JPH04320358A - Plastic sealed semiconductor device - Google Patents

Abstract

PURPOSE:To enhance heat resistance and to achieve low hygroscopicity and high adhesion by sealing a semiconductor device with a resin composition essentially containing a hardener which contains an epoxy resin and a resin of specified composition. CONSTITUTION:At least a resin shown by the formula is employed as a hardener. Consequently, glass transition temperature of sealing resin is elevated and high strength is maintained at the time of reflow, while furthermore hygloscopicity of resin is suppressed and adhesion is enhanced through increase of breaking elongation of resin. The resin shown by the formula is contained by 5-100wt% in the hardener. Viscosity of epoxy resin is set lower than 3 poise at 150 deg.C. Furthermore, filler composed of inorganic particles occupies 55-80vol.% of the entire composition.

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 having excellent solder reflow resistance.

0002

[Prior Art] A composition containing an epoxy resin, a novolac type phenolic resin as a hardening agent, and a hardening accelerator is used as a semiconductor encapsulation material because it has excellent moldability, moisture absorption characteristics, and heat resistance. .

However, with the recent increase in the degree of integration of semiconductors and changes in package size, package shape, mounting method, etc., there is a desire for further improvements in reliability, including heat resistance, moisture resistance, and low stress. ing. For example, with the shift in package mounting methods from pin insertion type to surface mount type, packages have come to be exposed to high temperatures of 200°C or higher when mounted on printed circuit boards, which can cause cracks in the packages. Problems such as peeling at the interface between the chip and the sealing resin, resulting in a decrease in moisture resistance, have occurred.

In response to this demand, the glass transition temperature of the sealing resin has been raised and the reflow temperature (200 to 2
Various attempts have been made to increase the high-temperature strength at 60° C., reduce the moisture absorption rate of the sealing resin, and reduce stress. Methods for raising the glass transition temperature of the sealing resin include polyfunctional epoxy resins as described in JP-A-64-9214 and JP-A-64-31816, and polyimide as described in JP-A-1-126321. It has been proposed to use resin. Also, JP-A No. 2-88621 and JP-A No. 2-110
Publication No. 958 describes a low moisture absorption epoxy resin containing naphthalene in its skeleton. Furthermore, the use of epoxy resins containing biphenyl in the skeleton as low stress epoxy resin compositions is disclosed in JP-A-1-268711 and JP-A-2-919.
No. 65 and Japanese Unexamined Patent Publication No. 2-99514.

[0005]

[Problems to be Solved by the Invention] The above-mentioned conventional technology does not sufficiently take into account the need to achieve both heat resistance, low moisture absorption, and low stress, and it is difficult to use polyfunctional epoxy resins or polyimide resins that have a high glass transition temperature. Resins with low moisture absorption and low stress tend to have high adhesive strength, but have a problem in that their glass transition temperature is inferior to that of conventional resins. Therefore, the improvement in reflow resistance was not satisfactory in any case.

An object of the present invention is to provide a resin-sealed semiconductor device that is encapsulated with a resin composition that has excellent heat resistance, low moisture absorption, and high adhesive strength, and has excellent reflow resistance.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have conducted various studies on sealing resins that are capable of achieving both high heat resistance, low moisture absorption, and high adhesive strength. Among them, we focused on epoxy resins that have excellent moldability such as curability and fluidity, and we have developed
We investigated the chemical structure and composition that can satisfy the above characteristics. As a result, at least the following general formula (2) is used as a curing agent.

0
008]

[Case 2]

(In the formula, R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a represents an integer of 1 to 4.) If the resin is used, the glass transition of the sealing resin can be reduced. Not only can it maintain high strength at reflow temperatures (200 to 260°C) by raising the temperature, but it also suppresses the increase in moisture absorption of the resin.
It has been discovered that the adhesive force can be improved by increasing the elongation at break of the resin, and the present invention has been achieved.

[0010] Also, since the epoxy resin composition containing at least the curing agent represented by the above general formula can lower the elastic modulus of the sealing resin compared to the conventional novolak type phenolic resin curing agent, It is also effective in reducing thermal stress, which causes distortion and damage to elements and breaks in bonding wires.

