Fused spherical silica powder

Abstract

To provide a silica powder which contains some amounts of particles having a large particle diameter to maintain flowability while reducing an amount of air bubbles existing in the particles to a level that poses no practical problems when used in a filler for an encapsulation material of a wafer level / package type semiconductor.SOLUTION: The invention relates to a fused spherical silica powder that has a cumulative volume 95% diameter (d95) when measured by laser diffraction in a range of 5-14.9 μm, a cumulative volume 50% particle diameter (d50) in a range of 1-20 μm, and an U (uranium) content of 0.1ppb or under, wherein when a part of a hardened body obtained by kneading and hardening the fused spherical silica powder with an epoxy resin at a mass ratio of 1:1 is polished and an exposed silica cross section is observed with a microscopic observation of 1,000-fold magnification, the number of detected air bubbles having the longest diameter of 5 μm or over is 50 or under per 10 cm2 of the polished surface of the hardened body.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a novel fused spherical silica powder and a method for producing the same. Specifically, the present invention relates to a fused spherical silica powder having a low bubble content, which is suitably used as a filler for a semiconductor encapsulant, and a method for producing the same.

Background Art

[0002] Silica is used in various applications, and one of them is as a filler for semiconductor encapsulants. When used as a filler for semiconductor encapsulants, in addition to electrical insulation, high thermal conductivity and low thermal expansion are required, and high filling of the filler is desired to satisfy these physical properties.

[0003] In order to obtain high fillability, it is better to have a certain particle size distribution rather than a single particle size for the filler. Furthermore, the larger the particle size, the higher the filling rate tends to be.

[0004] At the same time, high moldability is required, and the fluidity of the resin filled with the filler, that is, low viscosity (temperature: 25 ° C, shear rate: 1 s -1 viscosity: 1000 Pa·s or less) is desired. In recent years, in order to obtain such fluidity, spherical silica is usually used as the filler.

[0005] Furthermore, due to the increasing thinning, miniaturization of semiconductors, and mass encapsulation at the wafer level, the maximum allowable particle size of the filler is reduced to a small particle size, making high filling difficult. In this situation, the need to maintain a high filling rate of the filler is increasing more and more.

[0006] In terms of filling characteristics due to being spherical and having an appropriate particle size distribution, and also in terms of relatively low production cost, fused silica has advantages over silica produced by other manufacturing methods.

[0007] As methods for manufacturing fused silica, there are known: (1) a method of oxidizing while melting silicon powder; (2) a method of melting minute silica powder in a flame, fusing a plurality of molten particles, and causing grain growth and spheroidization; (3) a method of burning and oxidizing a compound containing silicon atoms in a flame to generate minute silica, and further melting the minute silica as it is in the flame, and causing grain growth and spheroidization by fusing of the molten particles. For example, in Patent Document 1, minute silica particles obtained by combustion of an organic silane compound are further caused to grow in a flame to obtain fused spherical silica powder having an average particle diameter of 0.05 to 5 μm. In Patent Document 2, fumed silica is melted in a flame to obtain fused silica containing a large amount of particles having a particle diameter of 3 μm or less.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] By the way, when there are bubbles inside silica particles, in the semiconductor manufacturing process, after sealing the semiconductor, when there is a process of cutting or grinding the sealing material portion, the silica particles filled in the sealing material are cut or ground, and the bubbles (voids) inside the particles are exposed. For this reason, recesses may occur on the cut surface or the ground surface of the sealing material. Fig. 1 shows a schematic plan view of the ground surface of the sealed body. The silica particles are usually dense particles 1 and no voids occur on the ground surface, but in the case of hollow particles 2 having bubbles inside the particles, the bubbles are exposed by grinding, and voids 3 occur on the ground surface. Fig. 2 shows a cross-sectional view taken along line A-A of Fig. 1. As shown in Fig. 2, the void 3 on the ground surface is a recess This occurs. The generation of such recesses becomes a problem particularly during the manufacture of semiconductor products by FOWLP (Fan-Out wafer level package). The manufacture of FOWLP is performed, for example, as follows. A plurality of singulated semiconductor chips are arranged on a substrate such as glass with the electrode surface facing upward. Next, the semiconductor chips are encapsulated together. Thereafter, the encapsulant is ground to expose the electrodes. Then, a photoresist is applied, exposed, and developed, and a conductive metal is deposited on the portion where the photoresist has been removed to form a rewiring layer. Finally, the encapsulated plurality of semiconductor chips are cut separately for each chip to obtain a FOWLP-type semiconductor product. When the silica particles contained in the encapsulant contain air bubbles, when the encapsulant is ground, the air bubbles are exposed, and recesses are generated on the grinding surface. When a photoresist is provided in this recess, the photoresist also has recesses, and the conductive metal is unevenly deposited in the recesses in the next process. As a result, problems such as a decrease in product yield due to rewiring layer formation defects and a decrease in the long-term reliability of semiconductor products may occur.

