BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an epoxy resin composition, and a prepreg and a printed wiring board using the epoxy resin composition, and more particularly to an epoxy resin composition including a composite curing agent, and a prepreg impregnated with such a composition and a printed circuit board (PCB) manufactured by using such a prepreg.

2. The Prior Arts

The quality of a PCB not only affects the reliability and efficiency of an electronic device, but also impacts the overall performance of the entire electronic system. The copper-clad laminate (CCL), which is widely used for manufacturing a printed circuit board, is generally composed of a reinforcing material, a thermosetting resin, and a copper foil. The thermosetting resin is, for example, an epoxy resin, a phenolic resin, a polyurethane resin, or a polyether-imide resin. The reinforcing material is, for example, glass cloth, kraft paper, or cotton fabric.

A conventional copper-clad laminate was typically manufactured via a three-step process. In a first step, a fiberglass cloth was impregnated with a thermosetting resin dissolved in a solvent, and followed by partially curing (B-stage) the impregnated fiberglass cloth at a temperature of not higher than 300Â° C. to form a prepreg. In a second step, a copper foil was laminated onto one side or both sides of the prepreg. In a third step, the prepreg and the copper foils are bonded together with heat and pressure to form the copper-clad laminate. The printed circuit board is thus obtained by printing an etching resist on the copper-clad laminate, etching the copper-clad laminate with the etching resist thereon, and removing the etching resist to form a predetermined circuit pattern on the copper-clad laminate.

The copper-clad laminate or the printed circuit board must meet the criteria for heat resistance, dielectric properties, and chemical resistance, and it is worthy of note that the thermosetting resin plays a key role in improving the properties of the copper-clad laminate or the printed circuit board. The thermosetting resin can be cross-linked with a multi-functional amine to form an interpenetrating polymeric network (IPN). Although IPNs have favorable properties such as high glass transition temperature and high chemical resistance, they have the drawback of being too brittle to be processed as prepregs. For instance, it proves impossible to cut up such prepregs without a portion of the resin blowing about in the form of a large quantity of dry dust.

TW patent No. 293831 and WO2006004118A1 disclose an epoxy resin composition including an amino-triazine-novolac (ATN) resin used as curing agent for epoxy resin. The ATN resin can be represented by the general formula given below:

[Image Omitted]

The ATN resin was prepared by reacting a phenolic compound, an aldehyde compound and a guanamine compound in the presence of an acid catalyst such as oxalic acid or p-toluene sulfonic acid. The phenolic compound used includes, for example, phenol, resorcin, and alkyl phenols such as cresol and xylenol. The aldehyde compound used includes, for example, formaldehyde. The guanamine compound can be represented by the general formula given below:

[Image Omitted]

where R is amino, phenyl, or alkyl such as methyl.

The guanamine compound used includes, for example, melamine, benzoguanamine, and methyl guanamine.

In TW patent No. 293831 and WO2006004118A1, when the ATN resin was used as a curing agent for epoxy resin, it could improve the heat resistance of the copper-clad laminate made from such epoxy resin. Also, the ATN resin, which is a phenolic-aldehyde resin, can react well with the epoxy resin used for the fabrication of the copper-clad laminate. However, the copper-clad laminate using ATN resin as a curing agent is not easily to be processed, and has unsatisfactory electrical performance.

On the other hand, TW patent No. 1231729 of the applicant of this present invention disclosed an epoxy resin composition that included dicyandiamide (DICY) used as a curing agent. The curing reaction scheme for epoxy resin with DICY is shown as following:

[Image Omitted]

The DICY is often used in the halogen-free flame-retardant epoxy resin composition because it can improve the properties of the laminate for PCB such as tenacity and processibility. However, the drawback to epoxy resin composition including DICY is that it has high water absorption and low heat resistance. Therefore, the epoxy resin cured with DICY often cannot withstand the high temperature and the long residence time associated with lead-free soldering processes. In addition, the drawback to DICY is that it has poor solubility to the commonly used solvents so that DICY may be undesirably precipitated on the surface of the prepregs from a varnish of the resin composition, which renders it unsuitable for use in the prepregs applied in the laminates for PCB. Furthermore, DICY has the disadvantage that it can only dissolve in toxic solvents, e.g., dimethylformamide (DMF) that is harmful to the human being. Notwithstanding the foregoing problems, DICY is still desirable to be applied to the epoxy resin composition for improving the reactivity of epoxy resin.

