Source: {"pile_set_name": "USPTO Backgrounds"}

(1) Field of the Invention
The present invention relates to a prepreg, a multilayer printed wiring board and a process for producing a multilayer printed wiring board. More particularly, the present invention relates to a prepreg which has high flexibility at room temperature, causes neither chipping nor peeling of resin, and is superior in heat resistance and electrical insulation after press molding; to a multilayer printed wiring board using said prepreg; and to a process for producing said multilayer printed wiring board.
(2) Description of the Prior Art
Prepregs obtained by impregnating a mat or roving made of a glass fiber or the like, with a thermosetting resin (e.g., an epoxy resin) which has been cured up to an extent slightly higher than the B-stage, are in use for molding or lamination in plastic industry. Other prepregs are also known in which the mat or roving made of a glass fiber or the like used for molding or lamination, is replaced by an aramid fiber, or the epoxy resin is replaced by a polyimide resin, a polyphenylene ether resin, a polytetrafluoroethylene resin or a polyaminobismaleimide resin.
The prepregs obtained by impregnating a glass cloth with a composition consisting of an epoxy resin and a curing agent and then semicuring the resulting material, have had problems in that they cause chipping or peeling of resin when bent.
The prepregs in which an aramid fiber is used in place of the glass cloth, are improved in bending strength but are higher in cost because the aramid fiber is expensive.
The prepregs in which a polyimide resin, a polyphenylene ether resin or a polytetrafluoroethylene resin is used in place of the epoxy resin, are relatively difficult to mold or process and moreover are expensive. The prepregs in which a polyaminobismaleimide resin is used in place of the epoxy resin, have high heat resistance; however, they are very hygroscopic and low in adhesivity and, moreover, because of the necessity of use of a high-boiling solvent when a varnish is made, contain a large amount of residual solvent and tend to generate voids during lamination.
The present invention aims at alleviating the above-mentioned problems of the prior art and providing (1) a prepreg which has high flexibility at room temperature, causes neither chipping nor peeling of resin, and is superior in heat resistance and electrical insulation after press molding, (2) a multilayer printed wiring board using such a prepreg of excellent properties, and (3) a process for producing such a multilayer printed wiring board.
The present invention provides:
a prepreg which is composed of a mixture of a polycarbodiimide resin and an epoxy resin and which has a film shape;
a prepreg composed of (1) a mixture of a polycarbodiimide resin and an epoxy resin and (2) a base material;
a multilayer printed wiring board obtained by alternately laminating an internal substrate and an insulating adhesive layer and adhering them to each other, wherein the above prepreg is used as the insulating adhesive layer; and
a process for producing a multilayer printed wiring board, which comprises alternately laminating an internal substrate and the above prepreg, adhering them to each other, and allowing all the internal substrates to communicate with each other at the required portions.