[0010] However, during the manufacture of fused silica, as described above, since grain growth due to melting and fusion of minute silica particles in the flame is involved, air bubbles are also entrapped during the fusion, and as a result, there is an inevitable problem that some of the manufactured silica has air bubbles.

[0011] The entrapment of such air bubbles has been reduced by improving combustion conditions during manufacture. As a result, it has become possible to reduce the air bubble content to a level that cannot be detected by conventional inspection methods. However, when attempting to use it for applications such as a filler for an encapsulant of a WLP-type semiconductor having a process of cutting or grinding the encapsulant portion, as described above, it is still at a level where problems can occur. In the manufacture of WLP-type semiconductor products, the grinding process is almost the final process, and the occurrence of defects at this stage directly leads to an increase in cost.

[0012] Of course, since bubbles larger than the particle size cannot exist, the above problem will not occur if particles with a large particle size are completely excluded from the powder. Therefore, when the silica particles have a small particle size, the adverse effects of bubbles are small. However, as described above, in order to obtain a high packing ratio, it is better to have particles with a certain degree of large particle size. The larger the particle size, the easier it is to contain bubbles.

[0013] Therefore, an object of the present invention is to provide a novel silica powder that contains a certain amount of particles with a large particle size and reduces the amount of such bubbles to a level that is substantially problem-free even when used in applications such as fillers for encapsulants of WLP type semiconductors.

Means for Solving the Problems

[0014] The inventors of the present invention have conducted intensive studies in view of the above problems. And in the method of producing fused spherical silica powder by fusing and spheroidizing fine silica powder in a flame, by specifying the raw material silica powder and combustion conditions, and also limiting the particle size of the recovered fused silica, it has been found that the above problems can be solved, and the present invention has been completed.

[0015] That is, the present invention is a fused spherical silica powder having a cumulative volume 95% diameter (d95) in the range of 5 μm to 30 μm when measured by laser diffraction, When a part of the cured product obtained by kneading and curing the fused spherical silica powder and an epoxy resin at a mass ratio of 1:1 is polished and the exposed silica cross-section is observed under a microscope at 1,000 times magnification, the number of bubbles with a maximum diameter of 5 μm or more that can be detected is such that the cured product polishing surface is 10 cm 2 It relates to a fused spherical silica powder characterized in that it is 50 or less per.

Effects of the Invention

[0016] The fused spherical silica powder of the present invention has an extremely small amount of bubbles. Therefore, when used as a filler for an encapsulant of a WLP type semiconductor, it has the effect of improving the product yield and long-term reliability of the semiconductor.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0018] When measured by laser diffraction, the fused spherical silica powder of the present invention has a cumulative volume 95% diameter (d95) in the range of 5 μm to 30 μm. If d95 is too small, it becomes difficult to obtain a high filling rate in the resin composition when used as a filler. On the other hand, if d95 is too large, there are problems such as poor permeability to the narrow parts of the resin composition when used as a filler. Preferably, d95 is 20 μm or less.

