WO2003035762A1

WO2003035762A1 - Curable liquid silicone composition and a semiconductor device prepared using the composition

Info

Publication number: WO2003035762A1
Application number: PCT/JP2002/010308
Authority: WO
Inventors: Kimio Yamakawa; Jyunji Nakanishi; Katsutoshi Mine
Original assignee: Dow Corning Toray Silicone Co., Ltd.
Priority date: 2001-10-26
Filing date: 2002-10-02
Publication date: 2003-05-01
Also published as: TW553895B; JP2003128920A

Abstract

A curable liquid silicone composition is characterized by good flowability and impregnating ability, even though said composition contains an increased amount of fine silica powder added for decreasing the coefficient of thermal expansion in a cured silicone body formed by curing the composition. The fine silica powder has a ratio of isolated silanol groups to the internal silanol groups equal to or exceeding 0.01. A semiconductor device is coated with the aforementioned composition and is characterized by high reliability.

Description

DESCRIPTION

CURABLE LIQUID SILICONE COMPOSITION AND A SEMICONDUCTOR DEVICE

PREPARED USING THE COMPOSITION

Technical Field [0001] The present invention relates to a curable liquid silicone composition and to a semiconductor device produced with the use of the aforementioned composition. More specifically, the invention relates to a silicone composition, which has a limited viscosity caused by thixotropy and is characterized by good flowabihty and impregnating ability, even though the silicone composition contains an increased amount of fine silica powder added for decreasing the coefficient of thermal expansion in a cured silicone body. The invention further relates to a semiconductor device coated with the aforementioned composition.

Background Art

[0002] A known curable liquid silicone composition is combined with a large amount of fine powder silica to increase mechanical strength and decrease coefficient of thermal expansion. For example, a composition that consists of a liquid organopolysiloxane with silicon-bonded alkenyl groups, a liquid organopolysiloxane with silicon-bonded hydrogen atoms, a hydrosilylation-reaction metal catalyst, and a fine silica powder; is suitable for forming low-stress silicone articles, which in a cured state possess improved resistance to heat and to moisture and, therefore, are used in the production of electrical and electronic devices as heat-radiation adhesives, potting agents, protective-coating agents, and especially as protective coatings and underfill agents for semiconductor elements. [0003] Recent developments in the semiconductor manufacturing industry are accompanied by miniaturization of semiconductor chips, increase in their reliability, narrowing of the pitch between conductive wires in patterns, and narrowing of distances between the semiconductor chips and substrates. Under conditions of these new developments, the use of curable liquid silicone compositions with large amounts of fine powder silica becomes a problem because such compositions have increased viscosities caused by thixotropy, as well as by lower flowabihty and impregnating ability. As a result, it becomes difficult to fill the spaces between the conductive wires or under the wires, or the spaces between the semiconductor chips and their respective substrates. The reduced filling and impregnating ability of the aforementioned composition leads to decrease in reliability of semiconductor elements coated with this composition. [0004] It is an object of the present invention to provide a curable liquid silicone composition which, even though containing an increased amount of fine silica powder added for decreasing the coefficient of thermal expansion in a cured silicone body, has a limited viscosity caused by thixotropy and is characterized by good flowabihty and impregnating ability. Another object is to provide a semiconductor device, which is coated with the aforementioned composition and is characterized by high reliability.

Disclosure of Invention [0005] A curable liquid silicone composition of the present invention contains a fine silica powder with a ratio of isolated silanol groups to the internal silanol groups of the fine silica powder equal to or exceeding 0.01. A semiconductor device of the present invention has a semiconductor element coated with the aforementioned curable liquid silicone composition.

Brief Description of Drawings

[0006] Fig. 1 is a sectional view of a semiconductor device corresponding to one example of the invention.

[0007] Fig. 2 is a sectional view of a semiconductor device corresponding to another example of the invention. [0008] The reference numerals used in the description are as follows.

