A method of bonding first and second microelectronic elements includes pressing together a first substrate containing active circuit elements therein with a second substrate, with a flowable dielectric material between confronting surfaces of the respective substrates, each of the first and second substrates having a coefficient of thermal expansion less than 10 parts per million/° C., at least one of the confronting surfaces having a plurality of channels extending from an edge of such surface, such that the dielectric material between planes defined by the confronting surfaces is at least substantially free of voids and has a thickness over one micron, and at least some of the dielectric material flows into at least some of the channels.