In the present invention, since the phenol resin represented by the general formula (2) is trifunctional, it is not only possible to improve the heat resistance, but also to improve the crosslinked resin after curing with the epoxy resin. Since a part of the crosslinking molecules is composed of bisphenol A type, the structure has both flexibility and toughness, and can simultaneously satisfy characteristics such as moisture absorption, high adhesion, and low elastic modulus. Ra (a represents an integer of 1 to 4) in the structural formula represents hydrogen or an alkyl group having 1 to 4 carbon atoms, but the substituents and their You can choose the number. When R is hydrogen, the resin has excellent curability and heat resistance, but the softening temperature of the resin tends to be high. When an alkyl group such as a methyl group is used as R, the softening temperature and moisture absorption rate of the resin are lowered, but the curability tends to be lowered. Therefore, in the present invention, one type of phenolic resin represented by the general formula (2) or a combination of two or more types of resins having different Ra can be used depending on the characteristics. Furthermore, if necessary, the general formula (
It is also possible to use in combination with a curing agent other than the resin represented by 2).

In the present invention, the curing agent to be used in combination with the phenolic resin of general formula (2) is a combination of phenols such as phenol, cresol, xylenol, and naphthol, and formaldehyde or phenolaldehyde in combination with p-toluenesulfonic acid, sulfuric acid, hydrochloric acid, or peroxide. A condensation product obtained by reacting under an acidic catalyst such as chloric acid or oxalic acid or a polycondensate of phenol and aralkyl ether can be used. Examples of these curing agents include, for example, phenol novolac resins, cresol novolak resins, phenol- or cresol-based polyfunctional curing agents, and resins obtained by polycondensation of phenol and aralkyl ether. In this case, the amount of the resin curing agent (A) represented by general formula (2) and the other curing agent (B) described above is
It is preferable to mix them in a ratio of A):(B)=100:0 to 5:95. Resin curing agent (A
) is less than 5% by weight, there is little effect on improving heat resistance, which is the objective of the present invention.

[0013] The epoxy resin used in the present invention refers to all epoxy resins containing two or more epoxy groups in one molecule, such as bisphenol A, bisphenol S, bisphenol F, phenol novolac resin, and cresol novolak resin. Bisphenol-based epoxy resins and novolac-based epoxy resins obtained by reacting with epichlorohydrin, or their brominated epoxy resins, epoxy resins having a naphthalene skeleton or biphenyl skeleton, phenol- or cresol-based polyfunctional Functional epoxy resin, epoxy resin obtained from alicyclic compounds such as cyclohexene, cyclopentadiene, dicyclopentadiene, epoxy resin obtained from vinyl polymer, epoxy resin obtained from polyhydric alcohol such as glycerin, general formula (2) There are epoxy resins obtained by reacting a phenol resin represented by the following with epichlorohydrin, and brominated epoxy resins thereof.

In the present invention, at least a resin represented by the general formula (2) is used as a curing agent, but this resin has a slightly higher softening temperature than other curing agents. Therefore, if the amount of this resin is increased, the heat resistance can be greatly improved without changing the moisture absorption properties and adhesiveness, but the fluidity will be reduced. In order to suppress this decrease, it is preferable to use an epoxy resin with low viscosity. If the viscosity of the epoxy resin is 3 poise or less at 150° C., even if the resin represented by the general formula (2) is used as the entire curing agent, the fluidity of the sealant can be ensured better than before. The above-mentioned epoxy resins can be used alone or in combination of two or more types as long as the effects of the present invention are not impaired.

In the present invention, at least general formula (2)
It is desirable that the curing agent containing the resin represented by the formula is blended in an amount of 0.5 to 1.5 equivalents to the epoxy resin. If the amount of the curing agent is less than 0.5 equivalent to the epoxy resin, the epoxy resin will not be completely cured, resulting in poor heat resistance, moisture resistance, and electrical properties of the cured product. On the other hand, if it exceeds this amount, a large amount of hydroxyl groups in the curing agent remain even after the resin is cured, resulting in poor electrical properties and moisture resistance.

