spherical crystalline silica particles become silica particles exhibiting excellent dielectric properties for high-frequency device applications. The crystalline silica obtained by heat treatment is quartz, cristobalite, or a mixture thereof. Since the physical property values are different between quartz and cristobalite, when used as a filler, it is preferable that the phase of the crystalline silica is a single phase.

[0015] In addition, when crystallized into cristobalite, the coefficient of thermal expansion of cristobalite becomes three times or more that before the heat treatment, and further, since it has a transformation point near 250°C, various problems in use occur. In particular, when used as a filler for semiconductor encapsulation, peeling occurs at the interface between the element and the encapsulant due to the mismatch in the thermal expansion behavior with the semiconductor element. For such applications, among crystalline silica, quartz with a transformation point of thermal expansion outside the mounting temperature range is suitable. When quartz is used as a filler for semiconductor encapsulation, it is possible to improve the mounting reliability while achieving low dielectric loss and an appropriate coefficient of thermal expansion.

[0016] As a method for crystallizing spherical amorphous silica to obtain quartz, Patent Document 1 discloses adding a zinc compound in an amount of 0.5% by mass or more in terms of oxide and heat-treating this mixture at 900 to 1100°C. However, as a result of a reproduction test by the present inventors, crystallization itself did not progress at a heat treatment temperature of 950°C or lower, and it remained amorphous silica. When heat treatment was performed at a temperature exceeding 950°C, although crystallization began to progress, the crystallinity remained at about 20% even at 1100°C. Also, the crystal phase that appeared had cristobalite as the main phase, and a single phase of quartz could not be obtained in a high content.

[0017] Patent Document 2 discloses a method for producing spherical crystalline silica particles including a step of heat-treating spherical silica particles mixed with 1 to 5% by mass in terms of oxide relative to the total mass of the alkaline earth metal in terms of oxide at 800°C to 1300°C and cooling the heat-treated spherical silica particles, wherein the cooled spherical silica particles have a crystal phase of 90% by mass or more and quartz crystals of 70% by mass or more of the whole. Calcium is shown as the alkaline earth metal in the examples, but in the case of adding 0.5% by mass of calcium in terms of oxide and heat-treating at 1100°C, which is a comparative example, the appearance of quartz is as low as less than 30%. Also, when less than 1% by mass of calcium is added in terms of oxide, spherical crystalline silica with a high quartz content has not been obtained.

[0018] In Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2, lithium is similarly shown as an element that promotes quartz crystallization. Patent Document 2 shows that it is mixed at a ratio of 0.4 to 5% by mass in terms of lithium oxide and heat-treated at 800°C to 1300°C. Non-Patent Document 1 shows that when 0.5% by mass or more of lithium oxide is added to synthesized amorphous spherical silica and fired at 800°C or higher, quartz can be obtained. Furthermore, Non-Patent Document 2 shows that when 10% by mass of lithium chloride (LiCl) is added to synthesized amorphous silica and heat-treated at 800°C, quartz appears as the most dominant phase.

[0019] However, alkaline earth metals such as calcium and alkali metals such as lithium are not preferable as elements added to semiconductor encapsulants. From the viewpoints of normal operation of semiconductor elements and maintaining mounting reliability, it is necessary to reduce the addition amounts of alkaline earth metals and alkali metal elements.

[0020] As factors affecting the crystallization of amorphous silica, temperature, pressure, and impurity elements are well known. Regarding the influence of pressure, for example, Non-Patent Document 3 describes that when heat-treated at 300°C to 1200°C under 20,000 to 30,000 atmospheres, it crystallizes into quartz. However, a pressurizing device of several tens of thousands of atmospheres has limitations in throughput and is not preferable because it is difficult to perform industrial mass production. Although there have been many reports of crystallization experiments using temperature and impurity elements as variable factors, spherical crystalline silica with a crystalline silica content of 40% or more and a quartz ratio of 80% by mass or more in the crystalline silica has not been obtained. From the viewpoints of normal operation of semiconductor elements and maintaining mounting reliability, it has been required to obtain silica particles with a high crystallization rate and substantially consisting of a quartz single phase while reducing lithium and calcium to less than 0.40% by mass and 1.0% by mass, respectively, in terms of oxide.

[0021] The present invention aims to provide spherical silica particles suitable for use as a filler for semiconductor encapsulants having excellent dielectric properties in the millimeter-wave band, that is, spherical crystalline silica particles with a low content of alkali metals and alkaline earth metals, a high crystallization rate, and a high proportion of quartz, and a method for producing the same.

