JPH08316374A - Semiconductor device - Google Patents

Abstract

(57) [Abstract] [Structure] Printed wiring board 3 having semiconductor element mounting surface
Has a mounting surface on which solder balls 4 are arranged in a grid pattern on the back surface of the mounting surface, and the semiconductor element is mounted and fixed on the mounting surface of the semiconductor element electrically connected to the mounting surface. In a semiconductor device having a structure in which a wiring board is electrically connected and at least a part of a semiconductor element mounting surface including a semiconductor element and an electrical connection portion is molded and sealed with a resin composition 6, a sealing layer Is molded at a temperature not higher than the glass transition temperature of the encapsulating resin composition 6. [Effect] Since the resin composition is sealed with a resin composition having a glass transition temperature equal to or higher than the molding temperature, the shrinkage rate during molding is small, the amount of package warpage is small, and the solder ball mounting surface is excellent in flatness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball grid array (BGA) type semiconductor device having a solder bump on a mounting surface and a resin mounting surface for mounting a semiconductor element.

[0002]

2. Description of the Related Art With the recent trend toward miniaturization and high performance of electronic equipment, semiconductor devices constituting electronic equipment and multilayer printed wiring boards for mounting the same have been made smaller, thinner, higher performance, higher speed and higher performance. Reliability is required. For example, semiconductor devices are shifting from pin-insertion packages to surface-mount packages due to the demand for smaller and thinner semiconductor devices, and a mounting method called bare chip mounting, in which semiconductor elements are directly mounted on a printed circuit board, has also been studied. ing. Also, as a method for improving the packaging density of these, COB (Ch
ip on board), FC (Flip chip), TCP (Tape carrie)
r package) is known.

Due to demands for high-density mounting, high pin count, and high speed, the quad flat package (QFP) has a narrow lead pitch and has leads in four directions.
Package), a pin grid array type package (PGA package) in which connection terminals are provided on the entire mounting surface of the package, and a solder ball grid array type package (BGA package).

The basic structure of the BGA package is USP5
216278, JP-A-6-202955, Japanese Patent Application No. 4-508695, and JP-A-62-177753. The BGA has a structure in which a semiconductor element is directly mounted on a carrier substrate, solder balls are arranged in a grid on the back surface, and the semiconductor mounting surface is molded on one side with a sealing resin composition.

In a BGA package having a structure in which one side is molded with a sealing material, semiconductor elements are mounted directly on a multilayer printed wiring board called a carrier substrate, so that the semiconductor element, the multilayer printed wiring board, and further sealing. There was a problem that the package warps during molding due to a mismatch in the coefficient of thermal expansion with the resin. This amount of warpage becomes large during solder reflow on the mounting board, and mountability becomes a problem. The total warpage of the package is 60 even during molding.
It is desirable to keep the thickness below μm.

In order to prevent this, it is considered effective to use a carrier substrate having the same coefficient of thermal expansion as that of the semiconductor element. In this case, the solder ball portion between the carrier substrate and the printed wiring board on which it is mounted is used. Since stress concentrates on the solder joint, the connection reliability of the solder joint is reduced.

Since the BGA package is composed of members having different thermal expansion coefficients as described above, there are problems of warpage during molding of the package and connection reliability of the solder ball portion after mounting.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the amount of warpage of a single sided BGA package.

[0009]

The amount of warpage of a BGA package is affected not only by the physical properties of the encapsulant and carrier substrate, but also by the package outline such as the thickness of the encapsulant layer and the carrier substrate. For this reason, these points are fully taken into consideration when designing the BGA.

As a result of intensive studies, the present inventor has found a method for reducing the amount of warpage in a single-sided molded BGA package. The method will be described in detail below.

The warp of the BGA package is largely due to the difference in the amount of heat shrinkage between the sealing layer formed on the semiconductor mounting surface and the carrier substrate during the temperature reduction process during the molding of the package. The elastic modulus of the sealing layer and the carrier substrate also influences, but most of them are caused by the difference in the amount of heat shrinkage.

In general, for a resin composition used as a sealing material, a method of filling a silica filler, which is a low thermal expansion component, with a high degree of filling is used in order to reduce the thermal shrinkage. This method is very effective, and even in the case of a BGA package, when the package outer shape is small, the warp amount can be reduced by adjusting the compounding amount of the filler. However, there is a limit to the high content of filler in a large package with 300 or more pins. Further, high filling of the filler causes an increase in viscosity during molding and an increase in elastic modulus of the sealing layer, which is inconvenient for package molding.

