Method of producing copper-clad laminated board

Abstract: Disclosed is a method of producing a copper-clad laminated board comprising the steps of laminating a glass epoxy prepreg between both-side roughened copper foils, holding the upper and bottom copper foils with a polyamide-type films having a melting point of 170°C or higher, and heating and press-molding the resultant structure while holding the top and bottom of the structure with press plates. The use of a polyamide-type film as a mold releasing film prevents the film from being stuck at all on the both-side roughened copper foil or the press plates, yielding a high separation property, and can maintain the shapes of the ruggedness on the roughened surface.

Description: BACKGROUND OF THE INVENTION The present invention relates to a method of producing copper-clad laminated board for a printed circuit board, which uses a mold releasing film, such as a polyamide-type film. A method of producing a copper-clad laminated board is disclosed in DE-A-0 135 407. Methods of producing a copper-clad laminated board (hereinafter abbreviated as "CCLB") for a multi-layered printed circuit board (hereinafter abbreviated as "MLPCB") include press molding of a both-side roughened copper foil (hereinafter abbreviated as "BSRCF") placed on a single prepreg therewith, and press molding of BSRCFs placed on both sides of a lamination of multiple prepregs therewith. The roughening of a copper foil is performed to improve the bonding between the copper foil and the prepreg. However, a BSRCF has such a shortcoming that when it is pressed with a prepreg, fine ruggedness on the roughened surface of the copper foil which is pressed with a press plate are likely to be crushed. To prevent the crushing of ruggedness on the surface of the BSRCF, a metal film such as a copper foil or aluminum foil, or a conventionally used organic film such as polypropylene, polyethylene terephthalate, polyethylene, triphenylpentene or Tedra ( trade name of a resin film made by Du Pont) is placed between a press plate and a BSRCF at the time of press molding. Hereupon prepregs are acquired by permeating a thermosetting resin, such as phenolic resin, epoxy resin, polyimide resin, epoxy modified polyimide resin or cyanate ester resin, in a fabric or nonwoven fabric of glass fiber, aramid fiber, polyester fiber, carbon fiber, or paper, and drying the resultant structure. However, with a metal foil in use, when there is resin powder or the like remaining on the press plate, the metal foil sticks on the press plate at that remaining portion and stays as a foreign matter on the press plate, producing socalled stamping marks. Besides, when the aforementioned plastic film is used, it does not have excellent property of separation from the press plate. Also, even when the plastic film is peeled off well from the BSRCF, printing of that film surface on the surface of the BSRCF would be seen on the electron microscopic level due to cleavage fracture of the film used. This printing will have bad effect upon the subsequent process of the molded CCLB. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method of producing a copper-clad laminated board for a printed circuit board, which can maintain the ruggedness on the roughened surface of a BSRCF which is opposite to the surface contacting with a prepreg, keeps the roughened surfaces from being stained, and is easily separable from a press plate. According to the present invention, in a step of yielding a CCLB for a printed circuit board by laminating a BSRCF on both sides or one side of a single prepreg or bonded plural prepregs, said prepreg acquired by permeating a thermosetting resin in a fabric or nonwoven fabric and drying the resultant structure to a half hardened state, and placing the resultant structure between press plates of a press machine; a method of producing a CCLB for a printed circuit board comprises a step to press-mold the CCLB with a polyamide-type film having a melting point equal to or higher than a lamination temperature placed between the BSRCF and the press plates. Generally the lamination temperature is 170°C or higher. Polyamide-type films to be used in this invention include nylon 6 expressed by a chemical formula of (-NH(CH₂)₅CO-) n or nylon 6.6 expressed by a chemical formula of (-NH(CH₂)₆NHCO(CH₂)₄CO-) n , which can be formed into a film industrially. The polyamide-type film has only to have a melting point equal to or higher than a lamination temperature, and preferably has a thickness of 10 to 100 µm for easier handling, though not particularly limited thereto. The measurement of the melting point of polyamide is conducted by ASTMD 2117-64. The press molding of CCLB is usually carried out under a condition of heating temperature 170°C or higher, pressure 10 kgf/cm² or higher and time 60 minutes or longer. Accordingly, the melting point of a polyamide-type film is preferably 170°C or higher in order to prevent adhesion of a portion of the film to the rugged portion on the surface of the BSRCF or to the press plate. Even when the conventional type films other than a polyamide-type film have a melting point of 170°C or higher, a portion of the films sticks on the ruggedness of the BSRCF or is fused on the press plate possibly for the following reason. These films are inferior to a polyamide-type film in cleavage, impact resistance, fracture resistance. A prepreg to be used in this invention is acquired by permeating a thermosetting resin, such as phenolic resin, epoxy resin, polyimide resin, epoxy modified polyimide resin or cyanate ester resin, in a fabric or nonwoven fabric of glass fiber, aramid fiber, polyester fiber, carbon fiber, or paper, and drying the resultant structure in a half hardened state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be more specifically described below. Example 1 With four glass epoxy prepregs EI-6765 (products of Sumitomo Bakelite, 180 µm in thickness and resin content of 45%) placed between BSRCFs, STD foils (products of Circuit Foil Japan), 70 µm in thickness, the upper and lower copper foils were sandwiched by nylon 6 films (melting point of 220°C and thickness of 20 µm) as a polyamide-type film, and the top and bottom portions of the resultant structure were held with press plates and were press-molded at a heated temperature of 170°C for 180 minutes. After the press molding, the product was separated from the press plates, and the peeling characteristic of the film from the copper foil and the easiness of separation of the film from the press plate were evaluated. Example 2 Example 2 was produced in the same manner as Example 1 except for the use of nylon 6.6 film (melting point of 230°C and thickness of 25 µm) as a polyamide-based film, and the same evaluation as made for Example 1 was also conducted. Comparative Example 1 Comparative Example 1 was produced in the same manner as Example 1 except that nothing was placed between the copper foil and the press plate, and the same evaluation as made for Example 1 was also conducted. Comparative Example 2 Comparative Example 2 was produced in the same manner as Example 1 except that the film of Example 1 was changed to an aluminum foil 100 µm in thickness, and the same evaluation as made for Example 1 was also conducted. Comparative Example 3 Comparative Example 3 was produced in the same manner as Example 1 except for the replacement of the film of Example 1 with polyethylene terephthalate film (melting point of 250°C and thickness of 37 µm), and the same evaluation as made for Example 1 was also conducted. Comparative Example 4 Comparative Example 4 was produced in the same manner as Example 1 except for the replacement of the film of Example 1 with triphenylpentene (melting point of 210°C and thickness of 30 µm), and the same evaluation as made for Example 1 was also conducted. The results of the evaluation on Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 1 below. Material for Protection Film Peeling Property to Copper Foil Remainder on Copper Foil Shape of Ruggedness on Copper Foil Separation Property to Press Plate Example 1 Nylon 6 ○ None No change ○ Example 2 Nylon 6.6 ○ None No change ○ Comparative Example 1 None ○ None Crush occurred × Comparative Example 2 Aluminum foil ○ Present No change × Comparative Example 3 Polyethylene terephthalate × Present No change ○ Comparative Example 4 Triphenylpentene × Present No change × Evaluated on: 1. Peeling property to copper foil: O: No film adhering to copper foil X: Film adhered to copper foil 2. Remainder on copper foil: Observed with an electron microscope (x 2000) 3. Shape of ruggedness on copper foil: Observed with an electron microscope (x 2000) 4. Separation property to press plate: O: No film or foil remaining on press plate X: Film or foil remained on press plate The production method of the present invention to provide a method of producing a copper-clad laminated board for a printed circuit board, which can prevent the film from being stuck on the BSRCF or prepreg, can maintain the ruggedness on that roughened surface of the BSRCF which is opposite to the surface contacting with the prepreg, and can facilitate production of a CCLBs with both sides roughened for a printed circuit board, which has an excellent separation property to the press plate. This method is therefore suitable for mass production of BSRCFs at low cost.

