The present invention relates to a method for bonding a copper foil to a substrate comprising a polymeric compound, a copper-lined laminate and a TAB film carrier tape produced by using this method.

More particularly, the method for bonding the copper foil to the substrate according to the present invention comprises the use of a resin composition as adhesive which composition is based on a dicyanate ester and/or a derivative thereof as main ingredient, and further comprises a curing catalyst, and as optional ingredient an epoxy resin.

It is known in the prior art to produce copper-lined laminate boards, in particular flexible copper-lined laminate boards, by laminating a film of polyimide, polyester or the like onto a copper foil by the use of an adhesive. As said adhesive, epoxy adhesives are used. Further, a thermoplastic resin is often used in combination with the epoxy adhesive for the purpose of giving the laminate board a flexibility.

Three layer type TAB carrier films are a special embodiment of such flexible copper-lined laminate boards. TAB carrier films are used for connecting the electrical contact pads of a chip (bumps) with a circuit board in order to meet the modern requirements of dense packaging and fine pitch, the three layer type mainly (but not exclusively) for mounting LCD drivers. The TAB technology is, for instance, described in the U.S. Patents (US-A-) 3,689,991 and 3,706,409. A flexible film of a polymeric material like polyimide (Kapton R, Upilex R), glass reinforced epoxy resin, polyester or BT Resin (Mixture comprising bismaleimides and triazine compounds), typically having a thickness of 0.075 to 0.150 mm, is supplied with holes for taking up the chip, either before or after coating the film with an adhesive and laminating it with a copper foil (typically 0.035 to 0.070 mm thick). The copper foil is then structured to provide the required lines for contacting the chip. These lines are usually metal plated and then connected with the bumps of the chip, usually by thermo- compression ("inner lead bonding"). For protection of the electrical contacts the contact area is casted with a resin. Then the chip and its contact lines are punched out of the film, the contact lines are suitably bent and soldered to the circuit board ("outer lead bonding").

These techniques are well known, as detailed in "TAB Gijutsu Nyumon" (Introduction to TAB Techniques), published by Kogyo Chosakai K. K., 1990; "Shin Epoxy Jushi" (New Epoxy Resins), edited by H. Kakiuchi, published by Shokoko, 1985, Page 477; Gazette of Japanese Patent Publication No. 5-62156; "N erarbeitung von Fine-Pitch-Bauteilen mit Tape Automated Bonding (TAB)" by A. Modi, VDI BERICHTE Nr. 966, 1992.

With the striking technical progress of the recent electronic industries, flexible copper-lined laminate board and, particularly, TAB film carrier tapes have been required which can withstand severe working conditions and have superior properties. Particularly, due to the tendency of increasing the signal speed and the density of integrated circuits, these materials are required to have a low dielectric constant, a low dielectric loss and a high heat resistance simultaneously.

A resin composition to be used as an adhesive for producing a three layer type TAB film carrier tape must provide a high heat resistance and a high flexibility, as detailed in the known papers cited above. A known adhesive composition for TAB carrier tapes comprises a bisphenol A type epoxy resin as main ingredient and dicyandiamide as a curing agent. In some cases, a thermoplastic resin must additionally be used in order to get a suitable flexibility. By the way of example, a reactive liquid rubber such as a liquid acrylonitrile- butadiene copolymer rubber having reactive groups such as carboxyl group or the like at both molecular terminals, or the like is used in addition to the above-mentioned ingredients.

Although the use of the above-mentioned flexibilizers enables a remarkable improvement of adhesiveness between the composition and polyimide film or copper foil, heat resistance of the composition is greatly deteriorated as the amount of flexibilizer increases. Further, it should be noted that prior resin compositions using epoxy resin as a fundamental element have a heat resistance of at most 170°C, even if no flexibilizer is used. Moreover, in such prior resin compositions, dielectric constant and dielectric losses are at least 3.5 and 0.015, respectively.