As a result of intensive studies, the present inventor has found that the warp can be reduced by increasing the glass transition temperature of the sealing layer to the package molding temperature or higher. The heat shrinkage rate of the sealing layer differs from the molding temperature to the glass transition temperature and from the glass transition temperature to room temperature.When using a general organic material as a base, the shrinkage rate at the glass transition temperature or higher is the glass transition temperature. 3 to 5 times larger than the following: Therefore, the amount of heat shrinkage can be reduced by raising the glass transition temperature to about the molding temperature or higher. In this case, it is desirable to use the amount of the filler to adjust the total amount of heat shrinkage.

In addition, the epoxy resin used in the encapsulating resin composition of the present invention is capable of increasing the glass transition temperature above the molding temperature and has a plurality of epoxy resins in one molecule, and is used for encapsulating semiconductors. Any resin may be used as long as it is generally used as a resin. Such epoxy resins include bisphenol A, F or S type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, and bifunctional or higher functional epoxy having a biphenyl skeleton, a naphthalene skeleton, or a dicyclopentadiene skeleton in the molecule. Examples thereof include resins, alicyclic epoxy resins, and epoxy resins obtained by brominated the above epoxy resins. In the present invention, these are used alone or as a mixture of several kinds.

In the present invention, the curing agent having a phenolic hydroxyl group is any one as long as it has a plurality of phenolic hydroxyl groups in one molecule and is generally used as a semiconductor encapsulating resin. Good. As such a curing agent, bisphenol A, F or S, phenol novolac, cresol novolac, biphenol having a biphenyl skeleton in the molecule, those having a naphthalene skeleton, those having a dicyclopentadiene skeleton,
Further, copolymers of the above resins or a mixture of several kinds are used. These are used according to various properties such as resin moldability such as reactivity and fluidity, and moisture absorption rate and mechanical properties of the cured product.

The encapsulating resin composition used in the present invention includes
A curing accelerator is added to accelerate the curing reaction. The curing accelerator used in the present invention is not particularly limited as long as it accelerates the curing reaction between the epoxy resin and the curing agent. Usually, storage stability and moldability of an epoxy resin composition, good electrical properties after curing, triphenylphosphine, triphenylphosphonium-triphenylborate, tetraphenylphosphonium-tetraphenylborate, And those containing phosphorus in the molecule such as derivatives thereof, triethylenediamine, diaminodiphenylmethane, 1,8-diazabicyclo (5,5)
Amine compounds such as 4,0) -undecene, imidazole and their derivatives, BF3, sulfonium salts, etc.
One kind or two or more kinds are used by adding to the epoxy resin. The addition amount can be arbitrarily determined according to the moldability of the epoxy resin composition and the physical properties of the cured product. For the purpose of increasing the glass transition temperature, amine-based, particularly imidazole-based curing accelerators are suitable. In the epoxy resin molding material of the present invention, in addition to the above-mentioned materials, a filler, a release agent, a coloring agent, a coupling agent, a softening agent, a flame retardant and the like are added and used as necessary. The filler is used for the purpose of reducing the thermal expansion coefficient of the epoxy molding material and for increasing the strength, and includes talc, clay, silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, glass fiber,
All inorganic fillers such as ceramic fibers can be used.

The blending amount of the filler is 50% by weight to 95% by weight.
However, if it is less than 50% by weight, a sufficient effect cannot be obtained for reducing the thermal expansion coefficient and improving the strength. Also, if the content exceeds 95% by weight, the closest packing density of the filler will be less than the content of the epoxy resin matrix, making it difficult to prepare a molding material, and the viscosity after preparation will be extremely high, resulting in moldability. Is reduced. 8 to adjust the heat shrinkage
0 to 90% by weight is suitable.

