METHOD OF MANUFACTURING TWO-LAYER TAB TAPE

Abstract: A method of manufacturing a two-layer TAB tape, wherein predetermined opening parts are provided in a semicured polyamic acid film or the one subjected to 10 % or more drawing which is formed on a release film, either of them is contact-bonded to a conductor foil or a semicured light-transmitting polyamic acid film formed on a conductor film, the film or films are changed to imide, and a desired pattern is formed in the conductor foil. Methods of manufacturing 10 % or more drawn polyamic acid film, flexible printed circuit boards using this film, and flexible printed circuit boards with cover-lays are also disclosed.

Description: The present invention relates to a method of producing a tape for TAB (tape automated bonding), used for mounting semiconductor elements thereon, particularly to a process for producing a two-layered tape for TAB. Semiconductor mounting techniques have undergone remarkable progress in recent years. TAB, in particular, is under active development in order to respond to the current requirement for high-density mounting technique, because TAB enables formation of conductor patterns at a very high density, making it easy to connect multiple pins, and moreover TAB enables simultaneous bonding of all leads with semiconductor chips (gang bonding) without using any wire. There are two kinds of tapes for TAB, i.e. tapes for TAB having a two-layered structure and tapes for TAB having a three-layered structure. The tape for TAB having a three-layered structure (hereinafter abbreviated as three-layered tape for TAB) is generally a laminate obtained by laminating a conductor foil (e.g., copper foil) with a heat-resistant resin film using an adhesive and has an adhesive layer of poor heat resistance; hence, the three-layered tape for TAB has been unable to fully exhibit the superior properties even when there is used, as the resin film, a polyimide film superior in properties such as heat resistance, chemical resistance and the like. Meanwhile, the tape having a two-layered structure for TAB (hereinafter abbreviated as two-layered tape for TAB) generally has excellent heat resistance as a tape for TAB because the base film has no adhesive layer; however, the two-layered tape for TAB has found only very limited applications because of difficulty in production. That is, the two-layered tape for TAB is produced by two processes, i.e., the one process which comprises forming a conductor layer on a heat-resistant film made of a polyimide or the like by a thin-film-forming technique such as sputtering, vapor deposition, plating or the like, and then applying an etching treatment to the base film and the conductor layer to form desired holes (device holes, sprocket holes) and a desired conductor pattern, and the other process which comprises coating a varnish of a heat-resistant resin (e.g., polyimide) directly on a conductor foil (e.g., copper foil), drying the coated varnish to form a two-layered base board, and then applying an etching treatment to the resin layer and the conductor foil to form desired holes and a desired conductor pattern. In the former process, however, there is a problem that a rolled foil of excellent flexibility, a Fe-Ni alloy foil of excellent modulus, etc. cannot be used; moreover, the base film holes must be formed by an etching method, resulting in significantly reduced productivity as compared with the case employing the punching method applied to three-layered tapes for TAB. Meanwhile in the latter process, it is necessary that the linear thermal expansion of the resin used be nearly the same as that of the copper foil (conductor layer) in order to prevent formation of curls and wrinkles; however, such resins are generally rigid and have excellent solvent resistance, making it difficult to apply alkali etching in many cases and requiring use of dry etching (e.g. excimer laser) in order to form holes in the film layer, which results in disadvantageous productivity and cost. Meanwhile, two-layered flexible materials for printed circuit, having no adhesive layer are finding increased applications, as electronic appliances become smaller and lighter. Further, not only conventional flexible materials for wiring but also materials having a supporting film with holes, such as the above-mentioned carrier tape for TAB have found increased applications recently. Each of these conventional processes has drawbacks in heat resistance, adhesion strength, processability and chemical resistance. First, the adhesive layer-containing three-layered flexible material for printed circuit has a drawback that since the adhesive layer has low heat resistance, the heat resistance of the flexible material for printed circuit is determined by the heat resistance of the adhesive layer even when a polyimide is used as the supporting film. When a conductor layer is formed by vapor deposition or sputtering, there is a drawback in that the adhesion strength