JPH0912994A - Bonding composition and bonding sheet - Google Patents

Abstract

PURPOSE: To obtain a bonding composition, comprising a specific epoxy resin mixture and a curing agent, having a moderate sheet strength and flexibility before bonding and further excellent heat resistance after the bonding and capable of readily and stably providing the bonding sheet used for the production, etc., of circuit substrates. CONSTITUTION: This bonding sheet comprises (A) an epoxy resin mixture, comprising two or more epoxy resins having different epoxy equivalents such as bisphenol A type and having 250-1500 apparent epoxy equivalent and (B) a curing agent such as a compound of the formula (ROH and R'OH are each hydroxyalkyl; X is phenyl or naphthalene). Furthermore, the bonding sheet is preferably produced by using the bonding composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive composition and an adhesive sheet used for manufacturing circuit boards, electronic parts and the like.

[0002]

2. Description of the Related Art Glass-epoxy resin-based, polyimide resin-based, for manufacturing circuit boards and bonding electronic components to circuit boards,
Electrically insulating adhesives or adhesive sheets that can be thermocompression-bonded, such as polyester resin, are often used, but these adhesives and adhesive sheets are being used in various ways as the performance and diversification of electronic devices have increased in recent years. Characteristics are required.

For example, an adhesive sheet used for a circuit board for applications such as a power source is required to have high thermal conductivity as the heat generated by the increase in electric power of electronic parts increases, and in Japanese Patent Laid-Open No. 5-179210. It is disclosed that high heat conductivity is achieved by filling the adhesive sheet with a heat conductive filler.

However, the filling of the filler lowers the ratio of the organic binder that exerts the strength of the adhesive sheet, so that there is a problem that the strength of the adhesive sheet is lowered or the flexibility is lost.

Japanese Patent Laid-Open No. 6-108016 discloses a method of using a high molecular weight epoxy resin, so-called phenoxy resin, as a part of a binder for the purpose of ensuring that the adhesive sheet has appropriate strength and flexibility. Though
There is a problem that the heat resistance of the circuit board obtained by using this is not sufficient.

[0006]

SUMMARY OF THE INVENTION An object of the present invention relates to an adhesive sheet used for manufacturing a circuit board or the like, which has appropriate sheet strength and flexibility before adhesion and excellent heat resistance after adhesion. An object of the present invention is to provide an adhesive sheet having the same and an adhesive composition that can easily obtain the same.

[0007]

The present invention is an adhesive composition containing an epoxy resin mixture comprising at least two epoxy resins having different epoxy equivalents and a curing agent, and the apparent appearance of the epoxy resin mixture. It has an epoxy equivalent of 250 or more and 1500 or less.

The present invention is the above adhesive composition, wherein the curing agent is an imidazole having a phenyl group or a naphthalene group at the 2-position and a hydroxyalkyl group at the 4- and 5-positions. , And more preferably,
The adhesive composition is characterized in that the imidazole is 2-phenyl4,5 dihydroxymethylimidazole.

Further, according to the present invention, among the epoxy resins constituting the epoxy resin mixture, the epoxy resin having the largest epoxy equivalent has an epoxy equivalent of 2000 or more and 5 or more.
The adhesive composition is characterized in that it is 000 or less.

Furthermore, the present invention is an adhesive sheet comprising the above-mentioned adhesive composition and having a thickness of 20 μm or more and 300 μm or less.

The present invention will be described in more detail below.

As a result of intensive investigations aimed at solving the above-mentioned problems, the present inventors have found that when an epoxy resin mixture having an apparent epoxy equivalent in a specific range is selected, the heat resistance of the cured product after curing the epoxy resin mixture is high. It has been experimentally found to be improved, and the present invention has been achieved.

The epoxy resin mixture obtained by mixing at least two kinds of epoxy resins having different epoxy equivalents has an apparent epoxy equivalent of 250 or more and 1500 or less. Here, the apparent epoxy equivalent is an average value obtained by weighting the respective epoxy equivalents of two or more kinds of epoxy resins with a mixing ratio on a weight basis. For example, the epoxy equivalent E of an epoxy resin mixture obtained by mixing W1 grams of an epoxy resin having an epoxy equivalent of E1 and W2 grams of an epoxy resin having an epoxy equivalent of E2 is calculated by the following formula. E = E1 * (W1 / W) + E2 * (W2 / W) where W = W1 + W2. Even if they have the same epoxy equivalents, when two or more epoxy resins with different epoxy equivalents are mixed, the sheet strength and flexibility are improved compared to the case where the epoxy resins are used alone, and further curing The heat resistance of the body is improved. The reason for this is unknown, but it can be interpreted as follows.

