JPH1045873A - Epoxy resin composition for sealing of semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an epoxy resin composition capable of being stably stored for a log period of time at a normal temperature, manifesting excellent moldability and giving a molded product having high quality by containing a specific epoxy resin, a hardener, a latent catalyst and an inorganic filler as essential components. SOLUTION: This epoxy resin composition comprises (A) an epoxy resin containing 30-100wt.% of a resin expressed by the formula I [R1 is H, a 1-6C (cyclic) alkyl, phenyl or a halogen; G is glycidyl], (B) a phenolid resin hardener having >=2 pieces of phenolic OH in a molecule, (C) an inorganic filler and (D) a latent catalyst composed of a compound of the formula II (X1 to X4 are each a monofunctional organic acid or an aliphatic group having an aromatic ring or a heterocycle; Y1 to Y4 are each X1 and at least one of them is a group obtained from a proton donor having a proton able to be emitted to outside of a molecule by emitting a proton to outside of a molecule) as essential components, and an equivalent ratio of an epoxy in the component A to OH in the component B is 0.5-2, and 250-1,400 pts.wt. of the component C and 0.4-20 pts.wt. of the component D are contained in 100 pts.wt. of the components (A+B).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy resin composition which is excellent in preservability at normal temperature and moldability and gives a high quality molded article.

[0002]

2. Description of the Related Art Conventionally, electronic parts such as diodes, transistors, and integrated circuits are mainly sealed with an epoxy resin composition. Particularly, in an integrated circuit, a biphenyl-type epoxy resin having excellent heat resistance and moisture resistance is used. Is cured with various phenolic resin curing agents, and an epoxy resin composition for semiconductor encapsulation (hereinafter, referred to as a resin composition) is used in which an inorganic filler such as fused silica or crystalline silica is blended as a filler. The biphenyl-type epoxy resin used in this resin composition has a molecule having a planar structure in the main chain, and has a relatively low molecular weight. Further, it is a crystalline solid at room temperature, but once melted, has the property of becoming a very low viscosity liquid. However, due to the lower molecular weight of the resin, the molecules become easier to move, and in the initial stage of the reaction, the crosslinking reaction starts quickly,
Therefore, the crosslinking reaction partially proceeds during the kneading of the resin, and a predetermined fluidity cannot be obtained. Further, after kneading the resin, the crystallinity is lost, and the reaction is likely to occur even at room temperature, and the fluidity at the time of molding is lowered, that is, there is a problem in storage stability.

[0003] Examples of curing accelerators for biphenyl epoxy resin and various phenol resin curing agents include, for example,
1,8-diazabicyclo (5,4,0) undecene-
7, benzyldimethylamine, triphenylphosphine, 2-methylimidazole, tetraphenylphosphonium / tetraphenylborate, and the like. However, resin compositions using these curing accelerators have a disadvantage that storage stability at room temperature is poor. . For example, Japanese Patent Publication No. 51-2439
No. 9 discloses that tetraphenylphosphonium tetraphenylborate is effective for improving room temperature storage stability and curability. However, tetraphenylphosphonium / tetraphenylborate has a strong ionic bond between a cationic tetraphenylphosphonium group and an anionic tetraphenylborate group, and has a melting point of 300 ° C.
As described above, even if the resin composition is kneaded at the time of preparation, it cannot be sufficiently uniformly dispersed, so that the catalyst activity is low and good curing reactivity cannot be exhibited at the time of molding. In order to solve this drawback, Japanese Patent Application Laid-Open No. 55-153358 proposes a method in which tetraphenylphosphonium / tetraphenylborate is previously melt-mixed into a part of raw materials and then kneaded at the time of preparing a resin composition. .

However, in this method, tetraphenylphosphonium / tetraphenylborate has a structure in which ionic bonds have already been removed during melt-mixing, so that reactivity at room temperature cannot be suppressed, and storage stability deteriorates. I do. The ionic bond between the anion part and the cation part has a certain level of strength, showing favorable behavior as a latent catalyst. In JP-A-5-76490, a tetra-substituted phosphonium / tetra-substituted borate is proposed as a latent catalyst. The substituent on the boron side of the tetra-substituted phosphonium / tetra-substituted borate is a hydrocarbon group, at least one of which is an alkyl group having 1 to 6 carbon atoms, which can be dry-blended when preparing the resin composition. Although it is considered to be excellent in storability, from the viewpoint of long-term storability at room temperature, the storability is still not sufficient. For this reason, when the resin composition is stored at room temperature, problems such as poor filling, breakage of the gold wire of the IC chip, and poor conduction occur due to a decrease in fluidity during molding. Therefore, such a resin composition needs to be refrigerated and transported under refrigeration, and at present it is costly to store and transport.

