Thermosetting adhesive film and printed wiring board

Abstract

This invention provides a thermosetting adhesive film that exhibits excellent reprocessability at room temperature (23°C), excellent adhesion upon heating, excellent adhesion of its cured product, and excellent dielectric properties and heat resistance. The thermosetting adhesive film comprises an adhesive layer containing at least a styrene-based elastomer, a resin having multiple reactive functional groups in its structure, and an inorganic filler. The cured product of the adhesive layer has a relative permittivity of 1.0 to 3.0 at 23°C, 50% RH, and 28 GHz, and a dielectric loss tangent of 0.0001 to 0.01. The content of aromatic vinyl compound-derived structural units in the styrene-based elastomer is 13% by mass or more and less than 40% by mass. The surface roughness Sa of at least one side of the adhesive layer before curing is 0.6 μm or more.