between the supporting film layer and the conductor layer is insufficient. When a polyamic acid is coated directly and then dried to form a thick film, and the stress due to the contraction caused by imidization is larger than the supporting strength of the conductor layer, producing large curls during drying. When a polyamic acid solution is directly coated on a conductor layer and dried a plurality of times, followed by imidization, the curls produced during these steps are reduced; however, since the film portion close to the conductor layer and the film portion distant from the conductor layer have different thermal histories, the imidization degree and residual solvent amount in film each differ depending upon the film portion, resulting in large curls, dimensional change, etc. of the film after etching of the copper foil. When a laser is used, in particular, an excimer laser, excellent fine processing is obtained and damage to copper foil is small; however, the strong imide bond must be cleaved, resulting in long processing time, low productivity and high running cost. Also, a polyimide having a molecular structure capable of being subjected to alkali etching after imidization has problems that it has somewhat low solvent resistance, that use of a strongly alkaline solution as an etching solution involves serious danger and that disposal of the waste solution is not easy. JP-A-63021115 relates to a process for preparing polyimide film. A solution of polyimide and/or its precursor is spread on a support film, and the solvent removed to provide a self-supporting polyimide film. The polyimide film is removed from the support film, dried, stretched and then used as a support film. JP-A-1228833 relates to a polyimide honeycomb core prepared from laminated aromatic polyimide film. A solution of polyimide or polyamic acid is spread on a rotating drum, heated and stretched. A number of the resulting polyimide films are laminated together under heat and pressure. JP-A-56118421 relates to a process for preparing heat-shrinkable polyimide film. A solution of polyamic acid is cast on a substrate, and part of the solvent evaporated to form a film having at least 50 wt. % polyimide. The film is then stretched monoaxially. The heat-shrinkable film produced can be heat-shrunk around a wire. JP-A-56015326 relates to a process for preparing heat-shrinkable laminated film. Molten layers of polyamide resin/ethylene vinyl acetate copolymer and a thermoplastic resin are ozonized and laminated. The laminate is then cooled and stretched. JP-A-63161023 relates to a process for preparing a base board for a printed circuit board. A polyamic acid is coated directly onto a metal foil and heated. JP-A-2273984 relates to a process for preparing a flexible printed circuit board. A heat resistant resin is coated directly onto a metal foil to obtain a two-layer printed circuit board. Two such boards are then bonded together, resin sides facing one another. EP-A-36330 relates to a process for continuously producing an aromatic polyimide film which uses a solution of polyimide as a starting material. JP-A-2174242 relates to a method of producing a tape carrier for two-layer TAB. A conductor layer is formed on a base film, and the conductor layer is then etched. An object of the present invention is to provide a process for producing a two-layered tape for TAB at high productivity without reducing heat resistance, alkali resistance, solvent resistance and electrical properties inherently possessed by two-layered tapes for TAB having no adhesive layer. A further object of the present invention is to provide a process for producing a two-layered tape for TAB which is free from curls and which has good adhesion between the copper foil and the film. Another object of the present invention is to provide a process for producing a two-layered tape for TAB which enables excellent registration and formation of fine lines and which enables high-density wiring. A still further object of the present invention is to provide a process for producing a stretched polyamic acid film having a desired thickness and, optionally, holes, which film enables production of a two-layered flexible printed circuit board having no adhesive layer, which board has a polyimide layer having the same folding resistance, alkali resistance, solvent resistance, heat resistance, electrical properties and mechanical properties as possessed by ordinary stretched polyimide films (such a polyimide layer has been unobtainable by the conventional varnish casting process) and which board enables use of any conductor is coated directly onto a metal foil and heated. JP-A-2273984 relates to a process for preparing a flexible printed circuit board. A heat resistant resin is coated directly onto a metal foil to obtain a two-layer printed circuit board. Two such boards are then bonded together, resin sides facing one another. EP-A-36330 relates to a process for continuously producing an aromatic