JP4386521B2 - High density semiconductor adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive for use in manufacturing a reliable, high- density semiconductor device at a low cost, which has superior adhesive property, storability, stability and workability and can relax thermal stresses generated in the semiconductor device at assembling and using of the semiconductor device. SOLUTION: A flexible, tough adhesive 26 for semiconductor contains spherical fine silica particles, having hydroxyl groups on their surfaces and containing and ultrrafine silica particles in optimum quantity and ratio. The adhesive contains two types of silica, having optimum particle diameters and playing different roles as solid state, adhering and viscous adjusting components in suitable quantities. The two types of silica are of spherical fine particles, having hydroxyl groups on their surfaces and having a mean particle diameter of 2-8 μm and of ultrafine particles having a means particle diameter of 2-80 μm. The two types of silica has a total content of 5-70 weight %, and the content of the spherical fine particle silica is larger than that of the ultrafine particle silica.

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an adhesive for high-density semiconductors. The adhesive referred to here is used to attach a semiconductor chip, a heat radiating plate, a circuit board, etc., and to dissipate different materials and to cushion the shock when assembling a semiconductor device.
[0002]
[Prior art]
In response to rapid advances in technology in the information and communication fields, there is a strong demand for improved performance, miniaturization, weight reduction, and cost reduction of electronic devices. In order to satisfy these demands, it is essential to increase the density of a semiconductor device that is the heart of an electronic device. High density semiconductor devices include, for example, a flip chip bonding method in which a semiconductor bare chip is directly attached to a substrate, a BGA (ball grid array) processing method in which electrodes are arranged in a plane, and a CSP (chip size).・ Packaging) This has been realized by technologies such as processing methods.
[0003]
In order to increase the density of a semiconductor device, a technique for attaching a semiconductor chip, a heat sink, a circuit board, and the like using an adhesive has been advanced. This technique serves to bond dissimilar materials to each other and to mitigate the impact caused by the thermal stress of the semiconductor device. When assembling a semiconductor device using an adhesive, it is necessary to precisely bond the semiconductor to a substrate or the like. For this reason, the adhesive is required to have quality uniformity and stability. Since conventional adhesives are mainly composed of liquid adhesive components, they partially change in composition and are not suitable for high-precision adhesive applications. There was a problem in that the adhesive strength was uneven and oozed out unevenly. Further, when assembling a semiconductor device, different materials must be bonded, and there is a problem that the adhesive strength is insufficient with a conventional adhesive.
[0004]
The semiconductor device has a problem that heat is applied at the time of assembly and use, which causes a thermal stress in the semiconductor, and this stress must be relieved. When the heat is applied, the thermal expansion of the semiconductor chip itself is small, and the thermal expansion of the adhesive is large. Therefore, the adhesive tries to expand, and the semiconductor tries to suppress the expansion. Cause the failure of the semiconductor device itself in the worst case.
[0005]
In conventional adhesives, silica is used as a filler in order to reduce thermal expansion. However, when a large amount is added, flexibility and strength are reduced. Moreover, the anisotropic filler with a large particle size has a problem of generating local stress. Furthermore, it is also known to use ultrafine particle anisotropic silica as an adhesion reinforcing agent, but there is a problem in that the viscosity increases and fluidity is lost due to the addition, resulting in poor processability. For this reason, a method of adding a liquid adhesive component has been adopted, but it has problems such as bleeding and non-uniform adhesion.
[0006]
[Problems to be solved by the invention]
The present invention provides a semiconductor adhesive that enables a semiconductor device to be densified to be assembled at low cost. This adhesive is excellent in dimensional accuracy, storage stability, and adhesive force, and can relieve thermal stress generated in the semiconductor device due to heat applied during assembly and use of the semiconductor device. That is, by using spherical fine silica having a hydroxyl group on the surface and ultrafine silica in an appropriate amount and ratio as a solid adhesive component and a viscosity adjusting component, high flexibility, uniformity, stability and processability are excellent. It is intended to provide a strong adhesive.
[0007]
[Means for Solving the Problems]
The invention of claim 1 is an adhesive for semiconductor containing spherical fine silica having an average particle diameter of 2 to 8 μm having a hydroxyl group on the surface and ultrafine silica having an average particle diameter of 2 to 80 nm. The invention according to claim 2 is the adhesive for semiconductor according to claim 1, wherein the total content of the spherical fine silica and the fine silica is 5 to 70% by weight. The invention according to claim 3 is the adhesive for semiconductor according to claim 1 or 2, wherein the content of the spherical fine silica is larger than the content of the ultrafine silica.
