JP2001164231A - High-purity adhesive for semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject highly reliable adhesive excellent in adhesivity, stability and workability, and capable of markedly improving the moisture resistance of high-density semiconductor devices. SOLUTION: This adhesive for semiconductors contains 0.1-20 wt.% of high- purity fumed silica (ultrafine particulate silica made by combustion method and having an average particle size of 5-100 nm and water-soluble chlorine level of <=25 ppm) and preferably contains 5-70 wt.% of high-purity silica balloons <=5 μm in average size, <=60% in CV value and <=10 μS/cm in the electric conductivity of the extract water; wherein a base adhesive is pref. at least one selected from flexible adhesives, i.e., silicone-, flexible epoxy- and thermoplastic elastomer-based ones.

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 device. Here, the adhesive is used to attach a semiconductor chip, a heat radiating plate, a circuit board, and the like to attach different kinds of materials when assembling the semiconductor device, and also to perform a role of security protection and shock absorption.

[0002]

2. Description of the Related Art In response to rapid advances in technology in the information and communication fields, there is a strong demand for improved performance, smaller size, lighter weight, and lower cost of electronic devices. To meet these demands, it is essential to increase the density of semiconductor devices, which are the heart of electronic devices. To increase the density of a semiconductor device, for example, a flip chip bonding method for directly attaching a semiconductor bare chip to a substrate, a BGA (ball grid array) processing method in which electrodes are arranged in a plane, or a CSP (chip size)・ Package) Realization is achieved by techniques such as processing methods.

In order to increase the density of semiconductor devices, techniques for attaching a semiconductor chip, a heat sink, a circuit board, and the like using an adhesive have been developed. This technique serves to adhere different materials and protect the semiconductor device 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 device 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 device and causing malfunction. Also, in order to prevent water intrusion from the outside, the semiconductor device needs to be bonded with high precision,
The workability of the adhesive is also an important factor.

[0005] In some cases, a semiconductor device may fail 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 semiconductor chip is small and the thermal expansion of the adhesive is large, the adhesive tends to expand and the semiconductor tries to suppress the expansion, so stress is generated, which causes a failure of the semiconductor device,
In the worst case, it causes destruction of the semiconductor device itself.

Conventional adhesives use silica as a filler to improve workability and reduce thermal expansion. Specifically, soot-like ultrafine silica (fumed silica) produced by a combustion process is used to adjust the viscosity and thixotropy of the adhesive to improve workability, and fused silica (fused silica) is used to reduce thermal expansion Have been. However, until now, it has been regarded as a supplementary or augmenting role and has not been regarded as important. In particular, fumed silica had a problem that it contained 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).
Further, the fused silica has been used in a crushed form or a spherical form containing coarse particles from the viewpoint of cost.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-quality adhesive which can cope with a higher density of a semiconductor device. This adhesive is excellent in dimensional accuracy and adhesive strength, and can guarantee high reliability of the semiconductor device. In particular, an object is to provide an adhesive having excellent corrosion resistance by using fumed silica having a low chlorine content.

[0008]

A first aspect of the present invention is to provide a high purity fumed silica (combustion-processed ultrafine silica having an average particle diameter of 5 to 100 nm and a water-soluble chlorine content of 25 ppm or less) in an amount of 0.1 to 20% by weight. % For semiconductors.

A second aspect of the present invention is to contain a high-purity spherical silica having an average particle diameter of 5 μm or less, a CV value of 60% or less, and an electric conductivity of extracted water of 10 μS / cm or less in an amount of 5 to 70% by weight. Semiconductor adhesive.

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. The adhesive for semiconductors according to claim 1 or 2.

The present invention uses fumed silica of high purity. 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 silica properties require an average particle size of 5 to 100 nm and a water-soluble chlorine content of 25 ppm or less. If the average particle size is too small or too large, the fluidity is adversely affected. It goes without saying that the smaller the chlorine amount, the better the corrosion resistance. The addition amount is 0.1 to 20% by weight. If the amount is too small, no effect is obtained, and if it is too large, problems such as an increase in viscosity occur.

Until now, the main focus of the study has been on the purifying and anticorrosion techniques of the resin which is the main raw material of the adhesive, and the fumed silica which is a trace additive has been neglected (ECC 198).
7, 5, 11-13). However, the present inventors have found that high purification of fumed silica is extremely important for improving corrosion resistance.