[0019] In the sense of excluding coarse particles, when measured by laser diffraction, it is preferable that the particles exceeding 100 μm are 0 mass%, more preferably that the particles exceeding 75 μm are 0 mass%, and particularly preferably that the particles exceeding 50 μm are 0 mass%.

[0020] Details of the measurement by laser diffraction will be described in the examples below.

[0021] Furthermore, when the silica powder of the present invention is measured under the above conditions, the cumulative volume 50% particle size (d50) is preferably in the range of 1 to 20 μm, and more preferably in the range of 3 to 15 μm. From the point of excluding coarse particles, when the fused spherical silica powder of the present invention is measured by a wet sieve, the amount of particles remaining on the 106 μm sieve is 0 mass%, and further preferably the amount of particles remaining on the 45 μm sieve is 0.1 mass% or less, more preferably 0.05 mass% or less, and particularly preferably 0.01 mass% or less. Note that "remaining on 106 μm" refers to the ratio of particles remaining on the mesh without passing through a mesh with an opening of 106 μm.

[0022] By having such a particle size and particle size distribution, high fluidity and good permeability to narrow parts can be obtained when used as a filler for semiconductor encapsulants, particularly as a filler for liquid encapsulants for applications such as WLP type semiconductors.

[0023] The silica powder of the present invention is spherical. Therefore, when used as a filler for various resins, it is excellent in the fluidity of the resin composition. Here, spherical means that the Wadell practical roundness (equivalent circle diameter / maximum diameter) is 0.7 to 1.0. Here, the equivalent circle diameter is the diameter of a circle having an area equal to the projected cross-sectional area of the particle, and the longest diameter is defined as the maximum distance between any two points on the projected outer periphery of the particle. The preferred Wadell practical roundness is 0.8 to 1.0. Generally, silica produced by the melting method is spherical.

[0024] The silica powder of the present invention substantially does not contain bubbles. Specifically, when a part of a cured product obtained by kneading and curing silica powder and an epoxy resin at a mass ratio of 1:1 is polished and the exposed silica cross-section is observed under a microscope at 1,000 times magnification, the number of bubbles with a longest diameter of 5 μm or more that can be detected is 2 50 or less per 10 cm of the polished surface of the cured product.

[0025] To describe this evaluation method in more detail, for a room temperature curable epoxy resin, mix so that the silica powder is 50% by mass and knead until uniform. Next, fill the kneaded product into an appropriate mold without entrapping air bubbles and cure at room temperature. The mold for curing is preferably of a shape such that a polished surface of 1 cm or more can be ensured when the cured product is polished. 2 or more can be ensured.

[0026] The sufficiently cured cured product is then polished in part to ensure an observation surface. The polishing conditions are as follows: first, rough polishing is performed with diamond abrasive grains of about 1 to 3 μm, and then colloidal silica is used as the abrasive grain, and the surface is polished for about 2 hours as a guide until the surface is smooth and shiny.

[0027] Observe the obtained polished surface under a microscope at a magnification of 1000 times. The microscope can be any type such as an optical microscope, a polarizing microscope, an electron microscope, etc., but preferably an optical microscope. In this microscopic observation, at least 1 cm 2 or more of the area of the polished surface is observed.

[0028] Due to the above polishing, the cross-section (polished surface) of the silica particles in the cured epoxy resin is in a state where it can be observed. Therefore, observe all the silica cross-sections that can be confirmed within the observation range by the above microscopic observation, and grasp the presence or absence of bubbles. Then, count the number of bubbles with a maximum diameter (the maximum length among the distances between any two points on the circumference of the object) of 5 μm or more. Here, when one silica particle has a plurality of bubbles, the number of bubbles is counted as a plurality, and the maximum diameter of each bubble is measured.

[0029] From the number of bubbles with a maximum diameter of 5 μm or more measured by such observation and the observation area, the number of bubbles per 10 cm 2 of the cured body polished surface can be calculated.

