Abstract: An electrical substrate material is presented comprising a thermosetting matrix of polybutadiene or polyisoprene and a co-curable second resin distinct from the first resin. A peroxide cure initiator and/or crosslinking agent may optionally be added. The presence of a very high surface area particulate filler, preferably fumed silica, is also preferred, in that its presence results in a prepreg which has very little tackiness and can therefore be easily handled by operators. This low tackiness feature allows for the use of conventional automated layup processing, including foil cladding, using one or more known roll laminators. While the prepreg of this invention is tack-free enough to be handled relatively easily by hand, it is also tacky enough to be tacked to itself using a roll laminator (e.g., nip roller) at room temperature.

Abstract: An electrical substrate material is presented which comprises a thermosetting matrix which includes a polybutadiene or polyisoprene resin and an unsaturated butadiene or isoprene containing polymer in an amount of 25 to 50 vol. %; a woven glass fabric in an amount of 10 to 40 vol. %; a particulate, preferably ceramic filler in an amount of from 5 to 60 vol. %; a flame retardant and a peroxide cure initiator. A preferred composition has 18% woven glass, 41% particulate filler and 30% thermosetting matrix. The foregoing component ratios and particularly the relatively high range of particulate filler is an important feature of this invention in that this filled composite material leads to a prepreg which has very little tackiness and can therefore be easily handled by operators. This low tackiness feature allows for the use of conventional automated layup processing, including foil cladding, using one or more known roll laminators.