JP2002309221A - High purity adhesive for semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable adhesive showing excellent adhesion, stability and workability, and capable of improving humidity resistance. SOLUTION: An adhesive for a semiconductor contains 0.5 to 20 wt.% of a high purity high density aerosol silica, that is, an ultra fine silica manufactured by an incineration method having an average diameter of 5 to 100 nm, amount of water soluble chlorine of not more than 25 ppm and a bulk density of not less than 70 g/l. The adhesive preferably contains 5 to 80 wt.% of a high purity fine spherical silica having a maximum particle diameter of not more than 10 nm and electric conductivity of extracted water of not more than 10 μS/cm. The basic adhesive is at least one selected from flexible adhesives such as a flexible silicone adhesive, a flexible epoxy adhesive and an elastomer adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive for a high-density semiconductor. Here, the adhesive is used for bonding different kinds of materials such as a chip, a heat radiating plate and a circuit board when assembling the semiconductor, and at the same time, plays a role of airtight protection and shock absorbing.

[0002]

2. Description of the Related Art In response to rapid technological progress in the field of information and communication, there is a strong demand for improved performance, smaller size, lighter weight and lower cost of electronic devices. In order to satisfy these demands, it is essential to increase the density of semiconductors, which are the heart of electronic devices. To increase the density of semiconductors, for example, a flip chip bonding method for directly attaching a bare chip to a substrate, a BGA (ball grid array) processing method in which electrodes are arranged in a plane, and a CSP (chip size package) ) This is achieved by techniques such as processing methods.

In order to increase the density of semiconductors, techniques for attaching chips, heat sinks, circuit boards, and the like using adhesives have been advanced. This technique serves to adhere different materials and protect the semiconductor from corrosion and thermal stress. That is, the adhesive is required to have not only adhesive strength but also high quality performance.

When a semiconductor is used for a long period of time in a natural environment, malfunction may occur due to electric leakage or disconnection. One of the major causes is corrosion of electric circuits and the like. Water enters from the outside and water-soluble impurities in the material are eluted, thereby corroding the electric circuit portion of the semiconductor and causing malfunction. Further, in order to prevent water from entering from outside, it is necessary to bond the semiconductor with high precision, and the workability of the adhesive is also an important factor.

[0005] A semiconductor may be defective due to thermal stress during assembly or use. One of the causes is a difference in thermal expansion between the semiconductor member and the adhesive. For example, since the thermal expansion of the chip is small and the thermal expansion of the adhesive is large, stress is generated at the time of thermal shock, which causes a failure of the semiconductor and, in the worst case, a destruction of the semiconductor itself.

[0006] Conventional adhesives use silica as a filler to improve workability and reduce thermal expansion.
Specifically, fumed silica is used for adjusting the viscosity and thixotropy of the adhesive to improve workability, and fused silica is used for reducing the thermal expansion. However, fumed silica has been regarded as an auxiliary role and has not been regarded as important. Further, fumed silica has a problem that it contains easily water-soluble chlorine, which is a corrosive substance, rather than the method of burning silicon chloride in an oxyhydrogen flame. This chlorine is one of the main corrosive substances in semiconductor devices (Abstracts of the Institute of Electronics, Communication and Communication Engineers R82-81, 23-28, 1983).

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-quality adhesive which can cope with a high density semiconductor. This adhesive has excellent dimensional accuracy and adhesive strength, and
High reliability of the semiconductor can be guaranteed.

[0008]

SUMMARY OF THE INVENTION The present invention relates to fumed silica having a low chlorine content and a high bulk density (a water-soluble chlorine content of 25 p.
pm or less, bulk density of 75 g / l or more, average particle size of 5
100 nm) in an amount of 0.5 to 20% by weight.

A second aspect of the present invention is the adhesive for semiconductors according to the first aspect, which contains 5-80% by weight of high-purity spherical silica having a maximum particle size of 10 μm or less and an electric conductivity of extracted water of 10 μS / cm or less. is there.

According to a third aspect of the present invention, the base adhesive is at least one selected from the group consisting of a flexible adhesive and a silicone-based / flexible epoxy-based / thermoplastic elastomer-based flexible adhesive. An adhesive for semiconductors according to claim 1 or 2.

The present invention uses high purity fumed silica. Fumed silica is an essential raw material for adjusting the viscosity and thixotropy of the adhesive, and the addition of the fumed silica significantly improves workability and enables precise bonding. The average silica particle size is 5
-100 nm, water-soluble chlorine content 25 ppm or less, bulk density 7
5 g / liter or more is required. If the average particle size is too small or too large, the fluidity is adversely affected. Needless to say, the smaller the amount of chlorine, the better the corrosion resistance. It is preferable that the bulk density is large, that is, twice or more that of a normal product. This is because when the bulk density is large, the outflow of impurities from the inside of the silica decreases. The addition amount is 0.5 to 20% by weight. If the addition amount is too small, the effect of addition cannot be obtained. If the addition amount is too large, problems such as an increase in viscosity occur.