polyimide film which uses a solution of polyimide as a starting material. JP-A-2174242 relates to a method of producing a tape carrier for two-layer TAB. A conductor layer is formed on a base film, and the conductor layer is then etched. An object of the present invention is to provide a process for producing a two-layered tape for TAB at high productivity without reducing heat resistance, alkali resistance, solvent resistance and electrical properties inherently possessed by two-layered tapes for TAB having no adhesive layer. A further object of the present invention is to provide a process for producing a two-layered tape for TAB which is free from curls and which has good adhesion between the copper foil and the film. Another object of the present invention is to provide a process for producing a two-layered tape for TAB which enables excellent registration and formation of fine lines and which enables high-density wiring. The present invention provides a method of producing a two-layered tape for TAB, which is characterized by forming desired holes in a polyamic acid film formed on a release film, the film having a degree of imidization of 10 to 50%, then laminating the polyamic acid film and the release film to a conductor foil so that the polyamic acid film 2 is brought in contact with the conductor foil 4, peeling off the release film, completing imidization and forming a desired pattern in the conductor foil. A polyamic acid film having an imidization degree of 10 to 50% is referred to herein as a "semi-cured" polyamic acid film. Advantageously, the method comprises forming a semi-cured polyamic acid film on a release film, making desired holes (e.g. device holes) in the polyamic acid film, pressure-bonding the two films to a conductor foil so that the semi-cured polyamic acid film contacts the foil, peeling off the release film, completing imidization, and thereafter forming a desired pattern in the conductor foil by an etching treatment or the like. The polyamic acid film is preferably formed by use of a varnish obtained by mixing (A) a polyamic acid solution obtained by reacting 3,3',4,4' -biphenyltetracarboxylic acid dianhydride and p-phenylenediamine with (B) a polyamic acid solution obtained by reacting pyromellitic acid dianhydride with 4,4' -diaminodiphenyl ether, at a solid content ratio of A/B = 55/45 to 75/25. In the method of the invention the holes are preferably filled with a desired filler after imidization and, after pattern formation, the filler is removed. Brief Description of Drawings Fig. 1 a to h are sectional views showing steps in the present invention. In Fig. 1, 1 to 8 refer to the followings. 1 ... Polyester release film 2 ... Polyamic acid film 3 ... Device hole 4 ... Copper foil 5 ... Photoresist 6 ... Polyimide film 7 ... Sprocket hole 8 ... Filler Detailed Description of the Invention As the method for forming desired holes (e.g., device holes) in a semi-cured polyamic acid-film, there can be used punching, cutting, alkali etching, laser processing, etc. When a desired resist pattern is formed on a conductor foil and then an etching treatment is applied, it is necessary to fill the holes beforehand with a desired filler having, for example, the same composition as the resist to prevent etching from the holes. After a conductor pattern has been formed, the resist remaining on the conductor foil and the filler are removed, and sprocket holes are formed by punching. As the method for forming a semi-cured polyamic acid film on a release film, there can be used a method which comprises coating a polyamic acid varnish directly on a release film and drying the coated varnish. Besides, there can be also used the following method if necessary. That is, there can be used a method which comprises bringing in a contiguous relation two polyamic acid films of same or different compositions, formed on respective release films so that the polyamic acid film sides face each other, or inserting, between them, a desired number of polyamic acid films, and simultaneously bonding these two or more polyamic acid films under heat and pressure to obtain a thick polyamic acid film. That is, a polyamic acid solution is coated on a release film and is dried until it becomes tack-free, whereby a semi-cured polyamic acid film is formed. The thus formed two polyamic acid films are brought in a contiguous relation so that the polyamic acid film sides face each other, and they are bonded under heat and pressure to obtain a polyamic acid film having a thickness of two times that of the film first obtained by coating and drying. In this case, it is possible to insert if necessary between the above two polyamic acid films, a desired number of polyamic acid films released from respective release films so that the polyamic acid film sides face each other, to obtain a thicker polyamic acid film. It is also possible, after laminating, to peel off one of the two release films and repeat the same procedure to obtain an even