The resin composition used for semiconductor encapsulation in the present invention may contain 55 to 80% of the total composition, if necessary.
% by volume of inorganic filler. Inorganic fillers are added for the purpose of improving the coefficient of thermal expansion, thermal conductivity, modulus of elasticity, etc. of the cured product, and if the amount added is less than 55% by volume, these properties cannot be sufficiently improved. This is because if the amount exceeds 80% by volume, the viscosity of the material will increase significantly and the fluidity will decrease. Various compounds can be used as inorganic fillers, but it is important to use thermochemically stable fillers for electronic components, and specifically at least one type selected from fused silica, crystalline silica, and alumina. of inorganic particles are desirable. Note that the average particle size of these fillers is preferably in the range of 1 to 30 μm. This is because if the average particle size is less than 1 μm, the viscosity of the resin composition will increase and the fluidity will be significantly reduced, and if it exceeds 30 μm, the resin component and filler will likely separate during molding, resulting in a hardened product. This is because the cured product becomes non-uniform, resulting in variations in the physical properties of the cured product, and the ability to fill narrow gaps becomes poor.

Furthermore, in the present invention, if necessary,
A flexibilizing agent can be used in the resin composition to improve the toughness and lower the elastic modulus of the cured product. The blending amount of the flexibilizing agent is preferably 2 to 20% by weight based on the total resin composition. If the amount of the flexibilizing agent is less than 2% by weight, it will have little effect on the toughness or lower elastic modulus of the cured product;
If it exceeds this, the fluidity of the resin composition will become extremely poor,
When the flexibilizing agent floats on the surface of the cured resin, the mold becomes noticeably contaminated. As a flexibilizing agent, one that is incompatible with the epoxy resin composition can lower the elastic modulus of the cured product without lowering the glass transition temperature, so butadiene,
Acrylonitrile copolymers and their terminal or side chain amino groups, epoxy groups, carboxyl group-modified copolymers, acrylonitrile-butadiene-styrene copolymers, butadiene-based flexibilizing agents, terminal or side chain amino groups, and hydroxyl groups. ，
Epoxy group- and carboxyl group-modified silicone resin-based flexibilizers are used, but silicone-based flexibilizers are particularly useful from the viewpoint of moisture resistance and high purity.

The composition used for the resin-sealed semiconductor device of the present invention may also contain, if necessary, a curing catalyst to accelerate the curing reaction of the resin, and a coupling to improve the adhesion between the resin component and the filler. Various additives such as dyes and pigments for coloring, mold release agents for improving the releasability of the cured product from the mold can be used within the range that does not impair the purpose of the invention. The curing catalyst is a phosphorus-containing organic basic compound such as triphenylphosphine or tetraphenylphosphonium tetraphenylborate, or a tetra-substituted boron salt thereof, a tertiary amine such as triethylenediamine or benzyldimethylamine, or 1,8-diazabicyclo(5 ,4,0)-
At least one type of undecene, imidazole, etc. can be used, and as a coupling agent, at least one type of epoxysilane, aminosilane, etc. can be used.

[0019] A general method for producing a molding material for semiconductor encapsulation using such raw materials is to sufficiently mix a raw material mixture of a predetermined amount, knead it using a hot roll or an extruder, cool it, and then heat it. A molding material can be obtained by crushing. Low-pressure transfer molding is usually used to encapsulate semiconductors using the molding material obtained in this way, but in some cases, methods such as injection molding, compression molding, and casting may also be used. be.

[0020]

[Operation] The reason why a resin-sealed semiconductor device with excellent heat resistance, moisture resistance, and reflow resistance can be obtained in the present invention is due to the structure of the resin curing agent represented by the general formula (2) used in the present invention. .

Since the resin curing agent represented by the general formula (2) is trifunctional, it can exhibit high heat resistance. In addition, the crosslinked resin formed after curing with the epoxy resin has a part of crosslinked molecules composed of bisphenol A type, so the resin has a structure with flexibility and toughness, and has high adhesiveness and low elasticity. Satisfied at the same time. Furthermore, although the resin curing agent represented by general formula (2) is trifunctional,
Because it has a certain degree of flexibility due to its molecular structure, it has the effect of reducing the free volume of the resin, and has the characteristic of lower moisture absorption than conventional multifunctional curing agents. Further, by using this curing agent in combination with a low hygroscopic epoxy resin, a further effect is produced in reducing the hygroscopicity of the sealing material. Semiconductor devices encapsulated with a resin composition containing a resin curing agent of general formula (2) and an epoxy resin as essential components, which have excellent heat resistance, high high-temperature strength, high adhesive strength, and low moisture absorption, can be reflow sold. It becomes difficult to adsorb moisture, which is the cause of package cracks that occur during heating. Furthermore, improved adhesiveness between the resin and the lead frame reduces moisture permeation at the interface between them, resulting in improved reflow resistance. Another factor in the reflow resistance is that it has high high temperature strength that can withstand water vapor pressure during reflow heating.

