JP2002020111A - Porous powder and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in the conventional case that amorphous silica gel is converted to cristofalite by heat-treatment and is not crystallized to quarts. SOLUTION: A Zn compound is added to silica gel of 0.1-20 μm average particle diameter by 0.5-20 wt.% (expressed in terms of ZnO) and this mixture is heat-treated at 900-1,100 deg.C to obtain the objective porous powder of <=20 μm average particle diameter based on SiO2, containing >=0.5 wt.% (expressed in terms of oxide) Zn and having a principal crystal phase comprising quartz as well as internal pores of <=15 μm average pore size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous powder having a controlled crystal phase using silica gel as a raw material and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, silica gel produced by a sol-gel method has been used as a desiccant, an adsorbent for a gas chromatography device, a catalyst carrier, and a filtering agent because of its large specific surface area and voids. Further, as a technique for further imparting functionality, a technique of compounding or supporting various metals and metal oxides has been proposed in JP-A-10-72210 or the like. Silica gel that has been put into practical use is basically amorphous, despite differences in specific surface area, porosity, and the like. The specific surface area and porosity of these porous silica gel materials are changed by heat treatment. Specifically, the heat treatment tends to reduce the specific surface area and the porosity. By applying a heat treatment utilizing such properties, a porous silica gel having desired characteristics can be obtained.

[0003]

Although silica gel is inexpensive and is a very useful material used for various applications, crystallization may occur due to the addition of heat history, and the characteristics may change. For this reason, various characteristics change and pose a problem. For example, when crystallized into cristobalite, the coefficient of thermal expansion becomes three times or more of that before heat treatment, and 250 ° C.
The use of the inflection point in the vicinity causes various problems in use. In particular, when used as a raw material of a wiring board for housing semiconductor elements, when cristobalite is contained in the board, and when the wiring board for housing semiconductor elements is mounted on a printed circuit board surface by soldering or the like, a temperature history of 250 ° C. or more is obtained. Therefore, there is a problem that stress due to a sudden change in thermal expansion is concentrated on the joint portion during cooling, leading to disconnection.

In recent years, the mounting form has been changed to a surface mounting type such as a BGA or a CSP using ball terminals, so that an attempt has been made to bring the thermal expansion coefficient of a wiring board for semiconductor storage closer to that of a printed circuit board. (See JP-A-8-279574 and JP-A-8-330690).

[0005] Quartz whose inflection point of thermal expansion is outside the mounting temperature is optimal among silica-based crystals for such applications, and high thermal expansion and improvement in mounting reliability can be achieved.

[0006] However, if amorphous silica gel is treated at a temperature suitable for manufacturing a wiring board for semiconductor storage, it is crystallized into cristobalite, which causes a problem that the mounting reliability is not sufficiently improved.

On the other hand, in a wiring board mounted with a semiconductor element, it is desired to lower the dielectric constant as an insulating substrate. However, the relative dielectric constant of a ceramic substrate material has been conventionally at most about 5 and less than 5 or less. It has been difficult to achieve a low dielectric constant. Therefore, recently, it has been proposed to introduce pores having the lowest relative permittivity into ceramics to lower the relative permittivity of the entire substrate.

Therefore, according to the present invention, a highly crystalline porous powder having fine pores, useful as an aggregate for lowering the dielectric constant, and having a stable thermal expansion coefficient,
It is an object of the present invention to provide a method of manufacturing the same.

[0009]

Means for Solving the Problems The inventors of the present invention have repeatedly studied the above problems, and as a result, have carried out a heat treatment by supporting ZnO at a predetermined ratio on silica gel of a specific size. As a result, it has been found that a porous powder having a crystal phase of quartz can be obtained.

That is, the porous powder of the present invention contains SiO ₂ as a main component, contains Zn in an amount of 0.5% by weight or more in terms of oxide, has an average particle size of 20 μm or less, and has an internal fine particle of 15 μm or less. It is characterized by having pores and a main crystal phase consisting of quartz. As a method for producing such a porous powder, a silica compound having an average particle size of 0.1 to 20 μm is prepared by adding a Zn compound to ZnO. 0.5% by weight in conversion
The mixture is heat-treated at 900 to 1100 ° C.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a porous powder of the present invention will be described in detail below. According to the production method of the present invention, silica gel is used as a starting material. This silica gel is produced by a so-called sol-gel method, and any production method can be used as long as it is an amorphous porous material containing silica as a main component.

However, the average particle size of the silica gel powder must be 0.1 to 20 μm. When the average particle size is smaller than 0.1 μm, the Zn compound is not sufficiently supported on all the silica gel particles, and the compound becomes non-uniform, and amorphous or cristobalite is easily generated. 20 powders
It is larger than μm and does not fit the purpose.

Next, with respect to this silica gel powder, Zn
The compound is added and mixed at a ratio of 0.5% by weight or more in terms of ZnO. By adding the Zn compound, crystallization of SiO ₂ into quartz and stabilization of quartz crystals can be promoted. Therefore, if the content of the Zn compound is less than 0.5% by weight, the above effects cannot be obtained.

