Abstract: A package structure includes a heat spreader, a ground plane affixed to the heat spreader, and a flex tape interconnect substrate affixed to the ground plane. An aperture in the ground plane reveals a die attach surface on the heat spreader, and an aperture in the flex tape interconnect structure is aligned with the ground plane aperture such that the aligned apertures together with the revealed ground plane surface define a die cavity. The aperture in the ground plane is formed so as to form aperture walls substantially perpendicular to the ground plane. According to the invention the heat spreader, the ground plane, and the flex tape interconnect substrate have specified characteristics. Particularly, the heat spreader is provided as a metal sheet or strip, usually copper, having a “velvet type” oxide, usually a velvet black copper oxide, on at least the surface of the heat spreader to which the ground plane is to be affixed.