Therefore, there is a need for providing a curing agent that will improve the processibility and the dielectric properties of the epoxy resin used for the fabrication of the copper-clad laminate or PCB while rendering the epoxy resin to have high glass transition temperature, high heat resistance, and low water absorption.

SUMMARY OF THE INVENTION

Accordingly, an objective of the present invention is to provide an improved epoxy resin composition having superior heat resistance, dielectric properties, water resistance, and processibility by use of a specific composite curing agent in order to solve the above-described problems of the resin composition by use of the conventional curing agents, and also to provide a prepreg and a printed circuit board prepared from such an epoxy resin composition.

To achieve the above objective, the present invention provides an epoxy resin composition comprising: (A) an epoxy resin having at least two epoxy groups in one molecule; and (B) a composite curing agent comprising 30 to 50 parts by weight of amino-triazine-novolac (ATN) resin, and 0.1 to 8 parts by weight of dicyandiamide (DICY), based on 100 parts by weight of the epoxy resin.

The epoxy resin composition of the present invention can preferably include a curing accelerator additionally.

The epoxy resin composition of the present invention can optionally include an inorganic filler.

The present invention further provides a prepreg produced by impregnating a reinforcing material with the epoxy resin composition of the present invention to form an impregnated substrate, and drying the impregnated substrate to a semi-cured state.

The present invention yet further provides a PCB produced by laminating a particular number of the prepregs of the present invention to form a prepreg laminate, placing a metal foil on at least one outermost layer of the prepreg laminate and heat pressure-molding the prepreg laminate to form a metal-clad laminate, and forming a particular circuit pattern on the surface of the metal foil on the metal-clad laminate.

The objective, characteristics, aspects, and advantages of the present invention will become more evident in the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the present embodiment, the epoxy resin composition for the printed circuit board comprises: (A) 100 parts by weight of an epoxy resin having at least two epoxy groups in one molecule; (B) a composite curing agent comprising 30 to 50 parts by weight of amino-triazine-novolac (ATN) resin, and 0.1 to 8 parts by weight of dicyandiamide (DICY); (C) 0.01 to 1.0 parts by weight of a curing accelerator; and (D) 0 to 80 parts by weight of an inorganic filler, wherein the weight ratio of the ATN resin to DICY is in the range of from 1:0.01 to 1:0.10, and preferably 1:0.05. The parts by weight of components (B), (C), and (D) are based on 100 parts by weight of the epoxy resin (component (A)).

The epoxy resin (A) used in the epoxy resin composition of the present invention has at least two epoxy groups in one molecule. Examples of the epoxy resin used in the present invention include, but are not limited to, bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, phenolic novolak epoxy resin, cresol novolak epoxy resin such as DOPO-CNE (which is obtained by reacting 10-dihydro-9-oxa-10-phosphahenanthrene-10-oxide (DOPO) with cresol novolac epoxy resin (CNE)), and glycidylamine epoxy resin. These epoxy resins can be used singly or in combination of two or more of them.

The composite curing agent (B) used in the epoxy resin composition of the present invention comprises ATN resin and DICY, wherein ATN resin and DICY can undergo a cross-linking reaction with the epoxy resin to form an interpenetrating polymeric network. The weight ratio of the ATN resin to DICY is in the range of from 1:0.01 to 1:0.10, and preferably 1:0.05. The amount of curing agents used usually depends on the ratio of the active hydrogen equivalent of the amine compound relative to the epoxy equivalent of the epoxy resin contained in the epoxy resin composition, and also depends on the properties of the reinforcing material used. Accordingly, 30 to 50 parts by weight of ATN resin and 0.1 to 8 parts by weight of DICY, based on 100 parts by weight of the epoxy resin, are used in the present invention. The main factors that affect the properties of the interpenetrating polymeric network are the interpenetrating degree, the component ratio and the crosslinking density. Accordingly, in the present invention, the weight ratio of the epoxy resin to the ATN resin is in the range of from 1:0.20 to 1:0.80, and preferably 1:0.40.

