JPH03259961A - Silica filler and its preparation - Google Patents

Abstract

PURPOSE:To prepare a silica filler giving a semiconductor-sealing resin compsn. excellent in flowability, prevention of flash formation, and high-temp. strengths by fusion bonding, to the surface of a fused spherical silica having a specified particle size, a fine-particle silica having a particle size smaller than that of the spherical silica. CONSTITUTION:A mixture of a coarse-particle fused spherical silica having a mean particle size of 10-40mum with a fine-particle silica having a mean particle size of 1-5mum is subjected to a thermal tratment at 1100-1300 deg.C to fusion-bond the fine-particle silica to the surface of the coarse particle silica, giving a silica filler. The obtd. filler has excellent properties, esp. improved high-temp. strengths which are the defects of the conventional spherical silica filler, and gives a semiconductor-sealing resin compsn. showing an excellent balance among flowability, prevention of flash formation, and high-temp. strenghs.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a silica filler and a method for producing the same. More specifically, the present invention relates to a silica filler having specific particle characteristics suitable as a silica filler for resin encapsulation of semiconductors, and an industrially advantageous manufacturing method thereof.

[Prior Art] Semiconductors are encapsulated with a resin composition using a resin composition, typically an epoxy resin, filled with a large amount of filler mainly composed of silica, but this relationship has already been studied. Many patents have been published.

Conventionally, pulverized fused silica has been used as a filler in resin encapsulants for semiconductors, but as the degree of integration of semiconductors has increased, highly filling resin encapsulants have been required, and resin fluidity has been improved. Therefore, fused spherical silica has become indispensable as a filler in place of conventional pulverized products.

Special Publication No. 54-43201, Special Publication No. 61-5734
The invention described in Publication No. 7, etc. is aimed at this type of resin m-kaimono, and includes fine spherical particles and average particle diameters of 1 to 1.
The use of 60 μm fused spherical silica is indicated.

In this way, silica fillers for resin encapsulants include crushed crystalline or amorphous silica crushed with a ball mill, etc., spherical silica melted in a high-temperature flame, etc., and one of these types or It is also known to use two or more types with particle sizes adjusted (JP-A-54-141569, JP-A-55-29532, JP-A-56-10947, JP-A-57-212225). Publication No., JP-A-62-
261161).

[Problem to be solved by the invention]

In recent years, in the field of highly integrated IC memories, there has been a growing trend for packages to shift from pin-insertion type to surface-mount type, thinner and smaller, and to have more pins. Furthermore, as the degree of integration of IC memories improves, the area of IC chips increases, and the chip occupies a larger proportion of the package. Along with this, the occurrence of cracks in packages due to thermal stress caused by the difference in coefficient of thermal expansion between the chip and the package composition has become an important problem.

The coefficient of thermal expansion of the packaging composition decreases as the content of silica filler in the composition increases. Therefore, increasing the silica content in the composition cannot be achieved without improving the fluidity of the composition, and therefore, the use of spherical silica in place of the conventionally used crushed silica has been considered. .

When spherical silica is used, the fluidity is certainly improved, so the silica content in the m-acid can be increased, but there is a problem that flakes are likely to occur during molding of the resin composition. Ta. In addition, as surface mounting methods become mainstream, package cracks (cracks that occur when placed in a flow furnace due to a decrease in heat strength at the solder temperature after absorbing moisture), which had not been a problem in the past, have become a new problem. It has been pointed out that this is a serious problem, and it has been found that especially when a large amount of spherical silica is blended, package cranking is likely to occur due to insufficient strength when heated.

In general, crushed silica has poor fluidity of resin compositions, but has excellent Paris properties and high-temperature strength properties, while spherical silica tends to have the opposite tendency. Therefore, in many cases, both types of silica are appropriately blended, and resin sealing is performed using a blending system that sacrifices fluidity.

For example, the above-mentioned Japanese Patent Application Laid-open No. 56-10947 and Japanese Patent Application Laid-open No. 5
7-212225 discloses a filler containing a mixture of crystalline silica powder and fused silica powder, and JP-A-62-261161 discloses a filler containing a mixture of crushed silica and spherical silica. However, according to experiments conducted by the present inventors, it cannot be used as a highly filling filler that simultaneously satisfies the fluidity and Paris characteristics of the sealing resin composition.

It has also been found that in many cases, simply mixing spherical silica and crushed silica not only fails to bring out the advantages of both, but also lacks reliability as a filler.

[Means for solving problems]

The inventors of the present invention have conducted numerous experiments and researches in view of the fact of ridges, and have found that the filler can be highly filled as a filler for resin sealing. The present invention was completed based on the discovery that the physical bonding relationship between the two is extremely important.