As have been mentioned above, in the current techniques of electronic industry, signal speed, signal frequency and circuit density are becoming so high that there have appeared

a number of fields which the prior techniques cannot cope with. Flexible copper-lined laminate board and TAB film carrier tape are also in the same situation as above. A simultaneous satisfaction of the increased requirements regarding heat resistance, electrical properties, adhesiveness and flexibility which are contradictory to one another is necessary.

For solving the mentioned technical problem the instant invention provides a method for bonding a copper foil onto a substrate comprising a polymeric compound which method comprises

- coating the substrate with a resin composition comprising:

[A] at least one cyanate ester or prepolymer thereof selected from the group consisting of: a cyanate ester represented by the following general formula (1 ):

wherein A represents a direct single bond or a group >CR ₅ R ₆ and

R _T to R ₆ each independently represents a hydrogen atom, methyl group,

CF ₃ group or halogen atom;

a polycyanate ester represented by the following general formula (2):

wherein R. to R ₃ each independently represents a hydrogen atom, methyl group or halogen atom, and n represents an integer of 0 to 6;

4,4'-(1 ,3-phenylenediisopropylidene)-diphenyl cyanate;

a cyanate ester resin obtained by polymerizing 0-50 % of the cyanate groups of the said cyanate ester resins; and

a mixture of cyanate ester and prepolymer thereof selected from at least one combination of the above-mentioned substances; and

[B] a curing catalyst; bringing the coated side of the substrate into contact with the copper foil and curing the resin composition by heat.

Preferred is the above-mentioned method if said cyanate ester or prepolymer thereof [A] is selected from the group consisting of: a phenol novolac polycyanate represented by the following formula (3):

wherein n represents an integer of 0 to 6, hexafluorobisphenol A dicyanate represented by formula (4):

ethylidene bis-4,1 -phenylene dicyanate represented by formula (5):

4,4'-(1 ,3-phenylenediisopropylidene)-diphenyl cyanate represented by formula (6):

tetra(orthomethyl)bisphenol F dicyanate represented by formula (8):

a biphenyl cyanate ester represented by formula (9):

wherein R, to R ₄ each and independently represents a hydrogen atom, a methyl group, a CF ₃ group or a halogen atom,

a cyanate ester resin obtained by polymerizing 0-50 % of the cyanate groups of the said cyanate ester resins, and

a mixture of cyanate ester and prepolymer thereof selected from at least one combination of the above-mentioned substances.

The curing catalyst [B] used in the method according to the instant invention is preferably at least one compound selected from a metal compound represented by formula (7): Y-Z (7) wherein Y represents a metallic ion selected from Mn ² \ Mn ³⁺ , Co ² \ Co ³ \ Cu ²⁺ , Zn ²⁺ , Ni ²⁺ , Al ³⁺ , and Fe ³ \ and Z represents an organic anion, a phenol compound, a tertiary amine compound or a mixture thereof.

The said organic anion may, for instance, be selected from the naphthenic acid anion, octylic acid anion and the acetylacetonate anion.

Examples of said metal compound include manganese octylate, manganese naphthenate, cobalt octylate, cobalt naphthenate, copper octylate, copper naphthenate and the like. As said phenol compound, phenol, cresol, Bispheπol A, nonylphenol, dinonylphenol, salicylic

acid and the like can be referred to. As said tertiary amine compound, imidazole, 2- methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole and the like can be referred to. Combined mixtures of more than one of these compounds are also usable, if desired.

The curing catalyst is preferably used in an amount of 0.001 -10, preferably from 0.01 -10 parts by weight per 100 parts by weight of the cyanate ester component [A].

Into the resin composition used in accordance with the present invention, an epoxy resin may optionally be mixed, too. Said epoxy resin may be any epoxy resin so far as it has at least two glycidyl groups. As one example of said epoxy resin, a bisphenol A type epoxy resin having, for instance, the epoxy equivalent 189 and obtained in a known manner by reacting Bisphenol A and epichlorohydrin can be referred to. As said bisphenol A type epoxy resin, a variety of ones different in the degree of polymerisation can also be used. Further, epoxy resins into which halogen atoms have been introduced for the purpose of giving the resin a flame retardance are also usable. As one example of such epoxy resin, the polycondensates formed by reaction between tetrabromobisphenol A and epichlorohydrin may be mentioned. A specific example of such epoxy resin has a bromine content 49 % by weight and epoxy equivalent 460 g/eq. Further, novolac type epoxy resins may be used.

