JPH0931166A - Resin-sealed semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the resistance to reflowing, the reliability in the moisture resistance and reliability when left to stand at a high temperature of a resin- sealed semiconductor device. SOLUTION: This semiconductor device sealed with an epoxy resin composition contains an epoxy resin, a curing agent, a cure accelerator and a filler, wherein the cure accelerator used comprises an organophosphorus compound represented by formula I (m is an integer of 1 to 5; and R is an alkyl or alkoxy) and wherein the curing agent used comprises a phenolic resin represented by formula II (n is an integer of 0 to 5).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-encapsulated semiconductor device encapsulated with an epoxy resin composition having excellent moldability and storage stability.

[0002]

2. Description of the Related Art For semiconductor packages such as transistors, ICs and LSIs, a resin encapsulation method which is excellent in mass productivity is used. As an encapsulating material, an epoxy resin composition is widely used in which a phenolic curing agent, an inorganic filler, and various additives are mixed with an o-cresol novolac type epoxy resin having excellent moldability, electrical characteristics, and heat resistance. There is.

By the way, in response to needs such as miniaturization, weight reduction, and high performance of various electronic equipments, there is a strong demand for high density mounting of semiconductor devices used for these devices, and recently, a surface mounting type semiconductor device suitable for high density mounting. Is becoming mainstream. In addition, packages are becoming smaller and thinner year after year. Accordingly, the thickness of the sealing resin layer has been significantly reduced. Especially TSOP (Thi Small Outline Packag
e), TQFJ (Thin QuadOutline J-lead Packag
Among semiconductor devices such as e) and TQFP (Thin Quad Flat Package), the demand for surface mount thin packages with a thickness of around 1 mm is rapidly increasing. Furthermore, the development of an ultra-thin surface mount package with a thickness of 0.5 mm or less is being earnestly pursued.

In general, the characteristics of the encapsulating material change during storage, so that it is stored at a low temperature as a preventive measure. However, the curing reaction gradually progressed and the fluidity decreased,
So-called storage stability is insufficient and long-term storage is not possible. In addition, since the sealing material gradually absorbs moisture during storage, there is a problem that depending on the type of the curing accelerator, curing is inhibited by hydrolysis or the like, and a homogeneous molded product cannot be obtained.

On the other hand, in the molding of semiconductor packages, conventionally, unused materials remaining after molding have been collected and stored again at low temperature. However, recently, due to the simplification of the molding process, an unused material may be left as it is in the molding machine or in the vicinity thereof, which causes a change in the characteristics, which is an obstacle to reuse.
Changes in the characteristics of the encapsulation material are major factors such as (1) it is not possible to obtain a homogeneous and stable molded product, (2) the molding yield of the semiconductor package decreases, and (3) the reliability decreases due to moisture absorption. Therefore, the encapsulating material is required to further improve the three characteristics such as moldability, storage stability and moisture resistance.

On the other hand, in the resin-encapsulated semiconductor device, the thinner the encapsulating resin layer is, the easier water permeates into the package, and the mechanical strength of the resin layer is reduced. Therefore, a small force is applied to the package. There is a problem that it will be easily damaged. Further, the so-called mounting for fixing the surface mount type semiconductor device to a supported body is mainly soldering by an infrared ray or vapor reflow method, in which case the package is exposed to a high temperature of about 250 ° C.
Therefore, when the package absorbs moisture, the absorbed moisture evaporates and the volume expands rapidly, and the vapor pressure causes the package to swell and peel at the interface between the chip and the sealing resin, or the sealing resin strength. If is less than the vapor pressure, the package may crack. as a result,
In the semiconductor device, the element characteristics change and the aluminum wiring is easily corroded, so that various reliability after mounting deteriorates.
Therefore, it is strongly desired to improve the solder reflow resistance in the surface mount type package having a thin resin layer.

There are the following two paths for the moisture to enter the package. (1) Diffusion and penetration from the resin sealing layer, and (2) Penetration from the interface between the lead frame and the sealing material. In order to improve the solder reflow resistance required for surface mount packages, it is extremely important to reduce such infiltration moisture.

In order to solve the above problems, various measures have been studied so far, and it has been particularly effective to reduce the moisture absorption of the sealing material and to strengthen the adhesive force. For example, JP-A-3-207714
As disclosed in JP-A-4-48759 and JP-A-4-48759, a package is constituted by an epoxy resin composition comprising an epoxy resin having a biphenyl skeleton and a phenol aralkyl resin curing agent, and JP-A-4-50223. As disclosed in Japanese Patent Laid-Open Nos. 4-199856, 4-199857, and 4-199857, a package is made of an epoxy resin composition having a naphthalene skeleton and having a low hygroscopic property. It has become possible to improve.