[0030] The measurement of the above number of bubbles may be by the naked eye, but it is advantageous in terms of time and labor to use a digital microscope and image analysis software.

[0031] The molten spherical silica powder of the present invention preferably has 10 or less bubbles with a maximum diameter of 5 μm or more per 10 cm 2 of the cured body polished surface, and more preferably 5 or less. Regarding bubbles with a maximum diameter of less than 5 μm, the smaller the number, the more preferable. However, since such minute bubbles tend to be filled by the resist resin during the formation of the rewiring layer, their existence is acceptable at the semiconductor wiring miniaturization level at the time of filing this application.

[0032] Considering its use as a filler for semiconductor encapsulants and the like, the molten spherical silica powder of the present invention preferably has an impurity content within the following ranges. That is, Fe is 10 ppm or less, preferably 7 ppm or less, Al is 0.7 ppm or less, preferably 0.6 ppm or less, U and Th are each 0.1 ppb or less, Na and K are each 1 ppm or less, and Cl is 1 ppm or less.

[0033] For the same reason, the molten spherical silica powder of the present invention preferably contains no ionic impurities. Therefore, the electric conductivity of the aqueous dispersion of the molten spherical silica powder is low, and the pH is preferably close to neutral. Specifically, when 0.8 g of silica powder is dispersed in 80 ml of pure water, the electric conductivity is preferably 1.5 μS / cm or less, more preferably 1.4 μS / cm or less, even more preferably 1.3 μS / cm or less, and the pH is preferably 5.0 to 7.0, more preferably 5.5 to 7.0.

[0034] Also, the specific surface area by the BET one-point method using nitrogen is preferably 1 to 5 m 2 / g, and more preferably 1.5 to 4 m 2 / g.

[0035] The molten spherical silica powder of the present invention preferably has a low water content, specifically preferably 0.05 mass% or less, and more preferably 0.02 mass% or less.

[0036] The molten spherical silica powder of the present invention may be treated with various surface treatment agents for the purpose of enhancing its compatibility and reactivity with resins. Examples of the surface treatment agent include various silane compounds, silane coupling agents, titanate-based coupling agents, aluminate-based coupling agents, silicone oils, and the like.

[0037] Specific examples of the silane compound and the silane coupling agent include hexamethyldisilazane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, phenyltrimethoxysilane, dimethyldiethoxysilane, dimethoxydiphenylsilane, 1,6-bis(trimethoxysilyl)hexane, trifluoropropyltrimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, 3-chloropropyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, and the like.

[0038] The method for producing the molten spherical silica powder of the present invention is not limited, but it can be preferably produced by the following method. That is, hydrophobized fumed silica is used with a multi-tube burner, and the ratio of the fumed silica is 0.3 kg / Nm 3 ~3 kg / Nm 3Oxygen gas or an oxygen-containing gas is entrained and supplied from the central tube of the multi-tube burner so as to melt and spheroidize at 1400°C to 1700°C in the flame, and then fused silica of 0.01 μm to 100 μm is recovered.

[0039] As the raw material, fumed silica (also called pyrogenic silica) that has been hydrophobized is used. It was difficult to obtain the fused spherical silica powder of the present invention using hydrophilic fumed silica as far as the inventor's examination was concerned. The degree of hydrophobization only needs to be such that the fumed silica is not completely dispersed in pure water, but preferably, the degree of hydrophobization (M value) by the methanol titration method is 25% by volume or more, more preferably 30% by volume or more. Incidentally, although fused spherical silica can be obtained using Si powder or quartz powder as raw materials, when these are used as raw materials, the impurity content in the obtained fused spherical silica tends to increase.

[0040] As a method of hydrophobization, a method of surface-treating fumed silica with silanes as described above (specifically, hexamethyldisilazane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, etc. are suitable) is suitable.