In a preferred embodiment of the method according to instant invention the epoxy resin forming the component [C] of the used resin composition comprises at least one epoxy resin selected from: a bisphenol A epoxy resin having an epoxy equivalent of 170 to 1000 grams per equivalent and a bromine content of 0 to 60% by weight,

an epoxy resin represented by the general formula (10)

wherein R. to R ₃ each independently represents a hydrogen atom, methyl group or halogen group and n represents an integer of 0 to 6, and

a combination of such epoxy resins.

The epoxy resins are used in an amount ranging from 0 to 400 parts by weight per 100 parts by weight of the cyanate ester compound [A]. When the amount of epoxy resin is 0 part by weight, that is when no epoxy resin is used at all, the cyanate ester compound [A] cures alone forming triazine rings. On the other hand, when an epoxy resin is used in combination with the cyanate ester compound [A], a reaction between cyanate groups and glycidyl groups also progresses in parallel while forming oxazolidone rings. The reaction between glycidyl group and cyanate group can take place so long as any quantity of unreacted glycidyl group remains in the reaction system. Accordingly, if too large an amount of epoxy resin is used, shortage of cyanate groups to be reacted with glycidyl group takes place. If desired, however, a curing agent for the epoxy resin may additonally be used. Examples of said curing agent for epoxy resin include organic acid anhydrides, amines, phenols, and the like. Nevertheless, the amount of epoxy resin should be at most 400 parts by weight per 100 parts by weight of the cyanate ester compound [A].

Further, the resin composition used as adhesive for the purposes of the present invention may also contain a solvent (diluent) such as methyl ethyl ketone, acetone or the like for the purpose of regulating viscosity of the resin composition, and further components, like a curing agent or an additional flexibilizer such as reactive liquid rubber (for example, liquid acrylonitrile-butadiene copolymer rubber having reactive groups such as carboxyl groups or the like at both molecular terminals), thermoplastic resin or the like.

The resin compositions used in the instant invention are usually mixed together in the state of liquid substances. The temperature should not exceed 150°C at this stage in order to avoid premature curing. If desired, a solvent (diluent) such as methyl ethyl ketone, acetone or the like can be used. In some cases, the use of a solvent is necessary for regulating viscosity. It is preferable from the practical point of view to adjust viscosity of the composition so as to fall in a range of from 100 centipoises to 50,000 centipoises by adding the solvent.

The resin compositions used in the present invention are relatively easy to produce industrially, by the use of an agitating apparatus equipped with an appropriate heater.

The resin compositions are cured by heating them to a temperature of more than 150°C, preferably of more than 170°C, to 300°C, either in one step or stepwise. When curing is conducted by stepwise heating, the compositions may firstly be heated to a temperature ranging from 150°C to 230°C. A post-cure at temperatures from 200°C to 300°C may follow, is however optional. The total curing time may range from a few minutes to about 10 hours. It is preferred to press the substrate and the copper-foil on one another while curing the adhesive composition, using a pressure of, for instance, about 15 kg/cm ² .

A cured product obtained from the resin composition used in the method of the present invention is excellent not only in heat resistance but also in adhesiveness, particularly to polyimide film and copper foil, as well as in its electrical properties, and therefore very suitable for use in the manufacture of high-performance copper-lined laminate boards and particularly flexible copper-lined laminate board and TAB film carrier tapes.

The invention therefore also relates to a, preferably flexible, copper-lined laminate board produced by using the method for bonding a copper foil to a substrate comprising a polymeric compound which has been described above, and to a corresponding TAB film carrier tape of the three layer type.