1 semiconductor element

2 circuit board

3 circuit conductor

4 wire 5 external lead

6 cured body made from the curable liquid siloxane composition

7 frame

8 bumps

Detailed Description of the Invention [0009] The composition of the invention has a fine silica powder with a ratio of isolated silanol groups to the internal silanol groups of said fine silica powder equal to or exceeding 0.01, preferably equal to or exceeding 0.05, more preferably equal to or exceeding 0.10, even more preferably equal to or exceeding 0.15, and in particular, preferably equal to or exceeding 0.20. If the aforementioned ratio of isolated silanol groups to the internal silanol groups is below the lower recommended limit, the obtained curable liquid silicone composition will have increased viscosity caused by thixotropy along with a reduced flowabihty and impregnating ability. Although there are no special restrictions with regard to the upper limit for the aforementioned ratio of isolated silanol groups to the internal silanol groups, it is recommended that the aforementioned ratio does not exceed 1.0. hi the context of the present invention, the internal silanol groups are those silanol groups which in infrared absorption spectra obtained by means of a spectrophotometer have absorption peaks near 3650 cm^-1, while the isolated silanol groups are silanol groups which in infrared absorption spectra obtained by means of a spectrophotometer have absorption peaks near

3745 cm^"1. [0010] The aforementioned ratio of isolated silanol groups to the internal silanol groups can be adjusted via surface treatment and calcining conditions during manufacture of the fine powder silica. The aforementioned ratio of isolated silanol groups to the internal silanol groups can be determined as a ratio of the height of the peak obtained for the internal silanol groups by means of a spectrophotometer (near 3650 cm^-1) to the height of the peak obtained by the same method for the isolated silanol groups (near 3745 cm"¹), or the above ratio can be determined as a ratio of areas of the aforementioned peaks. Furthermore, although there are no special restrictions with regard to the particle diameters of the fine powder silica, it is recommended that the average diameter of these particles be within the range of 0.1 to 20 micrometers (μm). [0011 ] The fine silica powder suitable for the purposes of the invention may comprise a crystalline fine silica powder or an amorphous fine silica powder. The powder particles may have a spherical or irregular shape. The shape which is most suitable for the amorphous fine powder silica is spherical. The fine powder silica may be represented by a fumed fine powder silica, fused fine powder silica, or a fine powder silica produced by deflagration of a metal silicon powder in an oxygen-containing environment. Most preferable for the invention is fine powder silica produced by deflagration of a metal silicon powder in an oxygen-containing environment. The surfaces of the silica particles can be treated with an organohalosilane, organoalkoxysilane, organosilazane, or a similar organic silicon compound, or with organic compounds of other types. [0012] Although there are no special restrictions with regard to amounts in which the fine powder silica can be added to the composition of the invention, it is recommended that this amount be within the range of 10 to 500 parts by weight, preferably 20 to 500 parts by weight, for each 100 parts by weight of the organopolysiloxane which is the main component of the composition of the invention. If the fine powder silica is used in an amount smaller than the lower recommended limit of the above range, it will either decrease mechanical strength or increase the coefficient of thermal expansion in a cured body. If the amount of the fine powder silica used exceeds the upper recommended limit, the obtained curable silicone composition will have low flowabihty. [0013] There are no special restrictions with regard to the mechanism suitable for curing the composition of the invention. The composition can be cured by a hydrosilylation reaction, condensation reaction, or a radical reaction with the use of an organic peroxide. The most suitable is curing based on a hydrosilylation reaction. The hydrosilylation- reaction-curable liquid silicone composition is one which comprises at least the following components:

100 parts by weight of (A) a liquid organopolysiloxane having at least two silicon- bonded alkenyl groups per molecule; 0.001 to 100 parts by weight of (B) a liquid organopolysiloxane having at least two silicon-bonded hydrogen atoms per molecule;

(C) a hydrosilylation-reaction metal-type catalyst (used in an amount such that the content of metal atoms (in weight units) in the catalyst is 0.01 to 1,000 parts per million (ppm) relative to the total weight of the composition); and 10 to 500 parts by weight of (D) a fine silica powder having a ratio of isolated silanol groups to the internal silanol groups equal to or exceeding 0.01. [0014] The liquid organopolysiloxane (A) contains at least two silicon-bonded alkenyl groups per molecule. Component (A) may have a linear, a partially-branched linear, branched, cyclic, or net-like molecular structure. The silicon-bonded alkenyl groups of this component may be bonded to molecular terminals or to molecular side chains, or both. The following groups, other than the aforementioned alkenyl groups, can be bonded to silicon atoms in component (A): substituted or non-substituted monovalent hydrocarbon groups, such as a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, or a similar alkyl group; a phenyl group, tolyl group, xylyl group, naphthyl group, or a similar aryl group; a benzyl group, phenethyl group, or a similar aralkyl group; a chloromethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, or a similar halogen-substituted alkyl group. The most preferable are a methyl group and phenyl group.