[0009]

However, although the above-mentioned prior art has a considerable effect on improving the solder reflow resistance, the encapsulating material undergoes a gradual curing reaction even at a relatively low temperature near room temperature to cause fluidization. The problem of poor storage stability and poor storage stability has not been solved. Moreover, there is a drawback that voids are likely to occur inside the molded product during molding, and it has been difficult to obtain a molded product with stable quality. Further, if the sealed product is left at a high temperature, the joint between the aluminum electrode on the surface of the semiconductor element and the gold wire that electrically connects the lead frame is easily corroded in a short time, and the connection reliability is significantly deteriorated. was there.

In view of these circumstances, an object of the present invention is to provide an epoxy which has excellent storage stability, is free from defects such as voids, and has excellent solder reflow resistance and connection reliability between the electrode and the gold wire. It is intended to provide a resin-encapsulated semiconductor device encapsulated with a resin composition.

[0011]

The inventors of the present invention have added various additives such as epoxy resin, curing agent, curing accelerator, filler, coupling agent, release agent, etc., which are considered to affect the above properties. Intensive examination was made on the kneading conditions and molding conditions of each material. As a result, they have found that the above problems can be improved by using a specific curing agent and a specific curing accelerator, and have reached the present invention. The gist of the present invention is as follows.

In a semiconductor device encapsulated with an epoxy resin composition containing an epoxy resin, a curing agent, a curing accelerator, an inorganic filler, various additives, etc., the curing accelerator is
formula

[0013]

Embedded image

(In the formula, m is an integer of 1 to 5, R is an alkyl group or an alkoxy group.) An organic phosphorus compound represented by the formula (6)

[0015]

[Chemical 6]

In the resin-sealed semiconductor device, which is a phenolic resin represented by the formula (n represents an integer of 0 to 5).

In the present invention, the tertiary phosphine-based curing accelerator represented by the formula (5) is specifically tris (alkylphenyl) phosphine, tris (alkoxyphenyl) phosphine, tris (alkylalkoxy). Phenyl) phosphine, tris (dialkylphenyl)
Examples include phosphine, tris (trialkylphenyl) phosphine, tris (tetraalkylphenyl) phosphine, tris (dialkoxyphenyl) phosphine, tris (trialkoxyphenyl) phosphine, and tris (tetraalkoxyphenyl) phosphine. Among these curing accelerators, the most preferable one is the chemical formula (7).

[0018]

[Chemical 7]

Tris (4-methylphenyl) represented by
Phosphine or (chemical formula 8)

[0020]

Embedded image

Examples include tris (4-methoxyphenyl) phosphine and the like. These curing accelerators may be used alone or in combination of two or more as required. Further, it can be used in combination with other known curing accelerators, if necessary. The above curing accelerator can be used in exactly the same manner as a usual curing accelerator. Moreover, it can be used after being heated and melted with the curing agent at 100 ° C. or higher in advance, if necessary. The curing accelerator is 1 to 500 mmol, preferably 3 to 100 parts by weight of the epoxy resin.
It is preferable to mix it in the range of 50 mmol.

In the present invention, the curing agent represented by the formula (2) is a phenol resin having dicyclopentadiene in the skeleton. The curing agent is applicable to known epoxy resins, but among them, it is particularly suitable for low moisture absorption of o-cresol novolac type epoxy resin, and 0.5 to 1.5 equivalents relative to the epoxy resin. It is desirable to mix them.
If the amount is less than 0.5 equivalent, the curing of the epoxy resin will be insufficient, and the cured product will have poor heat resistance, moisture resistance, and electrical properties such as volume resistivity and dielectric loss tangent. On the other hand, if the amount exceeds 1.5 equivalents, the curing agent component becomes excessive and a large amount of phenolic hydroxyl groups remain in the cured resin, so that the electrical characteristics and the moisture resistance deteriorate. The above curing agent can be used in combination with other known curing agents as long as the object of the present invention is not impaired.
The above-mentioned curing agent can be used in the same manner as a known ordinary curing agent.

The epoxy resin used in the present invention is not particularly limited, and known epoxy resins are widely used. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, biphenyl type epoxy resin, polyfunctional epoxy resin having a naphthalene skeleton, halogenated phenol novolac type epoxy resin, etc. Used.