That is, the silica filler provided by the present invention is
It is characterized in that silica particles finer than the silica particles are fused to the surface of fused spherical silica particles having an average particle diameter of 10 to 40 μm.

Furthermore, the present invention provides an industrially advantageous manufacturing method for the above-mentioned silica.
1100-130 mixture with ~5μm fine silica
The purpose is to perform heat treatment at a temperature of 0°C.

The present invention will be explained in detail.

The silica filler according to the present invention is characterized in that, as described above, fine particles of spherical silica are fused onto the surface of fused spherical silica having a relatively large particle size.

In other words, the silica filler according to the present invention maintains the high fluidity of spherical silica in the resin composition filled with it, and also has the crisp properties and high-temperature strength that cannot be obtained with spherical silica alone due to the shape effect due to fine particle fusion. These characteristics can be satisfied at the same time, and the degree of freedom when preparing a resin composition by applying the silica according to the present invention is expanded.

The coarse fused spherical silica according to the present invention has no particular restrictions on the starting materials before melting, and includes crushed natural silica, crushed synthetic quartz, those obtained by hydrolysis of alkoxysilane, etc., and those obtained by hydrolysis of sodium silicate and acid. Those obtained by reaction can be used. Usually, these powdered silicas are dispersed in an oxygen-combustible gas flame to melt and spheroidize them.

In the silica filler according to the present invention, it is important that the coarse fused spherical silica has an average particle size of 10 to 40 nm. The reason for this is that if the particle size is 40 or more, the coarse particles contained therein may clog the gate part of the mold, and slit burrs may occur due to the lack of fine particles, which is undesirable. In this case, there is an undesirable tendency to reduce fluidity due to lack of coarse particles and to generate air vent burrs. Further, such fused spherical silica often has a BET specific surface area of 0.3 to 51/g. The specific surface area is regarded as one of the indicators of the degree of melting of spherical silica, and if it is less than 0.3m"7g, economically advantageous industrial production is impossible;
If it is 7 g or more, melting and spheroidization will be insufficient and satisfactory fluidity will not be obtained.

The silica filler according to the present invention has fine silica particles fused to the spherical silica as described above, but the fine silica may be either crystalline or amorphous, and may be natural or non-crystalline. It can be either the bottom.

Further, although the shape is not particularly limited, it is preferably spherical.

Furthermore, although the degree of refinement varies depending on the average particle size of the fused spherical silica, the shape of the fine particles, and other physical properties, it is necessary that the average particle size is at least 1/2 or less of that of the coarse spherical silica. be. The reason for this is that if the degree of refinement is insufficient, the fluidity of the silica filler will decrease. Therefore, in most cases, particles having an average particle size of 1 to 5 μm are preferred.

The amount of fused spherical silica to coarse spherical silica is preferably in the range of 10 to 50 t% based on the total weight, and 10 wt%.
If it is less than 5, there is no effect of improving high temperature strength by fusion, and
If 0 wt % or more is fused, the fluidity will decrease.

As described above, the silica filler according to the present invention is characterized in that two types of silica particles having different particle sizes are bonded to each other in a fused state. Here, fusion refers to a state in which fine silica is sintered or welded to the surface of coarse silica particles under the firing conditions of 1100 to 1300°C, which will be described later, and is physically tightly bonded. Therefore, this fusion state is This does not necessarily mean complete fusion.

The specific surface area of the silica filler, in which fine silica is fused to the surface of coarse spherical silica, is about 1 to 10 m''/g,
Preferably 2 to 61/g @ z+w" If it is less than 7 g, the effect of improving high temperature strength is small and the fluidity is insufficient. On the other hand, if it exceeds 617 g, it is difficult to make a resin composition using it. Water absorption rate (PCT test 120″C)
x24hrs) increases, leading to the problem that the high-temperature strength after water absorption decreases.

The particle size characteristics of the spherical silica according to the present invention are all values based on a particle size distribution measurement method using a laser scattering method, and the measurement models include, for example, SK Laser (Seishin Enterprise ■) and Cirrus Laser (Cirrus Co., Ltd.). ) etc.

Furthermore, whether the particles of silica filler are spherical or crushed can be easily confirmed with an electron microscope or an ordinary microscope. It refers to something that is in a rounded particle state without any blemishes.

Next, the method for producing the silica filler according to the present invention will be described in detail. The coarse spherical silica according to the present invention can be industrially advantageously produced by the following method.

That is, it can be produced by supplying raw material silica powder having predetermined particle size characteristics and specific surface area to a flame melting furnace and melting it into a spheroid, and this method is well known.

