An interposer has conductive elements at a first side and terminals at a second side opposite therefrom, for connecting with a microelectronic element and a second component, respectively. The component includes a first element having a thermal expansion coefficient less than 10 ppm/° C., and an insulating second element, with a plurality of openings extending from the second side through the second element towards the first element. A conductive structure extending through the openings in the second element and through the first element electrically connects the terminals with the conductive elements.