The curing accelerator (C) used in the epoxy resin composition of the present invention can be any compound that is used for accelerating the curing of an epoxy resin. Examples of the curing accelerator used in the present invention include, but are not limited to, imidazoles, more particularly alkyl substituted imidazoles such as 2-methylimidazole and 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl, 4-methylimidazole. Other suitable accelerators include tertiary amines, e.g. benzyldimethylamine and 4,4â€² and 3,3â€² diaminodiphenylsulphone. These curing accelerators can be used singly or in combination of two or more of them. One preferred curing accelerator is 2-methylimidazole. The amount of curing accelerator used is dependent on the type of epoxy resin, the type of curing agent, and the type of curing accelerator. The curing accelerator is present in the epoxy resin composition of the present invention in an amount from about 0.01 to 1.0 parts by weight, based on 100 parts by weight of the epoxy resin.

The optional inorganic filler (D) used in the epoxy resin composition of the present invention serves to impart additional flame retardancy, heat resistance and humidity resistance to the epoxy resin composition. Examples of the inorganic filler used in the present invention include, but are not limited to, fused silica, crystalline silica, silicon carbide, silicon nitride, boron nitride, calcium carbonate, barium sulfate, calcium sulfate, mica, talc, clay, alumina, magnesium oxide, zirconium oxide, aluminium hydroxide, magnesium hydroxide, calcium silicate, aluminum silicate, lithium aluminum silicate, zirconium silicate, and molybdenum disulfide. These inorganic fillers can be used singly or in combination of two or more of them. Preferred inorganic fillers include talc, and aluminium hydroxide. If the inorganic filler exists in the epoxy resin composition of the present invention, it is present in an amount between 0 to 80 parts by weight, based on 100 parts by weight of the epoxy resin.

One or more solvents can be used for preparing the epoxy resin composition varnish in the present invention in order to provide resin solubility, and control resin viscosity. Examples of the solvents used in the present invention include, but are not limited to, acetone, methylethylketone, propylene glycol methyl ether, cyclohexanone, propylene glycol methyl ether acetate. These solvents can be used singly or in combination of two or more of them. Preferred solvents include methylethylketone, and propylene glycol methyl ether. The solvent is present in the epoxy resin composition of the present invention in an amount from about 60 to 100 parts by weight, based on 100 parts by weight of the epoxy resin.

If necessary, various additives such as silane coupling agents, releasants, and flame retardants can be used in the epoxy resin composition of the present invention

The epoxy resin composition of the present invention can be prepared by blending the components (A), (B), (C) and (D), and agitating the mixture uniformly, for example, in a mixer or blender.

The epoxy resin composition varnish of the present invention is prepared by dissolving or dispersing the obtained epoxy resin composition in a solvent.

A reinforcing material is impregnated with the resin varnish to form an impregnated substrate, and then the impregnated substrate is heated in a dryer at 150 to 180Â° C. for 2 to 10 minutes to give a prepreg in a semi-cured state (B-stage). Examples of the reinforcing material used in the present invention include, but are not limited to, glass fiber cloth, glass paper and glass mat, and also, kraft paper and linter paper.

A metal-clad laminate is prepared by laminating a particular number of the prepregs thus obtained, placing a metal foil additionally on at least one outermost layer and molding the composite under heat and pressure. As for the heat pressure-molding condition, the temperature is 160 to 190Â° C., the molding pressure is 10 to 30 kg/cm², and the molding time is 30 to 120 minutes. Then, a metal-clad laminate used for production of printed wiring boards is formed under such heat and pressure conditions. Examples of the metal foils used in the present invention include, but are not limited to, copper foil, aluminum foil, and stainless steel foil.