As an inorganic filler, fused silica, crystalline silica, alumina, calcium carbonate, zirconium silicate,
Fine powders of calcium silicate, talc, clay, mica, etc. can be used. The content of the inorganic filler is preferably 50 to 90% by volume with respect to the entire resin composition. These inorganic fillers are added for the purpose of improving the thermal expansion coefficient, thermal conductivity, elastic modulus, etc. of the cured product. If the compounding amount is less than 50% by volume, these characteristics cannot be sufficiently improved, and 9
If it exceeds 0% by volume, the viscosity of the resin composition will remarkably increase and the fluidity will decrease, making molding difficult. The average particle size of the inorganic filler is particularly preferably in the range of 0.1 to 100 μm. 0.
If it is less than 1 μm, the viscosity of the resin composition increases,
When it exceeds 0 μm, the resin component and the filler are easily separated from each other, the cured product becomes non-uniform or the physical properties of the cured product vary, and further, the filling property into a narrow gap is deteriorated. For example, when the filler is blended in an amount of 75% by volume or more, the filler particles are preferably spherical rather than square and have a particle size distribution of 0.1.
It is desirable that the particles are distributed over a wide range of 100 μm.
Since such a filler tends to have a close-packed structure, the viscosity of the material does not increase even if the compounding amount is increased, and a composition having excellent fluidity can be obtained.

In the present invention, a softening agent or the like for increasing the toughness and lowering the elastic modulus of the cured resin can be used if necessary. As the softening agent, those which are incompatible or partially compatible with the epoxy resin and the curing agent can lower the elastic modulus of the cured product without lowering the glass transition temperature so much that the butadiene / acrylonitrile copolymer is used. And modified copolymers having amino groups, epoxy groups, and carboxyl groups at their ends or side chains, butadiene-based flexible agents such as acrylonitrile / butadiene / styrene copolymers, and amino groups and hydroxyl groups at the ends or side chains A modified silicone-based elastomer having an epoxy group, a carboxy group or the like is used, and a silicone-based flexible agent is particularly effective in terms of moisture resistance and purity. The compounding amount of the softening agent is preferably 2 to 20% by weight based on the total resin composition. If the blending amount is less than 2% by weight, there is almost no effect on the toughness and low elastic modulus of the cured product. On the other hand, if it exceeds 20% by weight, the fluidity of the resin composition and the mechanical strength at high temperature are remarkably deteriorated, and the flexible agent is raised on the surface of the cured resin to stain the molding die, which is not preferable. In addition to the above various additives, various silane compounds, titanium compounds, aluminum chelates, as coupling agents for increasing the adhesion between the resin component and the filler,
Known additives such as aluminum / zirconium compounds can be used. Further, known compounds such as carnauba wax, montanic acid wax, polyethylene wax and polyalkylene wax may be used as a release agent. Known compounds such as carbon black, titanium oxide, red lead and red iron oxide may be used as the colorant.

Each of the above materials can be usually melted and kneaded at 50 to 120 ° C. using a mixing roll, an extruder, a kneader or the like to form a sealing material.

[0027]

The reason why the semiconductor device of the present invention exhibits excellent productivity and solder reflow resistance is considered as follows.
The resin-encapsulated semiconductor device encapsulated with the epoxy resin composition using the curing accelerator represented by the formula (1) and the curing agent represented by the formula (2) exhibits excellent reliability. This is because the curing accelerator is extremely stable at around room temperature and is excellent in curability, so that a homogeneous and stable molded product can be obtained. That is, since the curing accelerator has a latent reactivity, it prevents the increase of the melt viscosity at the time of curing the resin composition, improves the wettability with respect to the object to be sealed, and molds with extremely few voids. This is probably because the product is obtained. In other words, the encapsulating material of the present invention is easy to fill even the details of the mold, and since the curing is performed quickly, the mold releasability of the molded product is extremely good. Therefore, the mold releasing property of the molded product is excellent, the resin-encapsulated semiconductor device can be easily taken out from the mold without being damaged, and a homogeneous and stable molded product can be obtained. Therefore, it is considered that a highly reliable resin-sealed semiconductor device can be obtained.

Further, it has excellent solder reflow resistance because the curing agent represented by the formula (2) has a hydrocarbon structure which is a hydrophobic chemical structure in the resin-encapsulated skeleton.
Furthermore, since the obtained molded product has a semiconductor device with few voids and no damage as described above, it is considered that high reliability can be obtained even in the mounting test. The occurrence of voids in a molded article to which the resin composition of the present invention is applied is small when the curing accelerator selectively reacts with the low molecular weight component in the epoxy resin or the curing agent at a relatively low temperature, and the resin is cured. It is considered that this is because it has the effect of reducing the volatile components generated in.