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. Spherical silica having an average particle diameter of 5 μm or less, a CV value of 60% or less, and an extraction water electric conductivity of 10 μS / cm or less is used for 5 to 7 spherical silica.
It is preferably contained at 0% by weight. It is known that coarse grains cause local stress problems (Abstracts of IEICE,
2-244, 1985). By narrowing the particle size distribution of the silica, the silica functions as a spacer and contributes to increasing the bonding accuracy. The amount of addition has an optimum value for adjusting the coefficient of thermal expansion (in the range of 5 to 70% by weight).

The CV value is obtained from the following equation. CV value (%) = (D1−D2) ÷ 2Dp × 1
In the above formula, D2 represents the particle size at a total of 16% by weight, D1 represents the particle size at a total of 84% by weight, and Dp represents the average particle size, that is, the particle size at a total of 50% by weight.

The adhesive of the present invention is obtained by purifying fumed silica, which is an essential component of precision bonding, to greatly improve corrosion resistance. Further, high-purity spherical silica having an optimum particle size distribution is added to reduce thermal stress. These techniques enable high-precision bonding and high reliability of high-density semiconductor devices.

As the adhesive 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 a thermoplastic 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-based 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 the semiconductor device can be reduced.
Curing agents and catalysts are as described in catalogs of silicone manufacturers.

Many epoxy resins are generally hard and do not have flexibility after curing. In the present invention, it is preferable to use a flexible epoxy resin 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 thermoplastic elastomer-based adhesive, a styrene-based, olefin-based, polyester-based, polyamide-based, urethane-based adhesive, or the like is used. 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, by using high-purity fumed silica and high-purity fine-grained spherical silica, the reliability of the semiconductor device can be made higher and more stable.

The effect of improving the workability by adding fumed silica is known (Japanese Patent Publication No. Sho 62-4345).
2). The present invention has examined the purity aspect, especially the chlorine amount, which has been neglected so far, and has found out that there is a remarkably excellent effect by increasing the purity. It has also been found that further improvements can be achieved by using spherical silica of optimal particle size and a flexible adhesive base.

FIG. 1 shows an example in which 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 described specifically 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. The point of high purification is removal of by-product hydrogen chloride and hydrophobization by dechlorination. Both technologies can produce high-purity fumed silica by applying a publicly known purification technology and a hydrophobizing technology. Production method 1 (hydrophilic): A commercially available fumed silica (Aerosil # 200, Mitsubishi Materials) is subjected to a heat treatment in a fluidized bed to remove hydrogen chloride adhering to the surface. As a result, the chlorine content is reduced to about 1/10 (normal products 30 to 1).
50 ppm, high purity product 3-15 ppm). The dechlorination may use other methods, for example, adsorption of hydrogen chloride gas with ammonia gas (using a separation membrane) or the like. Production method 2 (hydrophobic): The hydrophilic high-purity fumed silica is reacted with silicone oils at a high temperature to make the surface hydrophobic. The chlorine content is reduced to 1/10 or less as compared with a normal production method by reaction with chlorosilane (Normal product 5).
0 to 200 ppm, high purity product 3 to 15 ppm). The hydrophobization may use another chemical substance, for example, hexamethyldisilazane.

The method for measuring the amount of chlorine is as follows. The test is performed by the following three methods, and the larger 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 extracted water is measured by ion chromatography and converted into the content in the sample. Test method 2: The specimen 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 specimen. Test Method 3: After dissolving the sample in an aqueous sodium hydroxide solution, adding nitric acid, then adding a mercuric thiocyanate alcohol solution and an iron alum solution, and quantifying the amount of the produced iron thiocyanate complex by a colorimetric method. .

[0029]

Example 1 5 parts of hydrophilic high-purity fumed silica (A) produced according to Production Example 1, 70 parts of rubber-modified epoxy resin (TB-16, Nippon Kayaku), and xylene-modified phenol resin (XL- 225, Mitsui Chemicals, Inc.) and 1 part of a catalyst (TPP, K Kasei) were mixed and kneaded with a three-roll mill for 5 minutes to produce an adhesive. Simulate this adhesive with BG
In A, screen printing was performed on an FPC (flexible print circuit) with a thickness of 100 μm, and a semiconductor chip was mounted. Thereafter, heating was performed at 175 ° C. for 30 minutes. The thickness accuracy of this 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 conducted, no failure such as disconnection of the circuit occurred up to 160 hours. The characteristics of the high-purity fumed silica (A) were an average particle size of 12 nm and a chlorine amount of 10 ppm.