Means for Solving the Problems

[0022] The inventors of the present application intensively studied for the purpose of solving the above problems. As a result, a mixed raw material powder obtained by mixing both a calcium raw material containing calcium in an amount of 0.004% or more and less than 1.0% by mass in terms of oxide and a lithium raw material containing lithium in an amount of 0.02% or more and less than 0.40% by mass in terms of oxide with a powder composed of amorphous silica particles having a circularity of 0.80 or more was heated at a heat treatment temperature of 850°C to 1150°C, thereby succeeding in promoting quartz crystallization while reducing the content of each of lithium and calcium as compared with the conventional method. Without being bound by a specific theory, it is considered that the simultaneous addition of lithium metal and calcium metal to silica exerts a synergistic effect on quartz crystallization, and the crystallization of quartz is promoted although the addition amount is reduced compared with the case where each element is added alone. The crystalline silica particles obtained by the heat treatment at 850 to 1150°C contain a phase of crystalline silica, and the phase of the crystalline silica is substantially a single quartz phase. Here, the single phase means that the proportion of quartz in the phase of crystalline silica 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 lithium in an amount of 0.02% by mass or more and less than 0.40% by mass in terms of oxide, containing calcium in an amount of 0.004% by mass or more and less than 1.0% by mass in terms of 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% by mass or more. (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% by mass or more. (3) The spherical crystalline silica particles according to (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) The spherical crystalline silica particles according to any one of (1) to (3), having an average particle diameter (D50) of 3 to 100 μm. (5) 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 and a lithium raw material with spherical amorphous silica particles having a circularity of 0.80 or more at 850°C to 1150°C. (6) A method for producing spherical crystalline silica particles according to any one of claims (1) to (4), The method for producing spherical crystalline silica particles includes 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 claims (1) to (4), The method for producing spherical crystalline silica particles includes 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 claims (1) to (4), A method for producing spherical crystalline silica particles, 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.

Effects of the Invention

[0024] According to the present invention, spherical silica particles suitable for use as a filler for a semiconductor encapsulant having excellent dielectric properties in the millimeter-wave band can be provided, that is, spherical crystalline silica particles having a low content of alkali metals and alkaline earth metals, a high crystallization rate, and a high proportion of quartz, and a method for producing the same.

Brief Description of the Drawings

[0025]

Figure 1

Embodiments for Carrying Out the Invention

[0026] Spherical crystalline silica according to one embodiment of the present invention is spherical crystalline silica particles having a circularity of 0.80 or more, containing lithium in an amount of 0.02% by mass or more and less than 0.40% by mass in terms of oxide, containing calcium in an amount of 0.004% by mass or more and less than 1.0% by mass in terms of oxide, and containing a phase of crystalline silica, wherein the proportion of the phase of crystalline silica in the spherical crystalline silica particles is 40.0% or more, and the proportion of quartz in the phase of crystalline silica is 80.0% by mass or more. Here, the phase of crystalline silica being 40.0% or more refers to the proportion of the phase of crystalline silica in the spherical crystalline silica particles, and the method for obtaining it will be described later.

[0027] Silica (SiO 2Examples of the crystal structure of ()) include cristobalite and quartz. Compared with amorphous silica, silica having these crystal structures has high thermal conductivity. Therefore, in the filler for semiconductor encapsulation, by replacing an appropriate amount of amorphous silica with crystalline silica, the heat dissipation property from the IC chip can be improved. Furthermore, since crystalline silica has a low dielectric tangent in the millimeter wave band, the more amorphous silica is replaced with crystalline silica in the filler for semiconductor encapsulation, the lower the dielectric tangent of the semiconductor encapsulant becomes.

[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 raw material and a lithium raw material and heat-treating the mixture (also referred to as a mixed raw material). According to one aspect, it may be produced by heat-treating a mixed raw material obtained by mixing a lithium raw material with spherical amorphous silica particles containing a calcium component. Alternatively, it may be produced by heat-treating a mixed raw material obtained by mixing a calcium raw material with spherical amorphous silica particles containing a lithium component. Or, it 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 as the raw material can be produced by a method such as a spraying method. In the spraying method, natural silica powder pulverized and adjusted to a desired particle size is passed through a flame, whereby the particles are melted and the shape of the particles becomes spherical due to surface tension. By such a spraying method, spherical amorphous silica particles having a roundness 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 finally obtained spherical crystalline silica particles are within a desired range. As one aspect, the composition of the spherical amorphous silica particles is such that 98.0 mass% or more is 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 % Zn.