The epoxy resin used in the present invention is not particularly limited, but biphenyl type epoxy resin,
The reason why the dicyclopentadiene type epoxy resin, naphthalene type epoxy resin, o-cresol novolac type epoxy resin, etc. are particularly preferable is that the cured product has a higher density than that of the conventional one, so that the molecular chain packing is denser. Therefore, it is considered that the formed network structure is difficult to permeate water, or that the hydroxyl group concentration in the cured product is low, resulting in low hygroscopicity. Therefore, it is considered that the sealing material using such a resin itself has low hygroscopicity. In addition, such a resin has a high glass transition temperature of a cured product, but has a low cross-linking density, so that the resin is flexible and the residual stress generated by curing is small. The adhesiveness to the lead frame is excellent, and it is considered that the amount of water entering the package from these interfaces can be greatly reduced. Therefore, it is considered that the reason why the solder reflow resistance is remarkably improved is that the amount of water entering the package is significantly reduced as described above. Further, it is considered that the solder reflow resistance is remarkably improved, as described above, because the amount of water entering the package is significantly reduced.

It was totally unexpected that the resin-encapsulated semiconductor device encapsulated with the epoxy resin composition containing the curing accelerator and the curing agent had excellent reliability.

[0031]

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

(Examples 1 to 7) Table 1 shows the compound names and abbreviations of the curing accelerators used in Examples and Comparative Examples.

[0033]

[Table 1]

[0034]

[Table 2]

The epoxy resin compositions having the compounding amounts shown in Table 2 were kneaded by a twin-screw roll heated to 50 to 120 ° C. for about 10 minutes, then cooled and pulverized to obtain a sealing material. These encapsulating materials were stored at 4 ° C for one day and then examined for moldability, hygroscopicity, and amount of ionic impurities. The results are shown in Tables 3 and 4.

[0036]

[Table 3]

[0037]

[Table 4]

In the table, the transfer molding condition is 180
° C., is 70kg / cm ^2, 90 seconds. Spiral flow measures the length of the molded product when a mold for spiral flow measurement specified in EMMI-1-66 is sandwiched between the upper and lower hot plates of the molding machine and 20 g of sealing material is molded under the above conditions. did.

The hot hardness was measured by using a Barcol hardness tester immediately after the molding die was opened by transfer molding of a disc having a diameter of 20 mmφ.

The internal void of the molded product has the above-mentioned diameter of 20 mmφ.
The disc was observed with a soft X-ray fluoroscope and evaluated.

The moisture absorption rate was calculated from the amount of moisture absorption by allowing a disc having a diameter of 90 mmφ and a thickness of 2 mm to absorb moisture for 240 hours in a constant temperature and humidity chamber at 85 ° C./85% RH.

The gelling time was generated by using a JSR type curast meter (Imanaka Machinery Industry Co., Ltd.), and inserting 2 g of the sample into a dedicated mold having irregularities heated to 180 ° C. and giving a constant amplitude vibration to the mold. The stress caused by the curing reaction of the sample was assumed to be the gelation time.

The ionic impurities were measured as follows. A test piece similar to the disk having a diameter of 90 mmφ and a thickness of 2 mm described above was molded, heat-cured at 180 ° C. for 5 hours, and then ground with a mill grinder TI-100 type (manufactured by HEIKO). 5 g of the fine powder was put into a polytetrafluoroethylene-stainless steel double pressure vessel together with 500 cc of pure water and 120 ° C.
After heating for a predetermined period of time, free halogen ions extracted in pure water were measured with an ion chromatograph type 10 (manufactured by Dionex). The extraction amount was converted per unit weight of the molded product.

(Comparative Examples 1 to 4) The epoxy resin compositions shown in Table 5 were kneaded with a biaxial roll heated to 50 to 120 ° C. for about 10 minutes in the same manner as in Examples 1 to 7, then cooled and pulverized. A sealing material was obtained. Similar to Examples 1 to 7, these sealing materials were stored at 4 ° C. for one day and then examined for moldability, hygroscopicity, and amount of ionic impurities, and the results shown in Tables 4 and 6 were obtained.