A circuit pattern formed on the surface of the metal-clad laminate is obtained by leaving circuit pattern-forming regions and removing the other regions thereof by using the subtractive process, otherwise known as the etching process. In this way, a printed wiring board carrying a circuit on the surface is obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples. It should be understood that the present invention is not restricted at all by these Examples.

<Preparation of Epoxy Resin Composition Varnishes>Example 1

100 parts by weight of bisphenol A novolac epoxy resin (EPON 828, manufactured by Shell Chemical Co., epoxy equivalence of 170 to 200 g/eq), 40 parts by weight of ATN resin (EPICLON N-7054, manufactured by Dainippon Ink and Chemicals Inc., epoxy equivalence of 125 g/eq), 2 parts by weight of DICY (hydroxyl group equivalence of 21 g/eq), 0.03 parts by weight of 2-methylimidazole, and 50 parts by weight of talc were mixed together by a mixer at room temperature for 60 minutes, and then the obtained mixture was dissolved in 80 parts by weight of methylethylketone, followed by stirring in a disperser at room temperature for 120 minutes to give the epoxy resin composition varnish.

Example 2

100 parts by weight of DOPO-CNE (KOLON 5138, manufactured by Kolon Chemical Co. epoxy equivalence of 250 to 390 g/eq), 40 parts by weight of ATN resin (EPICLON N-7054, manufactured by Dainippon Ink and Chemicals Inc., epoxy equivalence of 125 g/eq), 2 parts by weight of DICY (hydroxyl group equivalence of 21 g/eq), 0.05 parts by weight of 2-methylimidazole, and 50 parts by weight of talc were mixed together by a mixer at room temperature for 60 minutes, and then the obtained mixture was dissolved in 80 parts by weight of methylethylketone, followed by stirring in a disperser at room temperature for 120 minutes to give the epoxy resin composition varnish.

Example 3

100 parts by weight of DOPO-CNE (KOLON 5138, manufactured by Kolon Chemical Co. epoxy equivalence of 250 to 390 g/eq), 40 parts by weight of ATN resin (EPICLON N-7054, manufactured by Dainippon Ink and Chemicals Inc., epoxy equivalence of 125 g/eq), 0.4 parts by weight of DICY (hydroxyl group equivalence of 21 g/eq), 0.01 parts by weight of 2-methylimidazole, and 50 parts by weight of talc were mixed together by a mixer at room temperature for 60 minutes, and then the obtained mixture was dissolved in 80 parts by weight of methylethylketone, followed by stirring in a disperser at room temperature for 120 minutes to give the epoxy resin composition varnish.

Example 4

100 parts by weight of DOPO-CNE (KOLON 5138, manufactured by Kolon Chemical Co. epoxy equivalence of 250 to 390 g/eq), 40 parts by weight of ATN resin (EPICLON N-7054, manufactured by Dainippon Ink and Chemicals Inc., epoxy equivalence of 125 g/eq), 4 parts by weight of DICY (hydroxyl group equivalence of 21 g/eq), 0.06 parts by weight of 2-methylimidazole, and 50 parts by weight of talc were mixed together by a mixer at room temperature for 60 minutes, and then the obtained mixture was dissolved in 80 parts by weight of methylethylketone, followed by stirring in a disperser at room temperature for 120 minutes to give the epoxy resin composition varnish.

Example 5

50 parts by weight of bisphenol A novolac epoxy resin (EPON 828, manufactured by Shell Chemical Co., epoxy equivalence of 170 to 200 g/eq), 50 parts by weight of DOPO-CNE (KOLON 5138, manufactured by Kolon Chemical Co. epoxy equivalence of 250 to 390 g/eq), 40 parts by weight of ATN resin (EPICLON N-7054, manufactured by Dainippon Ink and Chemicals Inc.), 2 parts by weight of DICY (hydroxyl group equivalence of 21 g/eq), 0.03 parts by weight of 2-methylimidazole, and 50 parts by weight of talc were mixed together by a mixer at room temperature for 60 minutes, and then the obtained mixture was dissolved in 80 parts by weight of methylethylketone, followed by stirring in a disperser at room temperature for 120 minutes to give the epoxy resin composition varnish.

