Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1993-01-11
1994-08-09
Ball, Michael W.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156634, 156645, 156656, 156902, 1562739, 1562751, 156290, 1563077, B32B 3100, B32B 3128, H01L 21306
Patent
active
053363531
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the production of a multilayer printed circuit board composed of several so-called inner layers each consisting of an insulating base of thin laminate of reinforcement material impregnated with thermosetting resin, said laminate preferably having a layer of metal or metal alloy on both sides, in which layers a wiring pattern has been formed and so-called prepreg sheets of reinforcement material impregnated with thermosetting resin, whereby the resin is not fully cured, which prepreg sheets are placed between the inner layers.
Multilayer printed circuit boards are used for advanced electronic purposes and they are often composed of two or more inner layers of the kind mentioned above with intermediate prepreg sheets. In addition one outer layer consisting of a laminate of the above kind having a thin layer of metal or metal alloy on one side is placed on each side of the stack of inner layers. The metal layer is directed outwards. In certain cases the outer layers consist of a thin foil of metal or metal alloy instead of the disclosed laminate. Prepreg sheets are placed also between the outermost of the inner layers and the outer layers.
It is very important that the wiring pattern on the different inner layers are centered carefully in respect of each other and that they are not displaced at the subsequent pressing under heat and pressure which is used for bonding the different inner layers, outer layers and prepreg sheets together to a multilayer printed circuit board. After the lamination holes are namely drilled through the different layers. Then the holes must land in the intended place of the wiring pattern in the different layers. If the layers are displaced a bit in respect of each other so that the holes will land outside the wiring pattern in any layer, the necessary electric connection between the different wiring patterns will not be achieved when the walls of the holes are subsequently metallized. This results in a very costly cassation of the whole multilayer printed circuit board.
The outermost metal layers of the multilayer printed circuit board produced are provided with a wiring pattern. Then the different conventional components can be mounted on the printed circuit board.
Efforts have been in different ways to solve the above problem with the costly cassation. According to one known method the different inner layers, the prepreg sheets and the outer layers are provided with holes. These holes are drilled with a careful precision and in such a way that the different wiring patterns land in a correct position above each other when turned rivets are inserted through the holes. With this technique a precision of 125 .mu.m can be obtained. Thus, the present demand of 25 .mu.m needed at the production of multilayer printed circuit boards with close-packed signal circuits cannot be met. Therefore, often the cassation will reach 20% which is wholly unacceptable from the viewpoint of costs.
According to the present invention it has been possible to solve the above cassation problem and bring about a process for the production of a multilayer printed circuit board composed of a plurality of so-called inner layers, each consisting of an insulating base of thin laminate of reinforcement material impregnated with thermosetting resin said laminate preferably being provided with a layer of metal or metal alloy on both sides. In these layers a wiring pattern has been formed. So-called prepreg sheets of reinforcement material impregnated with thermosetting material are placed between the inner layers. The resin in the prepregs is not fully cured.
The process comprises centering the inner layers in respect of each other and fixing them in position by pressing the different layers together along the two long sides. Energy is then supplied within a limited area along the two long sides, whereby the resin is heated and cured so that all layers are bonded together with each other, preferably in a few spots or minor areas- Then the package obtained is laminated un
REFERENCES:
patent: 4481533 (1984-11-01), Alzmann et al.
patent: 4702785 (1987-10-01), Burger
G. Pohl et al Producing and Jointly Processing Base Laminates for Multilayer Printed Circuit Cards, "IBM Technical Disclosure Bulletin", vol. 27, No. 8, Jan. 1985, p. 4841.
Ball Michael W.
Crispino Richard
Polyclad Europe AB
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