JP2000273280A - Epoxy resin composition and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an epoxy resin composition for semiconductor sealing use excellent in filling property in and releasability from thin-type semiconductor devices and in the soldering resistance for semiconductor devices. SOLUTION: This epoxy resin composition essentially comprises an epoxy resin of the general formula (R is H, a 1-9C alkyl or halogen; n is a positive number of 1-5 on average), a phenolic resin, fused silica powder, and curing promoter(s) (esp. pref. at least one selected from the group consisting of amidine compounds, guanidine compounds and imidazole compounds); wherein it is characteristic that the number ratio of the epoxy groups in the total epoxy resin to the phenolic hydroxyl groups in the total phenolic resin is 1.1 to 1.3.

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 and solder resistance and is particularly suitable for a thin semiconductor package, and a semiconductor device using the same.

[0002]

2. Description of the Related Art Transfer molding of an epoxy resin composition is suitable as a method for encapsulating semiconductor elements such as ICs and LSIs at a low cost and suitable for mass production. The phenol resin has been improved to improve the characteristics. However, in the recent market trend of miniaturization, weight reduction and high performance of electronic devices, the integration of semiconductors has been increasing year by year, and the surface mounting of semiconductor devices has been promoted. Demands for resin compositions are becoming more stringent. For this reason, a problem which cannot be solved by the conventional epoxy resin composition has come out. The biggest problem is that
Due to the adoption of surface mounting, the semiconductor device is rapidly exposed to a high temperature of 200 ° C. or more in a solder immersion or reflow process, and cracks occur in the semiconductor device due to the stress when the absorbed moisture explosively evaporates, and This is a phenomenon in which peeling occurs at the interface between each of the plated joints on the lead frame and the inner lead and the cured product of the resin composition, and the reliability is significantly reduced.

Further, in recent years, as semiconductor devices have become thinner, the thickness of a resin composition occupying the semiconductor device has been further reduced. For example, in packages for 64M and 256M DRAMs, TSOP having a thickness of 1 mm has become mainstream. is there. These thin semiconductor devices are required to have a resin composition that has a good filling property at the time of molding, has little deformation of a gold wire, and has no deformation of a chip or a lead frame (referred to as chip shift or die pad shift). The material needs to have excellent fluidity during molding. In order to achieve both improvement in reliability due to soldering and improvement in fluidity during molding, the amount of fused silica powder in the epoxy resin composition is increased to reduce moisture absorption, increase strength, and reduce thermal expansion. And improving the solder resistance, and using a resin having a low melt viscosity to maintain a low viscosity and high fluidity during molding is becoming common. On the other hand, the adhesiveness at the interface between a cured product of an epoxy resin composition and a base material such as a semiconductor element or a lead frame existing inside a semiconductor package has become very important in reliability by soldering. If the adhesive force at this interface is weak, peeling occurs at the interface with the base material after the soldering, and further, a package crack due to the peeling occurs. From the viewpoint of improving the adhesive force at the interface, many epoxy resins have been proposed, but the epoxy resin of the formula (1) is particularly suitable for this application because of its flexibility and low moisture absorption. It has been known (Japanese Patent Application Laid-Open No. 8-143648).

[0004] However, a resin composition using the epoxy resin of the formula (1) and a low molecular weight phenol resin as a curing agent is characterized by a low melt viscosity at a molding temperature, but has a low epoxy group density. There is a drawback that the glass transition temperature of the cured product is lowered due to the limit of the number of functional groups of the combination of the flexible epoxy resin of the formula (1) and the low molecular weight phenol resin. For this reason, curing at the time of molding is slow, and therefore the hardness when heated is low, and the phenomenon that the molded product adheres to the mold or the molded product is broken at the time of mold release is observed. It is pointed out that the glass transition temperature must be increased. Further, since the molded products of these resin compositions have low mechanical strength at the temperature of the soldering treatment, the glass transition temperature is further increased in order to obtain sufficient strength to withstand the stress generated by the vapor pressure of vaporized and expanded water. There is a demand for improvement.

[0005]

DISCLOSURE OF THE INVENTION The present invention has a good filling property in a thin semiconductor device, and has a feature of a small deformation of a wire, a chip shift, and a shift of a die pad, that is, a high fluidity at the time of molding. The purpose of the present invention is to develop a resin composition that is excellent in mold release property during molding and solder resistance of a cured product.

[0006]

That is, the present invention provides (A)
A group consisting of an epoxy resin represented by the general formula (1), (B) a phenolic resin, (C) a fused silica powder, and (D) a curing accelerator, particularly an amidine compound, a guanidine compound, and an imidazole compound as a suitable curing accelerator. In the epoxy resin composition for semiconductor encapsulation containing at least one or more as an essential component selected from the group consisting of (A) and (B), the ratio of the number of epoxy groups of the epoxy resin to the number of phenolic hydroxyl groups of the phenol resin is 1.1 to 1. 3 is an epoxy resin composition for semiconductor encapsulation, and a semiconductor device obtained by encapsulating a semiconductor element using the epoxy resin composition.