[0015] At a temperature of 25°C component (A) is liquid. Although there are no special limitations with regard to viscosity of this component in a liquid state, it is recommended that this viscosity be within the range of 10 to 1,000,000 milliPascal-seconds (mPa-s), preferably within the range of 100 to 50,000 mPa-s. This is because viscosity of component (A) below the lower recommended limit at 25 °C will adversely affect physical properties of a cured body produced from the aforementioned composition. If viscosity of component (A) exceeds the upper recommended limit of the range, the composition of the invention will have low flowabihty. [0016] The liquid organopolysiloxane of component (B) is a curing agent of the aforementioned composition. Component (B) has at least two silicon-bonded hydrogen atoms per molecule. Component (B) may have a linear, partially-branched linear, branched, or a net-like molecular structure. Hydrogen atoms can be bonded to molecular terminals or to molecular side chains. The following groups, other than the aforementioned hydrogen atoms, can be bonded to silicon in component (B): substituted or non-substituted monovalent hydrocarbon groups, such as a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, or a similar alkyl group; a phenyl group, tolyl group, xylyl group, naphthyl group, or a similar aryl group; a benzyl group, phenethyl group, or a similar aralkyl group; a chloromethyl group, 3-chloropropyl group, 3,3,3- trifluoropropyl group, or a similar halogen-substituted alkyl group. The most preferable are a methyl group and phenyl group.

[0017] At a temperature of 25 °C component (B) is liquid. Although there are no special limitations with regard to viscosity of this component in a liquid state, it is recommended that this viscosity be within the range of 0.1 to 1,000,000 mPa-s, preferably within the range of 1 to 50,000 mPa-s. This is because with viscosity below the lower recommended limit at 25°C component (B) can easily become volatile. If viscosity of component (B) exceeds the upper recommended limit of the range, the composition of the invention will have low flowabihty. [0018] It is recommended to use component (B) in an amount of 0.001 to 100 parts by weight for each 100 parts by weight of component (A). If component (B) is used in an amount smaller than the lower recommended limit, there will be a possibility of incomplete curing of the obtained silicone composition. If component (B) is used in an amount exceeding the upper recommended limit, this will impair physical properties in a cured body formed from the composition.

[0019] A hydrosilylation-reaction metal catalyst of component (C) is a catalyst used for acceleration of a hydrosilylation reaction of the aforementioned composition. This catalyst can be represented by a platinum catalyst, rhodium catalyst, or palladium catalyst. The platinum catalyst is most preferable. The following are examples of such platinum catalysts: a platinum fine powder, platinum black, platinum-carrying silica powder, platinum-carrying activated charcoal, chloroplatinic acid, an alcoholic solution of a chloroplatinic acid, an olefin complex of platinum, an alkenylsiloxane complex of platinum, or a similar platinum-type catalyst. [0020] It is recommended to use component (C) in such an amount that the content of metal atoms (in weight units) in the catalyst is within the range of 0.01 to 1,000 ppm relative to the total weight of the composition. If component (C) is used in a smaller amount than the lower recommended limit, it will be difficult to provide sufficient acceleration of the hydrosilylation reaction. If component (C) is used in an amount exceeding the upper recommended limit, it will not further accelerate the hydrosilylation reaction but rather will cause coloration of the cured body formed from the composition. [0021] The silica fine powder of component (D) is characterized by the fact that a ratio of isolated silanol groups to the internal silanol groups of said fine silica powder is equal to or exceeds 0.01, preferably equal to or exceeds 0.05, more preferably equal to or exceeds 0.10, even more preferably equal to or exceeds 0.15, and in particular preferably equal to or exceeds 0.20. If the aforementioned silica fine powder is used in an amount less than the lower recommended limit of the above range, the obtained curable liquid silicone composition will have viscosity increased because of thixotropy, so that the composition will have low flowabihty and reduced impregnating ability. Although there are no special restrictions with regard to the upper limit of a ratio of isolated silanol groups to the internal silanol groups, it is recommended that the aforementioned ratio does not exceed 1.0. The internal silanol groups are those silanol groups, which in infrared absorption spectra obtained by means of a spectrophotometer have absorption peaks near 3650 cm^-1, while the isolated silanol groups are silanol groups, which in infrared absorption spectra obtained by means of a spectrophotometer have absorption peaks near 3745 cm^-1. The aforementioned ratio of isolated silanol groups to the internal silanol groups can be adjusted via surface treatment and sintering conditions during manufacture of the fine powder silica. The aforementioned ratio of isolated silanol groups to the internal silanol groups can be determined as a ratio of the height of the peak obtained for the internal silanol groups by means of a spectrophotometer (near 3650 cm^-1) to the height of the peak obtained by the same method for the isolated silanol groups (near 3745 cm^-1), or the above ratio can be determined as a ratio of surface areas of the aforementioned peaks. Furthermore, although there are no special restrictions with regard to the particle diameters of the fine powder silica, it is recommended that the average diameter of these particles be within the range of 0.1 to 20 μm. Silica fine powders suitable for use as component (D) are the same as exemplified above. [0022] It is recommended to use component (D) in an amount of 10 to 500 parts by weight, preferably 20 to 500 parts by weight for each 100 parts by weight of component (A). If component (D) is used in an amount smaller than the lower recommended limit of the above range, a cured body formed from the composition of the invention will have low mechanical strength and an increased coefficient of thermal expansion. If the amount of component (D) exceeds the upper recommended limit, the obtained curable silicone composition will have low flowabihty.