thicker polyamic acid film. Then, the semi-cured polyamic acid film formed on a release film is subjected to hole formation (holes are formed in the polyamic acid film and the release film or only in the polyamic acid film) by an ordinary method such as punching, cutting, alkali etching, laser or the like. Punching is preferred in view of the productivity and cost. After the hole formation is over, the semi-cured polyamic acid film is bonded to a conductor foil under heat and pressure; the release film is peeled off; then imidization is conducted sufficiently. In the present invention, appropriate conditions for drying the polyamic acid solution coated on a release film to form a semi-cured polyamic acid film, are 80-200°C and 5-30 minutes. When the drying temperature is lower than the above range and the drying time is shorter than the above range, the semi-cured polyamic acid film has high fluidity in bonding it to a conductor foil under heat and pressure; there appear high degrees of spreading and oozing-out in and around the holes; the film thickness has a large variation; and the dimensional change after imidization is large. When the drying temperature is higher than the above range and the drying time is longer than the above range, the semi-cured polyamic acid film has too low fluidity in bonding it to a conductor foil under heat and pressure; the peeling strength from the conductor foil is low; and many voids appear. The imidization degree of the semi-cured polyamic acid film is 10-50%, preferably 20-40%. When the imidization degree is less than 10%, the polyamic acid film still has a certain degree of tackiness, making the workability low, and sticks to the back side of the release film after winding, making difficult separation of each polyamic acid film. When the imidization degree is more than 50%, the polyamic acid film has poor melt property and, when two such polyamic acid films are bonded under heat and pressure, it is impossible to obtain a sufficiently laminated film. In coating a polyamic acid solution to form a polyamic acid film, appropriate thickness of the film is 50 µm or less in terms of thickness after imidization. When the thickness is larger than the above, the stress due to the contraction caused by imidization is larger than the supporting strength of the release film, generating large curls during drying; further, the large thickness reduces evaporation rate of the solvent, giving significantly low productivity. The appropriate conditions for bonding two semi-cured polyamic acid films or a semi-cured polyamic acid film and a conductor foil under heat and pressure, are 70-200°C, 5-100 kg/cm 2 and 5-30 minutes when a press is used, and 70-200°C, 1-500 kg/cm 2 and 0.1-50 m/min when a roll type laminator is used. With respect to the bonding temperature, in particular, a temperature 10-30°C lower than the drying temperature for the polyamic acid film is desirable because it generates no volatile material. The conditions for imidization may be those ordinarily employed in polyimide production. The polyamic acid solution used for preparing the semi-cured polyamic acid film is a solution of a polyamic acid dissolved in an organic solvent, the polyamic acid being ordinarily obtained by reacting an acid anhydride with a diamine. As the acid anhydride, there can be used, singly or in combination of two or more, various acid anhydrides such as trimellitic acid anhydride, pyromellitic acid anhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 3,3',4,4'-p-terphenyltetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 4,4'-hexafluoroisopropylidene-bis(phthalic anhydride) and the like. As the diamine, there can be used, singly or in combination of two or more, various diamines such as p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 3,3'-dimethylbenzidine, 4,4'-diamino-p-terphenyl, 4,4'-diamino-p-quaterphenyl, 2,8-diaminodiphenylene oxide and the like. The polyamic acid solution used in the present invention can be any as long as it has film formability and adhesive property to a metal foil. However, a polyamic acid solution as shown below meets intended purposes best. That is, it is a polyamic acid mixture solution obtained by mixing and stirring (A) a polyamic acid solution obtained by reacting 3,3',4,4'-biphenyltetracarboxylic acid dianhydride as an acid anhydride component with p-phenylenediamine as a diamine component and (B) a polyamic acid solution obtained by reacting pyromellitic acid dianhydride as an acid anhydride component with 4,4'-diaminodiphenyl ether as a diamine component, at a solid content ratio of A/B = 55/45 to 75/25. When the proportion of A is smaller than the above, the resulting polyamic acid tends to curl. When the proportion of A is larger than the above, the resulting polyamic acid film is too rigid and has no flexibility, and shows reduced adhesion to a copper foil. With respect to the monomers usable for obtaining a light-transmittable polyimide, the acid