JPH07157537A - Epoxy resin composition for sealing semiconductor - Google Patents

Abstract

PURPOSE:To obtain an epoxy resin composition extremely reduced in the content of a volatile substance generated in a molding process targeting the sealing of semiconductors, substantially not generating pin holes and voids in the molded product package, improved in the wettability of its interface between a lead frame and a semiconductor chip, increased in the adhesivity of the interface, and improved in package crack resistance and moisture-resistant reliability on dipping in a solder, because the content of an alcohol is reduced to a remarkably low level. CONSTITUTION:This epoxy resin composition comprises an epoxy resin, a phenolic resin-curing agent, a curing-accelerating agent, and an inorganic filled having a coupling layer produced by coating the surface of the inorganic filler with a silane coupling agent and subsequently thermally treating the coated inorganic filler under an atmosphere of 100-300 deg.C, wherein the content of an alcohol component left in the whole epoxy resin composition is <=500ppm by a weight ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy resin composition for semiconductor encapsulation which is excellent in moldability, solder heat resistance and moisture resistance reliability.

[0002]

2. Description of the Related Art As a sealing method for semiconductor elements such as IC and LSI, a transfer molding method of epoxy resin is adopted as a method suitable for low cost and mass production, and epoxy resin and curing agent are also used in terms of reliability. Improvements have been made by improving phenolic resins. However, in recent market trends of miniaturization, weight reduction, and high performance of electronic devices,
The demand for semiconductor encapsulation materials is becoming more and more stringent as the integration of semiconductors is increasing year by year and the surface mounting of semiconductor packages is being promoted. Therefore, there are problems that cannot be solved by the conventional sealing material. The first problem is that as the package becomes thinner, the thickness of the semiconductor encapsulating material in the package has become much thinner. For example, in the case of 1 mm thick TSOP, the top surface of the chip and the bottom surface of the island are reduced. The thickness of the sealing material formed in the above is about 0.2 to 0.3 mm. Because of this, pinholes and voids in the semiconductor encapsulation material
If present, there is a problem of moisture resistance reliability in which the electrical insulation property is significantly reduced.

Conventionally, pinholes and voids have been considered to be caused by tablet deformation, air entrainment during molding due to turbulent flow of flowing resin, or water contained in tablets (Japanese Patent Laid-Open No. 63-23791).
No. 0, JP-A-64-61028, JP-A-1-
129424, etc.). However, although the conventional methods such as the prevention of air entrapment and the prevention of tablet moisture absorption have the effect of reducing pinholes and voids, it is not possible to eliminate them at all.
Further improvements for preventing the following pinholes and voids are desired. The second problem is that the surface mounting of a semiconductor package causes the package to be dipped in solder.
Solder heat resistance that vapor face soldering or reflow process suddenly exposes it to a high temperature of 200 ° C or higher, which may lead to cracking of the package or delamination of the interface with the chip encapsulation resin, resulting in reduced moisture resistance. There is.
Regarding the improvement of solder heat resistance, use of heat resistant epoxy,
Use of flexible resin to reduce stress during solder immersion, lead frame, and improvement of adhesion to chips, addition of adhesiveness-imparting component, increase of blending amount of inorganic filler to reduce thermal expansion coefficient, Alternatively, many proposals have been made such as improvement of treatment conditions of a silane coupling agent on silica.
However, package cracks and interfacial peeling between the chip and the encapsulation resin are all due to the low adhesion between the encapsulation resin and the lead frame or the encapsulation resin and the chip. It is considered that one of the factors is a decrease in wettability of the sealing resin at the interface between the chip and the lead frame during molding. The effects of the above proposals cannot be sufficiently obtained unless the decrease in wettability is fundamentally improved.

[0004]

As a result of various studies on causes of pinholes and voids during molding of a semiconductor package and a decrease in adhesive strength at a chip / leadframe interface, these are found to be encapsulating resin compositions. It was clarified that it was caused by the alcohol component contained therein, and it was found that the characteristics were dramatically improved by reducing the amount of the alcohol component to a certain level or less. That is, the present invention provides an epoxy resin composition for semiconductor encapsulation which can prevent both the occurrence of pinholes and voids and the decrease in reliability in the soldering process in surface mounting.

