JPH0952228A - Manufacture of semiconductor sealing epoxy resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extremely reduce a void occurrence rate by removing air entrainment and bubble and to be able to improve solder heat resistance by setting specific pressure reduction and temperature by using a biaxial kneading extruder of the same direction as a kneader when epoxy resin composition is thermally kneaded. SOLUTION: (A) Epoxy resin having a melting point of 50 to 130 deg.C and containing 70wt.% or more of crystalline epoxy having two or more epoxy groups in one molecule in total epoxy resin, (B) phenol resin curing agent having 5 poise or more of melting viscosity at 150 deg.C, (C) curing accelerator, (D) molten silica powder of 76 to 94wt.% contained in the total resin composition, (E) epoxy resin composition indispensably containing silane coupling are thermally kneaded. In this case, the kneader of the same direction is held under the pressure reducing condition of 250mmHg or less, the temperature of the composition discharged from the extruder after kneading is the melting point or higher of the crystalline epoxy resin of the component (A), and 90 to 140 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing 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. For this reason, there are some problems that cannot be solved by conventional sealing materials. The biggest problem is that the surface mounting of the semiconductor package causes the package to be rapidly exposed to high temperature of 200 ° C or higher during solder dipping or reflow process, which may cause the package to crack or seal the chip or lead frame. Deterioration of the moisture resistance due to interfacial peeling from the resin, that is, solder heat resistance. For the purpose of improving this solder heat resistance, use of heat resistant epoxy for epoxy resin encapsulation material, use of flexible resin to reduce stress when dipping solder and improve adhesion to lead frame and chip. Many proposals have been made such as addition of an imparting component, increase in the amount of the inorganic filler compounded, or improvement of the treatment conditions of the silane coupling agent on silica.

Of these, the most effective and widely adopted at present are epoxy and a curing agent that use a resin having a low melt viscosity at the molding temperature and a flexible skeleton as a curing agent. A resin composition in which a phenolic resin having the above is used and the content of fused silica in the composition is increased. According to this composition, since the content of fused silica is high, it is possible to achieve low hygroscopicity and low thermal expansion, and the curing agent having a flexible structure improves the adhesive strength to the base material, resulting in solder heat resistance. Good, and by using a resin having a low melt viscosity, the molten resin composition at the time of molding maintains a low viscosity,
Since it has high fluidity, it can be easily filled into the mold. As the epoxy resin, a crystalline epoxy resin which is solid at room temperature and whose viscosity when melted extremely decreases has been widely used (for example, JP-A-5-175364, JP-A-5-343570, and JP-A-5-343570). 6-80763, etc.).

However, in recent years, the thickness of the semiconductor encapsulating material in the package has been further reduced with the thinning of the package. For example, in the case of 1 mm thick TSOP, the encapsulating material formed on the upper surface of the chip. Has a thickness of about 0.2 to 0.3 mm. Therefore, if pinholes or voids are present in the semiconductor encapsulating material, the moisture resistance reliability and electrical insulation will be significantly reduced. With regard to pinholes and voids, it has been conventionally considered to be caused by tablet deformation, air entrapment during molding due to turbulent flow of a flowing resin, or water contained in the tablet (for example, Japanese Patent Laid-Open No. 61-138620). Kaisho 6
3-237910, JP-A-64-61028, JP-A-1
-129424, etc.).

However, in the conventional methods such as prevention of air entrapment and prevention of tablet moisture absorption, pinholes and
It has the effect of reducing voids, but it has not completely disappeared. Volatile components other than water are also mentioned as a cause of voids (for example, Japanese Patent Laid-Open No. 61-261316), and therefore a method for reducing the volatile components of the epoxy resin composition has already been proposed (for example, , Japanese Patent Application No. 5-2
66192, Japanese Patent Application No. 6-34308). The void reduction effect in the resin compositions proposed by these is remarkably high, and it became possible to eliminate voids depending on the type of resin assembly. However, in order to further improve the solder heat resistance, in a resin composition in which the content of fused silica is increased by using a low-viscosity resin, particularly a crystalline epoxy resin, it is only necessary to reduce the volatile content. In particular, it was found that the pinhole voids of 0.2 mm or less, which is a problem in a thin package, are not sufficient, and further improvement is necessary.

[0006]

SUMMARY OF THE INVENTION The present invention has been made as a result of further studies on the mechanism of void generation in view of the above situation. Air generated in the step of heating and kneading an epoxy resin composition. The void entrapment is extremely reduced by efficiently removing the air bubbles generated in the resin composition during the entrainment of the resin and the melting process of the crystalline resin that occurs during kneading and molding, and the semiconductor encapsulation has excellent solder heat resistance. It is an object of the present invention to provide a method for producing an epoxy resin composition for use.