Furthermore, since the resin composition of the present invention is characterized by a low elastic modulus, the thermal stress generated in the semiconductor device is reduced.

[0023]

EXAMPLES The present invention will be explained in detail below with reference to Examples, but the scope of the present invention is not limited to these Examples.

<Example 1> Structural formula

[0025]

[Chemical formula 3]

Tetramethyldihydroxybiphenyl glycidyl ether (epoxy equivalent: 188,
Melt viscosity at 150°C 0.2 poise), brominated bisphenol epoxy resin (epoxy equivalent 375, softening temperature 68°C, melt viscosity at 150°C 1.3 poise) and structural formula

[0027]

[C4]

A trisphenol type resin curing agent with a hydroxyl equivalent of 141, a curing catalyst shown in Table 1, prismatic fused silica with an average particle size of 6 μm as a filler, and a trisphenol type resin curing agent with an average particle size of 30 μm as fillers.
A 30/70 mixture of m spherical fused silica, antimony trioxide as a flame retardant aid, epoxy silane as a coupling agent, montanic acid ester wax as a mold release agent, and carbon black as a coloring agent were used, as shown in Table 1. Molding materials were prepared with the blending ratios shown.

[0029]

[Table 1]

[0030] For kneading each material, a twin-screw roll having a diameter of 20 inches was used, and the kneading was carried out for about 10 minutes at a roll surface temperature of about 55 to 80°C.

Examples 2 to 13 As shown in Table 1, the types and amounts of other resin curing agents used in combination with the epoxy resin and the trisphenol resin curing agent of Example 1, and the type of curing accelerator were changed. A molding material was produced in the same manner as in Example 1 except for the above.

<Comparative Example 1> Phenol novolak resin as resin curing agent (hydroxyl equivalent: 106, softening temperature: 65°C)
A molding material was produced in the same manner as in Example 1 except that the following was used.

<Comparative Example 2> As a resin curing agent, the structural formula

0
034]

[C5]

Resin (C) represented by (hydroxyl equivalent: 173
A molding material was prepared in the same manner as in Example 1, except that a temperature of 69° C.) was used.

Comparative Example 3 A molding material was prepared in the same manner as in Example 1, except that 2.5 parts by weight of the trisphenol resin and 50 parts by weight of the phenol novolak resin of Example 1 were used as resin curing agents.

<Comparative Example 4> As an epoxy resin, 150
Molding was carried out in the same manner as in Example 1, except that an ortho-cresol novolac type epoxy resin (epoxy equivalent: 195, softening temperature 65 °C) having a melt viscosity of 3 poise at °C and the phenol novolac resin of Comparative Example 1 was used as the curing agent. The material was prepared.

<Comparative Example 5> As an epoxy resin, 150
Orthocresol type novolak resin with a melt viscosity of 6 poise at °C (epoxy equivalent: 196, softening temperature: 77
A molding material was produced in the same manner as in Example 1, except that the temperature (°C) was used.

<Examples 14 to 17> Using the same material as in the previous example as a resin component and a new side chain epoxy-modified silicone resin (molecular weight 73,600, epoxy equivalent 3,900) as a flexibilizer, the formulations shown in Table 2 were prepared. A molding material was prepared according to the ratio.

Comparative Example 6 Using the same materials as those in Examples 14 to 17, molding materials were prepared in the same manner as above at the compounding ratios shown in Table 2.