The upper limit of the amount of the Zn compound is not particularly limited, but the effect is not changed even if it is added in excess of 20% by weight, so that it is preferably 20% by weight or less.

Further, ZnO, ZnO, Zn
SO ₄ , ZnS, Zn (CH ₃ COO) ₂ , Zn (NO ₃ )
At least one is used selected from ₂ · 6H ₂ O groups. These Zn compounds have an average particle size of 0.5 to 2 μm.
It is desirable to add it as a powder. In the case of a compound that can be easily ionized, a solution containing Zn ions can be prepared, silica gel can be mixed in the solution, and dried.

After the Zn compound is added to the silica gel powder, they are uniformly mixed by a mixing means such as a ball mill. At this time, a more uniform mixture can be obtained by using an appropriate solvent. At this time, it is desirable that organic balls or containers can be used as much as possible and decomposed and removed by heat treatment so that impurities from the mixing means are not mixed.

Next, the above mixture is heated at 900 to 1100 ° C.
At a temperature of 0.5 to 10 hours. If the temperature at this time is lower than 900 ° C., crystallization to quartz does not proceed sufficiently and a large amount of amorphous component remains, and
If the temperature is higher than 00 ° C., the number of pores in the powder decreases. The atmosphere for the heat treatment may be an oxidizing atmosphere such as the air, a non-oxidizing atmosphere such as nitrogen, or an inert atmosphere such as argon.

The powder cooled to room temperature after the heat treatment can be appropriately pulverized and finely pulverized to an average particle size of 20 μm or less.

The prepared powder has an average pore diameter of 15 μm.
In the following, it has fine pores of 5 μm or less, especially 1 μm or less, and the crystal phase is a quartz crystal phase. Further, according to the present invention, a major feature is that cristobalite is not substantially precipitated.
Thereby, good and stable thermal characteristics are obtained in the thermal expansion characteristics.

For this purpose, the porous powder of the present invention can be applied to any application where it is necessary to exhibit the properties of a quartz crystal phase stably or where fine pores are required.

In particular, by using as a ceramic filler component dispersed in glass of an insulating substrate in a wiring board on which a semiconductor element is mounted, a stable thermal expansion characteristic can be exhibited at -150 ° C. to 400 ° C. by quartz, and pores can be dispersed. Thereby, the dielectric constant can be reduced.

[0022]

EXAMPLE The average particle size produced by the sol-gel method was 1
For a 5 μm silica gel powder, the average particle size is 0.5 to
Various metal oxides of 2 μm were added at the ratios shown in Tables 1 and 2, and the mixture was mixed with isopropyl alcohol using a urethane resin ball for 24 hours.

Thereafter, the powder was dried at 120 ° C., heat-treated in the air at the temperatures shown in Tables 1 and 10 for 10 hours, and allowed to cool. The powder after cooling was lightly crushed by a ball mill.

The average particle size of the obtained powder was measured by a laser sedimentation method.
The crystal phase was identified by T1400V type X-ray diffraction measurement. Further, the crystal phase when the above heat treatment was repeated five times was measured in the same manner. Further, the average pore diameter of the powder produced by the porosimeter was measured. The results are shown in Tables 1 and 2.

[0025]

[Table 1]

[0026]

[Table 2]

Sample No. containing no metal oxide 1-4
All changed to cristobalite after heat treatment.
When B ₂ O ₃ was used as the metal oxide, it changed to cristobalite after the heat treatment. When BaO and CaO were used as alkaline earth elements, they remained almost amorphous. Similarly, as a metal oxide, Z
Even when rO ₂ was used, it became amorphous.

On the other hand, Sample No. containing ZnO as a metal oxide in an amount of 0.5% by weight or more was used. 6-9, 11-1
In 4, 16, 19 and 21 to 24, the crystal phase after the heat treatment became quartz. However, the sample No. which was subjected to the heat treatment at 800 ° C. In Nos. 5 to 9, the amorphous component remained, and the amount of crystals changed after repeated heat treatment. In other samples, no amorphous component remained, and no change in the crystal phase was observed even after repeated heat treatment.

Sample No. 1 having a metal oxide content of less than 0.5% by weight. In all of 5, 10, 15, and 20, the crystal phase was cristobalite.

From the above results, it is possible to make the crystal phase after the heat treatment quartz by adding 0.5% by weight or more of the Zn compound in terms of oxide and further heat-treating at a temperature of 900 ° C. or more. Became clear.

Further, the obtained porous body was put into a heat cycle, but no change was observed in the crystal phase before and after the heat cycle, so that it is clear that the powder was thermally stable.

[0032]

As described in detail above, according to the present invention,
By adding a compound containing Zn to a porous powder containing silica as a main component, it is possible to obtain a porous powder having a crystalline phase with a stable crystal phase.

Claims (2)

[Claims] 1. It contains SiO ₂ as a main component, contains Zn in an amount of 0.5% by weight or more in terms of oxide, has an average particle diameter of 20 μm or less, and has pores having an average of 15 μm or less inside.
A porous powder, wherein the main crystal phase is made of quartz. 2. The method according to claim 1, wherein 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 weight or more in terms of ZnO, and the mixture is heat-treated at 900 to 1100 ° C. A method for producing a porous powder.