[0008]
A fourth aspect of the adhesive for a semiconductor according to any one of claims 1 to 3, wherein the spherical fine-grained silica has a particle size distribution of 60% or less in terms of CV value. [5] The semiconductor according to any one of [1] to [4], wherein the amount of hydroxyl groups in the spherical fine-grained silica is 0.01 to 1.0 mmol / g with respect to the silica. Adhesive.
[0009]
The invention of claim 6 is characterized in that the base adhesive is at least one selected from a flexible adhesive and a silicone-based / flexible epoxy-based / elastomer-based flexible adhesive. It is an adhesive for semiconductors of any one of Claim 5.
[0010]
The present invention provides a flexible and tough adhesive for semiconductors containing spherical fine silica having a hydroxyl group on the surface and ultrafine silica in an optimum amount and ratio. An adhesive containing appropriate amounts of two types of silica having different particle diameters as solid adhesive components and viscosity adjusting components is excellent in flexibility, storage stability, workability, and adhesiveness. A semiconductor device assembled using the adhesive of the present invention has excellent thermal stress relaxation, high density, high reliability, and low manufacturing cost.
[0011]
The present invention uses spherical fine-grain silica having a hydroxyl group on the surface. Hydroxyl groups form physical and chemical bonds with the base resin and are effective in terms of strength and reliability. Since conventional spherical fine silica has almost no hydroxyl group, it causes problems such as resin oozing, deterioration of strength and reliability.
[0012]
The ultrafine silica does not need to have a functional group such as a hydroxyl group on the surface. Since the surface area, that is, the contact area with the base adhesive is large, there is no problem of strength reduction even if there is no compatible or reactive functional group. However, most of the commercially available products have a hydroxyl group or an alkoxy group on the surface, and are familiar with the base resin.
[0013]
The present invention uses multiple types of silica. In general, when inorganic particles are added to the adhesive, the viscosity of the adhesive is increased and the adhesive processability is extremely deteriorated. In this regard, when spherical particles are used, the increase in viscosity can be suppressed and the filling property can be increased. By using ultrafine particles, the thixotropy of the adhesive can be increased and bleeding can be prevented. That is, it is important to add spherical fine silica and ultrafine silica in a balanced manner. Moreover, when there is too much content of a silica, there exists a problem that workability falls by the viscosity increase of an adhesive agent. Therefore, the content of spherical fine silica and fine silica is preferably 5 to 70% by weight, and the content of spherical fine silica is preferably larger than the content of ultrafine silica. Furthermore, other silicas or other types of fillers may be used within a range that does not adversely affect the adhesive properties.
[0014]
When the particle diameter of silica is large, there are problems that the processability of the adhesive is impaired and stress is concentrated locally. From such a viewpoint, the spherical fine particle silica preferably has an average particle diameter of 2 to 8 μm and a CV value of 60% or less. Here, the CV value is obtained from the following equation.
CV value (%) = (D1−D2) ÷ 2Dp × 100
In the above formula, D2 represents the particle diameter when the cumulative total is 16% by weight, D1 represents the particle diameter when the cumulative total is 84% by weight, and Dp represents the average particle diameter, that is, the particle diameter when the cumulative total is 50% by weight.
[0015]
Furthermore, the spherical fine-grained silica used in the present invention preferably has an amount of hydroxyl groups on the surface of 0.01 to 1.0 mmol / g with respect to the spherical silica. When the amount of the hydroxyl group is too large, thixotropy is increased and workability is lowered, or moisture in the air is adsorbed to reduce the reliability of the semiconductor device. Incidentally, if the minimum covering area of hydroxyl groups is 1770 square meters / g and the theoretical specific surface area of spherical silica (average particle size 5 μm) is 0.5 square meters / g, the amount necessary to coat the entire surface of the spherical silica with hydroxyl groups. Is 1.6 mmol / g.
[0016]
The lower limit of the amount of hydroxyl groups was determined from the measurement accuracy of hydroxyl groups and the measured values of conventional spherical silica. This is because when the number of hydroxyl groups is small, the content becomes extremely small and the problem of measurement accuracy increases. Incidentally, when 1000 hydroxyl groups are present in the silica particles, the amount of hydroxyl groups is 1.7 × 10E-6 mmol / g when the average particle size is 2 μm. Moreover, the result of measuring the amount of hydroxyl group of conventional spherical silica, which is theoretically considered to have almost no hydroxyl group sprayed at about 2000 ° C., is a numerical value smaller than 0.01 mmol / g (detection) which is the current measurement accuracy. Below the limit).