The release agent facilitates release from the molding die, and carnauba wax, montanic acid type wax, polyolefin type wax may be used alone or in combination. The addition amount is preferably 0.01 to 5% by weight of the total amount. That is, if it is less than 0.01%, the releasability is not effective, and if it exceeds 5%, the adhesion to the lead frame or the silicon chip is deteriorated. It is desirable to use carbon black as the colorant. Toughened cured products,
The softening agent that is blended to lower the elastic modulus is an amino group or epoxy group that is incompatible with the epoxy resin, a butadiene-acrylonitrile copolymer having a carboxyl group terminal, or an amino group or hydroxyl group at the terminal or side chain. An epoxy group- or carboxyl group-modified silicone resin-based flexible agent is used. The above materials are blended, mixed, kneaded and pulverized, and further granulated as necessary to obtain an epoxy resin molding material. The kneading is generally performed with a hot roll or an extruder.
The semiconductor device of the present invention can be obtained by sealing a semiconductor chip on a carrier substrate with the epoxy resin composition thus obtained. Low pressure transfer molding is usually used as the manufacturing method, but in some cases,
It is also possible by methods such as compression molding and casting. Further, in order to improve the reliability of the semiconductor device, it is desirable to perform aftercure at a temperature of 150 ° C. or higher for a predetermined time after molding with the epoxy resin composition.

As the constituent material of the printed wiring board which is the carrier substrate of the present invention, a mixture of an organic substance and an inorganic substance or an inorganic substance can be used alone. Suitable organic materials are thermosetting resins such as epoxy resin, maleimide resin, polyimide resin, cyanate resin, and phenol resin.
In addition, the filler used with these is aramid fiber,
In addition to fluorine resin, organic materials such as paper, S glass cloth,
E glass cloth, D glass cloth, H glass cloth, A
Glass cloth, C glass cloth, AR glass cloth, L
Fibrous inorganic materials such as glass cloth and quartz fibers, and powdery filling materials such as silica and alumina can also be used together. As the inorganic material matrix, alumina ceramic, ceramic-epoxy resin composite, aluminum nitride, low melting point glass, etc. are suitable. Since the inorganic filler is mainly used to adjust the thermal expansion coefficient of the printed wiring board, it is preferable to use glass cloth alone or to use silica and glass cloth having a small thermal expansion coefficient in combination. At this time, as the organic material of the matrix, epoxy resin is preferable from the viewpoint of balance between moldability and electric characteristics. However, these compositions are not limited to the above materials.

In the molding of the semiconductor device according to the present invention, first, a silicon chip is bonded to the silicon chip mounting surface of the carrier substrate through a die attachment, and then the chilicon chip and the carrier substrate are electrically bonded by gold wire bonding. Connect to. It is desirable that the carrier substrate on which the silicon chip is mounted is sealed on the chip mounting surface by low-pressure transfer molding at a predetermined temperature and then post-cured at a temperature higher than the molding temperature for several hours. Solder balls can be attached to the mounting surface of the carrier substrate after post-curing to obtain a semiconductor device.

For the purpose of improving mass productivity and workability, a lead frame for supporting a carrier substrate may be used.

[0022]

The amount of warpage can be reduced by raising the glass transition temperature of the sealing layer to the package molding temperature or higher or by lowering the molding temperature. This is because the amount of warp corresponds to the product of the difference in thermal shrinkage and the temperature difference (molding temperature-room temperature), so that it is possible to reduce the temperature difference and decrease the amount of warp by bringing the molding temperature close to room temperature. .

In the present invention, the naphthalene-type polyfunctional epoxy resin shown in Chemical formula 1, the trishydroxyphenylmethane-type polyfunctional epoxy resin shown in Chemical formula 3, the phenol novolac shown in Chemical formula 4, and the trishydroxyphenylmethane-type polyfunctional resin shown in Chemical formula 5 are used. By using the phenol curing agent as the base resin of the encapsulating resin composition, molding at a low temperature of 100 to 150 ° C. is possible.

[0024]

Embedded image

Further, in these resin systems, when molded at a normal molding temperature, the glass transition temperature becomes high, so that the amount of heat shrinkage decreases, and the amount of warpage can be greatly reduced.

In order to change the coefficient of thermal expansion of the printed wiring board, the coefficient of thermal expansion can be increased by changing the resin content relative to the glass cloth resin or introducing flexible particles into the resin component to increase the contribution of the glass component. A method of adjusting can be applied. The glass transition temperature of the resin component is preferably the package molding temperature or higher.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples.

Examples 1 to 6 and Comparative Examples 1 to 2 Epoxy resin and phenol resin curing agents shown below, triphenylphosphine as a curing accelerator, and crushed powder of fused silica having an average particle size of 8 μm as a filler. And average particle size 28μ
m spherical sphere fused silica mixed at a ratio of 3/7, antimony trioxide as a flame retardant aid, epoxysilane as a coupling agent, montanic acid ester as a release agent, carbon black as a colorant An epoxy resin molding material was prepared with the composition shown in Table 1.