Example 6

An epoxy resin composition varnish was prepared in substantially the same manner as in Example 2, except that talc was not used.

Comparative Example 1

100 parts by weight of DOPO-CNE (KOLON 5138, manufactured by Kolon Chemical Co. epoxy equivalence of 250 to 390 g/eq), 20 parts by weight of ATN resin (EPICLON N-7054, manufactured by Dainippon Ink and Chemicals Inc., epoxy equivalence of 125 g/eq), 4 parts by weight of DICY (hydroxyl group equivalence of 21 g/eq), 0.07 parts by weight of 2-methylimidazole, and 50 parts by weight of talc were mixed together by a mixer at room temperature for 60 minutes, and then the obtained mixture was dissolved in 80 parts by weight of methylethylketone, followed by stirring in a disperser at room temperature for 120 minutes to give the epoxy resin composition varnish.

Comparative Example 2

100 parts by weight of DOPO-CNE (KOLON 5138, manufactured by Kolon Chemical Co. epoxy equivalence of 250 to 390 g/eq), 50 parts by weight of ATN resin (EPICLON N-7054, manufactured by Dainippon Ink and Chemicals Inc., epoxy equivalence of 125 g/eq), 1 parts by weight of DICY (hydroxyl group equivalence of 21 g/eq), 0.01 parts by weight of 2-methylimidazole, and 50 parts by weight of talc were mixed together by a mixer at room temperature for 60 minutes, and then the obtained mixture was dissolved in 80 parts by weight of methylethylketone, followed by stirring in a disperser at room temperature for 120 minutes to give the epoxy resin composition varnish.

The 7628 (R/C: 43%) glass fiber cloths (product of Nitto Boseki Co., Ltd) were respectively impregnated with the resin varnish obtained in Examples 1 to 6 and Comparative Examples 1 to 2 at room temperature, and followed by heating the impregnated glass fiber cloths at approximately 180Â° C. for 2 to 10 minutes to remove the solvent in the resin varnish (here, the resulting epoxy resin compositions were semi-cured) to obtain the prepregs of Examples 1 to 6 and Comparative Examples 1 to 2.

Four prepregs (300 mm x.510 mm) of Examples 1 were held and laminated between two copper foils (thickness: 1 oz, product of Nikko Gould Foil Co., Ltd.), to give a laminate. The laminate was then molded under the heating/pressurization condition of the temperature of 180Â° C. (the programmed heating rate of 2.0Â° C./minutes) and the pressure of 15 kg/cm²(an initial pressure: 8 kg/cm²) for 60 minutes, to give a copper-clad laminate for printed circuit board. Then, a circuit pattern was formed on the surface of the copper-clad laminate by leaving circuit pattern-forming regions and removing the other regions thereof by etching, and thereby a printed circuit board carrying a circuit on the surface was obtained.

The copper-clad laminates and the printed circuit boards for Examples 2 to 6 and Comparative Examples 1 to 2 were respectively obtained in the same way as the above-mentioned method for producing the copper-clad laminate and the printed circuit board of Example 1.

The properties of the copper-clad laminates obtained in Examples 1 to 6 and Comparative Examples 1 to 2 were respectively determined by the following evaluation tests.

[Water Absorption]

The standard pressure cooker test was done at 121Â° C., 100% relative humidity, and 2 atmospheric pressures for 1 hour.

[Solder Floating]

The sample was kept floating on a solder bath of 288Â° C. for the time indicated in Table 1 and, then blister of the sample was visually observed.

[Peeling Strength of Copper Foil]

A 1 oz of copper foil on the copper-clad laminate was peeled off for determination of its 90Â° peel strength (JIS-C-6481).

[Glass Transition Temperature]

The glass transition temperature (Tg) was measured as peak temperature of tan Î´ at 1 Hz by a dynamic mechanical analyzer, manufactured by Seiko Instruments, Inc.

[Thermal Decomposition Temperature]

A resin was separated from a copper-clad laminate and analyzed in a thermogravimetric and differential thermal analyzer (TG-DTA). The programmed heating rate was 5Â° C./minute. The thermal decomposition temperature was a temperature at which the weight of the sample decreased by 5% from the initial weight.