[0017]
As the adhesive used in the present invention, a normal adhesive can be used, but it is preferable to use a flexible adhesive because it effectively acts to relieve stress. Specifically, at least one adhesive selected from a silicone-based adhesive, an epoxy-based flexible adhesive, and an elastomer-based adhesive is preferable. Each flexible adhesive preferably has at least one adhesive functional group such as an epoxy group, a carbinol group, a hydroxyl group, an amino group, an alkoxy group, and a vinyl group in the skeleton.
[0018]
As the silicone-based adhesive, a vinyl group-containing polysiloxane can be preferably used. Various additives can be added to the polysiloxane, and the polysiloxane is cured in the presence of a curing agent or a catalyst to form a silicone rubber having rubber elasticity. This rubber elasticity can relieve the thermal stress generated when the semiconductor device is assembled or used. Curing agents and catalysts are as described in the catalog of silicone manufacturers.
[0019]
Epoxy resins are generally hard and have no 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 is used. Cured products obtained by adding various additives to these resins have elasticity and can relieve stress.
[0020]
Next, examples of the elastomer adhesive include styrene, olefin, polyester, polyamide, and urethane. 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.
[0021]
You may add another adhesive component in the range which does not have a bad influence on the adhesive agent of this 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.
[0022]
Since conventional adhesives use a large amount of liquid adhesive components and ultrafine silica, they have problems such as poor adhesion accuracy, poor processability, uneven adhesion, uneven bleeding, and poor yield. .
[0023]
The adhesive of the present invention can be used in the form of a paste or solid, and can also be processed into a tape or the like. Even in the case of a tape, a stable and high adhesive force can be maintained.
[0024]
The adhesive of the present invention is one that is cured by attaching the adhesive between the materials to be bonded. That is, a semiconductor device is assembled by pasting and curing a semiconductor chip or the like with the adhesive body uncured. At that time, by using spherical fine silica having a hydroxyl group on the surface and ultrafine silica as a solid adhesive component and a viscosity adjusting component, the adhesive effect can be made larger and more stable.
[0025]
The present inventor has already announced the effect of a spherical ceramic having a hydroxyl group on the surface in Japanese Patent Application No. 10-330463. The present invention has been found to have an excellent effect by using a plurality of silicas of different sizes in combination.
[0026]
FIG. 1 shows an application of the adhesive of the present invention to BGA. The semiconductor chip 25 is attached to the substrate 28 via an adhesive 26. Reference numeral 29 denotes a solder ball. A semiconductor chip 25 is attached to a substrate 28 via an adhesive 26 and is entirely surrounded by a frame 30. The wiring 27 is connected to the outside. The adhesive 26 has a function of adhering the semiconductor chip 25 to the substrate 28 and relaxing thermal stress applied to the semiconductor device.
[0027]
FIG. 2 shows an application example to the wire bonding method. The semiconductor chip 47 is attached to the substrate 44 via an adhesive 43. Reference numeral 42 is a solder ball, and 46 is a sealing material. The wiring is connected to the outside. The adhesive 43 has a function of adhering the semiconductor chip 47 to the substrate 44 and relaxing thermal stress applied to the semiconductor device.
[0028]
Hereinafter, the present invention will be described in detail by way of study examples. Here, all parts are parts by weight.
[Example 1]
45 parts of spherical fine-grained silica A having a hydroxyl group on the surface (called high activity), 5 parts of ultrafine silica (DM-10, Tokuyama), 80 parts of cyclopentadiene-modified epoxy resin (XD-1000, Nippon Kayaku), xylene-modified 20 parts of phenolic resin (XL-225, Mitsui Chemicals) and 1 part of a catalyst (TPP-K, Hokuko Chemical Industries) were mixed and kneaded with 3 rolls for 5 minutes to produce an adhesive. This adhesive was screen printed with a thickness of 150 μm on an FPC (flexible printed circuit) in a simulated BGA, and a semiconductor chip was mounted. Thereafter, it was heated at 180 ° C. for 5 minutes. The thickness accuracy of the adhesive layer was ± 10 μm or less, and there was no problem of mounting on the substrate without seepage of the resin. Further, when the moisture absorption solder test of this simulated BGA was performed, no occurrence of defects such as cracks and popcorn was observed. Furthermore, when a moisture resistance test was performed, no defects such as circuit current leakage or disconnection occurred.
[0029]
The spherical fine silica A used in this example was produced according to JP-A-10-287415 (calcination temperature 950 ° C.), the average particle size was 3.8 μm, the CV value was 56%, and the hydroxyl group content was 0.2 mmol. / G. Ultrafine silica DM-10 is a methoxy modified product having an average particle size of 10 nm.