[0030] (Calcium source) The calcium source is mixed with the spherical amorphous silica particles and heat-treated. The composition and amount of the calcium source are not particularly limited as long as the spherical crystalline silica particles finally obtained are within the desired range, and are appropriately adjusted. The calcium source may be calcium hydroxide or calcium oxide, which are stable in the atmosphere, or a natural mineral. The calcium source may be added in the form of a powder or an aqueous solution so as to be uniformly mixed with the spherical amorphous silica particles. In addition, at least a part 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 and the spherical crystalline silica particles finally obtained have the desired calcium content, the spherical amorphous silica particles may also be used as the calcium source. In addition, when the spherical amorphous silica particles contain calcium but not enough, the calcium source can be added so that the spherical crystalline silica particles finally obtained have the desired calcium content.

[0031] (Lithium raw material) The lithium raw material is mixed with spherical amorphous silica particles and heat-treated. The composition and mixing amount of the lithium raw material are not particularly limited and can be adjusted as appropriate as long as the finally obtained spherical crystalline silica particles are within a desired range. The lithium raw material can be an oxide, carbonate, hydroxide, nitrate, etc., and the form of addition is not particularly restricted. It can be added in the form of a powder, aqueous solution, etc. so as to be uniformly mixed with the amorphous spherical silica particles. Also, at least a part of the lithium raw material may be a trace element contained in the spherical amorphous silica particles. For example, if the spherical amorphous silica particles contain sufficient lithium and the finally obtained spherical crystalline silica particles have a desired lithium content, the spherical amorphous silica particles may be used as both the lithium raw material. Also, when the spherical amorphous silica particles contain lithium but not sufficiently, a calcium raw material can be added so that the finally obtained spherical crystalline silica particles have a desired lithium content.

[0032] (Mixing) The spherical amorphous silica particles are mixed with both the calcium raw material and the lithium raw material. Note that the calcium raw material and / or the lithium raw material may be contained in the spherical amorphous silica. The mixing method is not particularly limited as long as each raw material is evenly dispersed and mixed in the mixture. Mixing may be performed using a powder mixer. By mixing, the calcium raw material and the lithium raw material come into contact with at least a part of the spherical amorphous silica, and in the subsequent heat treatment step, the crystallization of the spherical amorphous silica, particularly the crystallization into quartz, is promoted. During mixing, the raw materials are formulated and mixed such that the lithium contained in the produced spherical crystalline silica particles is 0.02% by mass or more and less than 0.40% by mass in terms of oxide, and the calcium contained is 0.004% by mass or more and less than 1.0% by mass in terms of oxide. Note that the total amount of the formulated lithium raw material and calcium raw material is not necessarily contained in the produced spherical crystalline silica particles, so it is preferable to formulate considering the contained ratio. Note that the mixing involves bringing the calcium raw material and the lithium raw material into contact with at least a part of the spherical amorphous silica, and does not promote the pulverization of the spherical amorphous silica. Therefore, its roundness hardly decreases before and after the mixing.

[0033] (Heat treatment) The heat treatment of the mixed raw material obtained by mixing the spherical amorphous silica particles, the calcium raw material, and the lithium raw material is carried out in a temperature range of 850°C to 1150°C. The atmosphere during the heat treatment can be carried out in an oxidizing atmosphere such as air and an inert gas atmosphere such as nitrogen or argon. The atmospheric pressure is preferably atmospheric pressure because of the large-scale industrial heat treatment. If the heat treatment temperature is lower than 850°C, crystallization does not proceed or proceeds extremely slowly. On the other hand, if the temperature is higher than 1150°C, the crystallization of cristobalite proceeds competitively with the quartz crystallization. As a result, it becomes impossible to obtain spherical crystalline silica particles that are substantially a single-phase quartz. Here, the substantial single-phase means a state in which the quartz phase occupies 80% by mass or more in 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 coexist uniformly in spherical amorphous silica particles, the synergistic effect of the two elements promotes the crystallization of quartz in spherical amorphous silica particles more than when a single element is present. In one aspect of the present invention, lithium may be added during mixing as a lithium raw material (such as lithium carbonate), or may be contained in spherical amorphous silica particles in advance. Calcium may be supplied during mixing as a calcium raw material (such as calcium oxide), or may be contained in spherical amorphous silica particles in advance. Since this lithium or calcium is uniformly present in spherical amorphous silica particles by diffusion during the heating process, it is considered that the entire spherical amorphous silica particles crystallize into quartz. Therefore, the longer the heat treatment time, the more lithium and calcium diffuse into the spherical amorphous silica particles, and thus the crystallization progresses. Typically, in other words, when the heating and cooling rates are greater than 60 °C / hour, the progress of crystallization is substantially determined by the heat treatment temperature, that is, the holding time at the maximum temperature. Therefore, the crystallization can be controlled by adjusting the holding time at the maximum temperature. In that case, the heat treatment time may be adjusted generally in the range of 1 hour to 48 hours, may be 3 hours or more, or may be 6 hours or more from the viewpoint of sufficiently promoting crystallization. Also, even if the heat treatment time is extended excessively, the crystallinity will saturate. Therefore, from the viewpoint of cost reduction, the heat treatment time may be 25 hours or less, may be 18 hours or less, or may be 12 hours or less. In addition, as the heat treatment temperature increases, the diffusion coefficient of lithium elements in spherical amorphous silica particles increases, so quartz crystallization progresses. However, when it exceeds 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. In addition, since the degree of diffusion varies depending on the types and addition amounts of lithium raw materials and calcium raw materials, suitable heat treatment times and temperatures may be appropriately selected according to them. Note that the heating rate and the cooling rate do not have a significant impact on the appearance of spherical crystalline silica particles when heat treatment is performed in an electric furnace.