Embedded image (R in the formula (1) is a group selected from a hydrogen atom, a halogen atom, or an alkyl group having 1 to 9 carbon atoms, and may be the same or different from each other. (Value, positive number from 1 to 5)

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The epoxy resin used in the present invention is an epoxy resin represented by the formula (1). Specific examples of the epoxy resin represented by the general formula (1) are shown below, but are not limited thereto.

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These epoxy resins are epoxy compounds having two or more epoxy groups in one molecule, and are characterized by having a hydrophobic structure between epoxy groups. The cured product with phenolic resin has a low crosslink density and a large hydrophobic structure, and therefore has a low moisture absorption rate. Therefore, thermal stress at the time of molding the epoxy resin composition or soldering after moisture absorption of a semiconductor device as a molded product. Reduces thermal stress generated during processing,
Excellent adhesion to substrate. On the other hand, since the hydrophobic structure between the epoxy groups is a rigid biphenyl skeleton, it has a feature that the heat resistance is not significantly reduced despite the low crosslinking density.

The epoxy resin used in the present invention may be used in combination with another epoxy resin. Epoxy resins that can be used in combination include monomers, oligomers, and polymers having an epoxy group, for example, biphenyl type epoxy resin, stilbene type epoxy resin, hydroquinone type epoxy resin, crystalline epoxy resin such as bisphenol F type epoxy resin, Bisphenol A type epoxy resin, orthocresol novolak type epoxy resin, dicyclopentadiene modified phenol type epoxy resin, triphenol methane type epoxy resin, naphthol type epoxy resin and the like can be mentioned. These epoxy resins may be used alone or as a mixture. In particular, in order to increase the filling amount of the fused silica powder of the epoxy resin composition, the above-mentioned crystalline epoxy resin which exhibits crystallinity at room temperature and extremely lowers the melt viscosity at the molding temperature is preferable.

The phenolic resin used in the present invention refers to all monomers, oligomers and polymers having a phenolic hydroxyl group capable of curing and reacting with an epoxy resin to form a crosslinked structure. Examples thereof include phenol novolak resins, cresol novolak resins, and xylylenes. Modified phenolic resins, terpene-modified phenolic resins, dicyclopentadiene-modified phenolic resins, bisphenol A, triphenolmethane, and the like are included, but are not limited thereto. The hydroxyl equivalent is preferably 130 to 21 in order to improve the low hygroscopicity of the cured product of the resin composition and the adhesion to the substrate.
Phenolic resins in the range of 0 are particularly preferred.

The fused silica powder used in the present invention includes, for example, natural silica melted in a flame and synthetic silica obtained by hydrolyzing tetramethoxysilane, tetraethoxysilane and the like. Further, there are spherical silica and crushed silica depending on the shape and production method. The blending amount of the fused silica powder is 75 to 9 in the total resin composition.
3% by weight is preferred. If the content is less than 75% by weight, the amount of moisture absorbed by the cured product of the resin composition increases, and the strength at the soldering temperature is reduced. On the other hand, if it exceeds 93% by weight, the fluidity during molding of the resin composition decreases,
Unfilling, chip shift, and pad shift are likely to occur, which is not preferable. Particularly, in order to highly fill the fused silica powder, a spherical one is preferable. Further, a broad particle size distribution is effective for reducing the melt viscosity of the resin composition during molding.

The curing accelerator used in the present invention refers to a curing accelerator which can serve as a catalyst for a crosslinking reaction between the epoxy resin and the phenol resin. Specific examples include tributylamine,
1,8-diazabicyclo (5,4,0) undecene-7
And the like, amine-based compounds such as triphenylphosphine, organic phosphorus-based compounds such as tetraphenylphosphonium / tetraphenylborate, and imidazole compounds such as 2-methylimidazole. Particularly preferred curing accelerators are amidine compounds and guanidines. At least one selected from the group consisting of compounds and imidazole compounds. These compounds are characterized in that they promote the cross-linking reaction between the epoxy resin and the phenol resin and also act as a catalyst for initiating ring-opening polymerization between epoxy groups in the epoxy resin due to its basic strength. is there. Examples of the amidine compound include 1,8-diazabicyclo (5,4,
0) Undecene-7,1,5-diazabicyclo (4,
3,0) nonene-5,6-dibutylamino-1,8-diazabicyclo (5,4,0) undecene-7 and the like, as guanidine compounds, for example, 1,5,7-triazabicyclo (4, 4,0) decene-5,7-methyl-1,
5,7-triazabicyclo (4,4,0) decene-5,
Pentamethylguanidine, tetramethylguanidine and the like, and examples of the imidazole compound include, for example, 2-methylimidazole, 2-ethyl-4-methyl-imidazole, 2-phenyl-4-methyl-imidazole, and the like. However, the present invention is not limited to this. The compounds of the above group can also be used in the form of salts with inorganic acids or organic acids. These may be used alone or as a mixture.