[0030]
The test method is as follows.
Moisture-absorbing solder test: after being left for 24 hours under conditions 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: A solder moisture absorption test is left at a temperature of 125 ° C. and a humidity of 100% for 1000 hours.
[0031]
Measurement of the amount of hydroxyl group: Silica gel is added to the specimen as an internal standard substance, the absorption at 3740 cm-1 is measured by the FT-IR diffuse reflection method, and the amount of hydroxyl group is calculated. In the method of reacting the sample with trimethylsilane and calculating the amount of hydroxyl group from the amount of silane consumed, the measurement accuracy was 0.1 mmol / g. In the future, it is considered that the optimum range of the amount of hydroxyl groups will become clearer by examining highly accurate measurement methods.
[0032]
[Example 2]
95 parts of vinyl group-containing polysiloxane (TSE260-3U, Toshiba Silicone), 5 parts of terpene polymer (YS-125, Yasuhara Chemical), 24 parts of highly active spherical fine silica B and ultrafine silica (# 200, Nippon Aerosil) An adhesive was produced in the same manner as in Example 1 using 1 part and 0.5 part of catalyst (TC-8, Toshiba Silicone). Printing showed excellent processability and no problems such as bleeding. Further, when the moisture absorption solder test and the moisture resistance test were carried out in the same manner as in Example 1, no defect occurred.
[0033]
The highly active spherical fine silica B is obtained by emulsifying an aqueous solution of sodium silicate and spheronizing it by adding an acid, filtering and drying it, and firing at 700 ° C. The average particle size was 6.2 μm, the CV value was 27%, and the amount of hydroxyl group was 0.8 mmol / g. The ultrafine silica has an average particle size of 15 nm and has a hydroxyl group.
[0034]
[Example 3]
Highly active spherical fine silica C185 parts and ultrafine silica (L-90, CABOT) 15 parts, thermoplastic elastomer (D-1117, Shell Japan) 95 parts and liquid synthetic rubber (B-1000, Nippon Soda) 5 parts Then, 0.5 part of benzoyl peroxide was kneaded with two rolls for 5 minutes to obtain a solid adhesive. Next, after a 150 μm adhesive layer was processed on the FPC by heat compression molding, a hygroscopic solder test and a moisture resistance test were performed. Thickness accuracy was good, and there was no defect in the simulated BGA test.
[0035]
Highly active spherical fine silica C is a product obtained by washing a commercial product (TSS-4, Tatsumori) with hydrofluoric acid to generate hydroxyl groups on the surface. The average particle size was 2.8 μm, the CV value was 32%, and the hydroxyl group amount was 0.15 mmol / g. The ultrafine silica has an average particle size of 8 nm and has a hydroxyl group.
[0036]
[Example 4]
47 parts of highly active spherical fine silica A, 10 parts of ultrafine silica (MIBK-ST, Nissan Chemical Industries), 90 parts of silicone-modified epoxy resin (SIN-620, Dainippon Ink and Chemicals) and polybutadiene glycol (G-1000, Japan) 10 parts of the soda were mixed and heated in a vacuum heating kneader to remove the solvent in which the ultrafine silica was dispersed. Thereafter, 1 part of a catalyst (TPP-K, Hokuko Chemical Co., Ltd.) was mixed with the mixture, and kneaded for 5 minutes with a three roll to produce an adhesive. As in Example 1, printing and hygroscopic solder / moisture resistance tests were performed, but there was no problem.
[0037]
Ultrafine silica is a 30% by weight solution of colloidal silica having an average particle size of 15 nm. This silica has a hydroxyl group on its surface, and the dispersion solvent is methyl isobutyl ketone (MIBK).
[0038]
[Comparative Example 1]
An air classification product (TSS-4, Tatsumori) of inert silica produced by a spraying method instead of the highly active spherical fine silica A in Example 1, that is, an average particle diameter having almost no hydroxyl group on the surface It processed similarly using the spherical fine-grain silica of 3.8 micrometers and CV value 51%. The obtained adhesive oozed out of the resin during screen printing, and 15% became defective during printing. When a good product was subjected to a hygroscopic solder test in the same manner as in Example 1, cracks occurred in 40%. Since there were many defects, the next moisture resistance test was stopped. Since spherical fine silica does not have a hydroxyl group on the surface, it seems that the compatibility with the base resin is poor and the separation phenomenon occurs. That is, it is considered that the interface breakage occurred due to the low adhesive strength with the base resin. In addition, the hydroxyl group measurement result of this silica showed the numerical value below a detection limit.