[0023] The composition of the invention is prepared at least from components (A) through (D). However, for adjusting the speed of the hydrosilylation reaction, the composition can be additionally combined with a 3-methyl-l-butyn-3-ol, 3,5-dimethyl-l- hexyn-3-ol, phenyl butynol or a similar alkyne alcohol; 3-methyl-3-penten-l-yne, 3,5- dimethyl-3-hexen-l-yne, or a similar enyne compound; l,3,5,7-tetramethyl-l,3,5,7- tetravinyl cyclotetrasiloxane, l,3,5,7-tetramethyl-l,3,5,7-tetrahexenylcyclotetrasiloxane, benzotriazol, or a similar reaction retarder. There are no special restrictions with regard to the amount in which the aforementioned reaction retarder should be used. It may be recommended, however, to use it in the amount of 0.0001 to 5 parts by weight for each 100 parts by weight of component (A) .

[0024] Furthermore, to improve adhesive properties of the composition, it can be combined with an adhesion-imparting agent, such as an organic silicon compound having at least one silicon-bonded alkoxy group per molecule. The following are examples of such alkoxy groups: a methoxy group, ethoxy group, propoxy group, butoxy group, or a methoxyethoxy group. The methoxy group is the most preferable. The following are groups other than the aforementioned silicon-bonded alkoxy groups that may be contained in the aforementioned organic silicon compound: a substituted or non-substituted monovalent hydrocarbon group, such as a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, or a similar alkyl group; a vinyl group, allyl group, butenyl group, pentenyl group, hexenyl group, or a similar alkenyl group; a phenyl group, tolyl group, xylyl group, naphthyl group, or a similar aryl group; a benzyl group, phenethyl group, or a similar aralkyl group; a chloromethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, or a similar halogenated alkyl group; an epoxy- containing monovalent organic group, such as a 3-glycidoxypropylgroup, 4-glycidoxy butyl group, or a similar glycidoxy alkyl group; a 2-(3,4-epoxycyclohexyl) ethyl group, 3- (3,4-epoxycyclohexyl) propyl group, or a similar epoxycyclohexylalkyl group; 4- oxiranylbutyl group, 8-oxiranyloctyl, or a similar oxiranylalkyl group; an acryl-containing monovalent organic group, such as a 3-methacryloxypropyl; or a hydrogen atom. From the point of view of good adhesion to substrates of various types, it is recommended to use organic silicon compounds having the epoxy-containing monovalent organic groups. The aforementioned organic silicon compounds can be exemplified by silane compounds and siloxane compounds. The aforementioned siloxane compounds may have a linear, partially-branched linear, branched, or net-like molecular structure. The most preferable are the linear, branched, and net-like structures. The following are examples of the aforementioned organic silicon compounds: 3-glycidoxypropyltrimethoxysilane, 2-(3,4- epoxychlorohexyl) ethyl trimethoxysilane, 3-methacryloxypropyltrimethoxysilane, or a similar silane; a siloxane group containing in one molecule at least one of the following ~ a silicon-bonded alkenyl group, a silicon-bonded hydrogen atom, or a silicon-bonded alkoxy group, a mixture composed of a siloxane or a silane compound having at least one silicon-bonded alkoxy group and a siloxane compound having in one molecule at least one of the following — a silicon-bonded hydroxy group or a silicon-bonded alkenyl group; a siloxane compound represented by the following formula:

{(CH₂ = CH)CH₃Si0₂/₂}a (CH₃O_1/2)b {CH₂-CHCH₂O (CH₂)₃SiO₃/2}c

O where a, b, and c are positive numbers; or

{(CH₂ = CH)CH₃SiO₂/2}_a (CH₃Oι/₂)_b {CH₂-CHCH₂O (CH₂)₃SiO₃/2}c

O

where a, b, c, and d are positive numbers. It is recommended that the aforementioned adhesion-imparting agent be a low-viscosity liquid. Although there are no special restrictions with regard to the viscosity of this agent, it is recommended that its viscosity at 25°C be within the range of 1 to 500 mPa-s. There are no special restriction also with regard to the amount in which this agent should be used. It is recommended, however, to use it in an amount of 0.01 to 10 parts by weight for each 100 parts by weight of component (A).

[0025] addition to the fine silica powder, the composition may include some optional components, such as a heat conductive filler, e.g., a quartz powder, an aluminum powder, aluminum nitride powder, boron nitride powder, etc.; an electrically conductive filler, such as silver powder, copper powder, etc.; an organic resin fine powder such as a silicone resin, fluororesin, etc.; as well as dyes, pigments, flame retarders, solvents, or the like. [0026] The composition of the invention is prepared by mixing components (A) through (D), if necessary, with an addition of some optional components. It is also possible first to premix component (D) with the entire or a part of component (A) and then to add and mix other components.

[0027] A cured silicone body can be produced by subjecting the aforementioned composition to a hydrosilylation reaction at room temperature or with heating. To increase the speed of the hydrosilylation reaction, it should be carried out at a temperature from 50 to 250°C, preferably from 80 to 200°C. The aforementioned cured body can be formed in a resin, rubber, or a gel state. The rubber and gel states are preferable. [0028] Even though the curable liquid silicone composition of the invention contains a large amount of a fine powder silica added for decrease in the coefficient of thermal expansion, the curable liquid silicone composition is characterized by low viscosity, an increase of which due to thixotropy is limited, as well as by improved flowabihty and impregnating ability.

[0029] The following is a detailed description of a semiconductor device of the present invention. This device consists of a semiconductor element coated with the aforementioned curable liquid silicone composition. The semiconductor element may be a diode, transistor, thyrister, monolithic integrated circuit (IC), or a semiconductor element in a hybrid IC. The semiconductor device itself can be represented by a diode, transistor, thyrister, monolithic IC, hybrid IC, large scale integrated circuit (LSI), or a very large scale integrated circuit (VLSI).

[0030] Figure 1 is a cross-sectional view illustrating an example of a semiconductor devices of the invention in the form of LSI. The semiconductor device shown in Fig. 1 has a semiconductor element 1 supported by a circuit board 2. The semiconductor element 1 and a circuit conductor 3, which is connected to an external lead 5, are electrically interconnected via a conductive wire 4. The semiconductor element 1 is coated with a cured body 6 of a curable liquid silicone composition that fills a plastic-made frame 7. The circuit board 2 can be made from a polyimide resin, bis-maleimidetriazine, glass-fiber- reinforced epoxy resin, bakelite resin, phenol resin, or a similar organic resin; alumina or a similar ceramic; or copper, aluminum, or a similar metal. The circuit conductor 3 can be made from gold, copper, or a silver-palladium alloy. The conductive wire 4 can be made of gold, gold alloy, aluminum, or copper. In addition to the semiconductor element 1, the circuit board 2 may support resistors, capacitors, coils, or other elements of electronic devices. [0031] The aforementioned semiconductor device can be produced by placing the semiconductor element 1 onto the circuit board 2, electrically connecting the semiconductor element 1 and the circuit conductor 3 by the wire 4, surrounding the semiconductor 1 with the frame 7, and filling the frame with the curable liquid silicone composition. The composition is cured, e.g., by heating it to a temperature from 50 to 200°C. [0032] Figure 2 is a cross-sectional view illustrating an example of a semiconductor device of the invention in the form of LSI. The semiconductor device shown in Fig. 2 consists of a semiconductor element 1 placed onto a circuit board 2 which is provided with external leads 5 and circuit conductors 3 formed by printing on the surface of the board. The semiconductor element 1 and the circuit conductors 3 are electrically connected to each other via conductive bumps 8. The bumps 8 can be made from gold, gold alloy, aluminum, silver, silver alloy, nickel, or the like. The space between the semiconductor element 1 and the circuit board 2 is filled with a cured body of a curable liquid silicone composition used as an underfill agent. [0033] The last mentioned semiconductor device can be produced by placing the semiconductor element 1 onto a circuit board 2. After the semiconductor element 1 and the circuit conductor 3 are electrically connected via the bumps 8, the space between the semiconductor element 1 and the circuit board 2 is filled with the curable liquid silicone composition, which is then cured by heating at a temperature from 50 to 200°C.