180 of the molding material thus obtained
Formability at ℃, mold temperature 180℃, molding pressure 70℃
Kg/cm2, 180℃ after molding for 90 seconds
Tables 1 and 2 summarize the results of various physical properties of molded products that were post-cured for 6 hours. In addition, all the compounding ratios in Tables 1 and 2 are expressed in parts by weight. Also, among the epoxy resins shown in the table, the resin represented by symbol (A) (epoxy equivalent: 145, melt viscosity at 52°C: 1.
The structural formula of 3 Poise is

[0042]

[C6]

The structural formula of the resin represented by the symbol (B) (epoxy equivalent: 215, melt viscosity at 150°C: approximately 1 poise) is

[0044]

[C7]

[0045] Among the resin curing agents in the table, the symbol (
Resin represented by D) (hydroxyl equivalent: 107, softening temperature: 10
The structural formula of 1℃) is

[0046]

[Chemical formula 8]

The resin represented by the symbol (E) (hydroxyl equivalent: 120, softening temperature: 62°C) has the following structural formula:

[
0048

[Chemical formula 9]

This is a novolac type cresol resin having the following properties. The curing catalysts indicated by symbols in the table are DBU; 1,8-diazabicyclo(5,4,0)-undecene, TPP; triphenylphosphine, 2E4HZ; 2-ethyl 4-methylimidazole.

Of the various properties listed in the table, the moisture absorption rate and adhesive strength were measured as follows.

(1) Moisture absorption rate: A disk of 90 mmφ and 2 mm t was molded and allowed to absorb moisture at 80° C./100% RH for 200 hours, and was determined from the change in weight.

(2) Adhesive strength: The aluminum peel strength between a 3 mmt aluminum foil and a molding material was measured at a pulling speed of 50 mm/min.

As is clear from Table 1, the resin composition for semiconductor encapsulation of the present invention has better adhesive properties than the resin composition using the novolac type phenolic resin curing agent and other resin curing agents shown in the comparative example. It is possible to improve the glass transition temperature and the bending strength at 215° C. without reducing the moisture absorption properties. Further, if the resin curing agent represented by the general formula (2) in the present invention is less than 5% by weight based on the total resin curing agent, no improvement in heat resistance is observed. Furthermore, epoxy resin 1
It can be seen that when the melt viscosity at 50° C. is high, the spiral flow of the molding material decreases significantly, indicating that there is a problem with fluidity. On the other hand, as is clear from Table 2, the resin composition containing the flexibilizing agent of the present invention exhibits almost the same characteristics as in Table 1, except that the elastic modulus of the molding material can be lowered. However, it can be seen that when the amount of the flexibilizing agent is less than 2% by weight, there is almost no effect on lowering the elastic modulus, and when it is more than 20% by weight, mold staining and a decrease in spiral flow are significant.

[0054]

[Table 2]

Next, using the above molding material, a silicon chip (6
×6mm) mounted on a 42 alloy lead frame,
Furthermore, a semiconductor device (external size 20 x 14 mm, thickness 2 mm) in which wire bonding was performed between the aluminum electrode on the chip surface and the lead frame with money (30 μmφ) was sealed, and 6
After being left at 5° C./95% RH for a predetermined time, a test was conducted in which the package was heated for 90 seconds in a vapor reflow oven at 215° C., and the number of cracks in the package is shown in Table 3.

[0056]

[Table 3]

As is clear from Table 3, the resin-sealed semiconductor of the present invention has low moisture absorption, good adhesion, and is encapsulated with a resin composition that has high high-temperature strength, so it has good reflow resistance. It's extremely good.

[0058]

[Effects of the Invention] Compared to conventional devices, the resin-sealed semiconductor device not only has high heat resistance and high strength at high temperatures, but also has the characteristics of high adhesiveness and low moisture absorption. Therefore, it has excellent solder reflow resistance.

Claims (4)

[Claims] Claim 1: An epoxy resin, and at least a compound having the general formula (
1) [Chemical formula 1] (wherein, R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a represents an integer of 1 to 4) as an essential component. A resin-sealed semiconductor device characterized in that it is sealed with a resin composition containing the resin composition. 2. The resin-sealed semiconductor device according to claim 1, wherein the resin represented by the general formula (1) accounts for 5 to 100% by weight based on the total amount of the curing agent. 3. The resin-sealed semiconductor device according to claim 1, wherein the epoxy resin has a viscosity of 3 poise or less at 150°C. 4. According to claim 1, 2 or 3, the filler made of inorganic fine particles is 55 to 80% by volume based on the total composition.
Resin semiconductor devices including.