A method to weld together two even substrate pieces (1, 1'; 2, 2'), the latter forming a closed place, in which a third piece is situated using a focused laser beam according to which method: a. the first piece to be welded is made of a material selected form glass, semiconductor substrate, silicon, technical glass, melted silicon oxide, borosilicate, calcareous glass, sapphire, ceramic material, zirconium oxide or LiTaO, and is transparent within the wave length of the laser beam that is used, b. the pieces to be welded, like the first piece (1, 1') and the second piece (2, 2') are placed against each other for the welding, c. the first piece (1, 1') and the second piece (2, 2') are pressed together with the help of the pressing force to remove a uniform or non-uniform air layer from between them at least in the area to be welded or the pieces are pressed near each other to obtain essentially an equal in height air layer between them at least in the area to be welded, d. to obtain and keep the pressing force at least one pressing apparatus is used, wherein pressing force is transferred to the first piece and the second piece (1, 1' 2, 2',) with the help of a support organ and a pressing organ so that the first piece (1, 1') and the second piece (2, 2') are placed between the pressing organ and the support organ, and wherein with the help of the pressing force, molecule bindings are achieved between the surfaces to be joined together or a binding of the tops of the roughness of the surfaces, wherein the pressing force is removed after achieving the binding, and then the pressing organ is removed from the welding setting before performing the welding(s), e. in the common boundary surface (a, b) or boundary area (a') of the first piece (1, 1') and the second piece (2, 2') a laser beam focal point is directed through a transparent piece to be welded and the above mentioned first piece (1, 1') and the second piece (2, 2') are set in movement in relation to the laser beam so that the focal point advances in the before mentioned boundary surface (a, b) or boundary area (a') in accord with the shape and the length of the weld or welds (7, 10), f. the energy of the focal point of the laser beam melts material of the first piece and the second piece (1, 1', 2, 2') at the same time, these melted materials get mixed and as the melts harden, a weld (7, 10) is formed that joins hermetically the first piece (1, 1') and the second piece (2, 2') and goes round and isolates hermetically the third piece(s). a. the first piece to be welded is made of a material selected form glass, semiconductor substrate, silicon, technical glass, melted silicon oxide, borosilicate, calcareous glass, sapphire, ceramic material, zirconium oxide or LiTaO, and is transparent within the wave length of the laser beam that is used, b. the pieces to be welded, like the first piece (1, 1') and the second piece (2, 2') are placed against each other for the welding, c. the first piece (1, 1') and the second piece (2, 2') are pressed together with the help of the pressing force to remove a uniform or non-uniform air layer from between them at least in the area to be welded or the pieces are pressed near each other to obtain essentially an equal in height air layer between them at least in the area to be welded, d. to obtain and keep the pressing force at least one pressing apparatus is used, wherein pressing force is transferred to the first piece and the second piece (1, 1' 2, 2',) with the help of a support organ and a pressing organ so that the first piece (1, 1') and the second piece (2, 2') are placed between the pressing organ and the support organ, and wherein with the help of the pressing force, molecule bindings are achieved between the surfaces to be joined together or a binding of the tops of the roughness of the surfaces, wherein the pressing force is removed after achieving the binding, and then the pressing organ is removed from the welding setting before performing the welding(s), e. in the common boundary surface (a, b) or boundary area (a') of the first piece (1, 1') and the second piece (2, 2') a laser beam focal point is directed through a transparent piece to be welded and the above mentioned first piece (1, 1') and the second piece (2, 2') are set in movement in relation to the laser beam so that the focal point advances in the before mentioned boundary surface (a, b) or boundary area (a') in accord with the shape and the length of the weld or welds (7, 10), f. the energy of the focal point of the laser beam melts material of the first piece and the second piece (1, 1', 2, 2') at the same time, these melted materials get mixed and as the melts harden, a weld (7, 10) is formed that joins hermetically the first piece (1, 1') and the second piece (2, 2') and goes round and isolates hermetically the third piece(s).