EXAMPLES

[0034] The curable liquid silicone composition and the semiconductor device of the present invention will now be described in more detail with reference to the ensuing practical examples. The values of viscosities are measured at 25°C. Given below are methods used for determining ratios of isolated silanol groups to the internal silanol groups of the fine silica powder, viscosities of the curable liquid silicone composition, thixotropy, coefficients of thermal expansion of a cured body, and reliability of the semiconductor devices.

Ratio of Isolated Silanol Groups to the Internal Silanol Groups of the Fine Silica Powder [0035] The aforementioned ratio of isolated silanol groups to the internal silanol groups was determined by measuring infrared spectrum absorption of internal silanol groups

(3650 cm^-1) and of isolated silanol group (3745 cm^-1), determimng absorption peak heights (infrared absorption intensities from the base line to the peak top) for groups of both types, and calculating a ratio of the obtained peaks (ratio of infrared absorption intensities).

Viscosity and Thixotropy of the Curable Liquid Silicone Composition [0036] Niscosity of the curable liquid silicone composition of the invention was obtained by measurements on a rotary-type viscosimeter with the use of a spindle at 30 revolutions per minute (rpm). Similar measurements were carried out at 6 rpm, and a ratio of the viscosity measured at 6 rpm to that measured at 30 rpm was used as a criterion for evaluation of thixotropy. The greater is the ratio, the greater is the thixotropy.

Coefficient of Thermal Expansion of the Cured Silicone Body

[0037] The coefficient of thermal expansion of the cured silicone body was measured on solid specimens at temperatures within the range of 25°C to 200°C with the use of an instrument for measuring coefficients of thermal expansion. Reliability of Semiconductor Device (No. 1)

[0038] The semiconductor device shown in Fig. 1 was produced by the following method. A semiconductor element 1 was placed onto a circuit board 2 made from a glass-fiber- reinforced epoxy resin and having external leads 5 and circuit conductors 3 printed on its surface. The semiconductor element 1 and the circuit conductors 3 were then electrically interconnected by metal wires 4. The semiconductor element 1 was surrounded by a resin- made frame 7. After the frame 7 was filled with the curable liquid silicone composition via a dispenser, the unit was placed into an oven and heated with circulation of air at 150°C. As a result, the composition was cured. Twenty semiconductors produced by the method described above were subjected to 500 thermal cycles. Each thermal cycle consisted of 30 minutes (min.) cooling at -65°C and 30 min. heating at 150°C. After completion of the thermal cycle test, conductivity between the external leads was checked, and a percentage of defective units was determined.

Reliability of Semiconductor Device (No. 2) [0039] The semiconductor device shown in Fig. 2 was produced by the following method. A semiconductor element 1 was placed onto a circuit board 2 made from a glass-fiber- reinforced epoxy resin and having on its edges external leads 5 and circuit conductors 3 printed on its surface. The semiconductor element 1 and the circuit conductors 3 were then electrically interconnected through metal bumps 8, and the space between the semiconductor element 1 and the circuit board 2 was filled with the curable liquid silicone composition from a dispenser via the edge of the semiconductor element 1. Twenty semiconductors produced by the method described above were subjected to a high- temperature, high-humidity test for 96 hours in an environment of 121 °C and 100% RH. After completion of the aforementioned test, conductivity between the external leads was checked in a 5 hour conductivity test, and a percentage of defective units was determined.