[0005]

According to the present invention, after (A) epoxy resin, (B) phenolic resin curing agent, (C) curing accelerator and (D) surface are coated with a silane coupling agent in advance, In an epoxy resin composition comprising an inorganic filler having a coupling layer formed by heat treatment in an atmosphere of 100 to 300 ° C., the content of the residual alcohol component in the total epoxy resin composition is 500 ppm by weight.
It is the following epoxy resin composition for semiconductor encapsulation.

The present invention will be described in detail below. The epoxy resin used in the present invention refers to all monomers, oligomers and polymers having an epoxy group, for example, bisphenol A type epoxy resin, biphenol type epoxy resin, orthocresol type epoxy resin, naphthalene type epoxy resin, triphenolmethane type epoxy resin. , A hydroquinone type epoxy resin and the like, but not limited to these. Further, these epoxy resins may be used alone or in combination. Phenol resin curing agent is a monomer having a phenolic hydroxyl group capable of forming a crosslinked structure by performing a curing reaction with the epoxy resin, an oligomer, a polymer in general, for example, phenol novolac resin, para-xylylene-modified phenol resin, terpene-modified phenol resin, Examples thereof include dicyclopentadiene-modified phenol resin, bisphenol A, triphenol methane and the like, but the invention is not limited thereto. These phenol resin curing agents may be used alone or in combination. The curing accelerator is one that can serve as a catalyst for the crosslinking reaction between the epoxy resin and the phenol resin curing agent, and examples thereof include amine compounds such as 1,8-diazabicycloundecene and organic phosphine compounds such as triphenylphosphine. Examples thereof include imidazole compounds such as methylimidazole. These curing accelerators may be used alone or in combination.

Examples of the inorganic filler coated with the silane coupling agent include fused silica powder, crystalline silica powder, alumina and silicon nitride. The content of the coated inorganic filler is preferably 70 to 90% by weight in the total epoxy resin composition from the viewpoint of balance between moldability and reliability. Particularly in the case of a compound having a large amount of filler, spherical fused silica is generally used. Examples of the silane coupling agent used for coating include γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-mercaptopropylmethoxysilane, vinyltriethoxysilane, and the like. It is not limited, and these may be used alone or in combination.

The most important point of the present invention is to use an inorganic filler having a coupling agent layer obtained by coating the surface with a silane coupling agent in advance and then heat-treating it in an atmosphere of 100 to 300 ° C. In the epoxy resin composition, the content of the residual alcohol component in the total epoxy resin composition is 500 ppm or less, further 250 ppm by weight ratio.
It should be kept below. Epoxy resins, phenolic resin curing agents, silane coupling agents, etc., which are the raw materials for epoxy resin compositions for semiconductor encapsulation, absorb moisture in the air during the manufacturing process and storage process, and these raw materials and inorganic substances are generally used. An epoxy resin composition produced by heating and kneading a filler and the like also absorbs moisture in the production process and storage process. There have been many reports that this moisture absorption causes deterioration of moldability and solder heat resistance. Then, as a countermeasure, a method of drying in dry air having a dew point of -10 ° C or less, a method of vaporizing and drying water by applying a reduced pressure treatment in a closed storage place, or a desiccant such as silica gel or phosphorus pentoxide is used. Many proposals such as a method of adsorbing moisture to a desiccant have been made. Certainly, the amount of water remaining in the encapsulant composition can be made substantially zero by these methods, and the volatile component at the time of molding is remarkably reduced by this, so that Effective to reduce the number of pinholes and voids, or to improve the decrease in adhesion caused by the decrease in the wettability of the interface between the resin composition and the chip / lead frame due to the generation of volatile gas. . However, as described above, it is a fact that this alone is not sufficient under the recent thinning of semiconductor packages and severe solder processing conditions.

