Method of making through hole with laser, copper-clad laminate suitable for making hole, and auxiliary material for making hole

Abstract

A method of making a small-diameter through hole having high reliability with regard to a hole wall at a high rate with the energy of a high-output carbon dioxide gas laser without pre-making any hole in a copper foil, forming or disposing a coating or a sheet of an organic substance containing 3 to 97% by volume of at least one powder selected from the group consisting of a metal compound powder, a carbon powder and metal powder which have a melting point of at least 900° C. and a bond energy of at least 300 KJ/mol on at least a copper foil surface to be irradiated with the carbon dioxide gas laser, and irradiating a surface thereof with necessary pulses of the carbon dioxide gas laser to form the penetration hole, and an auxiliary material for use when a penetration hole is made in the copper-clad laminate with a carbon dioxide gas laser, the auxiliary material being a coating or a sheet of an organic substance containing 3 to 97% by volume of at least one powder selected from the group consisting of a metal compound powder, a carbon powder and metal powder which have a melting point of at least 900° C. and a bond energy of at least 300 KJ/mol.

What is claimed is:  
     
         1 . A method of forming a penetration hole for a through hole in a thermosetting resin copper-clad laminate having at least two copper layers, in which copper foils of the thermosetting resin copper-clad laminate are processed with an energy of 20 to 60 mJ/pulse sufficient for removing the copper foils by means of the pulse oscillation of a carbon dioxide gas laser, the method comprising forming or disposing a coating or a sheet of an organic substance containing 3 to 97% by volume of at least one powder selected from the group consisting of a metal compound powder, a carbon powder and metal powder which have a melting point of at least 900° C. and a bond energy of at least 300 KJ/mol on at least a copper foil surface to be irradiated with the carbon dioxide gas laser, and irradiating a surface thereof with necessary pulses of the carbon dioxide gas laser to form the penetration hole.  
     
     
         2 . A method according to  claim 1 , wherein the organic substance is a water-soluble resin composition.  
     
     
         3 . A method according to  claim 1 , wherein, after the penetration hole is formed, both the copper foil surfaces are etched to remove part of the thickness thereof and form a smooth surface and at the same time to remove copper foil burrs fluffing on a penetration hole portion.  
     
     
         4 . A method according to  claim 3 , wherein the etching is carried out to remove ⅓ to ½ of the thickness of the copper foil.  
     
     
         5 . A method according to  claim 1 , wherein the metal compound powder, the carbon powder and the metal powder have an average particle diameter of 1 μm or less.  
     
     
         6 . A method according to  claim 1 , wherein coatings or sheets of an organic substance containing 3 to 97% by volume of at least one powder selected from the group consisting of a metal compound powder, a carbon powder and metal powder which have a melting point of at least 900° C. and a bond energy of at least 300 KJ/mol are formed or disposed on copper foil surfaces of 2 to 10 copper-clad laminates, one coating or sheet on the copper foil surface of one copper-clad laminate, the 2 to 10 copper-clad laminates are stacked, and the upper surface of the stacked copper-clad laminates is irradiated with the carbon dioxide gas laser to form the peneration holes at the same time.  
     
     
         7 . A method according to  claim 1 , wherein a backup sheet having a resin layer and a metal plate is at least partially bonded to an outermost copper foil surface of the copper-clad laminate opposite to a surface of the copper foil to be irradiated with the carbon dioxide gas laser.  
     
     
         8 . A method according to  claim 7 , wherein the resin layer is formed of a water-soluble resin composition, the resin layer is placed on the copper foil surface and the backup sheet is laminated on the copper foil surface under heat and pressure.  
     
     
         9 . A method according to  claim 7 , wherein the resin layer of the backup sheet has a thickness of 20 to 200 μm.  
     
     
         10 . A method according to  claim 9 , wherein the metal plate is a glossy metal plate having a thickness of 30 to 200 μm.  
     
     
         11 . A copper-clad laminate for use in a method of forming a penetration hole for a through hole in a thermosetting resin copper-clad laminate having at least two copper layers, in which copper foils of the thermosetting resin copper-clad laminate are processed with an energy of 20 to 60 mJ/pulse sufficient for removing the copper foils by means of the pulse oscillation of a carbon dioxide gas laser, the copper-clad laminate being a copper-clad laminate containing a prepreg of a glass fabric substrate which is impregnated with a resin composition containing a thermosetting resin having a glass transition temperature of at least 150° C. and 10 to 60% by weight an insulating inorganic filler, the copper-clad laminate having a cross section wherein the thermosetting resin and the inorganic filler from the resin composition are homogeneously mixed.  
     
     
         12 . A copper-clad laminate according to  claim 11 , wherein the thermosetting resin composition contains 0.1 to 10% by weight of a black or brown dye or pigment.  
     
     
         13 . An auxiliary material which is for use on a copper foil surface of a copper-clad laminate when a penetration hole is made in the copper-clad laminate with a carbon dioxide gas laser by irradiating the copper foil surface with an energy of 20 to 60 mJ/pulse sufficient by means of the pulse oscillation of a carbon dioxide gas laser, and which is a coating or a sheet of an organic substance containing 3 to 97% by volume of at least one powder selected from the group consisting of a metal compound powder, a carbon powder and metal powder which have a melting point of at least 900° C. and a bond energy of at least 300 KJ/mol.  
     
     
         14 . An auxiliary material according to  claim 13 , wherein the organic substance is a water-soluble resin composition.  
     
     
         15 . An auxiliary material according to  claim 13 , wherein the sheet is a product formed by bonding a water-soluble resin composition to one surface of a thermoplastic film.  
     
     
         16 . An auxiliary material according to  claim 15 , wherein the sheet is a product in which the total thickness of the layer of the water-soluble resin composition and the thermoplastic film is 30 to 200 μm.  
     
     
         17 . An auxiliary material according to  claim 15 , wherein the sheet is used by disposing the layer of the water-soluble resin composition on the copper foil surface side and laminating the layer of the water-soluble resin composition to the copper foil under heat under pressure.  
     
     
         18 . An auxiliary material according to  claim 15 , wherein the sheet is used by wetting the surface of the layer of the water-soluble resin composition 3 μm or less deep with water in advance, disposing the layer of the water-soluble resin composition on the copper foil surface side and laminating under pressure at room temperature.  
     
     
         19 . A backup sheet for making a hole with a carbon dioxide gas laser, which is for use on a reverse outermost copper foil surface of a copper-clad laminate when a hole is made in the copper-clad laminate with a carbon dioxide gas laser by irradiating a front copper foil surface with an energy of 20 to 60 mJ/pulse by means of the pulse oscillation of a carbon dioxide gas laser and which comprises a 20 to 200 μm thick resin layer and a metal plate.  
     
     
         20 . A backup sheet according to  claim 19 , wherein the resin layer is a water-soluble resin composition.