Practical Example 1

[0040] 60 parts by weight of a mixture composed of 65 wt.% of a dimethylpolysiloxane having both molecular terminals capped with dimethylvinylsiloxy groups and 35 wt.% of an organopolysiloxane resin consisting of (CH2=CH)(CH3)2 SiOι/2 units, (CH3)3SiO 2 units, and Siθ4/2 units (mixture viscosity = 6,000 mPa-s; content of silicon-bonded vinyl groups = 0.80 wt.%) was combined with 35 parts by weight of a spherical silica fine powder produced by deflagration of a metal silicon dust in an oxygen-containing environment (the ratio of isolated silanol groups to the internal silanol groups =0.26; average particle diameter = 1.5 μm). After the components were uniformly mixed, a pastelike product was obtained. [0041] A liquid silicone rubber composition was prepared by uniformly mixing the entire mass of the aforementioned paste with 3.0 parts by weight of a 20 mPa-s viscosity methylhydrogenpolysiloxane having both molecular terminals capped with trimethylsiloxy groups (the content of the silicon-bonded hydrogen atoms = 0.75 wt.%), a platinum complex of 1,3-divinyltetramethyldisiloxane (the content of the platinum metal of the complex in the entire composition in terms of weight was equal to 5 ppm), 0.01 parts by weight of 3 -phenyl- l-butyn-3-ol, and 1.0 part by weight of a 20 mPa-s viscosity adhesion- imparting agent represented by the following general formula:

{(CH₂ = CH) CH₃SiO_2/2}₀.₄₇(CH₃O_1/2)o.₃₅{CH₂ - CHCH₂O (CH₂)₃SiO_3/2}₀.₁₈

O

[0042] The viscosity and thixotropy of the obtained composition, as well as the coefficient of thermal expansion of the silicon rubber are shown in Table 1. Results of reliability testing of the semiconductor device produced with the use of the aforementioned composition are also shown in Table 1.

Comparative Example 1

[0043] A liquid silicone rubber composition was prepared by the same method as in Practical Example 1, with the exception that spherical silica fine powder produced by deflagration of a metal silicon dust in an oxygen-containing atmosphere (characterized by an average particle diameter of 5μm and by a ratio of isolated silanol groups to the internal silanol groups =0.005) was used instead of the spherical fine powder of Practical Example 1. The viscosity and thixotropy of the obtained composition, as well as the coefficient of thermal expansion of the silicon rubber are shown in Table 1. Results of reliability testing of the semiconductor device [produced with the use of the aforementioned composition] are also shown in Table 1. Comparative Example 2

[0044] A liquid silicone rubber composition was prepared by the same method as in Comparative Example 1, with the exception that the composition was prepared with 27 parts by weight of the spherical silica fine powder and with 68 parts by weight of a mixture prepared from 65 wt.% of a dimethylpolysiloxane having both molecular terminals capped with dimethylvinylsiloxy groups and 35 wt.% of an organopolysiloxane resin consisting of

units, (CH3)3SiOι/2 units, and Siθ4/2 units. The viscosity and thixotropy of the obtained composition, as well as the coefficient of thermal expansion of the silicon rubber are shown in Table 1. Results of reliability test of the semiconductor device produced with the use of the aforementioned composition are also shown in Table 1.

Practical Example 2

[0045] A paste-like product was obtained by uniformly mixing 35 parts by weight of a spherical silica fine powder (characterized by an average particle diameter of 2 μm and by a ratio of isolated silanol groups to the internal silanol groups =0.45) synthesized by a sol- gel method and then baked with 60 parts by weight of a mixture (viscosity = 6,000 mPa-s; content of the silicon-bonded vinyl groups = 0.80 wt.%) composed from 65 wt.% of a dimethylpolysiloxane having both molecular terminals capped with dimethylvinylsiloxy groups and 35 wt.% of an organopolysiloxane resin consisting of

units, (CH₃)₃SiOι/2 units, and Siθ4/2 units. [0046] A liquid silicone rubber composition was prepared by uniformly mixing the entire mass of the aforementioned paste with 3.0 parts by weight of a 20 mPa-s viscosity methylhydrogenpolysiloxane having both molecular terminals capped with trimethylsiloxy groups (the content of the silicon-bonded hydrogen atoms = 0.75 wt.%), a platinum complex of 1,3-divinyltetramethyldisiloxane (the content of the platinum metal of the complex in the entire composition in terms of weight was equal to 5 ppm), 0.01 parts by weight of 3 -phenyl- l-butyn-3-ol, and 1.0 part by weight of a 20 mPa-s viscosity adhesion- imparting agent represented by the following general formula:

{(CH₂ = CH) CH₃SiO_2/2}o.₄₇(CH₃O_1/2)o.35{CH₂ - CHCH₂O (CH₂)₃SiO_3/2}₀.ι₈

^"6^" [0047] The viscosity and thixotropy of the obtained composition, as well as the coefficient of thermal expansion of the silicon rubber are shown in Table 1. Results of reliability test of the semiconductor device produced with the use of the aforementioned composition are also shown in Table 1.