[0041] The particle properties of the silica used as the raw material are not particularly limited, but the specific surface area by the nitrogen adsorption BET one-point method is preferably 80 to 250 m 2 / g, more preferably 100 to 230 m 2 / g. Further, in order to reduce the amount of metal impurities in the fused spherical silica powder, it is preferable that the amount of impurities in the raw material silica is small. Specifically, the contents of Fe, Al, U, Th, Na, and K are preferably not more than the same level as the amount of metal impurities in the fused spherical silica powder.

[0042] In the method for producing the fused spherical silica powder of the present invention, the hydrophobized raw material fumed silica is melted in a flame, and grain growth and spheroidization are performed by fusion of the molten particles.

[0043] In the case of melting or the like in a flame, a multi-tube burner is used, and the proportion of raw material fumed silica is 0.3 kg / Nm 3 ~3 kg / Nm 3 so that oxygen gas or / and an oxygen-containing gas is supplied from the central tube of the multi-tube burner. As the multi-tube burner, a double-tube burner, a triple-tube burner, etc. can be used. When the proportion of the raw material fumed silica supplied into the flame is too small, the proportion of particles with a size of 1 μm or less in the obtained molten spherical silica powder becomes too large, and it is likely to become a powder with a particle size distribution not suitable for high filling. Also, when the raw material fumed silica supplied into the flame is too much, it is likely to become a powder containing unmolten fumed silica particles or particles with insufficient melting and low sphericity. The proportion of the raw material fumed silica is preferably 0.5 kg / Nm

[0044] ~2.0 kg / Nm 3 3 And as the oxygen-containing gas to be entrained, air is preferable.

[0045] When using, for example, a triple-tube burner as the multi-tube burner, it is preferable to supply oxygen from the second annular tube and hydrogen from the outermost peripheral tube.

[0046] The flame temperature is set to 1400°C to 1700°C, preferably 1500°C to 1600°C. If it is less than 1400°C, it will become a powder with insufficient molten spheroidization. On the other hand, if it exceeds 1700°C, the process temperature will rise, so it is necessary to increase the cooling capacity, or the fuel consumption will increase and the manufacturing cost will increase. Also, the higher the temperature, the stronger the tendency for the proportion of small particle size particles to increase.

[0047] The flame temperature can be adjusted by the gas composition such as oxygen, hydrogen, and nitrogen supplied to the burner and the supply rate.

[0048] ​In the method for producing the fused spherical silica powder of the present invention, among the fused spherical silica generated in the flame, those having a particle size in the range of 0.01 μm to 100 μm are recovered. As a recovery means, first, particles having an average particle size of 0.01 μm to 1000 μm are recovered using a cyclone, and then classified at a classification point of 8 μm to 100 μm using a sieve and / or an air classifier, and the fine particle side (below the classification point) is recovered. A method is preferably suitable because of its high efficiency. When using a sieve and / or an air classifier, the classification point is preferably in the range of 10 μm to 50 μm. By adjusting to such a classification point, it becomes easy to make the d95 on the fine particle side of the product manufactured by the above method fall within the range of 5 μm to 30 μm. Note that since the d95 does not fall within the range of 5 μm to 30 μm under all conditions, it is necessary to appropriately set the conditions according to the characteristics of the classifier used.

[0049] Recovery by a sieve has the advantage that there is substantially no possibility of recovering particles larger than the mesh size of the sieve used. On the other hand, the labor during recovery is large, and the industrial productivity is higher for an air classifier. However, in the case of an air classifier, since there is a tendency to recover a small amount of particles larger than the classification point, there is also a possibility of containing a small amount of particles larger than the target upper limit particle size. Recognizing such advantages and disadvantages and appropriately selecting according to the target particle size range, productivity, etc. is sufficient. Note that sieving classification and classification by an air classifier may be used in combination. Also, when classifying with a sieve, it may be dry classification or wet classification.

[0050] When surface-treating the fused spherical silica powder, it may be performed before or after the classification by the above sieve and / or air classifier.