[0035] The circularity of the spherical crystalline silica of the present invention hardly decreases before and after the heat treatment for crystallization. The spherical crystalline silica particles of the present invention are crystallized at a relatively low temperature by heat treatment at 850°C to 1150°C, and within this temperature range, the circularity hardly decreases. Although amorphous silica particles may bond by fusion or sintering when the temperature exceeds 1100°C, since the spherical crystalline silica particles of the present invention are already crystallized (not amorphous) by heat treatment at 850°C to 1150°C, bonding between particles by fusion or sintering can be completely suppressed.

[0036] [Spherical crystalline silica particles] (Circularity) The spherical crystalline silica particles of the present invention have a circularity of 0.80 or more. When the circularity is less than 0.80, when used as silica particles in a resin composite composition for semiconductor encapsulants, etc., the fluidity, dispersibility, and fillability may not be sufficient, and wear of the equipment for producing the encapsulant may be promoted. 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 hardly changes before and after the heat treatment. And in the case of the thermal spraying method, particles with a high average circularity can be easily obtained. As a result, with the method of the present invention, spherical crystalline silica particles with a desired high circularity can be realized. From the viewpoints of improving fluidity, dispersibility, fillability, and reducing equipment wear, the higher the circularity, the more preferable, and it may be 0.85 or more, or 0.90 or more. On the other hand, since it may be difficult to make the circularity 1.0, that is, a perfect circle, the upper limit of the circularity may be 0.99 or less or 0.97 or less.

[0037] The circularity is obtained by "the perimeter of the circle equivalent to the projected area of the photographed particle ÷ the perimeter of the photographed particle image", and the closer this value is to 1, the closer it is to a true sphere. The circularity of the present invention was determined by the flow-type particle image analysis method. In the flow-type particle image analysis method, spherical crystalline silica particles are flowed through a liquid and imaged as a still image of the particles, and image analysis is performed based on the obtained particle image to determine the circularity of the spherical crystalline silica particles. The average value of these multiple circularities was defined as the average circularity. When measuring the average circularity by the flow-type particle image analysis method, if the number of particles is too small, the average value cannot be obtained correctly. At least 100 or more particles are required, preferably 500 or more, and more preferably 1000 or more. In the present invention, about 100 particles were used using a flow-type particle image analyzer "FPIA-3000" (manufactured by Spectris Co., Ltd.). Note that 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 lithium in an amount of 0.02% by mass or more and less than 0.40% by mass in terms of oxide, and calcium in an amount of 0.004% by mass or more and less than 1.0% by mass, based on the mass of the silica particles (100% by mass). The preferable lower limit of lithium is 0.05% by mass, more preferably 0.10% by mass, and even more preferably 0.25% by mass. Also, the preferable upper limit of lithium is less than 0.35% by mass, more preferably less than 0.30% by mass. The preferable lower limit of calcium is 0.20% by mass, more preferably 0.6% by mass. Also, the preferable upper limit of calcium is 0.9% by mass, more preferably 0.8% by mass. The contents of lithium and calcium can be measured, for example, by atomic absorption spectrometry or ICP mass spectrometry (ICP-MS). Specifically, it was measured in accordance with JIS-K0133 using ICP-MS (Agilent's "7700X"). An aqueous solution obtained by completely dissolving silica particles with hydrofluoric acid was used as a sample. Here, the content of impurity elements contained in the silica particles was regarded as the content of impurity elements in the silica dissolution solution. A calibration curve may use a base solution of only the reagent. By performing a specific heat treatment with a composition containing lithium and calcium within the above ranges, spherical crystalline silica particles composed of a single phase with a high crystallization rate and a substantially high proportion of quartz can be obtained. Lithium and calcium exist in a substantially oxide form through heat treatment in the temperature range of 850 to 1150 °C for crystallization, and then react with silica and are incorporated into the silica structure. Their contents hardly change before and after the heat treatment in the above temperature range. When the contents of lithium and calcium change before and after the heat treatment, the composition of the raw material can be appropriately adjusted in consideration of the degree of change so that the finally obtained spherical crystalline silica particles have a predetermined content of lithium and calcium.