[0005]

SUMMARY OF THE INVENTION According to the present invention, it is possible to stably store a resin composition for a long period of time without curing at normal temperature, and a curing reaction starts when heated during molding, An object of the present invention is to provide an epoxy resin composition for semiconductor encapsulation capable of providing a molded article having good moldability and high quality.

[0006]

According to the present invention, there is provided an epoxy resin comprising (A) an epoxy resin represented by the formula (1) in an amount of 30 to 100% by weight based on the total amount of the epoxy resin;

Embedded image (In the formula, R ₁ is hydrogen, a chain or cyclic alkyl group having 1 to 6 carbon atoms, a phenyl group, a group selected from halogen, or an atom. May be.)

(B) Two phenolic hydroxyl groups in one molecule
A latent catalyst comprising a phenolic resin curing agent having at least one phenolic resin, (C) an inorganic filler, and (D) a phosphonium borate represented by the formula (2), and an epoxy group of the epoxy resin (A) and a phenolic resin. The equivalent ratio of the phenolic hydroxyl group of the curing agent (B) is 0.5 to 2, and the content of the inorganic filler (C) is 250 to 1,400 weight per 100 parts by weight of the total amount of the epoxy resin and the phenol resin curing agent. Wherein the content of the latent catalyst (D) is 0.4 to 20 parts by weight per 100 parts by weight of the total amount of the epoxy resin and the phenolic resin curing agent. A composition,

Embedded image (However, in the formula, X ₁ , X ₂ , X ₃ and X ₄ are monovalent organic acids or monovalent aliphatic groups having an aromatic ring or a heterocyclic ring, and they are different even if they are the same. Y ₁ , Y ₂ , Y ₃ and Y ₄ are a monovalent organic acid or a monovalent aliphatic group having an aromatic ring or a heterocyclic ring, and at least one of them is A proton donor having at least one proton that can be released outside the molecule is a group that releases one proton, and they may be the same or different from each other.)

[0008] Compared with the conventional resin composition, the resin composition can be stored stably for a long period of time without curing at room temperature at room temperature, and a curing reaction is developed during heat molding to achieve good molding. A molded product of high quality and high quality can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The epoxy resin of the formula (1) used in the present invention is a known substance usually called a stilbene type epoxy resin, and JP-A 64-85215 discloses a stilbene type epoxy compound having a glycidyl group terminal. And an epoxy resin composition containing a Schiff compound has been proposed,
Room temperature storage and moldability are not sufficient. (It contains a rigid olefin double bond and shows strong orientation.) This epoxy resin is a crystalline solid at room temperature, but has the property of becoming a very low-viscosity liquid when melted by heating. . However, it shows stronger orientation than the same crystalline biphenyl-type epoxy resin, and is mixed with a phenol resin curing agent and other components, cooled by heating and kneading, and as a resin composition, the crystallinity is impaired by a rigid olefin double bond. No reaction occurs even at room temperature. Therefore, even if the resin composition using this is stored at room temperature, the fluidity during molding does not decrease.

By controlling the amount of the epoxy resin used, the storage stability can be maximized. In order to bring out the effect of preservability, it is desirable that the epoxy resin represented by the formula (1) is contained in an amount of 30% by weight or more, preferably 50% by weight or more in the total epoxy resin amount. 3
If it is less than 0% by weight, the storage stability is insufficient. Equation (1)
When using an epoxy resin and another epoxy resin in combination, for example, biphenyl type epoxy compound, bisphenol type epoxy compound, phenol novolak type epoxy resin, cresol novolak type epoxy resin, dicyclopentadiene modified epoxy resin, triphenol methane Epoxy compounds, alkyl-modified triphenolmethane epoxy compounds, and the like.