[0029]

[Table 1]

The materials are kneaded by using a biaxial hot roll (65-85
C.) for 10 minutes.

Epoxy resin (a) Epoxy equivalent: 163 g / eq

[0032]

[Chemical 6]

(B) Epoxy equivalent: 176 g / eq

[0034]

[Chemical 7]

(C) Epoxy equivalent: 195 g / eq

[0036]

Embedded image

Phenolic resin curing agent (d) Hydroxyl equivalent: 106 g / eq

[0038]

[Chemical 9]

(E) Hydroxyl equivalent: 98 g / eq

[0040]

[Chemical 10]

Next, the structure of the semiconductor device to which the present invention is applied will be described with reference to the drawings.

FIG. 1 shows a silicon chip 1 which is a semiconductor element.
After being fixed to the carrier substrate 3 via the die attachment 2, the electrode portion on the element and the carrier substrate 3 are connected to the gold wire 7
Is a BGA type semiconductor device in which the surface of the carrier substrate on the element side is sealed with the sealing resin composition 6 after being electrically connected.

FIG. 2 shows a silicon chip 1 which is a semiconductor element.
Is fixed to the carrier substrate 3 via the die attachment 2 and the lead frame 9, and the electrode portion on the element and the carrier substrate 3 are electrically connected by the gold wire 7. Then, the carrier substrate surface on the element side is sealed with a resin composition. It is a BGA type semiconductor device sealed with an object 6.

FIG. 3 shows how the package is warped,
It is the figure which showed the measurement point 11 of the amount of curvatures, and the amount 10 of curvatures.

The characteristics in the table were measured by the following methods.

(1) Glass transition temperature and linear expansion coefficient:
Using a thermophysical tester, measurement was performed at a temperature rising rate of 5 ° C / min.

(2) Package warp amount: The warp amount of the mounting surface of the package after molding was measured using a depth of focus meter.
The amount of warpage is represented by the amount of displacement of the package end portion in the diagonal direction with respect to the center of the package.

In forming a BGA package, a 9 mm square silicon chip is bonded onto a carrier substrate, which is a 32 mm square 4-layer printed wiring board, through a die attachment, and the silicon chip electrode and the carrier substrate electrode are gold wires. Bonded. After that, transfer molding was performed under the conditions of a molding temperature of 150, 180 ° C. and a molding pressure of 7 MPa using the sealing resin having the composition of the example shown in Table 2 to mold a semiconductor resin having a total package thickness of 2.4 mm. The number of solder balls was 18 × 18 = 324 pins. The distance between the balls was 1.2 mm.

[0049]

[Table 2]

[0050]

[Table 3]

<Examples 1, 2, 3, 4 and Comparative Example 1> In each of Examples 1, 2, 3, 4 and Comparative Example 1, the filler content was 8
Coefficient of thermal expansion below glass transition temperature at 5 wt% is 10 pp
Although m / ° C., in Examples 1, 2, 3 and 4, the glass transition temperature was high, so the amount of heat shrinkage from the molding temperature to room temperature was small and the amount of warpage was smaller than that in Comparative Example 1. Example 2
In this case, since the heat shrinkage ratio is smaller than the heat shrinkage amount of the carrier substrate, warpage occurs in the opposite direction to the other examples.

<Examples 1 and 5> Example 1 and Example 5 are different from each other in the amount of filler. In Example 5 in which the filler content was small, the coefficient of thermal expansion was larger than that in Example 1, so the amount of warpage was also large. <Examples 1, 6 and Comparative Examples 1 and 2> Examples 1, 6 and Comparative Examples 1 and 2 compare molding temperatures. Comparing Example 1 and Example 6, the warpage amount of Example 6 molded at 150 ° C. was extremely small. Comparative Example 2 could not be molded at 150 ° C./90 seconds because the base epoxy resin was uncured.

<Examples 7 and 8, Comparative Examples 3 and 4> Examples 7 and 8 and Comparative Examples 3 and 4 compare the curability of the resin compositions of the present invention. In molding at 180 ° C., in Examples 7 and 8 and Comparative Example 3, hardness of 80 or more and spiral flow of 25 inch or more are satisfied, and the molding of the package is possible.
In the low temperature molding at 150 ° C., the hardness is as small as 17 in Example 7 in which the amount of TPP which is the curing accelerator is small, and molding of the package is impossible. Also in Comparative Examples 3 and 4, the hardness is 0, so that the package cannot be molded. On the other hand, in Example 8, the spiral flow is 25 inches or more and the hardness is 80 or more, which is suitable for package molding. In Example 7 and Comparative Example 3, since the spiral flow is 25 inches or more,
Although it is possible to obtain a hardness of 80 or more by lengthening the molding time, Example 8 of the present invention is suitable when considering the mass productivity of the package.