Until now, the main focus has been on the study of high-purification and anticorrosion techniques for resins, which are the main raw materials for adhesives, and fumed silica as a trace additive has been neglected (ECC, 1987,
5, 11-13). However, the present inventors have found that high purity and high density of fumed silica are extremely important for improving reliability.

In order to reduce the thermal expansion of the adhesive, it is preferable to use high quality spherical silica. By adding an appropriate amount of isotropic (spherical) silica having high purity and no coarse particles, thermal distortion of the semiconductor device can be optimized. It is preferable to contain 5 to 80% by weight of spherical silica having a maximum particle size of 10 μm or less and an extracted water electric conductivity of 10 μS / cm or less. It is known that coarse grains cause local stress problems (Abstracts of the Institute of Electronics, Information and Communication Engineers, 2-244, 19).
1985). On the other hand, if the addition amount is too small, the effect of reducing the coefficient of thermal expansion cannot be obtained, and if it is too large, the workability and strength are reduced.

[0014] The adhesive of the present invention is a fumed silica, which is an essential component of precision bonding, is highly purified and has a high density, thereby greatly improving reliability. Further, high-purity fine spherical silica is added to reduce thermal stress.

As the resin base used in the present invention, an ordinary adhesive can be used, but it is preferable to use a flexible adhesive in consideration of relaxation of stress. Specifically, at least one kind of adhesive selected from a silicone-based adhesive, an epoxy-based flexible adhesive, and an elastomer-based adhesive is preferable. Each flexible adhesive preferably has at least one of adhesive functional groups such as an epoxy group, a carbinol group, a hydroxyl group, an amino group, an alkoxy group, and a vinyl group in its skeleton.

As the silicone adhesive, a vinyl group-containing polysiloxane can be preferably used.
The polysiloxane can be added with various additives, and is cured in the presence of a curing agent or a catalyst to become a silicone rubber having rubber elasticity. Due to this rubber elasticity, thermal stress generated at the time of assembling or using a semiconductor can be reduced. Curing agents and catalysts are as described in catalogs of silicone manufacturers.

In the present invention, it is preferable to use an epoxy resin having flexibility and a curing agent, and specifically, a modified resin such as hydrocarbon-modified, elastomer-modified, rubber-modified, or silicone-modified. For these resins,
The cured product to which various additives are added has elasticity and can reduce stress.

Next, as the elastomer-based adhesive, there are styrene-based, olefin-based, polyester-based, polyamide-based, and urethane-based adhesives. Those having a reactive functional group such as a vinyl group, an epoxy group, a hydroxyl group, an alkoxy group, an acrylic group, and an isocyanate group are used.

Other adhesive components may be added within a range that does not adversely affect the adhesive of the present invention. A compound having a functional group such as an epoxy group, a hydroxyl group, an amino group, or an alkoxy group can be used.

Conventional adhesives have problems such as poor adhesion accuracy, poor workability, uneven adhesion, non-uniform oozing, and poor yield.

The adhesive of the present invention can be used in the form of a paste or a solid, and can also be processed into a tape or the like. Even in the case of a tape shape, stable and high adhesive strength can be maintained.

The adhesive of the present invention is to cure the adhesive by applying the adhesive between the materials to be bonded. That is, a semiconductor device is assembled by attaching and curing a semiconductor chip or the like in a state where the adhesive main body is uncured. At that time, the use of high-purity high-density fumed silica and high-purity fine-grained spherical silica as the filler makes it possible to make the reliability of the semiconductor higher and more stable.

The effect of improving the workability by adding fumed silica is known (JP-B-62-43452). The present invention has examined the purity aspects, especially the chlorine content and the density aspects, which have been neglected so far, and found that the purification and the densification have excellent effects. It has also been found that further improvement can be achieved by using high-purity fine-grained spherical silica and a flexible adhesive base.

FIG. 1 shows the case where the adhesive of the present invention is applied to a BGA. The semiconductor chip 25 is attached to a substrate 28 via an adhesive 26. 29 is a solder ball. The semiconductor chip 25 is connected to the substrate 28 via the adhesive 26.
, Which are entirely surrounded by a frame 30. The outside is connected by a wiring 27.
The adhesive 26 has a function of bonding the semiconductor chip 25 to the substrate 28 and relaxing thermal stress applied to the semiconductor device.

Hereinafter, the present invention will be specifically described with reference to Examples, Comparative Examples, and Study Examples. Here, all parts are parts by weight.

An example of a method for producing high-purity fumed silica is as follows. A commercially available hydrophilic fumed silica (Aerosil # 200, Mitsubishi Materials) is heat-treated in a fluidized bed to remove hydrogen chloride adhering to the surface. Thereby, the chlorine content is reduced to about 1/10. Next, the surface is hydrophobized by reacting with silicone oils at a high temperature. The chlorine content is reduced to 1/10 or less as compared with a normal production method by reaction with chlorosilane. Two types of products having different bulk densities were produced in the final processing step. The dechlorination and the hydrophobicity may be performed by other methods, such as adsorption with ammonia gas or reaction with hexamethyldisilazane.

