JP3703143B2 - Interlayer insulating adhesive for multilayer printed wiring board and copper foil with interlayer insulating adhesive for multilayer printed wiring board - Google Patents

Description

TECHNICAL FIELD The present invention relates to an interlayer insulating agent for multilayer printed wiring boards, and in particular, an epoxy resin-based interlayer insulation that is excellent in high heat resistance, high electrical properties, flame retardancy, and storage stability and can be rapidly cured at a high temperature of 100 ° C. or higher. It relates to adhesives.
The present invention also relates to a copper foil with an interlayer insulating adhesive for multilayer printed wiring boards.

  Conventionally, when manufacturing a multilayer printed wiring board, one or more prepreg sheets obtained by impregnating a glass cloth base material with an epoxy resin and semi-cured are stacked on an inner layer circuit board on which a circuit is formed, and copper foil is further formed thereon. Is subjected to a process of pressure integral molding with a stacked hot plate press. However, in this step, since the impregnated resin in the prepreg is reflowed by heat and cured under a constant pressure, 1 to 1.5 hours are required for uniform curing and molding. Thus, the manufacturing process takes a long time, and the cost is high due to the cost of the multilayer lamination press and the glass cloth prepreg. In addition, since the glass cloth is impregnated with the resin, the thickness between the circuit layers is limited by the glass cloth, and it is difficult to make the entire multilayer printed wiring board extremely thin. In recent years, in order to solve these problems, a technique of a multilayer printed wiring board by a build-up method that does not perform heat and pressure molding by a hot plate press and does not use glass cloth as an interlayer insulating material has attracted attention again.

JP-A-5-327208

  The present inventor is examining various methods for producing a multilayer printed wiring board at a low cost by a simplified build-up method as compared with the method of forming by the hot plate press. In multilayer printed wiring boards using the build-up method, when a film-like interlayer insulating resin layer is used, the inner layer circuit board is undercoated in order to eliminate the steps and smooth the surface. It has become common to apply agents. As a typical example of this, multilayer printed wiring is obtained by laminating a copper foil coated with an interlayer insulating adhesive and curing it integrally while the undercoat agent applied to the inner layer circuit board is uncured, semi-cured or cured. Get a board. By such a method, the level difference due to the circuit of the inner layer circuit board is reduced, so that it is easy to laminate the copper foil coated with the interlayer insulating adhesive, and the need to consider the copper foil remaining rate of the inner layer circuit board is reduced. .

The present invention relates to an interlayer insulating adhesive for multilayer printed wiring boards, comprising the following components (a), (b) and (c) as essential components.
(A) a polyethersulfone having a weight average molecular weight of 10 ³ to 10 ⁵ and having a hydroxyl group-modified terminal ;
(B) an epoxy resin having an epoxy equivalent of 500 or less,
(C) One or more acid anhydrides selected from methyltetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride Epoxy resin curing agent,
In the present invention, polyethersulfone whose component (a) has a weight-average molecular weight of 10 ³ to 10 ⁵ and has a hydroxyl group modified reduces the softening of the insulating adhesive during molding and maintains the thickness of the insulating layer after lamination. It is formulated for the purpose of imparting flexibility to the insulating layer and increasing the heat resistance of the insulating layer, but is expected to further improve flame retardancy and electrical characteristics. The proportion of the high molecular weight polyethersulfone is 10 to 90% by weight based on the whole insulating adhesive. If it is less than 10% by weight, the layer thickness cannot be ensured due to excessive softening due to heating during lamination molding. In addition, there is a problem that the melt viscosity is excessively lowered during heat curing and wrinkles are generated. On the other hand, if it is more than 90% by weight, the adhesive composition is hard and lacks elasticity, so that the followability to unevenness and adhesion at the time of laminate molding are poor, which causes generation of molding voids. Moreover, if the terminal of this high molecular weight polyether sulfone is modified with a hydroxyl group, the reactivity with the epoxy resin is good, so that the phase separation between the polyether sulfone and the epoxy resin after thermal curing is suppressed, and the cured product Also improves heat resistance. Therefore, it is desirable that the above modification is performed.