[0007]

According to the present invention, (A) a crystalline epoxy having a melting point of 50 to 130 ° C. and having two or more epoxy groups in one molecule is 70% by weight in the total epoxy resin.
Epoxy resin containing the above, (B) phenol resin curing agent having a melt viscosity of 5 poise or less at 150 ° C., (C) curing accelerator, and (D) fused silica powder contained in an amount of 76 to 94% by weight in the total resin composition. , (E) When heat-kneading an epoxy resin composition containing a silane coupling agent as an essential component, a same-direction biaxial kneading extruder is used as a kneading device, and the system of the same-direction biaxial kneading extruder is 250 mmHg. The temperature of the epoxy resin composition maintained under the following reduced pressure conditions and further discharged from the same-direction biaxial kneading extruder after kneading is equal to or higher than the melting point of the crystalline epoxy resin of the component (A) in the epoxy resin composition. And a temperature of 90 to 140 ° C., which is a method for producing a semiconductor epoxy resin composition.

The present invention will be described in detail below. The epoxy resin used in the present invention is an epoxy resin having a melting point of 50 to 130 ° C. and a crystalline epoxy resin having two or more epoxy groups in one molecule in an amount of 70% by weight or more in the total epoxy resin. The crystalline epoxy resin is solid below the melting point but melts at a temperature above the melting point and becomes a liquid having an extremely low viscosity. Therefore, even if the content of fused silica in the epoxy resin composition is increased, The melt viscosity is low, the fluidity is excellent, and the gold wire deformation of the element and the lead frame deformation can be prevented. However, when the melting point is less than 50 ° C., when the epoxy resin composition is mixed with other components to produce it, melting is started due to a temperature rise such as frictional heat and the workability deteriorates, resulting in poor productivity. On the other hand, when the melting point exceeds 130 ° C., a high temperature is required to melt the epoxy resin when the epoxy resin composition is heated and kneaded,
Therefore, the reaction progresses during kneading, and the fluidity at the time of molding decreases. The melting point can be easily obtained by a usual measuring method for judging the melting of the resin in the capillary glass by appearance or by measuring an endothermic peak at the time of crystal melting by DSC.

As an example of this crystalline epoxy resin,
3,3 ′, 5,5′-tetramethylbiphenol diglycidyl ether, 3,3 ′, 5,5′-tetramethylbisphenol F diglycidyl ether, hydroquinone diglycidyl ether, 4,4′-dihydroxydiphenyl ether diglycidyl ether However, the present invention is not limited to these. The amount of this crystalline epoxy resin used is preferably 70% by weight or more of the total amount of epoxy resin. If it is less than 70% by weight, the effect of reducing the melt viscosity of the epoxy resin is not sufficient, and the fluidity at the time of molding is reduced. The epoxy resin that can be used in combination with this crystalline epoxy refers to all monomers, oligomers, and polymers having an epoxy group, such as bisphenol A type epoxy resin, orthocresol novolac type epoxy resin, naphthalene type epoxy resin, triphenol methane type epoxy resin. Examples thereof include resins, naphthalene type epoxy resins, dicyclopentadiene-modified phenolic epoxy resins, and the like, but are not limited thereto. Further, these epoxy resins may be used alone or in combination.

The phenol resin curing agent which is the component (B) of the present invention is characterized by having a melt viscosity at 150 ° C. of 5 poise or less. When the melt viscosity exceeds 5 poises at 150 ° C., the melt viscosity of the obtained epoxy resin composition rises, so that the fluidity at the time of molding is lowered, resulting in unfilling of the molded product in the mold, deformation of the gold wire, and lead. Frame deformation (so-called pad shift) occurs. As a method for measuring the melt viscosity of a phenol resin at 150 ° C., the ICI viscometer is simple and common. Examples of the phenol resin curing agent as the component (B) include all monomers, oligomers and polymers having a phenolic hydroxyl group capable of forming a crosslinked structure by curing reaction with an epoxy resin, specifically, a phenol novolac resin, Examples thereof include, but are not limited to, xylylene-modified phenol resin, terpene-modified phenol resin, dicyclopentadiene-modified phenol resin, bisphenol A, and triphenolmethane. These phenol resin curing agents may be used alone or in combination. A phenol resin curing agent that is particularly effective from the viewpoint of solder heat resistance is a phenol resin modified with a p- or m-xylylene structure represented by the formula (1), and usually phenol and p
-Xylylene glycol dimethyl ether or m-
It is synthesized by a polycondensation reaction with xylylene glycol dimethyl ether. Phenolic resin with this structure has a lower elastic modulus when heated than ordinary phenol novolac resin,
It has features such as high adhesion to the base material and low water absorption, and is effective in reducing thermal stress during solder immersion and preventing package cracking.