Example 1 : A resin composition is prepared by charging a reactor equipped with a stirrer with 100 parts by weight of a cyanate resin of the following formula (3)

(phenol novolac polycyanate, n = ca. 1.0), 33.33 parts by weight of methyl ethyl ketone, 1 part by weight of nonylphenol and 0.1 125 part by weight of a solution of manganese octylate in mineral spirit (content of manganese ion 8 %), and stirring the mixture at 80°C for one hour under a reflux condenser.

The mixture thus obtained is formed into a coating film having a final thickness of 35 μm by means of a bar coater on a polyimide film (Capton 200H, manufactured by Toray Co.) and preliminarily cured at 170°C for 5 minutes. Then, a copper foil (CF T-8, manufactured by Fakuta Metallic Foil and Powder Co.) is superposed on the polyimide film, and pressed at 177°C for one hour under a pressure of 15 kg cm ² . Then, it is post-cured at 230°C for 5 hours to obtain a flexible copper-lined laminate board.

On the flexible copper-lined laminate board thus obtained, adhesive strengths of the polyimide and copper foil are measured in a usual state on the one hand and after immersion in a solder bath at 260°C for 5 minutes on the other hand.

In another experiment, a resin composition containing no methyl ethyl ketone is prepared by adding 1 part by weight of nonylphenol and 0.1 125 part by weight of a solution of manganese octylate in mineral spirit (content of manganese ion 8 %) to 100 parts by weight of the same cyanate ester resin as above, and stirring the resulting mixture at 90°C for one hour. The composition thus obtained is cast in a die having a length of 10 cm, a width of 10 cm and a thickness of 2 mm, and heated at 177°C for one hour and subsequently post- cured at 230°C for 5 hours.

On the cured product thus obtained, dielectric constant, dielectric loss and glass transition point are measured.

Example 2: The procedure of Example 1 is repeated, except that the cyanate ester resin used in Example 1 is replaced with a cyanate ester resin represented by the following formula (4):

provided that, in the cyanate ester resin of the formula (4), 30 % of the cyanate groups have previously been reacted.

Example 3: The procedure of Example 1 is repeated, except that the cyanate ester resin used in Example 1 is replaced with a cyanate ester resin represented by the following formula (5):

Example 4: The procedure of Example 1 is repeated, except that the cyanate ester resin used in Example 1 is replaced with a cyanate ester resin represented by the following formula (6):

provided that, in the cyanate ester resin of the formula (6), 26 % of the cyanate groups have previously been reacted.

Example 5: To a reactor equipped with a stirrer are charged 55 parts by weight of a cyanate resin of the following formula (3)

(phenol novolac polycyanate, n = ca. 1.0), 45 parts by weight of a bisphenol A epoxy resin (epoxy equivalent: 189), 33.33 parts by weight of methyl ethyl ketone, 0.018 part by weight of a solution of manganese octylate in mineral spirit (content of manganese ion 8 %) and 0.012 part by weight of 2-methylimidazole, and the resulting mixture is stirred under refluxing at 80°C for one hour to obtain a resin composition.

The mixture thus obtained is applied to a polyimide film (Capton 200H, manufactured by Toray Co.) by means of a bar coater to form a coating film having a final thickness of 35 μm and then precured at 170°C for 5 minutes. Then, a copper foil (CF T-8, manufactured by Fakuta Metallic Foil and Powder Co.) is superposed on the polyimide film, and pressed at 177°C for one hour under a pressure of 15 kg/cm ² . Then, it is post-cured at 210°C for 5 hours to obtain a flexible copper-lined laminate board.

On the flexible copper-lined laminate board thus obtained, adhesive strengths of the polyimide and copper foil are measured in a usual state on the one hand and after immersion in a solder bath at 260°C for 5 minutes on the other hand.

A resin composition containing no methyl ethyl ketone is obtained by charging 55 parts by weight of the same cyanate ester resin as above, bisphenol A type epoxy resin (epoxy equivalent: 189), 0.018 part by weight of a solution of manganese octylate in mineral spirit (content of manganese ion 8 %) and 0.012 part by weight of 2-methylimidazole, and stirring the resulting mixture at 90°C for one hour. The composition thus obtained is poured into a

mold having a length of 10 cm, a width of 10 cm and a thickness of 2 mm, and heated at 177°C for one hour and subsequently post-cured at 210°C for one hour.