The phenol resin curing agent having two or more phenolic hydroxyl groups in one molecule used in the present invention includes, for example, phenol novolak resin, cresol novolak resin, dicyclopentadiene-modified phenol resin, paraxylylene-modified phenol resin, terpene-modified Phenol resins, triphenol methane compounds and the like can be mentioned.
Further, these phenol resins may be used alone or in combination. The phenolic hydroxyl group of the phenol resin reacts with the oxirane ring of the epoxy resin to form a crosslinked structure. The equivalent ratio of the epoxy group of the epoxy resin to the phenolic hydroxyl group of the phenolic resin is preferably 0.5 to 2. If the equivalent ratio is outside this range, the curability of the resin composition may decrease, or the glass transition temperature of the cured product may decrease. May occur.

Examples of the inorganic filler used in the present invention include fused silica powder, spherical silica powder, crystalline silica powder, secondary aggregated silica powder, porous silica powder, alumina, clay, and talc. In particular, spherical silica is preferred from the viewpoint of improving fluidity. As for the shape of the spherical silica, it is preferable that the shape of the particles themselves be infinitely spherical and the particle size distribution be broad in order to improve fluidity. The content of the inorganic filler of the present invention is 250 to 14 per 100 parts by weight of the total amount of the epoxy resin and the phenol resin.
If the amount is less than 250 parts by weight, low thermal expansion and low water absorption cannot be obtained, and the solder stress resistance is insufficient. If the amount exceeds 1400 parts by weight, the fluidity of the resin is reduced, and poor filling occurs during molding, and inconveniences such as displacement of a die pad and a gold wire in a semiconductor package due to an increase in viscosity are caused.

The latent catalyst used in the present invention is a phosphonium borate represented by the formula (2). In the formula (2), X ₁ , X ₂ , X ₃ and X ₄ of the phosphonium group are a monovalent organic group or a monovalent aliphatic group having an aromatic ring or a heterocyclic ring, and they are the same as each other. Or different. Examples of such a phosphonium group include, for example,
Tetraphenyl phosphonium group, tetratolyl phosphonium group, tetraethyl phenyl phosphonium group, tetramethoxy phenyl phosphonium group, tetranaphthyl phosphonium group, tetrabenzyl phosphonium group, ethyl triphenyl phosphonium group, n-butyl triphenyl phosphonium group, 2-hydroxyethyl tri Examples include a phenylphosphonium group, a trimethylphenylphosphonium group, a methyldiethylphenylphosphonium group, a methyldiallylphenylphosphonium group, and a tetra-n-butylphosphonium group. In equation (2),
X ₁ , X ₂ , X ₃ and X ₄ are particularly preferably a monovalent organic group having an aromatic ring, and the melting point of the phosphonium borate represented by the formula (2) is not particularly limited. However, the temperature is preferably 250 ° C. or less from the viewpoint of uniform dispersion. In particular, a phosphonium borate having a tetraphenylphosphonium group has good compatibility with an epoxy resin and can be suitably used.

In the formula (2), a borate group represented by Y ₁ ,
Y ₂ , Y ₃ and Y _{4 each} represent an aromatic or heterocyclic 1
A monovalent organic group or a monovalent aliphatic group, at least one of which is a group in which a proton donor having at least one proton that can be released outside the molecule releases one proton. Yes, Y ₁ , Y ₂ , Y ₃ and Y ₄ may be the same or different. Examples of such a proton donor providing a borate group include acetic acid, trifluoroacetic acid, stearic acid, benzoic acid, 1-naphthoic acid, 2-naphthoic acid, phthalic acid, trimellitic acid, pyromellitic acid, 6-naphthalenedicarboxylic acid, partially ring-opened forms of carboxylic acids such as polyacrylic acid and anhydrides thereof, phenol, biphenol, bisphenol A, bisphenol F, 1-naphthol, 2-naphthol, polyphenol, isocyanuric acid, benzotriazole,
Further, among these, compounds having a substituent on the aromatic ring of the compound having an aromatic ring can be exemplified. Particularly preferred are aromatic carboxylic acids such as benzoic acid, 1-naphthoic acid, 2-naphthoic acid, phthalic acid, trimellitic acid, pyromellitic acid and 2,6-naphthalenedicarboxylic acid, phenol, biphenol, bisphenol A and bisphenol F. And phenolic compounds such as 1-naphthol, 2-naphthol and polyphenol are good and can be suitably used.

