the prior art the wafer is now transferred to a second bath that contains the second of the two plating solutions mentioned above i e to a plating solution in which there is dissolved a more powerful accelerator additive and or a higher concentration of accelerator electroplating is now resumed the plating solution in the second bath is now such as to be optimized for filling wide trenches the result is that electroplated material in the trench builds up faster than outside it so that electroplated layer 44 fig4 that is obtained once the wide trenches have been overfilled ends up with a surface that is essentially planar for an additional copper thickness that is between about 0 3 and 0 5 microns two other embodiments of the present invention apply the above process with some modifications both additional embodiments still make use of two different solutions but only a single plating chamber or container is required such an approach is useful for example in a small scale operation such as a pilot line in the first of these additional embodiments when the first plating step has been completed narrow trenches overfilled the wafer is left in place so that electrical connections to it need not be disconnected the first plating solution is emptied out of the container is replaced by the second plating solution and plating is resumed in the second additional embodiment when the first plating step has been completed narrow trenches overfilled the wafer is left in place so that electrical connections to it need not be disconnected while the first plating solution is gradually and continuously replaced.