That is, molten spheroidization is carried out using a flame resulting from the combustion of an oxygen-combustible gas, in most cases an oxygen or propane flame. The method is not particularly limited.

Note that the silica raw material that can be used in this step is not particularly limited, but it is desirable that it is natural or platform silica of as high purity as possible.

Examples of natural silica include purified silica, silica sand, and crystal, and examples of base silica include those obtained by hydrolysis of silicon halide, hydrolysates of organosilicate such as ethyl silicate, or neutralized aqueous alkali silicate solutions. Based on silica, etc.

In particular, the applicant has already successfully developed a method for producing high-purity silica obtained by neutralizing an aqueous alkali silicate solution with a mineral acid, and it can be used as an industrially advantageous raw material for silica. It is possible/, but the details can be found in, for example, JP-A-61-48421, JP-A-61-48422, and JP-A-61-178.
It is described in Japanese Patent Application Laid-open No. 414, Japanese Unexamined Patent Publication No. 12608/1983, and the like.

As with the coarse spherical silica, the fine silica according to the present invention may be made of any starting material, but it is important that the average particle diameter is from 1 to 5. When it is less than 1 p, there are problems in industrial handling (bulk height, adhesion during fusion, control of surface area, etc.), and fluidity is significantly reduced. On the other hand, if it is 5 or more, there is no effect of improving fluidity by mixing and fusing, and the specific surface area of the fine spherical silica is preferably 10 to 10"/g, and if it is less than 10"/g, it will not be possible to improve the fluidity by mixing or fusing. There is no effect of improving fluidity, and if it exceeds Loom''/g, there is a problem in controlling the specific surface area during fusion.

The present invention is characterized in that such coarse-grained spherical silica and fine silica are mixed and this mixture is poured into the bottom of a pit at 1100 to 1300°C.

Regarding the heat treatment of the mixture, either a batch type or a continuous type may be used. In the case of the batch type, it is sufficient to use an electric furnace, gas furnace, etc. that can achieve the specified temperature conditions at the bottom of the pit, and in the case of the continuous type, it is sufficient to use a rotary kiln. A continuous rotary firing device such as the following can be used.

Note that the heating time varies depending on the temperature, type of heating furnace, physical properties of the silica to be treated, etc., but in most cases it is 0.2~
A range of 3 hours is sufficient.

Additionally, if necessary, the powder after heat treatment may be subjected to a sieve operation to remove coarse sintered particles, or a spherical filler with a specific particle size may be added to adjust the particle size. The silica filler according to the present invention can be obtained by finally adjusting the particle size. A resin sealing composition using this as a filler can balance fluidity, Paris properties, and high-temperature strength properties.

[For production]

The silica filler according to the present invention is obtained by fusing a predetermined amount of fine silica having specific particle characteristics onto the surface of coarse fused spherical silica having specific particle characteristics. Such silica filler is prepared by heating the above-mentioned two different silica mixtures in a desired heating furnace to
By heat-treating at a temperature of 1300° C. for at most 3 hours, fine silica particles are fused to the surface of coarse spherical silica. In addition, the silica filler has a function of supporting desirable characteristics in resins and compositions, which is different from that of fillers that are simply a mixture of two types.

(Examples) Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. Parts represent weight.

(1) Preparation of coarse spherical silica R50=13. Otrm platform silica powder was dispersed in an oxygen-propane flame and molten and spheronized. The obtained silica has R50=33. On, BE 70.8 m''/g, and when confirmed using an electron microscope, it had a spherical shape.

(2) Preparation of fine silica A base silica powder with R50 = 4.5 μm was dispersed in an oxygen-propane flame and molten into spheroids. Obtained silica R
50=2. On, BET was 65.0 m''/g, and as confirmed by an electron microscope, it was substantially spherical.

(3) Preparation of sealing resin composition Composition blend Silica filler...8Q wt% Note 0' Epicron N665, [manufactured by Dainippon Ink ■] Note (H Barcam TD2131, [manufactured by Dainippon Ink ■) ]Note (3) Evaluation of the (4) m fat composition manufactured by Hoechst After kneading the above epoxy resin composition for sealing with a heated roll at 85 to 95°C, the fluidity, Paris properties, and high temperature of the composition were kneaded. The strength properties were evaluated.

In other words, the fluidity is EMMII in the transfer molding machine.
The spiral flow value based on -66 was measured, and the parry property was evaluated by measuring the paris length extending just before the mold with the slit width adjusted to 5 to 50 μm.

The transfer molding conditions are a mold temperature of 170°C.
'C1 resin pressure 70 kg/c+w'.