[0011]

Embedded image (R represents hydrogen or an alkyl group)

The ratio of the p-xylylene structure to the m-xylylene structure of the phenol resin curing agent of the formula (1) is not particularly limited, and the p-xylylene structure and the m-xylylene structure are independent resins. , Or even if each resin is used in combination, or p in one molecule
It does not matter if the -xylylene structure and the m-xylylene structure coexist. In order to have a melt viscosity at 150 ° C. of 5 poise or less, the value of m + n is 1 to 10 and a mixture thereof.

The component (C) curing accelerator serves as a catalyst for the crosslinking reaction between the epoxy resin and the phenol resin curing agent, and is specifically 1,8-diazabicyclo (5,4,0). amidine compounds such as undecene-7,
Organic phosphine compounds such as triphenylphosphine, 2
Examples thereof include imidazole compounds such as methylimidazole. These curing accelerators may be used alone or in combination. Although the fused silica powder of the component (D) can be used in either a crushed form or a spherical form, spherical silica is mainly used in order to increase the filler content and suppress the increase in the viscosity of the epoxy resin composition. preferable. In order to further increase the compounding amount of the spherical silica, it is desirable to adjust the particle size distribution of the spherical silica so as to be wider. The blending amount of the fused silica powder is 76 to 94 in the total epoxy resin composition from the balance of moldability and solder heat resistance.
It is desirable to include it by weight. Blended amount of fused silica is 76
%, The solder heat resistance is insufficient, while 94
If the content is more than wt%, the fluidity at the time of molding will be reduced even if a resin having a low melt viscosity is used.

Specific examples of the silane coupling agent as the component (E) include γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane and γ-.
Examples thereof include mercaptopropyltrimethoxysilane and vinyltriethoxysilane. However, the present invention is not limited thereto, and these may be used alone or in combination. Further, the silane coupling agent as the component (E) is previously prepared as the component (D).
The fused silica powder as the component may be uniformly treated and then heat-treated, or the component (D) may be added to and mixed with the components (A) to (C). In addition to the components (A) to (E), the epoxy resin composition for semiconductor encapsulation may optionally contain a brominated epoxy resin, a flame retardant such as antimony trioxide, and a colorant typified by carbon black. A release agent such as natural wax and synthetic wax, and a low stress additive such as silicone oil are appropriately blended, and they may be blended in the method for producing an epoxy resin composition of the present invention.

The present invention relates to a method for producing the epoxy resin composition for semiconductor encapsulation. As a result of detailed examination of the correlation between the pinhole voids generated when molding the above composition and the method for producing the epoxy resin composition, the following findings were obtained. In order to heat-knead an epoxy resin composition containing a resin component having a low viscosity during melting and a large amount of fused silica, it is most suitable to use a co-directional biaxial kneading extruder as a kneading method. As another kneading method, for example, a roll can be mentioned. However, as the content of the fused silica in the epoxy resin composition increases, the winding property around the roll becomes extremely low, and it is even impossible to melt the resin component. Also, a single-screw extrusion kneader or different direction 2
In the case of the axial extrusion kneading machine, since a sufficient melting zone cannot be obtained, many fused silica aggregates are recognized in the discharged material. With the same-direction biaxial kneading extruder, a much more stable kneaded product can be obtained as compared with the above kneading method, and a manufacturing method relating to this is already proposed (Japanese Patent Laid-Open No. 6-226).
736). However, in the epoxy resin composition of the present invention, that is, a composition in which a crystalline epoxy resin and a high content of fused silica are combined, a sufficient effect can be obtained simply by using the same-direction twin-screw extruder. Turned out not. That is, when the resin composition containing the crystalline epoxy is heated and kneaded by the same-direction biaxial kneader, the temperature of the resin composition is equal to or higher than the melting point of the crystalline epoxy resin, and 9
It is necessary to set and manage the conditions so that the temperature is in the range of 0 to 140 ° C.