[0051] The surface treatment may be carried out by applying a known method according to the silane compound or silane coupling agent used, and it may be either dry or wet. Since particle aggregation may occur in surface treatment, especially in wet surface treatment, if necessary, appropriate crushing or further classification may be carried out. By treating with a device that applies mechanical stress, the effects of aggregate crushing, bulk density adjustment, and crushing of gas-containing particles can be obtained. As the device for applying mechanical stress, a free-vortex type centrifugal classifier, a forced-vortex type centrifugal classifier, a ball mill, a jet mill, a two-roll mill, a three-roll mill, a mortar type crusher, a rotary blade type stirrer, etc. can be used.

Examples

[0052] Hereinafter, examples and comparative examples are shown to more specifically explain the present invention, but the present invention is not limited to these examples.

[0053] The production conditions for producing fused spherical silica in the examples and comparative examples, as well as the various physical property evaluation methods, are as follows.

[0054] The production method of producing fused silica is described below.

[0055] (1) Melting and spheroidization with a burner Using a triple-tube burner, raw material fumed silica and oxygen were supplied from the central tube, oxygen was supplied from the second annular tube, and hydrogen was supplied from the outermost peripheral tube. The flame temperature was adjusted by the hydrogen / oxygen ratio and the amount of silica.

[0056] (2) Classification The fused silica obtained above was first used to recover particles of 0.1 μm to 1000 μm by a cyclone, and then the recovered silica was classified at a predetermined classification point using an air classifier, and the fine particle side was recovered.

[0057] The physical property evaluation method is shown below.

[0058] (1) Hydrophobicity degree (M value) of raw material fumed silica While the raw fumed silica was floating on the surface of pure water, methanol was added dropwise with stirring. The amount of methanol required to suspend all the silica in pure water was determined in terms of volume percentage.

[0059] (2) Silica concentration The silica concentration per unit volume was determined by dividing the weight of silica introduced into the silica supply nozzle of the melting spheroidization burner by the volume of oxygen gas supplied to the central tube.

[0060] (3) Flame temperature The burner flame temperature was determined using the adiabatic calculation flame temperature calculation formula based on the amounts of hydrogen, oxygen, and fumed silica introduced into the silica melting spheroidization burner.

[0061] (4) Cumulative volume diameter Measurement was performed using a laser diffraction scattering type particle size distribution measuring device (MT-3300EX2) manufactured by Microtrac in an aqueous dispersion medium to calculate the cumulative volume 50% diameter (d50) and 95% diameter (d95). In the sample slurry circulation tank of the measuring device, 250 mL of the dispersion medium and 0.02 g to 0.1 g of the sample were introduced. Subsequently, while circulating the sample slurry, ultrasonic dispersion was performed at over 40 W for 1 minute, and then d50 and d95 were measured. Here, the above sample input amount was adjusted so that the sample slurry concentration value (SampleLoading value) displayed on the personal computer screen for device control was between 0.85 and 0.90 according to the device instruction manual.

[0062] (5) BET specific surface area Measurement was performed by the nitrogen adsorption BET one-point method using a specific surface area measuring device (SA-1000) manufactured by Shibata Rikagaku Co., Ltd.

[0063] (6) Measurement of Fe, Al concentrations The silica particles were dissolved in hydrofluoric acid and nitric acid and measured by ICP emission spectrometry.

[0064] (7) Moisture The moisture in the silica particles was measured by the drying loss method (at 110 °C for 6 hours).

[0065] (8) Measurement of pH and Electrical Conductivity An aqueous dispersion of silica particles (8.0 g of silica / 80 mL of pure water, 25 °C) was prepared, and the pH was measured with a glass electrode pH meter, and the electrical conductivity was measured with an alternating current two-electrode conductivity meter.

[0066] (9) U Concentration The silica particles were dissolved in hydrofluoric acid and measured by ICP-MS.