Claims: A method for preparing a copper-clad laminated board for a printed circuit board comprising the steps of:- i) preparing a prepreg by permeating a thermosetting resin in a fabric or non-woven fabric and then drying the resultant material to a half hardened state; ii) laminating both-sides roughened copper foil on at least one side of the prepreg; iii) placing a polyamide-type film having a melting point equal to or higher than the lamination temperature on the both-sides roughened copper-foil thereby to preserve the roughness of the copper foil surface adjacent a press plate; and iv) placing the resultant laminate between the press plates of a press machine and pressing the resultant laminate. A method according to claim 1, wherein the melting point of the polyamide-type film is 170°C or higher. A method according to claim 1, wherein the polyamide-type film is selected from the group consisting of a nylon 6 film and a nylon 6.6 film. A method according to claim 1, wherein the polyamide-type film has a thickness of 10 to 100 µm. A method for preparing a copper-clad laminated board for a printed circuit board comprising the steps of:- i) preparing a prepreg by permeating a thermosetting resin in a fabric or non-woven fabric and then drying the resultant material to a half-hardened state; ii) laminating both-sides roughened copper foil on at least one surface of the prepreg; iii) placing a polyamide-type film having a melting point equal to or higher than 170°C on the both-sides roughened copper foil; iv) placing the resultant laminate between the press plates of a press machine; v) pressing the laminate at a temperature of at least 170°C, and a pressure of at least 10kgf/cm² for at least 60 minutes; vi) separating the laminate from the press machine; and vii) peeling the polyamide-type film from the laminate to obtain a copper-clad laminated board.

Inventors: AZUMA KEIJI, KATOH KIMIKAZU, OGURO RYOICHI, AZUMA, KEIJI, KATOH, KIMIKAZU, OGURO, RYOICHI, Azuma, Keiji, Plastic Eng., c/o Sumitomo, Katoh, Kimikazu, Plastic Eng., c/o Sumitomo, Oguro, Ryoichi, Metal Eng., c/o Circuit Foil Japan
Applicants: CIRCUIT FOIL JAPAN, SUMITOMO BAKELITE CO, CIRCUIT FOIL JAPAN CO. LTD, SUMITOMO BAKELITE COMPANY LIMITED
Application year: 1992
Main classification: H05K3
IPC codes: B29C43, B29C33, H05K1, H05K3, B29L31, B32B15, B29L9, B29K105