The present invention relates to an interlayer insulating adhesive for multilayer printed wiring boards, which contains the following components as essential components.
(B) a weight-average molecular weight 10 ³ to 10 ⁵ polyether sulfone, (ii) an epoxy equivalent of 500 or less of the epoxy resin, (C) an epoxy resin curing agent, in the present invention, (i) weight average molecular weight 10 ³ components -10 ⁵ polyethersulfone reduces the softening of the insulating adhesive during molding, maintains the thickness of the insulating layer after lamination, imparts flexibility to the insulating layer, and provides high heat resistance to the insulating layer However, it is expected to improve the flame retardancy and electrical characteristics. The proportion of the high molecular weight polyethersulfone is 10 to 90% by weight based on the whole insulating adhesive. If it is less than 10% by weight, the layer thickness cannot be ensured due to excessive softening due to heating during lamination molding. In addition, there is a problem that the melt viscosity is excessively lowered during heat curing and wrinkles are generated. On the other hand, if it is more than 90% by weight, the adhesive composition is hard and lacks elasticity, so that the followability to unevenness and adhesion at the time of laminate molding are poor, which causes generation of molding voids. In addition, if the terminal of this high molecular weight polyether sulfone is modified with a hydroxyl group, a carboxyl group or an amino group, the reactivity with the epoxy resin is good, so that the phase separation between the polyether sulfone and the epoxy resin is performed after heat curing. In addition, the heat resistance of the cured product is improved. Therefore, it is desirable that the above modification is performed.

  The interlayer insulating adhesive for multilayer printed wiring boards of the present invention is excellent in storage stability in a varnish state or coated on a copper foil, and has good integrated curing when laminated on an inner circuit board coated with an undercoat agent. Therefore, the obtained multilayer printed wiring board is particularly excellent in heat resistance, and has excellent characteristics such as flame resistance and moisture resistance as well as electrical characteristics.

  The above high molecular weight polyethersulfone alone has poor coatability and adhesiveness at the time of roll laminating, insufficient adhesiveness after laminating, destruction of the base material by the hot melt method, and coating of copper foil Therefore, when it is dissolved in a solvent to form a varnish at a predetermined temperature, the viscosity is high and the coatability and workability at the time of coating are not good. In order to improve such defects, an epoxy resin (b) having an epoxy equivalent of 500 or less is blended. This blending ratio is 10 to 90% by weight of the whole resin. If it is 10% by weight or less, the above effect cannot be expected, and if it is 90% by weight or more, the effect of the high molecular weight polyethersulfone cannot be expected.

  (B) Component epoxy resin includes bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, aminophenol type epoxy resin, etc. For imparting flame retardancy, a brominated epoxy resin having a bromination rate of 20% or more is preferred. When the bromination rate is less than 20%, the obtained multilayer printed wiring board cannot achieve flame retardancy V-0. If the brominated material is used, the multilayer printed wiring board is more effectively flame-retardant.

  Next, the epoxy resin curing agent of component (c) is not particularly limited, such as an amine compound, an imidazole compound, and an acid anhydride, but the imidazole compound sufficiently cures the epoxy resin even if the blending amount is small. It is preferable because it can exhibit the flame retardancy of the brominated epoxy resin. It is particularly preferable that the imidazole compound is solid at room temperature with a melting point of 130 ° C. or higher, has a low solubility in the epoxy resin, becomes a high temperature of 150 ° C. or higher, and reacts rapidly with the epoxy resin. Specifically, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, bis (2-ethyl-4-methyl-imidazole), 2-phenyl-4-methyl-5-hydroxymethylimidazole, Examples thereof include 2-phenyl-4,5-dihydroxymethylimidazole and triazine addition type imidazole. These imidazoles are uniformly dispersed as fine powder in the epoxy resin varnish. Since the compatibility with the epoxy resin is small, the reaction does not proceed at room temperature to 100 ° C., so that the storage stability can be kept good. And when it heats to 150 degreeC or more at the time of lamination hardening, it will react with an epoxy resin and a uniform hardened | cured material will be obtained.

  Other curing agents include phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, anhydrous Examples include acid anhydrides such as hexahydrophthalic acid, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, boron trifluoride amine complexes, dicyandiamide or derivatives thereof, and these are epoxy adducts. Or microencapsulated ones can also be used. In addition to the epoxy resin and the curing agent, a component that reacts with the epoxy resin and the curing agent can be blended. For example, epoxy reactive diluents (such as phenyl glycidyl ether as monofunctional type, resorcin diglycidyl ether, ethylene glycol glycidyl ether as bifunctional type, glycerol triglycidyl ether as trifunctional type), resole type or novolac type phenol Resins, isocyanate compounds and the like.