The chlorine content is tested by the following three methods, and a large measured value is adopted. Test method 1: Put sample and pure water in pressure vessel at 121 ° C
After leaving for 4 hours, the amount of chlorine in the extraction water is measured by ion chromatography and converted into the content in the sample. Test method 2: The sample is left in an aqueous potassium hydroxide solution at 50 ° C. for 4 hours, and the chlorine content of the extraction water is measured by ion chromatography and converted into the content in the sample. Test method 3: After heating and dissolving the sample in an aqueous sodium hydroxide solution, nitric acid is added, then a mercuric alcohol solution of thiocyanate and an iron alum solution are added, and the amount of the formed iron thiocyanate complex is quantified by a colorimetric method. .

[0028]

Example 1 5 parts of high-purity high-density fumed silica (A) produced according to a production method example, and a rubber-modified epoxy resin (TB-1)
6, Nippon Kayaku) 70 parts, xylene-modified phenol resin (XL-225, Mitsui Chemicals) 25 parts and catalyst (TPP,
1 part) and kneaded with a three-roll mill for 5 minutes to produce an adhesive. This adhesive was screen-printed on a FPC (flexible print circuit) with a thickness of 100 μm in a simulated BGA, and a semiconductor chip was mounted. Thereafter, heating was performed at 175 ° C. for 30 minutes. The thickness accuracy of the adhesive layer was ± 10 μm or less, and there was no problem in mounting on the substrate. Further, when the simulated BGA was subjected to a moisture absorption soldering treatment and a moisture resistance test was performed, no failure such as disconnection of the circuit occurred up to 240 hours. The characteristics of the fumed silica (A) are as follows: average particle size 12 nm, chlorine amount 10 ppm, bulk density 10
It was 0 g / liter.

The test method of the simulated BGA is as follows. Semiconductor chip: A simulation element having a comb-shaped electric circuit was used. Moisture-absorbing soldering treatment: After being left for 24 hours in an environment of a temperature of 125 ° C. and a humidity of 100%, it is heated three times in an infrared furnace at 260 ° C. for 10 seconds. Moisture resistance test: Continuously energized (5 V) in an environment of a temperature of 125 ° C. and a humidity of 100%, and left.

[0030]

Example 2 10 parts of fumed silica (A), 40 parts of high-purity spherical silica fine powder (Toagosei, HPS2-19), 51 parts of silicone adhesive (TSE260-3U: 50 parts, catalyst T)
C-8: 1 part, Toshiba Silicone) was used to produce an adhesive in the same manner as in Example 1. Printing showed excellent workability.
In addition, as in Example 1, a moisture absorption treatment was performed and a moisture resistance test was performed. As a result, no defect occurred up to 240 hours.
The characteristics of high-purity fine-grained spherical silica are as follows:
The extracted water had an electric conductivity of 5 μS / cm.

The method for measuring the electrical conductivity of the extracted water is as follows. Measuring method: Pure water is added to the specimen (weight ratio: 8: 1) and left at room temperature for 24 hours, and the electric conductivity of the extracted water is measured.

[0032]

Comparative Example 1 An adhesive was produced in the same manner as in Example 1 except that the amount of the fumed silica (A) was changed to 25 parts. This adhesive had too high a viscosity and was difficult to print.

[0033]

Comparative Example 2 In Example 2, instead of the fumed silica (A),
An adhesive was similarly produced using a commercial product (Aerosil R-974, Mitsubishi Materials). This adhesive has a moisture resistance test of 10% in 20 hours,
100% failure occurred in 80 hours. Aerosil R-
The characteristics of 974 are that the average particle diameter is 12 nm and the chlorine amount is 150 pp.
m, and bulk density was 50 g / liter.

[0034]

[Examination Example] In Example 2, an adhesive was produced using high-purity fumed silica (B) having a bulk density of usually 50 g / l in place of fumed silica (A). The reliability of the simulated BGA assembled using this adhesive was evaluated.
At 0 hours, 50% of the defects occurred, and at 200 hours, they were completely eliminated. This result is superior to Comparative Example 2, but inferior to Example 2.

[0035]

The present invention provides a high quality adhesive which can be used for high density semiconductors. By using fumed silica having a low chlorine content and a large bulk density and high-purity fine spherical silica, an adhesive having excellent reliability can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

[Explanation of symbols]

 19 Bump 25 Semiconductor chip 26 Adhesive 27 Wiring 28 Substrate 29 Solder ball 30 Frame

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C09J 183/04 C09J 183/04 H01L 21/52 H01L 21/52 E

Claims (3)

[Claims] 1. A hydrophobic fumed silica having an average particle size of 5 nm or more and 100 nm or less, a water-soluble chlorine content of 25 ppm or less, and a bulk density of 75 g / L or more.
An adhesive for semiconductors containing 0% by weight or less. 2. The adhesive for semiconductors according to claim 1, comprising spherical silica having a maximum particle size of 10 μm or less and an extraction water electric conductivity of 10 μS / cm or less, in an amount of 5 to 80% by weight. 3. The adhesive according to claim 1, wherein the base adhesive is at least one selected from a silicone adhesive, a flexible epoxy adhesive, and an elastomer adhesive. Adhesive for semiconductors.