[0067] (10) Na + , Cl - Concentration The silica particles were immersed in pure water at 110 °C for 24 hours to prepare an eluted aqueous solution, and the Na + concentration was measured with an atomic absorption spectrophotometer, and the Cl - concentration was measured by ion chromatography.

[0068] (11) Viscosity of Resin Compound Epoxy resin (bisphenol A / F mixed resin ZX-1059 manufactured by Tohto Kasei Co., Ltd.) and the silica particles of each example and comparative example were blended at a ratio of silica 78: resin 22 (weight ratio), and using a planetary mixer (AR-250 manufactured by Shinki Co., Ltd.), stirred for 8 minutes at a rotation speed of 1000 rpm, and further kneaded under the conditions of a defoaming time of 2 minutes and a rotation speed of 2000 rpm to obtain an epoxy resin composition.

[0069] Subsequently, the epoxy resin composition was measured for viscosity using a rheometer viscometer (Rheostress RS600 manufactured by Hake) under the conditions of a temperature of 25 °C, a plate gap of 50 μm, and a shear rate of 1 s -1 of.

[0070] (12) Number of Air Bubbles Contained To a room temperature curable epoxy resin (Epocure 2 manufactured by BUEHLER), silica powder was mixed so as to be 50% by mass, and kneaded until uniform. Next, the kneaded product was filled into an embedding mold (plastic ring inner diameter 1 inch (25.4 mm) manufactured by BUEHLER) without entraining air bubbles, and cured sufficiently at room temperature.

[0071] Subsequently, a part of the cured body was polished to secure an observation surface. The polishing conditions were as follows: first, rough polishing was performed using abrasives with abrasive grain sizes of 3 μm and 1 μm (MetaDyne single-crystal diamond suspension aqueous / BUEHLER, abrasive grain size 3 μm, and then 1 μm was used), and subsequently, polishing was carried out using an abrasive for finish polishing (MasterMet 2 colloidal silica) until the surface became shiny.

[0072] A 1 cm 2 range of the obtained polished surface was observed at 1000 times magnification with epi-illumination / coaxial epi-illumination using an optical microscope (MICROSCOPE VHX-5000 manufactured by KEYENCE), and the number of bubbles with a major axis length (the maximum length among the distances between any two points on the circumference of the object) of 5 μm or more was counted.

[0073] Here, when one silica particle had multiple bubbles, they were counted as multiple. This observation was performed on 10 specimens, the total number of observed bubbles was summed up, and the number of bubbles per 10 cm 2 of the cross-sectional area of the cured body polished surface was calculated.

[0074] (13) Wadell's practical roundness Approximately 1 mg of silica powder was placed in the center of a slide glass (2 cm × 4 cm), 2 - 3 drops of pure water were dripped to prepare a silica slurry, and a cover glass was placed on the silica slurry so that no bubbles would enter to prepare an observation specimen. The specimen was observed with a Leica optical microscope DMLB (transmission light source, magnification 400 times), and the equivalent circle diameter / major axis length of each silica particle was determined using an image analysis device (Leica Q500IW). The measurement was repeated while moving the observation field until the total number of measured particles reached 500 or more, and the arithmetic mean value of the measured values was taken as the value of Wadell's practical roundness of the silica powder.

[0075] Example 1 Hydrophobized fumed silica with an M value of 47 and a BET specific surface area of 120 m 2 / g was used, and the supply amount of fumed silica to the burner was 0.7 kg / Nm 3It was carried out at a flame temperature of 1600 °C to obtain molten silica powder. Subsequently, the obtained silica powder was classified with a classification point of 10 μm and then recovered. The physical properties of the obtained molten spherical silica powder are shown in Table 1.

[0076] Examples 2 to 5 Using the hydrophobized fumed silica with the M value and BET specific surface area described in Table 1, molten spherical silica powder was produced in the same manner as in Example 1 with the silica supply amount, flame temperature, and classification point described in Table 1. The physical properties of the obtained molten spherical silica powder are shown in Table 1.