The reason for this is that the crystalline epoxy resin is
This is because once melted, it exhibits a liquid state of extremely low viscosity, while at temperatures below the melting point it exhibits a stable solid state.
In this respect, it differs from a resin having a wide molecular weight distribution such as a conventional orthocresol novolac type epoxy resin. In the conventional non-crystalline epoxy resin, since melting starts from a low temperature in order from a low molecular weight component, the high molecular weight component also melts due to the solvent effect of the once melted low molecular weight component.
On the other hand, the crystalline epoxy resin has a substantially constant molecular weight and melts only at a certain temperature (melting point). Therefore, when an epoxy resin composition using this crystalline epoxy resin is kneaded by heating, the epoxy resin is mixed with other components in a solid state unless the epoxy resin composition is heated to a temperature higher than the melting point of the crystalline epoxy resin. Nothing more than. The resin composition kneaded under such conditions has a crystalline component that is melted and remains dispersed in a microscopic state and causes a rapid volume change when the component melts during molding, resulting in micro voids. appear. Further, since this component alone flows as a low-viscosity component, burrs are generated.

However, in the case of kneading a composition containing a crystalline epoxy resin having a melting point of less than 90 ° C., when the resin composition temperature is less than 90 ° C., the crystalline epoxy resin is a curing agent although it melts. A sufficient kneading effect cannot be obtained in terms of the effect of the softening temperature of the phenol resin and the effect of homogenizing the kneading with the fused silica. When the temperature of the resin composition during kneading exceeds 140 ° C., the reaction between the epoxy resin and the curing agent resin component proceeds during kneading, resulting in a marked decrease in fluidity during molding. In order to realize this kneading condition, the shape of a twin screw (whether it has two threads or three threads), configuration (combination of elements that can feed or knead), screw speed, epoxy resin composition Can be variously set by the combination of the feeding rate per hour and the temperature of the jacket of the kneading part, but the most important point is to control the kneading state by the temperature of the kneaded resin composition. Regarding the temperature of the kneaded material, it is most suitable to directly measure the temperature of the epoxy resin composition which is kneaded and discharged from the same-direction biaxial extrusion kneader. When the kneading conditions were further investigated, two extremely large effects were obtained by keeping the inside of the system of the twin-screw extruder in the same direction at a reduced pressure. The first is that, surprisingly, the temperature of the kneaded epoxy resin composition rises by 20 to 50 ° C. as compared with kneading under normal pressure by reducing the pressure in the system even under the same kneading conditions. . The reason for this is speculated, but one is that the air contained in the kneaded product is removed by decompression, so that the thermal conductivity of the resin composition is improved, and even if the same thermal energy is applied, the resin composition can be efficiently used. The temperature of the object rises,
Secondly, it is considered that water and organic volatile components contained in the resin composition are removed by decompression.

The greatest advantage of this phenomenon is that it is not always necessary to heat the jacket to externally apply heat to heat the resin composition to a required temperature range. When heating from the jacket, only the peripheral part inside the kneading machine is likely to receive heat energy, resulting in uneven temperature, and the kneading effect on the outer peripheral part far from the screw is low, so the kneaded product on the outer peripheral part of the barrel is heated more than the inner part. Easy to receive energy. Therefore, a part of the kneaded material contains particles in which the reaction has proceeded and further gelled, which causes a defect during molding. On the other hand, in kneading under reduced pressure conditions, cooling or heating at a low temperature is sufficient for the jacket,
The heat history of the resin composition is much more stable, and a kneaded product having uniform properties can be obtained.

The second effect of kneading under reduced pressure is a large effect of reducing voids generated during molding of the resin composition.
One of the reasons for this is that moisture and organic volatile components in the resin composition can be efficiently removed under reduced pressure conditions, so that volatile components that cause voids are not generated during molding. The second reason is that it is possible to prevent entrapment of air that occurs when kneading a large amount of fused silica and a resin component having a low melt viscosity, or to remove entrapped air bubbles. It is considered that the entrained air is not only generated physically by stirring, but also includes bubbles generated due to a volume change when the crystalline epoxy resin suddenly becomes a liquid substance when melted. This is because the resin composition using the crystalline epoxy resin has a higher occurrence rate of voids at the time of molding than the composition using the non-crystalline epoxy resin under the condition of not reducing the pressure. However, it is estimated that voids do not occur during molding. Further, when observing the inside of the resin composition after kneading with a microscope, a large number of bubbles and microvoids are observed inside when kneading without reducing the pressure, whereas when kneading under reduced pressure, the bubbles and microvoids are extremely dense. You can see that it is in a state. Decompression degree at the time of kneading is at least 250 m
mHg or less, preferably 100 mmHg or less is required. At a degree of reduced pressure of more than 250 mmHg, the temperature rise during kneading of the resin composition is not sufficient and the effect of reducing voids during molding is also low, so that an insufficient effect is obtained.