[0039] (Crystal properties) The spherical crystalline silica particles of the present invention contain a crystalline silica phase, the proportion of the crystalline phase silica 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 abundance ratio of amorphous and crystalline silica (referred to as the so-called "crystallinity" and may be referred to as such in this specification) and the type of crystalline silica and its ratio can be determined by XRD. In XRD measurement, the ratio of the crystalline phase can be determined by calculating with the following formula from the sum of the integrated intensities of the crystalline peaks (Ic) and the integrated intensity of the halo part due to amorphous (Ia). More specifically, the ratio of the crystalline silica phase contained in the spherical crystalline silica particles can be determined. X (crystalline phase ratio) = Ic / (Ic + Ia) × 100 (%) In the present invention, XRD measurement was carried out in the range of 2Θ = 10° to 90°. The ratio of the crystalline phase was determined from the sum of the intensities of the crystalline peaks appearing in the 2Θ measurement range and the integrated intensity of the broad halo part caused by amorphous appearing near 2Θ = 22°. Furthermore, the types and respective ratios (mass%) of crystalline phases such as cristobalite and quartz can be determined by quantitative analysis by X-ray diffraction. In the present invention, quantitative analysis by X-ray diffraction was performed using an analysis method by 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 the crystalline phase by the Rietveld method was performed using crystal structure analysis software "TOPAS" (manufactured by Bruker).

[0040] The spherical crystalline silica particles of the present invention contain a crystalline silica phase, the proportion of the crystalline silica phase in the spherical crystalline silica particles is 40.0% or more, that is, it has a high crystallinity of 40.0% or more, and the dielectric tangent is significantly lower than that of amorphous silica, which is preferable. From the viewpoint of reducing the dielectric tangent, the higher the crystallinity, the more preferable, 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, being 80.0% by mass or more, and is substantially a single quartz phase. Therefore, various properties such as the thermal expansion coefficient and thermal conductivity of the spherical crystalline silica particles are substantially determined by the properties of quartz, that is, they do not vary, which is preferable when used as a filler or the like. From the above viewpoints, the higher the proportion of quartz, the more preferable, and it may be 85.0% by mass or more, and more preferably 90.0% by mass or more.

[0042] (Average particle size) In one aspect of the present invention, the average particle size (D50) of the spherical crystalline silica particles may be 3 to 100 μm. If the average particle size is less than 3 μm, the aggregability of the particles increases and the fluidity significantly decreases, which is not preferable. If the average particle size exceeds 100 μm, voids between the particles tend to remain and it becomes difficult to increase the filling property, which is not preferable. A range of 10 to 80 μm for the average particle size is more preferable. The particle size of the spherical amorphous silica particles before heat treatment hardly changes before and after heat treatment in the temperature range of 850 to 1150 °C.

[0043] The average particle diameter (D50) was determined as the median diameter D50 with a cumulative volume of 50% in the volume-based particle size distribution measured by the laser diffraction / scattering particle size distribution measurement method. The laser diffraction / scattering particle size distribution measurement method is a method of irradiating a dispersion liquid in which spherical crystalline silica particles are dispersed with laser light and obtaining the particle size distribution from the intensity distribution pattern of the diffraction / scattering light emitted from the dispersion liquid. In the present invention, a laser diffraction / scattering particle size distribution measuring device "CILAS920" (manufactured by Cilas) was used. Note that the average particle diameter of the spherical amorphous silica particles can also be determined in the same manner.

[0044] (Application example) 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] Using a slurry composition containing spherical crystalline silica particles and a resin, resin composite compositions such as semiconductor encapsulants (especially solid encapsulants) and interlayer insulating films can be obtained. Furthermore, by curing these resin composite compositions, resin composites such as encapsulants (cured bodies) and substrates for semiconductor packages can be obtained.

[0046] When manufacturing the resin composite composition, for example, in addition to 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 compounded by a known method such as kneading. Then, it is molded according to the application, such as in pellet form or film form.

[0047] Furthermore, when manufacturing a resin composite by curing the resin composite composition, for example, heat is applied to the resin composite composition to melt it, processed into a shape according to the application, and higher heat than during melting is applied to completely cure it. In this case, a known method such as the transfer molding method can be used.