When the latent catalyst comprising phosphonium borate represented by the formula (2) is mixed with an epoxy resin / phenol resin curing agent system, it does not exhibit catalytic activity at room temperature, so that the curing reaction of the epoxy resin proceeds. However, the catalyst activity is exhibited at a high temperature during molding, and once exhibited, exhibits a stronger catalytic activity than conventional curing accelerators, thereby increasing the degree of curing of the resin composition. The latent catalyst is capped by forming an ionic bond with a cationic tetra-substituted phosphonium group serving as an active site at normal temperature, in which an anionic tetra-substituted borate group acts as a protective group. Further, the protective group does not come off even by heating or heat generation when mixing the thermosetting resin and other components. That is, the energy required for dissociation of the ionic bond between the cationic tetra-substituted phosphonium group and the anionic tetra-substituted borate group can be obtained only during molding. At this time, the protective group of the phosphonium borate is removed, the active site is exposed, and the curing reaction proceeds. For this purpose, it is important that the ionic bond between the cationic tetra-substituted phosphonium group and the anionic tetra-substituted borate group is not too strong, and the conventional curing accelerator, tetraphenylphosphoniumtetraphenylborate, The bond is too strong. For this reason, the melting point becomes 300 ° C. or higher, and even if kneaded during the preparation of the resin composition, sufficient uniform dispersion cannot be achieved, and the effect as a curing accelerator cannot be sufficiently exhibited.

Therefore, when tetraphenylphosphonium / tetraphenylborate is used, a method has been proposed in which after melt-mixing with a part of the raw materials in advance, kneading is performed at the time of preparing the resin composition. However, in this method, the tetraphenylphosphoniumtetraphenylborate has a structure in which the tetraphenylborate group of the protective group has already been removed at the time of melt-kneading, so that the reactivity at a low temperature is increased, and the storage stability at room temperature is improved. And the intended effect is not sufficiently exhibited. Therefore, a structure in which the bonding force between the tetraphenylphosphonium group and its protective group is weakened to some extent as described above is preferable. Specifically, if the type of the functional group bonded to boron is changed to a functional group having a higher electron-withdrawing property than the phenyl group, the anionicity of the borate anion is reduced, and the ionic bond with the tetraphenylphosphonium group is weakened. At the same time, the melting point becomes 200 to 250 ° C., and the resin composition can be uniformly kneaded.

In the phosphonium borate which is a latent catalyst of the present invention, the anionic tetra-substituted borate as a protecting group is such that the substituent bonded to boron has an electron-withdrawing property higher than that of the phenyl group of tetraphenylphosphonium / tetraphenylborate. Because of the high substituent, the anionicity of the tetra-substituted borate group is reduced, the ionic bond between the cationic tetra-substituted phosphonium group and the anionic tetra-substituted borate group is weakened to some extent, and the melting point is also tetraphenylphosphonium / tetraphenyl 300 ℃ of borate
Compared to the above, the temperature is 180 to 260 ° C., and it is considered that the resin composition shows rapid curability only by dry blending at the time of preparing the resin composition without being melt-mixed with a part of the raw material in advance. In addition, the latent catalyst of the present invention is characterized in that the energy required for dissociation of the cationic tetra-substituted phosphonium group and the anionic tetra-substituted borate group is the amount of heat or heat generated when mixing the epoxy resin and other components. , The protecting group does not come off and the reactivity at low temperatures is low. At a high temperature during molding, energy required for dissociation can be obtained, so that the protective group is removed and shows high reactivity. In other words, the reactivity at low temperatures is low, but the reactivity at high temperatures is very high, indicating an ideal reaction behavior as a latent catalyst. For this reason, it is possible to improve the storage stability at room temperature, reduce the viscosity of the sealing resin due to little reaction during kneading, and achieve high reactivity when heated to a high temperature.