The reason for this is that the alcohol component remaining in the epoxy resin composition can hardly be removed by the method of removing water as described above, and therefore, it is vaporized and volatilized by the heat during molding. The alcohol component causes generation of voids and pinholes, deterioration of wettability of the interface between the chip or the lead frame and the sealing material, and eventually deterioration of adhesive strength. It is considered that these alcohol components remain in the epoxy resin composition for the following reasons. An alcohol component produced by the reaction between the hydroxyl group of the inorganic filler and the alkoxy group of the silane coupling agent during the production process and storage of the epoxy resin composition.
Specific examples include methanol, ethanol, and propanol. The following methods are industrially important as methods for reducing these alcohol components.

After coating the inorganic filler with a silane coupling agent in advance, the reaction between the two is completed by heating and alcohol as a reaction product is removed,
An epoxy resin composition is obtained by heating and kneading the inorganic filler having the coupling agent layer, an epoxy resin, a phenol resin curing agent, a curing accelerator, and the like. Conventionally, a method has been proposed in which the surface of an inorganic filler typified by silica is previously coated with a silane coupling agent and reacted, but in this case, what is important is the temperature and time for the reaction. In the epoxy resin composition of the present invention, the inorganic filler having a coupling agent layer obtained by coating the surface with a silane coupling agent in advance and then heat-treating it in an atmosphere of 100 to 300 ° C. The content of the residual alcohol component in the epoxy resin composition needs to be suppressed to 500 ppm or less by weight ratio. For that purpose, the heat treatment condition of the inorganic filler coated with the silane coupling agent is 24 at 100 ° C. More than 8 hours at 150 ° C, more than 2 hours at 200 ° C, 3 at 300 ° C
0 minutes or more is preferable, and particularly preferably 100 ° C to 200 ° C.
It is desirable to process in.

The amount of the silane coupling agent added to the inorganic filler is 0.1 to 2.0% by weight. When the alcohol component remaining in the entire composition exceeds 500 ppm, many pinholes and internal voids are generated in the molded product,
Moisture resistance reliability decreases. The inorganic filler having the coupling agent layer is preferably contained in the total epoxy resin composition in an amount of 70 to 90% by weight. Further, in the heating and kneading step performed when forming a molding material, a greater effect can be obtained even by combining a method of removing alcohol components by deaerating a kneader such as a kneader with a vacuum pump and reducing the pressure. . In this case, it is usually desirable that the temperature during heating and kneading be in the range of 80 ° C. to 150 ° C., and the degree of pressure reduction due to degassing at that time is 200 mmHg or less.
There are various methods for quantitatively determining the alcohol substance remaining in the total epoxy resin composition, and relatively simple ones include a gas claw mass spectrum method and a thermogravimetric balance-mass spectrum method. These are measurement methods in which a sample of the epoxy resin composition is heated to 60 to 250 ° C., and the alcohol component generated is identified and quantified by a mass spectrum.

The epoxy resin composition of the present invention contains an epoxy resin, a phenol resin curing agent, a curing accelerator, and an inorganic filler having a coupling agent layer as essential components. Resins, flame retardants such as antimony trioxide, colorants typified by carbon black, release agents such as natural wax and synthetic wax, and low stress additives such as silicone oil, silicone rubber, and synthetic rubber may be appropriately mixed. It doesn't matter. When forming a molding material, the desired composition for epoxy resin for semiconductor encapsulation is obtained by heating and kneading the entire composition with a heating kneader or a heating roll, followed by cooling and pulverizing.

The present invention will be specifically described below with reference to examples. Example 1 3,3,5,5-tetramethylbiphenol diglycidyl ether (melting point 103 ° C, epoxy equivalent 195) 9.1 parts by weight Paraxylylene-modified phenol resin (softening temperature 70 ° C, hydroxyl equivalent 175) 3.8 parts by weight Phenol novolac (softening temperature 85 ° C., hydroxyl equivalent 104) 3.0 parts by weight triphenylphosphine 0.3 parts by weight fused silica powder 80.0 parts by weight γ-aminopropyltriethoxysilane 0.5 parts by weight antimony trioxide 1. 0 parts by weight Brominated bisphenol A type epoxy resin 1.5 parts by weight Carnauba wax 0.5 parts by weight Carbon black 0.3 parts by weight In producing an epoxy resin composition with the above composition,
The fused silica powder and γ-aminopropyltriethoxysilane were thoroughly mixed and coated in advance with a mixer, and then 1
Heat treatment was performed at 50 ° C. for 8 hours. The silica having the coupling agent layer and other blended raw materials were mixed by a mixer, and then kneaded by heating with a biaxial kneader having a barrel temperature of 100 ° C. The kneaded product was formed into a sheet having a thickness of 2 mm with a sheeting roll, further cooled and pulverized to obtain a sealing material.