  In addition to the above components, in order to improve the linear expansion coefficient, heat resistance, flame resistance, etc., fused silica, crystalline silica, calcium carbonate, aluminum hydroxide, alumina, clay, barium sulfate, mica, talc, white carbon, You may mix | blend E glass fine powder etc. 40weight% or less with respect to resin content. When the blending amount is more than 40% by weight, the viscosity of the adhesive is increased, and the embedding property between the inner layer circuits is lowered. Furthermore, in order to increase the adhesion between the copper foil and the inner layer circuit board, or to improve moisture resistance, a silane coupling agent or titanate coupling agent such as epoxy silane, an antifoaming agent to prevent voids, or liquid or It is also possible to add a fine powder type flame retardant.

  As the solvent, after the adhesive is applied to the copper foil and dried, a solvent that does not remain in the adhesive must be selected. For example, acetone, methyl ethyl ketone (MEK), toluene, xylene, n-hexane, methanol, ethanol, methyl cellosolve, ethyl cellosolve, cyclohexanone, dimethylformamide (DMF) and the like are used. The copper foil with an interlayer insulating adhesive is an adhesive that is coated with an adhesive varnish obtained by dissolving an adhesive component in a predetermined solvent at a predetermined concentration on the anchor surface of the copper foil, and then dried at 80 ° C. to 130 ° C. It is made so that no solvent remains in it. The thickness of the adhesive layer is preferably 15 to 120 μm. If the thickness is less than 15 μm, the interlayer insulation may be insufficient. If the thickness is more than 120 μm, there is no problem with the interlayer insulation, but the fabrication is not easy, and it does not meet the purpose of the present invention to reduce the thickness of the multilayer board. .

  This copper foil with an interlayer insulating adhesive can be laminated and cured on an inner layer circuit board by a normal dry film laminator to easily form a multilayer printed wiring board having an outer layer circuit. Next, an undercoat agent used to eliminate a step due to the circuit of the inner layer circuit board will be described. The undercoat agent is usually made of the same type of material as that used for integrally curing with the interlayer insulating adhesive. Accordingly, in the present invention, an epoxy resin, preferably one containing a brominated epoxy resin as a main component is used. However, a varnish dissolved in a solvent or a varnish dissolved in a reactive diluent that reacts with heat or light may be used. Such an undercoat agent varnish is applied to the inner circuit board, and then heated to cause tack-free or prepolymerization by evaporation or reaction of the solvent, or by light irradiation for tack-free or prepolymerization by reaction.

(Example 1)
Terminal hydroxyl group-modified polyethersulfone (average molecular weight 24000) 100 parts by weight (hereinafter, all compounding amounts represent parts by weight), brominated phenol novolac type epoxy resin 200 parts (epoxy equivalent 285, Nippon Kayaku Co., Ltd. BREN) -S) and 100 parts of a bisphenol F type epoxy resin (epoxy equivalent 175, manufactured by Dainippon Ink & Chemicals, Inc., Epicron 830) were stirred and dissolved in a mixed solvent of MEK and DMF. Thereto, 5 parts of 2-methylimidazole, 0.2 part of titanate coupling agent (KR-46B manufactured by Ajinomoto Co., Inc.) and 20 parts of barium sulfate were added as a curing agent to prepare an adhesive varnish.

  Hereinafter, a multilayer printed wiring board was produced in the process shown in FIG. The adhesive varnish was applied to an anchor surface of a copper foil (1) having a thickness of 18 μm with a roller coater so that the thickness after drying was 50 μm, and dried to obtain a copper foil (3) with an insulating adhesive. (A). Next, 100 parts of bisphenol A type epoxy resin (epoxy equivalent 470, weight average molecular weight about 900) is dissolved in 40 parts of glycidyl methacrylate, and 3 parts of 2-methylimidazole and a photopolymerization initiator (Irgacure made by Ciba Geigy) are used as a curing agent. 651) 1.2 parts were added and stirred thoroughly to obtain an undercoat agent.