[0077] Comparative Example 1 Using hydrophobized fumed silica with an M value of 47 and a BET specific surface area of 126 m 2 / g, molten silica was produced in the same manner as in Example 1 except that the supply amount of fumed silica to the burner was 0.3 kg / Nm 3 , the flame temperature was 1800 °C, and the classification point was 3 μm. The physical properties of the obtained molten silica are shown in Table 1. However, since the flame temperature was high and the proportion of small particle size particles was high, and the classification point during production was also too small, d95 was small, and thus the thickening during the preparation of the resin compound was remarkable, and the resin compound could not be formed.

[0078] Comparative Example 2 Using hydrophobized fumed silica with an M value of 47 and a BET specific surface area of 115 m 2 / g, molten silica was produced in the same manner as in Example 1 except that the supply amount of fumed silica to the burner was 0.7 kg / Nm 3 , the flame temperature was 1600 °C, and the classification point was 5 μm. The physical properties of the obtained molten silica are shown in Table 1. However, since the classification point during production was too small, d95 was small. Different from Comparative Example 1, the formation of the resin compound was possible, but the viscosity was extremely high.

[0079] However, it is considered that if the molten silica of Comparative Example 1 or Comparative Example 2 is mixed and used with the molten silica of the examples, the viscosity of the resin compound will be lowered and the number of bubbles can also be kept small.

[0080] Comparative Example 3 Fused silica was produced in the same manner as in Example 1, except that hydrophilic fumed silica (M value = 0) was used as the raw material fumed silica. In this case, the number of bubbles contained was extremely large.

[0081] Comparative Example 4 Fused silica was produced in the same manner as in Example 2, except that hydrophilic (M value = 0) fumed silica with a BET specific surface area of 125 m 2 / g was used as the raw material fumed silica. In this case, the number of bubbles contained was extremely large.

[0082] Comparative Example 5 Commercially available fused silica (d95 is 29.5 μm, d50 is 10 μm) was evaluated, and the number of bubbles contained was extremely large. Furthermore, by mixing and using it with the small-particle-size fused silica of Comparative Example 1 or 2, large-particle-size particles and small-particle-size particles are combined, and the filling characteristics are improved and the viscosity of the resin compound can be reduced, but it was judged that the number of bubbles contained could not be sufficiently reduced.

[0083]

Table 1

Explanation of Reference Signs

[0084] 1…Dense silica particles 2…Hollow silica particles 3…Void (recess) exposed by grinding

Claims

1. When measured by laser diffraction, the cumulative volume 95% diameter (d95) is in the range of 5 μm to 14.9 μm, the cumulative volume 50% particle diameter (d50) is in the range of 3 to 7 μm, and the content of U (uranium) is 0.1 ppb or less. The fused spherical silica powder, When a part of a cured product obtained by kneading and curing the fused spherical silica powder and the epoxy resin at a mass ratio of 1:1 is polished and the exposed silica cross-section is observed under a microscope at 1,000 times magnification, the number of bubbles with a maximum diameter of 5 μm or more that can be detected is 50 or less per 10 cm of the polished surface of the cured product 2 The fused spherical silica powder is characterized in that it has the above properties

2. The fused spherical silica powder according to Claim 1, wherein the particle surface is treated with a silane compound and / or a silane coupling agent.

3. The BET specific surface area is 1.0 m 2 / g to 5.0 m 2 / g, and the fused spherical silica powder according to claim 1, which is in the range of

4. The BET specific surface area is 1.0 m 2 / g to 5.0 m 2 / g, and the fused spherical silica powder according to claim 2, which is in the range of

5. The fused spherical silica powder according to Claim 1, which is used as a filler for a liquid semiconductor encapsulant.

6. The fused spherical silica powder according to Claim 2, which is used as a filler for a liquid semiconductor encapsulant.

7. The fused spherical silica powder according to Claim 3, which is used as a filler for a liquid semiconductor encapsulant.

Images