[0048] For example, when manufacturing semiconductor-related materials such as substrates for packages and interlayer insulating films, known resins can be applied as the resin used in the resin composite composition, but it is preferable to adopt an epoxy resin. The epoxy resin is not particularly limited. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, naphthalene type epoxy resin, phenoxy type epoxy resin, etc. can be used. One of these can be used alone, or two or more types having different molecular weights can be used in combination. Among these, from the viewpoints of curability, heat resistance, etc., an epoxy resin having two or more epoxy groups in one molecule is preferable. Specifically, biphenyl type epoxy resin, phenol novolac type epoxy resin, ortho-cresol novolac type epoxy resin, an epoxy resin obtained by epoxidizing a novolac resin of phenols and aldehydes, glycidyl ethers such as bisphenol A, bisphenol F, and bisphenol S, glycidyl ester acid epoxy resin obtained by the reaction of polybasic acids such as phthalic acid and dimer acid with epichlorohydrin, linear aliphatic epoxy resin, alicyclic epoxy resin, heterocyclic epoxy resin, alkyl-modified polyfunctional epoxy resin, β-naphthol novolac type epoxy resin, 1,6-dihydroxynaphthalene type epoxy resin, 2,7-dihydroxynaphthalene type epoxy resin, bis-hydroxybiphenyl type epoxy resin, and further an epoxy resin into which a halogen such as bromine is introduced to impart flame retardancy, etc. can be mentioned. Among these epoxy resins having two or more epoxy groups in one molecule, bisphenol A type epoxy resin is particularly preferable.

[0049] In addition, as resins used in applications other than the composite material for semiconductor encapsulants, such as prepregs for printed circuit boards and resin composite compositions such as various engineering plastics, resins other than epoxy resins can also be applied. Specifically, in addition to epoxy resins, there are silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyimides, polyamide-imides, polyether-imides and other polyamides; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyester, polysulfone, liquid crystal polymer, polyether sulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin. As the curing agent used in the resin composite composition, a known curing agent may be used to cure the resin. For example, a phenolic curing agent can be used. As the phenolic curing agent, phenol novolak resin, alkylphenol novolak resin, polyvinylphenols, etc. can be used alone or in combination of two or more.

[0050] The blending amount of the phenolic curing agent is preferably such that the equivalent ratio with the epoxy resin (phenolic hydroxyl group equivalent / epoxy group equivalent) is 0.1 or more and less than 1.0. This eliminates the residue of the unreacted phenolic curing agent and improves the moisture absorption and heat resistance.

[0051] From the viewpoints of heat resistance and coefficient of thermal expansion, the addition amount of the spherical crystalline silica particles of the present invention in the resin composite composition is preferably large. Usually, it is appropriately 70% by mass or more and 95% by mass or less, preferably 80% by mass or more and 95% by mass or less, and more preferably 85% by mass or more and 95% by mass or less. This is because if the blending amount of the silica powder is too small, it is difficult to obtain effects such as improving the strength of the encapsulant and suppressing thermal expansion. On the contrary, if it is too large, segregation due to aggregation of the silica powder occurs easily in the composite material regardless of the surface treatment of the silica powder, and problems such as the viscosity of the composite material becoming too large make it difficult to be practical as an encapsulant.

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

Examples

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

[0054] (Examples 1 to 3) Amorphous silica particles containing calcium were produced by a thermal spraying method. After mixing lithium carbonate particles with the spherical amorphous silica particles, they were filled into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) using an electric furnace SUPER-BURN (manufactured by Motoyama Co., Ltd.). With respect to the total mass of the mass of the spherical amorphous silica and the mass of lithium in terms of oxide, the mixing amount of lithium carbonate was 0.25% by mass in terms of oxide, and the calcium contained in the amorphous silica particles was 0.004% by mass in terms of oxide. The heating rate was 300 °C / h, and the temperature was raised to 900 °C (Example 1), 1000 °C (Example 2), and 1100 °C (Example 3) and held for 6 hours. Then, it was cooled to room temperature at a cooling rate of about 100 °C / h.

[0055] (Examples 4 to 6) Amorphous silica particles containing calcium were produced by a thermal spraying method. The calcium contained in the amorphous silica particles was 0.0040% by mass. With respect to the total mass of the mass of the spherical amorphous silica and the mass of lithium in terms of oxide, lithium carbonate was mixed in terms of oxide at 0.10% by mass (Example 4), 0.07% by mass (Example 5), and 0.05% by mass (Example 6). The heating rate was 300 °C / h, and the temperature was raised to 930 °C (Example 4), 1030 °C (Example 5), and 1130 °C (Example 6) and held for 6 hours. Then, it was cooled to room temperature at a heating rate of 100 °C / h.

[0056] (Examples 7 to 9) Amorphous silica particles containing calcium were prepared by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.25% by mass in terms of oxide with respect to the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide, and the calcium contained in the amorphous silica particles was 0.24% by mass in terms of oxide. The heating rate was 300 °C / h, and the temperature was raised to 900 °C (Example 7), 1000 °C (Example 8), and 1100 °C (Example 9), and held for 6 hours. Otherwise, heat treatment was performed in the same manner as in Example 1.