Dielectric constant, dielectric loss and glass transition temperature of the resulting cured product are measured.

Example 6: The procedure of Example 5 is repeated analogously , except that the cyanate ester resin used in Example 5 is replaced with a cyanate ester resin represented by the following formula (4):

in which 30 % of the cyanate groups have previously been reacted.

Example 7: The procedure of Example 5 is repeated analogously, except that the cyanate ester resin used in Example 5 is replaced with a cyanate ester resin represented by the following formula (5):

Example 8: The procedure of Example 5 is repeated, except that the cyanate ester resin used in Example 5 is replaced with a cyanate ester resin represented by the following formula (6):

in which 26 % of the cyanate groups have previously been reacted.

Example 9: The procedure of Example 5 is repeated, except that the cyanate ester resin used in Example 5 is replaced with a cyanate ester resin represented by the above- mentioned formula (6) in which 30 % of the cyanate groups have previously been reacted.

Comparative Example:

A resin composition is prepared by charging a reactor equipped with a stirrer with 100 parts by weight of a brominated Bisphenol A type epoxy resin (epoxy equivalent 480, bromine content 20.5 %, 2.68 parts by weight of dicyandiamide, 0.1 part by weight of 2- methylimidazole, 33.33 parts by weight of methyl ethyl ketone and 34 parts by weight of methyl cellosolve, and stirring the mixture at 80°C for one hour under a reflux condenser.

The mixture thus obtained is formed into a coating film having a final thickness of 35 μm by means of a bar coater on a polyimide film (Capton 200H, manufactured by Toray Co.) and preliminarily cured at 170°C for 5 minutes. Then, a copper foil (CF T-8, manufactured by Fukuta Metallic Foil and Powder Co.) is superposed on the polyimide film, and pressed at 170°C for one hour under a pressure of 15 kg/cm ² .

On the flexible copper-lined laminate board thus obtained, adhesive strengths of the polyimide and copper foil are measured in a usual state on the one hand and after immersion in a solder bath at 260°C for 5 minutes on the other hand.

Further, in order to obtain a cast product, the resin composition is introduced into an evaporator and stirred at 100°C for 2 hours to remove the solvent therefrom. The solvent- free resin composition thus obtained is cast into a die having a length of 10 cm, a width of 10 cm and a thickness of 2 mm and cured at 170°C for one hour.

On the cured products obtained according to the examples and the comparative example, dielectric constant, dielectric loss and glass transition point are measured. The results are listed in Table 1 and in Table 2.

_El am _p ex

(Notes)

Adhesive strength: Measured according to the procedure mentioned in JIS-C6481.

^* ) Measured with Instrom MODEL 1 125 type tensile tester.

^** ) "A" means that a breakage took place in the film.

^*** ): Measured with TR100 type dielectric loss measuring apparatus manufactured by Ando Electric Co.

^**** ) Measured with viscoelasticity measuring apparatus DDV25PP manufactured by Orientec Co.

In Table 1 and Table 2, comparison of the Examples of the present invention with Comparative Example demonstrates an effectiveness of the present invention. The formulation shown in Comparative Example corresponds to that of a resin composition used in a copper-lined laminate board generally called FR-4. It is understandable from Table 1 and Table 2 that the flexible copper-lined laminate boards and cured products formed from the resin compositions of the present invention are superior in adhesiveness, heat resistance and electrical properties.

Since the resin composition used in the method according the the present invention contains a cyanate ester compound of specified structure, it exhibits excellent heat resistance, electrical properties, flexibility and adhesiveness simultaneously which are contradictory to one another. Particularly, the cured product obtained from the resin composition of the present invention is superior not only in heat resistance but also in the adhesive strength of polyimide film and copper foil and in electrical properties, which makes the cured product of the present invention suitable for use in the production of flexible copper-lined laminate board and TAB film carrier tape.