 In through-hole technology, the component leads are inserted in holes surrounded by conductive "pads"; the holes keep the components in place.In surface-mount technology (SMT), the component is placed on the PCB so that the pins line up with the conductive "pads" or "lands" on the surfaces of the PCB; solder paste, which was previously applied to the pads, holds the components in place temporarily; if surface-mount components are applied to both sides of the board, the bottom-side components are glued to the board.In both through hole and surface mount, the components are then soldered; once cooled and solidified, the solder holds the components in place permanently and electrically connects them to the board.