anhydride includes 2,2-bis(dicarboxyphenyl)hexafluoropropane dianhydride, oxydiphthalic anhydride, biphenyltetracarboxylic acid dianhydride, etc; and the diamine differs slightly depending upon the acid anhydride used in combination but includes m-substituted diamines containing a sulfone group, m-substituted diamines having an ether bond, diamines having a hexafluoropropylene group, etc. Preferably, the light-transmittable polyimide layer has a yellowness index (JIS K 7103) of 30 or less, desirably 20 or less. The reaction between the acid anhydride component and the diamine component is preferably conducted at an acid anhydride component/diamine component molar ratio of 0.90 to 1.00. When the molar ratio is smaller than 0.90, no sufficiently high polymerization degree is obtained and the film after curing has poor properties. When the molar ratio is larger than 1.00, a gas is generated during curing, making it impossible to obtain a smooth film. The reaction is ordinarily conducted in an organic polar solvent not reactive with the acid anhydride or the diamine. It is necessary that the organic polar solvent be inactive to the reaction system, be a solvent to a product obtained, and moreover be a good solvent to at least one of the reaction components, preferably both of them. Typical examples of such a solvent are N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfone, dimethyl sulfoxide, N-methyl-2-pyrrolidone, etc. These solvents can be used singly or in combination. Besides, non-polar solvents such as benzene, dioxane, xylene, toluene, cyclohexane and the like can be used in combination with the organic polar solvent, as a dispersing agent for raw materials, a reaction-controlling agent, an agent for controlling evaporation from the product, a film-smoothening agent, etc. Preferably, the reaction is conducted generally under water-free condition. It is because when water is present, there is a fear that the water gives rise to ring opening of the acid anhydride, makes the acid anhydride inactive and consequently stops the reaction. Therefore, it is necessary that the water in raw materials fed and the water in solvent be removed. However, in some cases water is added in order to control the progress of the reaction and thereby control the polymerization degree of the resin obtained. It is also preferable that the reaction be conducted in an inert gas atmosphere in order to prevent the oxidation of the diamine. As the inert gas, dry nitrogen gas is used generally. The reaction temperature is desirably 0-100°C. It is because when the reaction temperature is lower than 0°C, the reaction rate is low and, when the reaction temperature is higher than 100°C, there are initiated the ring-closing reaction and depolymerization reaction of the polyamic acid formed. The reaction is conducted ordinarily at about 20°C. As a material usable as the release film, there can be cited plastic films made of polypropylene, polyester, polyethersulfone, polyimide, polyethylene or the like. As a material usable as the conductor layer, there can be cited metal foils made of a single metal such as copper, aluminum, nickel or the like, and metal foils made of an alloy such as Fe-Ni alloy, Fe-Cr-Al alloy or the like. The present invention enables production of a two-layered tape for TAB having device holes and having excellent heat resistance, chemical resistance, etc., at high productivity. Further, the present invention has enabled production of a two-layered tape for TAB using a rolled foil (use of a rolled foil has been impossible in the vapor deposition process, etc.). Furthermore, the present invention enables production of a two-layered tape for TAB having no curl and having good adhesion strength between the copper foil and the film. Meanwhile, in the two-layered tape for TAB obtained using a light-transmittable polyamic acid film, there occurs no confusion of a circuit pattern even when the circuit pattern is made fine, because an inner lead pattern is formed on the transparent polyimide film layer; it is easy to conduct registration from the back side (polyimide side) using a CCD camera or the like because the device hole portions are constituted by only the transparent polyimide layer having a smaller thickness; and gang bonding can be conducted easily at a high precision by applying a heat bar from the back side via the highly heat-resistant transparent polyimide The present invention is easily applicable even to continuous steps and is suitable as an industrial process for producing a two-layered tape for TAB. Best Mode for Carrying Out the Invention Example 1 Fig. 1 shows the steps (a) to (h) employed in production of a two-layered tape for TAB according to the present invention. Purified anhydrous 108 g of p-phenylenediamine and 200 g of 4,4'-diaminodiphenyl ether were charged in a four-necked separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet. Thereto was added a mixed solvent consisting of anhydrous 