Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1993-05-19
1995-02-28
Ryan, Patrick J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
428105, 428297, B32B 900
Patent
active
053935918
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a process for producing copper-clad base materials and to a process for producing multilayers from these base materials.
Base materials (circuit boards) are boards copper-clad on one or both sides, consisting generally of fiber-reinforced thermosetting resins, the resin being in the C-stage. They are used for the manufacture of printed circuit boards for the electronics industry and, if appropriate, for further processing into multilayers.
Multilayers are laminates consisting of a plurality of base materials. For producing them, the base materials (resin in the C-stage), provided with appropriate conductive patterns, are pressed with interposed (adhesive) prepregs (resin in the B-stage) with application of pressure and heat, the resin of the prepregs curing fully to reach the C-stage.
Prepregs are resin-impregnated substrates, in general sheets of glass fiber fabric, the resin being in the not yet completely cured (B) state.
A conventional process for producing copper-clad base materials is the pressing of a plurality of plies of prepreg cut sheets with covering plies of copper foil with application of pressure and heat, the resin of the prepregs being cured fully to reach the C-stage.
BACKGROUND ART
WO 88/01,938 has disclosed a process of the generic type for producing base materials copper-clad on one or both sides by the so-called filament-winding technique and the use thereof for producing multilayers. In this process, the winding mandrel used is a steel sheet covered with a copper foil. This sheet is wound at the smallest possible inclination with one ply of yarn filaments of a reinforcing material, preferably alkali-free glass, initially across the width, with the winding mandrel rotating. After the whole surface of the sheet has been wound, this winding step is repeated at an angle of 90.degree., whereby a second ply is applied. The step of crosswise winding is repeated several times until the desired glass content or the desired thickness of the wound plies has been reached. Instead of the conventional fabric reinforcement, a laid fiber structure is thus formed, in which the individual filaments are not woven with one another but lie loosely on top of one another.
After completion of the winding step, a closed mold is formed by means of two metal sheets, covered on the inside with copper foil, and lateral sealing webs, which mold is evacuated to a residual pressure of less than 2 mm Hg. In an injection process or casting process, which is known to those skilled in the art, for example, as the RTM process (resin transfer molding), a prepared and, if appropriate, heated resin mixture is then allowed to flow in and, after the filling step has been completed, the resin mixture is allowed to cure fully at elevated temperature.
The casting resin mixture, described in WO 88/01,938, of epoxide resin and anhydride hardening agent has, however, a poor adhesion between copper and the plies, since a hardening agent must be added in relatively large quantities, and this impairs the adhesive force (peel strength).
In particular in the case of base material with a thin copper foil, for example 17.5 /um thickness, whose use is indispensable for fine line technology and very fine line technology, the peel strength drops down to 1.0N/mm and lower, so that the requisite values are not reached.
OBJECT
It is therefore the object of the invention to provide a process of the generic type for producing base materials, which process leads to boards having higher peel strength of the copper foil and improved bonding of the plies.
A further objective of the invention is to provide an improved process for producing multilayers, using base materials produced by the filament-winding process (WO 88/01,938).
DISCLOSURE OF THE INVENTION
According to the invention, a process for producing base materials copper-clad on at least one side, comprising (a) winding reinforcing fiber on a winding core carrying a copper foil, (b) impregnating the wound fibers with a solvent-free resin, and
REFERENCES:
patent: 4401499 (1983-08-01), Kaneko et al.
patent: 4609586 (1986-09-01), Jensen et al.
patent: 4788224 (1988-11-01), Muller et al.
patent: 4943334 (1990-07-01), Medney et al.
Fasbender Helmut
Voss Burkhard
Huls Troisdorf Aktiengesellschaft
Lee Kam F.
Ryan Patrick J.
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