That is, when two or more epoxy resins having different epoxy equivalents are mixed even if the apparent epoxy equivalents are the same, the epoxy equivalent is larger than the apparent value and a high molecular weight epoxy resin is present. Therefore, the sheet strength is increased and the flexibility is also improved. On the other hand, regarding the heat resistance of the cured product, the presence of a low molecular weight epoxy resin having an epoxy equivalent smaller than the apparent value effectively develops a crosslinked structure and improves the heat resistance.

When the apparent epoxy equivalent of the epoxy resin mixture containing at least two kinds of epoxy resins having different epoxy equivalents is less than 250, a strong adhesive force is obtained, but conversely, when an adhesive sheet is produced. Peeling from the carrier sheet or the like becomes difficult. When it exceeds 1500, the heat resistance of the cured product is not sufficient. 250 or more and 1500 or less are selected from the balance of both. In particular, 300 or more and 1000 or less are more preferable because both can be balanced.

Among the epoxy resins constituting the epoxy resin mixture, the epoxy equivalent of the epoxy resin having the largest epoxy equivalent is 2000 or more and 5000 or less. When an epoxy resin having an epoxy equivalent of less than 2000 is used, a strong adhesive force can be obtained, but the flexibility and the strength of the obtained adhesive sheet are not always sufficient, and the object of the present invention can be achieved. Can not. On the other hand, the epoxy equivalent of commercially available epoxy resin is 130-
It is not easy to industrially and inexpensively obtain an epoxy resin having an epoxy equivalent of 5000 or more than 5000.

As the epoxy resin of the present invention, bisphenol A type, bisphenol F type, naphthol type, those substituted with halogen such as bromine, and those having a skeleton such as an ether bond with glycidyl alcohol are known. Any of these can be used in the present invention. Further, the epoxy resin having the above skeleton partially contains a silicone rubber unit, an imide unit represented by polyimide, an ester unit derived from polyester, a carboxyl group derived from a polyacrylic derivative and a carbon-carbon single bond. It does not matter even if it is.

The curing agent in the present invention must have the property of not curing the epoxy resin only by mixing it with the epoxy resin, and also of curing the epoxy resin after heating (so-called latent curability). That is, it is important that the epoxy resin is kept in an uncured state (called a B stage state) before heating. The heating conditions are, for example, 180 ° C. and 30 kg in the manufacture of circuit boards.
A thermocompression bonding condition of / cm ² for 1 hour is common.

Dicyandiamide is generally used as a curing agent having the latent curability described above, but the cured product thereof swells in a heat resistance test under the conditions of, for example, 260 ° C. and 1 hour. Further, although imidazoles are known,
General-purpose imidazole, such as 2-methyl-4-ethylimidazole, cures quickly and cannot be stored in the B stage state. For this reason, measures are taken to reduce the reactivity of the imidazole by reducing the solubility of the imidazole in the epoxy resin or the solvent thereof, the resin to be added, and the like by the bulky substituent. As such an imidazole, 2 phenyl 4 methyl 5 hydroxymethyl imidazole can be mentioned, but it has a drawback that the obtained cured product has poor heat resistance.

The present inventors have experimentally studied various curing agents, and imidazole having a phenyl group or a naphthalene group at the 2-position and a hydroxyalkyl group at the 4- and 5-positions, especially 2phenyl-4. It was found that 5 dihydroxymethylimidazole has an excellent latent curability, and the present invention has been completed.

That is, by introducing a hydroxyalkyl group at both the 4 and 5 positions, the cross-linking point at the time of curing is increased as compared with the conventional curing agent having a hydroxyalkyl group at either the 4 or 5 position. Can be increased, and the heat resistance of the cured product can be improved. However, when a hydroxyl group is introduced into both the 4th and 5th positions, the reactivity becomes high probably due to the high solubility in the epoxy resin, and there is a drawback that the latent curing agent has poor stability. The present inventors further studied based on the idea of introducing a bulky functional group to improve the above-mentioned drawbacks, and as a result, by introducing a phenyl group or a naphthalene group at the 2-position,
In addition to the ability to impart latent curability, 4
It was found that the heat resistance of the cured product can be improved by introducing a hydroxyalkyl group at the 5 and 5 positions. It is preferable that the length of the alkyl moiety of the 4- and 5-position hydroxyalkyl groups is shorter from the viewpoint of heat resistance and strength of the cured product. It may or may not match the length of the alkyl portion of the alkyl group.
Further, the introduction position of the hydroxy group in the hydroxyalkyl group is generally selected at the terminal of the alkyl group, but the present invention is not limited to this.

An adhesive sheet made of an adhesive composition containing the above resin and a curing agent is formed on a carrier sheet such as a PET film by a general sheet forming method such as a doctor blade method, an extrusion method or a roll coater method. Obtainable. The thickness of the adhesive sheet is 20 μm or more and 30
0 μm or less. If it is less than 20 μm, a sufficiently homogeneous sheet cannot be stably obtained, and 300 μm
Those having a heat resistance of more than 50% have poor thermal resistance and cannot be of practical value for use in manufacturing circuit boards.