  Furthermore, a glass epoxy double-sided copper-clad laminate having a substrate thickness of 0.1 mm and a copper foil thickness of 35 μm was patterned to obtain an inner layer circuit board. After the copper foil surface was blackened, the undercoat agent was applied to a thickness of about 40 μm using a curtain coater. Thereafter, UV irradiation was carried out with two 80 W / cm high-pressure mercury lamps on a UV conveyor machine under the condition of about 2 J / cm 2 to make the undercoat agent tack-free. Insulating adhesion of the copper foil with an insulating adhesive on the inner circuit board having the undercoat agent layer using a hard roll under the conditions of a temperature of 100 ° C., a pressure of 4 kg / cm 2, and a laminating speed of 0.8 m / min. The copper foil with the agent was laminated and heat cured at 150 ° C. for 30 minutes to produce a multilayer printed wiring board.

(Examples 2-3)
Example 1 except that the imidazole used for the interlayer insulating adhesive and the undercoat agent was changed from 2-methylimidazole to 2-phenyl-4-methylimidazole or 2-phenyl-4-methyl-5-hydroxymethylimidazole, respectively. In the same manner, a multilayer printed wiring board was produced.

(Example 4)
Terminal hydroxyl group-modified polyethersulfone (average molecular weight 24000) 100 parts, brominated phenol novolac type epoxy resin 70 parts (epoxy equivalent 285, Nippon Kayaku Co., Ltd. BREN-S), bisphenol F type epoxy resin (epoxy equivalent 175) A multilayer printed wiring board was produced in the same manner as in Example 1 using 30 parts of Daikoku Ink Chemical Co., Ltd., Epiklon 830).

(Example 5)
Terminal hydroxyl group-modified polyethersulfone (average molecular weight 24000) 100 parts, brominated phenol novolac type epoxy resin 70 parts (epoxy equivalent 285, Nippon Kayaku Co., Ltd. BREN-S), aminophenol type epoxy resin (epoxy equivalent 107) , 35 parts of Sumitomo Chemical Co., Ltd. ELM-100) was stirred and dissolved in MEK. There, 35 parts of methyltetrahydrophthalic anhydride as a curing agent, 0.5 parts of 2-phenyl-4-methyl-5-hydroxymethylimidazole as a curing accelerator, titanate coupling agent (KR-46B, manufactured by Ajinomoto Co., Inc.) An adhesive varnish was prepared by adding 0.2 part and 20 parts of barium sulfate, and a multilayer printed wiring board was prepared in the same manner as in Example 1.

(Comparative Example 1)
Example 1 except that 100 parts of brominated phenoxy resin (bromination rate 25%, average molecular weight 30000) 100 parts and 50 parts of bisphenol F type epoxy resin (epoxy equivalent 175, Epiklon 830 manufactured by Dainippon Ink & Chemicals, Inc.) were used. In the same manner, a multilayer printed wiring board was obtained.

  About the obtained multilayer printed wiring board, surface smoothness, moisture absorption solder heat resistance, peel strength, and flame retardance were measured, and the results shown in Table 1 were obtained.

(Measuring method)
Inner layer circuit board test piece: 150 μm pitch between lines, clearance hole 1.0 mmφ
1. Surface smoothness: JIS B 0601 R (max)
2. Moisture-absorbing solder heat resistance moisture absorption conditions: pressure cooker treatment, 125 ° C., 2.3 atm, 30 minutes Test conditions: n = 5, all were 280 ° C. for 120 seconds and no bulge was evaluated as “Good”.
3. Peel strength: According to JIS C 6486.
4). By loss tangent of dynamic viscoelasticity measurement.

Schematic cross-sectional view showing the process of producing a multilayer printed wiring board (example) of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner layer circuit board 2 Inner layer circuit 3 Undercoat agent 4 Thermosetting type insulating adhesive 5 Copper foil 6 Hard roll 7 Multilayer printed wiring board

Claims (2)

An interlayer insulating adhesive for multilayer printed wiring boards comprising the following components (a), (b) and (c) as essential components.
(A) Epoxy resin having a weight average molecular weight of 10 ³ to 10 ⁵ and a terminal-modified polyethersulfone (b) epoxy equivalent of 500 or less (c) methyltetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride An epoxy resin curing agent which is one or more of acid anhydrides selected from methylbutenyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride A copper foil with an interlayer insulating adhesive for multilayer printed wiring boards, wherein the interlayer insulating adhesive according to claim 1 is coated on a copper foil.

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