The added amount of the latent catalyst is 0.4 per 100 parts by weight of the total amount of the epoxy resin and the phenol resin curing agent.
-20 parts by weight are preferred. If the latent catalyst is less than 0.4 parts by weight, sufficient curing may not be obtained during heat molding. If the amount exceeds 20 parts by weight, curing may be too fast and poor fluidity may cause poor filling. The latent catalyst of the present invention can be used alone or in combination with another curing accelerator. When used in combination with another curing accelerator, the latent catalyst of the present invention contains 5% of the total amount of the latent catalyst and the other curing accelerator.
It is preferably at least 0% by weight. If the latent catalyst of the present invention is less than 50% by weight, the object of the present invention may not be sufficiently achieved. Other curing accelerators that can be used in combination with the latent catalyst of the present invention include, for example, 1,8-diazabicyclo (5.4.0) undecene-7, tetraphenylphosphonium tetraphenylborate, triphenylphosphine And the like. The resin composition of the present invention may further comprise a coupling agent such as γ-glycidoxypropyltrimethoxysilane, a brominated epoxy resin, if necessary, in addition to the components (A) to (D).
Flame retardants such as antimony trioxide and hexabromobenzene,
Various additives such as a colorant such as carbon black and red iron oxide, a release agent such as natural wax and synthetic wax, and a low stress additive such as silicone oil and rubber may be appropriately compounded.

In order to produce the resin composition of the present invention as a molding material, an epoxy resin, a phenol resin curing agent,
After the latent catalyst, the inorganic filler, and other additives are sufficiently and uniformly mixed at room temperature by a mixer or the like, the mixture is further melt-kneaded with a hot roll or a kneader, cooled, and pulverized to form a sealing material. . These molding materials can be applied to covering, insulating, sealing, and the like of transistors and integrated circuits, which are electric or electronic components.

The present invention will be described by way of examples. Example 1 60.6 parts by weight of an epoxy resin represented by the formula (3) (melting point: 124 ° C.)

Embedded image

Phenol novolak resin (softening point 62 ° C., hydroxyl equivalent 105 g / eq) 38.6 parts by weight 7.1 parts by weight of a latent catalyst represented by the formula (4)

Embedded image

Fused spherical silica powder (average particle size 15 μm) 758.9 parts by weight Carbon black 1.8 parts by weight Carnauba wax 2.7 parts by weight Brominated phenol novolak type epoxy resin (epoxy equivalent 275 g / eq) 4.5 parts by weight 17.9 parts by weight of antimony trioxide was mixed at room temperature with a mixer, kneaded at 70 to 100 ° C. with a biaxial roll, cooled, and pulverized to obtain a molding material. The spiral flow of the obtained molding material is 112c.
m, gel time at 175 ° C. is 35 seconds,
After storage for one day, the storage stability was 100%, the curability was 82, and the solder resistance was 0/8.

Examples 2 to 5 In the same manner as in Example 1, the molding materials obtained by blending according to the compositions shown in Table 1 were evaluated. In Examples 2 and 3, the epoxy resin represented by the formula (5) (melting point: 96 ° C.) was used. Further, in Examples 2 and 5, YX4000H (Yukaka Epoxy Co., Ltd., melting point 105 ° C., epoxy equivalent 185)
g / eq).

Embedded image In Examples 2 and 4, a phenol aralkyl resin (Mitsui Toatsu Chemical Co., Ltd., XL-225-3L, softening point 95 ° C, hydroxyl equivalent 177 g / eq) was used. In Example 2, the latent catalyst represented by the formula (6) was used.

[0024]

Embedded image Note that the tetraphenylphosphonium.
The molten mixture of tetraphenyl borate is a phenol novolak resin (softening point 62 ° C., hydroxyl equivalent 105 g /
eq) 90 parts by weight and 10 parts by weight of tetraphenylphosphonium / tetraphenylborate are melt-mixed (hereinafter PT
1).

In Examples 3 and 5, the latent catalyst represented by the formula (7) was used.

Embedded image

The resin compositions of Examples 1 to 6 all have good fluidity immediately after production, and even after storage at 25 ° C. for 3 days, all have a spiral flow value of 90% or more immediately after production. It shows excellent storage stability. The gel time at 175 ° C. is in the range of 25 to 35 seconds, the molding workability is good, and the Shore D hardness is 82 to 8 by curing.
8 has been reached. No crack occurred in the solder resistance test. Table 1 shows the results of these evaluations.