[Flame Retardancy]

The flame retardancy of a copper-clad laminate was evaluated by the method specified in UL 94. The UL 94 is a vertical burn test that classifies materials as V-0, V-1 or V-2.

[Breaking Tenacity]

The laminate was set on a flat stage of the analyzer, and a vertical force was exerted on the laminate with a cross-shaped metal tool directly contacting with the surface of the laminate for 1 minute, which left a cross-shaped mark on the surface of the laminate. Breaking tenacity was evaluated by visually observing the cross-shaped mark on the surface of the laminate as follows: good: no white crease; normal: occurrence of slightly white crease; and bad: occurrence of cracking or breakage.

[Dielectric Properties]

The dielectric constant and the dissipation factor at 1 GHz were measured according to the procedures of ASTM D150-87.

The epoxy resin compositions and the test results of the test items above are summarized in Table 1.

TABLE 1Epoxy Resin CompositionsRelative to 100 parts by weight ExampleExampleExampleExampleExampleExampleComparativeComparativeof the epoxy resin123456Example 1Example 2Epoxy resinbisphenol A epoxy100â€”â€”â€”50â€”â€”â€”resinDOPO-CNEâ€”10010010050100100100CompositeATN resin4040404040402050curing agentDICY220.442241curing2MI0.030.050.010.060.030.050.070.01acceleratorInorganic fillerTalc505050505005050SolventMEK8080808080808080Test ResultsExampleExampleExampleExampleExampleExampleComparativeComparativePropertiesConditionsUnit123456Example 1Example 2WaterPCT121Â° C./%0.2120.2190.2210.2330.2200.2230.3790.331absorptionhrSolder floating288Â° C.min>10>10>108.5>10>107.27.1Peelinglb/in8.48.47.79.08.58.59.47.1strength (1 oz)GlassDMAÂ° C.171.5175.0174.0172.0171.0172.8165.0163.5transitiontemperatureThermalTGAÂ° C.363.0376.3364.0364.7362.0366.8339.0332.2decompositiontemperatureFlameratingUL94V-1V-0V-0V-0V-0V-0V-0V-0retardancyBreakingGoodGoodGoodGoodGoodGoodNormalGoodtenacityDielectricDk at 1 GHz4.544.484.514.544.504.524.514.50constantDissipationDf at 1 GHz0.0200.0180.0170.0190.0190.0200.0230.03factor

As seen from Table 1, the copper-clad laminates obtained according to the present invention (Examples 1 to 6) have the well-balanced properties and every required performance for use as printed circuit boards. These copper-clad laminates are excellent in breaking tenacity, dielectric properties, and peeling strength of copper foil. Although no inorganic filler was used in the epoxy resin composition in the case of Example 6, the copper-clad laminate obtained according to Example 6 still has the required performance for use as printed circuit boards. The dissipation factors of Examples 1 to 6 of the present invention are no greater than 0.02, and however the dissipation factors of Comparative Examples 1 and 2 are no less than 0.023. The dielectric constant of Examples 2 of the present invention reaches as low as 4.48. As compared with Examples 1 to 6 of the present invention, the copper-clad laminates of Comparative Examples 1 and 2 have higher water absorption, lower glass transition temperature, and lower heat resistance, and especially in Comparative Examples 2, the copper-clad laminate has high dissipation factor (0.03).

Thus, the copper-clad laminates or the printed circuit boards of the present invention can be used with high reliability. Accordingly, the copper-clad laminates or the printed circuit boards of the present invention prepared from the epoxy resin composition with ATN resin and DICY mixed in a certain proportion are not only excellent in breaking tenacity, dielectric properties, and peeling strength of copper foil, but also can be devoid of the disadvantages of the above-mentioned individual conventional curing agents ATN resin and DICY.

It is contemplated that various modifications may be made to the compositions, prepregs, laminates and printed circuit boards of the present invention without departing from the spirit and scope of the invention as defined in the following claims.