scope of the invention circular is used in the specification to mean circular or approximately circular such that the circular depressions are capable of receiving a disc shaped substrate in a further refinement of the invention a mask rests flat on the carrier palette and exhibits corresponding to the circular depressions circular openings having a diameter smaller than the diameter of the substrates in a further refinement of the invention each of the depressions exhibits a central overlay on which the substrate rests the depth of the depression is at least as deep as the substrate is thick and preferably 0 to 4 mm preferably 1 to 2 mm greater than the thickness of the substrate expediently each substrate includes a central hole having a diameter which is smaller than the diameter of the overlay preferably a mask of t shaped cross section is fitted in the central hole in which case the transverse part of the mask possesses a diameter greater than the diameter of the vertical part of the mask in a further development of the invention the diameter of the transverse part of the mask is greater than the diameter of the central hole in the substrate since the substrates are located in the depressions of the carrier palette during the.