[0045]

[Table 5]

[0046]

[Table 6]

From Table 3, Table 4 and Table 6, the encapsulating material of the present invention is characterized in that the spiral flow and the hardness at the time of heating are well balanced and the gelation time which is a measure of curability is short, as compared with the comparative example. . In addition, the molded product obtained from the encapsulating material of the present invention has few voids and a small moisture absorption rate, which indicates that it is effective for improving the long-term reliability of the package when packaged.

(Examples 8 to 14) Solder reflow resistance, moisture resistance reliability, and high temperature standing reliability tests were conducted using sealing materials made of the compositions shown in Table 2. The results are shown in Table 7.

[0049]

[Table 7]

The solder reflow resistance test was conducted on a silicon chip (6 × 6) having aluminum zigzag wiring formed on the surface.
mm) is mounted on a 42 alloy lead frame, and the semiconductor device (outer dimension 20 × 14 mm, thickness 2 mm) is wire-bonded between the lead electrode and the aluminum electrode on the chip surface with a gold wire (30 μmφ). Cured at 180 ° C. for 5 hours. As for the reliability test of solder reflow resistance, this resin-encapsulated semiconductor device was left at 85 ° C / 85% RH for 168 hours, and then heated in an infrared reflow oven at 240 ° C for 90 seconds. I checked the number.

The moisture resistance reliability test was conducted as follows. Surface mount type QFP (Quad Flat Package) -1H
(Tab 6.7 x 6.7 mm) element, 65 ° C, 95% R
After being left under high temperature and high humidity of H for 72 hours, vapor reflow at 215 ° C./90 seconds and immersion in salt water were performed. Furthermore, after leaving these elements under the conditions of 65 ° C. and 95% RH for 500 hours, the number of elements in which aluminum corrosion occurred was counted and the presence or absence of defects was examined.

The high temperature storage reliability test was conducted as follows. A resin-encapsulated semiconductor device of the same type as that used in the moisture resistance test was left in a thermostat at 200 ° C. for 200 hours, and defective joints between the gold wires and the aluminum wires were examined.

As is clear from Table 7, a tertiary phosphine type curing accelerator and a dicyclopentadiene type phenolic resin were sealed with an epoxy resin composition containing the curing agent.
It was found that the resin-sealed semiconductor device of the present invention has excellent reliability.

(Comparative Examples 5-8) Using the encapsulating materials composed of the compositions shown in Table 5, solder reflow resistance, moisture resistance reliability and high temperature leaving reliability test were conducted in the same manner as in Examples 8-14. . The results are shown in Table 7.

The encapsulating material of the present invention is excellent in moldability and storage stability, has a low moisture absorption rate, and has a small amount of free halogen ions, which is one of the factors controlling reliability. The resin-encapsulated semiconductor device encapsulated with this resin composition has excellent reliability.

[0056]

The resin-encapsulated semiconductor device of the present invention is excellent in solder reflow resistance, moisture resistance reliability, and reliability by a high temperature storage test.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akira Nagai, 1-1 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Masahiko Ogino 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd. Hitachi Research Laboratory

Claims (6)

[Claims] 1. A resin-encapsulated semiconductor device encapsulated with an epoxy resin composition containing an epoxy resin, a curing agent, a curing accelerator and a filler, wherein the curing accelerator is
Formula 1 (In the formula, m represents an integer of 1 to 5 and R represents an alkyl group or an alkoxy group.),
The curing agent is of the formula (2) (In the formula, n represents an integer of 0 to 5.) A resin-encapsulated semiconductor device, which is a phenolic resin. 2. The curing accelerator is of at least the formula (3): Or (formula 4) formula The resin-encapsulated semiconductor device according to claim 1, wherein the resin-encapsulated semiconductor device is encapsulated with the epoxy resin composition that is any one of the organic phosphorus compounds represented by. 3. The epoxy resin contains at least one of an epoxy resin having a biphenyl skeleton, an epoxy resin having a dicyclopentadiene skeleton, an epoxy resin having a naphthalene skeleton, and a novolac type epoxy resin. The resin-sealed semiconductor device according to claim 1. 4. The resin-encapsulated semiconductor device according to claim 1, wherein the curing agent is added in an amount of 0.5 to 1.5 equivalents based on 100 parts by weight of the epoxy resin. 5. The epoxy resin 100 is used as the curing accelerator.
The resin-encapsulated semiconductor device according to claim 1, wherein 1 to 500 mmol is blended with respect to parts by weight. 6. The filler has an average particle size of 0.1 to 100 μm.
The resin-encapsulated semiconductor device according to claim 1, wherein m is m.