Process for sealing at least one well out of a number of wells provided in a plate for receiving chemical and/or biochemical and/or microbiological substances, and installation for carrying out the process

A plate having wells therein for receiving chemical substances is provided with a coverplate covering said filled wells. The process for sealing the wells by providing a joining seam running around the wells provides the joining seam such that it has a profiled cross-section in order to increase the contact surface between the plate and the coverplate. To this end a welding die has a front surface provided with projecting profiled regions and being heated to a temperature in the region of the melting point of the coverplate. The welding die is placed on the coverplate means and remains there for a fixed first period. Then the welding die is pressed down through a fixed path and remains in this position for a fixed second period. Removing the welding die from the coverplate is the last step in the process.