In the resin composition of the present invention, it is important that the ratio of the total number of epoxy groups of the total epoxy resin to the total number of phenolic hydroxyl groups of the total phenolic resin is in the range of 1.1 to 1.3. The epoxy resin of the general formula (1) has low hygroscopicity,
Due to the flexibility, the adhesiveness at the interface between the substrate after the soldering of the semiconductor device and the cured product of the epoxy resin composition is good, and the solder crack resistance is also excellent as described above. However, on the other hand, there is a disadvantage that the curability at the time of molding is inferior. In particular, it is presumed that there is a steric hindrance due to the presence of a rigid biphenyl structure between the epoxy groups that are reaction points, but since the reaction of all the reactive groups in the epoxy resin composition is difficult to complete, In the case of an epoxy resin composition in which the ratio of the epoxy group to the hydroxyl group is 1: 1, there is a strong tendency that the epoxy group and the hydroxyl group remain after molding. When the phenolic hydroxyl group remains among the reactive groups remaining in the cured product, the moisture absorption rate is high, and mechanical properties such as bending strength are reduced, resulting in low solder resistance of the semiconductor device. Therefore, by increasing the number of functional groups of the epoxy group of the epoxy resin and the hydroxyl group of the phenol resin to an excess of the epoxy group, the curability of the epoxy resin composition can be improved and the residual ratio of the phenolic hydroxyl group in the cured product can be substantially reduced. It is possible to make it zero, and it is possible to prevent a decrease in moisture absorption characteristics and mechanical characteristics. If the ratio of the number of epoxy groups in the total epoxy resin to the number of phenolic hydroxyl groups in the total phenolic resin is less than 1.1, this effect cannot be obtained. On the other hand, if the ratio is more than 1.3, the crosslink density becomes too small.
Curability and heat resistance are impaired. The excess epoxy group remaining in the cured product is effective in improving the adhesiveness to a substrate such as a semiconductor element or a lead frame.

Further, the ratio of the total number of epoxy groups of the total epoxy resin to the total number of phenolic hydroxyl groups of the total phenolic resin is in the range of 1.1 to 1.3, and as a curing accelerator, an amidine compound, a guanidine compound or an imidazole compound is used. When one or more members selected from the group are used, the epoxy group undergoes an addition reaction with the phenolic hydroxyl group, and at the same time, the ring-opening polymerization of the epoxy groups is also performed to further improve the curability and raise the glass transition temperature of the cured product. Can be. The crosslink density of the cured product of the resin composition is improved by ring-opening polymerization between epoxy groups, and the glass transition temperature is increased, so that the mold releasability during molding is excellent, and the mechanical strength during soldering is increased. It is also possible to improve the solder resistance. Furthermore, unlike the case of the addition reaction with a phenolic hydroxyl group, the ring-opening polymerization between epoxy groups does not generate a hydroxyl group after the reaction, and thus has the characteristic that the moisture absorption of the cured product can be reduced.

The resin composition of the present invention comprises, in addition to the components (A) to (D), if necessary, a flame retardant such as a brominated epoxy resin or antimony trioxide, a low stress agent represented by a polysiloxane compound, Coupling agents, coloring agents represented by carbon black, release agents such as natural waxes and synthetic waxes, and the like can be appropriately compounded. The resin composition of the present invention,
It is obtained by mixing the components (A) to (D), other additives, and the like using a mixer or the like, heating and kneading using a heating kneader or a hot roll, and then cooling and pulverizing. In order to manufacture an electronic device such as a semiconductor device by encapsulating an electronic component using the resin composition of the present invention, it is only necessary to cure and mold by a conventional molding method such as transfer molding, compression molding and injection molding.

Hereinafter, the present invention will be described specifically with reference to Examples. The mixing unit is parts by weight. Example 1 7.6 parts by weight of an epoxy resin of the formula (2) (epoxy equivalent 270, softening point 60 ° C.)

