High density printed wiring board possessing controlled coefficient of thermal expansion with thin film redistribution layer

A high,density PWB having increased circuit density and improved electrical and mechanical properties at locations in which electrical/mechanical connection is made between said PWB and a surface mounted device comprising:

• a substrate comprising a thermoset resin selected from the group consisting of epoxy, bismaleimide, and cyanate resins, and combinations thereof, impregnated with an organic reinforcement material selected from the group consisting of a random oriented mat of chopped p-aramid fibers which are transversely isotropic and have an axial CTE of about −3 to about −6 ppm/° C. below the glass transition temperature and a thermoplastic liquid crystalline polymer paper.
• said impregnated substrate having a first major surface and a second major surface;
• a plurality of electrically conductive through-holes extending between and electrically interconnecting said first and second surfaces;
• and at least one of said first and second surfaces including a thin film redistribution layer affixed thereto;
• said organic reinforcement material having a dielectric of at least 3.25, and possessing in combination with said thermoset resin, a low overall CTE which is adjusted to match the CTE of a solder mounted silicon semiconductor chip in the range of about 3 to 10 ppm/° C.