The high temperature strength was measured using a test piece (4ar
m x 10mm x 100cm) after curing (180°
(: X 4 hrs baking) After that, JISK-6
The three-point bending strength at 220° C. was measured using an autograph (manufactured by Shimadzu Corporation) according to 911. After water absorption, the test piece after post-curing was subjected to PCT (120°
After absorbing water at (X24hrs), the three-point bending strength at 220°C was measured.

Note that six test pieces were used for one measurement, and the average value was taken as the measured value.

Example 1 After mixing 80 parts of coarse spherical silica and 20 parts of fine spherical silica, the mixture was burned in an electric furnace at 1200° C. for 2 hours to fuse the fine spherical silica to the surface of the coarse spherical silica. After cooling, the particle size distribution and specific surface area were measured and found that R50=22.
3n, BET3.1 m''/g.

Using this silica filler, a compound of all sealing resins was prepared, and the fluidity, Paris properties, and high temperature strength were measured, and the results shown in Table 1 were obtained.

Example 2 After mixing 70 parts of coarse spherical silica and 30 parts of fine spherical silica, the same operation as in Example 1 was performed to obtain R50=18.
44, B E T 4.2 m"/g silica filler was obtained. Using this silica filler, a sealing resin composition was prepared in the same manner as in Example 1, and the fluidity, Paris properties, and high temperature strength were measured. , the results shown in Table 1 were obtained.

Comparative Example 1 A sealing resin composition was prepared using coarse spherical silica alone, and its fluidity, Paris properties, and high temperature strength were measured. The results are shown in Table 1.

Comparative Example 2 A sealing resin composition was prepared by using the mixture of coarse spherical silica and fine spherical silica of Example 1 as it was without firing,
Fluidity, Paris properties, and high temperature strength were measured. The results are shown in Table 1.

Example 3 The mixture of the coarse spherical silica and the fine spherical silica of Example 1 was continuously fired at 1200° C. in a rotary kiln.

The average residence time in the kiln was approximately 20 minutes. When the particle size and specific surface area of the obtained silica were measured, R50 = 2
2.6s, BET 4.4+s''/g.

A sealing resin and acid was prepared using this silica filler, and its fluidity, Paris properties, and high temperature strength were measured.

The results are also listed in Table 1.

Comparative Example 3 95 parts of coarse spherical silica and 5 parts of fine spherical silica were mixed and heated in an electric furnace for 1200'c x l hrs.

After cooling, the particle size distribution and specific surface area were measured, and R50=
29. On, B E was 72.3 m''/g.

A sealing resin was prepared using this silica filler, and its fluidity, Paris properties, and high temperature strength were measured.

The results are also listed in Table 1.

As mentioned above, from the measurement results in Table 1, Examples 1 to 3 have a well-balanced fluidity, Paris properties, and high-temperature strength, and in particular, high-humidity strength after water absorption, which was previously unobtainable with spherical silica. It has a high value. On the other hand, Comparative Example 1 has insufficient fluidity, Paris properties, and high-temperature strength, while Comparative Example 2 has good fluidity but has a large water absorption rate due to the large specific surface area of the filler, and has low high-humidity strength after water absorption. Not enough. In Comparative Example 3, the high humidity strength after water absorption is insufficient because the mixing ratio of fine spherical silica is small.

Comparative Example 4 When the mixture of the coarse spherical silica and the fine spherical silica of Example 1 was boiled in an electric furnace at 1400°C for 30 minutes, a silica sintered body became hard in lumps, but no smooth silica powder was obtained. There wasn't.

〔Effect of the invention〕

As described above, according to the present invention, while making full use of the fluidity of spherical silica, the high temperature strength, which has conventionally been considered a drawback of spherical silica, is achieved by fusing fine spherical silica in a specific amount by a specific method. It is therefore possible to provide a silica filler with improved properties.

When a sealing resin composition is prepared using such a silica filler, the composition has an excellent balance of fluidity, Paris properties, and high-temperature strength properties. Strength properties can be significantly improved.

Claims (1)

[Scope of Claims] 1. A silica filler characterized in that silica particles finer than the silica particles are fused to the surface of fused spherical silica particles having an average particle diameter of 10 to 40 μm. 2. The silica filler according to claim 1, wherein the silica filler is formed by fusing 10 to 50 wt% of fine spherical silica having an average particle size of 1 to 5 μm based on the total weight. 3. Silica filler has a BET specific surface area of 2 to 6 m^2
3. The silica filler according to claim 1 or 2, wherein the silica filler is: 4. A mixture of coarse fused spherical silica with an average particle size of 10 to 40 μm and fine silica with an average particle size of 1 to 5 μm
A method for producing a silica filler, comprising heat treatment at a temperature of ~1300°C.