[0057] (Examples 10 to 12) Amorphous silica particles containing calcium were prepared by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.25% by mass in terms of oxide with respect to the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide, and the calcium contained in the amorphous silica particles was 0.66% by mass in terms of oxide. Then, the heating rate was 300 °C / h, and the temperature was raised to 900 °C (Example 10), 1000 °C (Example 11), and 1100 °C (Example 12), and held for 6 hours. Then, it was cooled to room temperature at a cooling rate of about 100 °C / h.

[0058] (Examples 13 and 14) Amorphous silica particles containing calcium were prepared by a thermal spraying method. Lithium carbonate particles were mixed in an amount of 0.05% by mass in terms of oxide with respect to the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide, and the calcium contained in the amorphous silica particles was 0.66% by mass in terms of oxide. Then, the heating rate was 300 °C / h, and the temperature was raised to 925 °C in Example 13 and 1080 °C in Example 14. Then, heat treatment was performed in the same manner as in Example 1, except that it was held for 6 hours in Example 13 and 24 hours in Example 14.

[0059] (Examples 15 and 16) Amorphous silica particles containing calcium were produced by a spraying method. Based on the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide, lithium carbonate particles were mixed in terms of oxide at 0.10% by mass (Example 15) and 0.02% by mass (Example 16). The calcium contained in the amorphous silica particles was 0.66% by mass in terms of oxide. Then, the heating rate was 300 °C / h, and the temperature was raised to 925 °C in Example 15 and 950 °C in Example 16. Thereafter, heat treatment was performed in the same manner as in Example 1 except that it was held for 6 hours.

[0060] (Examples 17 to 20) Amorphous silica particles were produced by a spraying method. After mixing calcium hydroxide particles and lithium carbonate particles with the spherical amorphous silica particles, they were filled into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) using an electric furnace SUPER-BURN (manufactured by Motoyama Co., Ltd.). Based on the total mass of the mass of spherical amorphous silica, the mass of calcium in terms of oxide, and the mass of lithium in terms of oxide, the mixing amount of calcium hydroxide was 0.48% by mass in terms of oxide, and the mixing amount of lithium carbonate was 0.04% by mass (Example 17), 0.06% by mass (Example 18), 0.08% by mass (Example 19), and 0.10% by mass (Example 20) in terms of oxide. The heating rate was 300 °C / h, and the temperature was raised to 925 °C and held for 12 hours. Thereafter, it was cooled to room temperature at a cooling rate of about 100 °C / h.

[0061] (Examples 21, 22) Amorphous silica particles containing calcium and lithium were produced by a spraying method. The spherical amorphous silica particles were filled into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) using an electric furnace SUPER-BURN (manufactured by Motoyama Co., Ltd.). The calcium contained in the amorphous silica particles was 0.82% by mass in terms of oxide, and the lithium was 0.08% by mass in terms of oxide. The heating rate was 300 °C / h, and the temperature was raised to 950 °C (Example 21) and 1050 °C (Example 22) and held for 24 hours. Thereafter, it was cooled to room temperature at a cooling rate of about 100 °C / h.

[0062] Also, amorphous silica particles containing lithium were produced by a spraying method. After mixing calcium compound particles with the spherical amorphous silica particles, the spherical amorphous silica particles were filled into an alumina container and heat-treated in an air atmosphere (atmospheric pressure) at 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% by mass of calcium in terms of oxide were produced by a spraying method. Without mixing lithium carbonate particles with the spherical amorphous silica particles, subsequent heat treatment was carried out in the same manner as in Example 1 except that the heating rate was 300°C / h and the temperature was raised to 900°C and held for 6 hours.

[0064] (Comparative Example 2) Amorphous silica particles containing calcium were produced by a spraying method. Lithium carbonate particles were mixed at 0.25% by mass in terms of oxide with respect to the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide. The calcium contained in the amorphous silica particles was 0.004% by mass in terms of oxide. Subsequently, heat treatment was carried out in the same manner as in Example 1 except that the heating rate was 300°C / h and the temperature was raised to 1200°C and held for 6 hours.

[0065] (Comparative Examples 3 and 4) Amorphous silica particles containing calcium were produced by a spraying method. Lithium carbonate particles were mixed at 0.25% by mass in terms of oxide with respect to the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide. The calcium contained in the amorphous silica particles was 0.24% by mass in terms of oxide. Subsequently, heat treatment was carried out in the same manner as in Example 1 except that the heating rate was 300°C / h and the temperature was raised to 1200°C (Comparative Example 3) and 800°C (Comparative Example 4) and held for 6 hours.

