Circuit board electrically insulating material, circuit board and method for manufacturing the same

A circuit board comprising:

• a desired number of electrically insulating layers and wiring layers which are laminated alternately, and
• an inner via hole for securing an electrical connection between the wiring layers by compressing and hardening a conductive paste including a conductive particle and a resin;
• wherein:
• the electrically insulating layer comprises a porous sheet in which a resin layer is laminated to at least one surface, and at least a central portion of the porous sheet is not impregnated with a resin;
• a through hole penetrating the electrically insulating layer in the thickness direction of the electrically insulating layer is filled with a conductive paste including a conductive particle and a resin, and pores that are present inside the porous sheet are filled with the laminated resin;
• and
• the average hole diameter of the pores that are present inside the porous sheet is smaller than the average particle size of the conductive particle.

A method for manufacturing a double-sided circuit board, comprising:

• providing a through hole in a laminate in which mold release films are formed on both surfaces of a circuit board electrically insulating material that is a circuit board electrically insulating sheet comprising a porous sheet in which a resin layer is laminated to at least one surface of the porous sheet and at least a central portion of the porous sheet is not completely impregnated with a resin;
• filling the through hole with a conductive paste;
• peeling off the mold release film from the laminate in which the through hole is filled with the conductive paste;
• superimposing metal foils on both surfaces of the circuit board electrically insulating material from which the mold release films have been peeled off to form a laminate;
• heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with resin and allow the metal foils to be adhered to the porous sheet, and compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole;
• and
• forming desired circuit patterns on the metal foil.

A method for manufacturing a double-sided circuit board, comprising:

• forming a laminate either by superimposing resin sheets on both surfaces of a porous sheet that is not completely impregnated with a resin, further superimposing mold release films on both surfaces of the laminated resin sheet, and pressing thereof;
• or by forming a resin layer on one surface of a pair of mold release films, further sandwiching a porous sheet that is not impregnated with a resin by the sides of the resin layer of the mold release films provided with the resin layers;
• and pressing thereof;
• providing a through hole in the laminate provided with the mold release films;
• filling the through hole with a conductive paste;
• peeling off the mold release films from the laminate in which the through hole has been filled with the conductive paste;
• superimposing the metal foils on both surfaces of the laminate from which the mold release films have been peeled off;
• heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with a resin and allow the metal foil to be adhered to the porous sheet, and compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole;
• and
• forming desired circuit patterns on the metal foil.

A method for manufacturing a double-sided circuit board, comprising:

• providing a through hole in a laminate in which mold release films are formed on both surfaces of a porous sheet that is not completely impregnated with a resin;
• filling the through hole with a conductive paste, and peeling off the mold release films from the laminate in which the through hole has been filled with the conductive paste;
• sandwiching the laminate from which the mold release films have been peeled off with transfer media, the transfer media being formed on a supporting base material by filling a resin in an exposed portion of the supporting base material at a side of a wiring layer provided one end surface of the supporting base material;
• and heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with a resin and allow the wiring layer to be adhered to the porous sheet, and compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole;
• and
• removing the supporting base material of the transfer medium from the heated and pressed laminate.

A method for manufacturing a double-sided circuit board, the method comprising:

• forming a resin layer at the side of a wiring layer of a transfer medium in which a wiring layer is provided on a supporting base material;
• sandwiching both surfaces of a porous sheet that is not completely impregnated with a resin between the transfer medium on which the resin layer is formed and a mold release film provided with a resin layer to form a laminate;
• providing a non-through hole at a desired position of the laminate from the side of the mold release film;
• filling the non-thorough hole with a conductive paste;
• peeling off the mold release film from the laminate on which the non-through hole has been filled with the conductive paste;
• superimposing a metal foil on the surface of the laminate from which the mold release film has been peeled off;
• heating and pressing the laminate on which the metal foil is superimposed to allow hollow pores of the porous sheet to be filled with a resin and allow the metal foils and the wiring layer of the transfer medium to be attached to the porous sheet, and compressing and hardening the conductive paste filled in the non-through hole, thereby providing an inner via hole;
• forming desired circuit patterns on the metal foil;
• and
• removing the supporting base material from the laminate in which the circuit patterns have been formed on the metal foil.

A method for manufacturing a multilayer circuit board, the method repeating the following steps once or more:

• providing a through hole in a laminate in which mold release films are formed on both surfaces of a circuit board electrically insulating material that is a circuit board electrically insulating sheet comprising a porous sheet in which the resin layer is laminated to at least one surface and at least a central portion of the porous sheet is not impregnated with a resin;
• and filling the through hole with a conductive paste;
• peeling off the mold release films from the laminate in which the through hole has been filled with the conductive paste;
• superimposing a desired number of the circuit board electrically insulating materials from which the mold release films have been peeled off and the circuit board provided with two or more of wiring layers alternately so that the circuit board electrically insulating material becomes the outermost layer, and furthermore superimposing metal foils on the surface thereof to form a laminate;
• heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with a resin and allow the metal foil and the circuit board to be adhered to the porous sheet, and compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole;
• and
• forming desired circuit patterns on the metal foil.

A method for manufacturing a multilayer circuit board, the method repeating the following steps once or more:

• forming a laminate either by superimposing resin sheets on both surfaces of the porous sheet that is not completely impregnated with a resin, further superimposing the mold release films on both surfaces of the laminated resin sheet, and pressing thereof;
• or by forming a resin layer on one surface of a mold release film, sandwiching a porous sheet that is not completely impregnated with the resin between the sides of the resin layer of the mold release film provided with the resin layer;
• and pressing thereof;
• providing a through hole in the laminate provided with the mold release films;
• filling the through hole with a conductive paste, and peeling off the mold release films from the laminate in which the through hole has been filled with the conductive paste;
• superimposing a desired number of the laminates from which the mold release films have been peeled off and the circuit board electrically insulating material provided with two or more of the wiring layers alternately so that the circuit board electrically insulating material becomes the outermost layer, and furthermore superimposing a metal foil;
• heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with a resin and allow the metal foil and the circuit board to be adhered to the porous sheet, and compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole;
• and
• forming desired circuit patterns on the metal foil.

A method for manufacturing a multilayer circuit board, the method repeating the following steps once or more;

• forming a resin layer on at least one surface of a circuit board provided with two or more wiring layers;
• superimposing a porous sheet that is not completely impregnated with a resin at the side of the resin layer of the circuit board;
• and furthermore superimposing a mold release film provided with a resin layer on one surface onto the porous sheet;
• providing a non-through hole at a desired position of the laminate from the side of the mold release film;
• filling the non-through hole with a conductive paste;
• and peeling off the mold release film from the laminate in which the non-through hole has been filled with the conductive paste;
• superimposing metal foils on the surfaces of the laminate from which the mold release films have been peeled off;
• heating and pressing the laminate to allow hollow pores of the porous sheet to be filled with a resin and allow the metal foil and the circuit board to be adhered to the porous sheet, and compressing and hardening the conductive paste filled in the through hole, thereby providing an inner via hole;
• and
• forming desired circuit patterns on the metal foil.