[0054]

EFFECT OF THE INVENTION By using the resin composition of the present invention, and by molding at a temperature not higher than the glass transition temperature of the encapsulating resin composition, the amount of warpage can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a ball grid array package according to the present invention.

FIG. 2 is a cross-sectional view of a package in which a lead frame is introduced between a silicon chip and a carrier substrate in order to improve mass productivity of BGA.

FIG. 3 is a package cross-sectional view showing the state of warpage after BGA molding and the measurement site of the warpage amount.

[Explanation of symbols]

1 ... Silicon chip, 2 ... Die attachment, 3 ... Printed wiring board, 4 ... Solder ball, 5 ... Inner layer wiring, 6
... Encapsulating resin composition, 7 ... Gold wire, 8 ... BGA having lead frame, 9 ... Lead frame, 10 ... Warpage amount,
11 ... Warp measurement site, 12 ... Warp amount reference point.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masanori Segawa, 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd. Hitachi Research Laboratory, Ltd. (72) Hiroyoshi Ogaku, 7-chome, Omika-cho, Hitachi, Ibaraki No. 1 Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Masahiko Ogino 7-1-1 Omika-cho, Hitachi City, Hitachi City, Ibaraki Prefecture 72 Hitachi Ltd. Hitachi Research Laboratory (72) Inventor, Ryo Mogi Omi Mika, Hitachi City, Ibaraki Prefecture 7-1-1, Machi, Hitachi Co., Ltd. Hitachi Research Laboratory

Claims (5)

[Claims] 1. A semiconductor element having a mounting surface on which solder balls are arranged in a grid pattern on the back surface of the mounting surface of a printed wiring board having a mounting surface for the semiconductor element, and being electrically connected to the mounting surface. The semiconductor element is mounted and fixed on the mounting surface of, and the electrode portion of the semiconductor element and the printed wiring board are electrically connected to each other, and at least the mounting surface of the semiconductor element including the semiconductor element and the electrical connection portion. In a semiconductor device having a structure in which a part is molded and sealed with a resin composition, sealing molding with the resin composition,
A semiconductor device, which is performed at a temperature not higher than the glass transition temperature of a cured product of a resin composition. 2. A semiconductor element having a mounting surface on which solder balls are arranged in a grid pattern on the back surface of the mounting surface of a printed wiring board having a mounting surface for the semiconductor element, and being electrically connected to the mounting surface. The semiconductor element is mounted and fixed on the mounting surface of, and the electrode portion of the semiconductor element and the printed wiring board are electrically connected to each other, and at least the mounting surface of the semiconductor element including the semiconductor element and the electrical connection portion. In a semiconductor device having a structure in which a part is molded and sealed with a resin composition, the resin composition contains an epoxy resin represented by Chemical formula 1 and a curing agent represented by Chemical formula 2 as essential components, and a silica filler. A semiconductor device containing 50 to 95% by weight. Embedded image Embedded image 3. A semiconductor element, which has a mounting surface having solder balls arranged in a grid pattern on the back surface of the mounting surface of a printed wiring board having a mounting surface of the semiconductor element, and is electrically connected to the mounting surface. The semiconductor element is mounted and fixed on the mounting surface of, and the electrode portion of the semiconductor element and the printed wiring board are electrically connected to each other, and at least the mounting surface of the semiconductor element including the semiconductor element and the electrical connection portion. In a semiconductor device having a structure in which a part is molded and sealed with a resin composition, the resin composition contains an epoxy resin represented by Chemical formula 3 and a curing agent represented by Chemical formula 4 as essential components, and a silica filler. A semiconductor device containing 50 to 95% by weight. Embedded image [Chemical 4] 4. The semiconductor device according to claim 1, wherein the printed wiring board and the silicon chip are supported by a lead frame. 5. The method according to claim 1, 2, 3 or 4, wherein the molding with the molding resin composition is 100 to 15
A semiconductor device operated in a temperature range of 0 ° C.