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Phenol aralkyl resin (XL225-LL, manufactured by Mitsui Chemicals, Inc., softening point 75 ° C., hydroxyl equivalent 175; hereinafter referred to as phenol aralkyl resin) 4.4 parts by weight Spherical fused silica powder 87.0 parts by weight triphenylphosphine 0.2 parts by weight of carnauba wax, 0.5 parts by weight of carbon black, and 0.3 parts by weight of carbon black were mixed using a mixer.
The mixture was kneaded 30 times using two rolls at 5 ° C., and the obtained kneaded material sheet was cooled and pulverized to obtain a resin composition. The obtained resin composition was evaluated by the following method. Table 1 shows the results.

Evaluation method Spiral flow: Using a mold for measuring spiral flow according to EMMI-I-66, using a mold temperature of 175 ° C.
The measurement was performed at an injection pressure of 70 kg / cm ² and a curing time of 2 minutes.
The unit is cm. Releasability: 50-pin lead-on-chip TSOP
(Package size is 10 × 21mm, thickness 1.0m
m, silicon chip size 9 × 18 mm, lead frame made of iron / nickel alloy (42 alloy), chip and inner lead are bonded with 100 μm thick polyimide tape), mold temperature 175 ° C., molding pressure 75
Transfer molding was performed at kg / cm ^{2 for} a curing time of 2 minutes. After the molding, the releasability from the mold when the mold was opened was evaluated. ○ indicates good releasability, and × indicates occurrence of mold adhesion or runner breakage. Hot hardness: TSO with 50-pin lead-on-chip structure
After molding P, 10 seconds after the mold is opened, Barcol #
The hardness of the package surface was measured using a 935 hardness meter. Glass transition temperature (Tg): A test piece formed by transfer molding at a mold temperature of 175 ° C., an injection pressure of 75 kg / cm ² , and a curing time of 2 minutes is further post-cured at 175 ° C. for 4 hours. TMA-
120, and a heating rate of 5 ° C./min]. The unit is ° C. Heat strength: Flexural strength at 240 ° C. is determined according to JIS-K6911.
It measured according to. The unit is kgf / mm ² . Solder resistance: 100-pin TQFP (package size is 1
4 × 14 mm, thickness 1.4 mm, silicon chip size 8.0 × 8.0 mm, lead frame made of 42 alloy), mold temperature 175 ° C., injection pressure 75 kg / c
transfer molding with m ² , curing time 2 minutes, 175
Post-curing was performed at 8 ° C. for 8 hours. The obtained semiconductor package was left in an environment of 85 ° C. and a relative humidity of 85% for 168 hours, and then immersed in a 240 ° C. solder bath for 10 seconds. Observe the external cracks with a microscope and calculate the number of cracks ((number of cracked packages) / (total number of packages) × 100) by%.
Displayed with. Also, the ratio of the peeled area between the chip and the resin composition was measured using an ultrasonic flaw detector, and the average value of five packages was determined as the peeling rate ((peeled area) / (chip area) × 100). ,%.

Examples 2 to 5 and Comparative Examples 1 to 4 Each component was blended in the proportions shown in Table 1 to obtain a resin composition in the same manner as in Example 1, and evaluated in the same manner as in Example 1. Table 1 shows the results. The properties of the epoxy resins used in Examples 2 to 5 and Comparative Examples 1 to 4 are shown below. An epoxy resin having the formula (3) as a main component (epoxy equivalent 195, melting point 1)
05 ° C), an epoxy resin having the formula (4) as a main component (epoxy equivalent: 200, softening point: 65 ° C), and a phenol resin of the formula (5) (hydroxyl equivalent: 195, softening point: 70 ° C). The structural formulas (3) to (5) are shown below.

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[0020]

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[0021]

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[0022]

[Table 1]

[0023]

The use of the resin composition of the present invention makes it possible to provide a thin semiconductor device with excellent filling properties and mold release properties, and to provide a sealed semiconductor device with excellent heat strength and low hygroscopicity. Excellent later solder resistance.

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Claims (3)

[Claims] (A) an epoxy resin represented by the general formula (1), (B) a phenol resin, (C) a fused silica powder,
And (D) in the epoxy resin composition for semiconductor encapsulation containing a curing accelerator as an essential component, the ratio of the number of epoxy groups in the total epoxy resin to the number of phenolic hydroxyl groups in the total phenol resin is 1.1 to 1.3. An epoxy resin composition for semiconductor encapsulation characterized by the following. Embedded image (R in the formula (1) is a group selected from a hydrogen atom, a halogen atom, or an alkyl group having 1 to 9 carbon atoms, and may be the same or different from each other. (Value, positive number from 1 to 5) 2. The epoxy resin composition for semiconductor encapsulation according to claim 1, wherein (D) the curing accelerator is at least one member selected from the group consisting of an amidine compound, a guanidine compound and an imidazole compound. 3. A semiconductor device comprising a semiconductor element encapsulated with the epoxy resin composition for semiconductor encapsulation according to claim 1.