Rotatable tool coupled to support body, and drive shaft detachably mounted to rotatable tool, such that rotatable tool is drivable in a working direction, in which support body includes an inlet opening defined by at least three eccentric segments and drive shaft includes an immersion area structured and arranged for insertion into the central inlet opening. The first tube is a complete cylinder of electrically conductive material; and the second tube is segmented into separate elements, each separately attached to the first tube. The upper and lower ones of the semiconductor chips mounted on a pair of the stacked substrates are electrically connected through first terminals provided in a region outside the region in which one of the semiconductor chips is mounted in each of the substrates.