[0066] (Comparative Example 5) Amorphous silica particles containing calcium were produced by a spraying method. With respect to the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide, 0.25% by mass of lithium carbonate particles were mixed in terms of oxide, and the calcium contained in the amorphous silica particles was 0.0014% by mass in terms of oxide. Thereafter, the heat treatment was carried out in the same manner as in Example 1 except that the heating rate was increased to 900 °C at 300 °C / h and held for 6 hours.

[0067] (Comparative Example 6) Amorphous silica particles containing calcium were produced by a spraying method. With respect to the total mass of the mass of spherical amorphous silica and the mass of lithium in terms of oxide, 0.01% by mass of lithium carbonate particles were mixed in terms of oxide, and the calcium contained in the amorphous silica particles was 0.66% by mass in terms of oxide. Thereafter, the heat treatment was carried out in the same manner as in Example 1 except that the heating rate was increased to 925 °C at 300 °C / h and held for 6 hours.

[0068] (Comparative Example 7) Amorphous silica particles containing 0.66% by mass of calcium in terms of metal were produced by a spraying method. Lithium carbonate particles were not mixed with the spherical amorphous silica particles. Thereafter, the heat treatment was carried out in the same manner as in Example 1 except that the heating rate was increased to 1100 °C at 300 °C / h and held for 6 hours.

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

[0070] The circularity was determined by the flow type particle image analysis method. In the present invention, a flow type particle image analyzer "FPIA-3000" (manufactured by Spectris) was used.

[0071] The contents of impurity elements such as lithium and calcium in the spherical silica particles of the present invention were measured by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, in accordance with JIS-K0133, measurement was carried out using ICP-MS (Agilent's "7700X"). An aqueous solution obtained by completely dissolving silica particles with hydrofluoric acid was used as a sample. Here, the content of impurity elements contained in the silica particles was regarded as the content of impurity elements in the silica dissolution solution. A calibration curve was prepared using only the reagent-based solution.

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

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

[0074] Comparing Example 1, Example 7 and Comparative Example 5, it can be seen that even when 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% for the first time when the calcium content exceeds 0.004% by mass in terms of oxide. It can be seen that the synergistic effect due to the coexistence of calcium and lithium elements is manifested and crystallization is promoted. Furthermore, looking at Comparative Example 1, even when calcium is contained at 0.004% by mass in terms of oxide, crystallization does not progress without the addition of lithium. It can be seen that the coexistence of lithium and calcium is necessary.

[0075] Comparing Examples 4 to 6, Examples 13 to 16 with Comparative Example 6 and Comparative Example 7, it can be seen that the lower limit of the lithium addition amount is 0.02% by 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 as the heat treatment temperature increases, the cristobalite content increases, and at 1200 °C, the proportion of quartz in the crystalline silica phase is less than 80% by 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%. The preferred heat treatment temperature is 850 °C to 1150 °C. A more preferred temperature range is 875 °C to 1100 °C.

[0077] When Example 12 is compared with Comparative Example 7, even if calcium is contained in an amount of 0.66% by mass or more in terms of oxide, when the lithium addition amount is zero, the proportion of the crystalline silica phase in the spherical crystalline silica particles is 11.4%, less than 40.0%. When lithium is 0.02% by mass or more in terms of oxide, the proportion of the crystalline silica phase in the spherical crystalline silica particles exceeds 40%, and the proportion of quartz in the crystalline silica phase exceeds 80% by mass. It has been found that this high quartz crystallization rate is a synergistic effect due to the coexistence of calcium and lithium. In addition, even when the contents of lithium and calcium are increased (0.02% by mass or more in terms of lithium oxide, 0.004% or more in terms of calcium oxide), there is no problem with the crystallinity and the degree of silicification, 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 exceeds 80% by mass.

[0078] The content of zinc in the spherical crystalline silica particles used in the examples and comparative examples of the present invention was less than 1.0 ppm in terms of metal content, the total of alkali metals (K and Na) other than lithium was 24 to 36 ppm in terms of metal content, the total of alkaline earth metals (Mg + Ba) other than calcium was 1.8 to 42 ppm, and the aluminum metal was 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] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] [Table 4]

Industrial Applicability

[0083] The spherical crystalline silica particles of the present invention are not limited to semiconductor encapsulation materials and can also be used for other applications. Specifically, they can also be used as prepregs for printed circuit boards, various engineering plastics, etc.

Claims

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

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

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

4. The spherical crystalline silica particles according to any one of claims 1 to 3, having an average particle diameter (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 a calcium raw material and a lithium raw material with spherical amorphous silica particles having a circularity of 0.80 or more 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 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 claims 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 claims 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 manufacturing method of the 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.

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