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 allowed to stand.

[0031]

Example 2 10 parts of hydrophobic high-purity fumed silica (B), 40 parts of high-purity spherical silica fine powder (TOA Gosei, HPS4-19), 51 parts of silicone adhesive (TSE260) -3U: 50 parts, catalyst TC-
8: 1, Toshiba Silicone) was used to produce an adhesive in the same manner as in Example 1. Printing showed excellent workability. or,
A moisture absorption test was performed in the same manner as in Example 1 to perform a moisture resistance test. As a result, no failure occurred up to 160 hours. still,
High-purity fumed silica (B) has an average particle size of 12
The characteristics of the high-purity spherical silica fine powder having an average particle diameter of 4 nm, a chlorine amount of 10 ppm, and an average particle size of 4 μm, a CV value of 45%, and an electric conductivity of extracted water of 5 μS / cm were obtained.

The method of measuring the electrical conductivity of the extracted water is as follows. Measuring method: Add pure water to the sample (weight ratio: 8: 1), and add 24 at room temperature.
Let stand for a while and measure the electrical conductivity of the extraction water.

[0033]

COMPARATIVE EXAMPLE 1 In place of high purity fumed silica A in Example 1, a commercial product having 100 ppm of chlorine (Aerosil #) was used.
200, Mitsubishi Materials Corporation). The obtained adhesive was subjected to a moisture resistance test after moisture absorption soldering in the same manner as in Example 1. As a result, a failure of 10% occurred in 40 hours and a failure of 100% in 100 hours.

[0034]

Comparative Example 2 High Purity Fumed Silica (B) in Example 2
Was replaced with a commercially available product (Aerosil R-974, Mitsubishi Materials) to similarly produce an adhesive. This adhesive produced a 10% failure in 20 hours and a 100% failure in 80 hours in a moisture resistance test, regardless of the presence or absence of the moisture absorbing soldering treatment. The characteristics of Aerosil R-974 were such that the average particle size was 12 nm and the amount of chlorine was 150 ppm.

[0035]

Comparative Example 3 An adhesive was produced in the same manner as in Example 1 except that the amount of the high-purity fumed silica (A) was changed to 25 parts. This adhesive had too high a viscosity and was difficult to print.

[0036]

[Examination Example 1] In Example 2, an adhesive was produced without adding high-purity spherical silica fine powder. When the reliability of the simulated BGA assembled using this adhesive was evaluated, a defect of 5% was generated in the moisture absorption soldering process, and a defect of 5% in 40 hours and 20% in 80 hours in the next moisture resistance test. Occurs and 16
It disappeared in 0 hours. This result is superior to Comparative Example 2, but inferior to Example 2. This is presumed to be because the thermal expansion coefficient of the adhesive was about 20% larger than that when spherical silica was added, resulting in partial failure due to the influence of thermal stress.

[0037]

[Examination Example 2] In Example 2, a commercially available epoxy resin adhesive (chip coat 1310,
(Namics) to produce an adhesive. The simulated BGA assembled using this adhesive has a 60%
Had crack defects. In addition, when the moisture resistance test was performed without performing the moisture absorption soldering treatment, the same result as in Example 2 was obtained. That is, only the effect of purifying fumed silica was confirmed.

[0038]

The present invention provides a high quality adhesive which can be used for high density semiconductor devices. In particular, an adhesive having excellent corrosion resistance is provided by using fumed silica having a low chlorine content. The semiconductor device manufactured according to the present invention has high reliability.

[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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 23/29 H01L 23/30 R 23/31

Claims (3)

[Claims] An average particle size of 5 to 100 nm and a water-soluble chlorine content of 2.
An adhesive for semiconductors containing 0.1 to 20% by weight of combustion-processed ultrafine silica having a characteristic of 5 ppm or less. 2. The method according to claim 1, wherein the average particle size is 5 μm or less.
An adhesive for semiconductors containing 5 to 70% by weight of spherical silica having a CV value of 60% or less and an extracted water electric conductivity of 10 μS / cm or less. 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 a thermoplastic elastomer adhesive. 3. The adhesive for semiconductors according to 1.).