Method of forming a multilayer printed circuit board and apparatus therefor

A method of forming a multilayer printed circuit board comprising the steps of:

• placing a laminated assembly of a plurality of printed circuit board components and a plurality of prepregs of bonding agent alternately laminated on each other between an upper jig plate and a lower jig plate, and
• applying heat and pressure to said laminated assembly in a thickness direction of said laminated assembly from upper and lower sides thereof through the upper and lower jig plates, thereby bonding said printed circuit board components and said prepregs with each other,
• characterized by inserting said laminated assembly placed between said upper and lower jig plates into a space within a vacuum and high pressure applying means constituted by an upper plate and a lower plate each provided with an enclosing frame located around said laminated assembly and shiftably engaged with each other in the thickness direction of said laminated assembly and having sealing means for preventing leakage of gas through said enclosing frames, sufficiently evacuating said space within said vacuum and high pressure applying means,
• thereafter heating and applying pressure to said laminated assembly in the thickness direction of said laminated assembly through the upper and lower jig plates, within said vacuum and high pressure applying means so as to melt said prepregs for filling vacancies between patterns on said printed circuit board components with said bonding agent, and
• pressurizing said space with a gas immediately after filling said vacancies with said bonding agent to a pressure above the vapor pressure of water and solvent contained in said bonding agent and maintaining the pressurization with said gas until said bonding agent solidifies, while continuing to apply pressure to said laminated assembly from upper and lower sides of the laminated assembly in the thickness direction thereof through the upper and lower jig plates, thereby permitting voids caused by air remaining in fine spaces between said printed circuit board components and said prepregs in said laminated assembly as well as voids generated by gasification of the water and the solvent in said bonding agent to be positively avoided.