The alcohol component generated when the above molding material was heat-treated at 200 ° C. for 30 minutes was identified and quantified using a gas spectrum-mass spectrometer. The weight ratio of ethanol was 50 ppm. Also, using each of the above molding materials, an 80 pQFP package (package size 14 × 20 mm, thickness 1.5 mm, chip size 9 ×)
9 mm) with a mold temperature of 175 ° C. and a molding pressure of 75 kgf / c
m ² , molding time was 2 minutes, and further post-curing was performed at 175 ° C. for 8 hours. The molded product package was observed using an ultrasonic flaw detector, and the number of internal voids of 0.1 mmφ or more (number / package) was expressed by the number of voids. Also,
This molded product package was left in an environment of 85 ° C. and 85% RH for 168 hours, and then immersed in a solder bath at 260 ° C. for 10 seconds. The packages were observed with a microscope, and the number of external cracks (the number of cracked packages / the total number of packages) was expressed by the number of solder cracks. Similarly, the 80 pQFP molded product package was left in an environment of 85 ° C. and 85% RH for 24 hours, and then reflowed at 240 ° C. for 10 seconds. Next, use this package with a PC at 125 ° C and 2.3 atmospheres.
The PCT treatment time until the defect rate reaches 50% after T treatment is expressed as moisture resistance reliability. The results are shown in Table 1.

Example 2 In the formulation of Example 1, the fused silica powder and γ-aminopropyltriethoxysilane were thoroughly mixed and coated in advance with a mixer, and then heat-treated at 100 ° C. for 24 hours. Silica having this coupling agent layer was kneaded in the same manner as in Example 1 to obtain a sealing material. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 1. Example 3 In the formulation of Example 1, the fused silica powder and γ-aminopropyltriethoxysilane were thoroughly mixed and coated in advance with a mixer, and then heat-treated at 120 ° C. for 16 hours. Silica having this coupling agent layer was kneaded in the same manner as in Example 1 to obtain a sealing material. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 1.

Comparative Example 1 Example 1 was repeated except that the fused silica powder and γ-aminopropyltriethoxysilane were thoroughly mixed and coated, and then the heat treatment conditions were changed to 120 ° C. for 1 hour.
A molding material was produced in the same manner as in. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 1. Comparative Example 2 In Comparative Example 1, heating and kneading with a twin-screw kneader was performed for 200 times.
A molding material was produced under exactly the same conditions as in Comparative Example 1 except that the pressure was reduced to mmHg. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 1. Comparative Example 3 After mixing all the compounded raw materials of Example 1 with a mixer, the mixture was heated and kneaded with a twin-screw kneader having a barrel temperature of 100 ° C. to obtain Example 1.
A molding material was obtained in the same manner as in. The evaluation results are shown in Table 1.

[0017]

[Table 1]

[0018]

According to the present invention, since the amount of alcohol contained in the epoxy resin composition is at a very low level, the volatile matter generated during molding for semiconductor encapsulation is extremely small, and Almost no pinholes or voids are generated in the product package, and the wettability of the interface between the lead frame or chip and the encapsulation material is improved. Improves crack resistance and moisture resistance reliability.

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Claims (1)

[Claims] 1. An epoxy resin (A), a phenolic resin curing agent (B), a curing accelerator (C) and a surface (D) are coated with a silane coupling agent in advance, and then 100-300.
In an epoxy resin composition composed of an inorganic filler having a coupling layer formed by heat treatment in an atmosphere of ° C, the content of the residual alcohol component in the total epoxy resin composition is 500 ppm or less by weight. A characteristic epoxy resin composition for semiconductor encapsulation.