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 group equivalent 195) 4.2 parts by weight Phenolic resin curing agent represented by the formula (2) (melting at 150 ° C. Viscosity 3.3 poise, hydroxyl equivalent 175) 4.3 parts by weight

[0021]

Embedded image (In the formula, the weight ratio is m / n = 3/1)

Triphenylphosphine 0.2 parts by weight Fused silica powder 86 parts by weight γ-glycidoxypropyltrimethoxysilane 0.5 parts by weight Antimony trioxide 1 part by weight Brominated bisphenol A type epoxy resin 1 part by weight Carnauba wax 0 0.5 parts by weight Carbon black 0.3 parts by weight After mixing the above components with a mixer, heating and kneading were performed using a biaxial extrusion kneader in the same direction. This kneader has L / D = 20, the kneading screw has three threads, the kneading / feeding ratio of the element is 2.5 / 7.5, the screw rotation speed is 300 rpm, the jacket is cooled by water, and the vacuum pump is used. Then, the mixture was heated and kneaded under the condition that the pressure inside the system was reduced to 80 mmHg. When the temperature of the resin composition kneaded and extruded from the discharge port was measured with a thermometer, it was 1
It was 10 ° C. The kneaded resin composition was formed into a sheet having a thickness of 2 mm with a sheeting roll, further cooled and pulverized to obtain a sealing material. Table 2 shows the characteristics.

Examples 2 to 4 and Comparative Examples 1 to 5 Using the epoxy resin composition of Example 1, kneading was performed under the kneading conditions shown in Table 2 to obtain sealing materials. Table 2 shows the characteristics. Example 5 and Comparative Examples 6 to 9 Using the epoxy resin compositions shown in Table 1, kneading was performed under the kneading conditions shown in Table 3 to obtain sealing materials. Table 3 shows the characteristics. The structures of the phenolic resins of formulas (3) and (4) are shown below.

[0024]

Embedded image

The following evaluations were carried out on the sealing materials obtained in the above Examples and Comparative Examples. Spiral flow: Using a mold for spiral flow measurement according to EMMI-1-66, mold temperature 175 ° C,
The measurement was performed at an injection pressure of 70 kg / cm ² and a curing time of 2 minutes. Burrs: The length of burrs generated in the molded product package used for void evaluation was measured. Void: Using each molding material, an 80 pQFP package (package size 14 × 20 mm, thickness 1.5 mm, chip size 9 × 9 mm) was molded for 2 minutes at a mold temperature of 175 ° C. and a pressure of 75 kg / cm ² , Further, post-curing was performed at 175 ° C. for 8 hours. This molded product package was observed using an ultrasonic flaw detector and found to be 0.1 mm
The number of voids inside φ and above is expressed by (number / package). Solder heat resistance: The molded product package used for void evaluation is left for 168 hours in an environment of 85 ° C. and 85% RH.
Then, it was immersed in a solder bath at 260 ° C. for 10 seconds. The package was observed with a microscope, and the number of external cracks was expressed by the number of solder cracks (the number of cracked packages / the total number of packages).

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

EFFECTS OF THE INVENTION According to the production method of the present invention, air bubbles generated in the heating and kneading step and bubbles generated in the melting process of the crystalline resin that occurs during kneading and molding can be efficiently removed from the resin composition. It is possible to obtain an epoxy resin composition for semiconductor encapsulation which has extremely low void generation rate and excellent solder heat resistance.

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Claims (1)

[Claims] 1. (A) The melting point is 50 to 130 ° C., and 1
An epoxy resin containing 70% by weight or more of crystalline epoxy having two or more epoxy groups in the molecule in the total epoxy resin,
(B) Phenolic resin curing agent having a melt viscosity of 5 poise or less at 150 ° C., (C) curing accelerator, (D) fused silica powder in an amount of 76 to 94% by weight in the total resin composition, (E)
When the epoxy resin composition containing the silane coupling agent as an essential component is heated and kneaded, the same-direction twin-screw kneading extruder is used as a kneading device, and the pressure reduction condition of the same-direction twin-screw kneading extruder is 250 mmHg or less. Keep it down,
Furthermore, after kneading, the temperature of the epoxy resin composition discharged from the same-direction biaxial kneading extruder is a temperature not lower than the melting point of the crystalline epoxy resin of the component (A) in the epoxy resin composition, and 90 to 140 ° C. A method for producing a semiconductor epoxy resin composition, wherein