As long as the adhesive composition and adhesive sheet of the present invention are kept in the B stage state,
It may contain a filler or various additives. As the resin other than the above resins, any resin having an epoxy functional group and capable of being cured may be used, and any resin having a monofunctional, bifunctional, trifunctional or higher functional epoxy group may be used.

As the above-mentioned filler, for example, gold, silver, copper, aluminum, nickel, carbon containing graphite, conductive materials such as titanium nitride and silicon carbide, aluminum oxide, aluminum nitride, and nitride are used depending on the application. Materials having high thermal conductivity such as boron, silicon oxide, silicon nitride, boron carbide, titanium oxide and diamond can be used. These fillers may be treated with a coupling agent such as glycidoxypropyltrimethoxysilane.

In the adhesive sheet for manufacturing a circuit board, electrically insulating aluminum oxide, silicon oxide, boron nitride, aluminum nitride or the like is highly filled from the above-mentioned filler for the purpose of obtaining high thermal conductivity. The blending ratio is 25% by weight to 95% by weight. If it is less than 25% by weight, the characteristics of the filler are not sufficiently exhibited, and if it exceeds 95% by weight, the strength is lowered and the sheet cannot be kept. Preferably 50% to 85% by weight is selected.

As various additives, a defoaming agent, a flame retardant, a chelating agent, an antioxidant, an antiaging agent, a wax, a dispersion aid, a leveling agent, an anticorrosive agent, and a solvent may be used in combination. You can As the solvent, toluene, aromatic hydrocarbon represented by xylene, methyl ethyl ketone,
Ketones such as acetone, or a cellosolve system or the like is used for the purpose of adjusting the evaporation rate and lowering the structural viscosity.

Hereinafter, the present invention will be described in more detail with reference to Examples.

【Example】

[Examples 1 to 10 and Comparative Examples 1 to 3] Epoxy resins having various epoxy equivalents were mixed in the proportions shown in Table 1,
100 parts thereof was mixed with 100 parts of toluene-methyl ethyl ketone mixed solvent (toluene / methyl ethyl ketone = 80/20).
Part, heated and dissolved at 80 ° C. After cooling to room temperature, 300 parts of aluminum oxide powder (average particle size 2.5 μm), 3 parts of a silane coupling agent (manufactured by Nippon Unicar Co., A-187) and a curing agent such as 2 phenyl 4,5 dihydroxymethylimidazole. Two parts were added and the mixture was passed through a three-roll mill and kneaded.
In addition, in some cases, three kinds of epoxy resins having different epoxy equivalents were used, or the case where the epoxy resin was used alone was examined. After the stability of the obtained slurry was examined, it was applied on a PET film with a predetermined thickness by the doctor blade method, and the solvent was removed in a blow dryer to obtain an adhesive sheet. This adhesive sheet was evaluated for releasability from the PET film and flexibility. Next, the above adhesive sheet was sandwiched between an aluminum plate having a thickness of 1.5 mm and a copper foil having a thickness of 35 μm,
A circuit board was produced by press-pressing at 30 ° C. and 30 kg / cm 2 for 1 hour. The dielectric strength of this circuit board was measured before and after heating at 260 ° C. for 1 hour. Table 1 shows the above results.
It is summarized and shown.

[0028]

[Table 1]

[0029]

EFFECTS OF THE INVENTION The adhesive composition of the present invention has suitable sheet strength and flexibility before adhesion and excellent heat resistance after adhesion, and is used for the manufacture of circuit boards. The elastic sheet can be easily and stably obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Kato 3-5-1, Asahimachi, Machida-shi, Tokyo Denka Kagaku Kogyo Co., Ltd.

Claims (5)

[Claims] 1. An adhesive composition comprising an epoxy resin mixture comprising at least two epoxy resins having different epoxy equivalents and a curing agent, wherein the epoxy resin mixture has an apparent epoxy equivalent of 250 or more and 1500 or less. An adhesive composition comprising: 2. The adhesive composition according to claim 1, wherein the curing agent is represented by the following chemical formula (1). Embedded image (However, ROH and R'OH in the chemical formula are hydroxyalkyl groups, and X is a phenyl group or a naphthalene group.) 3. The adhesive property according to claim 2, wherein in the chemical formula (1), the curing agent is a hydroxymethyl group for both ROH and R′OH, and X is a phenyl group. Composition. 4. The adhesive composition according to claim 1, wherein among the epoxy resins constituting the epoxy resin mixture, the epoxy resin having the largest epoxy equivalent has an epoxy equivalent of 2000 or more and 5000 or less. 5. An adhesive sheet comprising the adhesive composition according to claim 1, claim 2, claim 3 or claim 4.