Comparative Example 3

[0048] A liquid silicone rubber composition was prepared by the same method as in Practical Example 2, with the exception that spherical silica fine powder produced by gel- sol synthesis, baked, and then surface treated with a 3-glycidoxypropyltrimethoxysilane (characterized by an average particle diameter of 2 μm and by a ratio of isolated silanol groups to the internal silanol groups =0.001) was used instead of the spherical fine powder of Practical Example 2. The viscosity and thixotropy of the obtained composition, as well as the coefficient of thermal expansion of the silicon rubber are shown in Table 1. Results of reliability test of the semiconductor device produced with the use of the aforementioned composition are also shown in Table 1.

Comparative Example 4

[0049] A liquid silicone rubber composition was prepared by the same method as in Comparative Example 3, with the exception that the composition was prepared with 25 parts by weight of the spherical silica fine powder and with 70 parts by weight of a mixture prepared from 65 wt.% of a dimethylpolysiloxane having both molecular terminals capped with dimethylvinylsiloxy groups and 35 wt.% of an organopolysiloxane resin consisting of

units, (CH3)3SiOι/2 units, and Siθ4/2 units. The viscosity and thixotropy of the obtained composition, as well as the coefficient of thermal expansion of the silicon rubber are shown in Table 1. Results of reliability test of the semiconductor device [produced with the use of the aforementioned composition] are also shown in Table 1. Table 1

Industrial Applicability

[0050] The present invention provides a curable liquid silicone composition which, even though containing an increased amount of fine silica powder added for decreasing the coefficient of thermal expansion in a cured silicone body, has a limited viscosity caused by thixotropy and is characterized by good flowabihty and impregnating ability. Therefore the composition is suitable for use as an adhesive for electric and electronic devices, a potting agent, protective-coating agent, and an underfill agent. The most suitable applications are as a protective coating agent for semiconductor devices, and an underfill agent for filling spaces between semiconductor devices and substrates. A semiconductor device coated with the aforementioned composition is characterized by high reliability.

Claims

Claims:

1. A curable liquid silicone composition is characterized by a fine silica powder with a ratio of isolated silanol groups to internal silanol groups of said fine silica powder equal to or exceeding 0.01.

2. The curable liquid silicone composition of claim 1, where said fine silica powder has spherical particles with an average particle diameter from 0.1 to 20 μm.

3. The curable liquid silicone composition of claim 1, where said fine silica powder comprises a fine powder produced by deflagration of a metal-silicon dust in an oxygen- containing atmosphere.

4. The curable liquid silicone composition of claim 1, where said curable liquid silicone composition comprises an organopolysiloxane as a main component and said fine silica powder is used in an amount of 10 to 500 part by weight for each 100 parts by weight of the organopolysiloxane.

5. The curable liquid silicone composition of claim 1, where the curable liquid silicone composition is hydrosilylation-reaction-curable.

6. A curable liquid silicone composition characterized by:

100 parts by weight of (A) a liquid organopolysiloxane having at least two silicon- bonded alkenyl groups per molecule;

0.001 to 100 parts by weight of (B) a liquid organopolysiloxane having at least two silicon-bonded hydrogen atoms per molecule;

(C) a hydrosilylation-reaction metal-type catalyst in an amount such that the content of metal atoms, in weight units, in the catalyst is 0.01 to 1,000 ppm relative to total weight of the composition; and

10 to 500 parts by weight of (D) a fine silica powder where a ratio of isolated silanol groups to the internal silanol groups of said fine silica powder is equal to or exceeds 0.01.

7. A method for preparing the composition of claim 6, characterized by: (1) premixing component (D) with a part or with the entire component (A) and (2) mixing components (B) and (C) with the product of step (1).

8. A semiconductor device comprising a semiconductor element coated with the curable liquid silicone composition according to any of claims 1 to 6.

9. A method characterized by:

(1) coating a semiconductor element with a composition according to any of claims 1 to 6, and

(2) curing the composition.

10. The method of claim 9, where the semiconductor element is selected from a diode, transistor, thyrister, monolithic integrated circuit, or a semiconductor element in a hybrid integrated circuit.

11. The method of claim 9, where step (2) is carried out by heating the composition to a temperature of 50 to 250°C.

12. Use of a composition according to any of claims 1 to 6 for an industrial application selected from an adhesive for electric and electronic devices, a potting agent, a protective- coating agent, or an underfill agent.