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of toluene, in such an amount that the solid content in all the materials fed became 20% by weight, whereby the two materials charged first were dissolved in the mixed solvent. Dry nitrogen gas flowed during all the steps from preparatory step of the reaction to taking-out of the product. Then, purified anhydrous 294 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 218 g of pyromellitic acid dianhydride were added in small proportions with stirring. Since the reaction was exothermic, the reaction system was cooled by circulating cold water of about 15°C in an external water tank. After the addition, the internal temperature was set at 20°C and stirring was conducted for 5 hours to complete the reaction, whereby a polyamic acid solution was obtained. This polyamic acid solution was coated on a commercial release film 1 (a polyester film) using a roll coater so as to give a thickness after imidization, of 25 µm, followed by drying at 110°C for 15 minutes, to obtain a semi-cured polyamic acid film 2 with a release film (b). Device holes 3 were formed using a die (c). The side of the polyamic acid film was contacted with the roughened surface of a commercial copper foil 4, and bonding under heat and pressure was conducted at 90°C and 40 kg/cm 2 for 15 minutes. Then, the release film 1 was peeled off and heating was conducted at 380°C for 1 hour to complete imidization and form a polyimide film 6, whereby a two-layered base board with device holes (d) was obtained. Onto the conductor foil of the two-layered base board (d) were applied a desired resist pattern 5 and a desired filler 8 introduced into holes 3 (e), and etching treatment was carried out to form a conductor pattern (f). Then, the resist 5 remaining on the conductor foil and the filler 8 were removed (g). Punching was applied to form sprocket holes (7), whereby a two-layered tape for TAB was obtained (h). Example 2 Two similar semi-cured polyamic acid films each formed on a release film (these were the same as used in Example 1) were brought in a contiguous relation so that the polyamic acid film sides faced each other. They were bonded using a press under heat and pressure at 100°C and 20 kg/cm 2 for 10 minutes to obtain a polyamic acid laminate film. Then, one of the release films was peeled off. Using this semi-cured polyamic acid laminate film formed on a release film, the procedure of Example 1 was repeated to obtain a two-layered tape for TAB. Example 3 The same polyamic acid solution as used in Example 1 was coated on a commercial polyester film using a roll coater so as to give a thickness after imidization, of 25 µm, followed by drying at 110°C for 15 minutes to obtain a semi-cured polyamic acid film with a release film. Two of these films were brought in a contiguous relation so that the respective polyamic acid film sides faced each other, and bonded under heat and pressure using a roll type laminator at 90°C, 15 kg/cm 2 and 0.2 m/min. Then, holes were formed using a die. One of the release films was peeled off and the polyamic acid film side was contacted with the roughened surface of a commercial copper foil. They were bonded under heat and pressure using a press at 90°C and 40 kg/cm 2 for 15 minutes. Then, the release film was peeled off and heating was conducted at 380°C for 1 hour to complete imidization. The subsequent procedure was the same as in Example 1 to obtain a two-layered tape for TAB. Example 4 200 g of purified anhydrous 4,4'-diaminodiphenyl ether was charged in a four-necked separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet. Thereto was added a mixed solvent consisting of anhydrous 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of toluene, in such an amount that the solid content in all the materials fed became 20% by weight, whereby the material charged first was dissolved in the mixed solvent. Dry nitrogen gas flowed during all the steps from preparatory step of the reaction to taking-out of the product. Then, 218 g of purified anhydrous pyromellitic acid dianhydride was added in small proportions with stirring. Since the reaction was exothermic, the reaction system was cooled by circulating cold water of about 15°C in an external water tank. After the addition, the internal temperature was set at 20°C and stirring was conducted for 5 hours to complete the reaction, whereby a polyamic acid solution was obtained. This polyamic acid solution was coated on a commercial polyester film using a roll coater so as to give a thickness after imidization, of 25 µm, followed by drying at 110°C for 10 minutes, to obtain a semi-cured polyamic acid film with a release film (this polyamic acid film is referred to as film II). Then, the release film was peeled off and the film II was inserted between two polyamic acid films (films I) each with a release film, obtained in Example 1, so that the respective polyamic acid film sides of the films I faced each other. The three polyamic acid