The present invention relates to methods and apparatuses for assembling substrates with functional blocks, using a printhead to deliver individual functional blocks to the appropriate locations on the substrates. In an embodiment, the functional block releasing mechanism comprises a heat source to provide thermal energy and a light source to provide photon energy, wherein the heat source and the light source enable releasing individual functional blocks from the reservoir for positioning on the substrate. The heat source can comprise an array of heating elements, such as thin film heating elements, which can provide localized heating to individual elements, thus enabling releasing individual functional blocks. The light source can comprise a laser beam and a moving mechanism to move the laser beam to the individual functional blocks.