[0039]
[Comparative Example 2]
In Example 1, an adhesive was prepared in the same manner without adding ultrafine silica. This adhesive generated 4% bleeding failure and 1% thickness accuracy failure during printing. When a hygroscopic solder test and a moisture resistance test were performed on non-defective products, the defect rate was 0.1% or less, and there was no problem. That is, if ultrafine silica is not added, the yield at the time of processing deteriorates and the cost increases.
[0040]
[Comparative Example 3]
In Example 3, an adhesive was produced using 285 parts of highly active spherical fine silica C. This adhesive had a silica content of about 75% by weight and poor fluidity, and 7% unfilled defects occurred during compression molding.
[0041]
[Comparative Example 4]
In Example 2, instead of the highly active spherical fine silica B, an inert spherical silica (FB-6S, Denki Kagaku Kogyo) produced by a spraying method, an average particle size of 6 μm, and a CV value of 83%, Used to produce an adhesive. This adhesive produced a 20% defect when exuded during printing and a 10% defect in thickness accuracy. Silica with a large particle size has a significant adverse effect on processability. In addition, the amount of hydroxyl groups of this silica was below the detection limit.
[0042]
[Comparative Example 5]
In Example 3, instead of the highly active spherical fine-grain silica A, an adhesive was produced using silica having a hydroxyl group of 1.2 mmol / g, the firing temperature of which was lowered to 450 ° C. by the same production method. This adhesive generated 10% unfilled defects during molding. Further, the non-defective product had a moisture absorption rate of 0.3% by weight, 1.5 times that of 0.2% by weight of Example 3. If there are many hydroxyl groups, the compatibility and reactivity with the resin will become too high, leading to a decrease in fluidity and gelation. Moreover, since moisture is absorbed, there is a concern that the moisture resistance may be lowered.
[0043]
[Comparative Example 6]
In Example 1, it processed like Example 1 using 5 parts of silane coupling agents (A-186, Nippon Unicar) instead of 50 parts of 2 types of silica. This adhesive generated 45% non-uniform bleeding failure and 25% thickness accuracy failure during printing. When a few good products were evaluated by a moisture absorption solder test and a moisture resistance test, 86% of the test products were defective due to partial peeling and partial corrosion. It is apparent that when an adhesive is designed mainly based on a liquid adhesive component such as a silane coupling agent, a serious problem such as variation in adhesive strength and quality occurs.
[0044]
【The invention's effect】
The present invention provides an adhesive for processing an ultra-small and high-performance semiconductor device at low cost. That is, it is an adhesive for high-density semiconductors for bonding a semiconductor chip, a heat sink and the like to a circuit board. Furthermore, this adhesive. The thermal stress generated in the semiconductor device during assembly and use of the semiconductor device can be alleviated, and the semiconductor device manufactured according to the present invention has a stable operation and high reliability.
[0045]
Moreover, this adhesive agent is excellent in preservability, excellent in stability, and excellent in workability. Furthermore, this adhesive agent is excellent in adhesive force, and strongly adheres necessary parts to each other. Therefore, the completed semiconductor device is structurally strong and robust.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an embodiment of the present invention.
FIG. 2 is an example in which the present invention is applied to wire bonding.
[Explanation of symbols]
25, 47 Semiconductor chips 28, 41, 44 Substrate 29, 42 Solder balls 26, 43 Adhesive 46 Sealing resin 27, 45 Wiring 30 Frame

Claims (5)

Spherical fine silica having an average particle diameter of 2 to 8 μm having hydroxyl groups on the surface, and the amount of surface hydroxyl groups calculated by measuring absorption at 3740 cm ⁻¹ is 0.01 to 1.0 mmol / g with respect to the silica. The adhesive for semiconductors containing the spherical fine -particle silica which is these, and the ultrafine silica whose average particle diameter is 2-80 nm. 2. The adhesive for semiconductor according to claim 1, wherein the total content of spherical fine silica and ultrafine silica is 5 to 70 wt%. The semiconductor adhesive according to claim 1 or 2, wherein the content of the spherical fine silica is greater than the content of the ultrafine silica. 4. The adhesive for semiconductor according to claim 1, wherein the spherical fine silica has a particle size distribution of 60% or less in terms of CV value. 5. The underlying adhesive, according to any one of claims 1 to 4, characterized in that at least one selected from silicone-based adhesives, flexible epoxy adhesives, elastomeric adhesives Adhesive for semiconductors.

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