films were bonded under heat and pressure using a press at 100°C and 25 kg/cm 2 for 15 minutes. Thereafter, holes were formed using a die and one of the two release films was peeled off. The polyamic acid film side was contacted with the roughened surface of a commercial copper foil. Bonding was conducted under heat and pressure using a press at 90°C and 40 kg/cm 2 for 15 minutes. Lastly, the remaining release film was peeled off and heating was conducted at 380°C for 1 hour to complete imidization. The subsequent procedure was carried out similarly to Example 1 to obtain a two-layered tape for TAB. Example 5 108 g of purified anhydrous p-phenylenediamine was charged in a four-necked separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet. Thereto was added a mixed solvent consisting of anhydrous 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of toluene, in such an amount that the solid content in all the materials fed became 20% by weight, whereby the material charged first was dissolved in the mixed solvent. Dry nitrogen gas flowed during all the steps from preparatory step of the reaction to taking-out of the product. Then, 294 g of purified anhydrous 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added in small proportions with stirring. Since the reaction was exothermic, the reaction system was cooled by circulating cold water of about 15°C in an external water tank. After the addition, the internal temperature was set at 20°C and stirring was conducted for 5 hours to complete the reaction, whereby a polyamic acid solution (referred to as A) was obtained. Then, using the same apparatus and manner as in above, there were reacted 200 g of anhydrous 4,4'-diaminodiphenyl ether and 218 g of purified anhydrous pyromellitic acid dianhydride to obtain a polyamic acid solution (hereinafter referred to as B). A and B were mixed and stirred so as to give a solid content ratio of A/B = 60/40. Using the resulting polyamic acid solution and the same procedure as in Example 1, there was obtained a semi-cured polyamic acid film. Then, a two-layered tape for TAB was obtained from the film. Example 6 Two similar polyamic acid films both obtained as in Example 5 were brought in a contiguous relation so that the respective polyamic acid film sides faced each other. They were bonded under heat and pressure using a press at 100°C and 20 kg/cm 2 for 10 minutes to obtain a polyamic acid laminate film. Using this polyamic acid laminate film and the same manner as in Example 1, there was obtained a two-layered tape for TAB. Example 7 Using the same polyamic acid solution as in Example 5 and the same manner as in Example 3, there was obtained a two-layered tape for TAB. Example 8 Using the same apparatus and manner as in Example 5, there were synthesized a solution (referred to as A) of a polyamic acid consisting of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and a solution (referred to as B) of a polyamic acid consisting of 4,4'-diaminodiphenyl ether and pyromellitic acid dianhydride. A and B were mixed and stirred so as to give a solid content ratio of A/B = 70/30. Using the resulting polyamic acid solution and the same manner as in Example 4, there was obtained a two-layered tape for TAB. Example 9 Using the same apparatus and manner as in Example 5, there were synthesized a solution (referred to as A) of a polyamic acid consisting of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and a solution (referred to as B) of a polyamic acid consisting of 4,4'-diaminodiphenyl ether and pyromellitic acid dianhydride. A and B were mixed and stirred so as to give a solid content ratio of A/B = 80/20. The subsequent procedure was carried out similarly to Example 1, whereby a two-layered tape for TAB was obtained. The evaluation results for the two layered tapes for TAB produced in Examples 5 to 9 are shown in Table 1. Example 5 6 7 8 9 Appearance (curls) o ○ o ○ o ○ o ○ ○ Chemical resistance o ○ o ○ o ○ o ○ o ○ Adhesion strength o ○ o ○ o ○ o ○ Δ Soldering resistance o ○ o ○ o ○ o ○ o ○ Overall evaluation o ○ o ○ o ○ o ○ Δ Example 10 One mole of 3,3'-diaminodiphenylsulfone was charged in a four-necked separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet. Thereto was added a mixed solvent consisting of anhydrous 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of toluene, in such an amount that the solid content in all the materials fed became 20% by weight, whereby the material added first was dissolved in the mixed solvent. Dry nitrogen gas was flowed during all the steps from preparatory step of the reaction to taking-out of the product. Then, 1 mole of purified anhydrous 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added in small proportions with stirring. Since the reaction was exothermic, cold water of about 15°C was circulated in an external water tank to cool the reaction system. After the addition, the internal temperature was set at 20°C, followed by stirring for 5 hours to complete the