Evaluation method Spiral flow: Measured using a mold for measuring spiral flow according to EMMI-I-66, at a mold temperature of 175 ° C., an injection pressure of 70 kg / cm ² , and a curing time of 2 minutes. (C
m). Gel time: after melting the resin composition on a hot plate at 175 ° C,
Measure the time until hardening while kneading with a spatula. (Seconds). Storage at 25 ° C .: After storing the resin composition at 25 ° C. for 3 days, the spiral flow is measured and expressed as a percentage of the spiral flow immediately after the preparation of the resin composition. (%). Curability: The resin composition was molded at a mold temperature of 175 ° C. for a curing time of 2 minutes, and after opening the mold, the Shore D hardness was measured. measured value. Solder resistance: The obtained resin composition was tableted and subjected to low pressure transfer molding at 175 ° C and 100 kg / cm.
^{2. A} 6x6mm chip is 80pQF under the condition of 120 seconds.
P (1.5 mm thick) and packaged 8 packages at 85
168 hours at 85 ° C and 85% relative humidity, then 240 ° C
And the number of package cracks was observed with a microscope. When the number of cracked packages was n, n / 8 was displayed.

Comparative Examples 1 to 5 In the same manner as in Example 1, the resin compositions obtained according to the compositions shown in Table 2 were evaluated. The melt mixture of tetraphenylphosphonium / tetraphenylborate used in Comparative Example 3 is a phenol novolak resin (softening point: 62 ° C., hydroxyl equivalent: 105 g / eq), 85 parts by weight, and 15 parts by weight of tetraphenylphosphonium / tetraphenylborate. Is melt-mixed (hereinafter referred to as PT2). The resin compositions of Comparative Examples 1 to 3 and 4 contained 25
After storage at 3 ° C. for 3 days, the spiral flow value was reduced to 68 to 76% of the value immediately after production, and the storage stability was poor. The resin composition of Comparative Example 5 was insufficient in the amount of the latent catalyst, did not cure at all even by heating for 2 minutes, and could not be molded. Table 2 shows the evaluation results.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

The epoxy resin composition of the present invention does not progress curing at room temperature, has excellent storage stability for a long period of time, and exhibits a curing reaction only when heated during molding, and has good moldability and high quality. A semiconductor device can be obtained.

Claims (3)

[Claims] 1. An epoxy resin comprising (A) an epoxy resin represented by the formula (1) in an amount of 30 to 100% by weight based on the total amount of the epoxy resin. (In the formula, R ₁ is hydrogen, a chain or cyclic alkyl group having 1 to 6 carbon atoms, a phenyl group, a group selected from halogen, or an atom. (B) a phenolic resin curing agent having two or more phenolic hydroxyl groups in one molecule, (C) an inorganic filler, and (D)
A latent catalyst comprising a phosphonium borate represented by the formula (2) is an essential component, and the equivalent ratio of the epoxy group of the epoxy resin (A) to the phenolic hydroxyl group of the phenol resin curing agent (B) is 0.5 to 2. Yes, the content of the inorganic filler (C) is a total amount of the epoxy resin and the phenol resin curing agent of 10
It is 250 to 1400 parts by weight per 0 parts by weight, and the content of the latent catalyst (D) is 0.4 to 20 parts by weight per 100 parts by weight of the total amount of the epoxy resin and the phenol resin curing agent. Epoxy resin composition for semiconductor encapsulation. Embedded image (However, in the formula, X ₁ , X ₂ , X ₃ and X ₄ are monovalent organic acids or monovalent aliphatic groups having an aromatic ring or a heterocyclic ring, and they are different even if they are the same. Y ₁ , Y ₂ , Y ₃ and Y ₄ are a monovalent organic acid or a monovalent aliphatic group having an aromatic ring or a heterocyclic ring, and at least one of them is A proton donor having at least one proton that can be released outside the molecule is a group that releases one proton, and they may be the same or different from each other.) 2. The epoxy resin for semiconductor encapsulation according to claim 1, wherein the proton donor of the latent catalyst represented by the formula (2) is an aromatic carboxylic acid having at least one carboxyl group in one molecule. Composition. 3. The epoxy resin composition for semiconductor encapsulation according to claim 1, wherein the proton donor of the latent catalyst represented by the formula (2) is a phenolic compound having at least one hydroxyl group in one molecule. .