reaction, whereby a polyamic acid solution (A) was obtained. In the same apparatus and manner, purified anhydrous 1 mole of p-phenylenediamine and 1 mole of 4,4'-diaminophenyl ether were charged. Thereto was added a mixed solvent consisting of anhydrous 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of toluene, in such an amount that the solid content in all the materials fed became 20% by weight, whereby the two materials charged first were dissolved in the mixed solvent. Dry nitrogen gas flowed during all the steps from preparatory step of the reaction to taking-out of the product. Then, purified anhydrous 1 mole of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 1 mole of pyromellitic acid dianhydride were added in small proportions with stirring. Since the reaction was exothermic, cold water of about 15°C was circulated in an external water tank to cool the reaction system. After the addition, the internal temperature was set at 20°C, followed by stirring for 5 hours to complete the reaction, whereby a polyamic acid solution (B) was obtained. Example 11 One mole of 1,3-bis(3-aminophenoxy)benzene was charged in a four-necked separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet. Thereto was added a mixed solvent consisting of anhydrous 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of toluene, in such an amount that the solid content in all the materials fed became 20% by weight, whereby the material added first was dissolved in the mixed solvent. Dry nitrogen gas flowed during all the steps from preparatory step of the reaction to taking-out of the product. Then, 1 mole of purified anhydrous 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added in small proportions with stirring. Since the reaction was exothermic, cold water of about 15°C was circulated in an external water tank to cool the reaction system. After the addition, the internal temperature was set at 20°C, followed by stirring for 5 hours to complete the reaction, whereby a polyamic acid solution (C) was obtained. In the same apparatus and manner, 1 mole of purified anhydrous p-phenylenediamine was charged. Thereto was added a mixed solvent consisting of anhydrous 90% by weight of N-methyl-2-pyrrolidone and 10% by weight of toluene, in such an amount that the solid content in all the materials fed became 20% by weight, whereby the material charged first was dissolved in the mixed solvent. Dry nitrogen gas flowed during all the steps from preparatory step of the reaction to taking-out of the product. Then, 1 mole of purified anhydrous 3,3',4,4'- biphenyltetracarboxylic acid dianhydride was added in small proportions with stirring. Since the reaction was exothermic, cold water of about 15°C was circulated in an external water tank to cool the reaction system. After the addition, the internal temperature was set at 20°C, followed by stirring for 5 hours to complete the reaction, whereby a polyamic acid solution (D) was obtained. Possibility of Application in Industry The tape for TAB according to the present invention can be used as a method for very high density mounting of semiconductors in production of semiconductor-mounted flexible printed circuit boards used in cameras, liquid crystal display devices, etc.

Claims: A method of producing a two-layered tape for TAB, which is characterized by forming desired holes (3) in a polyamic acid film (2) formed on a release film (1), the film (2) having a degree of imidization of 10 to 50%, then laminating the polyamic acid film (2) and the release film (1) to a conductor foil (4) so that the polyamic acid film (2) is brought in contact with the conductor foil (4), peeling off the release film (1), completing imidization and forming a desired pattern in the conductor foil (4). A method as claimed in claim 1, wherein the polyamic acid film (2) has a degree of imidization of 20 to 40%. A method as claimed in claim 1 or claim 2, wherein the polyamic acid film (2) is formed by use of a varnish obtained by mixing A, a polyamic acid solution obtained by reacting 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and p-phenylenediamine, with B, a polyamic acid solution obtained by reacting pyromellitic acid dianhydride with 4,4'-diaminodiphenyl ether, at a solid content ratio of A/B = 55/45 to 75/25. A method as claimed in any one of claims 1 to 3, wherein after the completion of imidization, the holes (3) are filled with a desired filler (8) and, after pattern formation, the filler (8) is removed.

Inventors: MIKAMI S, NAKAO T, TAKEUCHI E, TOCHIMOTO T, YAMAMORI Y, MIKAMI, S., NAKAO, T., TAKEUCHI, E., TOCHIMOTO, T., YAMAMORI, Y., MIKAMI, S., RAIONZU MANSHON CHUO-RINKAN 10-312, NAKAO, T., GURIN HAIMU IZUMINO 41-208, TAKEUCHI, E., SUMITOMO BAKELITE TOTSUKA-RYO, TOCHIMOTO, T., 7-1395-9, SAKURAYAMA, YAMAMORI, Y., SUMIT. BAKELITE TOTSUKA-RYO2-32-36
Applicants: SUMITOMO BAKELITE CO, SUMITOMO BAKELITE COMPANY LIMITED
Application year: 1992
Main classification: H01L21
IPC codes: H05K3, H05K1, H01L21